Head And Neck – Histology

• The marked structure is the thyroid cartilage, a key component of the laryngeal skeleton.

• Histologically, the thyroid cartilage is composed of hyaline cartilage.

• Hyaline cartilage is:

  • The most common type of cartilage in the body

  • Glassy and bluish-white in appearance

  • Composed of type II collagen fibers

  • Provides support and flexibility, and ossifies with age, especially in the larynx

❌ Why Others Are Incorrect:

• Fibroelastic membrane – Not a type of cartilage; refers to connective tissue membranes with elasticity

• Elastic cartilage – Found in structures like epiglottis, external ear, and Eustachian tube, not the thyroid cartilage

• Fibrocartilage – Found in intervertebral discs, pubic symphysis, not in the laryngeal skeleton

• Dense connective tissue – Composes ligaments and tendons, not cartilaginous frameworks

• The marked blue structure in the image is the thyroid cartilage, the largest cartilage of the larynx.

• It has a shield-like shape and forms the Adam’s apple (laryngeal prominence) in the front.

• It provides protection to the vocal cords and is a key landmark in the upper airway.

❌ Why Others Are Incorrect:

• Cricoid cartilage – Located below the thyroid cartilage, shaped like a signet ring.

• Adam’s apple – This is actually the anterior projection of the thyroid cartilage, but not a separate structure.

• Tracheal ring – Found below the cricoid, composed of incomplete cartilage rings in the trachea.

• Hyoid bone – Sits above the thyroid cartilage, not part of the larynx proper.

The tarsal plate is a dense connective tissue structure in the eyelid that gives it shape and firmness. Within it lies the Meibomian glands, which are:

🔍 Meibomian Glands:

• Large sebaceous glands embedded in the tarsal plate

• Open onto the posterior margin of the eyelid (inner surface)

• Secrete meibum, an oily substance that:

  • Prevents evaporation of the tear film

  • Keeps the eyelids from sticking together

• Dysfunction leads to dry eye, blepharitis, or chalazion (cyst of the Meibomian gland)

❌ Why the Other Options Are Incorrect:

• Glands of Zeis
  → Small sebaceous glands associated with eyelashes, not in the tarsal plate

• Glands of Krause
  → Accessory lacrimal glands (tear secretion), located in the conjunctiva, not sebaceous and not in tarsal plate

• Glands of Moll
  → Modified sweat glands near the eyelash follicles, not in the tarsal plate

• Von Ebner’s glands
  → Serous glands of the tongue, associated with taste buds, not related to the eyelid

The dorsum of the tongue (top surface) is covered with tiny projections called lingual papillae, which help in mechanical functions like gripping food and in taste perception.

There are four main types of papillae on the tongue:

🔢 Types and Key Features:

• Filiform Papillae
  → Most numerous
  → Conical and slender, give the tongue its rough texture
  → Do not contain taste buds
  → Primarily involved in mechanical functions like manipulating food

• Fungiform Papillae
  → Mushroom-shaped, scattered between filiform
  → Contain some taste buds

• Circumvallate Papillae
  → Large, round, arranged in a V-shape near the back of the tongue
  → Contain many taste buds, but few in number (about 8–12)

• Foliate Papillae
  → Found on the sides of the tongue
  → Contain taste buds, more prominent in children

• Lingual Papillae
  → This is a general term for all the above — not a specific type

❌ Why the Other Options Are Incorrect:

• Fungiform Papillae
  → Present but not the most abundant

• Circumvallate Papillae
  → Very few in number (8–12)

• Foliate Papillae
  → Found on the lateral edges, not on the full dorsum, and less prominent in adults

• Lingual Papillae
  → Umbrella term, not a specific papilla type

The vermillion border of the lips is the reddish transition zone between the skin of the face and the mucous membrane of the oral cavity. It’s what you see when you look at someone’s lips — the pinkish/red part.

🔍 Key Histological Feature:

• The vermilion border has no salivary, sweat, or sebaceous glands in the submucosa.

• That’s why lips can dry out easily — there’s no natural moisture or oil secretion there.

• It is covered by thin keratinized stratified squamous epithelium, and contains capillary-rich dermis, giving it the red appearance.

❌ Why the Other Options Are Incorrect:

• Cornified stratified squamous epithelium
  → Present in parts of the vermillion, but not the most defining feature for this question.

• Submucosa with sweat and sebaceous glands
  → These are found in the skin part of the lip, not in the vermillion border.

• Fibers of buccinator in muscular layer
  → The buccinator is in the cheek, not the lips. The orbicularis oris muscle is the primary muscle in lips.

• Presence of hair follicles in dermis
  → Seen in the skin portion of the lip (outside), not in the vermillion border.

The typical respiratory epithelium, also called respiratory mucosa, lines most of the upper respiratory tract — including the nasal cavity, nasopharynx, trachea, and bronchi.

🧬 Structure:

• It is made up of columnar cells that appear stratified, but all cells touch the basement membrane.

• It includes:

  • Ciliated cells – to move mucus and trapped particles

  • Goblet cells – to secrete mucus

  • Basal cells – to regenerate the epithelium

Hence, the best description of typical respiratory epithelium is:
→ Ciliated pseudostratified columnar epithelium

❌ Why the Other Options Are Incorrect:

• Columnar epithelium
  → Too general; does not reflect the specialized structure of respiratory lining.

• Stratified columnar epithelium
  → Found in rare areas like parts of the pharynx and male urethra, not respiratory mucosa.

• Pseudostratified columnar epithelium
  → Close, but lacks the key feature: cilia, which are essential for moving mucus in airways.

• Cuboidal epithelium
  → Seen in terminal bronchioles and smaller airways — not typical respiratory mucosa.

Tenon’s Capsule is Correct:

• Tenon’s capsule (also called the bulbar fascia) is a thin fibrous sheath that:

  • Envelops the eyeball from the optic nerve to the limbus.

  • Lies between the sclera and the orbital fat.

  • Is pierced by the tendons of the extraocular muscles.

• Its inferior expansion forms the suspensory ligament of the eyeball (Lockwood’s ligament), which:

  • Acts like a sling or hammock.

  • Supports the inferior part of the globe.

  • Helps maintain the position of the eye within the orbit.

❌ Why the Other Options Are Incorrect:

 Filliform is Correct:

• Filiform papillae are the most numerous papillae on the tongue but are strictly mechanical.

• They:

  • Lack taste buds

  • Provide friction for handling food

  • Are keratinized, giving the tongue its rough texture

• Therefore, they do not participate in taste sensation.

Note: “Fulliform” is likely a misspelling or duplicate of “filiform” and is not a recognized papilla type.

❌ Why the Other Papillae Contain Taste Buds:

 Why This is Incorrect:

• The mucous membrane of the tongue—especially on the dorsal surface—is firmly bound to the underlying muscle. This allows it to withstand friction during chewing and speaking.

• The ventral surface, while smoother, still has its mucosa tightly adherent, especially centrally.

• So saying it is loosely bound is incorrect for the tongue (though true for parts of the cheek or lips).

✅ Why the Other Statements Are Correct:

• Posterior one third of tongue is irregular with lymphoid aggregations called lingual tonsils
  ✔ True — these form part of Waldeyer’s ring.

• It is firmly bound to underlying muscle
  ✔ True — ensures functional movement and durability.

• Anterior two third of tongue is covered by small projections called papillae
  ✔ True — includes filiform, fungiform, circumvallate, and foliate papillae.

• Ventral surface of tongue is covered by a smooth mucosa
  ✔ True — it lacks papillae and is smoother compared to the dorsal surface.

Superior Portion is Correct:

• The olfactory epithelium is found in the superior portion of the nasal cavity, specifically:

  • The roof of the nasal cavity

  • The superior nasal concha

  • The upper part of the nasal septum

• This specialized area contains olfactory receptor neurons, supporting cells, and basal stem cells.

• It connects with the olfactory bulb through the cribriform plate of the ethmoid bone.

❌ Why the Other Options Are Incorrect:

Inferior portion of the nasal cavity

• Lined by respiratory epithelium, not involved in smell.

It is not present in the nasal cavity

• Incorrect—olfactory epithelium is in the nasal cavity.

Posterior and lateral portion of nasal cavity

• Also lined by respiratory epithelium; not the olfactory zone.

Anterior and lateral portion of nasal cavity

• Mostly vestibule and respiratory areas—not olfactory.

 Why This is Incorrect:

• Most minor salivary glands (like labial, buccal, palatine, and lingual) are mucous or mixed (mostly mucous with some serous).

• They are responsible for mucus secretion to keep the oral cavity moist—not for producing digestive enzymes.

• Saying all are “serous” is incorrect—they are predominantly mucous, with a few exceptions like von Ebner’s glands (which are purely serous).

✅ Why the Other Statements Are Correct:

Serous cells are predominant cells of submandibular gland

• True. Submandibular gland is a mixed gland, but serous cells predominate (≈90%).

Intercalated ducts are wider and longer in the parotid gland

• True. Parotid gland is purely serous with well-developed ductal systems, including prominent intercalated ducts.

All minor salivary glands are not encapsulated

• True. Minor salivary glands are scattered, unencapsulated, and located throughout the oral mucosa.

Demilune cells secrete lysozyme in sublingual gland

• True. In mucous acini, serous demilunes cap the mucous cells and secrete lysozyme and other antimicrobial proteins.

📝 Summary:

• Taste buds are barrel-shaped sensory structures located in the epithelium.

• The apex (top) of each taste bud opens into the oral cavity via a taste pore.

• Through this taste pore, dissolved food substances can reach the gustatory (taste) receptor cells, allowing chemoreception.

❌ Why the Other Options Are Incorrect:

They are mainly located on the soft palate but few on the ventral surface of tongue

• Wrong: Majority of taste buds are on the dorsal surface of the tongue, especially on fungiform, foliate, and circumvallate papillae.

• Soft palate has some, ventral surface has none.

A taste bud consists of 10–12 cells

• Incorrect: Each taste bud typically contains 50–100 cells, including gustatory cells, supporting (sustentacular) cells, and basal cells.

Sustentacular cells of taste buds are also known as gustatory cells

• Incorrect: These are two distinct cell types.

  • Gustatory cells = sensory receptor cells.

  • Sustentacular cells = supportive cells, not involved in taste transduction.

Taste buds are embedded within epithelium covering the filiform papillae

• Wrong: Filiform papillae are the only papillae without taste buds.

• Taste buds are found in fungiform, foliate, and circumvallate papillae.

✅  Bowman’s membrane

The cornea is a transparent, avascular structure at the front of the eye, composed of several distinct layers that each serve specific roles in protection, structure, and optical function. Some of these layers have regenerative capabilities, while others do not — and understanding this is crucial for grasping corneal healing and pathology.

🧠 The Five Layers of the Cornea (anterior to posterior):

1. Corneal Epithelium

   • Outermost layer

   • Highly regenerative due to rapid turnover of epithelial cells.

2. Bowman’s Membrane ✅

   • Acellular layer composed of collagen fibrils.

   • Does not regenerate if damaged.

   • Instead, it is replaced by scar tissue, which can lead to loss of corneal transparency.

3. Corneal Stroma

   • Makes up 90% of the corneal thickness.

   • Contains collagen and keratocytes.

   • Limited regeneration; damage can cause scarring and opacification.

4. Descemet’s Membrane

   • Thin basement membrane of the endothelium.

   • Has some regenerative capacity, particularly from the endothelial side.

5. Corneal Endothelium

   • Monolayer of cells responsible for maintaining corneal deturgescence (hydration balance).

   • Does not regenerate mitotically, but adjacent cells can enlarge and spread to cover defects.

   • Limited capacity, but not entirely absent.

❌ Why the Other Options Are Incorrect:

1. Descemet’s membrane

   • Can regenerate to some extent, especially when damage is minor.

2. Corneal stroma

   • Has limited repair ability, and damaged areas may result in scar formation, but not a complete inability to heal.

3. Corneal endothelium

   • Although it does not divide, it can partially compensate through cell spreading and enlargement. So, some function may be preserved after damage.

4. Corneal epithelium

   • Highly regenerative — one of the fastest healing tissues in the body.

Salivary glands are exocrine glands, meaning they secrete their product (saliva) through ducts onto an epithelial surface (the oral cavity). Based on their structure, they are categorized by:

1. Duct system complexity – simple (unbranched) or compound (branched)

2. Secretory unit shape – tubular, acinar (alveolar), or tubuloacinar

🔬 Major Salivary Glands (Parotid, Submandibular, Sublingual):

• All three are compound (branched ducts)

• They contain a mixture of secretory units:

  • Acini: Round clusters of serous or mucous cells

  • Tubules: Especially in mixed glands like submandibular and sublingual

Thus, they are best classified as compound tubuloacinar glands.

📌 Secretory Profiles:

• Parotid: Purely serous

• Submandibular: Mixed, mostly serous

• Sublingual: Mixed, mostly mucous

❌ Why the Other Options Are Incorrect:

• Simple tubuloacinar glands:
  These have a single, unbranched duct. Salivary glands have branched ducts, so this is incorrect.

• Compound acinar gland:
  Suggests only acinar-shaped units; while this fits parotid somewhat, it ignores the tubular components in mixed glands.

• Compound tubular glands:
  Found in places like the duodenum (Brunner’s glands), but don’t have acinar elements.

• Simple acinar glands:
  Very small glands like sebaceous glands; salivary glands are too large and complex to be classified as “simple”.

“Mixed gland”

Why It’s Correct:

1. Mixed Secretory Nature:
   • The sublingual glands are predominantly mucus-secreting (60-70%) but also contain serous cells (30-40%).
   • They produce a viscous, mucin-rich saliva (for lubrication) with some serous fluid (containing enzymes like lingual lipase).
2. Key Features:
   • Location: Beneath the oral mucosa in the sublingual fold (not at the root of the tongue).
   • Ducts:
     • Major ducts (Rivinus ducts): 8-20 tiny ducts opening directly into the sublingual fold.
     • Bartholin’s duct: Occasionally, a larger duct joins the submandibular duct.

Incorrect Options:

1. Minor gland

• Why wrong:
  • The sublingual gland is a major salivary gland (one of the three pairs, alongside parotid and submandibular).
  • Minor glands are small, scattered glands in oral mucosa (e.g., labial, buccal, palatal).

2. Mucus gland

• Why wrong:
  • While the sublingual gland is mostly mucus-secreting, it is not purely mucous—it has serous components, making it mixed.

3. Serous gland

• Why wrong:
  • The parotid gland is the only purely serous major salivary gland. The sublingual gland is primarily mucous with some serous demilunes.

4. Present at the root of the tongue

• Why wrong:
  • The sublingual glands are located in the floor of the mouth (sublingual fold), not the tongue root.
  • The lingual glands (minor glands) are present at the tongue root.

The salivary duct system is a branched structure designed to collect and modify saliva before it reaches the oral cavity. It consists of a hierarchy of ducts, each with distinct locations, functions, and epithelial linings.

Let’s break it down in order of flow:

📌 1. Intercalated Duct → ✅ Correct Answer

• Location: These are the smallest and most proximal ducts, directly draining acini.

• Lined by: Simple cuboidal epithelium—often very small cells.

• Function: They contribute bicarbonate ions to saliva and absorb chloride.

📌 2. Striated Duct

• ❌ Lined by: Simple columnar epithelial cells with basal striations (due to mitochondria in basal infoldings).

• Function: Modify saliva by reabsorbing Na⁺ and secreting K⁺ and HCO₃⁻.

• Not lined by cuboidal cells.

📌 3. Intralobular Duct

• ❌ This is a collective term that includes both intercalated and striated ducts, depending on size.

• Not a distinct histological unit with a single epithelial type.

• So it’s not the best answer here—too broad and includes non-cuboidal segments.

📌 4. Interlobular Duct

• ❌ Found in connective tissue septa between lobules.

• Lined by: Stratified cuboidal or columnar epithelium, or even pseudostratified epithelium in larger glands.

• Too large and distal to be lined by small cuboidal cells.

📌 5. Main Salivary Duct

• ❌ This is the terminal duct (e.g., Stensen’s duct for parotid, Wharton’s duct for submandibular).

• Lined by: Stratified columnar epithelium or even non-keratinized stratified squamous near the opening.

• Far too distal and large for simple cuboidal lining.

🧪 Summary Table:

The hard palate plays a major role in mastication, forming a rigid surface against which the tongue presses food. Because of this mechanical function, its mucosa must be tough and protective.

📌 Key Histological Features of the Hard Palate:

• The epithelium is keratinized stratified squamous—especially in the anterior part and along the midline raphe, where there’s more friction from food and tongue movement.

• The submucosa is present posterolaterally, where it contains:

  • Minor salivary glands (mostly mucous)

  • Fat in the anterior lateral regions (to cushion)

  • Dense fibrous tissue attaching mucosa to the palatine process of the maxilla and horizontal plate of the palatine bone

• However, in the midline (over the palatine raphe), there’s no submucosa—the mucosa is bound tightly to the underlying bone (mucoperiosteum).

❌ Why the other options are incorrect:

Non-keratinized and has submucosa and minor salivary glands posteromedially

• ❌ Incorrect epithelium. The hard palate is keratinized, not non-keratinized.

• 🟥 “Posteromedially” also isn’t the main site of salivary glands—it’s posterolaterally.

Keratinized and has submucosa and minor salivary glands anteroinferiorly

• ❌ Although it is keratinized, the anteroinferior region contains fat but not many minor salivary glands.

• ✅ Salivary glands are more posterolateral, not anterior.

Keratinized and lacks submucosa and minor salivary glands

• ❌ This is only true at the midline raphe, not for the entire hard palate.

• ✅ The posterolateral region does have submucosa and glands.

Non-keratinized and lacks submucosa and minor salivary glands

• ❌ Completely incorrect for the hard palate—this description fits more with the soft palate or inner cheeks, not the hard palate.

This statement is true.

• The lingual glands (found beneath the tongue) include anterior lingual glands (of Blandin and Nuhn) and posterior lingual glands (of von Ebner and Weber).

• Most lingual glands, especially those near the tip and underside of the tongue, are mucous-secreting.

• Von Ebner’s glands, near the vallate papillae, are serous, but these are minor in quantity compared to the mucous lingual glands.

❌ Why the Other Options Are Incorrect:

• • Submandibular gland secretions are mainly mucus
  🔴 Incorrect. The submandibular gland produces mixed secretions, but they are predominantly serous, not mucous.

• • The submandibular gland is the largest salivary gland
  🔴 Incorrect. The parotid gland is the largest salivary gland, not the submandibular.

• • 20% of salivary secretions are produced by small salivary glands
  🔴 Incorrect. Minor salivary glands contribute less than 10% of the total saliva volume.

• • Parotid gland secretions are seromucous
  🔴 Incorrect. The parotid gland produces purely serous secretions, rich in amylase and electrolytes.

The ductal system in salivary glands (including the lingual glands) consists of several levels of ducts, each with its own histological features:

1. Intralobular ducts

• Includes intercalated and striated ducts

• Lined by simple cuboidal or low columnar epithelium

2. Interlobular ducts

• Located between lobules

• Typically lined by pseudostratified columnar epithelium

3. Excretory (main) ducts

• As ducts approach the oral cavity surface

• Lined by stratified columnar epithelium, sometimes becoming stratified squamous near the opening

❌ Why the Other Options Are Incorrect:

• Stratified columnar, simple cuboidal, pseudostratified columnar → Incorrect order and mismatch of duct levels

• All three are stratified columnar → Histologically inaccurate; duct epithelium varies based on location and function

• Simple cuboidal, simple cuboidal, stratified columnar → Interlobar ducts are not lined by simple cuboidal; should be pseudostratified

• Simple cuboidal, stratified columnar, stratified columnar → Interlobar is pseudostratified, not stratified columnar

Types of acini:

• Serous cells → produce a watery, enzyme-rich secretion (e.g., amylase).

• Mucous cells → produce a thick, glycoprotein-rich mucus.

• Mixed acini → contain both serous and mucous cells, sometimes with serous demilunes (serous cells capping mucous acini).

Sublingual Gland Specifics:

• Smallest of the three major salivary glands.

• Histologically, it contains:

  • Predominantly mucous acini

  • Some serous cells in the form of demilunes → so it is technically mixed, but overwhelmingly mucous.

• Therefore, the correct classification is: Predominantly mucous.

❌ Why the Other Options Are Incorrect:

• Predominantly serous → Applies to the parotid gland, not sublingual.

• Seromucous → Describes submandibular gland (mixed, mostly serous).

• Serous → Too restrictive; not accurate for sublingual.

• Mucous → Not entirely wrong, but doesn’t acknowledge the small serous component. “Predominantly mucous” is more precise.

Entirely serous from Von Ebner’s gland

Circumvallate papillae are large, dome-shaped projections located just anterior to the sulcus terminalis of the tongue. They are few in number (8–12 in humans) but are structurally and functionally significant. Each papilla is surrounded by a trench (or trough), which acts like a moat.

Within this trench, you’ll find secretions from specialized Von Ebner’s glands. These are purely serous glands, meaning they produce a watery secretion rich in enzymes, particularly lipase, which helps flush the trench and clear away food particles. This is crucial to allow taste buds located on the lateral walls of the papillae to continuously sample fresh stimuli.

❌ Why the Other Options Are Incorrect:

1. Entirely mucous from gustatory glands
   ❌ Incorrect because Von Ebner’s glands are serous, not mucous. Mucous secretions are thick and sticky, which would actually hinder taste sensation rather than aid it.
   Also, “gustatory glands” isn’t an anatomically or histologically correct term used for tongue glands—it’s a misleading label.

2. Predominantly mucous from parotid gland
   ❌ Parotid gland is entirely serous, not mucous. Also, the parotid duct opens near the upper 2nd molar, not into the circumvallate papillae trench—so anatomically irrelevant here.

3. Seromucous
   ❌ This refers to glands that produce both serous and mucous secretions (like submandibular glands). Von Ebner’s glands are strictly serous, so this choice is inaccurate for this specific location.

4. Predominantly serous from parotid gland
   ❌ Again, while the parotid is serous, its secretions do not drain into the circumvallate trenches—wrong anatomical target.

🧩 Step 1: Understanding the types of ducts in the salivary gland

Salivary glands, including the submandibular gland, have a system of ducts that carry saliva from the acini (glandular secretion units) to the oral cavity. These ducts are classified into several types:

1. Intercalated ducts:

• Located closest to the acini.

• Lined by low cuboidal or squamous cells.

• Function: Secretion of bicarbonate ions and reabsorption of sodium.

• Few mitochondria.

2. Striated ducts:

• Larger than intercalated ducts.

• Lined by columnar cells with numerous mitochondria at the base.

• Function: Modification of saliva (e.g., absorption of sodium and chloride, secretion of potassium and bicarbonate).

• Located within the lobules, making them intralobular.

3. Terminal ducts:

• Larger ducts formed from the joining of multiple striated ducts.

• No specific histological features mentioned in the question.

4. Excretory ducts:

• Larger ducts that transport saliva to the oral cavity.

• Lined by stratified cuboidal or columnar epithelium.

• These are located outside the lobules (interlobular) and are not intralobular.

5. Interlobular ducts:

• Larger ducts found in the connective tissue between lobules (interlobular).

• Lined by stratified cuboidal epithelium.

• These ducts are not intralobular.

🧩 Step 2: Analyze the given information

Key features of the duct in question:

• Low columnar secretory cells: This points toward a columnar epithelium typical of ducts that modify saliva (e.g., striated ducts).

• Multiple mitochondria at the base: The presence of numerous mitochondria is characteristic of striated ducts, which are involved in active transport of ions (e.g., sodium, potassium).

• Intralobular: This indicates the duct is within the lobule, ruling out the interlobular ducts (which are outside the lobules).

🧩 Step 3: Evaluate the options

1️⃣ Intercalated duct:

• Low cuboidal or squamous epithelium (not columnar).

• Few mitochondria, not a high number of mitochondria at the base.

• Not intralobular, located near the acini.
  → ❌ Incorrect

2️⃣ Terminal duct:

• Larger ducts formed from the joining of striated ducts.

• Does not typically match the description (lacks numerous mitochondria and the specific histology given).
  → ❌ Incorrect

3️⃣ Excretory duct:

• Stratified cuboidal or columnar epithelium.

• Located outside the lobules (interlobular), so not intralobular.
  → ❌ Incorrect

4️⃣ Interlobular duct:

• Larger ducts located between lobules.

• Lined by stratified cuboidal or columnar epithelium.

• Located outside the lobules, so not intralobular.
  → ❌ Incorrect

5️⃣ Striated ducts:

✅ Lined by columnar cells with numerous mitochondria at the base (specialized for ion transport).
✅ Located within the lobules, so intralobular.

• These ducts are involved in modifying the saliva (especially sodium, chloride, and bicarbonate ions).
  → ✅ Correct answer: Striated ducts

🎯 Final Answer:

✅ Striated ducts (Option 5)

📝 Why striated ducts?

• Striated ducts are characterized by columnar epithelium with numerous mitochondria at the base to support active transport processes.

• They are located intralobular (within the lobules) of the salivary glands and are involved in modifying the secretion from the acini.

• This matches the description of the duct in the question.

🧩 Step 1: Understand the Meibomian glands

• Meibomian glands are modified sebaceous glands.

• Their primary function is to secrete meibum, an oily substance that helps lubricate the eye and prevent tear evaporation.

🧩 Step 2: Anatomy of the eyelid

The eyelid consists of several layers:

• Epidermis: Outermost layer (skin)

• Dermis: Middle layer (connective tissue, blood vessels)

• Tarsal plate (or tarsus): Dense fibrous tissue that gives structure to the eyelid. This is where the Meibomian glands are located.

• Mucous layer: Lines the inner surface of the eyelid (conjunctiva).

• Muscular layer: Contains the orbicularis oculi muscle, which allows eyelid movement.

🧩 Step 3: Evaluate each option

1️⃣ Epidermis of skin:

• The epidermis is the outermost layer of the skin, and it does not contain Meibomian glands.
  → ❌ Incorrect

2️⃣ Dermis of skin:

• The dermis contains various structures like hair follicles, sweat glands, and blood vessels, but Meibomian glands are not located here.
  → ❌ Incorrect

3️⃣ Tarsal plate:

✅ Meibomian glands are located within the tarsal plate of the eyelid.

• The tarsal plate is a dense layer of connective tissue that provides structure to the eyelid.

• Meibomian glands are arranged within this plate and release meibum onto the edge of the eyelid.

• They open into the lid margin and secrete oil into the tear film.

→ ✅ Correct answer: Tarsal plate

4️⃣ Mucous layer:

• The mucous layer is part of the conjunctiva that lines the inner surface of the eyelid.

• It does not contain Meibomian glands.
  → ❌ Incorrect

5️⃣ Muscular layer:

• The muscular layer contains the orbicularis oculi muscle, which is involved in eyelid movement.

• Meibomian glands are not found here.
  → ❌ Incorrect

🎯 Final Answer:

✅ Tarsal plate (Option 3)

📝 Why tarsal plate?

• Meibomian glands are modified sebaceous glands located in the tarsal plate of the eyelid.

• These glands secrete oil into the tear film, preventing evaporation and keeping the eye lubricated.

🧩 Step 1: Understanding the types of papillae

Papillae on the tongue:

• Papillae are projections on the dorsal surface of the tongue, each having distinct structures and functions.

Broad categories of papillae:

• Filiform: Thread-like, no taste buds.

• Fungiform: Mushroom-shaped, scattered, with taste buds.

• Vallate (Circumvallate): Large, round, located at the back, contain many taste buds.

• Foliate: Leaf-shaped, located on the sides, with taste buds.

🧩 Step 2: Analyze the options

1️⃣ Vallate papillae:

• Large, round papillae arranged in a V-shape on the posterior aspect of the tongue.

• Contain many taste buds, located in the groove surrounding them.
  → ❌ Incorrect (has taste buds).

2️⃣ Fungiform papillae:

• Mushroom-shaped, scattered across the anterior part of the tongue.

• Contain taste buds, more concentrated at the tip of the tongue.
  → ❌ Incorrect (has taste buds).

3️⃣ Circumvallate papillae:

• Another term for vallate papillae.

• Contain many taste buds.
  → ❌ Incorrect (has taste buds).

4️⃣ Filiform papillae:

✅ Thread-like appearance, most abundant papillae on the tongue.
✅ Deficient in taste buds (function is mechanical, helps in moving food).
✅ Found primarily on the superior surface of the tongue (especially in the middle third).

• Not involved in taste, but helps in texture sensation.

→ ✅ Correct answer: Filiform

5️⃣ Foliate papillae:

• Located on the lateral sides of the tongue.

• Contain taste buds, but not thread-like.
  → ❌ Incorrect (has taste buds and different location).

🎯 Final Answer:

✅ Filiform papillae (Option 4)

📝 Why filiform?

• Thread-like appearance (like small filaments).

• No taste buds (function primarily in mechanical processing of food).

• Located on the superior surface of the tongue.

🧩 Step 1: Analyze each feature

Let’s decode each histological clue.

✅ Darkly stained acini:

• Suggests serous cells → basophilic cytoplasm (due to rough ER for protein synthesis)

• Acini full of protein-rich secretion stain darker than mucous cells

✅ Apical portion with secretory granules:

• Secretory granules accumulate toward the lumen

• Seen in serous glands making enzymes

✅ Striated ducts:

• Characteristic of salivary glands (especially those with significant serous secretion)

• Striations = infoldings of basal plasma membrane with mitochondria (active ion transport)

🧩 Step 2: Compare gland types

🧩 Step 3: Evaluate options

1️⃣ Sublingual:

• Mostly mucous acini (pale-staining)

• Few/no striated ducts
  → ❌ Incorrect (no dark acini, no prominent striated ducts)

2️⃣ Thyroid:

• Contains follicles filled with colloid (not acini)

• Lined by simple cuboidal epithelium
  → ❌ Incorrect (structure doesn’t fit)

3️⃣ Parotid:

✅ Pure serous acini → darkly stained
✅ Apical secretory granules (protein enzymes like amylase)
✅ Well-developed striated ducts

→ ✅ Perfect match

4️⃣ Parathyroid:

• Contains chief cells, oxyphil cells

• No acini, no ducts
  → ❌ Incorrect

5️⃣ Submandibular:

• Mixed gland → serous & mucous acini

• Has striated ducts but less than parotid

• Mucous acini → pale staining
  → ❌ Less likely (presence of mucous acini dilutes staining pattern)

🎯 Final Answer:

✅ Parotid gland (Option 3)

📝 Why parotid?

The parotid gland is histologically characterized by:

• Pure serous acini → dark basophilic staining

• Secretory granules at apical pole (protein secretion)

• Prominent striated ducts (active electrolyte modification)

No mucous cells → no pale-staining acini.

🧩 Step 1: Types of salivary glands

There are three major salivary glands and several minor ones. The glands differ in the type of secretion:

✅ Serous secretion = thin, watery, enzyme-rich
✅ Mucous secretion = thick, viscous, glycoprotein-rich

Minor salivary glands (glands of palate, buccal glands) are mostly mucous-secreting, except for some specialized glands like von Ebner’s glands.

🧩 Step 2: Analyze each option

1️⃣ Von Ebner’s glands:

• Located in vallate and foliate papillae of the tongue.

• Secrete pure serous fluid rich in lingual lipase (helps taste and initial fat digestion).
  ✅ They are serous glands.
  ✅ Secretion is thin, watery, enzyme-rich.

→ Strong contender.

2️⃣ Sublingual gland:

• Primarily mucous-secreting with a small serous component.
  → Secretion is thick/viscous, not purely watery.
  → ❌ Incorrect.

3️⃣ Glands of palate:

• Mostly mucous glands.
  → Secrete viscous fluid for lubrication.
  → ❌ Incorrect.

4️⃣ Parotid gland:

• Major salivary gland producing pure serous secretion.
  ✅ Secretes watery, enzyme-rich saliva (mainly amylase).
  ✅ Largest contributor of enzyme-rich saliva.

→ Also a strong contender.

5️⃣ Submandibular gland:

• Mixed gland, but predominantly serous (about 70% serous, 30% mucous).
  → Not purely serous; produces both watery and mucous secretions.
  → ❌ Incorrect.

🧩 Key Comparison:

Both parotid and von Ebner’s glands secrete purely serous, enzyme-rich fluid.

However:

• Parotid → large, major salivary gland → secretes amylase-rich saliva for digestion.

• Von Ebner’s → small, specialized minor salivary glands → secrete lingual lipase, aid in taste bud washing.

✅ Both match “thin, watery, enzyme-rich” criteria.
✅ But the question emphasizes “only” enzyme-rich, watery secretion.

👉 Von Ebner’s glands are unique because they secrete ONLY enzyme-rich serous fluid for taste and digestion at the circumvallate papillae, while parotid also contributes to bulk saliva.

🎯 Final Answer:

✅ Von Ebner’s glands

📝 Clinical Insight:

Von Ebner’s glands play an essential role in cleansing taste buds and helping taste perception by constantly flushing the trenches of vallate papillae.

✅ Modified sebaceous glands

• Correct.

• Zeis glands are a variant of sebaceous glands associated with eyelash follicles.

❌ Modified sweat glands

• Refers to glands of Moll, not Zeis.

• Glands of Moll are apocrine sweat glands near the eyelash margin.

❌ Mucus glands

• Not found in the eyelid margin.

• Mucus-secreting glands are more relevant in conjunctival areas (e.g., goblet cells).

❌ Meibomian glands

• These are tarsal glands (not Zeis), located within the tarsal plate.

• They are also sebaceous, but they open directly onto the eyelid margin, not into hair follicles.

❌ Modified lacrimal glands

• Refers to accessory lacrimal glands (of Krause and Wolfring).

• These secrete the aqueous part of the tear film — not oily secretions.

• Core of Skeletal Muscle
  ✔️ The tongue is composed of interlacing bundles of skeletal muscle fibers oriented in various directions, allowing for precise, voluntary movements essential for speech, swallowing, and mastication.

• Lymphoid Aggregates (Lingual Tonsils)
  ✔️ Located on the posterior third of the tongue (pharyngeal part), forming part of Waldeyer’s ring — a defense mechanism against ingested pathogens.

• Epithelial Projections (Papillae)
  ✔️ The anterior two-thirds of the tongue contains papillae, which may have taste buds (fungiform, circumvallate, foliate) or be mechanical (filiform).

• Seromucous Glands (von Ebner’s glands)
  ✔️ Found particularly near circumvallate papillae, these deep glands secrete serous fluid that helps wash taste buds.

❌ The Incorrect Statement:

• “It is lined by stratified columnar epithelium”
  🔻 This is false.

  ✔️ The tongue is lined by stratified squamous epithelium, not columnar.

  • The anterior two-thirds (oral part) is often keratinized, especially over the dorsum (resisting friction).

  • The posterior third is non-keratinized and covers the lingual tonsils.

  ❗ Stratified columnar epithelium is rare in the body and is typically found in parts of the male urethra, large ducts of some glands, and the conjunctiva — not on the tongue.

The canal of Schlemm, also known as the scleral venous sinus, is a circular channel in the limbal region of the eye, located at the junction of the cornea and sclera. Its primary function is to drain aqueous humor from the anterior chamber of the eye into the episcleral venous system. This drainage helps maintain intraocular pressure (IOP), and its dysfunction can lead to glaucoma.

🔬 Why “It is lined by endothelium” Is Correct:

The canal of Schlemm is lined by a continuous layer of endothelial cells, much like blood and lymphatic vessels. However, it is unique because although it resembles a blood vessel, it lacks a muscular wall and primarily serves a fluid-draining function, not nutrient transport. The endothelial lining allows for transcellular and paracellular transport of aqueous humor via a mechanism involving giant vacuoles and pores.

❌ Why the Other Options Are Incorrect:

It is lined by stratified squamous epithelium
This type of epithelium is found in areas exposed to friction and environmental stress, like the skin or corneal epithelium. The canal of Schlemm is an internal fluid channel, not a surface structure, so it is not lined with stratified squamous epithelium.

It contains red cells
Under normal physiological conditions, the canal of Schlemm does not contain red blood cells. It drains aqueous humor, which is a clear, protein-poor fluid. The presence of red blood cells would indicate abnormal communication with blood vessels or hemorrhage.

None of these
This is incorrect because one of the statements—“It is lined by endothelium”—is true.

It communicates with the vitreous chamber
The vitreous chamber is the space behind the lens filled with vitreous humor. The canal of Schlemm is involved in draining aqueous humor from the anterior chamber, which is in front of the lens. There is no anatomical or functional connection between the canal of Schlemm and the vitreous chamber.

To appreciate the epithelium covering the dorsum of the tongue, let’s examine both function and regional variation in epithelial types.

🧬 1. Structure and function of the dorsum:

• The dorsum (top surface) of the tongue is exposed to constant mechanical stress—friction, food movement, temperature, and microbial exposure.

• To withstand this, it is covered by stratified squamous epithelium, which is multilayered for protection.

🌟 2. Keratinization—complete or partial?

• The dorsum is not uniformly keratinized.

• It is partially keratinized, meaning:

  • Some regions (especially those with filiform papillae, primarily in the anterior dorsum) are keratinized.

  • Other regions (especially near the posterior third, which includes taste buds and lingual tonsils) are non-keratinized or less keratinized.

• This transitional pattern allows both protection and sensitivity—important for both mechanical and sensory roles.

❌ Why the Other Options Are Incorrect:

1. Pseudostratified columnar:

• Found in the respiratory tract, not in the tongue.

• This type includes cilia and goblet cells, which are unnecessary for the tongue’s abrasive surface.

2. Stratified columnar:

• Rare and found in parts of the conjunctiva, pharynx, or male urethra.

• Not suited for high-friction environments like the tongue.

3. Stratified squamous non-keratinized:

• Found in moist, protected surfaces like the oral cavity lining, esophagus, and vagina.

• Parts of the ventral tongue (underside) use this, but not the dorsum.

4. Stratified squamous keratinized:

• Partially true, as parts of the anterior dorsum are fully keratinized.

• However, this does not represent the entire dorsum, especially the posterior third, which lacks full keratinization.

• Therefore, “partially keratinized” more accurately describes the overall epithelial composition.

Laiq Hussain Page 182

✅ Correct Answer: Seromucous

To answer this, we need to understand the types of salivary glands associated with the tongue and the secretions they produce.

🏗️ Anatomy of tongue glands:

The tongue contains minor salivary glands scattered in different regions, and they vary in secretion type depending on their location:

👉 The glands at the tip of the tongue are known as the glands of Blandin and Nuhn, which are mixed glands: they produce both serous (watery, enzyme-rich) and mucous (viscous) secretions.

Hence, their secretion is classified as seromucous.

✅ Why  Seromucous is correct:

• The anterior lingual glands are mixed glands (containing both serous and mucous acini).

• Their secretions combine watery and mucous properties → seromucous secretion.

❌ Why the other options are incorrect:

📝 Key takeaway:

• Glands at the tip of the tongue (glands of Blandin and Nuhn) → seromucous secretion (both watery and mucous).

• Purely serous = von Ebner; purely mucous = glands of Weber.

🧠 The Retinal Pigmented Epithelium (RPE):

The RPE is the outermost layer of the retina, lying adjacent to the choroid, and plays essential roles in photoreceptor maintenance, light absorption, and visual cycle regulation.

Let’s evaluate each feature one by one:

✅ Correct Features:

1. “It consists of simple columnar epithelium”
   ✔️ True.
   The RPE is composed of a single layer of low columnar to cuboidal epithelial cells, not stratified. So this statement is correct.

2. “The cells show phagocytic activity”
   ✔️ True.
   RPE cells phagocytose the shed outer segments of photoreceptor cells (rods and cones) on a daily basis — essential for retinal health.

3. “It strongly adheres to Bruch’s membrane of choroid”
   ✔️ True.
   The basal side of the RPE is firmly attached to Bruch’s membrane, which lies between the RPE and the choriocapillaris of the choroid. This adhesion is critical for nutrient exchange.

4. “It contains stores of vitamin A”
   ✔️ True.
   RPE cells store and recycle vitamin A (retinol), which is essential for the visual cycle — particularly the regeneration of 11-cis-retinal, the light-sensitive molecule in rods.

❌ Incorrect Feature:

• “It consists of stratified columnar epithelium”
  ❌ False.
  This is incorrect — the RPE is a single layer (simple epithelium). The cells are not stratified. Stratified columnar epithelium is very rare in the human body and certainly not found in the retina.

The tongue is covered by stratified squamous epithelium, not stratified columnar epithelium.

• The dorsal surface has keratinized stratified squamous epithelium (especially on the anterior 2/3).

• The ventral surface has non-keratinized stratified squamous epithelium.

Why the Other Options Are Correct:

• Covered by stratified squamous epithelium ✅ Correct

• The tongue is indeed covered by stratified squamous epithelium.

• Contains elevations called papillae ✅ Correct

• The dorsal surface of the tongue has papillae (filiform, fungiform, circumvallate, foliate).

• Contains minor salivary glands that secrete seromucous secretions ✅ Correct

• Small salivary glands (von Ebner’s glands) secrete serous fluid, while other minor glands secrete mucous or mixed.

• Lingual papillae are formed by stratified squamous epithelium only ✅ Correct

• Papillae are projections of stratified squamous epithelium with connective tissue cores.

The retina is the light-sensitive layer of the eye responsible for detecting visual stimuli and transmitting signals to the brain via the optic nerve. It has multiple layers, including photoreceptor cells (rods & cones), bipolar cells, and ganglion cells.

Why Option  Is Incorrect:

• The innermost layer of the retina is the ganglion cell layer, which contains the cell bodies of ganglion cells that send signals to the brain.

• Rods and cones (photoreceptor cells) are actually found in the outer layer of the retina, next to the retinal pigment epithelium (RPE).

Why the Other Options Are Correct:

•  It is the photoreceptor layer ✅

• The retina contains rods (for night vision) and cones (for color vision), making it the primary photoreceptor layer.

•  Two retinal layers can easily be detached ✅

• The neural layer and the retinal pigment epithelium (RPE) are loosely attached, making retinal detachment possible.

•  It is highly vascular ✅

• The retina receives blood supply from the central retinal artery and the choroid, making it highly vascular.

• It terminates at ora serrata ✅

• The ora serrata is the anterior termination of the retina, marking the transition from the photosensitive retina to the non-photosensitive part of the ciliary body.

Meibomian glands (tarsal glands) are not sweat glands; they are modified sebaceous glands. These oil-producing glands are embedded within the tarsal plates of the eyelids and help prevent tear evaporation by secreting a lipid-rich substance.

Why the Other Options Are Correct:

•  Tarsal plates are covered by skin ✅

• The tarsal plates (dense connective tissue structures) give shape to the eyelids and are indeed covered externally by skin.

•  Contain sweat glands of Moll ✅

• Glands of Moll are modified apocrine sweat glands found at the eyelid margin.

•  Covered by layer of elastic skin ✅

• The eyelid skin is highly elastic and one of the thinnest layers of skin in the body.

•  Lined internally by palpebral conjunctiva✅

• The inner surface of the eyelids is lined by the palpebral conjunctiva, a thin mucous membrane that continues onto the eyeball as the bulbar conjunctiva.

The keratin layer is present in areas of the oral cavity that experience high mechanical stress, providing protection against friction and trauma. These keratinized regions include:

• Hard palate

• Gingiva (attached gingiva)

• Dorsal surface of the tongue (especially filiform papillae)

These areas are covered by keratinized stratified squamous epithelium, either orthokeratinized (without nuclei) or parakeratinized (with nuclei).

Why the Other Options Are Wrong:

• Lips ❌

• The external surface of the lips (vermilion border) is keratinized, but the inner mucosal surface is non-keratinized.

• Soft palate ❌

• The soft palate is lined by non-keratinized stratified squamous epithelium, as it is more flexible and involved in speech and swallowing.

• None of these ❌

• Incorrect because the hard palate is keratinized.

•  Alveolar mucosa ❌

• The alveolar mucosa (lining inside the cheeks and lips) is non-keratinized, making it softer and more flexible.

Von Ebner’s glands are serous glands located in the posterior tongue, specifically around the circumvallate and foliate papillae. Their serous secretions help:

• Dissolve food molecules to enhance taste perception

• Flush out taste buds to prepare them for new stimuli

Why the Other Options Are Wrong:

•  Found on anterior 2/3rd of tongue ❌

• Von Ebner’s glands are located posteriorly, mainly near the circumvallate papillae at the junction of the anterior 2/3rd and posterior 1/3rd.

• Present beneath filiform papillae ❌

• They are found beneath the circumvallate and foliate papillae, not filiform papillae (which lack taste buds).

• Simple tubular glands ❌

• They are compound tubuloacinar glands, not simple tubular glands.

• Produce mucous secretion ❌

• Von Ebner’s glands produce serous (watery) secretions, not mucus.

The lacrimal gland is actually a compound tubuloacinar gland, meaning:

• It has multiple lobules

• It contains both tubular and acinar (alveolar) secretory units

• It secretes serous fluid (tears)

Thus, stating that the lacrimal gland is “simple tubuloacinar” is incorrect.

Why the Other Options Are Correct:

• Tears flow to the lacrimal puncta: ✅

• Tears drain from the eye’s surface into the lacrimal puncta (tiny openings on the medial eyelid margins) before entering the lacrimal canaliculi and nasolacrimal duct.

• Lacrimal glands drain into superficial parotid lymph nodes ✅

• Lymphatic drainage of the lacrimal gland goes to the superficial parotid lymph nodes.

• Tears collect in the conjunctival fornix ✅

• The conjunctival fornix (junction between the conjunctiva of the eyelid and the eye) temporarily holds tears before they spread across the eye.

•  Secretions produced are called tears ✅

• The lacrimal gland secretes tears, which lubricate and protect the eye.

In the outer plexiform layer (OPL) of the retina, rods and cones synapse with both horizontal cells and bipolar cells. This layer is crucial for the initial processing of visual information before it is transmitted to the inner retinal layers.

•Bipolar cells receive direct synaptic input from rods and cones and transmit the signal to ganglion cells.

•Horizontal cells help integrate and regulate input from multiple photoreceptors, playing a role in lateral inhibition, which enhances contrast and visual sharpness.

Why the Other Options Are Wrong:

2.Bipolar cells (Partially correct, but incomplete) – While bipolar cells do synapse with photoreceptors, horizontal cells also contribute to processing in the outer plexiform layer.

3.Amacrine and bipolar cells (Incorrect choice) – Amacrine cells are involved in processing at the inner plexiform layer, not the outer plexiform layer.

4.Amacrine cells (Incorrect choice) – These cells do not synapse with photoreceptors. They mainly interact with bipolar and ganglion cells in the inner plexiform layer.

5.Ganglion cells (Incorrect choice) – Ganglion cells receive input from bipolar cells in the inner plexiform layer, not directly from photoreceptors.

Most minor salivary glands are predominantly mucous-secreting, except for Von Ebner’s glands, which are serous. These glands are scattered throughout the oral mucosa, including the buccal, labial, lingual, and palatal regions.

They play a crucial role in lubrication, protection, and moistening of the oral cavity, especially aiding in speech and swallowing.

Why the Other Options Are Wrong:

1.They have numerous excretory units (Incorrect choice) – Minor salivary glands have individual ducts that open directly into the oral cavity, unlike major salivary glands that have complex ductal systems.

2.They are seromucous (Incorrect choice) – While some minor salivary glands have a mixed secretion, most are purely mucous.

3.They are serous (Incorrect choice) – Most are mucous, with the exception of Von Ebner’s glands, which are purely serous and located near the circumvallate papillae.

4.They are encapsulated (Incorrect choice) – Unlike the major salivary glands (parotid, submandibular, and sublingual), minor salivary glands are not encapsulated; they are embedded within connective tissue.

Von Ebner’s glands are purely serous glands located in the posterior part of the tongue, specifically around the circumvallate and foliate papillae. These glands secrete watery, enzyme-rich saliva that helps in:

•Washing taste buds to enhance taste perception.

•Secreting lingual lipase, which helps in fat digestion.

Why the Other Options Are Wrong:

1.Seromucous (Incorrect choice) – Seromucous glands contain both serous and mucous cells, but Von Ebner’s glands are purely serous.

2.Sebaceous glands (Incorrect choice) – Sebaceous glands secrete sebum (oily secretion) and are found in the skin, not in the tongue.

3.Mucous (Incorrect choice) – Mucous glands produce thick, mucus-rich secretions, but Von Ebner’s glands secrete watery serous fluid.

4.Sweat glands (Incorrect choice) – Sweat glands (eccrine/apocrine) are involved in thermoregulation, not in taste perception.

Minor salivary glands are mostly mucous-secreting, except for a few exceptions:

•Von Ebner’s glands (located in circumvallate papillae of the tongue) are serous-secreting.

•The rest of the minor salivary glands (labial, buccal, palatine, and lingual glands) are predominantly mucous-secreting.

Since most minor salivary glands are mucous, the statement that all minor salivary glands are serous is incorrect.

Why the Other Options Are Correct:

1.“Serous cells are predominant in the submandibular gland” (Correct)

•The submandibular gland is a mixed gland but has predominantly serous cells (~80%) and a smaller proportion of mucous cells (~20%).

2.“Intercalated ducts are wider and longer in the parotid gland” (Correct)

•The parotid gland is a purely serous gland with well-developed intercalated and striated ducts, which help modify saliva composition.

3.“All minor salivary glands are not encapsulated” (Correct)

•Unlike the major salivary glands (parotid, submandibular, sublingual), which have a fibrous capsule, minor salivary glands are not encapsulated and are dispersed in the mucosa.

4.“Demilune cells secrete lysozyme in the sublingual gland” (Correct)

•Serous demilune cells (found in mixed glands like sublingual and submandibular) secrete lysozyme, an enzyme that helps break down bacterial cell walls.

Taste buds are specialized sensory structures primarily located on the tongue, but also found on the soft palate, pharynx, and epiglottis. Each taste bud consists of three main cell types:

•Gustatory (taste) cells – Sensory receptor cells that detect taste stimuli.

•Sustentacular (supporting) cells – Provide structural and metabolic support.

•Basal cells – Precursors that regenerate taste cells.

At the apex of each taste bud, there is a taste pore, a small opening that allows dissolved tastants (food molecules) to interact with taste receptor cells. This is crucial for taste perception.

Why the Other Options Are Wrong:

1.“They are mainly located on the soft palate but few on the ventral surface of the tongue” (Incorrect choice) – Taste buds are mainly found on the dorsal surface of the tongue, especially on the fungiform, foliate, and circumvallate papillae, rather than the ventral surface.

2.“Sustentacular cells of taste buds are also known as gustatory cells” (Incorrect choice) – Sustentacular cells are supporting cells, while gustatory cells are the actual sensory cells involved in taste perception.

3.“Taste buds are embedded within epithelium covering the filiform papillae” (Incorrect choice) – Filiform papillae are the most numerous papillae on the tongue, but they lack taste buds; their main function is providing friction for food manipulation.

4.“A taste bud consists of 10-12 cells” (Incorrect choice) – A single taste bud typically contains 50-100 cells, including gustatory, sustentacular, and basal cells.

The dorsum of the tongue is exposed to constant friction from food during chewing and also undergoes significant mechanical stress. To protect the underlying tissues, it is covered by stratified squamous epithelium. However, because different areas of the tongue face different levels of stress, the keratinization varies:

• Anterior 2/3 (especially over the filiform papillae): Keratinized

• Other regions (like interpapillary zones or near taste buds): Non-keratinized

So, the correct and most comprehensive description is:
➡ Stratified squamous partially keratinized epithelium

❌ Why Other Options Are Wrong:

Pseudostratified columnar – This lines respiratory passages, not the oral cavity or tongue.

Stratified squamous non-keratinized – Found in less exposed areas like ventral tongue, esophagus, and vagina, but not on the dorsum.

Stratified squamous keratinized – Not fully accurate; only some areas are keratinized.

Stratified columnar – Rare; seen in conjunctiva and salivary ducts, not the tongue.

The papillae of the tongue are small, raised structures that are involved in taste and texture sensation. Some papillae contain taste buds, which are specialized sensory organs responsible for detecting the five basic tastes (sweet, sour, salty, bitter, and umami). However, not all types of papillae contain taste buds. Let’s go over the different types of papillae listed in the options:

1. Filliform Papillae (Correct answer):

• Filliform papillae are the most numerous type of papillae found on the tongue. These papillae are thin and conical and are primarily involved in the mechanical sense of touch and texture. They do not contain taste buds. Their main function is to grip and move food around the mouth, not to detect taste.
• Therefore, filliform papillae do not contain taste buds.

2. Circumvallate Papillae:

• The circumvallate papillae are larger and located at the back of the tongue in a V-shaped row. They do contain taste buds, and they are responsible for a significant portion of the taste sensation on the tongue.
• This option is incorrect because circumvallate papillae do contain taste buds.

3. Fungiform Papillae:

• Fungiform papillae are mushroom-shaped structures found mainly on the tip and sides of the tongue. They also contain taste buds. These papillae are involved in taste perception, especially for sweet and salty tastes.
• This option is incorrect because fungiform papillae do contain taste buds.

4. All of These:

• Since filliform papillae do not contain taste buds, but circumvallate, fungiform, and foliate papillae do, this statement is incorrect.

5. Foliate Papillae:

• The foliate papillae are located on the sides of the tongue. These papillae do contain taste buds, although they are not as numerous as the other types.
• This option is incorrect because foliate papillae do contain taste buds.

Correct Answer: Filliform

• Filliform papillae do not contain taste buds. They are involved in the mechanical processing of food and do not contribute to taste sensation.

Why the Other Options Are Incorrect:

• Circumvallate: These papillae contain taste buds and are involved in taste sensation.
• Fungiform: These papillae contain taste buds and are located mainly at the tip of the tongue.
• Foliate: These papillae contain taste buds and are located on the sides of the tongue.
• All of these: Since filliform papillae do not contain taste buds, the statement “all of these” is incorrect.

To answer this question, we need to review what neuroepithelium is and its functions. Neuroepithelium refers to specialized epithelial cells that are involved in sensory reception. They are modified epithelial cells that have characteristics of both epithelial cells and neuronal cells because they are responsible for sensing stimuli and relaying information to the nervous system. They are typically found in sensory organs like the taste buds, olfactory epithelium, and inner ear.

Breaking down each option:

1. “These are specialized cells for the reception of taste”:

   • This statement is correct. Neuroepithelial cells in the taste buds are responsible for taste reception. They detect chemical stimuli (taste molecules) and send signals to the brain via cranial nerves. These cells are a specialized form of neuroepithelium involved in taste perception.

2. “It forms nasal mucosa”:

   • This statement is incorrect. Neuroepithelium is not the primary component of the nasal mucosa. While olfactory epithelium (a type of neuroepithelium) is present in the olfactory region of the nasal cavity, it does not form the entire nasal mucosa. The nasal mucosa is made up of ciliated pseudostratified columnar epithelium with goblet cells that help trap debris and pathogens, not neuroepithelium.

3. “It is simple cuboidal epithelium”:

   • This statement is incorrect. Neuroepithelium is typically not simple cuboidal epithelium. In sensory organs like the taste buds, olfactory epithelium, and cochlea, neuroepithelium may appear as columnar or modified epithelium, and it is not cuboidal. The structure of neuroepithelium varies based on its function in sensory organs, but it is not described as cuboidal in general.

4. “It is present in cochlea”:

   • This statement is correct. Neuroepithelium is present in the cochlea in the form of hair cells in the organ of Corti. These cells are responsible for detecting sound vibrations and converting them into neural signals that are sent to the brain via the auditory nerve.

5. “None of these”:

   • This option would be incorrect because one of the statements is indeed incorrect (specifically, “It is simple cuboidal epithelium” and “It forms nasal mucosa”).

Correct Answer: “It is simple cuboidal epithelium”

The statement “It is simple cuboidal epithelium” is incorrect because neuroepithelium is typically not simple cuboidal epithelium; it can have a columnar or specialized form in sensory organs, but not cuboidal.

Why the Other Options Are Correct:

• “These are specialized cells for the reception of taste”: This is correct because neuroepithelial cells in taste buds are responsible for detecting taste stimuli.
• “It forms nasal mucosa”: This is incorrect as neuroepithelium does not form the entire nasal mucosa. The olfactory part is neuroepithelium, but the rest is not.
• “It is present in cochlea”: Correct because the cochlea contains neuroepithelial cells (hair cells) that are involved in hearing.

The rods and cones of the retina are photoreceptor cells responsible for detecting light and color. They are located in the outer nuclear layer of the retina.

Retinal Layers (From Innermost to Outermost):

1.Inner limiting membrane

2.Nerve fiber layer

3.Ganglion cell layer

4.Inner plexiform layer

5.Inner nuclear layer

6.Outer plexiform layer

7.Outer nuclear layer ✅ (Contains photoreceptor cell bodies: rods & cones)

8.External limiting membrane

9.Photoreceptor layer (Rods & Cones: Outer Segments)

10.Retinal pigment epithelium (RPE)

Why the Other Options Are Incorrect:

1.Inner limiting membrane  ❌ Incorrect

•The innermost layer of the retina, separating the retina from the vitreous humor.

•Does not contain photoreceptors.

2.Inner nuclear layer  ❌ Incorrect

•Contains bipolar, amacrine, and horizontal cells, which help process visual signals, but not photoreceptors.

3.Outer plexiform layer  ❌ Incorrect

•Contains synapses between photoreceptors and bipolar cells, but not the cell bodies of rods and cones.

4.Inner plexiform layer ❌ Incorrect

•Contains synapses between bipolar cells and ganglion cells, but not photoreceptors.

Circumvallate papillae are large, dome-shaped papillae found in a V-shaped row at the back of the tongue. They have several characteristic features:

✅ Supplied by the glossopharyngeal nerve (CN IX)

✅ 8–12 in number

✅ Largest papillae

✅ Surrounded by grooves (moats) lined with taste buds

However, the glands in these grooves secrete serous fluid, not mucus. This secretion comes from Von Ebner’s glands, which are serous glands, helping to wash away food particles and enhance taste perception. Since the statement  mentions mucous secretions, it is incorrect.

Why the Other Options Are Correct:

2.“They are supplied by the glossopharyngeal nerve”✅ Correct

•Unlike other papillae, circumvallate papillae are innervated by CN IX (glossopharyngeal nerve) rather than the facial nerve (CN VII).

3.“They are 8–12 in number”  ✅ Correct

•Circumvallate papillae are few in number (8–12) but large in size.

4.“They are the largest papillae”  ✅ Correct

•These are the largest papillae on the tongue.

5.“They are surrounded by grooves”  ✅ Correct

•They are encircled by deep grooves (moats) that contain taste buds.

The retinal pigmented epithelium (RPE) is a single layer of simple columnar epithelium with pigmented cells that play a crucial role in supporting photoreceptors.

Key Features of the Pigmented Epithelium of the Retina:

✅ Simple columnar epithelium → Provides structural integrity (Option  is correct).

✅ Stores vitamin A → Required for photopigment regeneration (Option  is correct).

✅ Phagocytic activity → Helps remove shed photoreceptor outer segments (Option  is correct).

✅ Strong adherence to Bruch’s membrane → Forms a critical barrier between the retina and choroid .

Since the RPE consists of simple columnar epithelium, the statement “It consists of stratified columnar epithelium”

Why the Other Options Are Correct:

“It consists of simple columnar epithelium” ✅ Correct

•The RPE is a single layer of simple columnar cells.

“It contains stores of vitamin A”  ✅ Correct

•The RPE stores and metabolizes vitamin A, essential for visual pigment synthesis.

“The cells show phagocytic activity” ✅ Correct

•RPE cells phagocytose the outer segments of photoreceptors, preventing debris accumulation.

“It strongly adheres to Bruch’s membrane of the choroid”  ✅ Correct

•The RPE is tightly bound to Bruch’s membrane, facilitating nutrient exchange between the choroid and retina.

The corneal epithelium is composed of stratified squamous non-keratinized cells. This type of epithelium is made up of multiple layers of cells that provide protection to the cornea while maintaining moisture. The non-keratinized nature of these cells allows the cornea to remain transparent, which is essential for vision.

Why the other options are incorrect:

• Simple columnar cells: These cells are typically found in the lining of certain organs like the intestines and stomach, but not in the corneal epithelium.

• Transitional cells: Transitional epithelium is found in organs that need to stretch, such as the bladder, but it does not form the corneal epithelium.

• Stratified squamous keratinized cells: While stratified squamous keratinized epithelium is found in the skin, the cornea has non-keratinized cells to maintain transparency for vision.

• Stratified columnar cells: This is a rare form of epithelium found in parts of the male urethra and some excretory ducts, but it is not present in the corneal epithelium.

Filiform papillae are the most numerous type of papillae on the tongue. They are keratinized, which gives them a rough texture. These papillae do not contain taste buds; instead, they help with the mechanical process of moving food around in the mouth and assist in tactile sensation. The keratinization of these papillae is particularly important for their function in the mechanical handling of food.

Why the other options are wrong:

1. Taste buds are only found in filiform papillae: This statement is incorrect. Taste buds are actually found in fungiform, circumvallate, and foliate papillae, not in filiform papillae. Filiform papillae do not contain taste buds.

2. Dorsal surface of tongue is smooth and shows prominent lingual veins: This statement is incorrect. The dorsal surface of the tongue is not smooth; it is covered with various papillae (including filiform, fungiform, circumvallate, and foliate), which give it a textured appearance. Prominent lingual veins are typically visible on the ventral (underside) surface of the tongue, not the dorsal surface.

3. Circumvallate papillae are present behind the sulcus terminalis: This statement is partially correct. Circumvallate papillae are located in front of the sulcus terminalis (the V-shaped groove that separates the anterior two-thirds from the posterior one-third of the tongue). So, they are not behind the sulcus terminalis; they are positioned just in front of it.

4. Lingual papillae are formed of stratified squamous epithelium only: This statement is inaccurate. The lingual papillae are formed by stratified squamous epithelium, but they also have specialized structures, including taste buds (in some types) and underlying connective tissue layers that provide structure and support. The statement misses these additional components.

Imagine the retina as a complex, multi-layered film at the back of your eye, designed to capture light and convert it into signals your brain can understand. Now, here’s the crucial point: the retina is structured in an “inside-out” fashion. This means that the light-sensitive cells, the photoreceptors (rods and cones), are actually located at the back of the retina, furthest from the incoming light.

Therefore, when light enters your eye, it must traverse through several layers before reaching these photoreceptors. Let’s trace the path of light:

1. Ganglionic Cell Layer: This is the innermost layer, closest to the vitreous humor (the gel that fills the eye). Light passes through this layer first. These cells are the output neurons, whose axons form the optic nerve.
2. Inner Plexiform Layer: Next, light passes through this layer, which contains synapses (connections) between ganglion cells, bipolar cells, and amacrine cells (interneurons).
3. Bipolar Cell Layer: This layer contains the cell bodies of bipolar cells, which act as intermediaries, transmitting signals between photoreceptors and ganglion cells.
4. Outer Plexiform Layer: Another synaptic layer, this one connects photoreceptors to bipolar and horizontal cells.
5. Receptor Cell Layer (Photoreceptor Layer): Finally, light reaches the rods and cones, the photoreceptors that convert light into electrical signals.
6. Pigmented Layer: This is the outermost layer, adjacent to the choroid (the blood vessel-rich layer). It absorbs stray light, preventing it from scattering and blurring the image.

Why the other options are incorrect:

• Pigmented Layer: This is the outermost layer, where light is absorbed after it has passed through all the other layers.
• Bipolar Layer: Light passes through this layer after the ganglionic layer and before the photoreceptor layer.
• Inner Plexiform Layer: Light passes through this layer after the ganglionic layer and before the bipolar layer.
• Receptor Cell Layer: Light reaches this layer last, where the photoreceptors are located.

The retina is the light-sensitive layer at the back of the eye that detects light and sends signals to the brain, allowing us to see. Photoreceptors are the specialized cells within the retina that respond to light. There are two main types of photoreceptors in the human retina: rods and cones.

Correct Answer: D) Rods and Cones

1. Rods:
   • Function: Rods are responsible for vision in low-light conditions (scotopic vision). They are highly sensitive to light but do not detect color. They are crucial for seeing in dim lighting, such as at night.
2. Cones:
   • Function: Cones are responsible for color vision and sharp vision (visual acuity) in bright light (photopic vision). There are three types of cones: red, green, and blue, which enable us to perceive a range of colors.

Rods and Cones together form the photoreceptors in the retina. While rods are better in dim light, cones work best in brighter conditions and help with color differentiation.

Why the Other Options are Wrong:

1. A) Melanocytes:

   • Explanation: Melanocytes are not photoreceptors. These cells produce the pigment melanin, which gives color to the skin, hair, and eyes (including the iris and the retina). Melanocytes are not involved in light detection for vision. Therefore, they cannot be photoreceptors.
   • Reason for Rejection: Melanocytes are involved in pigmentation, not light perception.

2. B) Rods:

   • Explanation: While rods are indeed photoreceptors, this option is incomplete. Cones are also photoreceptors in the retina, and the question asks for the photoreceptors of the retina, so both rods and cones are needed for the full answer.
   • Reason for Rejection: The answer is incomplete because it misses cones, which are essential for color vision.

3. C) None of these:

   • Explanation: This option implies that none of the choices are photoreceptors. However, rods and cones are indeed the two types of photoreceptors in the retina, making this option incorrect.
   • Reason for Rejection: Since rods and cones are the correct photoreceptors, this answer is false.

4. E) Cones:

   • Explanation: While cones are photoreceptors responsible for color vision and sharpness of vision, the question asks for all photoreceptors in the retina, which includes both rods and cones.
   • Reason for Rejection: This is incomplete, as it omits rods, which are necessary for low-light vision.

The fovea centralis is a small central area in the retina that is responsible for sharp central vision (high visual acuity).

• It contains only cones and no rods.
• It is located within the macula lutea.
• It is specialized for daylight vision (photopic vision) and color perception.
• The highest concentration of cones is found here, making it the sharpest point of vision.

Since the fovea centralis contains no rods, the correct answer is:
✅ “Fovea centralis”

Why the Other Options Are Incorrect:

1. “Outer nuclear layer” – ❌ Incorrect

   • The outer nuclear layer contains the nuclei of both rods and cones, so rods are present here.

2. “Macula” – ❌ Incorrect

   • The macula lutea contains both cones and some rods, especially in its peripheral areas.

3. “Granular layer” – ❌ Incorrect

   • This term is non-specific, but if referring to the inner granular layer, it contains bipolar, amacrine, and horizontal cells, not photoreceptors (rods/cones).

4. “None of these” – ❌ Incorrect

   • The fovea centralis does lack rods, making this option incorrect.

The optic disc (also called the blind spot) is the region in the retina where the optic nerve exits the eye. This area lacks both rods and cones, meaning it cannot detect light, creating a blind spot in the visual field.

Since the optic disc is devoid of rods and cones, the correct answer is:
✅ “Optic disc”

Why the Other Options Are Incorrect:

1. “Neural layer” – ❌ Incorrect

   • The neural layer of the retina contains photoreceptors (rods and cones) and neurons involved in visual processing.

2. “Fovea centralis” – ❌ Incorrect

   • The fovea centralis is the area with the highest concentration of cones for sharp central vision, not an area devoid of photoreceptors.

3. “Macula lutea” – ❌ Incorrect

   • The macula lutea surrounds the fovea and contains a high concentration of cones for detailed vision.

4. “Retina” – ❌ Incorrect

   • The retina as a whole contains both rods and cones. Only the optic disc lacks photoreceptors.

The tarsal plate is a dense connective tissue structure within the eyelid that provides rigidity and support. It contains Meibomian glands, which are specialized sebaceous glands that secrete an oily lipid layer that helps prevent tear evaporation.

• The Meibomian glands are arranged in parallel rows within the tarsal plate and open along the eyelid margin.
• Dysfunction of these glands can lead to dry eye syndrome or Meibomian gland dysfunction (MGD).

Why the Other Options Are Incorrect?

1. Dense Connective Tissue Layer with Gland of Zeis ❌

   • The glands of Zeis are sebaceous glands associated with eyelash follicles, but they are not embedded within the tarsal plate.
   • Instead, they are located near the base of the eyelashes.

2. Dense Connective Tissue Layer with Gland of Molls ❌

   • The glands of Moll are modified sweat glands located near the base of the eyelashes, but not within the tarsal plate.

3. Loose Connective Tissue Layer with Sebaceous Glands ❌

   • The tarsal plate is made of dense connective tissue, not loose connective tissue.
   • Loose connective tissue is found in the subcutaneous layer of the eyelid, not in the tarsal plate.

4. Loose Connective Tissue Layer with Sebaceous Glands ❌

   • This is a duplicate option and remains incorrect for the reasons stated above.

Olfactory cells (also called olfactory receptor neurons) are located in the olfactory epithelium, which is a specialized area of the mucous membrane found in the upper part of the nasal cavity. This epithelium contains the sensory cells responsible for detecting odors, and their axons form the olfactory nerve (CN I), transmitting sensory information to the brain.

Why the other options are incorrect:

• Conchae: The nasal conchae (also called turbinates) are bony structures in the nasal cavity that help to filter, humidify, and warm the air, but they do not contain olfactory cells.

• Respiratory epithelium: This epithelium lines most of the nasal cavity, but it is not involved in the sense of smell. It is involved in filtering and conditioning the air.

• Vestibule: The vestibule of the nose is the external part that contains coarse hairs and is involved in filtering larger particles from the air, but it does not contain olfactory cells.

• Uncus: The uncus is part of the temporal lobe of the brain and is involved in olfactory processing, but it is not where olfactory cells are located.