Respiration – 2016

Correct Answer:
✅ Respiratory acidosis

• Explanation: The patient’s symptoms — chronic cough, chest tightness, and difficulty breathing — suggest an obstructive lung disease such as COPD (common in elderly). In such cases, hypoventilation occurs, leading to CO₂ retention (hypercapnia). Increased CO₂ in blood shifts the equilibrium of carbonic acid:

This results in respiratory acidosis, with elevated PaCO₂ and decreased blood pH.

Incorrect Options:

❌ Metabolic alkalosis

• Caused by vomiting, diuretic use, or excess bicarbonate intake. It presents with weakness or muscle cramps, not cough and chest tightness.

❌ Respiratory alkalosis

• Occurs due to hyperventilation (e.g., anxiety, altitude, pulmonary embolism). It leads to low CO₂, not CO₂ retention.

❌ Metabolic acidosis

• Results from renal failure, diabetic ketoacidosis, or lactic acidosis. Symptoms include Kussmaul breathing, not chronic cough with chest tightness.

❌ Compensatory respiratory alkalosis

• Seen in metabolic acidosis as a compensatory mechanism (e.g., deep, rapid breathing in DKA). That doesn’t fit this clinical scenario.

Correct Answer:
✅ Sphingomyelinase

• Explanation: Sphingomyelinase is the enzyme that specifically hydrolyzes sphingomyelin into ceramide and phosphorylcholine. Deficiency of this enzyme leads to the accumulation of sphingomyelin in cells, which is the basis of Niemann–Pick disease (a lysosomal storage disorder).

Incorrect Options:

❌ Phosphatase

• Removes phosphate groups from molecules, but does not act on sphingomyelin.

❌ Ceramidase

• Hydrolyzes ceramide into sphingosine and free fatty acids. It acts downstream, not directly on sphingomyelin.

❌ Glucocerebrosidase

• Degrades glucocerebroside into ceramide and glucose. Its deficiency causes Gaucher disease, not Niemann–Pick.

❌ Glucosidase

• General enzyme that breaks down glucose-containing polysaccharides or oligosaccharides, unrelated to sphingomyelin metabolism.

Correct Answer:
✅ Sternal angle

• Explanation: The trachea bifurcates into the right and left main bronchi at the level of the sternal angle (Angle of Louis), which corresponds to the T4–T5 intervertebral disc level. This landmark is important in anatomy because it also marks the beginning and end of the aortic arch and is a key surface landmark in thoracic anatomy.

Incorrect Options:

❌ Gastroesophageal junction

• This is located at the level of T10–T11, where the esophagus joins the stomach. It has no relation to the trachea.

❌ T4

• Close, but the exact level is the sternal angle at T4–T5, not just T4 alone.

❌ T3

• This is too high; the trachea is still above the bifurcation here.

❌ T6

• This is too low; the trachea has already bifurcated by this point.

Correct Answer:
✅ Nucleus pulposus

• Explanation: The notochord is a midline structure formed during the 3rd week of development, important for signaling and inducing the development of the neural tube and axial skeleton. In adults, most of the notochord disappears, but it persists as the nucleus pulposus of the intervertebral disc — the gelatinous central portion that acts as a shock absorber between vertebrae.

Incorrect Options:

❌ Transverse process

• This is derived from the vertebral arch and mesenchymal condensations, not the notochord.

❌ Sternum

• Develops from somatic mesoderm, not the notochord.

❌ Vertebral arch

• Derived from the sclerotome of somites, not from the notochord.

❌ Vertebral body

• The vertebral body develops around the notochord from the sclerotome, but the notochord itself regresses here and does not persist.

Correct Answer:
✅ Atypical pneumonia

• Explanation: Patients with HIV and other immunocompromised states are especially prone to atypical pneumonias, often caused by organisms such as Pneumocystis jirovecii (previously PCP), Mycoplasma pneumoniae, Chlamydophila pneumoniae, or viral agents. These infections present with cough, fever, chills, and wheezing, but their pattern of lung involvement and clinical presentation differ from classic bacterial pneumonia. In HIV, Pneumocystis pneumonia is the hallmark atypical pneumonia, presenting with productive cough, fever, and respiratory distress.

Incorrect Options:

❌ Typical pneumonia

• Usually caused by bacteria like Streptococcus pneumoniae or Haemophilus influenzae. It presents with sudden high fever, productive “rusty” sputum, and lobar consolidation. More common in immunocompetent patients.

❌ Aspiration pneumonia

• Occurs when oropharyngeal/gastric contents enter the lungs (common in alcoholics, stroke patients, unconscious patients). Usually affects the right lower lobe due to bronchial anatomy. Not the most expected in HIV.

❌ Pneumoconiosis

• Occupational lung disease due to dust inhalation (coal, silica, asbestos). Presents with chronic interstitial changes, not acute infection with fever and sputum.

❌ Bronchopulmonary pneumonia

• Patchy consolidation around bronchioles, often bacterial in origin (e.g., Staph aureus). Seen after viral infections or aspiration. Not the most characteristic pneumonia in HIV patients.

Correct Answer:
✅ Right bronchus

• Explanation: The right main bronchus is wider, shorter, and more vertical compared to the left. Because of this anatomical orientation, inhaled or aspirated foreign bodies are most likely to enter and lodge in the right bronchus. This is especially true in children, where foreign body aspiration is a common emergency presenting with cough, wheezing, and sometimes obstructive emphysema or collapse of the affected lung segment.

Incorrect Options:

❌ Bronchioles

• Foreign bodies usually get trapped earlier in the main or lobar bronchi, not the tiny bronchioles, unless they are very small particles.

❌ Lobule of lung

• The lobule is too distal. Large objects like a coin cannot reach this level.

❌ Left bronchus

• The left main bronchus is longer, narrower, and more oblique, so it is less likely to trap foreign bodies compared to the right.

❌ Trachea

• A foreign body can temporarily lodge here, but it usually either causes complete obstruction (life-threatening stridor, choking) or moves down into one of the main bronchi.

Correct Answer:
✅ Has its own vein

• Explanation: A bronchopulmonary segment is the smallest independent functional unit of the lung. Each segment is supplied by its own segmental (tertiary) bronchus and its own segmental branch of the pulmonary artery. However, the veins are intersegmental, meaning they lie in the connective tissue between segments and drain blood from adjacent segments. Therefore, a bronchopulmonary segment does not have its own vein.

Incorrect Options:

❌ Pyramidal in shape

• Correct characteristic. Each segment is roughly pyramidal, with its apex pointing toward the hilum and base facing the pleural surface.

❌ Segmental bronchus

• Correct characteristic. Each segment is ventilated by its own tertiary (segmental) bronchus.

❌ Has its own artery

• Correct characteristic. Each segment receives a branch of the pulmonary artery that runs with the bronchus.

❌ Independent functional unit

• Correct characteristic. Each segment can be surgically removed without affecting the function of neighboring segments, making it clinically important in segmentectomy.

Correct Answer:
✅ 6 mEq/L

• Explanation: In respiratory acidosis (such as from brain trauma causing hypoventilation), CO₂ accumulates, leading to increased H⁺ in the blood. To buffer this acidosis, H⁺ moves into cells, and in exchange, K⁺ moves out of cells (H⁺/K⁺ exchanger). This shift results in hyperkalemia. A normal serum potassium is around 3.5–5.0 mEq/L, so a patient with respiratory acidosis can show a significantly elevated value, such as 6 mEq/L.

Incorrect Options:

❌ 2.5 mEq/L

• This indicates hypokalemia, which is not typical in respiratory acidosis. Hypokalemia is more often seen in metabolic alkalosis.

❌ 3.5 mEq/L

• This is the lower limit of normal potassium, not reflecting the hyperkalemia expected in acidosis.

❌ 4.5 mEq/L

• This is within the normal range and would not fit the pathophysiology of respiratory acidosis with significant H⁺/K⁺ shift.

❌ 4 mEq/L

• Also within normal range, again not consistent with the hyperkalemia induced by acidosis.

Correct Answer:
✅ 7–10

• Explanation: The bucket handle movement refers to the way the lower ribs (7–10) move during inspiration. Their curved shafts swing upward and outward, like the handle of a bucket, which increases the transverse diameter of the thoracic cavity. This movement is facilitated by the orientation of the costotransverse and sternocostal joints in these ribs. It is especially important for efficient lung expansion in quiet and deep breathing.

Incorrect Options:

❌ 3–8

• Ribs 3–6 are mainly involved in the pump handle movement, which increases the anteroposterior diameter of the thorax.

❌ 10–12

• These ribs are called floating ribs (11–12) and false ribs (10). They do not contribute significantly to bucket handle movement.

❌ 2–6

• Again, ribs in this range are more associated with pump handle movement, not bucket handle.

❌ 1–7

• Rib 1 is fixed and moves very little. Upper ribs (1–6) mainly contribute to the anteroposterior expansion (pump handle), not the transverse one.

Correct Answer:
✅ Hydrogen ion concentration

• Explanation: pH is mathematically defined as the negative logarithm of the hydrogen ion concentration:

pH=−log⁡10[H+]\text{pH} = -\log_{10} [\text{H}^+]pH=−log10​[H+]

This gives a convenient way to express very small concentrations of hydrogen ions in solution. For example, if [H+]=1×10−7 M[H^+] = 1 \times 10^{-7} \, M[H+]=1×10−7M, then pH = 7. A low pH means high hydrogen ion concentration (acidic), while a high pH means low hydrogen ion concentration (basic).

Incorrect Options:

❌ Weak acid

• A weak acid contributes to [H+][H^+][H+], but pH is not the negative log of the acid itself — it is of the hydrogen ion concentration.

❌ Hydroxyl ion concentration

• This is related to pOH, not pH.

pOH=−log⁡10[OH−]\text{pOH} = -\log_{10} [\text{OH}^-]pOH=−log10​[OH−]

pH and pOH are linked through water: pH+pOH=14pH + pOH = 14pH+pOH=14.

❌ Weak base

• A weak base affects the solution’s hydrogen ion concentration indirectly, but pH is not defined in terms of the base itself.

❌ Strong acid

• A strong acid dissociates completely to release [H+][H^+][H+], but pH is still defined as the negative log of hydrogen ion concentration, not the acid.

Correct Answer:
✅ Inferior vena cava

• Explanation: The central tendon of the diaphragm has an opening at the level of T8 vertebra where the inferior vena cava (IVC) passes. A stab wound reaching this area can injure the IVC, leading to massive hemorrhage. The IVC is thin-walled, large, and under low pressure but can bleed profusely due to its caliber. This is the most clinically relevant structure at risk in this case.

Incorrect Options:

❌ Inferior phrenic artery

• Supplies the diaphragm itself but does not pass through the central tendon. It runs along the diaphragm’s undersurface.

❌ Aorta

• The aorta passes through the aortic hiatus at T12, located posteriorly, not through the central tendon.

❌ Azygos vein

• The azygos vein also passes with the aorta at the aortic hiatus (T12), not the central tendon.

❌ Hemiazygos vein

• Like the azygos vein, it drains into the azygos system and traverses near the aortic hiatus at T12, not the central tendon.

Correct Answer:
✅ 1st rib

• Explanation: The 1st rib has a distinct groove on its superior surface for the subclavian artery (posterior groove) and another for the subclavian vein (anterior groove). This feature is unique to the 1st rib, which is short, broad, and curved. It also serves as an important landmark in the thoracic inlet.

Incorrect Options:

❌ 4

• The 4th rib is a typical rib with no grooves for major vessels.

❌ 2

• The 2nd rib has a tuberosity for the serratus anterior muscle but no groove for the subclavian artery.

❌ 3

• The 3rd rib is also a typical rib without special vascular grooves.

❌ 6

• The 6th rib is a typical rib, not involved in forming the thoracic inlet, and does not have grooves for large vessels.

Correct Answer:
✅ Acid and conjugate base

• Explanation: The pH of a buffer solution is determined by the relative concentrations of a weak acid and its conjugate base (or a weak base and its conjugate acid). This relationship is mathematically expressed by the Henderson–Hasselbalch equation:

pH=pKa+log⁡([A−][HA])\text{pH} = \text{p}K_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right)pH=pKa​+log([HA][A−]​)

Here, [HA] is the weak acid, and [A⁻] is its conjugate base. It’s the ratio of these two that decides the buffer’s pH, not the absolute amounts.

Incorrect Options:

❌ Weak acid

• A weak acid alone cannot resist pH changes effectively. Without its conjugate base, it cannot neutralize added base.

❌ Weak and strong acid

• Mixing acids does not form a buffer. A strong acid fully dissociates, destroying the delicate balance required for buffering.

❌ Weak base

• A weak base alone is insufficient. It needs its conjugate acid to form a buffer pair.

❌ Strong acid

• Strong acids completely ionize and cannot establish the equilibrium needed for buffering action.

Correct Answer:
✅ Pneumoconiosis and rheumatoid arthritis

• Explanation: Caplan syndrome is a rare condition seen in patients with rheumatoid arthritis (RA) who also develop pneumoconiosis (usually coal workers’ pneumoconiosis). The combination leads to multiple, well-defined, round pulmonary nodules that develop rapidly and are superimposed on the background of pneumoconiosis. These nodules can cavitate and are different from the usual rheumatoid lung nodules. The key hallmark is RA + occupational dust-related pneumoconiosis.

Incorrect Options:

❌ Silicosis and tuberculosis

• This combination is known as Silicotuberculosis, not Caplan syndrome. Silica predisposes the lung to TB infection by impairing macrophage function.

❌ Byssinosis and rheumatoid arthritis

• Byssinosis occurs from cotton dust exposure, producing “Monday fever” or chest tightness at the beginning of the work week. It is not linked to RA.

❌ Berriliosis

• Beryllium exposure causes a granulomatous lung disease resembling sarcoidosis. It has no association with rheumatoid arthritis.

❌ Asbestosis and tuberculosis

• Asbestos exposure is linked to asbestosis, mesothelioma, and bronchogenic carcinoma, but not to TB or RA in Caplan syndrome.