The Lungs

A patient experiences respiratory alkalosis during a panic attack. Which receptor is most responsible for detecting the primary chemical change driving this response?

Central chemoreceptors in the medulla detect increased pH and decreased CO₂ levels in cerebrospinal fluid. Though peripheral chemoreceptors detect O₂, central chemoreceptors are more sensitive to CO₂, which drives respiratory changes.

Why is CO₂ transported more efficiently in blood than O₂, despite both gases diffusing across the alveolar membrane?

CO₂ is ~22 times more soluble in water than O₂, according to Henry's Law. This allows CO₂ to dissolve more readily into plasma and convert to bicarbonate for efficient transport.

During inspiration, what change in intrathoracic pressure allows air to flow into the lungs, and what muscles are primarily involved?

Inspiration causes intrathoracic volume to increase, which decreases pressure below atmospheric levels, drawing air in. The diaphragm contracts (C3–C5) and intercostal muscles (T1–T11) elevate the ribs.

A researcher disrupts elastin proteins in alveolar tissue of mice. What mechanical consequence is most likely?

Impaired elastic recoil of alveoli during exhalation. Elastin allows alveoli to return to resting shape, contributing to passive expiration. Loss leads to air trapping, similar to emphysema.

How does Fick’s Law explain the efficiency of gas exchange in alveoli, and how would pneumonia impair this?

Fick’s Law:
V = (P₁ - P₂) × A × D / T
Pneumonia increases T (thickness) due to fluid buildup, which reduces V (gas diffusion rate). The diffusion barrier is thicker, slowing O₂ entry into blood.

What neural pathway allows voluntary control of breathing (e.g., during singing or speaking)?

The cerebrum modulates breathing via descending pathways that bypass or influence the medullary respiratory center.

Why does oxygen take longer to equilibrate in blood than CO₂ during gas exchange?

Oxygen has lower solubility and must cross multiple barriers before binding to hemoglobin, whereas CO₂ diffuses faster and dissolves readily in plasma.

In a case of cervical spinal cord injury at C4, which aspect of ventilation would be impaired?

Diaphragmatic movement would be compromised due to damage to the phrenic nerve (C3–C5). The patient may require mechanical ventilation.

Inhaled air reaches the alveoli via coordinated anatomical structures. What role does the Adam’s apple play in this process?

The Adam’s apple is part of the larynx, marking the entrance to the trachea. It ensures air enters the lower respiratory tract rather than the esophagus.

What mechanism underlies thermoregulation through respiration during exercise or heat stress?

Increased breathing allows cool air to enter alveoli, where it absorbs heat from capillary blood before being exhaled as warmer air, facilitating heat loss.

A scuba diver descends to a depth where the partial pressure of O₂ is 3 atm. If Henry’s law constant for O₂ in blood at body temperature is 1.3 × 10⁻³ mol/(L·atm), what is the concentration of dissolved oxygen in the diver’s blood plasma at that depth?

Use Henry’s Law:
C = k × Pgas
Where:

• C = solubility (mol/L)

• k = Henry’s constant = 1.3 × 10⁻³ mol/(L·atm)

• Pgas = 3 atm

Step-by-step:
C = (1.3 × 10⁻³ mol/L·atm) × (3 atm)
C = 3.9 × 10⁻³ mol/L

A researcher models oxygen diffusion across alveolar membranes. The pressure difference between alveolar air and capillary blood is 60 mmHg, the surface area is 70 m², membrane thickness is 1 μm (1 × 10⁻⁶ m), and the diffusion coefficient for oxygen is 3 × 10⁻⁹ m²/s. What is the rate of diffusion (V) in mol/s?

Use Fick’s Law:
V = (P₁ - P₂) × A × D / T

Convert units:

• A = 70 m²

• D = 3 × 10⁻⁹ m²/s

• T = 1 × 10⁻⁶ m

• ΔP = 60 mmHg → convert to atm:
   60 mmHg × (1 atm / 760 mmHg) = 0.0789 atm

Plug in:
V = (0.0789 atm) × (70 m²) × (3 × 10⁻⁹ m²/s) / (1 × 10⁻⁶ m)
V = (0.0789) × (70) × (3 × 10⁻³)
V ≈ 0.0166 mol/s