BIO EXAM 3C

Respiratory System Physiology and Biochemistry

Ventilation and Its Physiological Drivers

Ventilation refers to the movement of air into and out of the lungs, enabling gas exchange with the blood. It is driven by physiological actions that create pressure differences between the atmosphere and the alveoli.

• Definition: Ventilation is the process of air exchange between the lungs and the environment.

• Physiological Actions: Diaphragm contraction, intercostal muscle movement, and changes in thoracic cavity volume drive ventilation.

• Example: During inspiration, the diaphragm contracts and moves downward, increasing thoracic volume and decreasing alveolar pressure.

Bulk Flow of Air and Gas Laws

Bulk flow of air in the respiratory system is determined by pressure gradients, modeled mathematically by gas laws such as Boyle's Law.

• Boyle's Law: $P_1V_1 = P_2V_2$ (Pressure and volume are inversely related for a given amount of gas at constant temperature.)

• Compartment Pressures: Intrapulmonary (alveolar), intrapleural, and atmospheric pressures are involved.

• Example: Air flows into the lungs when alveolar pressure falls below atmospheric pressure.

Mechanisms of Inspiration and Expiration

Inspiration and expiration are controlled by muscle actions and pressure changes. Forced breathing involves additional muscles.

• Inspiration: Diaphragm and external intercostals contract, increasing thoracic volume.

• Expiration: Usually passive; forced expiration uses abdominal and internal intercostal muscles.

• Example: Deep inspiration recruits accessory muscles like the sternocleidomastoid.

Lung Pathologies: Atelectasis and Pneumothorax

Atelectasis (collapsed lung) and pneumothorax (air in pleural space) disrupt normal lung function and highlight the importance of pleura.

• Atelectasis: Loss of air from alveoli leads to lung collapse.

• Pneumothorax: Air enters pleural cavity, equalizing pressure and collapsing the lung.

• Critical Role of Pleura: Maintains negative pressure for lung expansion.

Lung Compliance

Compliance is the ability of the lungs to stretch and expand. It is determined by lung tissue elasticity and surface tension.

• Definition: Compliance = change in lung volume per unit change in pressure ($C = \frac{\Delta V}{\Delta P}$)

• Factors: Elastic fibers, surfactant, and chest wall flexibility.

Lung Surfactant: Chemistry and Function

Lung surfactant is a complex mixture of phospholipids and proteins that reduces surface tension in alveoli.

• Chemical Nature: Mainly dipalmitoylphosphatidylcholine (DPPC).

• Role: Prevents alveolar collapse, increases compliance.

Dead Space and Ventilation Parameters

Anatomical and alveolar dead space affect the efficiency of ventilation and gas exchange.

• Anatomical Dead Space: Air in conducting airways not involved in gas exchange.

• Alveolar Dead Space: Alveoli ventilated but not perfused.

• Minute Ventilation: $\text{Minute Ventilation} = \text{Tidal Volume} \times \text{Respiratory Rate}$

Respiration vs. Ventilation

Respiration refers to gas exchange at cellular and alveolar levels, while ventilation is the physical movement of air.

• Respiration: Exchange of O2 and CO2 between alveoli and blood, and between blood and tissues.

• Ventilation: Movement of air in and out of lungs.

External and Internal Respiration

External respiration occurs at the lungs; internal respiration occurs at tissues.

• External Respiration: Gas exchange between alveoli and blood.

• Internal Respiration: Gas exchange between blood and tissue cells.

Oxygen Transport in Blood

Oxygen is carried in the blood dissolved in plasma and bound to hemoglobin.

• Hemoglobin: Protein in red blood cells that binds O2.

• Importance: Increases O2 carrying capacity.

Hemoglobin Function and Oxygen Release

Hemoglobin releases more oxygen in active tissues due to factors like pH and CO2 concentration (Bohr effect).

• Bohr Effect: Lower pH and higher CO2 promote O2 release.

Carbon Dioxide Transport

CO2 is transported dissolved in plasma, as bicarbonate, and bound to hemoglobin.

• Three Ways: Dissolved, carbaminohemoglobin, bicarbonate ion ($\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3 \rightarrow \text{HCO}_3^- + \text{H}^+$)

Hypoxia and Hypercapnia

Hypoxia is low oxygen; hypercapnia is high carbon dioxide. Both have distinct causes and effects.

• Types of Hypoxia: Hypoxic, anemic, circulatory, histotoxic.

• Contrast: Hypercapnia leads to acidosis; hypoxia impairs cellular function.

Respiratory Centers of the Brain Stem

The brain stem contains centers that regulate breathing rhythm and depth.

• Centers: Medullary respiratory center, pontine respiratory group, dorsal and ventral respiratory groups.

Neural Control of Breathing

Other brain structures, including the cortex, influence voluntary breathing. Diaphragm and intercostal muscles are skeletal muscles.

• Structures: Cerebral cortex, limbic system, hypothalamus.

Hering-Breuer Reflex

This reflex prevents over-inflation of the lungs by inhibiting inspiration when stretch receptors are activated.

• Importance: Protects lung tissue from damage.

COPD: Pathophysiology and Risk Factors

COPD involves chronic airway inflammation and obstruction. It is a leading cause of morbidity and mortality.

• Physiological Components: Chronic bronchitis and emphysema.

• Risk Factors: Smoking, air pollution, genetic predisposition.

SARS-CoV2 and the Respiratory/Cardiovascular Systems

SARS-CoV2 infects respiratory and cardiovascular systems via ACE2 receptors, leading to inflammation and impaired gas exchange.

• Mechanism: Viral entry via ACE2, cytokine storm, vascular damage.

Gas Transport	Mechanism	Key Molecule
Oxygen	Hemoglobin binding, dissolved in plasma	Hemoglobin
Carbon Dioxide	Bicarbonate formation, carbaminohemoglobin, dissolved	Hemoglobin, carbonic anhydrase

Additional info: Some explanations and examples have been expanded for academic completeness and clarity.