Physiology 9 Resp.

External respiration

Gas exchange between alveoli and pulmonary capillaries

Internal respiration

Gas exchange between systemic capillaries and tissues

Conducting zone

Main function is moving, warming, humidifying, and filtering air; no gas exchange

Respiratory zone

Contains alveoli where gas exchange occurs

Type I alveolar cells

Flat cells responsible for gas exchange

Type II alveolar cells

Produce surfactant

Surfactant

Reduces surface tension, increases compliance, and prevents alveolar collapse

Infant respiratory distress syndrome

Low surfactant leading to low compliance and alveolar collapse

Normal intrapleural pressure

Approximately -4 mmHg

Purpose of negative intrapleural pressure

Keeps lungs expanded

Pneumothorax

Air enters pleural space causing lung collapse

Boyle's Law

Pressure and volume are inversely related

What happens during inspiration?

Thoracic volume increases, alveolar pressure decreases, air flows into lungs

What happens during expiration?

Elastic recoil decreases lung volume and air flows out

Compliance

Ability of lungs to stretch

High compliance

Lungs inflate easily but recoil poorly

Low compliance

Lungs are stiff and difficult to inflate

Disease with high compliance

Emphysema

Disease with low compliance

Fibrosis

Asthma

Increased airway resistance due to bronchoconstriction

Bronchitis

Increased airway resistance due to excess mucus

Dead space

Air that does not participate in gas exchange

Alveolar ventilation equation

RR × (TV − Dead Space)

Why are deep breaths more efficient than shallow breaths?

Dead space remains constant so more fresh air reaches alveoli

Dalton's Law

Total pressure equals the sum of all partial pressures

Henry's Law

The amount of gas dissolved is proportional to its partial pressure

Hypoventilation

Increased CO₂, decreased PO₂, respiratory acidosis

Hyperventilation

Decreased CO₂, respiratory alkalosis

Factors affecting diffusion

Surface area, membrane thickness, pressure gradient, diffusion coefficient

Fibrosis effect on diffusion

Increases membrane thickness and decreases diffusion

Emphysema effect on diffusion

Decreases surface area and decreases diffusion

Ventilation-perfusion matching

Airflow must match blood flow for efficient gas exchange

Most oxygen transport

Bound to hemoglobin

Right shift of oxyhemoglobin curve

Hemoglobin releases more oxygen to tissues

Causes of right shift

Increased CO₂, increased temperature, decreased pH, increased 2,3-DPG

Carbon monoxide poisoning

CO binds hemoglobin with very high affinity reducing oxygen delivery

Three forms of CO₂ transport

Dissolved, carbaminohemoglobin, bicarbonate

Major form of CO₂ transport

Bicarbonate

Carbonic anhydrase

Converts CO₂ and water into carbonic acid

DRG

Main inspiratory center in the medulla

VRG

Controls forced expiration

Pons

Smooths breathing rhythm

Most important regulator of ventilation

Arterial CO₂

Central chemoreceptors

Respond primarily to CO₂

Peripheral chemoreceptors

Respond to low oxygen, high CO₂, and low pH

At what PO₂ does oxygen strongly stimulate ventilation?

Below 60 mmHg

Exercise effect on oxyhemoglobin curve

Shifts curve to the right

Moderate exercise effect on PO₂ and PCO₂

Both remain near normal because ventilation matches metabolism

Respiratory acidosis

Caused by CO₂ retention from hypoventilation

Respiratory alkalosis

Caused by excessive CO₂ loss from hyperventilation

Why does emphysema make expiration difficult?

Loss of elastic recoil traps air in the lungs

Why does surfactant increase compliance

It lowers surface tension so alveoli expand more easily