Respiratory System Overview and Structure

Study Notes

The respiratory system's main function is supplying body tissues with oxygen and removing carbon dioxide produced by cellular metabolism.
Respiration involves:
- Pulmonary ventilation: Air exchange between the atmosphere and alveoli.
- External respiration: Movement of oxygen from lungs into blood and carbon dioxide from blood to lungs.
- Internal respiration: Movement of oxygen from blood to tissue cells and carbon dioxide from cells to blood.

Location: Thorax, from neck to diaphragm.
Thoracic wall includes intercostal muscles.
Lungs: Passive, elastic structures that change volume based on pressure differences inside and outside the lungs.
Upper Airway: Air travels to the larynx (where vocal cords are).
Lungs contain:
- Pharynx
- Larynx
- Trachea
- Bronchi
- Bronchioles
- Alveoli: Tiny sacs where gas exchange occurs with blood. Alveolar sacs are the location where gas exchange occurs.
- Alveoli are supplied by capillaries, providing a large surface area for quick diffusion.
- Type I alveolar cells form a continuous layer.
- Type II alveolar cells produce surfactant, a substance that reduces surface tension and prevents alveolar collapse.

Boyle's Law describes the inverse relationship between pressure and volume.
Intrapulmonary pressure (pressure inside the lungs) changes to drive air movement.
Inspiration: Intrapulmonary pressure is less than atmospheric pressure.
Expiration: Intrapulmonary pressure is greater than atmospheric pressure.

Inspiration:
- Diaphragm and intercostal muscles contract.
- Thoracic cavity expands.
- Lungs expand, increasing lung volume.
- Intrapulmonary pressure decreases, causing air to flow into the lungs.
Expiration:
- Diaphragm and intercostal muscles relax.
- Thoracic cavity recoils.
- Lung volume decreases.
- Intrapulmonary pressure increases, causing air to flow out of the lungs.
Breathing is an active process during inspiration and a passive process during expiration.

Respiratory rhythm is controlled by the medulla oblongata.
Major cardio control centers are in the medulla oblongata.
Motor neurons control muscle movements (especially the diaphragm) for breathing.

Carotid bodies are strategically located to monitor oxygen supply to the brain.
Peripheral chemoreceptors in carotid bodies respond to changes in H+ concentration.
Peripheral chemoreceptors indirectly influence ventilation by impacting chemoreceptor sensitivity to PCO2 and PO2.
Input from the receptors modifies respiratory rate and depth.

Alveolar PO2 is higher than blood PO2.
Oxygen diffuses from alveoli into plasma.
Cells obtain more oxygen during activity by decreasing tissue PO2, increasing blood-to-tissue PO2 gradient.
Binding oxygen with hemoglobin, via oxyhemoglobin.
Release of oxygen from hemoglobin forms deoxyhemoglobin.
Oxygen is transported both dissolved in plasma and bound to hemoglobin in erythrocytes.

CO2 is a waste product that can lower blood pH if not removed.
CO2 is transported in the blood in three ways
- Dissolved in plasma.
- Bound to hemoglobin.
- Converted to bicarbonate ions (HCO3-)
- Bicarbonate ions then diffuse out of blood into plasma.
Enzymes (carbonic anhydrase) facilitate CO2 conversion.
H+ levels in blood affect blood pH homeostasis.

Both respiratory systems and urinary systems work together to maintain blood pH homeostasis.
Acidosis occurs when plasma H+ concentration increases and blood pH falls, caused partially by respiratory issues that prevent CO2 removal.
Alkalosis occurs when plasma H+ concentration decreases and blood pH rises, caused partially by respiratory issues that increase CO2 removal rates.

Hypoventilation: Slow alveolar ventilation, leading to low blood pH and high CO2.
Hyperventilation: Fast alveolar ventilation, leading to high blood pH and low CO2.