Ch5 Respiratory system
Airway anatomy (conducting → respiratory zone)
- trachea
- bronchus
- bronchioles
- terminal bronchioles
- respiratory bronchioles
- alveolar ducts
- alveolar sacs
Lung location and pleura
- the bottom of the lung is attached to the diaphragm
- the lungs lie in the chest cavity, which is separated into two
-
pleural structure :
-
visceral pleura
- intrapleural fluid
- parietal pleura outside of it
Ventilation mechanics
- inspiration: air in
- expiration: air out
Driven by:
- diaphragm (contracts)
- external intercostal muscles
Gas exchange pathway (high level)
- alveoli → lung capillaries → tissue capillaries → cells
Hemoglobin (Hb) and O\(_2\) binding
O\(_2\) binding curve
Cooperative binding
- Hb has four subunits
- binding of 1 unit of O\(_2\) makes binding of more O\(_2\) more likely (cooperativity)
What Hb can bind
- hemoglobin can bind to oxygen and CO\(_2\)
CO\(_2\) transport in blood
CO\(_2\) is transported:
- via Hb (~30%)
- as HCO\(_3^-\) (~60%)
- dissolved in fluids (~10%)
Carbonic anhydrase (CA)
-
carbonic anhydrase facilitates:
-
CO\(_2\) + H\(_2\)O → HCO\(_3^-\)
Anion exchanger 1 (AE1)
- AE1 transports 1 HCO\(_3^-\) while Cl\(^-\) moves in the opposite direction
- HCO\(_3^-\) leaves Hb near cells and enters near alveoli
O\(_2\) unloading and tissue metabolism
- Hb can remain bound from ~75% to ~10% with oxygen
- increased metabolism (increased CO\(_2\) content and/or H\(^+\)) in peripheral tissue increases O\(_2\) release by decreasing Hb affinity for O\(_2\)
Ventilatory control: negative feedback loops
Negative feedback loop 1 (peripheral H\(^+\))
- controlled variable: peripheral H\(^+\)
- sensor: chemoreceptor neurons
- controller: brainstem (medulla oblongata)
- actuating signal: motor neurons
- effectors: muscles controlling ventilation
Effect :
- increasing ventilation increases CO\(_2\) release and increases O\(_2\) brought in
Negative feedback loop 2 (central H\(^+\))
- controlled variable: central H\(^+\)
- sensor: chemoreceptor neurons
- controller: brainstem (medulla oblongata)
- actuating signal: motor neurons
- effectors: muscles controlling ventilation
Effect :
- increasing ventilation increases CO\(_2\) release and increases O\(_2\) brought in
Negative feedback loop 3 (peripheral O\(_2\))
- controlled variable: peripheral O\(_2\)
- sensor: chemoreceptor neurons
- controller: brainstem (medulla oblongata)
- actuating signal: motor neurons
- effectors: muscles controlling ventilation
Effect :
- increasing ventilation increases CO\(_2\) release and increases O\(_2\) brought in
Erythropoietin (EPO): long-term O\(_2\) regulation
- erythropoietin increases RBC level (long-term)
EPO control loop
- sensor: peritubular interstitial cells in kidney
- controller: peritubular interstitial cells in kidney
- actuating signal: EPO
- effector: RBC precursor cells in bone marrow
- controlled variable: \(P_{O_2}\) level in kidney interstitial space