Respiratory Physiology (Day 2) Flashcards
Chemoreceptors
Automatic control of breathing influenced by feedback from chemoreceptors
- -> monitor pH of fluids in brain & pH, PCO2 and PO2 in blood.
1. Central chemoreceptors in medulla
2. Peripheral chemoreceptors in carotid and aorta arteries
Central Chemoreceptors
–> in medulla
Increased CO2 in fluids of brain decrease pH–sensed by chemoreceptors in medulla –> increased ventilation
Senses CO2, not H+ which does not cross the blood-brain barrier
Takes longer, but responsible for 70−80% of increased ventilation
Peripheral Chemoreceptors
Aortic and carotid bodies respond to rise in H+ due to increased CO2 levels.
Respond faster than medullary chemoreceptors
Effect of Blood P(O2) on Ventilation
Indirectly affects ventilation by affecting chemoreceptor sensitivity to PCO2
Low blood O2 makes carotid bodies more sensitive to CO2.
Hypoxic drive: carotid bodies respond directly to low oxygen dissolved in plasma (below 70mmHg)
–>REMEMBER: major control by chemoreceptors is achieved by monitoring CO2, NOT O2
What are the three levels of gas exchange?
- atmosphere lung
- lung blood
- blood cells
Full process of gas exchange
- O2 enters the blood at alveolar-capillary interface
- O2 is transported in blood dissolved in plasma or bound to hemoglobin inside RBCs (IMPORTANT)
- O2 diffuses into cells
- CO2 diffuses out of cells
- CO2 is transported dissolved, bound to hemoglobin or as HCO3
- CO2 enters alveoli at alveolar-capillary interface
Causes of Low Alveolar P(O2)
- Inspired air has abnormally low oxygen content
- Altitude: as altitude increases, TOTAL atmospheric pressure and PO2 decrease
- -> Ex. 21% O2 at 10,000 ft (same as at sea level) but Patm = 523 mmHg
- -> Ex. At sea level Patm = 760 mmHg —thus, PO2 at 10,000 ft = 523/760 = only 69% of what it is at sea level - Alveolar ventilation is inadequate
- Decreased lung compliance (ex. fibrotic, restrictive pulmonary diseases, lack of surfactant)
- Increased airway resistance (ex. narrowing/obstruction by mucus - CF, bronchoconstriction - asthma)
- CNS depression: slows breathing rate, decreases depth of breathing (ex. alcohol poisoning, drug overdose)
Respiratory System Bulk Flow
DIDN’T COVER IN LECTURE
Entire mixture of gases is moving
- Flow from regions of higher to lower pressure —recall: Flow α ΔP/R
- Muscular pump creates pressure gradients —breathing is active process which requires muscle contraction to create ΔP. Muscles of thoracic cage and diaphragm act as the pump
- -> when muscles contract: chest wall expands, and lungs expand with it - Resistance to flow —recall: R α Lη/r4, in lungs, L, η are not significant
Partial Pressure of Gases in Blood
- Alveoli and blood capillaries quickly reach equilibrium for O2 and CO2.
a. This helps maximize the amount of gas dissolved in fluid.
b. The amount of gas that can dissolve in liquid depends on:
1. Partial pressure of the gases: major determining factor
2. Solubility of the gas in the liquid (constant)
3. Temperature of the fluid (more gas can dissolve in cold liquid) –>for blood, T = constant
Pulmonary Circulation: high flow, low pressure system
Right ventricle –> pulmonary trunk –> pulmonary arteries –> lungs –> pulmonary veins –> left atrium
***Blood pressure (ΔP) is LOW, but resistance to flow is VERY LOW, so flow through pulmonary circulation is very HIGH (important for exchange)
- Pulmonary blood flow = cardiac output, controlled primarily by the factors regulating cardiac output
- IMPORTANT to match blood perfusion and ventilation in the lung to maximize gas exchange (to reach equilibrium)
- Pulmonary arterioles: constrict when alveolar pO2 is low, dilate when pO2 is high. (Fig 17.14)
- ->Blood flow to alveoli is increased when they are full of oxygen and decreased when not. (want to send O2 to the well-ventilated alveoli so they will thrive)
Hypoxic Vasoconstriction
local mechanism for regulating the distribution of blood flow away from hypoxic alveoli
decreased tissue PO2 around underventilated alveoli constricts their arterioles, diverting blood to better ventilated alveoli
What influence gas exchange?
Diffusion and Solubility
What are the constants in gas exchange?
(under normal conditions)
- SA
- membrane thickness
- diffusion distance
- temp
What is the primary factor affecting gas exchange?
concentration gradient (depends on solubility)
Gas solubility
affects amount of dissolved gas that can be carried by plasma
O2 solubility is low –> very little O2 can be carried dissolved in plasma
–> concentration depends on gas’s solubility
