Physiology 18 Gas Exchange Notes PDF

**[18.1 Gas Exchange in the Lungs and Tissues]** 1. [List three arterial blood parameters that influence ventilation] - 3 regulated variables: - Oxygen, Carbon dioxide, pH 2. [Diagram the normal partial pressures of O2 and CO2 in the atmosphere, alveoli, arterial blood, resting...

**[18.1 Gas Exchange in the Lungs and Tissues]** 1. [List three arterial blood parameters that influence ventilation] - 3 regulated variables: - Oxygen, Carbon dioxide, pH 2. [Diagram the normal partial pressures of O2 and CO2 in the atmosphere, alveoli, arterial blood, resting cells, and venous blood] - **Atmosphere**: PO2 =160 mm Hg / PCO2 = 0.25 mm Hg - **Alveol**i: PO2 = 100 mm Hg / PCO2 =40 mm Hg - **Arterial blood**: PO2 = 100mmHg / PCO2 = 40mmHg - **Resting cells**: PO2 = 40 mmHg / PCO2 = 46mmHg - **Venous blood**: PO2 = 40 mmHg / PCO2 = 46mmHg Diagram of blood flow diagram Description automatically generated 3. [Describe all the factors that influence gas exchange between the atmosphere and arterial blood] - **Diffusion rate ∞ surface area x concentration gradient x barrier permeability** - Diffusion rate ∞ 1/distance^2^ - Normal physiology constants = [SA, barrier permeability, & diffusion distance] - NOTE: THESE ARE NEGATIVELY AFFECTED BY PATHOLOGICAL CHANGES - These affect gas exchange between pulmonary capillaries and arterial blood - **Concentration gradient = changing variable primary factor in gas exchange**  \*\*\*REVIEW 4. [Explain the difference between the concentration of a gas in solution and the partial pressure of that gas in solution, using O2 and CO2 as examples] - **Gas solubility affects Diffusion** - Equilibrium is based off partial pressure... NOT concentration of gas - O2 is not very soluble in water compared to air... so concentration of O2 in air will be much greater even if partial pressures are in equilibrium - CO2 is much more soluble than O2 in water so more dissolves. There will be greater CO2 concentration in water than the O2 was... But still more concentration in air vs water. - **This is why we need a much higher gradient for oxygen than CO2!!!** - Gas dissolving in liquid is proportional to partial pressure + solubility - CO2 is 20 times more soluble than O2 - O2 needs way higher concentration gradient than CO2 A diagram of a solution Description automatically generated  **\*\*\*RECAP OF WHAT AFFECTS GAS MOVEMENT:** - **Pressure gradient of gas** - **Solubility of the gas in liquid** - **Temperature (constant in human body)** 2. **[Gas Transport in the Blood]** 5. SKIP 6. [Explain the role of hemoglobin in oxygen transport from the molecular level to the systemic level] - 98% of oxygen transport is bound to hemoglobin in RBC's - High PO2 shifts Hb + O2 = HbO2 (oxyhemoglobin) transports to cells - Low pO2 shift Hb + O2 HbO2 - Free O2 is used in cellular respiration - **Partial pressure depends on how much oxygen is in plasma pO2** A diagram of blood cells Description automatically generated 7. [Describe the relationship between plasma PO2 and oxygen transport] - **pO2 of plasma determines how much oxygen binds to hemoglobin!** - **More pressure = more oxygen carrying capacity** - **Partial pressure depends on how much oxygen and RBC's is in plasma... NOT in the alveoli**  A diagram of a structure Description automatically generated 8. [Draw the oxyhemoglobin saturation curve, explain the physiological significance of the shape of this curve, and draw the shifts in the curve that result from changes in pH, temperature, and 2,3-BPG] - **SHIFT RIGHT (lower)**: decrease pH/more acidic, increase temperature, increase pCO2, high 2,3-BPG - **SHIFT LEFT (higher):** increase pH/less acidic, decrease temperature, low pCO2, low 2,3-BPG 9. SKIP 10. [Write the chemical reaction for the conversion of CO2 to HCO3-, including the enzyme that catalyzes the reaction]  A diagram of blood cells Description automatically generated 11. [Map the transport of carbon dioxide in the arterial and venous blood, including the exchanges of CO2 between the blood and the alveoli or cells] - Venous blood carries 7% of CO2 dissolved in plasma - 23% as carbaminohemoglobin (HbCO2) - 70% as bicarbonate ion (HCO3^-^) in plasma **\*REFER to diagram above**  3. **[Regulation of ventilation]** 12. [Map the reflex control of ventilation including appropriate neurotransmitters and their receptors] A diagram of a human body Description automatically generated \***Ventilation is subject to continuous modulation by chemoreceptor and mechanoreceptor linked reflexes and higher brain centers.** 13. [Diagram the current model for the brain stem neural networks that control breathing] - Inspiratory neurons active positive feedback - At end of respiration, activity shuts off abruptly - Expiration occurs through recoil of elastic lung tissue  **Dorsal Respiratory group** -- to muscles of inspiration (diaphragm intercostal muscles) - Sensory input to pons **Pontine respiratory groups** **Ventral respiratory group (VRG)** -- basic pacemaker activity / areas for active expiration or greater than normal inspiration 14. [Explain the mechanisms by which central and peripheral chemoreceptors monitor CO2 and O2 levels] - **Peripheral chemoreceptors**: rarely activated... only when pO2 is low - Located in carotid bodies - Sense changes in pO2, pH, and pCO2 - Has **specialized glomus cells** - **MOST SENSITIVE TO O2 CHANGES** A black text on a white background Description automatically generated  - **Central chemoreceptors**: what normally causes us to breath - Located in CNS - Respond to changes in pCO2 - When pCO2 is high crosses into brain ECF converted into bicarbonate & H+ A diagram of a blood vessel Description automatically generated High plasma pCO2 CO2 leaves cerebral capillary & first enters cerebrospinal fluid there CO2 is converted to bicarbonate and H+ H+ is detected at central chemoreceptor