Lecture 18 Flashcards
External respiration
Diffusion of o2 from alveoli into blood in pulmonary capillaries + diffusion of co2 in opposite direction
In pulmonary gas exchange (external respiration), each gas diffuses
Independently
Deoxygenated blood from right side goes in lungs to get
oxygenated and go back to heart by left side
P of a specific gas in a mixture is called
Partial P
Po2 (partial pressure of o2) and Pco2 in atm
Po2: 159 mmHg
Pco2: 0.3mmHg
The greater the diff in partial pressure
The faster the rate of diffusion
External respiration occurs in
Lungs
Po2 and pco2 in alveolar air
Po2: 105 mmHg
Pco2: 40 mmHg
Diffusion of o2 in external respiration
From alveolar air (105 mmHg) to blood in pulmonary capillaries (40 mmHg)
Diffusion of co2 in external respiration
From deoxygenated blood (45 mmHg) to alveoli (40mmHg)
Diffusion of o2 in blood occurs until pulmonary capillary blood Po2 is
105 mmHg (like alveolar air)
Blood at 105 mmHg (after diffusion to equalize) mixes with blood supply to lung so that po2 in pulmonary veins returning to left side of heart =
100 mmHg
Pco2 45 mmHg of deox blood diffuses into alveoli until 40 mmHg in both so that oxy blood going back to left side of heart has pco2 of
40mmHg
During exercise, is the po2 in pulmonary capillaries higher or lower than 40 mmHg
Lower due to increase use of o2
3 factors influence external respiration
- Partial P gradient and gas solubilities
- Thickness and surface area of respiratory membranes
- Ventilation-perfusion coupling
Co2 is ___x more soluble than oxygen
20x
The greater the surface area, the
More efficient gas exchange
Respiratory membrane is very tuin (0,5 um) so it allows
Rapid diffusion of gases
Thickness of respiratory membrane increases with
Edema, pneumonia, heart failure (slows rate if gas exchange)
For optimal gas exchange, rate of ventilation (gas reaching alveoli) must
Match rate of perfusion (blood flow in pulmonary capillaries)
Ventilation-perfusion coupling is the process that
Coordinates respiratory and cardiovascular systems to deliver o2 to body tissues
Body responds to changes in ventilation by
Adjusting blood flow (airflow increases, blood flow too)
Internal respiration
Exchange of gases between systemic capillaries and tissue cells
Po2 in tissue cells
40 mmHg
Po2 in systemic capillaries
100 mmHg
Pco2 in tissue cells
45 mmHg
Pco2 in systemic capillaries
40 mmHg
Why is pco2 higher in tissue cells than in capillaries
Bc co2 is product of ATP
O2 doesn’t dissolve well in water so only 1,5-2% is
Dissolved in plasma of blood
98-98.5% of o2 is
Bound to Hb in RBC
Hb composed of four subunits with each a heme group and can carry
4 o2 atoms
Hemoglobin is what type of molecule
Protein
Each heme group (on every globin protein chain) has an iron atom at the center that binds with
1 o2 molecule.
1 RBC contains ~ 1 billion hb molecules
O2 sat =
Amount of o2 bound/max that could bind X100 = __%
When o2 binds to heme group it causes a
Confirmational change (increases affinity of 3 other o2 molecules )
Once o2 unloads, all other o2 molecules
Loose affinity for heme groups
Po2 bet 60-100 mmHg Hb is
90% or more saturated with o2
Affinity of Hb yo o2 is affected by
- Temperature
- PH
- Pco2 and co
- 2,3- diphosphoglycerate (2,3-DPG)
In Hb graph: green red and blue curves mean
Green: higher Hb affinity (po2 of 50 = 90%)
Red: normal (po2 50 = 83%)
Blue: reduced affinity (po2 50 = 73%), Hb is letting go of o2 (usually in tissues)
Temperature on Hb graph
T increases, affinity decreases. Heat is product of metabolic reactions, metabolically active cells need more o2
Ph on Hb graph
Decrease in ph = decrease in affinity.
H+ ions bind to Hb (protein) so alters structure slightly -> decrease o2 carrying capacity. More o2 available for tissue cells
Pck2 and ph are related bc
Low blood ph results from high pco2
As pco2 rises, Hb affinity
Decreases (releases o2)
Why does co2 lower ph
Bc when entering blood most is temporarily converted to carbonic acid -> unstable and dissociates in H+ and bicarbonate-> [H+] increases
During exercise, lactic acid (byproduct of anaerobic metabolism within muscles) does what to blood ph
Decreases ph
DPG (substance found in RBC) increases, Hb affinity
Decreases bc Hb binds o2 less tightly when combined with DPG
After entering the bloodstream, a co2 molecule
- Dissolves in plasma (7%)
- Binds to hb within rbc (23%)
- Converted to carbonic acid (70%)
Co2 that dissolves in plasma dies what when reaching lungs
Diffuses into alveolar air and is exhaled
When co2 binds to hb it makes
Carbaminohemoglobin on rbc
Co2 binds where on hb
Globin proteins (doesn’t compete with o2 bc not same place)
Pco2 is high in systemic capillaries which promotes formation of
Carbaminohemoglobin
Co2 in Carbaminohemoglobin exits body how
In pulmonary capillaries, pco2 is low so Hb releases co2 that enters alveoli but diffusion
Enzyme turning co2 in carbonic acid
Anhydrase
How co2 that transforms into carbonic acid exit body
Carbonic acid dissociates into h+ and bicarbonate ions (either peed out or kept in buffer system) and reenters rbc, leaves it and diffuses out
Co poisoning how
Co combines to heme group too but binding is 200x stronger than o2 so can’t be released as well. At [0,1%] of CO, half available Hb are bound with it so o2 carrying capacity is reduce by 50%.
