Download Physiology Objectives 43

Physiology Objectives 42
1.
Oxygen transport in the blood: oxygen is not very soluble in plasma (.003 ml in
100 ml of blood/mmHg of pressure), and therefore, oxygen transport in blood
primarily relies on hemoglobin (oxygen is highly soluble in hemoglobin).
Factors that alter hemoglobin-oxygen dissociation curve: fetal hemoglobin
has a higher affinity for O2 than regular hemoglobin, and thus, shifts the curve to
the left. Exercising and high altitude conditions (low pH, high heat, high PCO2,
and high 2,3-BPG) increase oxygen delivery to the tissue and decrease affinity for
O2, shifting the curve to the right.
Factors that shift and importance of P50: shifting of the hemoglobin-oxygen
dissociation curve shifts P50 and can change the PO2 at which oxygen is delivered
to the tissues. If P50 occurs at a high PO2, then oxygen will not bind hemoglobin
as easily at normal concentrations in the lungs; conversely, if P50 occurs at a low
PO2, then oxygen will bind hemoglobin more vigorously and will have more
trouble releasing oxygen in the tissues.
2.
Oxygen capacity: oxygen can combine with 1.34 ml of hemoglobin when
hemoglobin is fully saturated. Thus, the oxygen capacity for a solution with a
given concentration of hemoglobin at a specific volume is equal to the total
amount of hemoglobin/ml multiplied by full oxygen saturation (1.34).
Oxygen saturation: the amount of oxygen carried by hemoglobin in a setting;
can be measured by taking the amount of oxygen carried and dividing it by total
oxygen capacity.
3.
Requirements of adequate tissue oxygenation: adequate oxygen delivery to the
bloodstream, adequate oxygen uptake (both by hemoglobin and delivery of RBCs
by cardiac output), and adequate oxygen delivery to the tissues from the
bloodstream.
Causes of tissue hypoxia:
a.
Hypoxemic hypoxia: low PaO2, low oxygen saturation of hemoglobin
b.
Anemic hypoxia: low oxygen capacity; anemia
c.
Circulatory hypoxia: low blood flow to tissues; shock
d.
Histotoxic hypoxia: low cellular use of oxygen; cyanide poisoning
Blue blood (hypoxemic) vs. no blood (perfusion failure): blue blood is better
than no blood; because hemoglobin can carry a little oxygen at low PO2, poor
delivery of O2 is better than no O2 delivery at all.
4.
Carbon dioxide transport: carbon dioxide is transported in the plasma at 20
times higher solubility than oxygen (.06 ml in 100 ml of blood/mmHg of
pressure), as bicarbonate, and as carbamino compounds bound to hemoglobin
Carbon dioxide dissociation curve vs. oxygen dissociation curve: the carbon
dissociation curve differs from the oxygen dissociation curve in three ways:
higher CO2 per partial pressure, steeper slope, and no maximum plateau.
5.
Carbon dioxide exchange in the lung: blood PCO2 is lower than alveolar PCO2
and therefore, CO2 diffuses into the alveoli from the pulmonary capillaries; drop
in PCO2 also causes carbamino compounds to release CO2 into the plasma for
release into the alveoli; HCO3- is released from RBCs to make CO2 for release
into the alveoli
Haldane effect: as PO2 goes up, the CO2 dissociation curve shifts downward,
meaning that less CO2 is carried in the blood
Role of carbonic anhydrase in the chloride shift: carbonic anhydrase catalyzes
the conversion of carbon H2CO2 to H+ and HCO3-; in the tissue, where HCO3- is
being taken up, H+ is left behind and thus, Cl- shifts out of the cell to maintain
neutrality. Conversely, in the lung, where HCO3- is being secreted, H+ remains
in the cell, and Cl- shifts into the cell to maintain neutrality.