Hemoglobin (Oxygen Buffering Function of Hemoglobin)

Oxygen Buffering Function of Hemoglobin

hemoglobin

She becomes __ (the iron-containing protein in red blood cells that carries oxygen)

heme

a four-subunit molecule with a ___ (an iron-containing ring that binds one oxygen molecule) in each subunit.

partial pressure of oxygen (PO2)

Gelo arrives in the lung capillaries, where ___ (the pressure exerted by dissolved oxygen, which determines how readily it binds) is about 100 mmHg. Every heme grabs an oxygen molecule until Gelo is almost fully saturated.

interstitial fluid

Next Gelo is swept into a muscle capillary. The working muscle is burning oxygen, so the PO2 in the surrounding ___ (the fluid that bathes tissue cells) is falling.

oxygen-hemoglobin dissociation curve

Gelo follows the ___ (the S-shaped graph relating PO2 to the percentage of hemoglobin saturated). Around tissue PO2 values she is on the steep part of the curve, so a small drop in PO2 makes her release a large amount of oxygen.

oxygen buffering

Around tissue PO2 values she is on the steep part of the curve, so a small drop in PO2 makes her release a large amount of oxygen. The more the muscle consumes, the more Gelo unloads. This is ___ (hemoglobin's ability to keep tissue PO2 relatively constant by releasing oxygen when tissue levels fall and holding it when levels are adequate). Even if the horse's oxygen use triples, tissue PO2 barely changes, because Gelo gives up the extra oxygen on demand. When the muscle rests and PO2 rises, she keeps hold of her cargo for the next trip.

Bohr effect

Exercise also pushes the curve rightward. Muscle produces CO2 , acid, and heat, and red cells produce 2,3-BPG. These changes drive the ___ (a rightward shift of the curve by higher CO2 , H+, and temperature, which lowers oxygen affinity and promotes unloading).

hypoxia

Gelo releases even more oxygen exactly where it is needed. So hemoglobin protects cells from ___ (inadequate oxygen supply to tissues) without sending PO2 swinging up and down.