Transport of O2 and CO2 Flashcards

Comprehensive vocabulary flashcards covering the chemical structure of respiratory pigments, the dynamics of oxygen and carbon dioxide transport, and physiological adaptations to hypoxia and exercise.

Hemoglobin Oxygen Carrying Capacity

The ability of blood to carry approximately $200\,mL$ of $O_2$ per liter of blood, which is a $50\times$ increase over the $4\,mL$ that can be carried by dissolved $O_2$ alone.

Methemoglobin

A form of hemoglobin that occurs when the iron is accidentally oxidized from $Fe^{2+}$ to $Fe^{3+}$, rendering it unable to carry $O_2$.

Heme

A flat ring structure containing one iron atom ($Fe^{2+}+$) that is identical in all hemoglobins across all species; one molecule of $O_2$ binds to one heme.

Globin

The protein portion of the hemoglobin molecule that varies between species and stages of life, determining how tightly $O_2$ is held.

Adult Human Hemoglobin (HbA)

A tetramer composed of four subunits (2 alpha ($\alpha$) and 2 beta ($\beta$) globin chains), with each subunit holding one heme for a total of 4 $O_2$ molecules.

Myoglobin

A monomeric muscle respiratory pigment consisting of one subunit and one heme that holds $O_2$ more tightly than blood hemoglobin and facilitates $O_2$ diffusion to mitochondria.

Fetal Hemoglobin (HbF)

A form of hemoglobin composed of $\alpha$-globin and $\gamma$-globin that has a higher $O_2$ affinity than adult hemoglobin to allow the fetus to extract $O_2$ from maternal blood.

Hemocyanins

The second most common respiratory pigment, containing copper bound directly to protein; they are always plasma-dissolved and turn bright blue when oxygenated.

Chlorocruorins

Iron-porphyrin respiratory pigments found in four families of marine annelid worms that are greenish in dilute solution and use a formyl group instead of a vinyl chain.

Hemerythrins

Iron-based respiratory pigments that contain no heme, are always intracellular, and turn reddish-violet when oxygenated; found in sipunculid worms and brachiopods.

Mammalian Red Blood Cells (RBCs)

Biconcave discs approximately $7.4\,\mu m$ in diameter that, in mature form, lack a nucleus, mitochondria, and ribosomes, resulting in a lifespan of roughly 4 months.

Erythropoietin (EPO)

A hormone released by the kidneys in response to hypoxia that travels to the bone marrow to stimulate the production of new red blood cells.

HIF-1 (Hypoxia-Inducible Factor 1)

A transcription factor that acts as a molecular switch to detect low $O_2$ levels and trigger the release of erythropoietin.

Cooperativity

A phenomenon in multi-subunit pigments like hemoglobin where binding $O_2$ at one site increases the affinity of the remaining sites, resulting in a sigmoid (S-shaped) equilibrium curve.

$$P_{50}$$

The partial pressure of $O_2$ at which 50% of the pigment binding sites are saturated; a higher $P_{50}$ indicates a lower $O_2$ affinity.

Bohr Effect

The decrease in $O_2$ affinity (rightward shift of the equilibrium curve) caused by a decrease in pH or an increase in $PCO_2$, facilitating $O_2$ release in active tissues.

Root Effect

A phenomenon in teleost fish where low pH reduces the maximum $O_2$-carrying capacity of hemoglobin, used to inflate swim bladders or oxygenate the retina.

Bicarbonate ($HCO_3^-$)

The dominant form of $CO_2$ transport in the blood ($\sim 90\%$), formed by the reaction $CO_2 + H_2O \rightleftharpoons HCO_3^- + H^+$.

Carbamate

A form of $CO_2$ transport ($\sim 5\%$) where $CO_2$ binds directly to the amino groups on the hemoglobin protein.

Carbonic Anhydrase (CA)

An enzyme localized inside red blood cells that catalyzes the conversion of $CO_2$ and $H_2O$ into $HCO_3^-$ and $H^+$ at a rate approximately $1,000\times$ faster than the spontaneous reaction.

Chloride Shift

The 1:1 electroneutral exchange of intracellular $HCO_3^-$ for extracellular $Cl^-$ via the band 3 protein, allowing bicarbonate to be transported in the plasma.

Haldane Effect

The property where deoxygenated hemoglobin carries more $CO_2$ than oxygenated hemoglobin because it acts as a better buffer for $H^+$ ions.

Venous Reserve

The amount of $O_2$ remaining in venous blood; it is roughly 75% in resting humans and can be tapped during exercise. In contrast, cephalopods have almost no venous reserve.