Adrenal Cortical Hormones and Bile Acid Metabolism

Vocabulary flashcards covering adrenal cortex anatomy, steroid hormone synthesis, transport, urinary metabolites, bile acid pathways, and biliary secretion parameters from the lecture material.

Zona Glomerulosa

The smallest and outermost zone of the adrenal cortex responsible for the production of $C21$ steroids, mineralocorticoids, which affect water and electrolyte balance.

Zona Fascicularis

The middle zone of the adrenal cortex that mainly produces glucocorticoids, as well as adrenal androgens and estrogens to a lesser extent.

Zona Reticularis

The innermost zone of the adrenal cortex that produces androgens ($C19$) and estrogens ($C18$).

Pregnenolone

A $21$-carbon steroid formed from cholesterol by desmolase, which serves as the common precursor for all steroid hormones.

Desmolase

An NADPH-dependent enzyme that cleaves a $6$-carbon unit from cholesterol to yield pregnenolone, acting as the rate-limiting step stimulated by ACTH.

Progesterone

The first steroid hormone formed from pregnenolone in two steps, involving conversion of the beta hydroxyl group to a keto group by $3\text{-beta-ol-dehydrogenase}$ and shifting of the double bond to $\Delta 4$.

Transcortin (CBG)

An alpha-1-globulin in blood that binds approximately $70\%$ of circulating cortisol.

11-Oxygenation Index

A measurement of adrenal steroid production based on the fact that $11\text{-hydroxylation}$ occurs exclusively in the adrenal cortex.

Zimmerman Reaction

A colorimetric reaction used to estimate $17\text{-ketosteroids}$, where the $17\text{-keto}$ group reacts with meta-dinitrobenzene to produce a purple color.

Porter-Silber Reaction

A chemical reaction used to measure $17\text{-hydroxy}$ steroids derived directly from adrenal glucocorticoids and mineralocorticoids.

17-Ketogenic Steroids

A group name for all steroid compounds possessing a keto or hydroxyl group at the $17\text{th}$ carbon atom.

7-Alpha-Hydroxylase

A microsomal enzyme that catalyzes the initial rate-limiting step of bile acid synthesis by introducing an alpha-oriented hydroxyl group at position $7$ of cholesterol.

Glycocholic Acid

The major conjugated bile acid formed in the liver by conjugating cholic acid with glycine.

Deoxycholic Acid

A secondary bile acid produced in the intestine when bacterial action deconjugates cholic acid and removes its alpha hydroxyl group at position $7$.

Lithocholic Acid

A secondary bile acid produced in the intestine through the bacterial dehydroxylation of chenodeoxycholic acid at position $7$.

Enterohepatic Circulation

The physiological cycle where $15\text{--}30\,\text{g/day}$ of bile salts in the intestine are reabsorbed from the ileum to the liver, with only $300\text{--}500\,\text{mg/day}$ excreted in feces.

Choleretics

Substances or factors—such as bile salts, secretin, and vagal stimulation—that stimulate the secretion of bile by the liver.

Cholagogues

Agents that stimulate the evacuation and release of bile from the gallbladder, with cholecystokinin being the most powerful.

24-Hydroxycholesterol (24-OHC)

An oxysterol transported from the brain into circulation, serving as a major pathway for the elimination of excess cholesterol from the brain.

27-Hydroxycholesterol (27-OHC)

An oxysterol moving from circulation into the brain that is capable of suppressing expression of Arc protein in hippocampal cells.