The adrenocortical hormones Flashcards
How many adrenal glands do we have and where are they located?
2, located on the superior poles of the kidneys.
What are the two distinct parts of the adrenal gland?
The adrenal medulla and the adrenal cortex
Describe the adrenal medulla.
The central part of adrenal gland.
It is regulated by the sympathetic nervous system
Its major secretion is epinephrine (E)
Its minor secretion is norepinephrine (NE)
Describe the adrenal cortex.
The adrenal cortex secretes corticosteroids which include more than 30 types of hormones. They are synthesized from cholesterol. These hormones are grouped into mineralocorticoids, glucocorticoids, androgens.
What are the different adrenal cortex.
Inner layer: Zona reticularis
Middle layer: Zona fasciculata
Outer layer: Zona glomerulosa
Describe mineralocorticoids.
Aldosterone is the principal mineralcorticoid
Secreted from outer layer (zona glomerulosa)
Affect electrolytes Na, K ions in extracellular fluid.
Mineralcorticoids have a weak glucocorticoid effect
Describe glucocorticoids
Cortisol is the principal glucocorticoid
Secreted from both middle layer (zona fasciculata ) and inner layer (zona reticularis ).
Mainly increase glucose concentration in the blood
Glucocorticoids have a weak mineralcorticoid effect
Describe androgens
These are sex hormones but play a minimal role as compared to estrogen and testosterone.
They are secreted from middle layer and inner layer
Have similar effects on body as testosterone
True or False. All the adrenocortical hormones are steroid-based compounds.
True
What are the steps to adrenocortical hormone synthesis
They are formed mainly from cholesterol:
Low-density lipoprotein (LDL) in blood contains cholesterol.
LDL-cholesterol is absorbed from blood by endocytosis through cell membrane.
The cell membrane of adrenal cortex promotes endocytosis.
Small amounts of cholesterol are also synthesized in the cortical cell from acetyl-coA.
Cholesterol becomes pregnenolone, which is a precursor to many hormones.
Are adrenocortical hormones hydrophilic or hydrophobic?
they are hydrophobic so they rely on carrier proteins to get them around
What happens to cortisol in the blood?
About 94% of the cortisol binds with globulin (aka cortisol-binding globulin or transcortin)
6% floats freely in the blood. They are in a dynamic equilibrium.
What happens to aldosterone in the blood?
About 50% of aldosterone binds with plasma proteins, the rest float freely in the blood. This is also a dynamic equilibrium.
What is the mineralocorticoid function of aldosterone?
It involves the concept of sodium and potassium balance. A membrane ‘wants’ to maintain an equal electrical charge across the membrane. An imbalance can create energy, and also affect osmosis (transport of water).
What is the effect of aldosterone on transport of sodium and potassium?
Aldosterone promotes transport of Na+ and K+ ions through renal tubular walls and in the cortex and collecting ducts. The cells that do this are called the principal cells.
That increases the reabsorption of Na+ which means that Na+ is conserved in extracellular fluid. It decreases the loss of Na+ into urine.
When sodium is reabsorbed it increase the excretion of K+ into urine.
When sodium is reabsorbed it also caused water to be reabsorbed by osmosis.
What is the cascade of events that explain the cellular mechanism of aldosterone action that increases sodium reabsorption
The lipid soluble aldosterone can diffuse readily into the principal epithelial cells, binds with a receptor in the tubular cell, diffuses into the nucleus, ==> Causes the formation Channel proteins and Na-K ATPase pump ==> now Na+ can be reabsorbed, K+ excreted.
Channel proteins are inserted into luminal membrane of principal cell and result in rapid diffusion of Na+ ions from lumen side, into cell cytoplasm. The luminal side is the one pointing inwards, where the kidney filtrate (urine) is located.
Na-K ATPase enzyme works together with membrane transport proteins to pump Na+ and K+ at the basolateral membrane of renal principal cells. Basolateral is the side of the tubule cell that faces outwards, to the interstitial fluid. The interstitial fluid is connected to the blood circulation.
What is the effect of aldosterone on extracellular fluid volume and arterial pressure?
Aldosterone causes Na ions to be conserved ==> tendency of increasing concentration of sodium ==> simultaneous osmotic absorption of water by principal cells ==> keep the concentration of Na constant ( very little rise ) in extracellular fluid ==> absorption of water increases the volume of extracellular fluid ==> increase blood pressure ==> cause great increase of excretion of both water and salt (sodium chloride) from kidney at hypertension ( called pressure diuresis ).
What is the effect of aldosterone on sweat glands, salivary glands and intestinal absorption?
Aldosterone increase reabsorption of NaCl and secretion of K ions by principal cells to conserve body salt when water is secreted by sweat gland and salivary gland.
Enhance NaCl absorption by intestine especially in the colon to prevent salt loss in the stools.
What happens with a lack of aldosterone?
Lack of Aldosterone causes loss of salt (Na) in urine ==> decrease sodium-chloride in extracellular fluid and the volume of fluid ==> great reduction of total volume of extracellular fluid (dehydration) and diminished cardiac output ==> low blood pressure ==> circulatory shock ==> cause death in few days.
How can chronically low or defective aldosterone due to a genetic mutation be treated before it leads to death?
by providing supplemental aldosterone or mineralocorticoids.