The Adrenal Gland Flashcards
Anatomy of adrenal glands
- Each adrenal gland lies superior to each kidney in the retroperitoneal space
- Large , peripheral adrenal cortex
- Small central adrenal medulla
Adrenal cortex
- Adrenal cortex produces steroid hormones
* Subdivided into three different zones
Three zones of adrenal cortex
- outer zone -ZONA GLOMERULOSA - secrete mineralcorticoids
- middle zone- ZONA FASCICULATA-glucocorticoids
- inner zone- ZONA RETICULARIS- weak androgen
Mineralcorticoid
a hormone involved in maintaining salt balance of the body
Aldosterone
A mineralcorticoid
•It regulates homeostasis of two mineral ions NA and K
•Helps blood pressure and blood volume
Control of Aldosterone secretion
Renin-angiotensin-aldosterone (RAA) pathway
RAA pathway
- Stimuli that initiate the renin–angiotensin–aldosterone path- way include dehydration, Na deficiency, or hemorrhage.
- These conditions cause a decrease in blood volume.
- Decreased blood volume leads to decreased blood pressure.
- Lowered blood pressure stimulates certain cells of the kidneys, called juxtaglomerular cells, to secrete the enzyme renin.
- The level of renin in the blood increases.
- Renin converts angiotensinogen a plasma protein produced by the liver, into angiotensin I.
- Blood containing increased levels of angiotensin I circulates in the body.
- As blood flows through capillaries, particularly those of the lungs, the enzyme angiotensin-converting enzyme (ACE) converts angiotensin I into the hormone angiotensin II.
- Blood level of angiotensin II increases.
- Angiotensin II stimulates the adrenal cortex to secrete aldosterone.
- Blood containing increased levels of aldosterone circulates to the kidneys.
- In the kidneys, aldosterone increases reabsorption of Na, which in turn causes reabsorption of water by osmosis. As a result, less water is lost in the urine. Aldosterone also stimulates the kidneys to increase secretion of K and H into the urine.
Effect of RAA
- With increased water reabsorption by the kidneys, blood vol-ume increases.
14 As blood volume increases, blood pressure increases to normal.
15 Angiotensin II also stimulates contraction of smooth muscle in the walls of arterioles. The resulting vasoconstriction of the arterioles increases blood pressure and thus helps raise blood pressure to normal
Glucocorticoids
Controls the glucose metabolism
Cortisol regulates metabolism and stress
Control of Glucocorticoids
- Low blood levels of glucocorticoids, mainly cortisol, stimulate neurosecretory cells in the hypothalamus to secrete corticotropin-releasing hormone (CRH).
- CRH (together with a low level of cortisol) promotes the release of ACTH from the anterior pituitary.
- ACTH flows in the blood to the adrenal cortex, where it stimulates glucocorticoid secretion. (To a much smaller extent, ACTH also stimulates secretion of aldosterone
Androgens
The adrenal cortex secretes small amounts of weak androgens.
• The major androgen secreted by the adrenal gland is dehydroepiandrosterone (DHEA)
- After puberty in males, the androgen tes- tosterone is also released in much greater quantity by the testes. Thus, the amount of androgens secreted by the adrenal gland in males is usually so low that their effects are insignificant.
- In females, however, adrenal androgens play important roles. They promote libido (sex drive) and are converted into estrogens (feminizing sex steroids) by other body tissues.
After menopause, when ovarian secretion of estrogens ceases, all female estrogens come from conversion of adrenal androgens.
Adrenal Medulla
- Inner region of the adrenal gland is the adrenal medulla
- Chromaffin cells secrete hormones in the adrenal medulla
- Two major hormones secreted are adrenaline and noradrenaline
Control of secretion of adrenaline and noradrenaline
These two hormones greatly augment the fight-or-flight response that you learned about in Chapter 15. By increasing heart rate and force of contraction,
epinephrine and norepinephrine increase the output of the heart, which increases blood pressure. They also increase blood flow to the heart, liver, skeletal muscles, and adipose tissue; dilate airways to the lungs; and increase blood levels of glu- cose and fatty acids.
