Adrenal Glands

Posted by e-Medical PPT
Adrenal Glands Anatomy
Composed of a cortex and medulla, which have separate embryology.
The adrenal cortex arises fro m the coelomic mesoderm between the fourth and sixth weeks of gestation.
 The adrenal medulla is derived from cells of the neural crest that also form the sympathetic nervous system and the sympathetic ganglia.Some of these neural crest cells migrate into the adrenal cortex to form the adrenal medulla, but chromaffin tissue may also develop in extraadrenal sites.
The most common site of extraadrenal chromaffin tissue is the organ of Zuckerkandl, located adjacent to the aorta near IMA.
The glands weigh about 4g each, located in the retroperitoneum along the superior-medial aspect of the kidneys.
Yellow appearance because of their high lipid content.
3-5 cm in length, 4-6mm in thickness
Receive arterial blood from branches of the inferior phrenic artery, aorta, and renal arteries.
The right adrenal vein is short and exits the gland medially to enter the vena cava. The left adrenal vein exits anteriorly and usually drains into the left renal vein. As a result, adrenal venous catheterization is accomplished more easily on the left than the right.

The adrenal cortex is composed of three zones histologically.
Outer zona glomerulosa, site for aldosterone synthesis.
Central zona fasciculata and inner zona reticularis produce both cortisol and androgens.

Most of the blood supply to the medulla comes from venous blood draining through the cortex. This provides the adrenal chromaffin cells with high concentration of the enzyme phenyethanolamine N- methyltransferase (PNMT) required for conversion of norepinephrine to epinephrine.

The Cortex
Zona glomerulosa is the exclusive site of production of aldosterone because it lacks the enzyme 17 alpha hydroxylase necessary for production of 17 a- progesterone and 17 a-pregnalone, which are the precursors to cortisol and androgens.
Zona fasciculata and reticularis function as a unit to produce cortisol, androgens, and small amounts of estrogen, but it lacks the enzymes necessary to convert 18-hydroxycorticosterone to aldosterone.
Cholesterol is the precursor from which all adrenal steroids are synthesized.
Conversion of cholesterol to pregnenolone is the rate limiting step in adrenal steroidogenesis and is the major site of action of ACTH..

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