Adrenal (Exam II) Flashcards
Chromaffin cells of the adrenal medulla can produce either epinephrine or norepinephrine. How do the cells of the adrenal cortex determine which hormone a particular chromaffin cell will produce?
Epinephrine (E) is synthesized from norepinephrine (NE) in a reaction catalyzed by the enzyme phenylethanolamine-N-methyl transferase (PNMT). Synthesis of the PNMT enzyme is induced by glucocorticoids.
Some chromaffin cells are situated near sinusoidal blood vessels that have also passed through the cortex as sinusoids. These highly permeable vessels are able to pick up a significant amount of glucocorticoids and carry them to the medulla where they will induce PNMT in the chromaffin cells that they supply. These cells will therefore convert NE to E. Other chromaffin cells are situated near sinusoids that passed through the cortex as arterioles. These thicker walled vessels pick up very little glucocorticoid. Therefore PNMT will not be induced in the chromaffin cells that they supply, and the synthetic pathway will stop at NE in these cells.
How are mitochondria, SER and lipid droplets involved in steroid synthesis?
The mitochondrial membranes and the membranes of the SER each contain one or more enzymes that are needed in the synthesis of steroids. The lipid droplets contain molecules such as cholesterol that serve as starting material for steroid synthesis. The substrates shuttle back and fort between cytosol, mitochondria and SER at different steps in the pathway. It is not clear why the mitochondria of most steroid secretors have tubular cristae, but it may be that this shape is imposed upon the membrane by the nature of the proteins (including the steroidogenic enzymes) that they contain.
Adrenal Glands (Suprarenal Glands)
- Divided into cortex & medulla
- Both contain fenestrated sinusoidal capillaries (sinusoids)
Zona Glomerulosa
- Lies just deep to capsule
- Small closely packed cells arranged mainly in clusters (glomeruli)
- Produce mineralocorticoids: (e.g., aldosterone)
- Secretion is stimulated by angiotensin II (produced via the renin-angiotensin system in response to a fall in blood pressure or low blood sodium)
Zona Fasciculata
- Largest & palest-staining cortical region
- Cells arranged in straight cords (fascicles) that are 1 or 2 cells thick
- Sinusoidal capillaries lie between the cords
- Cords run perpendicular to surface of gland
- Extraction of lipid during tissue processing makes cytoplasm pale-staining
- Cells sometimes called spongiocytes because extracted lipid droplets give cytoplasm a spongy or lacy appearance
- Produce glucocorticoids: (e.g., cortisol and corticosterone) & small amount of adrenal androgens
- Secretion is regulated by ACTH
Zona Reticularis
- Cells arranged in irregular anastomosing network (hence reticularis) rather than straight cords
- Fewer lipid droplets than fasciculata, therefore cytoplasm stains darker
- Cells are smaller than in fasciculata
- Cytoplasm often contains lipofuscin pigment
- Secrete mainly weak androgens (mostly dehydroepiandrosterone)
- Secrete minor amount of glucocorticoids (mostly cortisol)
- Secretion controlled by ACTH
Adrenal Cortex by EM
- Zona glomerulosa has unusual steroid-secreting cells because they have mitochondria with shelf-like cristae (not tubular)
- Zona fasciculata & zona reticularis cells have the 3 features typical of steroid-secretors:
- Extensive SER
- Many lipid droplets in cytoplasm
- Mitochondria with tubular cristae
- Zona reticularis cells have more residual bodies (which contain the lipofuscin)
Adrenal Medulla
- Composed mainly of chromaffin cells
- True postganglionic neurons are present but rare
- Probably innervate vascular smooth muscle
- Contains large veins that unite to form the adrenal vein
Describe the dual blood supply that the adrenal medulla recieves
- Blood from cortical sinusoids (rich in glucocorticoids)
- Blood from medullary arterioles that pass through cortex without breaking up into sinusoids (low glucocorticoid concentration)
- Glucocorticoids induce the synthesis of the enzyme PNMT in chromaffin cells PNMT catalyzes conversion of norepinephrine (NE) to epinephrine (E) Therefore chromaffin cells that receive blood from:
- Cortical sinusoids (high glucocorticoid concentration) make E
- Medullary arterioles (low glucocorticoids) make NE
- Glucocorticoids induce the synthesis of the enzyme PNMT in chromaffin cells PNMT catalyzes conversion of norepinephrine (NE) to epinephrine (E) Therefore chromaffin cells that receive blood from:
Chromaffin Cells
- Called chromaffin because they stain with chromium salts
- Derived from neuroectoderm (neural crest)
- Innervated by preganglionic sympathetic neurons
- Are essentially modified postganglionic sympathetic neurons that lack axons & dendrites
- By EM contain many small, dark-staining secretory granules containing either NE or E NE-producing & E-producing chromaffin cells are distinguishable by EM based on morphology of their secretory granules:
- NE-producing cells have larger, darker secretory granules that often contain an eccentrically located dense core
- E-producing cells have less intensely staining granules whose contents are more centered in the granule
Fetal Adrenal
- Has no well-defined medulla
- Precursors of chromaffin cells are scattered in clusters throughout the fetal gland
- Fetal cortex resembles zona fasciculata in cell arrangement
- Permanent cortex appears outside fetal cortex
- At first resembles zona glomerulosa in cell arrangement
- Fetal cortex regresses a few weeks after birth
- Chromaffin cells coalesce to form the medulla
Cushing’s syndrome
- Adrenocortical hypersecretion:
- Causes “puffy” appearance and “moon face”
- Due largely to changes in carbohydrate and protein metabolism
- Hypertension, hyperglycemia and muscular weakness are also seen
Addison’s Disease
- Adrenocortical insufficiency
- Hypoglycemia, K+ and Na+ imbalance, dehydration, rapid weight loss, hypotension and general weakness
Pheochromocytoma
- Rare tumor of the adrenal medullary cells results in an increased production and release of epinephrine and norepinephrine thus mimicking the activity of the sympathetic division of ANS.
- This leads to increase heart rate and blood pressure § Also results in weight loss
- Can usually be successfully treated with surgical intervention
What do the arrows indicate?
Zona glomerulosa
Zona fasciculata
Zona reticularis
Adrenal Medulla
What is this an image of? What are the arrows pointing to?
Adrenal medulla. Chromaffin cells & ganglion.
What is the purpose of these cells?
Chromaffin cells in the adrenal medulla receive preganglionic sympathetic innervation to release NE or E
What is this an image of? What are the two arrows pointing to?
Fetal adrenal gland. Precursors to chromaffin cells.
What neurotransmitter is being produced in the images?
Top: norepinephrine
Bottom: epinephrine
NE producer (top) (eccentric dark and then space)
E producer (bottom) (central located )
Where would you find this image?
Zona fasiculata or zona reticularis.
Where would you find this image?
Zona glomerulosa.
