Exam #4: Adrenal Physiology Flashcards
Outline the HPA axis & the control mechanisms of the HPA axis.
The HPA axis regulates GLUCOCORTICOID production, which in humans is 95% cortisol
What are the zones of the adrenal cortex?
From outer to inner:
1) Zona glomerulosa
2) Zona fasciculata=
3) Zona reticularis
What are the main steroid hormones that are secreted by each of the zones of the adrenal cortex?
1) Zona glomerulosa= aldosterone (minercorticoid)
2) Zona fasciculata= primarily glucocorticoids
- Cortisol
- Corticosterone
3) Zona reticularis= primarily androgens
- Dehydroepiandosterone (DHEA)
- Andorostenedione
Outline the pathways of cortisol, aldosterone, and the adrenal androgen synthesis.
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What is the function of 17a-hydroxylase? What is the clinical outcome of a deficiency in 17a-hydroxylase?
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What is the function of 3B-hydroxysteroid dehydrogenase? What is the clinical outcome of a deficiency in 3B-hydroxysteroid dehydrogenase?
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What is the function of 21-hydroxylase? What is the clinical outcome of a deficiency in 21-hydroxlase?
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What is the function of 11B-hydroxylase? What is the clinical outcome of a deficiency in 11B-hydroxylase?
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How does ACTH increase adrenal steroid synthesis?
Generally, ACTH stimulates the rate-limiting steps in cortisol synthesis. Specifically,
1) MC2R–>Gas–>cAMP–>PKA–>phosphorylation of cholesterol ester hydrolase, increasing availability of free cholesterol
2) Increased synthesis of StAR (Steroid Acute Regulatory Protein)
3) Increases activity of cholesterol desmolase
What are the physiological effects of cortisol?
1) Metabolic= increased blood glucose
- Increased gluconeogensis
- Degradation of muscle & prevention of protein synthesis
- Lipolysis in fat cells
- Stimulation of hepatic glycogen synthesis
2) Anti-inflammatory= decreased synthesis of the precursor to prostaglandins & leukotrienes
3) Immunosuppressive= decreased lymphocyte production
4) Vascular reactivity= maintains the responsiveness of vascular smooth muscle to catecholamines
*****Note that in fetal development, glucocorticoids promote lung development
What are the physiological effects of aldosterone?
Generally, aldosterone functions to increase Na+ & H20 REABSORPTION & K+ SECRETION in the distal convoluted tubule & collecting ducts of the kidney
How does cortisol increase plasma glucose levels?
Cortisol increases plasma glucose by a variety of mechanisms including:
1) Increased gluconeogenesis
2) Muscle degradation and decreased amino acid uptake (shunted into gluconeogenesis)
3) Lipolysis of fat (shunted into gluconeogenesis)
How does aldosterone increase water and Na+ reabsorption?
1) Expression of the amiloride sensitive epithelial sodium channel (ENaC)
2) Expression of the basolateral Na+/ K+ ATPase pump
List the catcholamines released by the adrenal medulla.
NE
Epi
DA
How does cortisol regulate synthesis of epinephrine?
The catecholamines are synthesized from tyrosine. Eventually, DA is packaged into secretory vesicles, and in the vesicles, DA can be converted to NE. NE leaks into the cytoplasm.
- **The cytoplasmic enzyme, PNMT converts NE into Epi.
- Cortisol increases the expression of PNMT, and thus increases concentrations of Epi.