Endocrinology 2 Flashcards
The Adrenals, Gonads and Parathyroids
Describe the vasculature of the adrenal glands.
Both adrenal glands have many arteries but only one vein each.
The right adrenal vein drains into the inferior vena cava.
The left adrenal vein drains into the renal vein.
Give the basic anatomy of an adrenal gland.
From medial to lateral: Adrenal medulla Zona reticularis Zona fasciculata Zona glomerulosa Capsule ((the zona reticularis, zona fasciculata and zona glomerulosa comprise the adrenal cortex)).
Which hormones are produced by chromaffin cells in the adrenal medulla?
Adrenalin (80%)
Noradrenaline (20%)
Dopamine
Which hormones are produced in the zona glomerulosa?
Mineralocorticoids, mainly aldosterone.
Which hormones are produced in the zona fasciculata and zona reticularis?
Glucocorticoids, mainly cortisol.
Small amounts of androgens and oestrogens.
What is the difference in circulating levels of aldosterone and cortisol?
Cortisol circulates at around 1000 times higher concentrations than aldosterone.
Which receptors do aldosterone and cortisol bind to?
Cortisol binds to the glucocorticoid receptor (GR) and the mineralocorticoid receptor (MR), whereas aldosterone only binds to MR.
How do certain tissues prevent cortisol from entering, and thus rely on aldosterone for MR binding?
They have high levels of an enzyme - 11b-hydroxysteroid dehydrogenase 2 (11b-hsd 2).
The placenta and kidneys have a lot of this enzyme.
This converts cortisol to cortisone, an inactive hormone.
Describe the renin-angiotensin-aldosterone system.
Renin is released from granular cells in the kidneys in response to:
Decreased renal perfusion pressure (RPP).
Renal sympathetic activity.
Decreased Na+ load at macular densa cells in the DCT
Renin is an enzyme, which converts angiotensinogen from the liver) into angiotensin I. ACE (angiotensin converting enzyme) in the lungs converts angiotensin I to angiotensin II.
Angiotensin II causes aldosterone to be released from the zona glomerulosa of the adrenal cortex.
Other than angiotensin II, what other two stimuli cause aldosterone to be released from the zona glomerulosa?
Low blood sodium ion concentration; high blood potassium ion concentration.
Which two hormones are involved in the control of the rate of cortisol release?
A hypothalamic hormone, corticotrophin releasing hormone, and an adenohypophyseal hormone released from Corticotrophs: ACTH (Adrenocorticotrophic hormone).
What are the physiological effects of aldosterone?
Aldosterone acts on distal tubule cells. It increases the numbers of sodium ion channels on the apical membrane and sodium/potassium ATPases on the basal membrane by acting on the nucleus to increase transcription and translation. Result is increased sodium ion reabsorption.
What are the physiological effects of cortisol?
Increases gluconeogenesis and glycogenolysis by promoting enzymes involved in both of these processes.
Stops glucose being stored peripherally by decreasing blood flow to adipose tissue and skeletal muscle and decreasing numbers of lipoprotein lipase and GLUT 4 respectively. Also prevents free fatty acids being stored: the result is that energy substrates remain in the blood, available for use.
It is also pro-memory by upregulating serotonin.
Give the supra-physiological effects of cortisol.
Anti-inflammatory/immunosuppressive.
Excess GR activation - negative effect on serotonin, becoming anti-memory (hippocampus may get smaller).
How is calcium found in the body?
99% is found in the bone as complex hydrated calcium.
In the blood:
50% is found as bioactive ionised calcium (Ca2+)
45% is bound to plasma proteins.
5% is found as diffusible salts (citrate, lactate).
Which hormones have effects on levels of calcium in the blood?
Plasma calcium ions INCREASED by calcitriol (1,25 (OH)2 Vitamin D3) and parathyroid hormone (PTH).
Levels DECREASED by calcitonin.
Which cells release calcitonin?
Parafollicular cells of thyroid.
How is PTH synthesised and how does it signal to cells?
Initially synthesised as pre-pro PTH. Binds to transmembrane G-protein linked receptors. Activates adenyl cyclase and also probably phospholipase C (PLC).
What are the effects of PTH?
On BONE osteoclasts are stimulated and osteoblasts inhibited, resulting in bone resorption.
On KIDNEYS: increased Ca2+ reabsorption and increased phosphate excretion. Stimulates 1-a hydroxylase activity which results in increased calcitriol synthesis.
Calcitriol acts on SMALL INTESTINE to increase absorption of both Ca2+ and phosphates.
How does PTH result in bone resorption?
It binds to the PTH receptor on OSTEOBLASTS which produce osteoclast activating factors (OAFs). These act on osteoclasts to result in bone resorption.
