Lecture 10 - The Adrenals and their Hormones Flashcards
Where are the adrenal glands found?
On the superior pole of each of the 2 kidneys
What are the sections of the adrenal gland - from outside to inside?
Capsule Cortex: 1) Zona Glomerulosa 2) Zona Fasciculata 3) Zona Reticularis
Adrenal Medulla
Tributary of central vein
How is the Zona Fasciculata arranged?
Cells line up as strings
How does the blood flow into adrenal cortex and to the zones?
To adrenal cortex via arteries that feed the outside of the gland 2 ways for the zones: Most passes through the cells and there are some vessels which go through the cortex to get to adrenal medulla
What is the medulla made up of?
Chromaffin cells - post-ganglionic nerve fibres in a specialised form
What type of hormones does the medulla secrete?
CATECHOLAMINES from Chromaffin cells
What type of hormones does the cortex secrete?
Corticosteroids
What specific hormones are released by the medulla?
Adrenaline - 80% Noradrenaline - 20% Dopamine - very small amounts
What specific hormones are released by the cortex?
Mineralocorticoids - aldosterone Glucocorticoids - cortisol Sex steroids - Androgens and Oestrogens
In which zone is aldosterone produced?
Zona Glomerulosa
In which zone are cortisol/androgens/oestrogens produced?
Zona Fasciculata and Reticularis
What is the nucleus of cholesterol?
Cyclopentanoperhydrophenanthrene
Which steroids are produced in the adrenals?
Mineralocorticoids Glucocorticoids
Which steroids produced in the gonads?
Progestogens Androgens Oestrogens
Where androgens produced and then moved to become stronger?
Produced in the adrenals (weak) and become stronger in the gonads (testes)
What is androstenedione useful for?
Its a less weak androgen and can be converted into testosterone and DHT
What is the precursor for aldosterone?
Progesterone
What is the precursor for Oestrogen?
Androgens
How is cortisol transported around the blood?
75% bound to corticosteroid binding globulin (Transcortin) 15% bound to albumin 10% free - BIOACTIVE
How is Aldosterone transported around the blood?
60% bound to corticosteroid binding globulin 40% free - BIOACTIVE
What happens to cortisol levels?
Levels change during day Released in pulses In morning higher than evening MORE cortisol than aldosterone
What happens to aldosterone levels?
They remain the same during the day Controlled by position - involved in control of fluid and balance
What are the main actions of aldosterone?
Stimulate Na+ reabsorption and K+ and H+ secretion in DISTAL CONVOLUTED TUBULE and cortical collecting duct
When does the adrenal gland form during pregnancy?
Week 6 when the adrenal glands form but only one zone- fetal zone One week after birth is when the 3 zones develop
What is the main target tissue for aldosterone?
Kidneys
What is the mechanism of action of aldosterone?
Aldosterone enters cell and binds to receptors in cytoplasm HR complex enter the nucleus and attach to genes Causes increase in ion channel and enzyme production Na/K channel causes Na to move in and K to move out Na is also pumped out into the blood as Na reabsorption is increased
What are the key features of the juxtaglomerular apparatus (JGA)?
Efferent and afferent arterioles Glomerulus Macula densa Distal tubule Juxtaglomerular cells
What does the macula densa react to?
To Na concentration in tubule fluid
What are stressors?
Variety of things perceived by an organism as a threat e.g. Hypoglycaemia, trauma (NOT chronic)
What are the causes of renin release?
Decreased renal perfusion pressure Increased renal sympathetic activity Decreased Na load to top of loop of Henle - macula densa
Describe the renin-angiotensin-aldosterone system
Where is Renin produced?
In the juxta-glomerular cells
Where is ACE produced?
Lungs and kidneys
What are the metabolic actions of cortisol?
Peripheral protein catabolism Hepatic gluconeogenesis ^ BGL Fat metabolism - lipolysis in adipose cells Enhanced effects of glucagon and catecholamines
What are the other effects of cortisol?
Some mineralocorticoid effects Cardiovascular and renal effects - excretion of water load, ^ vascular permeability Other effects - on bone (^ breakdown), growth, CNS (^ = associated with depression)
What are the effects of large pharmacological amounts of cortisol?
Anti-inflammatory action Immunosuppressive action Anti-allergic action Associated with decrease production of prosteoglandins, histamine and interleukins and movement and function of leukocytes
What does cortisol bind to?
Glucocorticoid receptors Turns into Cortisone (inactive) via T2 Aldosterone receptors (also aldosterone)
What is the full name for enzyme T2?
11beta-hydroxysteroid dehydrogenase
What are the problems that are caused by binding to aldosterone receptors?
It inhibits greatly as there is 1000x higher concentration of cortisol c.f. aldosterone
What is the mechanism of action of cortisol?
Cortisol enters and forms a hormone-receptor complex which acts as a transcription factor
New proteins - Annexin: controls prostaglandin synthesis - synthesis AUTOCRINE - acts on Annexin receptor
Release of Arachidonic acid which inhibits prostglandin synthesis
What does POMC turn into?
POMC > Pro-ACTH and beta-LPH > Pro-gamma-MSH, ACTH, gamma-LPH, b-endorphin
What is hypothalamic enzymes are secreted to release ACTH?
CRH and VP
How is ACTH released?
In a cicadian rhythm - BIOLOGICAL CLOCK otherwise it inhibits CRH
Where does ACTH act on in adrenal?
Adrenal cortex - zona fasciculata and reticularis
What does the adrenal cortex do when stimulated by ACTH?
Releases CORTISOL and small amounts of androgens
What does DHEA stand for?
Dehydroepiandrosterone
What is DHEA?
Precursor for androgens and oestrogens Converted to active form when in target cells
When is the peak serum level for DHEA?
20-30 years with a particularly important effect
What does DHEA do?
Important in postmenopausal women as precursor for oestrogen synthesis by target tissues in absence of ovarian steroids
How is cortisol production regulated?
