17 - Adrenal Glands Flashcards
Where are the adrenal glands found, what is their structure and what do they produce and secrete?
- Cap the upper part of the kidneys and like against the diaphragm
- 6-8g combined
- CT capsule has capsular plexus of blood vessels
What is the embryological origin of the adrenal glands?
- Medulla: neural crest cells that migrate into developing medulla
- Cortex: mesoderm
What are the corticosteroids released from each part of the adrenal glands?
Where are steroid hormones produced, what from, and how do they act on their target tissues?
- Gonads and adrenal glands from cholesterol
- Bind to nuclear receptors to modulate gene transcription
- Glucocorticoids, mineralcorticoids, androgens, oestrogens, progestins
What type of hormone is adolsterone, where is it produced, what is it carried by in the blood and what action does it have?
- Controls rate at which Na ions are reabsorbed
- Prime regulator of blood pressure
- Upregulates sodium pump and ENaC in the collecting duct and colon
- Part of RAAS
Briefly explain the process of the renin-angiotensin-aldosterone system and what the outcome is?
What are the two classes of hyperaldosteronism and how can they be distinguished between one another?
What are the signs of hyperaldosteronism and how can it be treated?
What is the structure of cortisol and what controls it’s secretion?
- Glucocorticosteroid synthesised and released from zona fasiculata in response to ACTH
- Negative feedback to hypothalamus to inhibit CRH and ACTH release
- Steroid transported by transcortin (and albumin) and synthesised from cholesterol
What is CRH secreted in response to?
Secreted from hypothalamus in response to:
- Physical (temp and pain) stressors
- Emotional stressors
- Chemical stress (hypoglycaemia)
How does blood cortisol vary at different times in the day?
- Peak at about 7am and trough at 7pm so time should be noted when taking cortisol measurement and repeat measurements should be taken at the same time
- Therefore, ACTH follows the same pattern
What actions does cortisol have on its target tissues?
- Increased protein breakdown in muscle, lipolysis in fat, gluconeogenesis in liver
- Anti-inflammatory effects
- Depression of immune system
- Decrease aa uptake
- Decrease glucose uptake
What can cortisol be used for clinically?
- Medication for allergic reactions: prevents macrophage activity and mast cell degradation
- Anti-rejection for organ transplants: depresses immune system
What is the precursor of ACTH and what is the process by which it is synthesised?
- Pro-opiomelanocortin (POMC)
- Post translocational processing of POMC leads to ACTH, alpha-MSH and ADH
- a-MSH present in ACTH sequence so in excess of ACTH there is some a-MSH activity
How does ACTH cause the secretion of cortisol?
- ACTH is a peptide hormone
- Binds to high affinity receptors on surface of cells in ZF and ZR
- Activates cholesterol esterase increasing conversion of cholesterol esters to cholestrol
- Binds to GPCR called melanocortin receptor (MC2) which uses CAMP as a second messenger. Differrent receptor to steroid hormones
What are the clinical consequences of excess ACTH secretion?
- Increased pigmentation
- Adrenal hyperplasia
- Overproduction of cortisol
Why are all corticosteroids transported by plasma proteins?
They are lipophillic
What is phaeochromocytoma and what are the symptoms?
- Overproduction of adrenaline by the adrenal medulla usully due to a chromaffin cell tumour
- Secretes mainly noradrenaline
- Life threatening hypertension
How does the adrenal medulla link the neuro and endocrine systems and how does it synthesise what it secretes?
- Secretes catecholamines
- They are stored in chromaffin cells vesicles before being released into the blood stream
When is adrenaline released and what effect does it have on the body?
Flight, fright or fight response
Where are androgens secreted from and what do they promote?
Where are the different adrenergic receptors found and what action do they have when stimulated?
How does adrenaline act as a positive chronotrope?
What drug can be given to a patient with hypertension from overactive RAAS?
- ACE inhibitors
- Angiontensin receptor blockers
- Inhibitors of renin as an enzyme
Compare the two types of hormones released from the adrenal glands in terms of their structure, their synthesis and their action, also include what a patient would need if they had a bilateral adrenalectomy.
