Physiology 6 - Adrenal Flashcards
Where are the adrenal glands found?
On the superior pole of the kidneys at roughly T12.
How are the adrenal glands peritonised?
Retroperitoneal just like the kidneys
Describe the arterial blood supply of the adrenal gland?
Aorta:
- > Inf Phrenic Art -> Sup suprarenal Art
- > Middle Suprarenal Art
- > Renal Artery -> Inf Suprarenal Art
DEscribe the venous drainage of the adrenal gland?
Different on each side
Left adrenal veins –> Left renal vein
Right Adrenal veins –> IVC
Describe the structure of the adrenal gland?
Adrenal Cortex: (Steroid hormones)
Zona Glomerulosa
Zona Fasciculata
Zona Reticularis
Then the adrenal medulla in the middle
The whole thing is surrounded by a fibrous capsule
What kind of tissue makes up the adrenal cortex vs medulla?
Adrenal cortex is a true endocrine gland derived from mesoderm
Adrenal Medulla is a modified symp. ganglion made of neural crest tissue
What is secreted the zona glomerulosa?
Outer section of Adrenal cortex secreates Mineralocorticoids e.g. Aldosterone
What is secreted by the zona fasciculata?
Middle section of adrenal cortex secretes glucocorticoids e.g. Cortisol
What does the Zona reticularis do?
Inner layer of adrenal cortex secretes sex steroids e.g. testosterone
(most sex steroids are produced in the gonads)
What is produced in the adrenal medulla?
Catecholamines (tyrosine derived, water soluble amines)
E.g. Epinephrine, Norepinephrine and dopamine
The adrenal medulla has an unusual autonomic nerve supply, how so?
Pre-ganglionic fibres synapse to cells in the adrenal medulla.
Instead of having post-synaptic fibres, the medulla secretes its neurohormones directly into the blood
Briefly describe the pathway of steroid synthesis in the adrenal cortex?
All start with cholesterol.
Different enzymes are found in each layer, sending them down different branches and so producing the different hormones.
The most important is 21-hydroxylase, found in the pathway for producing aldosterone and cortisol.
remind yourself of the HPA axis (Specifically for glucocorticoids) and the hormones involved?
Hypothalamus = Corticotrophin Releasing Hormone (CRH)
Ant Pituitary = Adrenocorticotrophic Hormone (ACTH)
Zona Fasciculata = Cortisol
As a steroid hormone, describe how Cortisol travels the blood?
95% of cortisol is bound to Cortisol Binding Globulin
Describe the -ve feedback control of Cortisol
Cortisol has a -ve feedback on CRH & ACTH
ACTH has a -ve feedback on CRH
How does cortisol work?
It bind to cytoplasmic glucorticoid receptors (found in all nucleated cells)
- > Hormone-receptor complex migrates to nucleus
- > Binds to DNA
- > Alters gene expression, transcription & translation
Does cortisol secretion follow any pattern or rhythm?
Yes a Marked Circadian rhythm!
Cortisol peaks at 6-9am and has its nadir at 12pm
Preceded by a similar ACTH rhythm
Smaller fluctuations occur throughout the day due to stress stimuli
What are cortisols affects on glucose?
- Permissive to GLucagon
- Increased Gluconeogenesis (stimulates gluconeogenic enzyme formation)
- Increased Proteolysis
- Increased Lipolysis
- Decreases Insulin sensitivity
What are cortisols affect on calcium?
- Decreases gut absorption
- Increases Kidney excretion
- Increases bone resorption
What are cortisols affects on the brain?
Excess cortisol linked to depression and impaired cognitive function
What are cortisols affect on norepinephrine?
Permissive to norepinephrine
Specifically in regards to vasoconstriction
What are cortisols effects on immunity?
Depresses immunity by:
- Reducing lymphocyte count
- Reducing Antibody formation
- Reducing inflammatory response
Summary of cortisols affects?
- Increases plasma glucose
- Decreases plasma Calcium
- Increases bone resorption
- Permissive to vasoconstrictive action of norepinephrine
- Supresses Immunity
In what way is cortisol particularly essential for life?
Its permissive effect on glucagon is most important.
Without cortisol glucagon can’t sufficiently respond to hypoglycaemia and your brain would die.
How is cortisol related to diabetes?
Cortisol is glucose counter-regulatory, meaning it raises blood glucose.
Therefore excess cortisol is considered diabetogenic
What does it mean to be a mineralocorticoid?
A hormones that effects resorption/excretion of minerals
What are the effects of aldosterone?
Increases Na+ resorption
Incerases K+ Excretion
What triggers secretion of aldosterone?
The Renin-angiotensin-Aldosterone system (RAAS)
Part of the long term control of blood pressure
What would happen with excess or insufficient aldosterone?
Excess aldosterone –> Excess Na+ –> Increased blood volume & hypertension
Insufficient aldosterone –> Insufficient Na+ –> DIminished blood volume and hypotension
Pathology in the hypothalamus effect on HPA
- Increased CRH
- Increased ACTH
- Increased Cortisol
Pathology in adrenal cortex effect on HPA
- Decreased CRH
- Decreased ACTH
- Increased Cortisol
Pathology on anterior pituitary effect on HPA
- Decreased CRH
- Increased ACTH
- Increased Cortisol
Why do you need to be careful when removing therapeutic treatment of Glucocorticorticoid
Need to be careful as it will lead to an XS response from the negative feedback loop:
- When therapeutic cortisol provided this reduces activity of CRH and ACTH
- Reduced activity of ACTH can lead to atrophy of the gland
- So risk of adrenal insufficiency if the therapeutic hormone is released too quickly
Pheocromocytoma
- Rare tumour which leads to the release of XS catecholamines from the adrenal medulla (e.g. epinephrine, norepinephrine, Ach).
- Bind to smooth muscle and cardiac muscle, some adipose tissue and some glands
- Leads to increased HR, CO and therefore BP
- Has a DIABETOGENIC EFFECT as it has an adrenergic effect upon glucose metabolism
Main causes for hyper secretion of cortisol
Main causes:
- Tumour in the adrenal cortex: primary
- Tumour in the pituitary: secondary
Presentation
- Depletion of proteins/fats in the extremities due to catabolic actions of cortisol
- For some unknown reason redistributed to the trunk
IATROGENIC
-Too much cortisol administered therapeutically
Main causes for hyposecretion of cortisol
ADDISON’S DISEASE
- Hyposecretion of all the steroid hormones of the adrenal gland
- Due to autoimmune destruction of the adrenal cortex
Effects of caffeine/ alcohol/stress on CRH and ACTH release
- These substances disinhibit the HPA axis
- This increases the release of cortisol
- Increases suppression of the immune system which can be cause for increased risk of infection
(Alcohol in particular depresses the negative feedback system)
How can cortisol release lead to muscle wastage
- Too much lipolysis
- Too much protein catabolism
- Makes skin appear thin and fragile
How can cortisol release lead to infection
Suppression of the immune system
-stronger and more frequent infections
