Endocrine Flashcards
What general system controls cortisol release
The HPA axis (hypothalamic pituitary adrenal axis)
What is cortisol
A glucocorticoid produced by the zona fasciculata of the adrenal gland
What are the initial stimuli for the HPA axis cortisol release
Stress, infection, blood loss, diurnal rhythm (sleep wake cycle)
What is the pathway of cortisol release
1) Stimulus
2) Corticotropic releasing hormone (CRH) from hypothalamus
3) CRH binds to corticotrope cells in anterior pituitary
4) ACTH is releases from anterior pituitary
5) ACTH travels in blood and binds to MC2r receptor in adrenal cortex
6) Cortisol released from zona fasciculata
7) Cortisol acts on tissues in the body via nuclear receptor
What are the byproducts of ACTH formation
melanocyte stimulating hormone, endorphins, enkephalins
What does cortisol do
- Gluconeogenesis
- Lipolysis
- Increase of proteins –> amino acids
- Immunosuppression + anti-inflammation
- Regulates behaviour, mood, cognition
- Increase in appetite
Can cortisol pass through the phospholipid bilayer
Yes. It binds to a glucocorticoid receptor in the cytoplasm. The glucocorticoid-cortisol complex can pass into the nucleus
What are nuclear receptors
Receptors that are found either in the cytoplasm or the nucleus of a cell
What are the 2 endogenous glucocorticoids
Cortisol and corticosterone
What is the negative feedback of the HPA azis
- ACTH and cortisol inhibit CRH release from hypothalamus
- Cortisol reduces the sensitivity of corticotropin cells in a pituitary, so release less ACTH
How are glucocorticoids transported in the blood
- 90% bound to corticosteroid binding globulin (CBG)
- 5% bound to albumin
- 5% free
What does the zona glomerulus secrete
Mineralcorticoids eg aldosterone
What does the zona fasciculata secrete
Glucocorticoids - cortisone + corticosteroid
What does the zona reticularis secrete
Androgen precursors (converted into testosterone or oestrogen in the gonads)
What are the layers of the adrenal gland outside –> in
- Capsule
- Zona glomerulus
- Zona fasciculata
- Zona reticularis
- Adrenal medulla
–> Growing means finding great raves aswell
What can a tumour of the pituitary gland cause
Bitemporal hemianopoiea –> compresses optic chiasm crossing fibres, causes temportal loss of vision
What is the thyroid gland composed of
Thyroid follicular cells surrounding colloid (fluid)
What system controls thyroid hormone release
Hypothalamic-pituitary-thyroid axis
What are the thyroid hormones
T4 = Thyroxine
T3 = triiodothyronine
(calcitonin but this isn’t really counted)
What is the HPT axis
1) Thyrotropin releasing hormone (TRH) from hypothalamus
2) TRH causes Thyroid stimulating hormone (TSH) to be released from thyrotrophs in anterior pituitary
3) TSH stimulates T3/T4 release from the thyroid gland
How is thyroxine produced
By thyroid peroxidase in thyroid gland adding iodide to tyrosine
How + where is T4 converted to T3
Via the deiodination of T4 in the liver, kidney, muscles
What is the negative feedback of the HPT axis
T3 desensitises anterior pituitary and inhibits TSH secretion from anterior pituitary
How are T3/T4 transported in the blood
They are hydrophobic so 99% are transported bound to proteins, mostly thyroid-binding-globulin
