ENI - Endocrine glands in detail 2 Flashcards
What is produced by the zona glomerulosa of the adrenal cortex?
Mineralocorticoids e.g. aldosterone
What is produced by the zona fasciculata of the adrenal cortex?
Glucocorticoids e.g. cortisol (and some androgens)
What is produced by the zona reticularis of the adrenal cortex
Androgens e.g. testosterone (and some glucocorticoids)
In what proportions are the regions of the adrenal cortex?
- Most: fasciculata (60%)
- Middle: glomerulosa (25%)
- Least: reticularis (15%)
Describe the blood supply to the adrenal gland
- High blod volume for size
- Superior, middle and inferior suprarenal artereis
- Branch before entering adrenal capsule
- Within capsule, branch to give 3 patterns of blood distribution: capsular capillaries, cortical fenestrated capillaries and medullar arterioles
Describe the cortical fenestrated capillaries of the adrenal cortex
- Supply cortex
- Drain into medullar fenestrated capillaries
Describe the medullary arterioles of the adrenal cortex
- Direct to medulla
- No supply to cortex or branching prior to medulla
What are corticosteroids?
Gluco and mineralocorticoids (but ofen used as synonym for glucocorticoid)
Describe glucocorticoids
- e.g. cortisol
- Steroid hormones that bind to glucocorticoid receptor
- Role in regulation of metabolism of glucose
- Synthesis in adrenal cortex and steroidal role
Describe mineralocorticoids
- e.g. aldosterone
- Class of steroid hormone characterised by effects on salt and water balance
Describe the control of glucocorticoid release
- PVN of hypo. synthesises and release CRH
- Control partly diurnal and in response to stress
- CRH down axons to median eminence, terminate in portal capillary bed
- CRH released, into pituitary portal blood system to pars distalis
- Stimulates ACTH production and secretion (POMC)
- ACTH then through systemic circulation to adrenal glands where stimulates adrenal cortex to make glucocorticoid steroid hormones esp cortisol
Outline mineralocorticoid release
- Low blood pressure main stimulus via RAAS
- High serum potassium also stimulates release
Describe steroid hormone synthesis
- Begin with cholesterol
- Converted to pregnenlone by P-450-side-chain cleavage enzyme
- P450 activated by ACTH
- Pregnenloone converted to different corticoids according to zone, due to presence of different enzymes in each zone
What enzyme is required to convert pregnenolone to glucocorticoid, androgen and oestrogen substrates?
17-alpha-hydroxylase
- Lacking in zona glomerulosa
What hormone is required to convert corticosterone to aldosterone?
Aldosterone synthase
What is zonation of the adrenal cortex dependent on in dogs and why?
- 17-alpha-hydroxylase
- Only have one type of 11-hydroxylase
Describe the intracellular mechanisms of cortisol
- Binds to intraccellular receptor
- Cytoplasmic activation produces active GR monomer and another molecule
- Dimerisation of active GR monomer
- Binds to glucocorticoid response elements (GRE) on gene to alter gene expression
What are the effects of glucocorticoids on metabolism?
- Stimulate gluconeogenesis and glycogenolysis
- Stimulate proteolysis and lipolysis
- Inhibit insulin
Describe cortisol in the early fasting state
- Cortisol stimulates gluconeogenesis (formation of glucose)
- Activates anti-stress and anti-inflammatory pathways
- Indirect role in liver and muscle glycogenolysis
- Via passive influence on glucagon
Desribe cortisol in the late fasting state
- Increases glycogenesis
- Allows liver to take up glucose not being used by peripheral tissues and turn into liver glycogen fo use if move into starvation state
- Prolonged elevated cortisol can lead to proteolysis and muscle wasting
Describe the effect of cortisol on fat
- Mobilisation from peripheral stores
- manifests as redistribution of body fat causing altered body shape
Describe the effect of cortisol on muscle
- Catabolism
- Muscle weakness, poor exercise tolerance
- Panting
- Pot belly
Describe the effect of cortisol on the liver
- Gluconeogenesis
- Antagonise insulin
Describe the effect of cortisol on the kidney
- Increase GFR
- Block ADH action (increased excretion of water)
Describe the effect of cortisol on the ski
- Follicular atrophy
- Sebaceous gland atrophy
- Pyoderma
- Calcinosis cutis
- Collagen
Describe the effect of cortisol on bone
- Reduce calcium levels
- Osteopaenia
Describe the effect of cortisol on the brain
Stimulates hunger and thirst
Describe the effect of cortisol on the immune system
- Release of neutrophils from marginated pool
- Downregulates immune responses (T cell function and recruitment, B cell activation)
Desribe the actions of aldosterone
- Central role in BP regulation
- Acts on cells in distal tubule and collecting duct to increase reabsorption of NA, Cl and hence water
- Stimulates K+ secretion into tubular lumen
- Stimulates secretion of H+ in exchange for K+ in collecting tubules
- Overal increased water retention and increased blood volume and pressure
Describe androgens
- Steroid hormones
- Stimulate or control development and maintenance of male characteristics by binding to androgen receptors
- Are precursors for all oestrogens
Name the most improtant androgens
- Testosterone
- Dihydrotestosterone (DHT)
- Dehydroepiandrosterone (DHEA)
What are the anabolic effects of androgens?
- Protein syntehsis from AAs
- Increase muscle fibre size
- increase bone growth and remodelling
- Stimulate bone marrow
Give examples of glucocorticoid diseases
- Hyperadrenocorticisim (akak Cushing’s in small animas)
- Primary and secondary hypoadrenocorticism
What is primary hypoadrenocorticism?
Undresecretion of the glucocorticoids and mineralocorticoids due to pathology of the adrenal glands themselves
- Aka Addison’s disease
What is secondary hypoadrenocorticism?
- Just under-secretion of glucocorticoids
- Due to pathology of the pituitary preventing ACTH release
