Endrocrine System 4 Flashcards
Adrenal Glands (Suprarenal)
- lie along superior border of each kidney
- subdivided into: superficial adrenal cortex and inner adrenal medulla
- structurally and functionally two separate glands
Adrenal Cortex
Manufactures steroid hormones from cholesterol:
Andrenocortical steroids (corticosteroids)
-essential for life, determine which genes transcribed in target tissues
-changes are a consequence of enzymes in target cells affecting cellular metabolism
Subdivided into three regions:
- zona glomerulosa - outermost layer
- zona fasciculata - middle layer
- zona reticularis - innermost layer
Mineralocorticoids “salt”
- from zone glomerulosa
- regulate electrolyte concentration of the ECF, especially Na+ and K+
- mainly aldosterone
- targets kidneys (+ sweat, salivary glands, and pancreatic tissue to retain Na+)
- part of renin-angiotensis-aldosterone pathway
- Na+ (and H2O resorption - secondary effect)
- K+ and H+ secretion (prevention of acidosis pH
Aldosternosism
Hypersecretion of aldosterone from adrenal neoplasms or overactivity of adrenal glands
Glucocorticoids “sweet:
From zona fasciculata (middle layer)
- glucocorticoids = mainly cortisol
- glucocorticoids help to maintain blood sugar levels and movement of water into and out of cells: increase rate of glucose synthesis and glycogen formation
- also anti-inflammatory and immunosuppressive: decrease migration of phagocytes, decrease histamine from mast cells, decrease swelling and inflammation, but decrease healing time
- secretion controlled by negative feedback
Glucocorticoids
Release of cortisol
-cortisol released in bursts ie. circadian rhythm
-stress induces increased secretion of cortisol
-results in increased levels of: glucose, fatty acids, amino acids,, (facilitated) vasoconstriction
If under stress, higher levels of these are going to persist which can result in increased blood-glucose levels, extending vasoconstriction and thereby leading to an increase in blood pressure
Diurnal rhythm:
surge of cortisol when wake uo and lowers as come closer to going to sleep
Cushing’s syndrome
- increased ACTH from pituitary tumour
- increased glucocorticoids from adrenal cortex
- increased glucocorticoid drugs
Causes:
- hyperglycaemia
- loss of muscle tone and bone
- water and salt retention due to hypertension and edema
- easily bruised
- moon face
- fat distributed to abdomen and back
Gonadocorticoids “sex”
From zona reticularis
Androgens
-released in response to ACTH
-sexual differentiation in puberty
-mainly dehydroepiandrosterone (DHEA):
-converted to estrogens in females: promotes libido, musclemass and RBC formation; only source of androgens after menopause
-their secretion is insignificant in comparison with the secretion of the gonads
Adrenal medulla
- adrenal medulla chromatin cells produce catecholamines: epinephrine and norepinephrine
- under direct control of the sympathetic NS
- during fight/flight response the sympathetic nerve stimulates the adrenal medulla to release E (80%) and NE (20%)
- cortisol from the adrenal cortex is necessary to convert NE into E
- action: increase fuel mobilisation and cardiac output; increase blood glucose by breakdown of liver glycogen stores
- metabolic changes persist for several minutes
Adrenal glands produce hormones that adjust metabolic activities at specific sites
These effect either:
- pattern of nutrient utilisation
- mineral ion balance, or
- rate of energy consumption by active tissues
Pancreas
- pancreas is both and endocrine and exocrine gland (located in the curve of the duodenum)
- 99% of pancreatic cells arranged in clusters called acini: produce digestive enzymes
- rest are clustered into pancreatic islets (Islets of Langerhans) = 1-2 million clusters
Pancreatic islets
Islets contain 4 types of hormone-secreting cells that regulate blood glucose levels
- Alpha cells (~15%) - secrete glucagon
- raises blood glucose - Beta cells (~80%) - secrete insulin
- lowers blood glucose - Delta cells (~5%) - secrete somatostatin
- inhibits glucagon and insulin secretion
- slows nutrient absorption from the GI tract - F cells (~1%) - secrete pancreatic polypeptide
- inhibits somatostatin secretion
- inhibits gall bladder contraction
- inhibits secretion of pancreatic digestive enzymes
Blood glucose levels
When levels rise:
-beta cells secrete insulin, stimulates transport of glucose across cell membranes
When levels decline:
-alpha cells secrete glucagon, stimulates glucose release by liver
5 effects of insulin
- accelerates glucose uptake
- increases number of glucose transport proteins on cell membranes - accelerates glucose utilisation and enhanced ATP production
- stimulates glycogen formation
- excess glucose stored as glycogen - stimulates amino acid absorption and protein synthesis
- stimulates triglyceride formation in adipose tissue
Overall insulin stimulates glucose utilisation to support growth and promote stores of glycogen and lipid reserves
Insulin
Circulating insulin lowers blood sugar by increasing membrane transport of glucose into:
- muscle
- connective tissue
- WBCs
Once glucose enters the cells, insulin binding triggers enzymatic activities
- catalyses oxidation of glucose for ATP production
- joins glucose molecules together to form glycogen
- converts glucose to fat
As cells take up glucose, plasma levels drop and insulin secretion is suppressed
