Endocrinology Flashcards
What does hemocrine mean?
Secretion from cells into extracellular fluid, which then diffuses into blood vessels
What does autocrine mean?
Hormone released from the cell acts on the same cell
What does paracrine mean?
Hormone released has an effect on nearby cells
What does solinocrine mean?
Hormone released into a duct (e.g. GI system)
Where are peptide hormones stored?
In vesicles within endocrine cells
Which amino acid are the small amino acid hormones based on?
Tyrosine
How do peptide hormones act on target cells?
Act on cells with appropriate cell surface receptors; activation of receptor leads to downstream signalling
How do steroid hormones act on target cells?
Act at a cytoplasmic or nuclear receptor
How do amino acid hormones act on target cells?
Act at nuclear receptors only
Which structure acts as the link between the hypothalamus and anterior pituitary?
Hypophyseal portal circulation
What is the function of the neuroendocrine cells of the hypothalamus?
Focus point for information on internal well-being - detects circulating hormones/metabolites/electrolytes and stress/cold/trauma/hunger/pain etc.
What is the effect of oxytocin released from the PP?
Contraction of uterus in labour, milk let-down in lactation (NEURAL feedback, not hormonal)
What is the effect of vasopressin/ADH released from the PP?
Aiding water reabsorption in the kidney
What does the thyroid gland look like histologically?
Composed of follicles filled with colloid, lined with cuboidal follicular epithelium, highly vascularised
What is thyroid hormone derived from?
Thyroglobulin, a polymer of tyrosine (amino acid)
What are the matured thyroid hormones called?
Thyroxine (T3) and tri-iodothyrine (T4)
Which thyroid hormone causes most of the physiological effects?
T3 - T4 is typically just a pool for T3 (half-life of 6 days compared to 1 day for T3)
What stimulates TRH release from the hypothalamus?
Sympathetic stimulation, or cold
What inhibits TRH release from the hypothalamus?
Cortisol and growth hormone
How does T3 act on thyroid cells?
Enters cell and nucleus, binds to thyroid hormone receptor (TRH) on the thyroid response element, binding of THR to promoter elements activates gene transcription
What does hypertrophy mean?
Increase in cell size
What does hyperplasia mean?
Increase in cell number
What type of hormone is growth hormone?
A peptide hormone
In what form does growth hormone circulate in the body?
Weakly bound to GH-binding protein
Where is growth hormone secreted from?
Somatotrophs in the anterior pituitary (stimulated by GHRH)
What inhibits release of growth hormone releasing hormone?
Somatostatin
In which pattern is growth hormone released?
Diurnally (during sleep) and pulsatile
What molecule mediates the local effects of growth hormone?
Insulin-like growth factor (IGF-1)
What conditions does excess growth hormone cause?
Giantism or acromegaly
What condition does deficiency of growth hormone cause?
Dwarfism
Why is it a risk to inject growth hormone into adults?
Encouraging cells to grow when they are naturally stopping may induce cancer
What hormones are produced in the adrenal medulla (chromaffin cells)?
Adrenaline and noradrenaline
What hormones are produced in the adrenal cortex?
Corticosteroids
Which zones make up the adrenal cortex?
Glomerulosa (mineralocorticoids), fasciculata (glucocorticoids), reticularis (androgens and oestrogens)
What is the precursor molecule to adrenal steroids?
Cholesterol
How do steroids action in cells?
Act on cytoplasmic receptor in target tissues, translocates to the nucleus upon steroid binding, modulates transcription of genes to produce new proteins (and therefore biological effects)
In what form does cortisol/corticosterone circulate in the body
Bound to transcortins (plasma proteins)
What is the function of aldosterone (mineralocorticoid)?
Regulating extracellular sodium/potassium concentration
What occurs in the body when there is too little glucose?
CNS dysfunction
What occurs in the body when there is too much glucose?
Dehydration and microvascular damage (e.g. blindness)
What is the ideal glucose value?
5.5mmol/L
What is glycolysis?
Glucose –> pyruvate
What is gluconeogenesis?
Pyruvate –> glucose
What is the role of glucagon?
Mobilises fuel in the catabolic phase of glucose metabolism
What is the role of insulin?
Stores fuel in the anabolic phase of glucose metabolism
What is the receptor for insulin?
Receptor tyrosine kinase
What is the overall effect of insulin?
Concentration of glucose, amino acids and fatty acids in the blood goes down
What is the principle target tissue of glucagon?
Liver
What is the overall effect of glucagon?
Increased glucose output via glycogenolysis and gluconeogenesis, and increased lipolysis
What other molecule can be used as fuel when glucose is low?
Ketone bodies
What are the 3 other regulators of blood glucose?
Growth hormone, glucocorticoids, adrenaline
What 3 hormones are involved in daily calcium balance?
Parathyroid hormone, calcitonin, 1,25-DHCC (active vit D)
Under what condition is parathyroid hormone released?
In response to falling levels of circulating calcium
What is the effect of parathyroid hormone on bone?
Calcium release from calcium salts in bone ECF
What is the effect of parathyroid hormone on the kidneys?
Increase tubular reabsorption of calcium
What is the effect of parathyroid hormone on the gut?
Increased formation of active vitamin D causes enhanced absorption of calcium from intestine
How is active vitamin D involved in long-term calcium homeostasis?
Acts to increase absorption of calcium from the intestine in order to protect bone
When is calcitonin secreted?
In response to an elevation in blood calcium
What is the overall effect of calcitonin?
Reduce blood calcium levels
