Endocrine Flashcards
What 3 hormones does the thyroid gland produce?
- Thyroxine (T4)
- Triiodothyronine (T3)
- Calcitonin
What enzyme converts T4 –> T3?
Deiodinase
Are T3 or T4 levels higher in the blood?
T4 (store of T3)
Describe thyroid hormone synthesis (7)
- TSH binds to TSHR
- Na+/I- symporter transports I- into follicular cells
- Iodination of thyroglobulin via thyroperoxidase enzyme
- Iodinated tyrosines on thyroglobulin combine via thyroperoxidase enzyme
- Mature thyroglobulin stored in colloid
- Colloid absorbed into follicular cells via endocytosis
- Hydrolytic enzymes in lysosomes liberate T3 & T4
What are the actions of thyroid hormone?
- Increases metabolic rate (more energy produced, heat produced)
- Increases catecholamine effect (adrenaline)
- Growth & development
Is T3 or T4 more active?
T3
Describe the process of thyroid hormone secretion
- HT: increases TRH secretion
- AP: increases TSH secretion
- TG: increases thyroid secretion
- Increased plasma thyroid hormone has a negative feedback on the AP (and the HT)
What stimulates parathyroid hormone secretion?
- Low serum Ca2+
- High serum phosphate
What are the actions of PTH? (4)
- Increase Ca2+ absorption (in intestines)
- Increase Ca2+ reabsorption from DCT (via activation of vit D)
- Increase Ca2+ release (resorption) from bone
- Decrease phosphate reabsorption in kidneys
Define endocrine
Hormones released into the blood, acting at distant sites
Define paracrine
Hormones acting on adjacent cells
Define autocrine
Hormones acting on the same cell that secreted it
What hormone regulates GH and how? (2)
GHRH +
SST (somatostatin) -
What hormone regulates TSH and how?
TRH +
What hormone regulates Prolactin (PLN)?
Dopamine -
What hormone regulates ACTH?
CRH +
What hormone regulates FSH and LH?
GnRH +
How is prolactin different from the other anterior pituitary hormones?
Prolactin is under inhibitory control by dopamine.
Stopping the inhibition will cause prolactin levels to increase
What are the anterior pituitary hormones? (5)
FSH & LH GH ACTH TSH PLN
What does GH do? (3)
Stimulates.liver to secrete IGF-1
Lipid + carb metabolism
Protein synthesis
What does TSH do?
Stimulates release fo T3 & T4 from thyroid gland
What does prolactin do? (2)
Stimulates breast development
Milk production
What does ACTH do?
Stimulates cortisol release from adrenal cortex
What do FSH and LH do? (2)
Germ cell (ovum + sperm) development Stimulate sex hormone secretion (testesterone, progesterone)
What can result from tumours of the anterior pituitary gland?
Optic chiasm affected –> bitemporal hemianopia
What are the hormones and associated nuclei of the posterior pituitary?
Supraoptic nuclei –> vasopressin
Paraventricular nucle –> oxytocin
What does vasopressin do?
Controls water secretion - inserts more aquaporin channels onto the CD
What does oxytocin do?
Initiates labour
Stimulates milk ejection
What receptors do all hypothalamic and pituitary hormones act on?
G-protein coupled receptors
What controls ADH release on a day-to-day basis?
Osmoreceptors
What controls ADH release in emergency situations?
Baroreceptors in brainstem and great vessels
What cells of the pancreas are involved in endocrine activity?
Islets of Langerhans
What hormones are steroid hormones?
All hormones from the adrenal glands (+ calcitriol - activated vit D)
What hormones are amino acid hormones?
T3 & T4
What cells secrete glucagon?
Alpha cells of islets of Langerhans
What cells secrete insulin?
Beta cells of islets of Langerhans
What cells secrete somatostatin?
Delta cells of islets of Langerhans
What does somatostatin do in the pancreas?
Inhibits the release of insulin and glucagon
What does insulin do? (3)
- Suppresses hepatic glucose output (reduces glycogenolysis, gluconeogenesis)
- Increases glucose uptake into insulin-sensitive tissues (muscle + fat)
- Suppresses lipolysis and breakdown of muscle
What does glucagon do? (3)
- Increases hepatic glucose output (increases glycogenolysis, gluconeogenesis)
- Reduces peripheral glucose uptake
- Stimulates lipolysis, muscle glycogenolysis and breakdown
The main effect of insulin is to:
Remove glucose from the bloodstream
[Insulin draws K+ into cells (hypokalemia)]
The main effect of glucagon is to:
Increase blood glucose concentration
How can you differentiate endogenous insulin from synthetic insulin?
Endogenous insulin production causes the release of c-peptide, which isn’t present w/ synthetic insulin
Describe the process of insulin secretion by beta cells? (6)
- When insulin levels are HIGH, it binds to GLUT2 receptors
- Glucose enters the beta cell
- Glucose is metabolised, and this produces ATP
- ATP binds to K+ATP channel, closing it, so K+ builds up in the cell
- Cell becomes depolarised and this opens Ca2+ channels
- Ca2+ entry causes vesicles containing insulin to be released
Describe the action of insulin on muscle & fat cells (4)
- Insulin binds to insulin receptors
- Triggers intracellular signalling cascade
- Vesicles containing GLUT4 channels fuse w/ cell membrane
- Glucose entry via GLUT4
How is the first phase response to rising blood glucose different to the second phase response?
First phase response: rapid, release of STORED insulin
Second phase response: slower, release of NEWLY SYNTHESISED insulin (initiated if glucose levels remain high)
What are incretins?
Secretory cells in endothelial cells in GI tract that amplify insulin response to glucose
