Pituitary Flashcards
T3 and T4 are transported by what proteins in the blood
- thyroxine binding globulin
- transthyretin
- albumin
Levels of these carrier proteins increase in pregnancy, HRT and oral contraceptive use. + hepatitis
Decrease in steroid use, malnutrition, chronic liver disease, nephrotic syndrome and acromegaly
How are thyroid hormones produced
Action of TSH stimulates the follicular cell to:
• increase number of specific proteins and channels (iodine)
• Increase production of thyroglobulin. Produced within the cell to be stored outside in colloid
• Increase production of enzymes TPO and dual oxygenase
• Increase in channel for T3 + t4 to leave the cell
Organic action carried out by TPO which adds iodide groups to tyrosine residues on thyroglobulin. When production of hormones is complete thyroglobulin is removed from the structure
Role of thyroid hormones
• growth and brain development
• Thermogenesis
• Metabolism (carb fat and protein)
• Sensitises Ad NA receptor
Effect of endogenous release of steroids
Increase blood glucose via GLUCONEOGENESIS
Suppress the immune system
Metabolism of fat, protein and carbs
What stimulates the release of CRH (corticotropin releasing hormone)
Cells in the hypothalamus are stimulated by the amygdala and hippocampus in times of stress
Briefly explain the action of HPG axis
Hypothalamus releases GnRH (gonadotropin releasing hormone) which stimulates the anterior pituitary to release LH and FSH
Causes release of oestrogen and testosterone
LH acts on leidig cells to release testosterone and in females act on theca cells (secretion of oestrogen, formation of corpus leuteum and secretion of progesterone)
FSH acts on Sertoli cells to start spermatogenesis and in females acts on granulosa cells (convert androgens produced by theca cells to oestrogens)
Briefly explain how the growth hormone axis works
GH or somatotropin released by anterior pituitary in pulsatile bursts during deep sleep
GHRH release from the arcuate nucleus in the hypothalamus triggers release of GH.
Released GH is transported by proteins and acts on all cells to:
Fat breakdown
Inhibit glucose uptake by cells to increase levels in blood
GLUCONEOGENESIS
IGF1 production in liver - is an anabolic hormone like insulin - promotes cellular division and growth
Causes of hypopituitarism
- radiation therapy or surgery
Inflammation
Ischaemia - sheehans syndrome
Conditions affecting the hypothalamus - tumours, infections (TB + meningitis), sarcoidosis,
What is kallmanns syndrome
- hypothalamus does not secrete GnRH leading to low levels of LH and FSH and no testosterone.
Commonly causes lack of smell in boys with delayed puberty
How does sheehans syndrome present
Lack of post-partum milk production
Amennorrhoea
What is the insulin stress test or glucagon test
Put the patient in a state of hypoglycaemia. This should cause release of cortisol and GH as they are stress hormones. If there is pituitary lesion no cortisol or GH will be released
How would FSH and LH deficiencies present
Oligomenorrhoea
Amenorrhoea
Osteoporosis
Breast atrophy
Dyspareuria
ED
Hypogonadism
Infertility
Decreased libido
How would GH hormone deficiency present
Central obesity
Atherosclerosis
Dry skin
Short stature if children
Osteoporosis
Decreased strength, CO and hypoglycaemia
which drugs impact dopamine thus affecting tonic inhibition of prolactin
anti-psychotics
anti-depressants
metoclopramide (anti-emetic)
decrease dopamine
