Hypothalamic pituritary axis Flashcards
what are the features of endocrine glands
ductless
may be endocrine, paracrine or autocrine
very vascular with fenestrated capillaries
some are discrete organs and some are associated with other tissues
may have complex embryology
what stimulated secretion of parathyroid hormone
low Ca blood conc
what hormone is released by the pineal gland
melatonin
what hormone is released by the thymus
thymopoietin
what hormone is released by adipose tissue
leptin
what structure encloses the pituritary gland superiorly
diaphragma sellae
what structures are the pituitary gland related to
optic chiasma and spenoid sinus
what is the neurohypophysis
posterior pituitary gland
what is the adenohypophysis
anterior pituitary gland
contains the pars anterior, pars tuberalis and pars intermedia
what is the pars intermedia derived from
rathke’s pouch
lies between the ant and post lobes
contains colloid filled, epithelial lined follicles
obscure function
contains basophilic cells
how does the anterior pituitary gland develop
up growth of epithelium from the oral cavity (Rathke’s pouch)
Rathke’s pouch loses contact with the oral cavity
how does the posterior pituitary develop
down growth from the brain infundibulum as a diverticulum
what is a craniopharyngioma
slow growing tumour which may develop along the track of Rathke’s pouch (benign)
how can secretory cells of the anterior gland be classified
how they stain
chromophils: acidophils (GH and prolactin)
Basophils (the others)
chromophobes do not stain
what neurohormones are released by the hypothalamus
Thyrotropin releasing hormone
corticotropin releasing hormone
growth releasing hormone
somatostatin growth hormone release inhibiting hormone
gonadotrophin releasing hormone
prolactin releasing factor
prolactin release inhibiting factor (PIF)
what neurohormones are released from the posterior pituitary
vasopressin
antidiuretic peptide
oxytocin
what are trophic hormones
act on other endocrine glands
what trophic hormones are released by the anterior pituitary
thyrotropin (thyroid stimulating hormone)
corticotropin (adrenocorticotropic hormone, ACTH)
Lutinising hormone
follicle stimulating hormone
what hormones acting on peripheral targets are released by the anterior pituitary gland
somatotropin (growth hormone)
prolactin (PL)
melanotropin (melanocyte stimulating hormone)
describe the release of growth hormone
cells in the arcuate nucleus secrete growth hormone releasing hormone that is released into the hypophyseal portal blood supply
this causes somatotrophs to release GH
in order to inhibit growth hormone somatostatin is released by cells in the periventricular region
when is growth hormone release greatest
during sleep
what are the functions of growth hormone
inhibits growth hormone release
increases cartilage and bone growth
increased protein synthesis, cell growth and proliferation
increased lipolysis
increased blood glucose and other anti insulin effects
how does growth hormone increase cartilage, bone, protein synthesis
by stimulating insulin like growth factors from the liver
what are the consequences of growth hormone release
increased linear growth and lean body mass
important for post natal development and rapid growth throughout puberty
maintenance of protein synthesis and tissue function in adults
what are the effects of GH deficiency in children
dwarfism
decreased availability of lipids and glucose for energy
(treatment is effective with human growth hormone)
what is the effect of GH excess before puberty
gigantism due to excess stimulation of epiphyseal plates
what is the effect of GH excess after puberty
periosteal bone growth causing enlarged hand, jaw and feet
soft tissue growth leading to enlarged tongue, and coarse facial features
insulin resistance (diabetes)
can be treated with somatostatins (octreotide) varying success
what are the signs and symptoms of acromegaly/ gigantism
enlargement of hands and feet rapid growth soft tissue swelling skin tags muscle weakness fatigue skin changes hirsutism coarsening of facial features joint pain amenorrhea hyperhidrosis sleep apnea headaches paraesthesia/ carpal tunnel impotence hypertension goiter visual field defects
where is vasopressin synthesised
neurosecretory cells in the supra optic nucleus and paraventricular nucleus
what stimulates ADH release
increase in blood osmolality
decrease blood volume
angiotensin 2 release
what are the effects of ADH
recruitment of APQ channels
water retention
what are the causes of ADH deficiency (diabetes insipidus)
tumours, trauma, disease induced, familial disorders
nephrogenic - sex linked genetic defect in collecting tubule
what are the symptoms of diabetes insipidus
polyuria and polydipsia
where is oxytocin produced
hypothalamic neurons in the paraventricular and supraoptic nuclei
where is oxytocin released
posterior pituitary (stored in vesicles in the expanded ends of the axons) release is controlled by impulses from the hypothalamus
describe the hypothalamic control of milk production and ejection
sucking stimulus travels from breast to hypothalamus
dopamine release from the arcuate nucleus is inhibited
dopamine normally inhibits lactotrophs in the anterior pituitary.
prolactin is released which stimulates milk production
oxytocin is released from the paraventricular and supraoptic nuclei, it then travels to the posterior pituitary and is released into the blood
it travels to the breast and myoepithelial cells
GnRH is inhibited which inhibits the menstrual cycle
where is the pineal gland
midline of the posterior part of the roof of the 3rd ventricle
what hormone is melatonin derived from
tryptophan
what are the features of melatonin
secreted in darkness regulates circadian rhythms regulates onset of puberty effects on aging and immune system accumulates calcium phosphate with time - 'brain sand' visible on x-ray
