pituitary Flashcards
adenohypophysis: explain the principle features of the anterior pituitary, list the adenohypophysial hormones and explain their homeostatic control, explain the synthesis, storage, release and physiological actions of these hormones and how dysregulation may present
where is the pituitary gland located
just below the hypothalamus within the brain
what are the two distinct pituitary lobes
anterior and posterior
what is the anterior lobe also called
adenohypophysis
adenohypophysis lobe: origin
upgrowth from mouth
principle features of anterior pituitary
hypothalamic factors secreted within median eminence; endocrine action as diffuse into blood vessels through portal vessels and into endocrine cells for hormone secretion; secretory so requires bloodstream circulation
what does the pituitary gland lie in
sella turcica bone
where do hypothalamic neurone axons feed into the anterior pituitary
median eminence
significance of region of median eminence
devoid of blood-brain barrier so rich in capillaries to allow release of hormones
sections of adenohypophysis lobe
pars tuberalis, pars distalis
what is the purpose of the pars tuberalis
wraps pituitary stalk which connects hypothalamus, posterior lobe with pars distalis
what is the purpose of the pars distalis
where most hormone production occurs
which section of the brain dictates actions of anterior pituitary
hypothalamus
where is the primary fenestrated capillary plexus
median eminence
what connects the primary and secondary fenestrated capillary plexus
long portal veins
where does blood arrive into the pituitary gland
superior hypophysial artery
what is a portal network
where blood from the systemic circulation drains from one capillary network to another before returning to the heart
where does blood flow from the secondary fenestrated capillary plexus
into the venous system via the cavernous sinus
fenestrated definition and importance
“leaky”, so allows hormones to leak out and cause an effect
define hypothalamic neurone
neurones from hypothalamus to median eminence which secrete neurosecretions
where are hypothalamic neurosecretions released into
hypothalamo-hypophysical portal system
what do the hypothalamic neurosecretions do when they pass out of the secondary capilary plexus
inform secretory cells to exocytose stored hormones into systemic circulation
hypothalamo-adenohypophysial axis
hypothalamic nuclei → neurones to median eminence → neurosecretions released by hypothalamic neurone into adenohypophysis → adenohypophysial hormones → target organs
effect of hypothalamic hormones on adenohypophysial hormones and purpose
regulate (releasing or inhibitory) to maintain homeostasis
example of adenohypophysial hormone target organ
thyroid
adenohypophysial cells
somatotrophs, lactotrophs, thyrotrophs, gonadostrophs, corticotrophs
somatotroph production
growth hormones (somatotrophin)
lactotroph production
prolactin
thyrotroph production
thyroid stimulating hormone (TSH, thyrotrophin)
gonadotroph production
luteinising hormone (LH), follicle stimulating hormone (FSH)
corticotroph production
adrenocorticotrophic hormone (ACTH, corticotrophin)
adenohypophysial hormone synthesis and release
long precursor (prohormone) cleaved by enzyme to produce bioactive hormone; stored in secretory granules and released by exocytosis
adenohypophysial hormones: long proteins
growth hormone (somatotrophin), prolactin
adenohypophysial hormones: glycoproteins
TSH, thyrotrophin, LH, FSH
adenohypophysial hormones: polypeptide (shortest)
ACTH, corticotrophin
somatotrophin hypothalamic stimulator hormone
growth hormone releaseing hormone (GHRH)
somatotrophin hypothalamic repressor hormone
somatostatin
prolactin hypothalamic stimulatory hormone
thyrotrophin releasing hormone (TRH)
prolactin hypothalamic repressor hormone
dopamine
by which process does dopamine suppress prolactin secretion
negative inhibition, so less dopamine causes less prolactin
thyroid stimulating hormone hypothalamic stimulatory hormone
thyrotrophin releasing hormone (TRH)
LH and FSH hypothalamic stimulatory hormone
gonadotrophin releasing hormone
ACTH hypothalamic stimulatory hormone
corticotrophin releasing hormone, vasopressin
growth hormone main target cells
general body tissues, especially liver
prolactin main target cell
breasts in lactating women
thyrotrophin main target cell
thyroid
gonadotrophin main target cells
testes (men), ovaries (women)
corticotrophin main target cell
adrenal cortex
growth hormone effect on body tissue
increase metabolic actions causing growth and development
growth hormone effect on liver
causes liver to make IGF I and IGF II
significance of IGF I on body tissue
indirect effect on metabolic actions, promoting metabolic actions causing growth and development
metabolic actions affected by growth hormone
stimulation of amino acid transport into cells (e.g. muscle) and protein synthesis; increased gluconeogenesis; stimulation of lipolysis leading to increased fatty acid production; increased cartilaginous growth and somatic cell growth
stimulators of growth hormone somatotrophin production
ghrelin (from stomach), amino acids, fasting (hypoglycaemia), exercise, oestrogens, stress, sleep
what type of feedback is anterior pituitary under from IGF I to reduce somatotrophin
direct negative feedback
what type of feedback is the hypothalamus under from IGF I to reduce GRHR
indirect negative feedback
define neuro-endocrine reflex arc
nerve pathway involved in a reflex action, with a neuronal input and hormonal output
prolactin as a hormone under neuro-endocrine reflex arc
suckling stimulates neuronal feedback, which supresses dopamine release, meaning more prolactin released to lactating breast, so more milk produced
