001 introduction to endocrine systems and reproduction and the hypothalamo-pituitary axes Flashcards
what is a primary endocrine disorder?
where the production of the hormone is not functioning properly
- e.g. Cushing’s disease
what is a secondary endocrine disorder?
where there is a lack of a particular hormone or the hormone
what is the anatomical location of the pituitary gland?
- base of brain, protected by sphenoid bone
- connected to the hypothalamus via the pituitary stalk
- just inferior to the optic chiasm ( clinically important for pituitary tumours)
what is the embryological development/origin of the anterior pituitary gland?
- upgrowth from roof of the mouth called Rathke’s pouch
- ’ adenohypophysis’
- not neural origin
what is the embryological development/origin of the posterior pituitary gland?
- grows down from neural tissues from basal floor of the diencephalon
- ’ neurohypophysis’
- of neural origin
what is the anatomy of the posterior pituitary gland?
- smaller of the 2 lobes
- neurons in the hypothalamus (including periventricular and supraoptic nucleus) send projections down through the pituitary stalk and terminate in the posterior pituitary gland
- these nerve endings release chemicals that directly enter the blood via the plexus supplied by inferior hypophyseal artery
what are the 2 nuclei that feed into the posterior pituitary gland?
- paraventricular nucleus = sits at base of 3rd ventricle
- supraoptic nucleus = just next to optic chiasm
what is the artery that supplies the posterior pituitary gland?
- inferior hypophyseal artery which forms a plexus which hormones enter the bloodstream through
what is a?
optic chiasm
what is b?
infundibulum (connecting stalk)
what is c?
hypothalamic-hypophyseal tract
what is d?
axon terminals
what is e?
inferior hypophyseal artery
what is f?
supraoptic nucleus
what is g?
paraventricular nucleus
what are the 2 posterior pituitary hormones?
- oxytocin
- anti-diuretic hormone (ADH) / vasopressin (AVP), 2 names as it has 2 receptors
- called neurohypophyseal hormones
what is the process of releasing hormones from the posterior pituitary gland?
- hormones oxytocin/ADH are synthesized in the magnocellular neurones of the periventricular and supraoptic nuclei in the hypothalamus
- the hormones are transported down the axons in the infundibulum in the hypothalamic-hypophyseal tract into the posterior pituitary gland and stored in the axon terminals
- they are stored here until action potentials from the hypothalamus fire to release the hormones into the blood
What are the neurons called in the PVN and SON that produce oxytocin and ADH?
magnocellular neurones
what is the median eminence?
area of fenestrated blood vessels which act as a funnel which ship contents of hypothalamus down into the anterior pituitary
what is the process of releasing hormones from the anterior pituitary gland?
- hypothalmaus neurons are stimulated and secreat releasing or inhibiting hormones e.g. TRH, CRH…
- these hormones travel down the median eminence / primary capillary plexus into the anterior pituitary gland where they either stimulate or inhibit hormones made there
- the anterior pituitary gland then secretes hormones into the secondary capillary plexus which enters the general circulation e.g. TSH, ACTH
what are the 5 different cell populations in the anterior pituitary?
- thyrotrophs = TSH
- gonadotrophs = LH/FSH
- corticotrophs = ACTH
- somatotrophs = GH
- lactotrophs = prolactin
what hormones does the anterior pituitary produce/secrete (6)?
- TSH = thyroid stimulating hormone
- LH = luteinising hormone
- FSH = follicle-stimulating hormone
- ACTH = adrenocorticotrophic hormone
- GH = growth hormone (somatotrophin)
- Prolactin
what hormones do the hypothalamus produce/secrete?
- GHRH = growth hormone releasing hormone
- GnRH = gonadotropin-releasing hormone
- CRH = corticotropin-releasing hormone
- TRH = thyrotropin-releasing hormone
- Dopamine (affect prolactin)
what are the general structures of TSH, LH, FSH?
- heterodimeric glycoproteins
- common alpha subunit
- specific to hormone Beta subunites
what is the general structure of ACTH?
- peptide
- 39 amino acid cleaved fragment of POMC
what is the general structure of GH and prolactin?
- 3D peptides
- 190 amino acids
- internal disulfide bonds
- homologous receptors
what part of the pituitary is pars nervosa?
- posterior pituitary gland
what part of the pituitary is pars distalis?
- anterior pituitary gland
what part of the pituitary is pars intermedia?
- intermediate lobe
- separates anterior and posterior glands
- closely associated with posterior, separated from anterior via hypophyseal cleft
what hormone does the pars intermedia of the pituitary gland secrete?
- MSH = melanocyte-stimulating hormone
describe the pathway/ dual control of GH secretion
- hypothalamus secretes GHRH –> stimulates GH secretion from anterior pituitary gland –> liver to produce IGF-1
- negative feedback loop of IGF-1 to turn off hypothalamus and anterior pituitary
- GH release is also controlled by somatostatin which is produced near GHRH neurons
- somatostatin inhibits GH production
- stress also inhibits GH production
why is prolactin an exception?
- instead of being stimulated or inhibited by the hypothalamus, it is under dominant negative control by dopamine (from arcuate nucleus)
- so more dopamine = less prolactin
what are the 3 steps of the hypothalamo-pituitary-thyroid (HPT) axis?
- hypothalamus secrete TRH –> Stimulates anterior pituitary gland to secrete TSH –> stimulate thyroid to produce thryoid hormones (T3,T4)
- negative feedback loop
what are the 3 steps of the hypothalamo-pituitary-gonadal (HPG) axis?
- hypothalamus secretes GnRH –> stimulates anterior pituitary gland to secrete LH/FSH –> stimulates gonads to produce progesterone/testosterone/oestrodiol
- negative feedback loop
what are the 3 steps of the hypothalamo-pituitary-adrenal (HPA) axis?
- hypothalamus secretes CRH –> stimulates anterior pituitary gland to secreted ACTH –> stimulates adrenal gland to produce cortisol
- negative feedback loop
what 2 factors can override negative feedback of the hypothalamus-pituitary axes?
- higher centres of the brain
- chronic stress = CRH, GcRH, GHRH all affected
what can cause pituitary gland defects? (5)
- cranial trauma
- tumours
- inflammation/infection
- midline defects e.g. septo-opticdysplasia
- defects in migration of hypothalamic neurons e.g. Kallman’s syndrome when GnRH hormones do not migrate = don’t go through normal puberty
what can cause hyposecretion of anterior pituitary hormones?
- adenohypophyseal cells are sensitive to radiation, particularly somatotrophs (GH)
- other than that it is very rare, very specific diseases
what can cause hypersecretion of anterior pituitary hormones?
- pituitary tumours
- specific hormones syndromes e.g. cushings diseases, hypothyroidism, acromegaly
- ectopic, tumours else where in the body
where is oxytocin secreted from?
- posterior pituitary gland
- ovaries
- testes
what is the general structure of oxytocin?
- 9 amino acid peptide hormone
- differs from ADH by 2 aa
- packaged into granules with ADH and secreted along with carrier proteins called neurophysics
what are the 3 main actions of oxytocin?
- stimulation of milk ejection
-stimulation of uterine contractions at birth - acts within brain to establish maternal behaviour and bonding
- all positive feedback
what are the neural reflexes that mediate oxytocin positive feedback?
- suckling reflex = act of nursing / suckling on mother nipple cause reflex to stimulate oxytocin release from neurons to stimulate milk ejection
- Fergusson reflex = stimulation of uterine smooth muscle contractions during birth
