001 introduction to endocrine systems and reproduction and the hypothalamo-pituitary axes Flashcards
1
Q
what is a primary endocrine disorder?
A
where the production of the hormone is not functioning properly
- e.g. Cushing’s disease
2
Q
what is a secondary endocrine disorder?
A
where there is a lack of a particular hormone or the hormone
3
Q
what is the anatomical location of the pituitary gland?
A
- 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)
4
Q
what is the embryological development/origin of the anterior pituitary gland?
A
- upgrowth from roof of the mouth called Rathke’s pouch
- ’ adenohypophysis’
- not neural origin
5
Q
what is the embryological development/origin of the posterior pituitary gland?
A
- grows down from neural tissues from basal floor of the diencephalon
- ’ neurohypophysis’
- of neural origin
6
Q
what is the anatomy of the posterior pituitary gland?
A
- 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
7
Q
what are the 2 nuclei that feed into the posterior pituitary gland?
A
- paraventricular nucleus = sits at base of 3rd ventricle
- supraoptic nucleus = just next to optic chiasm
8
Q
what is the artery that supplies the posterior pituitary gland?
A
- inferior hypophyseal artery which forms a plexus which hormones enter the bloodstream through
9
Q
what is a?
A
optic chiasm
10
Q
what is b?
A
infundibulum (connecting stalk)
11
Q
what is c?
A
hypothalamic-hypophyseal tract
12
Q
what is d?
A
axon terminals
13
Q
what is e?
A
inferior hypophyseal artery
14
Q
what is f?
A
supraoptic nucleus
15
Q
what is g?
A
paraventricular nucleus
16
Q
what are the 2 posterior pituitary hormones?
A
- oxytocin
- anti-diuretic hormone (ADH) / vasopressin (AVP), 2 names as it has 2 receptors
- called neurohypophyseal hormones
17
Q
what is the process of releasing hormones from the posterior pituitary gland?
A
- 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
18
Q
What are the neurons called in the PVN and SON that produce oxytocin and ADH?
A
magnocellular neurones
19
Q
what is the median eminence?
A
area of fenestrated blood vessels which act as a funnel which ship contents of hypothalamus down into the anterior pituitary
20
Q
what is the process of releasing hormones from the anterior pituitary gland?
A
- 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
21
Q
what are the 5 different cell populations in the anterior pituitary?
A
- thyrotrophs = TSH
- gonadotrophs = LH/FSH
- corticotrophs = ACTH
- somatotrophs = GH
- lactotrophs = prolactin
22
Q
what hormones does the anterior pituitary produce/secrete (6)?
A
- TSH = thyroid stimulating hormone
- LH = luteinising hormone
- FSH = follicle-stimulating hormone
- ACTH = adrenocorticotrophic hormone
- GH = growth hormone (somatotrophin)
- Prolactin
23
Q
what hormones do the hypothalamus produce/secrete?
A
- GHRH = growth hormone releasing hormone
- GnRH = gonadotropin-releasing hormone
- CRH = corticotropin-releasing hormone
- TRH = thyrotropin-releasing hormone
- Dopamine (affect prolactin)
24
Q
what are the general structures of TSH, LH, FSH?
A
- heterodimeric glycoproteins
- common alpha subunit
- specific to hormone Beta subunites
25
what is the general structure of ACTH?
- peptide
- 39 amino acid cleaved fragment of POMC
26
what is the general structure of GH and prolactin?
- 3D peptides
- 190 amino acids
- internal disulfide bonds
- homologous receptors
27
what part of the pituitary is pars nervosa?
- posterior pituitary gland
28
what part of the pituitary is pars distalis?
- anterior pituitary gland
29
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
30
what hormone does the pars intermedia of the pituitary gland secrete?
- MSH = melanocyte-stimulating hormone
31
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
32
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
33
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
34
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
35
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
36
what 2 factors can override negative feedback of the hypothalamus-pituitary axes?
- higher centres of the brain
- chronic stress = CRH, GcRH, GHRH all affected
37
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
38
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
39
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
40
where is oxytocin secreted from?
- posterior pituitary gland
- ovaries
- testes
41
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
42
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
43
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
