Flashcards in Week 2 - HPG axis Deck (38):
1
What is the adrenohypophysis/pars distalis?
-Anterior portion of pituitary
2
What is the neurohypophysis/pars nervosa?
-Posterior portion of pituitary
3
Which side of the pituitary stains darker?
-Anterior
4
What type of tissue composes the posterior pituitary?
-Nervous tissue
5
What is the function of the posterior pituitary?
-It is a neuro-secretory gland producing ADH and oxytocin
6
What is the median eminence?
-Upper portion of neural stalk which projects into hypothalmus
7
What tissue is the anterior pituitary composed of?
-Glandular cells
8
How is the posterior pituitary connected to the hypothalamus?
-Hypothalamic neurones
9
How is the anterior pituitary connected to the hypothalmus?
-Superior hypophyseal artery
10
What 6 hormones are produced from the anterior pituitary?
-TSH
-GH
-ACTH
-Prolactin
-FSH
-LH
11
How does the hypothalmus regulate the anterior pituitary?
-Releases Hypothalamic Releasing Hormones into the hypothalamic pituitary portal which act on specific trophic cells in the anterior pituitary to control secretion of their hormones
12
How is the whole hypothalamic-pituitary-gonadal axis controlled?
-Negative feedback from trophic hormones
13
How are hypothalamic releasing hormones characterisically secreted?
-Pulsatile release synchronised by external signals eg light/dark
14
How do hypothalamic releasing hormones act on target cells?
-Bind to specific membrane receptors and transduce signals via secondary messangers which stimulate the release f stored pituitary hormones and synthesis of new ones
15
Name the hypothalamic releasing hormones and their corresponding effects
-Corticotrophin releasing hormone -> Stimulates ACTH secretion
-Thyrotropin releasing hormone -> Stimulates TSH and prolactin secretion
-Growth hormone releasing hormone -> Stimulates GH secretion
-Somatostatin -> inhibits GH secretion
-Gonadotropin releasing hormone -> Stimulates FSH/LH secretion
-Prolactin releasing hormone -> stimulates PRL secretion
-Dopamine -> inhibits prolactin secretion
16
How is GnRH characteristically released?
-Pulsatile -> once an hour
17
What type of receptors does GnRH stimulate on gonadotrophic cells of pituitary?
-GPCR
18
How do FSH and LH exert their effects on the gonads?
-Bind to GsPCR -> Gas -> Increase Adenylate Cyclase activity -> Increased cAMP -> Activation of PKA
19
Which cells specifically do FSH and LH act on?
-Ovarian granulosa cells and theca interna in females
-FSH -> Sertoli cells and LH ->leydig cells in males
20
What are the two major effects of FSH and LH regarding reproduction?
-Stimulate sex steroid synthesis
-Control gamete production
21
What effect does testosterone have on GnRH, FSH/LH?
Negative feeback on the hypothalmus and pituitary causes:
-Reduces GnRH secretion
-Reduced FSH/LH
22
What effect does high levels of oestrogen alone have on GnRH, FSH/LH?
Positive feeback on the hypothalmus and pituitary causes:
-Promotes GnRH secretion
-Promotes FSH/LH secretion
(LH surge)
23
What effect do moderate levels of oestrogen have on GnRH, FSH/LH?
Negative feeback on the hypothalmus and pituitary causes:
-Reduced GnRH secretion
-Reduced FSH/LH secretion
24
How does Progesterone influence the effect which oestrogen has on GnRH? What effect does this have on LH?
-Increases the inhibitory effects of moderate oestrogen -> Minimal FSH/LH production
-Prevents positive feedback of high oestrogen -> no LH surge
25
What is different between the way which oestrogen and progesterone reduce GnRH secretion?
-Oestrogen reduced the amplitude of GnRH pulse
-Progesterone reduced the frequency of GnRH pulse
26
What is the function of inhibin?
-Selectively reduces FSH secretion
27
From where is inhibin produced?
-Gonads
28
Which cells in the male produce testosterone?
-Leydig cells
29
Which cells in the male produces androgen binding globulin and inhibin?
-Sertoli cells
30
What is androgen binding globulin?
-A protein which binds to testosterone and keeps in within the seminiferous tubules
31
What is the function of inhibin in males?
-Supports spermatogenesis and inhibits the production of FSH, LH and GnRH
32
What are the functions of LH in the male?
-Promote testosterone secretion
-Promote spermatogenesis
33
What happens, with regards to controlling the system,if testosterone reaches a high level in the male? What is the advantage of this
-Negative feedback on hypothalmus and pituitary causing decreased GnRH, LH and FSH which causing a reduction in testosterone secretion ->returns to normal
-Produces a constant level of testosterone and spermatogenesis
34
What happens if spermatogenesis speeds up?
-more inhibin secreted -> reduces FSH secretion -> returns to normal
35
In what type of rhythm is testosterone produced?
-Long term testosterone levels are constant but is under circadian rhythm so is highest in the morning (also effected by environmental stimuli)
36
What drives secondary sexual characteristics in male puberty?
-Testosterone
37
What is the function of inhibin in females?
-Inhibition of activin which stimulates GnRH
-Selective inhibition of FSH allowing LH surge
38