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Mpharm 1 > PH1124 - Reproductive hormones 2 > Flashcards

PH1124 - Reproductive hormones 2 Flashcards

1
Q

what is the role of progesterone on the body?

A
  • stimulate gene expression and so cell growth in tissues that express the PR
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2
Q

what are the effects of progesterone on the body? (3)

A
  • contribution to breast development
  • maintain uterus structure; control secretory changes in uterus (endometrium) in preparation for and to maintain pregnancy
  • causes rise in basal body temperature (after ovulation in luteal phase when progesterone is highest)
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3
Q

what is progesterone clinically used to treat? (2)

A
  • combined with oestradiol as part of HRT

- IVF (to supplement body’s natural progesterone to aid pregnancy)

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4
Q

what are the side effects of clinically using progesterone?

A
  • a very slightly increased risk of breast cancer with certain HRT strategies
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5
Q

what is the general mechanism for reproductive hormones?

A
  • hormone enters cells and binds to specific hormone receptor
  • receptor conformation change, dimerization and translocation of this hormone receptor complex to the nucleus
  • DNA binding of hormone receptor complex to its specific ‘Hormone Response Element’ (HRE is a short sequence of DNA in the promoter of target genes that can bind the specific ligand-bound hormone receptor)
  • influences transcriptional activity of certain genes so there is gene expression (or repression)
  • encoded protein synthesis & impact on target cell growth
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6
Q

what regulates gonadal steroidogenesis?

A
  • the endocrine function of the gonads to synthesise reproductive hormones is carefully regulated by the Hypothalamic-Pituitary-Gonadal axis (HPG axis)
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7
Q

where is the HPG axis?

A
  • hypothalamus is a small structure at the base of the forebrain
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8
Q

what does the HPX axis link?

A
  • links the nervous system to the endocrine system via the pituitary gland that is also in the brain
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9
Q

what is the hypothalamus composed of? (3)

A
  • composed of 11 zones or ‘nuclei’
  • each is able to secrete several different hormones (which are produced from neurons)
  • these are secreted directly into the bloodstream to easily reach and regulate the pituitary gland as there is no effective BBB (blood brain barrier)
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10
Q

what processes does the hypothalamus indirectly control? (2)

A
  • hypothalamic nuclei have indirect control of different body processes eg. hunger, body temperature, mood, sleep, thirst etc
  • also controls reproductive hormone secretion from the gonads
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11
Q

what does the hypothalamus release? (2)

A
  • releases gonadotrophin releasing hormone (GnRH=LHRH) from ventromedial neurons
  • act via the bloodstream (hypophyseal portal system) on the nearby anterior pituitary gland
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12
Q

how does GnHR release gonadotrophins? (3)

A
  • GnRH acts on GnRH receptors found on pituitary ‘gonadotrope’ cells
  • activates intracellular enzymes in the pituitary gonadotropes
  • enzymes trigger synthesis of gonadotrophins
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13
Q

what is the anterior pituitary able to synthesise?

A
  • anterior pituitary contains the specialised cells (gonadotropes) that are able to synthesise both gonadotrophins FSH & LH in response to GnRH
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14
Q

what does LH or FSH production depend on?

A
  • depends on pulsatile GnRH; FSH and LH is released into the bloodstream & comprises the endocrine stimulation for the gonads
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15
Q

what is the gonadotrophin mechanism of action on the gonads? (3)

A
  • gonadotrophins = LH and FSH
  • LH and FSH each bind to different GPCR-type transmembrane receptors expressed on cells within ovary and testes
  • this then activates GPCR signalling, and thereby gonad function
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16
Q

what are the main functions of LH? (2)

A
  • in females they act on ovarian follicles and helps induce ovulation
  • in males they act on testes leydig cells so they can produce testosterone (which in turn is important for spermatogenesis)
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17
Q

what are the main functions of FSH? (2)

A
  • in female they promote ovarian follicle development and oestrogen production from granulosa cells
  • in males they stimulate spermatogenesis in testes by acting on the sertoli cells
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18
Q

what is the direct negative feedback mechanism for reproductive hormone synthesis?

A
  • steroid hormones (testosterone/oestrogen) directly feedback onto anterior pituitary to decrease secretion of gonadotrophins FSH/LH
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19
Q

what is the indirect negative feedback mechanism for reproductive hormone synthesis?

A
  • steroid hormones inhibit their own production indirectly by inhibiting hypothalamus production of GnRH
20
Q

what are other negative regulators of gonadal steroidogenesis?

A
  • inhibin
21
Q

what is inhibin and what does it do? (3)

A
  • a protein hormone that is additional negative regulator of FSH
  • in females inhibin is released by the ovary granulosa cells in response to either FSH stimulation or oestrogens
  • in males inhibin is released by the testes sertoli cells in response to either FSH stimulation or androgens
22
Q

what is the positive feedback of the HPG axis? (2)

A
  • occurs during the follicular phase of the menstrual cycle where high oestrogen levels induce further LH production
  • this leads to further increases in the reproductive hormone level to trigger ovulation
23
Q

what are the other hormones that are secreted from pituitary gland contribute to reproductive biology? (2)

A
  • oxytocin

- prolactin

24
Q

what is oxytocin and what is it secreted by? (2)

A
  • an important peptide hormone for childbirth that stimulates uterine motility (during labor) & breast milk production
  • produced by the hypothalamic neurons and transported down axons then stored in and subsequently secreted by the posterior pituitary
25
Q

when is oxytocin secreted? (2)

A
  • secreted in response to increasing oestrogens by labour contractions and by breast feeding
  • positive feedback as oxytocin induces contractions during labor which in turn promotes further oxytocin release to further progress labor to delivery
26
Q

what is prolactin? (2)

A
  • peptide hormone secreted by anterior pituitary lactotropes in response to elevated oestrogens (during ovulation or pregnancy)
  • classed as a further gonadotrophin because it influences reproductive organs and breast
27
Q

what are the main functions of prolactin?

A
  • in breast it stimulates lactation and also maternal behaviour
  • provides further negative feedback of oestrogen production
28
Q

what is the negative feedback mechanism for prolactin?

A
  • during lactation prolactin suppresses GnRH release from the hypothalamus which decreases LH, FSH
  • thereby oestrogens (disrupting return of menstrual cycle so it may result in lactational amenorrhea)
29
Q

what is gametogenesis?

A
  • formation of female or male gametes
30
Q

what are mature gametes called? (2)

A
  • ovum (egg)

- spermatozoa (sperm cells)

31
Q

what is gametogenesis call in females and males? (5)

A
  • females oogenesis process
  • males spermatogenesis process
  • gametogenesis occurs in the gonads (ovary or testis)
  • ova produced from ‘germ cells’ called oogonium/primary oocyte
  • sperm produced from ‘germ cells’ called spermatogonium
32
Q

what is spermatogenesis and what does it start with? (2)

A
  • formation of mature male gametes (the sperm cells) in testes within seminiferous tubules
  • starts with precursor (germ or stem) cells called spermatagonia
33
Q

what happens in the seminiferous tubules? (3)

A
  • spermatagonia (germ cells) undergo mitosis to give diploid primary spermatocytes
  • spermatocytes then undergo meiosis to give haploid spermatides
  • they then differentiate into sperm (spermatozoa)
34
Q

where is the location of spermatogenesis

A

seminiferous tubules

35
Q

why are leydig cells and sertoli cells in the seminiferous tubules important for spermatozoa development?

A
  • they create the physical & chemical environment that favours spermatogenesis
  • they secrete hormones & further essential factors to regulate spermatogenesis
36
Q

what are the hormones secreted to aid spermatozoa development? (3)

A
  • testosterone (from leydig cells only)
  • androgen binding protein (ABP) (from sertoli cells only)
  • inhibin (from sertoli cells only)
37
Q

what are leydig cells?

A
  • interstitial cells (pale with crystals) adjacent to seminiferous tubules in the testes
38
Q

what are leydig cells stimulated by?

A
  • they are stimulated by pituitary-derived gonadotrophin LH (LH is driven by fast GnRH pulses, so non-cyclical input)
39
Q

what is the function of leydig cells? (3)

A

LH acts via LH receptors on the leydig cells

  • the LH drives testosterone production from androstenedione by the leydig cells
  • testosterone is needed at high levels for spermatogenesis
40
Q

where do the sertoli cells extend from and to?

A
  • sertoli cells are ‘nurse’ cells extending from basement membrane of tubule to lumen
41
Q

what is the function of sertoli cells? (3)

A
  • provide structural, nutrient and metabolic support required for developing sperm
  • secrete substances initiating the meiosis (eg growth factors)
  • guide sperm to lumen via their junctions
42
Q

what are sertoli cells stimulated by?

A
  • stimulated by testosterone from leydig ells

- simulated by pituitary-derived FSH as they express FSH receptors

43
Q

what do sertoli cells secrete?

A
  • androgen binding protein (ABP)

- secrete inhibin in response to FSH or testosterone

44
Q

what does ABP serecreted by sertoli cells do?

A
  • the ABP binds testosterone from Leydig cells to ensure testosterone is at a high enough concentration in seminiferous tubule lumens to allow spermatogenesis
45
Q

what does inhibin serecreted by sertoli cells do? (2)

A
  • inhibin negatively feedsback onto pituitary to inhibit FSH

- inhibin thus acts to negatively regulate spermatogenesis

Mpharm 1 (59 decks)

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