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REPRO > Reproductive hormones and the HPG axis > Flashcards

Reproductive hormones and the HPG axis Flashcards

1
Q

Name the different types of hormone signalling

A
  • Endocrine
  • Paracrine
  • Neuro-endocrine
  • Autocrine
  • Neural
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2
Q

Describe endocrine signalling

A

Delivered to blood to get to remote site of action (not every cell in teh body will have the necessary receptors for every hormone)

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3
Q

Describe paracrine signalling

A

Does not require systemic blood flow, passed through interstitial flow

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4
Q

Describe neuro-endocrine signalling

A

Hormone passed into blood from neurone to be passed to the target cell

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5
Q

Describe neural signalling

A

Neurone produces active substance and delivers to target cells without circulation

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6
Q

Explain the importance of hormone receptors for hormone signalling

A
  • Receptors are expressed by target cells and are specific to a hormone
  • No receptor = no response
  • The ligand (hormone) will bind to or “fit” a site on the receptor
  • Have to bind to carry out function
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7
Q

Describe lipid soluble hormones (give examples)

A
  • Must be transported in blood by carrier proteins
  • May be specific to the hormone or general bulk carriers
  • Diffuse through plasma membrane and bind to intracellular receptors
  • Alter expression of genes at level of nucleus
  • e.g. steroid hormones
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8
Q

Describe water soluble hormones

A
  • Easily travel in blood
  • Excluded from cells by lipid bilayer
  • Bind to receptors on surface of cells
  • Results in series of intracellular events
  • e.g. GnRH, FSH, LH, IGF
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9
Q

Describe peptide hormones

A
  • Work at cell surface
  • Result in second messenger signalling
  • Peptie can be considered priamry messenger
  • Binding leads to cascade of enzymatic actions
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10
Q

Describe steroid hormones

A
  • Not received at cell surface, pass through plasma membrane into cytosol
  • Bind to intracellular receptors
  • Receptor-hormone complex into nucleus to act on DNA
  • Slower rate of action (more needs to happen before get a response)
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11
Q

What reproductive hormones are produced by the hypothalamus?

A

GnRH

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12
Q

What reproductive hormones are produced by the pituitary?

A
  • ADH, chorionic gonadotrophins (FSH and LH) from anterior pituitary
  • Prolactin from ant pit
  • ## Oxytocin from post pit
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13
Q

Where is oxytocin synthesised?

A

Hypothalamus

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14
Q

What reproductive hormones are produced by the ovary?

A
  • Oestrogens
  • Progesterone
  • Inhibin
  • Oxytocin
  • Relaxin
  • Some testosterone
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15
Q

What reproductive hormones are produced by the testes

A
  • Testosterone and other androgens
  • Inhibin
  • Oestrogen
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16
Q

What reproducive hormones are produced by the placenta?

A
  • Prostaglandin F2alpha (PGF2a)
  • Progesterone
  • Oestrogen
  • eCG and hCG (equine and human chorionic gonadotrophins)
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17
Q

Describe the structure of gonadotrophins

A
  • Formed of standard alpha subunit and varying beta-subunits
  • Glycoprotein heter-dimers with shared alpha chain
  • Different beta-chain depending on which gonadotrophin
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18
Q

Describe the gonadotrophin receptors

A
  • Act on G-protein-7-transmembrane receptors

- LH and chorionic gonadotrophs bind a common receptor

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19
Q

What has to happen to gonadotrophins before excretion?

A

A series of metabolic conversions

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20
Q

Describe the synthesis of steroids

A
  • From dietary cholesterol thorugh series of enzymatic conversions
  • e.g. testosterone to oestradiol via aromatase
  • All have similar structure
21
Q

How are steroids inactivated and where?

A
  • Liver, 2 ways
  • Saturation of all double bonds = inactivated
  • Sulfate or glucuronide attached making it water soluble allowing excretion in urine as glucuronide or sulfate salt
22
Q

How is progesterone inactivated?

A

Saturation of all double bonds

23
Q

How is testosterone inactivated

A

Formation of glucuronide or sulfate salts

24
Q

Describe the main features of prostaglandins

A
  • Synthesised from arachidonic acid
  • High levels in seminal fluid
  • At least 6 biocehmical PGs and many metabolites
  • Bind to cell memrbane G protein coupled receptors- 2 importna tin repro: PgF2a and PGE2
  • Rapidly degraded (seconds, single passage through pulmonary system)
25
Q

Describe the hypothalamic pituitary gonadal axis in general

A
  • Hypothalamus released GnRH, acts on pituitary to stimulate release of LH and FSH, act on the gonads
  • Have feedback loops throughout the HPG axis
26
Q

Describe the input of the CNS to the HPG axis

A
  • Information on physical and environmental state
  • Pheromones, tactile, visual reaction to bellowing of animal etc
  • Stimulates the hypothalamus
27
Q

What are the 2 GnRH rich areas of the hypothalamus in the male?

A
  • Optic chiasma

- Paraventricular nucleus

28
Q

What is the connection between the hypothalamus and the anterior pituitary?

A
  • Hypothalamo-hypophyseal-poral system
  • 2 vascular networks in series
  • Primary portal plexus in the stalk areas, down into the secondary portal plexus
29
Q

Describe the function of the hypothalamic-hypophyseal-portal system

A
  • Neurones from hypothalamus to portal plexus, release small amounts
  • Ok to be small amounts as not diluted by circulation
  • Transports GnRH from hypothalamus to ant. pit.
  • Neurohormones diffuse out, bind to receptors on endocrine cells
  • Stimulate release of LH and FSH
30
Q

Describe the connection between they hypothalamus and the posterior pituitary

A
  • Neuronal connection

- Release into post. pit for storage and then secretion from there to target cells via blood

31
Q

Describe the Leydig cells

A
  • LH receptor
  • Testosterone production
  • Outside of seminiferous tubules
32
Q

Describe the Sertoli cells

A
  • FSH receptors
  • Produce inhibin
  • Found within seminiferous tubules
33
Q

What is the effect of testosterone on the hypothalamus?

A

Inhibitory to GnRH release

34
Q

What is the effect of testosterone on its target tissues?

A

Stimulatory

35
Q

What is the effect of inhibin?

A

Inhibitory to the production of FSH and LH

36
Q

What structures can be found within the ovary?

A
  • Follicles (at various stages of development)

- Corpus luteum

37
Q

Give a brief overview of the develoment and release of the oocyte in the ovary

A
  • Primordial follicle to antral phase
  • Dominant follicle ready for ovulation
  • then release of oocyte
  • Following release, follicle becomes corpus haemorrhagicum, then corpus luteum and regressing CL is corpus albicans
38
Q

What is the function of the follicle?

A
  • Oocyte development
  • Multiple stages of development
  • Oestradiol secretion
39
Q

What is the function of the corpus luteum?

A
  • Follows ovulation
  • transient endocrine gland
  • Progesterone secretion
40
Q

Where is GnRH produced in the female?

A
  • 2 groups of hypothalamic neurons
  • surge (pre-ovulatory) centre
  • Tonic centre
41
Q

Describe the basal GnRH secretion

A
  • Numberous small pulses, regular and brief
42
Q

Describe the preovulatory surge of GnRH

A
  • High levels of GnRH secretion for extended period of time

- Stimulated by increased oestrogen

43
Q

What is the function of the pre-ovulatory surge?

A

Stimulates ovulation in the absence of progesterone

44
Q

Briefly describe the HPO axis in females

A
  • GnRH stimulates secretion of LH and FSH
  • Stimule follicle to produce oestroadiol
  • High levels has positive feedback, threshold reached and pre-ovulatory surge occurs
  • Inhibin secreted from follicle, inhibitory to FSH
45
Q

Explainthe FSH to LH shift at to ovulation

A
  • Prior to ovulation FSH more dominant than LH
  • Inhibin has negative feedback effect on FSH
  • Nearer to ovulation follicle depends more on LH than FSH (as FSH is being inhibited)
46
Q

Briefly describe the hormonal events at ovulation

A
  • Dominant folllicle producing oestradiol
  • GnRH stimulates LH surge
  • Leads to ovulation
  • Following ovulation get early CL which produces progesterone
47
Q

What is the function of the progesterone produced by the CL?

A
  • Negative feedback to GnRH
  • Prevents follicle development, oestradiol production, oestrus and GnRH/LH surge
  • Positive actions on mammary gland and endometrium (preparation for pregnancy)
  • Inhibits myometrium
  • Inhibits ovulation
48
Q

Briefly describe luteolysis

A
  • Stimulated by PGF2a from uterus
  • Rapid deteriation of CL
  • Progesterone removed

REPRO (30 decks)

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