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ESA 4 > Reproductive System Week 2 > Flashcards

Reproductive System Week 2 Flashcards

1
Q

What is required for successful reproduction?

A

Each sex to produce right number of gametes at right time
Effective apparatus to transfer sperm from male to female
The creation of opportunities to use that apparatus
Sperm transport and fertilisation
Support of the conceptus, embryo and foetus
Successful parturition
Support of the neonate

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2
Q

Where are the major controlling structures of reproduction located in males and females?

A

The hypothalamus, pituitary gland (particularly anterior), gonads, and placenta (in pregnant females)

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3
Q

How do the controlling structures of reproduction interact with each other?

A

Primarily by secretion of hormones

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4
Q

Where does the anterior pituitary gland arise from embryologically?

A

Rathke’s pouch

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5
Q

Hormones of which axis are crucial to reproduction?

A

Hypothalamic-pituitary-gonadal (HPG) axis

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6
Q

Which other glands are regulated by the hypothalamus-pituitary unit?

A

Thyroid (HPT)

Adrenal (HPA)

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7
Q

What other actions does the hypothalamus-pituitary unit control?

A

Somatic growth, lactation, milk secretion, water metabolism

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8
Q

Where does the pituitary gland sit?

A

In the sella turcica of the sphenoid bone of the skull

Beneath the hypothalamus

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9
Q

What is the alternative name for the anterior pituitary gland?

A

Adenohypophysis

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10
Q

What is the alternative name for the posterior pituitary gland?

A

Neurohypophysis

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11
Q

What is the embryological origin of the pituitary gland?

A

Ectoderm

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12
Q

What tissue makes up the posterior pituitary gland?

A

Nervous tissue

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13
Q

How is the posterior pituitary gland connected to the hypothalamus?

A

Physical connection

Hypothalamus drops down through the infundibulum to form the posterior pituitary gland

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14
Q

How does the anterior pituitary gland communicate with the hypothalamus?

A

The hypophyseal portal system

Superior hypophyseal artery

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15
Q

Where in the hypothalamus is oxytocin released from?

A

Supraoptic nucleus

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16
Q

Where in the hypothalamus is ADH released from?

A

The Paraventricular nucleus

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17
Q

Describe the function of the posterior pituitary gland

A

Oxytocin and ADH produced by neurones in hypothalamus
Transported down nerve cell axons to posterior pituitary
Stored and released from posterior pituitary into circulation to act on distant targets

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18
Q

Describe the function of the anterior pituitary gland

A

Hormones produced in the hypothalamus are transported down axons and stored in the median eminence before being released into the hypophyseal portal system
These hormones act on target endocrine cells in the anterior pituitary
Endocrine cells of the anterior pituitary secrete hormones into the blood stream to act on distant target cells

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19
Q

What function do the hormones released by the hypothalamus have?

A

Neurocrine function
Both direct effects on distant tissues (from posterior pituitary) and tropic effects on endocrine cells of anterior pituitary

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20
Q

What function do the hormones released by the anterior pituitary gland have?

A

Endocrine, autocrine and paracrine functions

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21
Q

Describe the hormones produced by the hypothalamus and their function

A

Oxytocin - milk let down, uterine contractions
ADH - water regulation

Tropic:
TRH - thyrotropin releasing hormone - stimulates release of TSH and prolactin
PRH - prolactin releasing hormone - stimulates release of prolactin
PIH - prolactin release-inhibiting hormone - inhibits release of prolactin
CRH - corticotropin releasing hormone - stimulates release of ACTH
GnRH - Gonadotropin releasing hormone - stimulates release of LH and FSH
GHRH - growth hormone releasing hormone - stimulates release of growth hormone
GHIH (Somatostatin) - growth hormone inhibiting hormone - inhibits release of growth hormone

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22
Q

Describe the hormones produced by the anterior pituitary gland and their function

A

TSH - stimulates thyroid hormone release from thyroid gland
ACTH - stimulates secretion of hormones from adrenal cortex
LH - ovulation and secretion of sex hormones
FSH - development of eggs and sperm
PRL - mammary gland development and milk secretion
GH - growth and energy metabolism - stimulates IGFs

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23
Q

How is the hypothalamus pituitary unit regulated?

A

Negative feedback

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24
Q

Describe the characteristics of hormones released by the hypothalamus

A

Secretion in pulses tied to internal biological clock (synchronised external signals e.g. Light)
Act on specific membrane receptors
Transduce signals via second messengers
Stimulate release of stored pituitary hormones
Stimulate synthesis of pituitary hormones
Stimulates hyperplasia and hypertrophy of target cells
Regulates own receptor

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25
Q

What does the HPG regulate

A

Development
Reproduction
Ageing etc.

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26
Q

Describe GnRH and its release

A

10 AA peptide
Release is pulsatile (every 1-3 hours, lasting 5-25 minutes)
Intensity of stimulus affected by frequency of release and intensity of release

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27
Q

Which cells does GnRH act on?

A

Gonadotrophs of the anterior pituitary gland

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28
Q

What percentage of the anterior pituitary gland is made up by gonadotropic cells?

A

5-10%

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29
Q

What happens in the absence of GnRH?

A

Gonadotropic cells produce little to no FSH or LH

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30
Q

Describe the control of GnRH secretion by the hypothalamus in the male

A

Influenced by other parts of brain (e.g. Body weight, Outside environment)
Testosterone reduces secretion of GnRH

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31
Q

Describe the control of GnRH secretion from the hypothalamus in the female

A

Influenced by other areas of brain (e.g. Body weight, outside environment)
Oestrogen (mainly oestradiol) at intermediate concentrations reduces secretion of GnRH - reduces amount produced per pulse
Progesterone increases inhibitory effect of oestrogen - through reducing the frequency of pulses
Oestrogen alone at high concentrations promotes the release of GnRH –> surge
Progesterone prevents a surge at high oestrogen levels

32
Q

Describe the control of FSH and LH secretion from the anterior pituitary in both sexes

A

Amount of FSH and LH secreted in each pulse is affected by oestrogen at intermediate concentration (reduces it)
Oestrogen at high concentration (increases it)
Amount of FSH produced in response to GnRH is reduced by inhibin
Testosterone will reduce the sensitivity of gonadotrophs to GnRH (-) FSH and LH

33
Q

Describe the control of hormonal secretion by the ovary in the antral phase

A

LH binds to theca interna cells – > stimulate them to produce androgens (androstenedione)
FSH binds to granulosa cells –> stimulates them to develop enzymes which convert androgens to oestrogens
As follicle grows more oestrogens produced for a given gonadotropic stimulation

34
Q

Describe the control of hormone secretion by the ovary in the pre-ovulatory phase

A

LH receptors develop in outer layers of granulosa cells
Lots of oestrogen produced
Surge of LH stimulates ovulation

35
Q

Describe the control of hormone secretion by the ovary in the post-ovulation phase

A

LH stimulates the corpus luteum to secrete progesterone and oestrogen
As the corpus luteum grows more steroids are produced for a given LH concentration
Inhibin released from granulosa cells of corpus luteum –> inhibits secretion of FSH from anterior pituitary (same as males) and has small inhibitory effect on LH

36
Q

What is the major difference between the control of hormone secretion from the gonads in females and males?

A

The amount of testosterone secreted for a given LH concentration is relatively constant where as the events of the ovarian cycle influence the response to gonadotropins producing an ovarian or pelvic clock

37
Q

What is the name for the variation in response to gonadotropins over the ovarian cycle?

A

The ovarian or pelvic clock

38
Q

Describe the control of hormone secretion from the testes

A

LH acts on Leydig cells –> promotes testosterone secretion (enhanced by prolactin and inhibin)
Testosterone diffuses into seminiferous tubules
FSH acts on Sertoli cells –> makes them grow and secrete spermatogenic substances and become responsive to testosterone
Testosterone acts on Sertoli cells to promote spermatogenesis
Testosterone acts elsewhere in the body to maintain male reproductive system (Determinative and regulatory effects)
Testosterone inhibits GnRH secretion from hypothalamus and reduces sensitivity of gonadotrophs to GnRH
If spermatogenesis proceeds too rapidly - inhibin secreted from Sertoli cells - reduces secretion of FSH from gonadotrophs

39
Q

Describe the actions of FSH and LH in the male (briefly)

A

Act via GaS
PCR –> adenylate cyclase

Stimulate sex hormone synthesis (steroidgenesis)
Control gamete production (spermatogenesis)

40
Q

How much testosterone is typically produced per day in the male ?

A

4-10 mg per day
Relatively constant in medium-long term
Circadian rhythm (highest in morning)
Environmental stimuli have an effect

41
Q

Describe the actions of FSH and LH in the female (briefly)

A

Acts on GaS
PCR –> adenylate cyclase

Stimulates sex hormone synthesis (steroidgenesis)
Controls gamete production (folliculogenesis and ovulation)

42
Q

What is an alternative name for the pituitary gland?

A

Hypophysis

43
Q

What class of hormones do testosterone, progesterone and oestrogen belong to?

A

Steroid hormones

44
Q

What is the function of androgen binding protein?

A

Produced by the Sertoli cells
Binds specifically to testosterone
Makes it less lipophilic –> concentrates it in the seminiferous tubules
The high levels of testosterone enables spermatogenesis and sperm maturation

45
Q

What happens to the HPG axis in males with age?

A

FSH and LH start to rise at age 20 and testosterone slowly declines after age 40

46
Q

What is different about the release of FSH v.s. LH?

A

LH release is pulsatile where as FSH release is not

FSH release depends on the intensity of GnRH release

47
Q

What are pars distalis and pars nervosa?

A

The anterior and posterior pituitary gland

48
Q

What are the two phases of the menstrual cycle?

A

Follicular or proliferative phase

Luteal or secretary phase

49
Q

What happens in the follicular phase? (Briefly)

A

The ovaries and reproductive tract etc. Are prepared for ovulation
To maximise the chance of fertilisation

50
Q

What happens in the luteal phase? (Briefly)

A

Wait for signal from the developing placenta
Physiological changes occur in preparation for potential pregnancy
If no signal - cycle ends and new one begins

51
Q

When does the menstrual cycle begin?

A

First day of menstruation (though this is physiologically the end of the previous cycle)

52
Q

How long is the follicular phase?

A

12-14 days

Variable

53
Q

How long is the luteal phase?

A

14 days

54
Q

How long is the menstrual cycle?

A

21-35 days

Varies among different women and in the same woman

55
Q

When does ovulation occur?

A

Usually day 14 of the menstrual cycle

56
Q

Describe the levels of gonadotropins and steroid hormones in the follicular phase

A 
The early follicular phase:
- low levels of oestrogen and inhibin lead to...
- Relatively high levels of FSH and LH
- Low but rising levels of oestrogen
- Very low levels of progesterone
Late follicular phase:
- FSH levels fall due to inhibin secretion
- LH levels rise
- Oestrogen levels rise dramatically
- Leading to surge in LH levels 
- Ovulation occurs
57
Q

Describe the levels of gonadotropins and steroid hormones in the luteal phase

A

Early:
- FSH and LH are low due to decrease in oestrogen
- Low levels of progesterone, increasing
Late:
- FSH and LH continue to decrease
- Progesterone and oestrogen increase to high levels (progesterone higher than oestrogen)
- Progesterone falls and then oestrogen falls
- Menstruation begins

58
Q

Which gonadotropin causes ovulation?

A

LH

59
Q

Which gonadotropins maintain the corpus luteum?

A

FSH and LH

60
Q

What is the ovarian cycle?

A

Preparation of the gamete for ovulation and fertilisation

61
Q

What is the uterine cycle?

A

Preparation of the endometrium for ovulation and fertilisation

62
Q

How long after ovulation can a signal be produced indicating that fertilisation has occurred?

A

14 days

63
Q

Where do gonadotropins act?

A

On the ovary

64
Q

Where do steroid hormones / ovarian steroids act?

A

Act on tissues of the reproductive tract

Control the cycle

65
Q

What class of hormones does inhibin belong to?

A

Peptide hormone

66
Q

Describe the actions of gonadal steroids in the follicular phase

A

Stimulate secretion and muscular contraction of the Fallopian tube and the growth and motility of fallopian cilia
Stimulate growth and motility of myometrium
Stimulate thickening of the endometrium and increase in number and size of glandular invaginations - cells secrete watery fluid conductive to sperm
Stimulate secretion of cervical mucous which is thin and alkaline - conductive to sperm transport
Stimulates increased mitotic activity in vaginal epithelium
Stimulates mildly anabolic metabolic changes, depresses appetite and maintains bone structure
Has effects on the CVS
Hair, skin changes

67
Q

What is the consequence of progesterone stimulation of oestrogen primed cells in the luteal phase?

A

Reduces Fallopian tube motility, secretion and cilia motility
Stimulates further growth of myometrium but reduces motility
Stimulates further thickening of the endometrium, increased secretion and development of the spiral arteries
Stimulates thickening and acidification of cervical mucous - inhibits sperm transport
Stimulates a mildly catabolic metabolic change
Elevates basal body temperature
Promotes change in salt and water excretion which may in combination with high oestrogen produce net sodium and water retention
Changes mammary tissue

68
Q

What is the effect on the uterine cycle of a sudden fall in progesterone and oestrogen?

A

The secretary epithelium of the endometrium undergoes apoptosis
Tissue is shed as a menstrual bleed
The spiral arteries contract to reduce blood loss

69
Q

Describe the follicular phase of the menstrual cycle

A

Day 0 - oestrogen, progesterone and inhibin levels low
GnRH secretion released from inhibition
LH and FSH rise
FSH rises more due to additional effect of reduced selective inhibition at the pituitary by inhibin
FSH, followed by LH, cause follicles to grow
Oestrogen and inhibin secretion rises
FSH secretion selectively inhibited by inhibin
LH receptors develop on granulosa cells
As the follicles grow more and more oestrogen is released for the same amount of LH concentration
Rising levels of oestrogen causes positive feedback on GnRH
Leads to LH surge - precise timing of this may be influenced by environmental factors
LH surge produces ovulation

70
Q

Describe the luteal phase of the menstrual cycle

A

Because the ovum has been released, oestrogen levels drop dramatically
The corpus luteum forms spontaneously
LH promotes secretion of oestrogen and progesterone from corpus luteum
Rising oestrogen levels do not exert positive feedback on GnRH due to progesterone levels rising
Exert a negative feedback - causing LH FSH and GnRH to fall
In absence of pregnancy corpus luteum regresses spontaneously 14 days after ovulation
Therefore progesterone and oestrogen levels fall
This triggers a menstrual bleed
Relieving inhibition of FSH and LH –> triggers development of new follicles and beginning of new cycle

71
Q

What happens if conception has occurred?

A

The implanted embryo develops a placenta which secretes human chorionic gonadotropin
This prevents regression of corpus luteum –> continues to secrete oestrogen and progesterone until placenta takes over
Supports the early weeks of pregnancy
Maintains suppression of the ovarian cycle

72
Q

Describe the effect of menopause on gonadotropins and gonadal steroids

A

No developing follicles
Oestrogen decreases
Therefore GnRH, FSH and LH increase
FSH increases more than LH due to reduced inhibin secretion as well as reduced oestrogen

73
Q

What is clomephine and how does it work?

A

It is an “anti-oestrogen” used in the treatment of infertility
Exerts weak oestrogenic effect - achieves binding and uptake by oestrogen receptors
Reduces the concentration of oestrogen receptors by inhibiting receptor replenishment
Therefore the hypothalamic-pituitary axis is blinded to endogenous oestrogen levels
Given for 5 days at start of menstrual cycle
Reduces the inhibition of GnRH secretion caused by moderate levels of oestrogen
Therefore GnRH secretion increases, increasing FSH and LH levels

74
Q

What is bromocriptine and how does it work?

A

An analogue of dopamine (PIH)
Works by inhibiting prolactin secretion which restores the pulsatile secretion of GnRH to normal and therefore increases fertility

75
Q

What are haloperidol, metoclopramide and domperidone and how do they work?

A

Dopamine antagonists
Increase prolactin secretion
Prolactin acts to disturb the pulsatile release of GnRH, decreasing fertility

76
Q

What is HCG analogous to?

A

LH

Acts on the corpus luteum to increase progesterone and estranged secretion

77
Q

What factors can affect the menstrual cycle?

A

Low body weight
Emotional stress
Pregnancy
Lactation

ESA 4 (28 decks)

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