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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
What does the HPG regulate
Development Reproduction Ageing etc.
26
Describe GnRH and its release
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
27
Which cells does GnRH act on?
Gonadotrophs of the anterior pituitary gland
28
What percentage of the anterior pituitary gland is made up by gonadotropic cells?
5-10%
29
What happens in the absence of GnRH?
Gonadotropic cells produce little to no FSH or LH
30
Describe the control of GnRH secretion by the hypothalamus in the male
Influenced by other parts of brain (e.g. Body weight, Outside environment) Testosterone reduces secretion of GnRH
31
Describe the control of GnRH secretion from the hypothalamus in the female
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
Describe the control of FSH and LH secretion from the anterior pituitary in both sexes
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
Describe the control of hormonal secretion by the ovary in the antral phase
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
Describe the control of hormone secretion by the ovary in the pre-ovulatory phase
LH receptors develop in outer layers of granulosa cells Lots of oestrogen produced Surge of LH stimulates ovulation
35
Describe the control of hormone secretion by the ovary in the post-ovulation phase
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
What is the major difference between the control of hormone secretion from the gonads in females and males?
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
What is the name for the variation in response to gonadotropins over the ovarian cycle?
The ovarian or pelvic clock
38
Describe the control of hormone secretion from the testes
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
Describe the actions of FSH and LH in the male (briefly)
Act via GaS PCR --> adenylate cyclase Stimulate sex hormone synthesis (steroidgenesis) Control gamete production (spermatogenesis)
40
How much testosterone is typically produced per day in the male ?
4-10 mg per day Relatively constant in medium-long term Circadian rhythm (highest in morning) Environmental stimuli have an effect
41
Describe the actions of FSH and LH in the female (briefly)
Acts on GaS PCR --> adenylate cyclase Stimulates sex hormone synthesis (steroidgenesis) Controls gamete production (folliculogenesis and ovulation)
42
What is an alternative name for the pituitary gland?
Hypophysis
43
What class of hormones do testosterone, progesterone and oestrogen belong to?
Steroid hormones
44
What is the function of androgen binding protein?
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
What happens to the HPG axis in males with age?
FSH and LH start to rise at age 20 and testosterone slowly declines after age 40
46
What is different about the release of FSH v.s. LH?
LH release is pulsatile where as FSH release is not | FSH release depends on the intensity of GnRH release
47
What are pars distalis and pars nervosa?
The anterior and posterior pituitary gland
48
What are the two phases of the menstrual cycle?
Follicular or proliferative phase | Luteal or secretary phase
49
What happens in the follicular phase? (Briefly)
The ovaries and reproductive tract etc. Are prepared for ovulation To maximise the chance of fertilisation
50
What happens in the luteal phase? (Briefly)
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
When does the menstrual cycle begin?
First day of menstruation (though this is physiologically the end of the previous cycle)
52
How long is the follicular phase?
12-14 days | Variable
53
How long is the luteal phase?
14 days
54
How long is the menstrual cycle?
21-35 days | Varies among different women and in the same woman
55
When does ovulation occur?
Usually day 14 of the menstrual cycle
56
Describe the levels of gonadotropins and steroid hormones in the follicular phase
``` 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
Describe the levels of gonadotropins and steroid hormones in the luteal phase
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
Which gonadotropin causes ovulation?
LH
59
Which gonadotropins maintain the corpus luteum?
FSH and LH
60
What is the ovarian cycle?
Preparation of the gamete for ovulation and fertilisation
61
What is the uterine cycle?
Preparation of the endometrium for ovulation and fertilisation
62
How long after ovulation can a signal be produced indicating that fertilisation has occurred?
14 days
63
Where do gonadotropins act?
On the ovary
64
Where do steroid hormones / ovarian steroids act?
Act on tissues of the reproductive tract | Control the cycle
65
What class of hormones does inhibin belong to?
Peptide hormone
66
Describe the actions of gonadal steroids in the follicular phase
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
What is the consequence of progesterone stimulation of oestrogen primed cells in the luteal phase?
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
What is the effect on the uterine cycle of a sudden fall in progesterone and oestrogen?
The secretary epithelium of the endometrium undergoes apoptosis Tissue is shed as a menstrual bleed The spiral arteries contract to reduce blood loss
69
Describe the follicular phase of the menstrual cycle
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
Describe the luteal phase of the menstrual cycle
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
What happens if conception has occurred?
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
Describe the effect of menopause on gonadotropins and gonadal steroids
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
What is clomephine and how does it work?
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
What is bromocriptine and how does it work?
An analogue of dopamine (PIH) Works by inhibiting prolactin secretion which restores the pulsatile secretion of GnRH to normal and therefore increases fertility
75
What are haloperidol, metoclopramide and domperidone and how do they work?
Dopamine antagonists Increase prolactin secretion Prolactin acts to disturb the pulsatile release of GnRH, decreasing fertility
76
What is HCG analogous to?
LH | Acts on the corpus luteum to increase progesterone and estranged secretion
77
What factors can affect the menstrual cycle?
Low body weight Emotional stress Pregnancy Lactation

ESA 4 (28 decks)

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