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*LCRS Endocrinology Y1* > Gonads > Flashcards

Gonads Flashcards

1
Q

What are the gonads?

A

Testes in males

Ovaries in females

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2
Q

What are the main functions of the gonads?

A

Gametogenesis

Steroidogenesis of Androgens (more in males) and Oestrogens/Progesterones (more in females)

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3
Q

What are the names for immature sperm and egg cells?

A

Spermatogonia

Oogonia

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4
Q

When does production of Oogonia ‘stop?’

A

After 24 weeks

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5
Q

When does spermatogenesis begin?

A

Puberty - due to testosterone and gonadotrophin releasing hormone

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6
Q

How long does spermatogenesis take?

A

~70 days in total

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7
Q

Describe the steps of Spermatozoa production:

A

Germ Cells 44+XY

Differentiate to spermatogonia 44+XY

Mitotic division to primary spermatocytes 44+XY (50:50 to produce spermatogonia as well)

First meiotic division to produce secondary spermatocytes 22X/Y

Second meiotic division to produce spermatids 22X/Y

Spermatids become spermatozoa 22X/Y

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8
Q

Describe the spermatogonia pool:

A

Undergo differentiation and self-renewal, so pool remains throughout life; males retain some capability for whole life - producing 300-600 sperm/gm testis/second (1000 sperm for every heartbeat)

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9
Q

Describe Oogenesis:

A

Germ Cells 44XX

Differentiate to oogonia 44XX

Mitotic division to primary oocytes 44XX - early in embryogenesis, also develop a layer of cells around self to form a primordial follicle

Primordial follicles undergo arrest of meiosis until puberty

First meiotic division to produce secondary oocytes 22X and first polar body (just membrane and chromosomes - with no cytoplasm or resources)

Second meiotic division occurs to produce ovum 22X (retains all cell resources) with second polar body (that has no cell resources)

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10
Q

What is the initial number of primordial follicles and how many remain by puberty?

A

6 million to 0.5 million

Due to atresia

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11
Q

Describe the anatomy the testes:

A

Coiled seminiferous tubules connect to the rete testis.

Semen leaves the testis through the Vasa efferentia through the epididymis into the vas deferens

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12
Q

What happens to the testis during puberty?

A

Testosterone causes maturation of coiled seminiferous tubules to allow spermatogenesis

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13
Q

How does the Vas Deferens expel fluid?

A

Surrounded with smooth muscle

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14
Q

What are the cells in the testes that produce Testosterone and androgens?

A

Leydig cells

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15
Q

What are the cells present in the Seminiferous tubules, and how are they arranged?

A

Sertoli cells

Elongates, connected at periphery by tight junctions forming the blood-testes barrier.

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16
Q

What does the blood-testis barrier do?

A

Stops blood molecules entering the tubules

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17
Q

Where are spermatogonia present in seminiferous tubules?

A

Around the outside

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18
Q

How do spermatogonia undergo maturation?

A

Cross membrane of sertoli cells, in which they mature and develop before release into the lumen of the tubule

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19
Q

What receptors do Sertoli cells contain and why?

A

FSH/Androgen receptors which act as the primary control of spermatogenesis

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20
Q

What happens when FSH binds to sertoli cells?

A

Inhibin and androgen binding protein produced which are associated with developing spermatocytes and forming their protective enviroment

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21
Q

What is contained in the ovaries?

A

Graafian follicles
Follicles undergoing atresia
Corpus luteum

22
Q

What is a Graafian follicle?

A

Ovum in follicular fluid surrounded by Granulosa and Thecal cells

23
Q

What is the corpus luteum?

A

After an egg is released, the follicle converts to an empty corpus luteum

24
Q

When does the menstrual cycle start?

A

On the first day of bleeding.

25
Q

What are the two parts of the menstrual cycle?

A

Ovarian cycle - Follicular phase followed by luteal phase
Endometrial cycle - Lining of uterus with superficial and deep stromal layer; proliferative phase followed by secretory phase

26
Q

What is the Proliferative phase of the Endometrial cycle?

A

Mitosis of cells lining uterus, causing wall thickening inducing oestrogen and progesterone receptors

27
Q

What is the secretory phase of the menstrual cycle?

A

Progesterone and oestradiol produced in the luteal phase causes the endometrium to stop proliferating by reducing oestrogen receptors whilst increasing secretory activity to make it suitable for implantation

28
Q

What are the four main hormones active in the menstrual cycle?

A

FSH
LH
Oestradiol
Progesterone

29
Q

Describe the levels of FSH during the cycle:

A

Increased at beginning to stimulate follicles to start growing and developing oestradiol.
Peaks around 13 days
Looks like ‘W’

30
Q

Describe levels of oestradiol during the cycle:

A

Negative feedback decreases of FSH levels
Low at beginning
Peaks at 12 days, peaks again (less) around 20 days
(Looks like ‘M’)

31
Q

Describe the levels of LH during the cycle:

A

Surge of gonadotrophins on day 14 triggers ovulation of dominant follicle

32
Q

Describe the levels of Progesterone during the cycle:

A

Corpus luteum secretes progesterone (and a little oestrogen) to have a negative feedback effect, keeping LH/FSH low; decline if no fertilisation, so negative feedback lessons so LH/FSH rise to cause follicle maturation

33
Q

Describe the four stages of the ovarian cycle:

A

Follicles spontaneously selected in groups for development to the pre-antral stage with no gonadotrophin stimulation

FSH causes development to early antral follicles, growing and developing to late antral follicles, and producing oestrogen

Dominant follicle selected, and others die in atresia, while dominant grows to Graafian follicles for ovulation

After ovulation, forms corpus luteum; granulosum cells grow, enlarge and produce a lot of progesterone for release to the blood for 13-14 days

34
Q

Which days of the cycle are the proliferative phase and secretory phase?

A

Proliferative: 1-14
Secretory: 15-28

35
Q

Where does reduction of testosterone occur?

A 
Reduction to Dihydrotestosterone:
Prostate
Testes
Seminal vesicles
Skin
Brain 
Adenohypophysis
36
Q

Where does aromatisation of testosterone occur?

A 
Aromatisation to oestrogens:
Adrenals
Testes
Liver
Skin 
Brain
37
Q

What are the principle uses of androgens?

A

Development of genitalia and promotion of foetal growth

Spermatogenesis and growth of secondary sex characteristics in adults

38
Q

What are the main effects of Oestrogens?

A

Stimulate endometrial mitosis and LH surge in menstrual cycle

Decreases renal salt reabsorption by competitively inhibiting aldosterone

Negative feedback on gonadotrophin releasing hormone

39
Q

What are the main effects of progestogens?

A

Stimulates secretory activity in endometrium/cervix ready for implantation of eggs
(Negatively regulates Gonadotrophin releasing hormone)

40
Q

Describe the Hypothalamo-Pituitary-Testicular Axis:

A

GnRH released in pulses every hour from hypothalamus

Causes pulses of LH/FSH release from APG

LH = endocrine, FSH = gametes

LH stimulates Leydig cells to make testosterone

FSH stimulates Sertoli cells to support spermatogenesis

Testosterone negatively feedbacks hypothalamus/APG

Inhibin produced by Sertoli cells also has negative feedback on hypothalamus/APG

41
Q

Describe the Hypothalamo-Pituitary-Ovarian Axis:

A

GnRH released in pulses every hour from hypothalamus

Causes pulses of LH/FSH release from APG

LH/FSH release oestradiol (feedback on LH/FSH)

Inhibin release also has negative feedback on hypothalamus

42
Q

Name the 5 phases of the Menstrual cycle:

A 
Early Follicular 
Early-mid follicular
Mid follicular
Late follicular
Luteal Phase
43
Q

What happens in the early follicular phase?

A

Day 1 - Day 5;
5-10 eggs start to enlarge and grow, competing with each other to grow, so only one (Graafian) follicle will become dominant; FSH produced by APG causes follicles to grow and produce oestradiol

44
Q

What happens in the early-mid follicular stage?

A

Follicles growing release oestradiol (begins to negatively feedback on LH/FSH to decrease levels; autocrine feedback loop arises, where more oestrogen production stimulates increased granulosa cell growth, in turn leading to more oestrogen

45
Q

What happens in the Mid follicular stage?

A

Oestrogen and inhibin reduces FSH to LH to very low levels, so all follicles regress except the Graafian follicle

46
Q

What happens in the Late follicular stage?

A

Oestrogen reaches high level and when bypasses threshold, causes a positive feedback loop on GnRH/LH secretion to cause an LH surge and ovulation

47
Q

What happens in the Luteal phase?

A

Corpus luteum produces progesterone (men should NOT produce) to prepare the endometrium for implantation

48
Q

What happens if the egg is not fertilised by the end of the Luteal phase?

A

If no fertilisation then progesterone, oestrogen and inhibin have a direct negative feedback on the APG to reduce LH/FSH production, and indirectly on GnRH

49
Q

What is Amenorrhoea?

A

Absence of menstrual cycle

50
Q

What is the difference between primary and secondary amenorrhoea?

A

Primary: periods never start
Secondary: periods stop after having some

51
Q

What is Oligomenorrhoea?

A

Infrequent periods; less than every six weeks

52
Q

What is Infertility defined as?

A

Couple unable to get pregnant following 12 months of regular unprotected sex; can be caused by pituitary failure, prolactinoma (prolactin inhibits LH/FSH), testicular failure (e.g. Klinefelter), ovarian failure (e.g. Turner’s), polycystic ovarian syndrome (most common - 1in8)

*LCRS Endocrinology Y1* (11 decks)

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