Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Endocrinology > The Gonads 1 > Flashcards

The Gonads 1 Flashcards

1
Q

What do the gonads develop as in males

A

The testes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What do the gonads develop as in females

A

The ovaries

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Describe the 2 functions of the gonads

A
  1. PRODUCTION OF GAMETES FOR REPRODUCTION (GAMETOGENESIS)

2. PRODUCTION OF STEROID HORMONES (STEROIDOGENESIS)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Describe how the two different functions of the gonads differ in males and females

A

IN MALES: SPERMATOGENESIS
(production of mature spermatozoa)IN FEMALES: OOGENESIS
(production of ripe ova)
IN MALES: ANDROGENS (oestrogens, progestogens)
IN FEMALES: OESTROGENS, PROGESTOGENS (androgens)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Describe the embryonic development of the gonads

A

Develop from the same undifferentiated structure (consisting of primordial germ cells, supporting cells and steroidogenic cells). Develop after 6 weeks. Before this stage both male and female reproductive tracts are found in the foetus, called Wolffian and Mullerian tracts respectively.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is critical for the differentiation of this cell into the testes

A

The presence and expression of the SRY gene on chromosome Y. This is known as the sex determining region.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe the actions of the SRY gene

A

Primordial germ cells become spermatocytes
Supporting cells become Sertoli cells
Steroidogenic cells become Leydig cells- synthesise androgens, including testosterone, which stimulates the further development of the Wolffian ducts into the male reproductive system. Sry protein is also produced and this acts as a transcription factor inducing the synthesis of the protein called Mullerian Inhibitory Hormone, blocking any further development of the primitive Mullerian ducts, which disintegrate, to be absorbed into the surrounding tissue.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What happens once the indifferent gonads have developed into the testes

A

The SRY gene is no longer expressed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Explain some problems that can arise in sexual development

A

Occasionally, both ovarian and testicular tissue are found to be present in certain individuals. These true hermaphrodites generally arise because they have a mix of both XY and XX cells. It is also possible to have both sets of XX sex chromosomes but develop testes and subsequently male characteristics. In this case, it is generally because some of the Y chromosome containing the SRY gene has been translocated to the X chromosome during meiosis in the father. Likewise, it is possible that the SRY gene on the Y chromosome is deleted or mutated, so that it is not expressed in males, the indifferent gonads will thus become ovaries.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe the activation of the germ cells in embryogenesis

A

During embryogenesis, the germ cells proliferate reaching numbers around 6-7 million (oogonia and spermatogonia).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe the production of spermatogonia in males

A

In males, the spermatogonia remain high throughout life but they have a dormant period until puberty, that’s to say they become quiescent during childhood.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Describe the production of oogonia in females

A

In females, the oogonia reach maximal number at 24 weeks and then atresia begins to occur. o Atresia – Cells degenerate and die off. o This process is rapid at first – by birth there are only 2 million oogonia left (from 6-7 million). o By puberty – 400,000 left. o By menopause – Ovaries are depleted.
▪ Females have a finite number of oogonia.
Only 300-400 mature to reach ovulation, only a few of these will be fertilised.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What do spermatogonia and oogonia develop into

A

Spermatogonia- sperm

Oogonia- ovum

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe spermatogenesis in males

A

In males, the germ cells remain quiescent until puberty when they are activated, at this stage they are called A1 spermatogonia. These cells then undergo a series of mitotic divisions, each time producing clones of identical cells. The final one of these mitotic divisions produced B spermatogonia, and these become primary spermatocytes, which are still diploid. The primary spermatocytes then undergo meiosis to produce haploid secondary spermatocytes, containing either 22X or 22Y chromosomes. Under the influence of Sertoli cell secretions these secondary spermatocytes divide by mitosis to produce spermatids, the spermatids then continue to develop into spermatozoa which finally enter the seminiferous fluid, which is continuously being secreted by the Sertoli cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What causes the spermatogonia to become activated

A

Puberty – FSH begins to be released → spermatogonia divide by mitosis to produce EITHER more spermatogonia or primary spermatocytes (DIPLOID). Spermatogenesis begins at puberty.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How long does spermatogenesis take

A

Around 70 days- differs in different species.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Do all germ cells enter the cyclic development phase

A

No, some germ cells return to the quiescent state until they are stimulated.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why do males retain the capacity for spermatogenesis throughout life

A

Spermatogonia undergo differentiation and self-renewal; consequently, a pool of spermatogonia remains available for subsequent spermatogenic cycles throughout life.
Thus males normally retain some spermatogenic capability throughout life, producing 300-600 sperm/gm testis/second

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Describe oogenesis in females

A

As soon as the oogonia get to the first meiotic division (prophase), development is HALTED (primary oocytes). ▪ The primary oocytes form a layer of cells around them to create the primordial follicles (happens pre-birth). ▪ Oocytes lie dormant for 12-50 years (arrested). ▪ Puberty – Some oocytes rescued by FSH release and some cells begin atresia (degeneration). ▪ At ovulation, oocytes complete first meiotic division to create a secondary oocyte and a polar body (oocyte with no cytoplasm – there is an uneven split of the cytoplasm, dies quickly). ▪ Secondary oocyte enters 2nd division which completes upon fertilisation → Ovum and second polar body.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the 2 events that can take place once the cell is arrested

A

The number of oocytes diminishes steadily as they become absorbed into the surrounding stromal tissue by a process called atresia. Secondly, form puberty ova (within their follicles) enter cyclic developmental processes called ovarian cycles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is meant by a polar body

A

Essentially a bag containing the other chromosomes, it eventually dies.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Describe the production of gametes in females

A

Initial total number of oogonia in primordial follicles (in fetus) is approximately 6 million; early entry into meiosis halted in prophase.
Primordial follicles, arrested in their development, enter process of atresia.
By the time of birth the total number of oogonia remaining for potential development has dwindled to approximately 2 million, and by puberty less than 0.5 million remain.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the final maturation of the ovum during each menstrual cycle associated with

A

The restart of the meiotic process that was arrested at prophase, resulting in the formation of two cells. While both cells are haploid, containing 22X chromosomes, one of these called the secondary oocyte, contains most of the cytoplasm. The other is a polar body. The secondary oocyte then enters the second meiotic division which again becomes arrested, at this time the metaphase stage. The secondary oocyte is then released at ovulation. Final completion of the second meiotic division, with the formation of a second polar body which is also discarded, only takes place, if and when, the ovum is fertilised.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does testosterone cause

A

The development of secondary sexual characteristics

Maturation of the testes and seminiferous tubules, which allows spermatogenesis to take place.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Describe the basic structure of the testes

A

▪ Spermatogenesis takes place in seminiferous tubules.
▪ Spermatozoa travel down to collection in Rete Testis and are then drained by Vasa efferentia into the epididymis to be stored. ▪ In epididymis, nutrients secreted to mature spermatozoa and maintain their motility. ▪ Propelled via the vas deferens (smooth muscle) through the urethra.
NOTE: the vas deferens from each of the testes finally joins the urethra.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Where do the testes descend from

A

Testes develop in abdomen and descend into scrotum. o Scrotum is 2-3 degrees cooler for genesis-optimal for spermatogenesis. o Not descending → infertility (although androgen production is unaffected).

27
Q

Describe the structure of the seminiferous tubule

A

The basic unit of the testes is the seminiferous tubule. The seminiferous tubule is surrounded by a peritubular layer comprising of a basement membrane lining a layer of myoid cells, fibrocytes and spermatogonia. Below this we have elongated Sertoli cells which are connected at the periphery by tight junctions. This provides a major barrier to the steady diffusion of water-soluble molecules from basal to luminal fluids.

28
Q

What is the importance of the blood testis barrier

A

Prevents the movement of spermatozoa into the blood, where they could induce an immune response, and also to prevent the non-selective passage of molecules into the seminiferous tubules. Thus the later stages of spermatogenesis take place in the specialised environment of the luminal or seminiferous fluid, regulated by the selective transport and secretory properties of the seminiferous fluid.

29
Q

How do the spermatogonia pass through the blood-testis barrier

A

They have their own mechanisms (push through the zonal junctions linking each Sertoli cell) In the Sertoli cell they develop into the primary and secondary spermatocytes. Spermatogenesis takes place in the Sertoli cells.

30
Q

Describe the Sertoli cells

A

Sertoli cells provide structural and metabolic support for spermatogenesis of the spermatogonia.
form the seminiferous tubules- primary control of spermatogenesis.
synthesise FSH and androgen receptors
in response to FSH produce various molecules including INHIBIN, androgen binding protein.
are intimately associated with developing spermatocytes, etc..
They also contain the enzyme necessary to convert testosterone into either the more potent androgen dihydrotestosterone or to the oestrogen 17 beta-oestradiol.

31
Q

Describe the Leydig cells

A

The endocrine Leydig cells are located within the interstitial fluid compartment in between the seminiferous tubules.
Leydig cells secrete testosterone needed for spermatogenesis (so needs to be close).
lie outside seminiferous tubules
synthesise LH receptors
In response to LH are the principal source of testicular androgens (mainly testosterone)

32
Q

Why is the close connection between Leydig cells and Sertoli cells important

A

Intra-testicular levels of testosterone higher than circulating levels, spermatogenesis cannot take place without the high levels of testosterone.

33
Q

Describe the basic structure of the ovaries

A

Each ovary consists of an outer cortex and an inner medullary stroma comprised mainly of connective tissue. Aligned along the outer cortical edge of he ovary is a layer of primordial germ cells, frozen at the prophase divisional stage.
In the stroma:
▪ Some follicles will be undergoing atresia. ▪ This follicle is a Graffian Follicle – The follicle that doesn’t undergo atresia and is fully matured and ready for ovulation- has a large fluid filled space. ▪ All follicles are embedded in the ovarian stroma. ▪ Once ovulation has occurred, the Graffian follicle becomes a corpus luteum.

34
Q

Describe a follicle

A

Oocyte and one or more layers of cells.
Granulosa cells
Thecal cells.

35
Q

What steroid hormones are produced in the adrenals

A

MINERALOCORTICOIDS
GLUCOCORTICOIDS
(ANDROGENS

36
Q

What steroid hormones are produced in the gonads

A

PROGESTOGENS (C21)
ANDROGENS (C19)
OESTROGENS (C18)

37
Q

Why can’t the gonads produce cortisol or aldosterone

A

No 21 hydroxylase enzyme to convert progesterone to deoxycorticosterone and 11-deoxycortisol.

38
Q

What enzyme to the testes contain to produce testosterone

A

Testes contain 17-hydroxysteroid dehydrogenase enzyme which converts androstenedione → testosterone.

39
Q

Which enzyme do the ovaries contain to produce oestrogen

A

Ovaries aromatase androstenedione and testosterone → oestrone → 17b-oestradiol. ▪

40
Q

How can dihydrotestosterone be produced

A

Testosterone can be 5-alpha reduced, normally takes place in epididymis, prostate or peripheral tissue

41
Q

What activates the enzymes to produce oestrogen

A

FSH.

42
Q

Describe the menstrual cycle

A

Usually taken as lasting approximately 28 days (but can last from 20 to 35+ days)
Historically taken to begin on the first day of menstruation (loss of blood and cellular debris from necrotic uterine epithelium)
The important reproductive event during the cycle is OVULATION (release of the ripe ovum) which occurs around day 14

43
Q

What is meant by the menstrual cycle

A

The cyclic production of follicles, with their ripening oocytes, which occurs regularly throughout a woman’s reproductive life from puberty to the menopause.

44
Q

What are the two interrelated cycles of the menstrual cycle

A

The ovarian and endometrial cycle. The two cycles are related by the production and activity of specific hormones.

45
Q

Describe the endometrium

A

Endometrium – lining of the uterus that contains a superficial epithelial layer and a deep stromal layer.

46
Q

What are the three phases of the ovarian cycle

A

Follicular phase — ovulation — luteal phase

47
Q

What are the two phases of the endometrial cycle

A

Proliferative phase and secretory phase

48
Q

What is the dominant hormone produced in the follicular phase

A

Oestrogens cause the effects of proliferative phase. o Oestrogens stimulate mitosis and an increase in progesterone and oestrogen receptors. ▪ Endometrium gets thicker, glands get bigger and blood vessels lengthen.

49
Q

Which hormones are produced in the luteal phase, which is dominant

A 
PROGESTERONE
 and 
17b-OESTRADIOL
Progesterone is dominant 
▪ In the luteal phase, oestrogen and progesterone are produced which induce a secretory phase. ▪ Progesterone reverses the effects of oestrogen:  o Reduced proliferation by reducing oestrogen receptors. o Increases secretory activity of cells of myometrium – Glands become wider and produce substances which make the environment suitable for implantation to occur.
50
Q

Describe the hormone level changes that take place in the menstrual cycle

A
  1. FSH levels are slightly raised at beginning → rescue dormant follicles to continue development. 2. Follicles grow and produce 17b-oestradiol → has a negative feedback effect on LH and FSH secretion. 3. Dominant follicle selected and others atresia. 4. Dominant follicle secretes lots of oestrogen quickly (in about 36 hours) → stimulates a positive feedback effect which creates lots of LH and FSH. 5. Surge of FSH and LH stimulates ovulation. 6. Remaining corpus luteum produces 17b-oestradiol and large amounts of progesterone → negative feedback on LH and FSH. 7. If fertilisation doesn’t occur, oestrogen and progesterone levels fall (don’t support endometrium). 8. Endometrium becomes necrotic and falls away. 9. Decrease in progesterone and oestrogen → negative feedback reduced → FSH rises again to start of cycle.
51
Q

What is an additional effect of progesterone

A

One effect of progesterone is an effect on body temperature. There is a measurable increase in body temperature after ovulation.

52
Q

Describe the development of follicles up to the pre-antral stage

A

Gonadotrophin independent, the follicles are spontaneously selected.

53
Q

Describe the ovarian cycle

A

Some of the pre-antral follicles grow in size and develop into antral follicles in the presence of FSH and LH. If not, they undergo atresia.
Ovum surrounded by granulosa cells and thecal cells, produce oestrogen, other follicles die off
Graffian follicle remains- ready for ovulation
After ovulation- corpus luteum- granulosa cells proliferate, enlarge, invaded by blood vessels, produce lots of progesterone, continue to produce oestrogen (for next 13-14 days).

54
Q

How does the LH surge cause ovulation

A

LH surge occurs and causes rupture of follicle to release the ovum (and ovum does 2nd meiosis).

55
Q

Describe hormone production during the ovarian cycle

A

In follicle there are: o Thecal Cells – outer – LH receptors. o Granulosa Cells – inner – FSH receptors. ▪ Thecal cells create androgens from LH stimulation but cannot convert androgens to oestrogens. ▪ Granulosa cells convert androgens to oestradiol with aromatase enzyme under FSH influence. ▪
Androgens diffuse into the granulosa cells to be converted into oestrogen.
Corpus luteum- FSH and LH continues to act- androgen production continues.

56
Q

When does the proliferative phase occur

A

Between day 6 and day 14- oestrogen is the dominant influence

57
Q

When does ovulation occur

A

Day 14

58
Q

When does the secretory phase occur

A

Between day 15 and day 25

59
Q

When does menstruation occur

A

Day 1 to day 5

60
Q

Describe the differences in the endometrium between early phase and late phase of the proliferative phase

A

Early- thin

Late- thickens (mitosis).

61
Q

Describe the differences in the glands between early phase and late phase of the proliferative phase

A

Early- straight

Late- enlarge, coil, increase blood supply.

62
Q

What happens to the endometrium in the secretory phase

A

Becomes secretory

63
Q

What happens to the glands in the secretory phase

A

Secrete (glycogen, mucopolysaccharides), mucosa engorged with blood.

64
Q

What happens if fertilisation has not taken place

A

Blood vessels constrict, ischaemia of the tissue, becomes necrotic, endometrium releases prostaglandins, contraction of endometrium, shedding (with blood) necrotic ischaemic tissue. Caused by decrease in progesterone

Endocrinology (11 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions