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Human Development > Reproductive Endocrinology and The Menstrual cycle > Flashcards

Reproductive Endocrinology and The Menstrual cycle Flashcards

1
Q

what are the two main molecules involved in development

A
  • steroids

- glycoproteins

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2
Q

what are steroids

A
  • lipids characterised by a 27 carbon skeleton with four fused rings and with a variety of groups attached
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3
Q

how do steroids pass through the cell membrane

A
  • lipophilic - this means that they pass through cell membrane by simple diffusion and bind to their receptor which can be nuclear or cytoplasmic
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4
Q

name the steroids and there size

A
  • testosterone = 288Da
  • oestradiol = 272 Da
  • progesterone = 314 Da
  • cortisol = 362 Da
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5
Q

what is the core molecules of the steroids oestrogens progesterone and testosterone.

A

Cholesterol is the central core molecule

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6
Q

what are the three oestrogen molecules

A

oestradiol E2 - most common
oestriol E3 - only found in pregnancy
oestrone E1

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7
Q

what are the differences due to in steroids

A
  • due to functional groups attached to the four ring structures
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8
Q

describe o estradiol

A
  • oestrogen

- C18 steroids

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9
Q

describe progesterone

A
  • progestagens

- C21 steroids

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10
Q

describe testosterone

A
  • androgens

- C19 steroids

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11
Q

Where is testosterone produced in males and in females

A

Males
- Ledwig

Females
Thecal cells (ovary)(25%), adrenals (25%)
peripheral conversion in adipose tissue (50%)

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12
Q

where is dihydrotestosterone produced in males and in females

A

Males
- Conversion from testosterone in Sertoli cells (testes) and target tissues

Females
- peripheral conversion from testosterone

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13
Q

where is in progesterone in males and in females

A

Males
- Adrenals

Females

  • Corpus luteum (ovary), syncytiotrophoblasts (placenta)
  • (adrenals as an intermediate)
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14
Q

where is oestradiol produced in males and in females

A

Males
- Peripheral conversion from testosterone (depending on presence of aromatase) (eg adipose tissue)

Females

  • Granulosa cells (ovary), peripheral conversion from testosterone
  • syncytiotrophoblasts (placenta)
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15
Q

where is androstenedione produced in males and females

A

Males
Leydig cells, adrenals

Females 
Ovary (50%), adrenals (50%)
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16
Q

where is dehydropiandrosterone produced in males and females

A

Males
Leydig cells, adrenals

Females
Ovary (20%), adrenals (80%)
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17
Q

what does the first step in steroid synthesis

A

the conversion of cholesterol to pregnenolone

- requires oxidative enzymes located in the mitochondria and endoplasmic reticulum

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18
Q

How does steroid synthesis happen in males

A
  • GnRH stimulates follicle stimulating hormone and LH secretion by anterior pituitary
  • LH stimulates testosterone production by leydig cells
  • main target of testosterone and pituitary FSH are sertoli cells
  • in the Sertoli cells the enzyme 5alpha reductase converts testosterone to DHT
  • Sertoli cells then secrete androgen binding protein (ABP)
  • ABP binds to testosterone and carries it to the semiferouh tubule where it stimulates spermatogenesis
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19
Q

how does steroid synthesis happen in females

A
  • LH stimulates testosterone production by theca cells in the ovarian follicle
  • testosterone enters granucosa cells where it is converted by aromatase into oestrogen
  • oestradiol stimulates formation of LH receptors on granulosa cells
  • this will enable follicle to respond to LH surge thus giving rise to ovulation
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20
Q

what do granulsoa cells surround

A

it surrounds the oocyte

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21
Q

what do androgens do

A
  • Maintain male somatic tissue differentiation
  • Induce male secondary sexual characteristics
  • Support spermatogenesis
  • Influence sexual and aggressive behaviour (male & female)
  • Promote protein anabolism, somatic growth & ossification
  • Regulate gonadotrophin secretion (testosterone)
  • Induce body hair (in females – pubic & axillary)
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22
Q

what does oestrogen do

A

Stimulate growth of mammary gland & endometrium

Induce female secondary sexual characteristics

Prepare uterus for spermatozoa transport

Increase vascular permeability

Mildly anabolic

Regulate gonadotrophin secretion

23
Q

what are the potency of androgens

A

DHT 100%
Testosterone 50%
Androstenedione 8%
DHEA 4%

24
Q

what is the potency of oestrogen

A

17b oestradiol 100%
Oestriol 10%
Oestrone 1%

25
Q

What do progestogens do

A

Luteal progesterone prepares the endometrium for implantation during the secretory phase of the menstrual cycle.

Effects cervix, vagina and breast

Placental progesterone maintains the endometrium (decidua) in pregnancy (after approximately 10-12 weeks)

26
Q

what are glycoproteins

A

These are proteins that contain oligosaccharide chains covalently attached to their polypeptide side-chains

27
Q

name some glycoproteins and their sizes

A 
LH = 32 000 Da
FSH = 30 000 Da
hCG = 37 900 Da
28
Q

what is produced in the anterior pituitary

A

luteinising hormone (LH)
follicle stimulating hormone (FSH)
TSH (thyrotrophs)

29
Q

what is placenta (syncytiotrophoblast cells)

A

human chorionic gonadotrophin (hCG)

30
Q

what are gonadotrophin made out of

A
  • two of these glycosylated proteins come together and form the functional glycoprotein called the alpha and beta subunits
31
Q

describe the alpha subunit of gonadotrophin

A
  • the α subunit is identical in FSH, LH and hCG (and TSH) and is composed of 92 amino acids
32
Q

describe the beta subunit of gondatrophin

A
  • the beta subunit is different in FSH, LH, hCG(and TSH) and confers specific biological action
  • the β subunit of LH and hCG contain the same sequence of amino acids and both stimulate the same receptor
  • however, the hCG beta subunit contains an additional 24 amino acids
33
Q

what is the difference in the beta subunit of gondatrophin between LH and hCG

A

the β subunit of LH and hCG contain the same sequence of amino acids and both stimulate the same receptor but the hCG beta subunit contains an additional 24 amino acids

34
Q

what stimulates the secretion of LH and FSH

A

Gonadotrophin releasing hormone (GnRH)

35
Q

where is GnRH produced

A

hypothalamus

36
Q

what does FSH do

A
  • stimulates the growth of immature follicles (ovary) to maturity (female)
  • enhances the production of androgen-binding protein by the Sertoli cells of the testes and is needed for spermatogenesis.
37
Q

what does LH do

A

surge triggers ovulation and converts the residual follicle into a corpus luteum (female)

is necessary to maintain luteal function (female)

stimulates thecal cells in the ovary to produce testosterone for oestradiol production (female)

acts upon the Leydig cells of the testis and is responsible for the production of testosterone (male)

38
Q

what does hCG do

A

maintains corpus luteum in pregnancy

39
Q

what is inhibin produced by

A
  • it is a glycoprotein which is produced by males and females

in males
- Sertoli cells
in females
- granulose cells

40
Q

what does inhibin do

A

in males

  • When sperm count high inhibin secretion increases and inhibits pituitary release of FSH and hypothalamic release of GnRH.
  • When sperm count <20 million/ml inhibin secretion decreases.

in females
- helps exert negative control on FSH production during the menstrual cycle

41
Q

what is activin

A

a glycoprotein belonging to the transforming growth factor β family

42
Q

what does activin do

A

Increases FSH activity and enhances the actions of LH in both males and females

43
Q

what produces relaxin and what does it do

A

in males
- found in seminal fluid and enhances sperm motility

in females
- it is produced in the menstrual cycle and in pregnancy

44
Q

what are the peptides and where are they released

A

Gonadotrophin releasing hormone (GnRH) – 10 amino acid peptide (hypothalamus)

Growth hormone releasing hormone (GHRH) – 44 amino acid peptide (hypothalamus)

Oxytocin – 9 amino acid peptide (hypothalamus)

Prolactin – 198 amino acid polypeptide (anterior pituitary)

45
Q

what is the menstrual cycle

A
  • it is a series of cyclic changes in the uterine endometrium
46
Q

what are the three stages of the menstrual cycle and what are there day length

A

Menstrual phase
1-5 days

Proliferative phase 6-14 days

Secretory phase 15-28 days

47
Q

what happens within the menstrusal phase

A

Due to withdrawal of steroid support of oestrogen & progesterone the endometrium collapses

Endometrium is shed together with blood from ruptured arteries (spiral arteries contract to reduce bleeding).

Blood loss is usually between 50-150ml.

Detached endometrial tissue and blood pass through the vagina as the menstrual flow.

48
Q

what happens within the proliferative phase

A

Oestrogen from the mature follicle stimulates thickening of endometrium

Glands and spiral arteries form.

Oestrogen stimulates the synthesis of progesterone receptors on endometrial cells

49
Q

what happens within the secretory phase

A

Progesterone from corpus luteum act on the endometrium.

Progesterone stimulates enlargement of glands which begin secreting mucus and glycogen in preparation for implantation of the fertilised oocyte.

If fertilisation does not occur, the corpus luteum degenerates

Progesterone levels fall and the endometrium degenerates.

The cycle starts again with the first day of menstrual flow.

50
Q

what happens if fertilisation does not occur

A

Corpus luteum degenerates and forms the corpus albicans.

Progestrone levels fall.

Endometrium breaks down.

Menstruation occurs.

51
Q

what happens if fertilisation does occur

A
  • Blastocyst implants into maternal endometrium
  • Developing placenta secretes human chorionic gonadotrophin (hCG)
  • Corpus luteum does not degenerate because of hCG
  • Progesterone levels do not fall because progesterone secretion is maintained by the corpus luteum
  • Progesterone maintains the endometrium.
52
Q

the basic steroid molecule is made up of a …. carbon skeleton with 4 fused rings

A

27

53
Q

what is the most potent form of androgen

A

dihydrosterosterone DHT

Human Development (28 decks)

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