Ovarian function

Question 1

Think about ova.

What is special about the female reproductive system?

Answer 1

• The woman is born with the full quota of ova/follicles that she will ever have
• Around 7 million oocytes at 20 weeks
• 1.2 million at birth
• 4000,000 at puberty
• 400-500 will ovulate
• pool of follicles is never replenished

Question 2

think about eggs

What is the case of attrition? Why is this?

Answer 2

• A woman is born with more eggs than she’ll ever need
• This is due to the survival of our species so that we can reproduce
• This is why we have a mestrual cycle

Question 3

What controls part of folliculogenesis (what controls what happens in the ovary and testes)?

Answer 3

• The hypothalamic -pituitary axis
• Feedback loop
• Hypothalamus increases GnRH to median eminence
• Leads to the release of LH and FSH from the pituitary gland
  -Released to target organs (ovaries/testses)
• Leads to release of Estradiol and Progesterone

Question 4

Where is GnrH produced?

Answer 4

• In gonadotrophs

Question 5

What is the anatomy of the ovary?

Answer 5

• 2 oval shaped glands located on the sides of the uterus
• Atttached to the pelvic sidewall by suspensory ligaments
• Responds to cyclic gonadotropin secretion

Question 6

What are the two main functions of the ovary?

Answer 6

• The generation of a mature fertilisable ovum for the preservation of the species
• Production of female sex hormones ( Oestrogen and Progesterone).

Question 7

Where does folliculogenesis take place in the ovary?

Answer 7

• The cortex of the ovary (edges near yellow)
• There are primordial follicles (no function until puberty)
• These are then converted into primary follicles if selected
• Then become secondary follicles
• Become fluid filled antrums
• The ovum is surrounded by other layers (theca )
• At ovulation, the Graafian follicle (bulge as it is about to be ovulated) expels the ovum into the fallopian tube
• What’s left is the corpus luteum (secretes a yellow compund known as lutean)
• Happens constantly

Question 8

produces something

What is the function of the corpus luteum?

Answer 8

• Produces hormones such as oestrogen and progesterone etc

Question 9

it becomes something else

What happens to the corpus luteum if there is no fertilisation?

Answer 9

• It degenerates and becomes absorbed into the wall of the ovary/body (Scar tissue)
• Becomes the corpus albicans (white body)

Question 10

PGCS are first observed in the yolk sac during 4-6 weeks of pregnancy.

What can primordial germ cells give rise to ?

Answer 10

• Teratomas = germ cell tumours
• generate from either ovum or sperm
• can become cancerous
• PGCS are germ cells and have the capacity to become any cell type (pluripotent)
• formed by 3 germ cell layers = endoderm , ectoderm and mesoderm)
• develop in either in the ovary,testes , but also nervous system, abdomen

Question 11

What is folliculogenesis?

Answer 11

• the maturation/ development of ovarian follicules
• progression of a small no. of primordial follicules into a large graafian follicule
• starts after puberty and with the first menstruation due to an increase in hormone levels
• quite small cells
• only have one layer of cells = grnaulosa cells
• ## Gonadotrophin independent.

Question 12

What are follicles?

Answer 12

• The functional unit of the ovary

Question 13

Think about getting the best eggs

What are the stages of folliculogensesis?

Answer 13

• Recruitment ; the follicle departs from the resting pool to begin a well-characterised pattern of growth and developement during early follicular phase
  
  • involves several follicles in one ovarian cycle (EVERY MONTH)
  • Selection : the sorting of the maturing follicular cohort by atresia (smaller follicles are thought to be less healthy because of less FSH and LH so are killed off). Depends on the follicle size with smaller cells <10mm destined to undergo apoptosis.’
  • Dominance - status of the follicle destined to ovulate fiven its presumed key role regulating the size of the ovulatory quota ( inhibits the growth of other follicules).

Question 14

Describe the ovarian cycle?

Answer 14

• Primordial follicles start to grow everyday, a cohort will start to grow 3-4 = primary follicles
• Primary follicles : 70 days - small antral ( secondary/tertiary follicles- water filled antrum) follicles (2-5 mm)
• Smalla antral follicles :
  
  • FSH window recruited into ovulatory cycle
  • No FSH window = atresia

Question 15

What kind of receptors do follicles have? what do these indicate?

Answer 15

• FSH and LH receptors
• The ones with the most FSH receptors are thought to be the best follicles / healthiest
• Response and amount of receptors indicates a healthy follicle
• primary follicles are FSH independent
• When they become secondary follicles, the granulosa cells have FSH receptors on them and begin to respond to them.
• These then become FSH and LH dependent
• A number of follicles will die off due to lack of layers, response and receptors
• The Dominant preovulatory follicle is the one that is ovulated

Question 16

What are oogonia (+ characteristics)?

Answer 16

• egg cells that are kept within the follicle
• inactive until puberty
• the ovum inside secretes a glycoptotein extracellular matrix known as the zona pellucida = selective physical narrier
• The ovum is larger than somatic cells and spem

Question 17

What is the biosynthesis of sex steroids?

Answer 17

• The production of progesterone, oestrogen and androgens
• Aromatase converts androgens to oestrogens
• cholesterol is what leads to the production of sex steroids
• Cholesterol makes pregenolone = precursor of progesterone
• This involves the dehydrogenase and dehydroxylase groups
• Aromatase is important for oestrogen conversion

Question 18

What does aromatase convert androstenedione, testosterone and dihydrotestosterone (DHT) into?

Answer 18

Androstenedione - Oestrone
Testosterone - Oestradiol
Dihydrotestsosterone (DHT) - Oestriol

Question 19

Androgen TO Estradiol

What is the two cell oestrogen biosynthesis theory?

Answer 19

• Has two layer of cells : granulosa cells, then theca cells once it is developed
• Cholesterol (LDL) transported from the outer to inner mitochondrial protein by StAR
• In response to LH , cholesterol and progesterone are made and converted into androgens.
• LH stimulates androgen production by binding to LH receptors on theca cells during follicle development
• Androstenedione (androgens) is then transported into the granulosa cell from the theca cell by diffusion
• Theca cells produce proesterone and androgens but no oestrogens
• Granulosa cells convert androgens and progesterone to oestrogens by aromatase enzyme
• The androstenedione is acted upon by aromatase to make estradiol
• Aromatase is induced by FSH acting on FSH receptors on granulosa cells
• G protein couple receptors- FSH and LH both act through GPCR
• Through cAMP and protein kinase A, they upregulate the enzymes involved in steroidogenesis

Question 20

What is the ovarian reserve?

Answer 20

• The total number of primordial follicles in the ovary at any given time
• often exhausted at menopause
• If women are infertile , it is tested by the ovarian reserve
• OR rate of loss is accelerated at 37.5+ years due to age-related increase in FSH
• Anti-mullerian hormone used clinically to test OR
• Measures AMH levels in blood
• Produced by the antral follicles
• important in differentiating male or female embryos
• Used in IVF procedures to check egg production after stimulation with drugsm ovarian hyperstimulation (not itself a test of ferility)
• Used to test for ovarian tumours

Question 21

What are some ovarian disorders?

Answer 21

• Ovulatory dysfunction
• Anovulation, primary ovarian insufficiency (premature ovarian failure), PCOS
  
  • can also be caused by hypothyroidusn, piuitary tumoursm adrenal gland (Cushings)
• Ovarian cysts
• Ovarian cancer