Ovarian function, pregnancy, and contraception

Progesterone is needed to support a pregnancy, what anti-progestrone is given to terminate a pregnancy

Mifepristone

How does progesterone turn into oestrogen

Progesterone is converted into oestrogen through a series of enzymatic reactions involving aromatase, which transforms androgens into estrogens, primarily in the ovaries.

What is the metabolic screwdriver of pregnancy (prioritises nutrients to developing foetus)

Human Placental Lactogen (hPL)

Human Placental Lactogen (hPL) function and place of production

Human Placental Lactogen (hPL) is produced by the placenta and functions to prioritize nutrients for the developing fetus by altering maternal metabolism and promoting glucose availability.

Prolactin function

Prolactin is a hormone produced by the pituitary gland that stimulates milk production in breastfeeding mothers and plays a role in regulating the menstrual cycle.

How is prolactin produced

Prolactin is produced by lactotroph cells in the anterior pituitary gland in response to oestrogen,

When does the oestrogen:progesterone ratio increase?

At term, to increase oxytocin receptor levels to cause myometrial contractions

Where is oxytocin synthesised and secreted

Oxytocin is synthesised in the hypothalamus and secreted from the posterior pituitary gland and decidual tissue

Why doesn’t prolactin produce until baby delivery?

Oestrogen and progesterone inhibit milk secretion until parturition by making cells unresponsive to prolactin

Name 5 types of contraception

Hormonal

Barrier

IUDs

Permanent

Natural

what is the Pearl index?

Number of failures/100 women years of exposure

e.g 100 women using a contraceptive for 1 year or 10 women using it for 10 years

How does the morning after pill work, what is its active ingredient

The morning after pill works primarily by preventing ovulation or fertilization. Its active ingredient is usually levonorgestrel or ulipristal acetate.

How do hormonal methods of contraception work

Mimicking hormonal levels during pregnancy (e.g. progesterone)

Constant exposure to progesterone suppresses ovulation

Progesterone also causes thickening of cervical mucus and decreases endometrial receptivity

Oestrogenfurther suppresses ovulation and stabilizes the endometrium.

What primordial cells give rise to gametes in early embryonic development

Primordial germ cells (PGCs)

How is the motion of primordial germ cells controlled?

Guided by chemotaxis

What do sex cord cells do in week 7 of embryonic development

Form granulosa, which cluster around primordial germ cells (PGCs). Which then forms oogonia, which then forms primordial follicles

Steps of oocyte formation (include cell type and what type of division)

1. Primordial germ cells - mitosis

2. Oogonium - mitosis

3. Primary oocyte - 1st meiotic division

4. Secondary oocyte - 2nd meiotic division

5. Mature oocyte - becomes haploid (due to meiosis)2

What gene regulates the start of meiosis

Stra8 - Stimulated by retinoic acid

Women - retinoic acid builds up in foetal period, stimulating production of all oocytes they’ll ever have

Men - can metabolise retinoic acid via cytochrome p450, and only allows levels to build at puberty

When do primary oocytes become secondary oocytes

Primary oocytes complete meiosis I to go from prophase I to secondary oocytes at metaphase II just before the oocyte is ovulated

When do secondary oocytes become mature oocytes

When a sperm penetrates the secondary oocyte, it finishes meiosis II, and become fully mature

What are polar bodies

Discarded genetic material that is a by-product of meiotic division. Divides this way so the mature oocyte can have the lion’s share of cytoplasm

Overview of ovary

Describe the structure of a primordial follicle

Primary oocyte surrounded by a single layer of flattened granulosa

Describe the structure of a primary follicle

Granulosa go from flat to cuboidal

theca and zona pellucida become visible

Functions of the zona pellucida

• Provides a sperm binding site

• Induces acrosome reaction (reaction where acrosome vesicle on sperm head breaks through outer layer of ovum)

• Prevents polyspermy

• Protects early embryo

Describe structure of the secondary follicle

Granulosa proliferate, and become a stratified cuboidal layer

Theca now has two distinct layer - external, internal

Now requires gonadotrophin to develop to tertiary follicle

Describe structure of the tertiary follicle

Granulosa secrete follicular fluid

Oocyte surrounded by a layer of corona radiata

What Neuropeptide triggers the start of puberty

kisspeptin-1 (KISS-1) Matches GnRH pulses

Why does GnRH have do be released in pulses?

Continuous GnRH secretion leads to downregulation of GnRH receptors on surface of gonadotroph cells, and FSH and LH are no longer stimulated to release

FSH function and location of action

Acts on ovary to stimulate follicular development

Function and location of action of LH

Acts of ovary to stimulate follicle maturation, ovulation and development of corpus luteum [[luteum - luteinising hormone]]

3 Families of sex steroids and their main functions

Progestogens - Pregnancy

Androgens - Maleness

Oestrogens - Femaleness

Functions of oestrogens

• Growth of body and sex organs at puberty

• Development of secondary sexual characteristic

• Follicular maturation

• Preparation of endometrium for pregnancy

  • Thinning of cervical mucus (just before ovulation)F

Functions of progesterone

• Completes the preparation of and maintains endometrium for pregnancy

Produced by corpus luteum post-ovulation

The whole menstrual cycle in a diagram

What happens in the follicular/proliferative phase (day 1-10)

• Shedding occurs in days 1-5

• Hypothalamus secretes GnRH

  • Medium pulses, so most FSH and a little bit of LH released

• Up to 15 follicles are ‘rescued’ - their granulosa and theca cells develop

• In days 5-10, the endometrium tries to rebuild after menstrual shedding

  • Theca cells produce testosterone, which is converted by granulosa to oestrogen

    • Oestrogen thickens endometrium and thins cervical mucus

  • Oestrogen also suppresses FSH production via -ve feedback on HPG axis

• Only one of the 15 follicles are selected to develop further

Days 10-14 of menstrual cycle

Granulose in dominant follicle express LHCG receptors

High levels of oestrogen at mid cycle cause LH surge from ant.pit

Day 14 of menstrual cycle (ovulation)

• Primary follicle completes meiosis I, and secondary oocyte enter meiosis II and stops at metaphase II.

• Increase in follicular fluid and number of granulosa

• Cumulus oophorus (stalk thing) loosens

• Follicle wall weakens due to proteases

• Follicle wall is broken through due to pressure buildup, releasing cumulus-oocyte complex

Luteal (secretory) phase - Days 14 - 21

• Corpus luteum forms, producing progesterone

• Granulosa turn into large lutein cells, which produce progesterone and oestrogen

• Many theca cells disperse to stromal tissue

  • Some stay as lutein cells, which produce progesterone and androgens (which then converts to oestrogen)

• High levels of progesterone and oestrogen provide negative feedback on FSH and LH production, so levels are low

What hormone is produced when pregnancy occurs

hCG - chorionic gonadotrophin

Function of hCG (chorionic gonadotrophin)

Binds to LHCGR on lutein cells, which maintains the corpus luteum, thus upkeeping progesterone production and suppressing ovulation