Reproductive (BS)

BODY SYSTEMS
REPRODUCTIVE

,Medic_Summaries (Body Systems)
Reproductive Strand



Menstrual cycle:
- Purpose:
- Generate oocyte
- Facilitate fertilisation
- Optimise endometrium for implantation
- Protect developing embryo
- Begins at MENARCHE
- Ends at MENOPAUSE




Endocrine control:




Gonadotrophin releasing hormone (GnRH):
- Decapeptide
- Secreted by mid basal hypothalamic neurones
- Hourly pulses
- Transported to pituitary via hypophyseal portal blood system
- Secretion affected by:
- Bereavement
- Anxiety
- Time zone
- Day/night duty
- Exercise
- Weight loss/gain
Anterior pituitary:
- Basophils secretes follicle stimulating hormone (FSH) and luteinising hormone (LH)
- FSH stimulates follicular activity, thus promoting estradiol (E2; oestrogen) production
- LH triggers release of egg from dominant follicle, promoting development of corpus luteum
and production of progesterone

Negative/positive feedback:
- GnRH, LH and FSH production inhibited by rising E2 levels
- Near midcycle, high levels of E2 lead to surge in LH release, which triggers ovulation




2 Adapted from Lectures at the University of Leeds Medical School

, Medic_Summaries (Body Systems)
Ovaries (primordial follicles):
- In foetus at 6 months (2,000,000)
- At birth (750,000)
- At puberty (400,000)
- Ca. 450 follicles develop and produce an egg (remainder degenerate)
- No new follicles produced
- Progression:
- Primordial follicle
- Primary/preantral follicle
- Secondary/antral follicle
- Preovulatory follicle
- Ovulation
Follicular development:
- Proliferation of granulosa cells; antrum develops (fluid)
- Gap junctions and cytoplasmic processes between oocyte and granulosa cells allows
communication and passage of low molecular weight materials (nutrients)
- Proliferation of thecal cells (external to granulosa cells):
- Theca interna: glandular and highly vascularised
- Theca externa: fibrous capsule
- Interaction between follicular cell types critical:
- Androgens secreted by theca interna cells
- Convert to estradiol 17-beta in granulosa cells
Post-ovulation:
- Empty Graafian follicle (granulosa cells undergo luteinisation to corpus luteum)
- If no fertilisation, corpus luteum degenerates/fibroses to become corpus albicans
Endometrium (uterus lining):
- Proliferative phase:
- Endometrium thickens
- Estradiol dominant
- Increased stromal cells, glands and blood vessels
- Endometrium is 2-3mm thick
- Secretory phase:
- Progesterone dominant
- Increased secretion, lipids and glycogen, and blood supply
- Endometrium 4-6mm thick
- Optimal conditions for implantation of fertilised egg
- Menstrual phase:
- Vasodilation (vasospasm of blood vessels - PGF2-alpha)
- Necrotic outer layers of endometrium separate from uterus
- Separated tissue and blood initiate uterine contractions (expel contents)
Cervix:
- Mucus production from columnar glands
- Stringy/runny midcycle (spinnbarkeit; facilitates sperm access at ovulation)
- Tenacious/inelastic in luteal phase (prevents microbial ingress to protect embryo; critical to
pregnancy (mucus ‘plug’))




Timing of ovulation:




3 Adapted from Lectures at the University of Leeds Medical School