👶

Human Reproduction

Reproductive systems, menstrual cycle, pregnancy, STIs

Male Reproductive System

Testes (two): Produce sperm (meiosis) & testosterone (hormone). In scrotum (cool for sperm production).

Sperm duct: Transports sperm from testes → penis. Contracts during ejaculation.

Prostate gland: Makes fluid (seminal plasma). Mixes with sperm → semen.

Penis: Delivers semen during sexual intercourse. Contains erectile tissue (fills with blood).

Testosterone: regulates sperm production, secondary sex traits (deep voice, facial hair)

Female Reproductive System

Ovaries (two): Produce eggs (ovules) & hormones (oestrogen, progesterone). Release ~1 egg per month.

Oviduct (fallopian tube): Carries egg from ovary → uterus. Fertilisation happens here.

Uterus (womb): Thick muscular wall (myometrium), lined with endometrium. Implantation site for embryo.

Cervix: Narrow opening to uterus. Produces mucus (changes with cycle).

Vagina: Elastic passage. Receives penis, birth canal.

Menstrual Cycle (28 days)

Day 1-5 — Menstruation: Endometrium lining breaks down, sheds blood/tissue. FSH rises.

Day 5-14 — Follicular phase: FSH stimulates ovary → follicle develops → oestrogen rises → endometrium thickens (prepares for implantation)

Day 14 — Ovulation: LH surge triggers egg release. Ovary ruptures, egg into oviduct.

Day 14-28 — Luteal phase: Follicle becomes corpus luteum → produces progesterone → maintains thick endometrium. If no fertilisation: progesterone drops → cycle restarts.

Hormones of Menstrual Cycle

Hormone	Source	Role
FSH	Pituitary	Stimulates follicle development & oestrogen production
Oestrogen	Ovary (follicle)	Thickens endometrium. Inhibits FSH (negative feedback)
LH	Pituitary	LH surge triggers ovulation
Progesterone	Ovary (corpus luteum)	Maintains thick endometrium. If no pregnancy → falls → menstruation

Fertilisation & Early Development

Fertilisation: Sperm + egg in oviduct. Nucleus fusion → zygote (46 chromosomes).

Mitosis: Zygote divides (2 → 4 → 8 → 16 cells). Forms blastocyst (hollow ball).

Implantation: Blastocyst attaches to thick endometrium (day 7-12). Embryo embeds into wall.

Progesterone prevents menstruation: If implantation occurs, corpus luteum continues making progesterone → prevents endometrium shedding

Placenta — The Exchange Organ

Structure: Grows from outer cells of embryo. Attaches to endometrium via umbilical cord.

Exchange (mother ↔ fetus):
IN: glucose, amino acids, oxygen, antibodies
OUT: CO₂, urea, waste, nitrogenous compounds

Large surface area: Villi on fetal side, sinusoids on maternal side. Efficient exchange.

Barrier function: Prevents most pathogens crossing. Some antibodies pass (temporary immunity for newborn).

Sexually Transmitted Infections (STIs)

HIV (Human Immunodeficiency Virus): Virus. Attacks immune system (CD4 T-cells). Leads to AIDS. Transmission: sexual contact, blood, mother-to-child.

Gonorrhoea: Bacterium. Infects urinary/reproductive tract. Discharge, pain. Antibiotics treat (some antibiotic resistance).

Chlamydia: Bacterium. Often no symptoms. Can cause infertility. Antibiotics treat.

Prevention: Condoms (barrier), monogamy, testing, antiretrovirals (HIV)

Exam Tips

✓ Testes produce sperm; ovaries produce eggs

✓ Menstrual cycle: 28 days, 4 phases (menstruation, follicular, ovulation, luteal)

✓ FSH → follicle development; LH surge → ovulation

✓ Placenta: exchanges O₂, glucose, CO₂, urea. Barrier to most pathogens.

✓ HIV attacks immune system. Condoms prevent STIs.

Key Takeaways

✅ Testes: sperm + testosterone; ovaries: eggs + oestrogen/progesterone

✅ Menstrual cycle: 28 days, regulated by FSH, LH, oestrogen, progesterone

✅ Ovulation (day 14): egg released; if not fertilised → menstruation

✅ Fertilisation in oviduct; implantation in uterus

✅ Placenta: exchanges nutrients/O₂/waste; barrier to pathogens

✅ STIs: HIV (virus), gonorrhoea (bacterium). Condoms prevent.

Life begins with reproduction! 👶✓