Reproduction in Humans — Quick Reference Notes

Reproduction in Humans

• Sex organs and gametes
  • Male: testes, prostate gland, scrotum, penis, urethra, sperm ducts.
  • Female: ovaries, oviducts, uterus, cervix, vagina.
  • Gametes: 23 chromosomes each; sperm (male) and ova (female).
  • Fertilisation: occurs in oviducts when haploid gametes fuse to form a diploid zygote with 46 chromosomes: $23+23=46.$
  • Zygote | embryo | fetus | placenta: zygote divides, implants in uterus, develops into embryo and then fetus; placenta forms early to support growth.
• Hormones and sex characteristics
  • Male: testosterone.
  • Female: oestrogen and progesterone.
  • Key gonadotropic hormones: FSH and LH regulate ovaries; LH surge triggers ovulation; progesterone supports pregnancy; oestrogen supports uterus lining.
• Placenta and fetal exchange
  • Placenta supports growth by exchanging nutrients, oxygen, and wastes between mother and fetus; secretes hormones; protects fetus and aids immune function.
  • Placenta structure: placental villi + maternal blood space enable diffusion; two circulations (maternal and fetal blood) remain separate.
  • Umbilical cord: contains arteries (to placenta, deoxygenated blood and wastes) and a vein (to fetus, oxygenated blood and nutrients).
• Gestation and development at a glance
  • Gestation: about $40\text{ weeks}$ or ~9 months.
  • Growth vs development: growth is cell division; development is tissue/organ formation.
  • Embryo becomes fetus at about 8 weeks; placenta begins early and grows with the fetus; afterbirth includes placenta, amniotic sac, and umbilical cord.
• Amniotic sac and fluid
  • Amniotic fluid cushions and supports movement and temperature; amnion forms the sac.
  • Amniocentesis: test for fetal abnormalities (chromosome/gene mutations); usually performed at $16-18\text{ weeks}$; carries miscarriage risk; more common for older mothers.
• Antenatal care and checks
  • Diet and lifestyle: extra calcium, iron, protein, carbohydrates; vitamin supplements.
  • Weight gain: about $12\text{ kg}$ (≈30 lb) during pregnancy; about $450\text{ g}$ per week from ~3rd month.
  • Checks: regular weight, blood pressure; fetal size, position, and heartbeat (approx. $120-160\text{ bpm}$); ultrasound for age/size/position/twin pregnancies.
  • Hormonal and placental health: estrogen levels reflect placental function.
• Diffusion and placenta efficiency
  • Diffusion adaptations: large surface area, short diffusion distance, and maintained concentration gradient; antibodies can cross late in pregnancy to provide neonatal immunity.
• Amniotic fluid and amniocentesis recap
  • Amniotic fluid protects fetus from shocks, temperature changes, and dehydration.
  • Amniocentesis provides information on chromosome and gene mutations but carries miscarriage risk.
• Birth and labour
  • Labour stages: Stage 1 (dilation, latent and active phases), Stage 2 (expulsion of baby), Stage 3 (placental expulsion/afterbirth).
  • Processes: waters break (amniotic sac rupture), cervix dilates, crowning occurs, baby delivered head-first or breech; umbilical cord clamped and cut; placenta expelled.
• Birth outcomes and complications
  • Breech births possible; pre-term births may occur; rising medical support improves survival with incubators and respiratory care.

The Newborn: Feeding and Care

• Suckling reflex and lactation
  • Suckling triggers oxytocin release, causing milk ejection (lactation).
  • Colostrum: early milk rich in antibodies; breast milk provides nutrients and antibodies for the first months.
• Breast milk vs formula
  • Breast milk: balanced nutrients, antibodies, low cost, supports bonding; protects against infections (e.g., gastroenteritis).
  • Formula: cow’s milk-based, requires preparation; may lack antibodies; cost and handling considerations.
• Weaning
  • Solid foods generally introduced around 4–6 months when teeth begin to appear; gradual transition from milk to solids.

Contraception and Birth Control

• Principles
  • Birth control methods prevent pregnancies by: stopping sperm reaching egg, stopping egg production/ovulation, or preventing implantation.
• Barrier methods
  • Condom and femidom; diaphragm/cap with spermicidal cream.
  • Pros: protect against STIs (condoms); easy to obtain.
• Intrauterine devices (IUDs)
  • Plastic or copper coils placed in uterus; copper IUD prevents implantation; some use progesterone to thicken cervical mucus.
• Hormonal methods
  • Combined pill (estrogen + progesterone): suppresses FSH/LH, so no ovulation; may be taken 21 days on, 7 days off.
  • Mini-pill (progesterone only): thickens cervical mucus; may be used when estrogen is undesirable.
  • Other hormonal methods: injections, implants.
• Sterilisation
  • Male: vasectomy (cut/tie sperm ducts).
  • Female: tubal ligation (oviducts cut/blocked).
• Contraception effectiveness and considerations
  • Table-like comparison of methods (failure rates and pros/cons) is commonly used for quick reference.

Menstrual Cycle and Hormones

• Key hormones and targets
  • FSH: target organ is the ovary; stimulates follicle growth and estrogen production.
  • LH: surge triggers ovulation; stimulates corpus luteum to secrete progesterone.
  • Relationship: FSH and LH rise and fall during cycle; LH peak occurs around day ~14, synchronizing with ovulation.
• Lining of the uterus
  • Menstrual cycle: lining builds up under estrogen, then is shed if no fertilisation; regrowth occurs in the second week.
• How fertilisation links to pregnancy
  • After ovulation, fertilisation occurs if a sperm meets an ovulated egg; zygote implants in the uterus, initiating pregnancy.

Reproduction Health: STIs and Sex Chromosomes

• STIs overview
  • Bacterial: gonorrhea (antibiotics can treat); resistance rising.
  • Viral: HIV/AIDS (no cure; antiviral therapies slow progression).
  • Transmission: sexual contact, blood, mother-to-child, or shared needles.
• Sex chromosomes in sperm
  • Sperm can carry either X or Y chromosome; egg always carries X; this determines the offspring’s sex when fertilisation occurs.

Twins and Multiple Births

• Types of twins
  • Identical twins: same genetic material; one zygote splits.
  • Non-identical (fraternal) twins: two eggs fertilised by two different sperms.
• Fertility and multiple births
  • Fertility treatments can increase multiple births; medical care required due to higher risk of pre-term birth.

Quick Calculations and Key Formulas

• Percentage decrease example (birth to puberty eggs)
  • Given: births ~1.5 million eggs; puberty ~0.35 million eggs.
  • Percentage decrease: $ext{decrease} = \frac{1.5 - 0.35}{1.5} imes 100\% = 76.7\%.$)
• Gestation duration
  • $\approx 40\text{ weeks}$ or $\approx 9\text{ months}$
• Heartbeat range during pregnancy
  • Typical fetal heart rate: $120-160\text{ bpm}$
• Nutrient and waste exchange in placenta
  • Diffusion depends on: large surface area, short diffusion distance, and concentration gradient; antibodies cross late in pregnancy.

Quick reference: Stages of Labour (Summary)

• Stage 1: cervix dilates; contractions begin; waters may break.
• Stage 2: delivery of the baby through the birth canal.
• Stage 3: delivery of the placenta (afterbirth).

Note on References in the Material

• The material covers human reproduction, pregnancy development, antenatal care, birth, breastfeeding, contraception, and STIs, with emphasis on diffusion in the placenta, hormonal regulation of the menstrual cycle, and practical aspects of birth and postnatal care.