--- module: 025-01 language: en chapter: 25 title: "Reproductive Physiology, Pregnancy, and Lactation" module_title: "Foundations" source_sha256: b8cc410f10e2155219dfe9ee44fde86a776bbc78eb17a49843456168c69e97c2 --- # Reproductive physiology, pregnancy, and lactation ## Sexual differentiation and puberty ### Chromosomal sex fixed at fertilisation #### Gonadal and anatomical sex need genes and hormones ### Testis makes anti-Mullerian hormone and androgens #### Absent: ovarian and female tract pathways ### Variation needs precise, respectful assessment ### Puberty: pulsatile activity drives gonadotropins #### Gonadal steroids: secondary traits, growth, bone ### Adrenal androgens: body hair, partly independent ## Ovarian cycle ### Granulosa converts theca androgens to oestradiol ### Oestradiol first restrains gonadotropins #### Sustained high levels flip to positive feedback #### Luteinising-hormone surge: ovulation, luteinisation ### Corpus luteum makes progesterone and oestradiol #### Secretory endometrium ready for implantation ### No pregnancy: luteal regression #### Hormones fall, spiral arteries constrict, shedding ### Length varies in follicular phase, luteal steady ### Amenorrhoea or abnormal bleeding: test for pregnancy ## Testicular function and sexual response ### Luteinising hormone drives Leydig testosterone ### Follicle-stimulating hormone and testosterone aid Sertoli ### Production takes weeks and is vulnerable ### Erection: parasympathetic nitric oxide #### Smooth-muscle relaxation, inflow, venous occlusion ### Ejaculation: sympathetic and somatic pathways ### Assess dysfunction domains separately ## Fertilisation, implantation, and placenta ### Blastocyst implants in receptive endometrium ### Chorionic gonadotropin preserves corpus luteum ### Exchange without mixing circulations #### Depends on flow, area, membrane, metabolism, gradients ### Active endocrine organ, not passive filter ### Poor invasion: growth restriction, pre-eclampsia ### Separation before birth: painful bleeding ### Placenta praevia: typically painless bleeding ## Maternal physiological adaptation ### Plasma, red cells, output, heart rate rise #### Plasma exceeds red cells: haemodilution ### Stasis and coagulation raise thrombosis risk ### Supine uterine compression cuts venous return ### Progesterone raises ventilation #### Low carbon dioxide and bicarbonate, mild alkalosis ### Filtration rises, creatinine falls ### Later insulin resistance preserves fetal nutrients #### Failed compensation: gestational diabetes ### Changes reference ranges and drug handling ## Fetal circulation and transition at birth ### Ductus venosus, foramen ovale, ductus arteriosus #### High lung, low placental resistance keep shunts ### Birth: lung expansion lowers pulmonary resistance ### Cord clamping raises systemic resistance #### Left atrial pressure closes foramen ovale ### Oxygen and less prostaglandin close the ductus ### Some lesions depend on a patent ductus ## Labour, postpartum, and lactation ### Cervical stretch and oxytocin positive feedback ### Uterine contraction compresses vessels after delivery #### Atony a major cause of haemorrhage ### Steroids build breast but restrain secretion #### Fall after placenta permits prolactin synthesis ### Suckling lowers dopamine, raises prolactin #### Oxytocin ejects milk ### Effective removal maintains supply ## Contraception and fertility ### Long-acting methods reduce user dependence ### Combined methods raise thrombotic risk ### Infertility: earlier assessment with risk factors ### Evaluate both partners ## Menopause and reproductive ageing ### Follicle loss lowers oestradiol and inhibin #### Gonadotropins rise ### Cardiovascular risk from age and metabolism ### Hormone therapy best for vasomotor symptoms #### Oestrogen without endometrial protection: cancer ## Pregnancy prescribing and teratology ### Untreated illness can be more dangerous ### Early exposure disrupts organ formation ### Later exposure: growth, labour, neonate ### Folate lowers neural-tube risk ### Avoid abrupt withdrawal of essential treatment