Human reproduction and contraception explained
Homeostasis and response • Hormonal coordination in humans
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Key concepts
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Basic reproductive units and processes
Gametes are haploid sex cells: ova from ovaries and sperm from testes. Fertilisation restores the diploid chromosome number and initiates embryo development. Meiosis produces gametes with half the chromosomes; fertilisation combines parental genomes to create genetic variation .
Roles of the four main hormones
FSH (follicle-stimulating hormone) is released from the pituitary and causes an ovum to mature within an ovarian follicle and stimulates the ovary to produce oestrogen. LH (luteinising hormone) from the pituitary triggers ovulation and the formation of the corpus luteum. Oestrogen from the ovary thickens the uterine lining and, at high mid-cycle levels, stimulates an LH surge while inhibiting FSH release. Progesterone from the corpus luteum maintains the uterine lining after ovulation and inhibits further FSH and LH release; progesterone levels fall if no implantation occurs, causing menstruation .
Hormonal interactions and feedback
Rising FSH at cycle start causes follicle growth and increased oestrogen. Increasing oestrogen exerts negative feedback to reduce FSH and then, when sustained at a high level, produces a positive feedback effect on the pituitary that triggers an LH surge and ovulation. After ovulation, progesterone from the corpus luteum provides negative feedback to suppress FSH and LH and maintain the uterus lining; decreased progesterone triggers menstruation if fertilisation does not occur .
Reading hormone-level graphs
Hormone-concentration graphs show FSH and oestrogen rising in the follicular phase, a sharp LH peak at ovulation (around day 14), then elevated progesterone in the luteal phase. Cause→effect interpretation links peaks and falls to follicle maturation, ovulation and uterus preparation. Axes and timing must be labelled and units understood for accurate extraction and interpretation .
Causes of infertility
Infertility arises from many causes including blocked fallopian tubes, low sperm count or quality, ovulation problems, age-related decline in egg quality and certain diseases or injuries. Diagnosis requires medical investigation to identify specific causes before selecting treatments.
Hormonal infertility treatments (FSH and LH)
Exogenous FSH and LH injections stimulate the maturation of multiple ovarian follicles and can induce ovulation. Controlled ovarian stimulation increases the number of available ova for assisted reproduction or timed intercourse; dosage requires medical monitoring to reduce risks such as ovarian hyperstimulation syndrome and multiple pregnancies .
In Vitro Fertilisation (IVF) steps
Medical stimulation with FSH/LH matures several ova. Surgical egg retrieval removes ova from ovaries. Collected ova and sperm are combined in vitro; fertilisation may occur naturally or by direct sperm injection into an ovum. Fertilised ova develop into embryos; one or more embryos are implanted into the uterus. Remaining embryos raise ethical and storage considerations. Success rates remain limited, prompting careful clinical decision-making .
Evaluation of infertility treatments
Benefits include enabling biological parenthood and use when natural conception is impossible. Drawbacks include physical risks (procedural complications, ovarian hyperstimulation), emotional stress, high cost, variable success rates and ethical issues over embryo handling and multiple births. Clinical decisions balance patient priorities, risks, success probability and resource availability .
Contraception methods overview
Hormonal methods (combined oral pill, progesterone-only pill, patch, implant, injection, hormonal IUD) prevent pregnancy primarily by preventing ovulation, thickening cervical mucus and/or thinning the uterus lining. Non-hormonal methods include barrier methods (condom, diaphragm, sponge), intrauterine devices (copper coil), spermicides, abstinence and surgical sterilisation (vasectomy or tubal ligation). Condoms provide the extra effect of reducing transmission of sexually transmitted infections; many methods vary in reversibility, effectiveness and side-effect profiles .
Key notes
Important points to keep in mind