Human reproductive systems and the menstrual cycle

Last time

Before we start: last time, in Flowers, pollination, fertilisation and germination, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Making a new human

Every one of us started as a single cell, made when one sperm met one egg. Today: the male and female reproductive systems, where each gamete is made, and the monthly cycle that prepares a woman's body for a possible pregnancy.

The male system

The testes make sperm and the hormone testosterone. They are held in the scrotum, a little cooler than the body. The sperm ducts carry sperm to the urethra. Glands add fluid to make semen. The urethra carries semen, or urine, out through the penis.

The female system

The ovaries contain eggs, and make the hormones oestrogen and progesterone. Each month an egg is released into the oviduct, where it may be fertilised. The oviduct is lined with cilia. The uterus is where a fetus develops. The cervix is its neck, and the vagina leads to the outside.

Where things happen

Here is the table to learn. Where each event happens. The examiner loves asking where fertilisation happens: the oviduct.

Puberty

At puberty, testosterone causes male changes: a deeper voice, body hair, and sperm production. Oestrogen causes female changes: breasts develop, hips widen, and the menstrual cycle starts.

The menstrual cycle

The cycle lasts about twenty-eight days. Days one to five: menstruation. The lining of the uterus breaks down and leaves the body. After that, the lining thickens again, ready to receive an embryo. Around day fourteen, an egg is released from an ovary: ovulation.

The hormones

F S H, from the pituitary gland, makes an egg develop in the ovary, and stimulates oestrogen release. Oestrogen makes the uterus lining thicken. L H, also from the pituitary, triggers ovulation. Progesterone keeps the lining thick. When it falls, the lining breaks down and menstruation begins.

Hormone summary

Here is a summary. Two hormones from the pituitary, two from the ovary. During pregnancy, progesterone stays high, made at first by the ovary and later by the placenta, so there is no menstruation.