Reproduction Definition Purpose Stages Each stage in detail

Definition of Reproduction Producing new individuals Two types – Sexual reproduction: Involves the production of special sex cells - called gametes - and fertilisation. Asexual Reproduction: No sex cells produced, no fertilisation.

Purpose of Reproduction To maintain the numbers of a particular species Since this is so important the urge or “drive to reproduce is very strong

Stages in animal reproduction Gametogenesis – making eggs and sperm Sexual intercourse or Mating (technical terms Copulation or Coitus) – sperms close to the egg. Fertilisation – fusing of sperm nucleus and egg nucleus Development of the embryo – by cell division, cell enlargement and differentiation Birth (or hatching) After care – quite a long time in humans

Gametogenesis Male reproductive system - structure and function of testis, penis, urethra, sperm duct, scrotum, prostate gland. Female reproductive system – structure and function of ovary, egg tube, uterus, cervix, vagina, clitoris.

Human Spermatozoa Sperm take about 70 days to be produced and survive in the female body for hours. Sperms have only half the normal number (46 in humans) of chromosomes, i.e. 23 so that when the sperm nucleus and the egg nucleus fuse the normal number is produced. Sperms can be frozen and used for artificial insemination “AI”. They are produced in the testes (left bigger than right) in seminiferus tubules (small tubes).

Human Spermatozoa The testes are outside the body because sperms only develop properly and in sufficient numbers at 2 or 3 degrees below body temperature of 37°C The penis has evolved in land animals to transfer sperm from male to female, in fish and amphibians there is no such problem and sperms are released in to the water close to the eggs.

Testis tubules

Testis tubule higher magnification

Spermatozoa

Egg production About to egg producing cells are present in the human female at birth. Only about 500 develop and are used, the rest degenerate (break down) Eggs develop inside follicles inside the ovaries Each ovary is suspended close to and just below the egg tube (oviduct or fallopian tube)

Egg production About once every 28 days an egg grows to full size and is released from one ovary – they alternate – this is called ovulation The egg cannot move by itself so it is carried by surrounding fluid which is moved by ciliated epithelial cells into the oviduct In the oviduct if sexual intercourse has occurred within a day or two the egg may be fertilised by one sperm

Ovum in a follicle in the ovary

Comparison of eggs and sperm Eggs Larger Cannot move, non-motile In some animals contain a large food store Contain ½ the normal number of chromosomes (23) Made in the female ovary Released in smaller numbers Sperm Small Can move using “tail” Contain no food store Contain ½ the normal number of chromosomes (23) Made in the male testes Released in large numbers

Puberty Changes that occur to the body concerned with the production of eggs and sperm that enable an individual to reproduce – called primary sexual characteristics Changes the occur to the body at the same time as the above but not directly concerned with the production of eggs and sperm - called secondary sexual characteristics