Reproduction

1
Reproduction

• Definition
• Purpose
• Stages
• Each stage in detail

2
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.

3
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

4
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

5
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.

6
Human Spermatozoa

• Sperm take about 70 days to be produced and
  survive in the female body for 24 - 72 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).

7
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 37C
• 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.

8
Testis tubules
9
Testis tubule higher magnification
10
Spermatozoa
11
Egg production

• About 500000 to 1000000 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)

12
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

13
Ovum in a follicle in the ovary
14
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
15
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