Humans

Humans

Male Reproductive System

  • The male reproductive system includes the testes, sperm ducts, prostate gland, and penis.
  • The testes are responsible for the production of sperm and the male hormone, testosterone.
  • Sperm are produced in the testes and stored briefly in the epididymis before being transported through sperm ducts.
  • During ejaculation, sperm mix with seminal fluid produced by the prostate gland; this mixture is called semen.
  • The penis is used to deposit semen inside the female during sexual intercourse.

Female Reproductive System

  • The female reproductive system consists of the ovaries, fallopian tubes, uterus, cervix, and vagina.
  • The ovaries release an egg approximately every 28 days in a process known as ovulation.
  • Once released, the egg travels down the fallopian tube towards the uterus; if the egg is fertilised by sperm, it will implant in the uterus and begin development.
  • The uterus provides a protected environment where the embryo can develop.
  • The cervix is a strong ring of muscle at the bottom of the uterus, which keeps the baby in place until birth.
  • The vagina is a muscular tube leading from the cervix to outside of the body; it’s where sperm is deposited during sexual intercourse and the passageway for childbirth.

Fertilisation and Pregnancy

  • Fertilisation occurs when a sperm penetrates an egg.
  • The fertilised egg, or zygote, divides to form an embryo which implants itself in the uterus.
  • The placenta forms and attaches the embryo to the uterus, providing nutrients and oxygen while removing waste products.
  • The embryo develops into a fetus over a period of about nine months before birth.

Inheritance and Genetics

  • DNA in sex cells is organised into chromosomes – humans have 23 pairs, or 46 in total.
  • Chromosomes carry genes which are made from DNA and determine a person’s characteristics.
  • When a child is conceived, they get 23 chromosomes from the mother’s egg and 23 from the father’s sperm, resulting in a unique combination.
  • Certain genes are dominant and will express their trait even if only one is present, while recessive genes require two copies for their trait to be expressed.
  • Some characteristics are determined by a combination of genes, these are known as polygenic characteristics.
  • Genetic mutations can occur naturally or due to environmental factors; these can sometimes lead to different characteristics or health conditions.