B11. Reproduction in humans

Oviduct:
- Connects the ovary to the uterus.
- Lined with ciliated cells to push the ovum down.
- Fertilisation occurs here.
Ovary:
- Contains ova (female gametes).
- Ova mature and develop when hormones are released.
Uterus:
- Muscular bag with a soft lining.
- Fertilised egg (zygote) implants here to develop into a foetus.
Cervix:
- Ring of muscle at the lower end of the uterus.
- Keeps the developing foetus in place during pregnancy.
Vagina:
- Muscular tube leading to the inside of the woman's body.
- The penis enters during sexual intercourse, and sperm are deposited here.

Sperm is made in the testes (starting at 12-14 years old).
Testes are located outside the body in two sacs called the scrotum.
Sperm is transported by the sperm duct to the urethra, then to the tip of the penis.
The urethra transports sperm or urine.
The prostate gland makes fluid for the sperm to swim in (where sperm ducts join the urethra).

Prostate Gland:
- Produces fluid called semen that provides sperm cells with nutrients.
Sperm Duct:
- Sperm passes through the sperm duct to be mixed with fluids produced by the glands before entering the urethra for ejaculation.
Urethra:
- Tube running down the centre of the penis that carries urine or semen.
- A ring of muscle in the urethra prevents urine and semen from mixing.
Testis:
- Contained in a bag of skin (scrotum).
- Produces sperm (male gamete) and testosterone (hormone).
Scrotum:
- Sac supporting the testes outside the body to keep sperm at a temperature slightly lower than body temperature.
Penis:
- Passes urine out of the body from the bladder.
- Allows semen to pass into the vagina of a woman during sexual intercourse.

Sperm Cell:
- Acrosome: Contains enzymes in the head region.
- Haploid nucleus: Contains genetic material.
- Midpiece: Contains mitochondria for energy.
- Tail (flagellum): Enables swimming.
Egg Cell:
- Cell membrane.
- Cytoplasm: Contains a store of energy.
- Haploid nucleus: Contains genetic material.
- Jelly-like coating: Changes after fertilisation.
Adaptive Features:
- Sperm: Flagellum for swimming to the egg, acrosome to digest through the jelly coat and cell membrane.
- Egg: Store of energy for the dividing zygote, jelly-like coating forms an impenetrable barrier after fertilisation.
Reason for Adaptive Features:
- Sperm: Enables it to swim to the egg and digest through the jelly coat and cell membrane of an egg cell when it meets one.
- Mitochondria: Provide energy from respiration so that the flagellum can move back and forth for locomotion.
- Egg: Provides energy for the dividing zygote after fertilisation, forms an impenetrable barrier after fertilisation to prevent other sperm nuclei from entering the egg cell.

Sexual intercourse: The man places the penis inside the vagina to ensure sperm gets as close as possible to the egg.
Ejaculation: Deposits semen (containing about 1 million sperm) at the top of the vagina - cervix.
Rhythmic muscle contractions of the walls of tubes send semen from testes to sperm ducts to the penis.
Sperm swim (4 mm/min) up the cervix, uterus, and oviduct (ciliated cells assist).
Fertilisation: The nucleus of the sperm fuses with the nucleus of the egg inside the oviduct.
The tail of the sperm is left outside; the head goes inside the egg.
Once fertilised, the egg membrane becomes impenetrable.

Primary sexual characteristics are present during development in the uterus, representing differences in reproductive organs between males and females.
Secondary sexual characteristics: changes occurring during puberty as children become adolescents.
Controlled by the release of hormones:
- Oestrogen in girls.
- Testosterone in boys.

Controlled by hormones.
Starts around 12 years old.
The lining of the uterus becomes thick and spongy, containing tiny blood vessels with oxygen and food for the embryo.
If no fertilisation occurs, the egg is expelled through the vagina.
Menstruation: The lining gradually disintegrates and exits through the vagina (approximately 5 days every month).
Mature egg is released.
Follicles: A structure within the ovary in which the egg develops.
In puberty, there are 200,000 to 300,000 follicles in the ovaries.
Each follicle can release 1 egg for ovulation and fertilisation.

Unprotected sexual intercourse can lead to the transfer of pathogens via the exchange of body fluids.
Infections passed on in this way are known as sexually transmitted infections (STIs).

AIDS = Acquired Immune Deficiency Syndrome (Infection/Disease).
HIV = Human Immunodeficiency Virus (Pathogen).
Mode of action: The virus infects a type of white blood cell (T cell) and slowly kills them, impairing the ability to fight against pathogens.
An HIV-positive person must undergo treatment with antiretroviral drugs.
Common diseases associated with AIDS are pneumonia and cancer.

HIV can be contracted via:
- Sexual activity (fluids of the vagina, rectum, urethra, and blood).
- Blood contact (transfusions and hypodermic needles).
- Mother to baby (pregnancy, birth, or breastfeeding).

They mimic some of the hormone levels during pregnancy.
By raising the levels of progesterone and oestrogen, the uterus lining is maintained, and development of another egg cell is prevented.
This means that sex at any time of the month cannot cause pregnancy, as no egg is released to be fertilised.