10.3 - Reproduction in Humans

Question 1

What are the female reproductive organs?

Answer 1

The two ovaries (where eggs are made), oviducts/fallopian tubes (funnel shaped opening into ovaries), uterus (thick walls, made of muscle so can stretch), the cervix (base of uterus, leads to vagina).

Question 2

What are the three tubes that open to the outside in a woman’s body?

Answer 2

Vagina, urethra, rectum.

Question 3

What are the male reproductive organs?

Answer 3

Two testes (where sperm are made, outside body in sacs of skin called scrotum), Sperm duct (carries sperm away from testes, join up with urethra just below bladder), urethra continues downwards and opens at the tip of the penis (carries urine and sperm), prostate gland (where sperm duct joins urethra, makes fluid which sperm swim in).

Question 4

When are eggs formed?

Answer 4

They begin to be formed in a girl’s ovaries before she’s born, at birth she’ll have thousands of partially developed eggs, and at puberty these eggs will begin to mature.

Question 5

What is ovulation?

Answer 5

When an egg cell is mature, it bursts out of the ovary and into the funnel at the end of the oviduct. It happens once a month.

Question 6

Where and how are sperm cells made?

Answer 6

The testes. They develop from cells in the walls of the tubules of the testes, which divide by meiosis and sperm are made continually from puberty onwards.

Question 7

What affects sperm production?

Answer 7

Heat. If it gets too hot, the cells in the tubules won’t develop into sperm. This is why they are on the outside of the body, where they’re cooler.

Question 8

What is the oviduct lined with?

Answer 8

Cilia which beat rhythmically, wafting egg into entrance of oviduct from the funnel they’re in, and then help the oviduct sweep it along to the uterus.

Question 9

What is peristalsis?

Answer 9

Movement of muscles in the wall of the oviduct to help move the egg cell along to the uterus.

Question 10

When does an egg cell die?

Answer 10

If it isn’t fertilised by a sperm within 8-24 hours after ovulation. At this time it’s only travelled a short way along the oviduct, so a sperm must reach an egg while it is near the top of the oviduct for the fertilisation to be successful.

Question 11

What happens when a man is sexually aroused?

Answer 11

Blood is pumped into spaces inside the penis, making it erect.

Question 12

What is sexual intercourse?

Answer 12

To bring the sperm as close as possible to the egg, the man’s penis is placed inside the vagina of the woman.

Question 13

What is ejaculation?

Answer 13

When the sperm are pushed out of the penis into the vagina. It occurs when muscles in the walls of the tubes containing the sperm contract, which begins in the testes, travels along the sperm ducts, into the penis. The sperm are squeezed along.

Question 14

What is semen?

Answer 14

Fluid containing sperm. Ejaculation deposits the semen at the top of the vagina, near the cervix.

Question 15

How do the sperm cells get to the egg cells?

Answer 15

They swim, through cervix, uterus and into oviduct at a rate of about 4mm per minute.

Question 16

How many sperm cells are ejaculated?

Answer 16

Million, so there’s a good chance at least one will reach the egg.

Question 17

How does the sperm enter the egg?

Answer 17

Only the head goes in, tail left outside. Nucleus of the sperm fuses with the nucleus of the egg (Fertilisation).

Question 18

What happens to the unsuccessful sperm?

Answer 18

As soon as the sperm enters the egg, the egg membrane becomes impenetrable, so no other sperm can get in, causing the unsuccessful sperm to die.

Question 19

What is implantation?

Answer 19

When the fused nuclei of the sperm and egg form a zygote and that zygote divides by mitosis as it moves down the oviduct. After hours, it forms a ball of cells called an embryo, obtaining food from the yolk of the egg.

Question 20

What is the placenta?

Answer 20

Soft and dark and red, with finger like projections called villi that fit closely into the uterus wall. It is where substances are exchanged between mother’s blood and embryo’s blood.

Question 21

What is a fetus?

Answer 21

The embryo develops into a fetus after 11 weeks. The placenta is joined to the fetus by the umbilical cord, inside of which are two arteries and a vein. The arteries take blood from fetus into placenta, vein returns blood to fetus.

Question 22

How are the fetus and mother’s blood separated?

Answer 22

By the wall of the placenta, but they’re very close together as the wall of the placenta is very thin.

Question 23

How are oxygen and food given to the fetus?

Answer 23

They diffuse across the placenta into the fetus’s blood and are then carried along the umbilical cord to the fetus.

Question 24

How big will the placenta be once the baby is born?

Answer 24

A flat disc, about 12 cm in diameter and 3 cm thick.

Question 25

What is amniotic fluid?

Answer 25

The liquid made by the strong membrane, amnion, surrounding the fetus. It helps support and protect the embryo.

Question 26

What happens when the embryo divides?

Answer 26

As the embryo begins to divide, they develop into different types, specialised for different functions. (Skin cells, muscle cells, blood cells).

Question 27

What happens 6 weeks after fertilisation?

Answer 27

All the major organs begin to grow

Question 28

What happens at 8 weeks?

Answer 28

The embryo (1.5 cm long), has muscles and has started moving.

Question 29

When is a fetus ready to be born?

Answer 29

38 weeks from fertilisation

Question 30

When does birth begin?

Answer 30

When the strong muscles in the wall of the uterus start to contract (Labour). The amniotic sac breaks and the muscles slowly stretch the opening of the cervix.

Question 31

What happens after the cervix has widened enough?

Answer 31

The muscles start to push the baby down through the cervix and the vagina. The baby is still attached to the uterus, but can breathe for itself so placenta is not needed.

Question 32

What is afterbirth?

Answer 32

When the placenta falls away from the wall of the uterus and passes out through the vagina. The umbilical cord is cut and clamped, stump forming the baby’s navel.

Question 33

What occurs before an egg cell is relased?

Answer 33

The lining of the uterus becomes thick and spongy, full of tiny blood vessels to supply an embryo with food an oxygen if it arrives. If the egg isn’t fertilised, it’s dead by the time it reaches the uterus, so it doesn’t remain there.

Question 34

What is menstruation?

Answer 34

The unfertilised egg cell passes downwards through the vagina, along with the unused spongy lining of the uterus. Usually lasts about five days, and after, the lining builds up again.

Question 35

What are the male and female hormones responsible for the development of secondary sexual characteristics?

Answer 35

Male hormone is testosterone, female hormone is oestrogen.

Question 36

What else do the ovaries produce?

Answer 36

Progesterone. The secretion of oestrogen and progesterone are controlled by two hormones secreted by the pituitary gland in the head, called LH and FSH.

Question 37

How do the hormones affect menstruation/ovulation?

Answer 37

FSH induces the growth of a follicle inside an ovary, which then secretes oestrogen to make the uterus lining thicker. Then, LH and FSH are secreted to stimulate the follicle to keep secreting oestrogen. When the follicle is developed, there is a surge in LH, causing ovulation. The empty follicle stops secreting oestrogen and becomes a corpus luteum, that secretes progesterone, levels of FSH and LH fall.

Question 38

What does progesterone do?

Answer 38

It keeps the lining of the uterus thick and well supplied with blood. If the egg isn’t fertilised then the corpus luteum disappears

Question 39

What are STI’s caused by?

Answer 39

Bacteria or viruses that can pass from one person to another during sex. Most important infections are HIV/AIDS.

Question 40

What is AIDS?

Answer 40

Acquired immune deficiency syndrome, caused by HIV

Question 41

What is HIV?

Answer 41

Human immunodeficiency virus. It affects lymphocytes, and destroys T cells (that kill viruses). This makes them unable to fight against other pathogens effectively.

Question 42

If treatment isn’t given, what happens to a person with HIV in ten years?

Answer 42

They develop symptoms of AIDS. They may become vulnerable to pneumonia, and develop cancer. There’s no cure for AIDS.