B10.3 : Menstrual cycle and Pregnancy

Question 1

The Stages of menstrual cycle

Answer 1

1. The menstrual cycle can be divided into four stages depending on the levels of the hormones.

Question 2

Stage 1 of the menstrual cycle

Answer 2

The uterus lining breaks down, resulting in a ‘period’.

Question 3

Stage 2 of the menstrual cycle

Answer 3

The uterus lining starts to build up again into a thick, spongy layer full of blood vessels.

Question 4

Stage 3 of the menstrual cycle

Answer 4

Ovulation happens. This is when an egg is released from one of the ovaries.

Question 5

Stage 4 of the menstrual cycle

Answer 5

1. The uterus lining is maintained, which means that it is now ready for the arrival of a fertilised egg (which will eventually grow into a baby).
2. If no fertilised egg is attached to the uterus lining, the lining breaks down and the cycle begins again.

Question 6

Menstrual cycle

Answer 6

1. The menstrual cycle is a monthly cycle, which involves the maturation and release of an egg.
2. If sexual intercourse has occurred, it can result in pregnancy.
3. usually one egg is released into the oviduct every month

Question 7

Eggs in the menstrual cycle

Answer 7

A female is born with all of her eggs ready, but only one egg will mature each month once the female reaches puberty.

Question 8

Duration of each stage of the menstrual cycle

Answer 8

1. Stage 1 (days 1-4)
2. Stage 2 (days 4-14)
3. Stage 3 (day 14)
4. Stage 4 (day 15-28)

Question 9

Pregnancy

Answer 9

Pregnancy starts with fertilisation, when the nucleus of a sperm fuses with the nucleus of an egg, and involves many more stages

Question 10

stages of pregnancy

Answer 10

1. zygote
2. embryo
3. Connecting the embryo to the mother (placenta and umbilical cord)
4. Foetus

Question 11

zygote

Answer 11

1. Once an egg is fertilised by a sperm, it is called a zygote.
2. The zygote cell then starts to divide to form a ball of cells
3. Once a zygote is made, it slowly moves down the oviduct

Question 12

Embryo

Answer 12

1. Once a ball of cells has formed from the zygote, this is called an embryo.
2. The embryo then implants itself into the wall of the uterus.
3. Embryo obtains food from the yolk of the egg
4. It can take hours for the embryo to reach the uterus, by this time, it is usually a ball of 16 or 32 cells

Question 13

Connecting the embryo to the mother

Answer 13

1. Once the embryo has implanted, various structures form to connect the embryo to its mother;
2. A placenta forms between the embryo and the wall of the uterus.
3. The umbilical cord is a thick knot of blood vessels that connects the embryo and the placenta.
4. An amniotic sac filled with amniotic fluid forms around the embryo to protect it from damage in the uterus.

Question 14

Foetus

Answer 14

1. 6 weeks after fertilisation, the embryo can be called a foetus.
2. The foetus continues to grow and become more complex.
3. The baby is fully formed at around 38 to 40 weeks.
4. The foetus is connected to its mother via the umbilical cord and the placenta which forms on the wall of the mother’s uterus. The foetus is protected by an amniotic sac.

Question 15

Health during pregnancy

Answer 15

1. It is important that the foetus is connected to the mother’s bloodstream through the placenta so it can get everything it needs.
2. But, this means that any harmful substances in the mother’s blood can easily reach the foetus.

Question 16

Placenta

Answer 16

1. As the embryo grows, a placenta also grows which connects it to the wall os the uterus
2. The placenta is a soft and dark red. It is lined with villi which fit closely into the uterus wall. By the time of birth, it will be a flat disk
3. The placenta is where the substances are exchanged (through diffusion) between the mother’s blood and the embryo’s. It is basically the embryo’s life support system. Nutrients are passed from the mother’s blood to the baby’s blood
4. It provides the foetus with oxygen, nutrients for growth.
5. It also removes excretory waste products such as carbon dioxide and urea from the foetus.
6. The placenta acts as barrier and can stop many (but not all) toxins and pathogens from passing from the mother’s blood to the foetus.
7. Blood is not transferred as the mother and baby may not be the same blood type

Question 17

Harmful substances while pregnant

Answer 17

1. Pregnant women are advised not to smoke or drink alcohol, because nicotine (in cigarettes) and alcohol can pass through the placenta into the blood of the foetus.
2. This can seriously harm its development.
3. Pregnant women are also told to avoid foods that are more likely to carry pathogens such as undercooked meat.
4. The rubella virus is a pathogen can pass through the placenta and harm the foetus.

Question 18

Successful fertilisation

Answer 18

1. If the released egg is not fertilised by a sperm within 8-24 hours after ovulation, it will die
2. By this time, it has travelled a short way along the oviduct. So a sperm must reach an egg while it is quite near the top of the oviduct if fertilisation is to be successful

Question 19

Sexual intercourse

Answer 19

1. When a man is sexually excited, blood is pumped into spaces inside the penis, making it erect
2. To bring the sperm as close as possible to the egg, the man’s penis is placed inside the vagina of a women, this is called sexual intercourse.

Question 20

Semen

Answer 20

1. sperm mixed with a fluid

2. fluid containing the sperm

Question 21

Ejaculation

Answer 21

1. sperm are pushed out of the penis into the vagina
2. This happens when muscles in the walls of the tubes containing the sperm contract rhythmically
3. The wave of contraction begins in the testes, travels along the sperm ducts, and into the penis
4. The sperm are squeezed along, out of the man’s urethra and into the woman’s vagina
5. This is known as ejaculation which is when semen is deposited at the top of the vagina, near the cervix
6. Ejaculation involves depositing millions of sperm in the vagina

Question 22

Sperm swimming to the egg

Answer 22

1. The sperm are still quite a long way from the egg after ejaculation
2. They swim, using their tails, up through the cervix, through the uterus and into the oviduct
3. Sperm don’t swim very fast so it takes quite a while for them to get there. many will never get there at all. Unsuccessful sperm will all die
4. However, since so many are deposited, there is a good chance that at least some of them will reach the egg

Question 23

Fertilisation

Answer 23

1. One sperm enters the egg. Only the head of the sperm goes in, the tail is left outside
2. Fertilisation is when the nucleus of the sperm fuses with the nucleus of the egg to form a zygote
3. As soon as the successful sperm enter the egg, the egg membrane becomes impenetrable so that no other sperm can get in

Question 24

Implantation

Answer 24

1. The uterus has a thin, spongy lining that the embryo sinks into. This is called implantation
2. After implantation, the embryo will continue to divide

Question 25

Giving birth

Answer 25

1. The embryo grows and develops in the uterus for around 9 months
2. After that time, muscles in the wall of the uterus contract and push the baby out through the cervix (which will open) and vagina
3. The baby is still attached to the uterus by the umbilical cord and the placenta

Question 26

After birth

Answer 26

1. The placenta falls away from the uterus wall and passes out through the vagina
2. This is called afterbirth

Question 27

Umbilical cord

Answer 27

1. The umbilical cord is a thick knot of blood vessels that connects the embryo and the placenta.
2. Inside there are 2 arteries and a vein. The arteries take blood from the foetus into the placenta, and the vein returns the blood to the foetus

Question 28

Amnion

Answer 28

1. Surrounds the foetus

2. Makes a liquid called amniotic fluid which supports the embryo and protects it

Question 29

testosterone

Answer 29

hormone produced by testis in males that instigate secondary sex characteristics at puberty and (primary) production of sperm

Question 30

Oestrogen

Answer 30

oestrogen is involved in repairing and thickening the uterus lining,

Question 31

Progesterone

Answer 31

progesterone maintains the uterine lining