Human Reproduction - Part 2 (T3)

Question 1

Briefly describe the menstrual cycle..

Answer 1

• generally a monthly cycle of about 28 days, but it can vary from 2 weeks to 6 weeks in duration
• during the cycle, the woman’s uterus develops its lining in preparation to receive a fertilised egg
• if an egg is fertilised, the uterus will be ready to receive it and the egg will settle into the uterus where it will grow and develop into a foetus, then a baby
• by definition, a cycle has no beginning, but the first day of a woman’s period is knows as ‘day 1’ of the menstrual cycle
• the duration of the period usually lasts 3-7 days

Question 2

Describe how the body controls human fertility..

Answer 2

• human fertility is controlled by a number of hormones and specialised cells
• in the nuclei of the gametes, chromosomes carry genetic information of the new offspring
• the genetic info they carry is about gender as well as genetic disorders

Question 3

Between what years, in general, is a woman fertile?

Answer 3

12 - 50

Question 4

What is menstruation?

Answer 4

During the menstrual cycle, if pregnancy does not happen the uterus lining breaks down and the woman has a period - this is known as menstruation

Question 5

What is the blood of the period made up of and how does it leave the body?

Answer 5

• a mixture of blood and the broken down lining of the uterus
  – this passes out of the body through the vagina

Question 6

What happens to the uterus after menstruation, and why?

Answer 6

• the lining of the uterus repairs and thickens as a result of the hormone oestrogen
• the oestrogen is secreted in response to the follicle stimulating hormone (FSH)
• the repairing of the uterus is in preparation for receiving a fertilised egg

Question 7

What is ovulation?

Answer 7

Around the middle of the menstrual cycle, around day 14, an egg is released from a follicle in the ovaries. This is known as ovulation.

Question 8

What are two of the main hormones that control the menstrual cycle? Explain how…

Answer 8

Oestrogen

• produced by the ovaries
• makes the lining of the uterus repair itself and grow again after menstruation

Progesterone

• produced by the empty follicle, corpus luteum, which is in the ovary and formed from what is left once an egg has been released from a follicle
• maintains and completes the lining of the uterus during the second half of the menstrual cycle
• inhibits the release of FSH and the luteinising hormone (LH)

Question 9

Describe the follicle stimulating hormone (FSH) and the luteinising hormone (LH) …

Answer 9

• both the FSH and LH are produced in the pituitary gland, found in the brain
• both hormones are transported in the blood
• low levels of progesterone enable FSH levels to stimulate the maturation of an egg in a follicle in the ovary
• this then encourages the production of oestrogen, which repairs the uterus wall and stimulates an increase in LH
• this stimulates ovulation at around day 14 of the cycle

Question 10

What is the corpus luteum?

Answer 10

• after an egg is released from a follicle, the empty follicle develops into a body called the corpus luteum
• the corpus luteum produces the hormone progesterone which maintains the lining of the uterus and stops menstruation
  – if a woman becomes pregnant, the corpus luteum continues to produce progesterone and a placenta is formed

Question 11

Why are the ova and sperm cells known as haploid cells rather than diploid cells?

Answer 11

• because the nuclei of ova and sperm cells possess 23 chromosomes, which is half the number of chromosomes (ie: half the genetic information) that a normal body cell contains
• the ova and sperms cells are therefore referred to as haploid cells
• normal body cells, containing 46 chromosomes, are referred to as diploid cells

Question 12

When does fertilisation occur in sexual reproduction and what does it produce?

Answer 12

• fertilisation occurs when an egg and a sperm cell fuse to form a single cell
• this single cell is called a zygote