Aspects of Human Reproduction

Question 1

What is the production of gametes called?

Answer 1

Gametogenesis

Question 2

What is SPERMATOGENESIS?

Answer 2

The production of sperm.

Question 3

Where does spermatogenesis take place?

Answer 3

SEMINIFEROUS TUBULES in the testes. Process begins at outer edge of GERMINAL EPITHELIUM and new cells form towards inner edge.

Question 4

Outline spermatogenesis (4)

Answer 4

1) SPERMATOGONIA (diploid cells) divide by mitosis to form more diploid cells which grow into spermatogonia and the larger PRIMARY SPERMATOCYTES.
2) Primary spermatocyte divides by the first division of meiosis into haploid SECONDARY SPERMATOCYTES.
3) Secondary spermatocytes go through the second division of meiosis to form haploid SPERMATIDS.
4) The spermatids differentiate into SPERMATOZOA. Their tails hang free in the luman of the tubule and their heads are attached to the wall.

Question 5

What protects the cells involved in spermatogenesis, and how?

Answer 5

SERTOLI CELLS. Nourish and protect developing sperm cells, ineract with hormones produced in pituitary gland to help regulate sperm production.

Question 6

What happens during the MENUSTRUAL CYCLE? (7)

Answer 6

1) The ANTERIOR PITUITARY GLAND secretes LH and FSH.
2) In the ovary, one follicle becomes the ‘dominant’ follicle (GRAFIAN FOLLICLE), The follicle cells around the SECONDARY OOCYTE proliferate to form a wall many cells thick called the THECA. The presence of FSH and LH stimulates cells surrounding the follicle (granulosa cells) to secrete OESTROGEN.
3) Presence of oestrogen in blood has negative feedback effect on production of FSH and LH, levels of the two hormones fall.
4) Oestrogen stimulates the ENDOMETRIUM (uterus lining) to proliferate (thicken and develop blood capillaries).
5) When oestrogen concentration reaches 2-4times its level at the beginning of the cycle, it stimulates a surge in the secretion of LH and (lesser extent) FSH.
6) Surge of LH causes dominant follicle (GRAFIAN FOLLICLE) to burst and shed its SECONDARY OOCYTE into the OVIDUCT.
7) The Grafian follicle collapses to form the CORPUS LUTEUM formed from GRANULOSA CELLS, which secrete PROGESTERONE (maintains lining of the uterus, making it ready to receive and embryo).

Question 7

What is OVULATION?

Answer 7

When the SECONDARY OOCYTE is released.

Question 8

What is MENSTRUATION?

Answer 8

When the endometrium lining is shed. This is caused by the degeneration of the corpus luteum, which secretes progesterone.

Question 9

What is CONTRACEPTION?

Answer 9

Prevention of the fertilisation of the secondary oocyte.

Question 10

What methods prevent the embryo from implanting into the lining of the uterus?

Answer 10

ANTI-IMPLANTATION METHODS.

Question 11

How are BIRTH CONTROL PILLS taken?

Answer 11

For most types of oral contraceptive, one pill is taken daily for 21 days, and stop (or take an inactive pill) for 7 days during menstruation.

Question 12

How do BIRTH CONTROL PILLS work?

Answer 12

They contain STEROID HORMONES that suppress ovulation. Usually synthetic rather than natural, as they are broken down less rapidly.

Question 13

What do birth control pills contain, and what do they do?

Answer 13

Some contain PROGESTERONE only but most contains both PROGESTERONE and OESTROGEN (combined oral contraceptives). These inhibit the secretion of LH and FSH from the anterior pituitary gland.

Question 14

Describe follicular activity throughout the days when a pill is taken.

Answer 14

Follicular activity remains low and consistent during days when the pill is taken. During days 21-28, when no pill is taken, follicular activity rise. Disappearance of oestrogen and progesterone allows LH and FSH to be secreted, and they stimulate the development of a follicle in the ovary.

Question 15

Describe OOGENESIS (5)

Answer 15

1) When a girl is still an embryo, GERMINAL EPITHELIAL CELLS in her developing ovaries divide to form diploid OOGONIA.
2) Within a few weeks, these begin to divide by meiosis, but only reaching prophase I. These are PRIMARY OOCYTES.
3) At puberty, some of these primary oocytes move from prophase I to end of first meiotic division, forming two haploid cells (the much bigger SECONDARY OOCYTE and the other POLAR BODY).
4) the secondary oocyte continues into second meiotic division, but doesn’t get further than metaphase II.
5) If the girl’s released secondary oocyte in her oviduct is fertilised, it becomes an ovum and continues division by meiosis.

Question 16

What surrounds developing oocytes?

Answer 16

Developing oocytes are inside follicles in the ovary, also produced by the germinal epithelium. The wall of the follicle contains several types of cell, including GRANULOSA CELLS, which surround and protect the oocyte, and secrete hormones.

Question 17

What is the function of GnRH in both sexes?

Answer 17

It stimulates the anterior lobe of the pituitary gland.

Question 18

What is the function of FSH in women, and where is it secreted from?

Answer 18

Secreted from the pituitary gland, FSH stimulates the development of follicles within the ovary.

Question 19

What is the function of oestrogen and where is it secreted from?

Answer 19

Secreted by ganulosa cells, it stimulates the repair of the uterus wall, and inhibits release of FSH (no new follicles develop incase pregnancy results) and also inhibits release of LH until shortly after ovulation. Then the level of oestrogen rises in a surge, which then stimulates the release of LH and FSH.

Question 20

What is the function of LH in women, and where is it secreted from?

Answer 20

Secreted from the pituitary gland, a surge of LH causes ovulation and developement of the corpus luteum. LH feeds back to inhibit oestrogen release, as a result, LH and FSH levels fall.

Question 21

What is the function of progesterone and where is it secreted from?

Answer 21

Secreted by the corpus luteum, it stimulates the thickening and vascularisation of the uterus wall (preparation for pregnancy).

Question 22

What is the function of LH (also known as ICSH) in men, and where is it secreted from?

Answer 22

Released by the anterior lobe of the pituitary gland, it stimulates the leydig cells that produce testosterone.

Question 23

What are LEYDIG CELLS?

Answer 23

Found adjacent to the seminiferous tubules in the testicle. They produce testosterone in the presence of luteinizing hormone (LH).

Question 24

What is the function of FSH in men, and where is it secreted from?

Answer 24

Released from the anterior pituitary gland, it stimulates the seminiferous tubules, including Sertoli cells, which produce sperm in response.

Question 25

What is the function of testosterone, and where is it secreted from?

Answer 25

Secreted from the leydig cells, it acts on the seminiferous tubules and stimulates sperm production. It feeds back to the hypothalamus and pituitary gland to switch off GnRH and ICSH release.

Question 26

What is the function of inhibin and where is it secreted from?

Answer 26

Secreted from Sertoli cells, inhibin feeds back to pituitary gland, switching off FSH release. Since the action of the interstitial cells and Sertoli cells are inhibited, less testosterone and inhibin are released as a result. The inhibition of the hypothalamus and pituitary is lifted and the process can start again. Due to the levels of the hormones and their effects, the process is not noticeably cyclical - there aren’t noticeable peaks and troughs in the levels of the hormones.

Question 27

Where is sperm stored?

Answer 27

The EPIDIDYMIS.

Question 28

How does the MORNING AFTER PILL work?

Answer 28

The pill works for up to 72 hours after unprotected sex. It contains synthetic progesterone-like hormone. If taken early, it reduces the chance of a sperm reaching and fertilising an egg, but in most cases, it probably prevents the embryo implanting into the uterus.

Question 29

What are the biological, social and ethical implications against birth control? (4)

Answer 29

AGAINST

1) Greater rate of infection with STDs (eg HIV)
2) Sexual conferred, may have contributed to breakdown of a higher percentage of marriages.
3) Increase in promiscuity
4) Children may be sexually active without parents’ knowledge

Question 30

What are the biological, social and ethical implications for birth control? (3)

Answer 30

FOR

1) Prevents unwanted pregnancies (and stress)
2) Increased control over their bodies for women
3) Urgent need to reduce world population growth

Question 31

Outline IN VITRO FERTILISATION (IVF) (5)

Answer 31

1) Ovulation is stimulated using hormones, aiming to cause several follicles to develop simultaneously.
2) Oocytes are collected from the woman using a tube, inserted through the vagina and cervix, into the oviducts, using ultrasound for guidance.
3) On the same day, semen is collected from the man. They are washed and placed into nutrient containing liquid to help them become active.
4) 4 hour later, each oocyte is placed in a separate dish, with approximately 100 000 mobile sperm in each. Alternatively, DNA of a sperm can be injected into an oocyte.
5) 3 day later, oocytes are collected and inspected for fertilisation. 2 are chosen and inserted into the uterus ( gives greater likelihood that at least one will implant while avoiding triplets or more babies).

Question 32

Briefly outline frozen embryo replacement

Answer 32

Embryo is frozen in liquid nitrogen and implanted into mother later. Suitable for women who have to undergo treatment that damage her ovaries (eg cancer patients, radiotherapy). Embryos may be mixed up, or the male partner may not want the baby (both peoples’ permission is required).

Question 33

What is the ethical debate around ‘unused’ embryos? (3)

Answer 33

1) Some people believe they are human.
2) Others think that the loss of embryos after IVF merely mirrors a natural bodily process, as many naturally conceived embryos are lost naturally before they can implant into the unterus.
3) Questions raised over whether embryos can be used as a source of pluripotent cells.

Question 34

Briefly outline intracytoplasmic sperm injection (ICSI)

Answer 34

Modification of IVF where sperm is actually injected into the egg, suitable for males who do not have normal/fully active/healthy sperm.
Increased risk of congenital abnormality.

Question 35

Briefly outline how SPERM BANKS work

Answer 35

Sperm are frozen (cryopreservation) and stored in sperm banks. Suitable for men who are facing medical treatment/illness that may make them infertile.
Sperm donors undergo DNA and health checks, and give their background to build up a DONOR PROFILE.