11.4 Reproduction

Question 1

Outline the process of spermatogenesis

Answer 1

• Spermatogenesis describes the production of spermatozoa in the seminiferous tubules of the testes
  
  • First, the germinal epithelium divide by mitosis to produce spermatogonia
  • Spermatogonia then undergo a period of growth and mitosis to form two primary spermatocytes
  • This is followed by two meiotic divisions that result in four haploid daughter cells (spermatids)
  • These haploid cells then differentiate to form spermatozoa cells
  • The developing sperm cells are nourished throughout by the Sertoli cells

Question 2

State the role of LH in spermatogenesis

Answer 2

Stimulates the interstitial cells (Leydig cells) to produce testosterone

Question 3

State the role of FSH in spermatogenesis

Answer 3

Stimulates the 1st meiotic division of spermatogonia

Question 4

State the role of testosterone in spermatogenesis

Answer 4

Stimulates the 2nd meiotic division of spermatogonia and the maturation of spermatozoa through differentiation

Question 5

Outline the processes involved in oogenesis within the ovary

Answer 5

• Oogenesis is the process by which female gametes are produced
  
  • It begins during foetal development
  • Oogonia are formed by mitosis
  • Oogonia undergo growth and become primary oocytes
  • The primary oocytes begin the first meiotic division but stop in prophase I until puberty
  • At puberty, some follicles develop each month in result to FSH
  • During this development, primary oocytes complete the first meiotic division and form two cells of different sizes, one of which is a polar body which eventually degenerates
  • The larger cell proceeds to meiosis II, but stops at prophase II
  • Meiosis II is completed if the cell is fertilized
  • Upon fertilisation, ovum and second polar body formed

Question 6

Outline the role of the epididymis in the production of semen

Answer 6

Testicular fluids removed, concentrating spermatozoa; Spermatozoa mature and gain motility

Question 7

Outline the role of the seminal vesicle in the production of semen

Answer 7

Adds a large amount of fluid (~70%), which is contains fructose for energy

Question 8

Outline the role of the prostate gland in the production of semen

Answer 8

Adds more fluid (~30%) which is alkaline, and therefore neutralises vaginal acids

Question 9

Compare spermatogenesis and oogenesis in terms of when the begin

Answer 9

Spermatogenesis: Starts at puberty
Oogenesis: First stages occur in foetal development

Question 10

Compare spermatogenesis and oogenesis in terms of numbers of gametes produced/unit time

Answer 10

Spermatogenesis: millions of gametes daily
Oogenesis: one gamete every ~28 days

Question 11

Compare spermatogenesis and oogenesis in terms of when they stop

Answer 11

Spermatogenesis: continues throughout adult life of males
Oogenesis: stops at menopause

Question 12

Compare spermatogenesis and oogenesis in terms of number of gametes produced per germ cell

Answer 12

Spermatogenesis: 4 sperm per germ cell
Oogenesis: 1 mature ovum per germ cell

Question 13

List two similarities between the processes of spermatogenesis and oogenesis

Answer 13

• Result in the formation of haploid gametes

* Involve meiosis, growth and mitosis

Question 14

Explain how the structure of the placenta helps maintain pregnancy

Answer 14

• Disk-shaped structure connected to the foetus by an umbilical cord
  
  • Formed when embryonic tissue grows into the uterine wall
  • Placental villi increase surface area
  • Foetal capillaries in placent

Question 15

Explain how the function of the placenta helps maintain pregnancy

Answer 15

• Transfer of nutrients and antibodies from mother to foetus
  
  • Transfer of excretory products from foetus to mother
  • Foetal gas exchange
  • Secretion of oestrogen and progesterone

Question 16

Describe the process of fertilisation

Answer 16

• Spermatozoa attracted by a chemical signal from the secondary oocyte.
  
  • Spermatozoa break through layers of follicle cells from the zona pellucida and bind to the zona pellucida.
  • The acrosome merges with the cell membrane of the spermatozoa, releasing proteolytic enzymes. A path is digested through the zona pellucida.
  • The spermatozoa moves to the oocyte cell membrane and releases its nucleus into the oocyte. This stimulates the cortical reaction and the completion of meiosis II by the oocyte (becomes ovum).
  • Cortical reaction leads to the hardening of the zone pellucida, forming the ‘fertilisation membrane’ around oocyte. This prevents entry to other sperm.
  • Entry of the sperm into the oocyte is the stimulus for completion of the 2nd meiotic division. The mature ovum is produced along with a second polar body.
  • The male sperm nucleus fuses with the female ovum nucleus. This is the act of fertilisation.
  • The new nucleus now has two sets of chromosomes, and therefore the cell is now diploid, and known as a zygote.

Question 17

Outline the role of hCG in early pregnancy

Answer 17

• Human Chorionic Gonadotrophin (hCG) is secreted by the embryo once is it implanted in the wall of the uterus.
  
  • This prevents the corpus luteum from degenerating, allowing it to grow and continue producing oestrogen and progesterone.
  • This maintains the endometrium.
  • Eventually the placenta will take the place of the corpus luteum, secreting oestrogen and progesterone.

Question 18

Outline early embryo development up to the implantation of the blastocyst

Answer 18

• Fertilisation occurs within the fallopian tube.
  
  • When zygote is formed, it travels down the fallopian tube, dividing by mitosis to create a solid ball of cells called blastomeres, which organise themselves to form the blastocyst, which is also filled with fluid.
  • The inner mass of cells which will develop into the embryo
  • The outer layer which will develop into the placenta
  • When the blastocyst reaches the uterus, it will embed in the endometrium

Question 19

Describe the function of the amniotic sac and amniotic fluid

Answer 19

• The embryo develops in a fluid filled sac called the amniotic sac, which is filled with amniotic fluid.
  
  • Protects and supports foetus.
  • Amniotic fluid prevents dehydration of tissues while the amniotic sac provides an effective barrier against infection.

Question 20

Outline the role function of the placenta

Answer 20

The placenta is attached to the foetus, allowing for exchange of materials between the mother and child. This occurs through diffusion and active transport.

Question 21

List 6 materials transported from maternal blood to foetal blood (supply)

Answer 21

• Oxygen
  
  • Water
  • Glucose
  • Hormones
  • Amino acids
  • Antibodies

Question 22

List 3 materials transported from foetal blood to maternal blood (excretion)

Answer 22

• Carbon dioxide
  
  • Urea
  • Water

Question 23

Outline the process of birth and its hormonal control

Answer 23

• The placenta secretes progesterone, and in the later weeks of pregnancy progesterone levels in the blood are very high.
  
  • The onset of childbirth is caused by the foetus stretching the walls of the uterus, and a dramatic fall in progesterone levels in the blood.
  • Oxytocin is released by the pituitary gland in response to stretching of the uterine wall. It inhibits progesterone, which was inhibiting uterine contractions.
  • Oxytocin stimulates uterine contractions, initiating the birthing process.
  • The contraction of the uterine wall causes further stretching, which triggers more oxytocin to be released.
  • Positive feedback: as the cervix stretches further, more oxytocin is released, which makes the cervix stretch more
  • Contractions become stronger and more frequent meaning that the amnion ruptures, the baby is born, and then the placenta is released as ‘afterbirth’.