Female Sexual Reproduction in Animals (DONE)

Question 1

What is oogenesis?

Answer 1

Production of female gametes.

Question 2

What is a primary follicle?

Answer 2

Ball of diploid cells surrounding an primary oocyte. Follicle cells/granulosa nourish the oocyte.

Question 3

What is a Graafian follicle?

Answer 3

A mature secondary follicle, which contains a secondary oocyte ready for ovulation.

Question 4

What is the function of the corpus luteum?
What happens when there is no pregnancy?
(3 marks)

Answer 4

• Secretes progesterone and oestrogen when fertilisation takes place.
• Progesterone maintains uterus lining so that implantation into the endometrium can occur.
• No pregnancy results in corpus luteum breaking down and stops releasing progesterone. Period occurs.

Question 5

What is the process called when a Graafian follicle turns into a corpus luteum after ovulation?

Answer 5

Lutenisation

Question 6

What happens before birth in oogenesis?

Answer 6

Oogonia divide by mitosis and enlarge to produce primary oocytes.

Question 7

What happens between birth and puberty in oogenesis?

Answer 7

Primary oocyte being meiosis 1 but development is stopped at prophase 1 (crossing over of bivalents).

Question 8

What happens at puberty for oogenesis?
(4 marks)

Answer 8

• One of the follicles containing a primary oocyte matures. It completes meiosis 1 and results in two structures being formed (First polar body and a secondary oocyte).
• Secondary oocyte starts meiosis 2 and stops at metaphase 2.
• Meiosis 2 is only completed if fertilizations occurs and forms an ovum (n).
• If fertilizations does not occur, ovum dissolves and menstruation occurs.

Question 9

What is capacitation and what are the changes to the spermatozoa?

Answer 9

Physiological changes spermatozoa must undergo in order to have the ability to penetrate and fertilize an egg.
Increases motility
Increases membrane permeability due to the removal of cholesterol and glycoproteins to allow fertilization and fusion with egg.

Question 9

Where does capacitation take place?

Answer 9

Increased motility in the epididymis
Fertilization competence and hypermotility in the female reproductive tract

Question 10

Describe the sequence of events that happen during the acrosome reaction.
(4 marks).

Answer 10

Spermatozoa passes through the corona radiata and penetrates the zona pellucida.
1. Sperm head makes contact with zona pellucida and calcium ions enter sperm causing the acrosome membrane to fuse with the sperm membrane.
2. Hydrolytic enzymes released from acrosome to digest zona pellucida.
3. Fusion of sperm and secondary oocyte membranes.
4. Sperm DNA enters egg, triggering oocytes completion of meiosis 2.

Question 11

Describe the sequence of events for the cortical reaction.
(3 marks)

Answer 11

1. Entry of sperm nucleus causes wave of depolarisation.
2. Cortical granules fuse with the cell membrane and modify the zona pellucida to form the feralization membrane (this prevents polyspermy)
   3, Nuclei of the sperm and ovum fuse to form a zygotic nucleus.

Question 12

Describe the sequence of events after fertilisation.
Also describe what is formed.
(3 marks)

Answer 12

• Zygote moves down the oviduct and divides many times by mitosis to form a ball of cells known as a blastocyst.
• This is known as cleavage
• By day 7 a blastocyst is formed, which is a hallow ball of undifferentiated cells (inner cell mass)

Question 13

Describe what happens during implantation.
(2 marks)

Answer 13

• Blastocyst moves into the uterus where it attaches and sink into the endometrium
• Cells on the outside of blastocyst (trophoblast cells) form the trophoblastic villi, which increase the surface area for absorption of nutrients.

Question 14

How is the placenta formed?

Answer 14

Developed from the trophoblastic villi.

Question 15

Describe the follicular stage in the menstrual cycle. (FSH)
(3 marks)

Answer 15

• Anterior pituitary gland secretes follicle stimulating hormone (FSH)
• FSH stimulates maturation of a primary follicle to a secondary follicle
• Maturing follicle will secrete oestrogen

Question 16

What is the role of oestrogen in the menstrual cycle?
(3 marks)

Answer 16

• Stimulates the growth of lutenising hormone (LH) which is secreted by the pituitary gland
• Inhibits secretion of FSH
• Triggers the growth of the endometrium (blood supply increases)

Question 17

Describe the ovulation stage in the menstrual cycle. (LH)
(3 marks)

Answer 17

• Caused by a peak LH levels (day 14)
• LH stimulates the secretion of FSH and as a result oestrogen levels decrease
• LH stimulates the conversion of the Graafian follicle into corpus luteum

Question 18

Describe the luteal phase in the menstrual cycle. (Progesterone)
(2 marks)

Answer 18

• The corpus luteum secretes progesterone
• Progesterone maintains endometrium and inhibits secretions of FSH and LH

Question 19

What will occur if there is no implantation during the menstrual cycle?

Answer 19

• Low levels of FSH and LH cause the corpus luteum to degenerate
• Progesterone levels decrease so LH and FSH no longer inhibited
• Low progesterone and oestrogen levels cause the endometrium to breakdown
  causing menstruation

Question 20

Describe what happens after the first few days of fertilisation

Answer 20

The blastocyst begins to secrete human chorionic gonadotrophin (hCG)

Question 21

What is the importance of hCG?

Answer 21

Maintenance of the corpus luteum for the first 16 weeks of pregnancy

Question 22

What is the importance of the corpus luteum during pregnancy?

Answer 22

Secretes oestrogen and progesterone which inhibit LH and FSH

Question 23

What is the importance of progesterone in pregnancy?
(2 marks)

Answer 23

• Maintains the wall of the endometrium
• Suppresses the uterine wall’s ability to contract by inhibiting secretions of oxytocin

Question 24

What is the importance of oestrogen in pregnancy?
(2 marks)

Answer 24

• Stimulates growth of the uterus to accommodate the foetus
• Stimulates growth and development of mammary glands

Question 25

What happens to the corpus luteum during pregnancy?

Answer 25

Degenerates and is replaced by the placenta to take responsibility over secretions of progesterone and oestrogen.

Question 26

What happens to hormones at birth?
(3 marks)

Answer 26

• Just before birth oestrogen levels increase and progesterone levels decrease
• Oxytocin secreted by the posterior pituitary gland which stimulates contraction of the uterine wall, which stimulates secretion of more oxytocin (positive feedback)
• Prolactin is secreted by the anterior pituitary gland during and after birth, which stimulates production of milk by mammary glands

Question 27

Describe the functions of the placenta.
(3 marks)

Answer 27

• Exchange gases and nutrients, waste products, oxygen and carbon dioxide
• Providing barrier between maternal and foetal blood
• Secretion of hormones ( hCG, progesterone and oestrogen)

Question 28

How does the placenta provide a barrier between maternal and foetal blood?
(2 marks)

Answer 28

• Protects foetal capillaries from higher blood pressure by stepping down pressure
• Mother’s antibodies provide passive immunity

Question 29

How are chorionic villi within the placenta adapted?
(4 marks)

Answer 29

• Many chorionic villi to provide large surface area for exchange
• Short diffusion pathway (thin walls)
• Counter-current flow to maintain concentration gradient
• High blood pressure in mother to keep blood flowing