Reproduction: fertilisation and implantation - pregnancy and development

Question 1

Where does fertilisation take place?

Answer 1

Uterine tube

Question 2

When must sperm be introduced to the female and what are the time spans involved? (3)

Answer 2

• sperm must enter 5 days before ovulation
• sperm viable for 5 days
• oocyte available for 12-24 hours

Question 3

What are the movements of the oocyte in the uterine tube? (4)

Answer 3

• fluid causes oocyte to move at ovulation
• peristaltic contractions move oocyte towards uterus - minutes
• Cilia move oocyte towards uterus - days
• Entire trip takes 4 days

Question 4

What are the sperm movements in the uterine tube? (4)

Answer 4

• Millions of sperm deposited into vagina during sex
• Swim to uterus and uterine tube
• Survive 5 days in tract
• Only few hundred sperm make it to uterine tube

Question 5

How can sperm become capacitated and where does this occur?

Answer 5

• Occurs in reproductive tract

- Tail movement causes plasma membrane to be altered

Question 6

What are the events of fertilisation before the egg is penetrated? (4)

Answer 6

1. Several sperm generally reach ovum and penetrate corona radiata
2. Sperm bind to sperm-binding protein
3. Acrosome reaction triggered - acrosomal enzymes released
4. Enzymes break through zona pellicuda allowing sperm to access oocyte

Question 7

What are the events of fertilisation after the egg is first penetrated? (3)

Answer 7

1. First sperm to access oocyte binds to receptor on plasma membrane
2. Sperm transported into cytoplasm - fusion
3. Sperm-binding proteins become inactivated and zona pellucida hardens to stop other sperm

Question 8

What are the events of fertilisation once the sperm has fully penetrated the egg and pre zygote formation? (5)

Answer 8

1. Fusion stimulates 2nd meiotic division of oocyte
2. Oocyte –> ovum
3. Sperm plasma membrane disintegrates
4. Chromosomes from sperm and ovum migrate to centre
5. DNA replication –> zygote

Question 9

What are the 3 stages 3-4 days post fertilisation?

Answer 9

1. Zygote
2. Early cleavage (4-cell stage)
3. morula (mitotic divisions - still totipotent)

Question 10

What and when does a blastocyst occur? (5)

Answer 10

• Zona pellucida is lost
• Outer cell layer = trophoblast (becomes placenta)
• Inner cell mass (becomes embryo)
• Fluid filled cavity = blastyocoele

4-5 days post fertilisation

Question 11

What is implantation and when does it occur? (5)

Answer 11

6-7 days post fertilisation

• Trophoblast responsible for implantation
• Secretes enzymes that provide nourishment for embryo
• Secretes paracrines that stimulate decidual response
• Infiltrates endometrial tissue (placenta)

Question 12

What does the blastocyst attach itself too and what does this lead to? (2)

Answer 12

• Endometrial lining (increases glycogen stores)

- Trophoblast penetrates endometrium

Question 13

What disorders can arise from implantation? (3)

Answer 13

Ectopic pregnancy:

• Fertilised ovum implants in fallopian tube
• Growth of fetes and placenta causes issues
• Have to kill/remove fetus

Question 14

What is gestation and how long does it last? (4)

Answer 14

• Period from conception to birth
• 9 months
• Consists of 3 trimesters
• Dated from last period before conception

Question 15

What are the 3 components of a blastocyst?

Answer 15

• Single layered sphere of cells (trophoblast) required for implantation
• Fluid filled cavity (blastocoele) develops into amniotic sac
• Inner cell mass - develops into fetus

Question 16

What does the trophoblast form once implanted? (2)

Answer 16

Chorion (2 layers)

Produces more digestive enzymes which produce more cavities - placenta development

Question 17

What are the stages of placenta development? (3)

Answer 17

Fetal component - chorionic villi
Maternal component - endometrial tissue
Blood flow to placenta - uterine artery and vein/umbilical

Question 18

What is the placenta doing after 5 weeks? (2)

Answer 18

Heart beating

Breathing

Question 19

What is the role of the placenta? (3)

Answer 19

• Allows for free exchange of nutrients, energy & waste
• Provides an immunological barrier between mother and fetus
• Secretes hormones that support the development of the fetus

Question 20

What are the 6 placental hormones?

Answer 20

Human Chorionic gonadotrophin
Estrogen
Progesterone
Human Chorionic somatotrophin 
Relaxin
Placental PTHrp

Question 21

What prevents further ovulation during pregnancy?

Answer 21

Progesterone - inhibts GnRH, LH and FSH

Question 22

What are the maternal changes during the first trimester of pregnancy? (6)

Answer 22

• First trimester - 1-14 weeks
• 1-2kg weight gain
• Increased cardiac output etc
• Increased breast size
• Increase in uterus
• Morning sickness

Question 23

What are the maternal changes during the second trimester of pregnancy? (5)

Answer 23

• 2nd trimester 14-28 weeks
• Increase of weight
• Heartburn
• Constipation
• Improvement of wellbeing

Question 24

What are the maternal changes during the third trimester of pregnancy? (3)

Answer 24

• Deeper breaths
• Braxton-Hicks contractions of the uterus
• Tired and anxious

Question 25

What is eclampsia? (4)

Answer 25

• Pregnancy disorder
• Elevated blood pressure
• Rapid increase
• Life threatening

Question 26

What are the 2 main disorders of pregnancy?

Answer 26

• Eclampsia

- Diabetes melitus