Sexual reproduction in Humans

Question 1

Sexual intercourse (copulation)

Answer 1

1. Sexual arousal
2. Penis becomes erect (blood pumped into into spongy tissue)
3. Semen containing 100 mil sperms ejaculated into vagina
4. Sperms swim up the oviduct to meet egg
5. Only one sperm can fertilise egg

Question 2

Define fertilisation

Answer 2

• haploid nucleus of sperm
• haploid nucleus of ovum
• fuse, diploid zygote

Question 3

What happens during fertilisation

Answer 3

• to happen, sperm must penetrate ovum (surrounded by few layers of follicle cells)
• acrosome releases enzyme that:
  1. disperse follicle cells
  2. break down part of egg membrane
• only 1 sperm enters ovum
• once it enters, membrane of ovum (zona pellucida) hardens, no more can enter

Question 4

Development of embryo stages

Answer 4

1. Implantation
2. Development of placenta
3. Development of amniotic sac

Question 5

Implantation

Answer 5

• occurs when embryo embeds itself into uterine lining
• cilia lining in oviduct sweep fertilised ovum towards uterus
• zygote undergoes mitosis, form embryo (as it travels along)
• takes abt 5 days for embryo to reach uterus
• embryo may float freely for another 2 days before implanting into uterine lining (implantation occurs 7 days aft fertilisation)

Question 6

Development of placenta

Answer 6

• after implantation, villi (finger-like) grow frm embryo into uterine lining
• villi contain blood capillaries of embryo
• embryonic villi + uterine lining make up placenta
• umbilical cord attaches embryo to placenta

Question 7

Development of amniotic sac

Answer 7

• membrane that encloses embryo in fluid-filled space (amniotic cavity)
• fluid is amniotic fluid
• embryo develops major organs (10-12 weeks) aft fertilisation, becomes foetus

Question 8

Fetal blood system

Answer 8

• fetal blood capillaries not connected to maternal ones (separated by thin layer of tissue, 1 cell thick)
• they’re surrounded by maternal blood spaces (pools of blood for diffusion)
• diffusion of substances occur across layer of tissue

Question 9

Why is the fetal and maternal blood system separated?

Answer 9

• mother’s blood pressure too high
• blood types may be diff
• mixing of diff blood types may lead to agglutination (fatal)

Question 10

Functions of placenta

Answer 10

• allows oxygen, glucose and nutrients to diffuse from m blood to f blood
• excretory product diffuse from f blood to m blood
• produces progesterone, maintain and repair uterine lining
• allows antibodies to diffuse from m to f, protect f against diseases

Question 11

Functions of umbilical cord

Answer 11

• made of 2 umbilical arteries, 1 umbilical vein
• umbilical vein: transports oxygenated blood, glucose, nutrients from placenta to fetus
• umbilical arteries: transport deoxygenated blood, metabolic waste products from fetus to placenta

Question 12

Functions of amniotic fluid

Answer 12

• amniotic sac encloses fetus in amniotic cavity (contains amniotic fluid)
• allows fetus to move freely, promote muscular development
• lubricates, reduce friction in vagina during birth
• cannot be compressed, protects fetus from physical injury by absorbing shock