Chapter 12: Fertilisation and Baby Development

Question 1

Fertilisation

Answer 1

Sperm must come contact with ovum (egg) by sexual intercourse.

Question 2

1.

Answer 2

Requires male penis erection. Sexual stimulation causes blood to fill erectile tissue of penis (enlarging it).

Question 3

2.

Answer 3

Male orgasm involves contraction of epididymis, vas deferens and 3 glands = ejaculation.

Question 4

3.

Answer 4

Pathways: Seminiferous tubules → epididymis → vas deferens → urethra → penis → vagina → cervix → uterus → uterine tubes (only several 1000 of 100-300 million sperm reach uterine tubes where fertilisation occurs. Many die, reasons many sperm needed for fertilisation).

Question 5

Erectile tissue in vagina

Answer 5

Fills with blood, tightens increasing penis stimulation during sexual intercourse in aroused female. Also produces copious mucus by glands around cervix and vagina lubricating vagina for easy penis entry.

Question 6

Fertilisation 2 (in uterine tube)

Answer 6

Secondary oocyte (cell in ovary) is released during ovulation at metaphase 2 surrounded by 2 cell layers:

Question 7

Corona Radiata

Answer 7

Outer made of follicle cells. Joined by acidic material surrounding oocyte membrane.

Question 8

Zona Pellucida

Answer 8

Inner, a glycoprotein matrix surrounding oocyte membrane.

Question 9

Fertilisation 3:

Answer 9

Sperm acrosome has enzyme which breaks acid material in corona radiata, but amount of enzyme in 1 sperm is ineffective. So, reason why many sperm is needed to break it, allowing 1 sperm through corona radiata.

Question 10

2.

Answer 10

Sperm goes through corona radiata and reaches zona pellucida triggering acrosome reaction secreting digestive enzymes breaking glycoprotein matrix in zona pellucida. Gives sperm access to oocyte membrane for fusion of sperm and oocyte membrane.

Question 11

3.

Answer 11

When sperm enters, it activates meiosis completion for oocyte. Also activates secondary oocyte to form membrane around oocyte preventing access of other sperm, ensures only 1 haploid chromosomes set of sperm joins oocyte chromosomes.

Question 12

4.

Answer 12

Sperm enters oocyte it’s tail absorbed (with mitochondria) and head moves through ovum’s cytoplasm turning into male pronucleus (haploid sperm nucleus).

Question 13

5.

Answer 13

Sperm entrance also triggers secondary oocyte to form female pronucleus (haploid egg nucleus) that fuses with male pronucleus forming 1 nucleus with diploid chromosomes. Fertilisation completes and fertilised egg is zygote.

Question 14

Gestation

Answer 14

Time between fertilisation and birth (parturition). 280 days or 40 weeks.

Question 15

Birth stages

Answer 15

1st 2 weeks after fertilisation is germinal stage.

Week 3-8 is embryonic period.

Week 9-birth is foetal period.

Question 16

Birth trimesters

Answer 16

1st trimester: 1-12 weeks.

2nd trimester: 13-26 weeks.

3rd trimester: 27 week-birth.

Question 17

Hormonal changes required before birth

Answer 17

• Ligaments soften (makes pelvis easier to move apart for birth).
• Increase strength+sensitivity of uterus for birth.

Question 18

Embryo

Answer 18

Early baby development stage.

Question 19

Foetus

Answer 19

Unborn baby. Foetal (relates to foetus/baby).

Question 20

Maternal

Answer 20

Relates to mom

Question 21

Zygote —> blastocyst (baby development 1):

Answer 21

Zygote, fertilised egg (diploid single cell) becomes new life (totipotent stem cell).

Question 22

3-5 days

Answer 22

Zygote travels down uterine tube and divides by mitosis, producing identical totipotent cells (2, 4, 8). Twins occur by 2 totipotent cells separating, becoming 2 genetically identical embryos.

Question 23

6 days

Answer 23

Zygote reaches uterus and totipotent cells specialise, turning zygote to blastocyst.

Question 24

Blastocyst

Answer 24

Hollow cells ball filled with fluid. Made from inner cell mass and outer layer.

Question 25

Inner cell mass

Answer 25

Embryoblast. Has 30 embryonic pluripotent stem cells that differentiate to different human body cells to form embryo for developing foetus.

Question 26

Outer layer

Answer 26

Trophoblast. Forms placenta and other tissues for foetus development.

Question 27

Implantation

Answer 27

7-8 days after fertilisation, blastocyst sinks into uterus wall (endometrium). For food ensuring growth, development by absorbing nutrients from glands and blood vessels of endometrium. So, blastocyst developing to embryo relies on endometrium.

Question 28

What maintains endometrium?

Answer 28

High oestrogen and progesterone levels maintains endometrium, preventing it to breakdown. During embryonic period (early pregnancy), corpus luteum keeps hormone levels high till developing placenta takes over after 8-12 weeks.

Question 29

3rd week

Answer 29

Inner cell mass (embryoblast) of blastocyst differentiate from pluri to multipotent stem cells forming 3 germ layers that produce all the tissues of foetus.

Question 30

Ectoderm

Answer 30

Outer germ layer, forms outer layers of body. Skin, hair, cornea, epithelium of openings, nervous system, anterior pituitary.

Question 31

Mesoderm

Answer 31

Middle germ layer. Muscle, connective tissues, skeletal & smooth & cardiac muscles, lymphoid tissue, epithelium of kidneys, stomach.

Question 32

Endoderm

Answer 32

Inner germ layer. Epithelium of alimentary canal, bladder, urethra.

Question 33

Embryonic membranes

Answer 33

Blastocyst also forms this in embryonic period outside embryo for protection, nourishment

Question 34

Amnion

Answer 34

1st embryonic membrane to develop. Encloses embryo and amniotic cavity (formed within embryoblast).

Question 35

Amnion function

Answer 35

Secretes amniotic fluid, a shock absorber protecting embryo from physical injury, controls temp (keeping baby warm), free movement for baby.

Question 36

Chorion

Answer 36

Forms from blastocysts outer layer cells and becomes main foetal part of placenta by containing amnion (fuse chorion+amnion as amnion enlarges not amnion role). Attaches to mother via chorionic villi.

Question 37

Yolk sac and allantois

Answer 37

2 embryonic membranes helps form outer structure of umbilical cord.

Question 38

Placenta

Answer 38

Organ made from half foetal and half maternal tissues during 1st 3 months of pregnancy. Completely formed after 3 months to maintain endometrium (corpus luteum disintegrates). Placenta attached to foetus by umbilical cord

Question 39

Placenta function

Answer 39

Supplies nutrients and antibodies (immunity), remove waste (excretory), produce oestrogen and progesterone, provides nutrients & gas exchange for lungs by blood transport.

Question 40

Chorionic villi

Answer 40

After implantation, trophoblast of blastocyst develop finger-like projections from chorion that penetrate into endometrium called chorionic villi (has many blood vessels).

Question 41

Chorionic villi purpose

Answer 41

As chorionic villi penetrate into endometrium it’s surrounded by mother’s blood in endometrium allowing material exchange by diffusion and active transport, but foetal and maternal blood don’t mix because a cell layer separates them.

Question 42

Chroionic villi diffusion

Answer 42

Oxygen, nutrients from mother diffuse into foetal blood and waste leaves foetus by diffusing into maternal blood. The large number of chorionic villi provides surface area so substances pass.

Question 43

2 Umbilical arteries

Answer 43

Transports deoxygenated blood away from foetus to placenta, mother.

Question 44

Umbilical vein

Answer 44

Transports oxygenated blood from mom, placenta back to foetus.

Question 45

(By placenta) uterine arteries

Answer 45

Mom’s blood enters placenta by uterine arteries to exchange.

Question 46

(By placenta) uterine veins

Answer 46

Blood goes back to mom by uterine veins from placenta.

Question 47

Week 4 (1 month)

Answer 47

Blocks of mesodermal tissue becomes muscles and vertebrae of vertebral column. Heart, liver, brain begins developing. 3 clefts of throat becomes face, throat, associated glands.

Question 48

Week 5

Answer 48

Arm and leg buds appear.

Question 49

Week 8 (embryonic period)

Answer 49

Embryo is now human-form and now called foetus. All organs present but not functional. Sexual organs present allows to determine which sex.

Question 50

Week 16 (4th month)

Answer 50

18cm long, 100g. Foetus rapidly growing. Mom senses movement & mom’s abdomen will bulge. Heart rate 120-160.

Question 51

Week 20 (5th month)

Answer 51

25cm long, 300g. Foetal movements felt clearly.

Question 52

Week 24

Answer 52

27-35cm long, 500g. Obvious pregnancy.

Question 53

Week 28

Answer 53

38cm long, 1 kg. Vigorous movement, male testes descend into scrotum. Brain enlarges significantly.

Question 54

Week 32

Answer 54

41-45cm long, 1.8-2.2kg.

Question 55

Week 36

Answer 55

46-48cm long, 2.7kg. Foetus circulatory system developed but digestive system still needs to develop.

Question 56

Week 40

Answer 56

50cm long, 3.4 kg. Very slow growth as placenta begins to fail. Full term, no room to move. Male heavier than female.

Question 57

Changes to mom

Answer 57

Growing abdomen and foetus, pressing on bladder feeling like it’s filled with urine (more urination).

Breasts enlargement because development of milk secreting tissues by hormones: progesterone from corpus letuem, prolactin from pituitary and oestrogen.

Question 58

Changes to mom pt.2

Answer 58

Increased heart size and urine production for extra blood flowing through placenta.

Emotional changes by hormones and pregnancy fears.