Grade 12 Human Reproduction Part 5 Gestation (Pregnancy)

Question 1

Define gestation:

Answer 1

• The time between **conception (fertilisation) **and birth, during which the embryo and then the foetus develops in the uterus.
• Usually about 40 weeks (280 days)

Question 2

What are the two phases of pre-natal development:

Answer 2

1. Early development (0 - 2 months)
2. Later development (3 months to birth)

Question 3

Discuss the early development phase in prenatal development:

Answer 3

1. Fertilisation
2. Blastocyst and implantation formation
3. Embryo formation

Question 4

Discuss the process of fertilisation in detail: (10)

Answer 4

• Occurs in fallopian tube - when nuclei of the sperm and egg fuse to form zygote
• Sperm lives for 48 hours and egg for 24 hours
• If fertilisation doesnt occur - gametes will degenerate

1. After semen is deposited in vagina, **sperm move through cervix, uterus and into fallopian tubes **until it reaches the egg
2. Egg, surrounded by follicle cells, is sucked into fallopian tube by the action of** FIMBRIAE**
3. Fertilisation usually occurs in the tp part / outer part of hte fallopian tube
4. Thousands of sperm surround the egg
5. Hydrolytic enzymes released from the acrosomes break down follicle cells
6. Only one sperm penetrates the membrane of the egg - the tail is discarded
7. Nuclei of the sperm and egg fuse forming a diploid zygote
8. A f**ertilisation (egg) membrane froms **immediately, which prevents other sperm from entering the egg

Question 5

Discuss the BLASTOCYST formation and IMPLANTATION phase of prenatal development:

Answer 5

Diploid zygote divides immediately by **mitosis to form two cells
Each of these divides repeatedly until a solid ball of cells, the morula** (resembles a mulberry) is formed
Morula
* develops into a hollo, fluid filled ball of cells, the blastocyst
* Outer cells forming the wall of the blastocyst form a layer known as TROPHOBLAST (trophy - relates to feeding)

Inner cell mass - develops form trophoblast

As developing embryo **moves along fallopian tube **towards uterus by combination of peristaltic movements & rythmic beating of the tube’s cilia

Implantation - uterus and blastocyst sinks into thickened, highly vascular endometrium. Implantation occurs after 10 days

Question 6

Describe the process of implantation:

Answer 6

Implantation** - uterus and blastocyst sinks into thickened, highly vascular endometrium. Implantation occurs after 10 days

Question 7

What causes the movement of the embryo along the fallopian tube?

Answer 7

As developing embryo **moves along fallopian tube **towards uterus by combination of peristaltic movements & rythmic beating of the tube’s cilia

Question 8

Discuss the formation of the embryo in the prenatal development:

Answer 8

1. Inner cell mass forms the embryo, amnion and yolk
2. Trophoblast (later called chorion) develops **villi ** (finger like projections) that grow into endometrium to form the placenta
3. Embryo develops into three layers - ectoderm, endoderm and mesoderm
4. Differentiation takes place - major organs appear, critical time, risk of embryonic malformations

Last from third week to end of week 8, after fertilisation

Question 9

The inner cell forms the embryo, amnion and yolk sac. Explain each of these shortly.

Answer 9

• Embryo - Future baby
• Amnion - membrane that becomes fluid filled
• Yolk sac - which forms part of umbillical cord

Question 10

The period of differentiation is a most critical period as embryological malformations can lead to birth defects caused by:

Answer 10

• drugs
• viruses (geman measles)
• environmental factors - pesticides

Question 11

Study the diagrams on page 107 - 108 of your textbook.

Question 12

How is the pregnancy maintained?

Answer 12

Through high levels of progesterone - keeping the endometrium thickened and also by preventing menstruation

Question 13

For how long does the later development phase or foetal period of pregnancy last?

Answer 13

From nine weeks till end of pregnancy.

Question 14

What major changes take place during the later development / foetal period of pregnancy?

Answer 14

• Some cell differentiation
• Mostly rapid growth of the body
• As foetus approaches term, bones ossify, much subcutaneous adipose (fat) tissue is formed and **antibodies **enter the foetus via the placenta to fight disease.
• Foetus turns so that head turns downwards towards cervix

Question 15

What is an ultrasound?

Answer 15

• Technology that uses high-pitched sound waves that cannot be heard by human ear.
• Sound is bounced off a solid structure e.g. embryo and foetus
• Echoes form ultrasound or sonogram image
• Enables viewing of foetal age, size, growth during normal development
• Early diagnosis of complications

Question 16

Study the table on page 110 - 111 of our textbook on human development during gestation.

Question 17

What is the difference between an embryo and a foetus?

Answer 17

Embryo = developing zygote until 8 weeks (all organs of body are being formed)
**Foetus **= From 9 weeks until birth, after organs have developedGrowth and organ specialisation takes place during this time. See diagram page 111 of textbook.

Question 18

Explain the structure of the PLACENTA

Answer 18

• A disc shaped temporary organ richly supplied wth material and foetal blood vessels.
• It connects the foetus with its mother’s blood at the end of the umbillical cord.
• It develops from the chorion and its villi that penetrate the endometrium.
• The villi provide a **large surface area of attachment of the placenta to the endometrium. **
• Each villus contains a capillary network, which provides a large surface area for exchagne of substances by diffusion.
• Surrounded by the mother’s blood, so that mother’s blood supply and foetal capillaries are very close together
• BUT Foetal and Mother’s blood DO NOT MIX - foetal capillaries have thin walls.
• Sustances move between maternal and foetal blood by** DIFFUSION**. **

Question 19

Discuss the 5 main functions of the placenta:

Answer 19

1. Nutrition of embryo = Oxygen and dissolved food substances such as glucose, amino acids, fatty acids, ions and vitamins passes from mother to foetal blood system
2. Excretion = foetal waste. Metabolic waste such as urea and carbon dioxide pass into maternal blood system
3. Gaseous exchange = Oxygen transported from the placenta to foetus, carbon dioxide from foetus to placenta
4. **Microfilter & Maternal antibodies ** = Prevents the entry of pathgenic organisms into the blood of the foetus - provides foetus with passive immunity
5. **Endocrine function **= After12 weeks of pregnancy the placenta takes over the function of the corpus luteum. Secretes oestrogen and large quantities of progesterone, which pevents break down of endometrium and maintains pregnancy.

Question 20

What is the chorion?

Answer 20

• Outermost extra-embryonic membrane surrounding the embryo.
• During implantation, finger-like projections of the throphoblast, challed** chorionic villi**, develop around the blastocyst
• Most of villi disappear, but where chorion is attached to uterine wall, the villi enlarge and become more vascular to form placenta.

Question 21

What is the the umbilical cord?

Answer 21

• Foetus is connected to the placenta by umbillical cord.
• Consists of 2 arteries and 1 vein, surrounded by connective tissue.

Question 22

What functions does the umbillical cord perform?

Answer 22

• 2 arteries carry deoxygenated blood (O2-poor) and waste (e.g. carbon dioxide and other excretory waste products) from foetus to placenta
• **Umbillical vein **carries oxygenated blood (O2 rich), rich in nutrients from placenta to foetus.

Question 23

What is the amnion?

Answer 23

• Tough membrane lining the chorion.
• Encloses the amniotic cavity, filled with amniotic fluid.
• Amniotic fluid contains:
• water
• discarded foetal cells,
• waste products and
• micro-organism.

Question 24

Discuss the function of the amnion:

Answer 24

1. Provides a watery medium in which the foetus can freely move and develop
2. Protects foetus from shock, dehydration and temperature changes
3. Provides a medium in which foetus can practice breathing and swalllowing
4. **Holds urine **as it is released from foetus

Question 25

Study the diagram on page 112 of your textbook and page 2.39 of Answer Series as well as Development of foetus table on page 2.39 of Answer series.

Question 26

List the stages of pregnancy:

Answer 26

• First trimester (first 12 weeks)
• Second trimester (weeks 13 - 28)
• Third trimester (weeks 29 - 40)

Question 27

Describe changes that take place during the FIRST TRIMESTER of pregnancy: (7)

Answer 27

1. Menstrual period stops
2. Tiredness
3. Cravings/ distaste for certain foods
4. Mood swings
5. 70% pregnant people experience morning sickness/ nausea
6. Occurs at anytime
7. Breasts: tender & swollen, areola and nipples darken

Question 28

Describe changes that take place during the SECOND TRIMESTER of pregnancy: (6)

Answer 28

1. More energy
2. Morning sickness lessens/ disappears
3. Uterus expands up to 20x
4. Visible ‘baby bump’ by end of 2nd trimester
5. ‘Quickening’ (movement of foetus) – 16 weeks
6. Patches of darker skin on face – ‘mask of pregnancy’

Question 29

Describe changes that take place during the THIRD TRIMESTER of pregnancy: (13)

Answer 29

1. Final weight gain - rapid foetal growth
2. More frequent & stronger movements of foetus
3. Difficulty breathing – foetus pushes against diaphragm & lungs
4. Abdomen of pregnant person changes shape/ drops low
5. Foetus turns into downward position
6. Engagement of the head – foetal head descends into pelvic cavity
7. Breathing becomes easier -less pressure on upper abdomen
8. Reduced bladder capacity
9. Backache
10. Breasts tender
11. May leak colostrum (watery pre-milk fluid)
12. Braxton-Hicks (uterus) contractions preparation for labour
13. Frequent/ painful contractions sign of real labour

Question 30

What is foetal Alcohol Syndrom (FAS)?

Answer 30

• Foetus is well protected BUT can be affected by diet, health, lifestyle of mother
• Condition that develops in a foetus exposed to high levels of alcohol during pregnancy.
• Alcohol passes placenta and affects the growth and development of the foetus
• **Permanent nervous tissue damage **- the FAS baby has MENTAL and PHYSICAL disabilites from birth to adulthood

Question 31

What are some features of FAS?

Answer 31

In New Born:
* Short stature
* Low birth weight
* Poor weight gain
* Microcephaly

Other features as child gets older:
* Poor attention span
* Poor motor skills
* Slow language development
* Hyperactivity
* Learning disabilities
* Poor social skills

Note: There is NO treatment. Mentally and socially defective for life. NB: Don’t drink while pregnant. But, that means woman must know that she is pregnant… often found out at a later stage, crucial stage already passed.