Chapter 8 - Third Month to Birth: The Fetus and Placenta

Question 0

What characterize the fetal period?

Answer 0

• Maturation of tissues and organs

- Rapid growth of the body

Question 1

When is the fetal period?

Answer 1

The period from the begining of 9th week to birth

Question 2

Sitting hight

Answer 2

• Crown-rump lenght (CRL)

- Lenght of the fetus

Question 3

Standing hight

Answer 3

• Crown-heel lenght

- Lenght of the fetus

Question 4

How long is the pregnancy?

Answer 4

• 280 days, or 40 weeks after the normal mensturation

- 266 days or 38 weeks after fertilization

Question 5

When does the head constituet 50% of the CRL?

Answer 5

At the beginning of the 3rd month

Question 6

When is the head 1/3 of the CHL?

Answer 6

By the beginning of the 5th month

Question 7

When is the head 1/4 of the CHL?

Answer 7

At the time of birth

Question 8

When does the face become more human looking?

Answer 8

During the 3rd month

Question 9

When is the primary ossification center are present in the long bones and skull?

Answer 9

By the 12th week

Question 10

When does the external ganglia develop to such a degree that the sex of the fetus can be determined by external examination (ultrasound)?

Answer 10

By the 12th week

Question 11

When can reflex activity be avoked in aborted fetuses, indicating muscular activity?

Answer 11

At the end of the 3rd month

Question 12

When does the fetus lengthen rapidly?

Answer 12

During the 4th and 5th months

Question 13

First half of intrauterine life

Answer 13

• CRL 15 cm = half of the total length of a new born
• Over 500 g
• Lanugo hair
• Eye browns and head hair

Question 14

When can the movements of the fetus be felt by the mother?

Answer 14

During the 5th month

Question 15

Second half of intrauterine life

Answer 15

• Wight will increase, especially during the last 2,5 months..(3,200 g)

Question 16

Premature

Answer 16

Fetuses born much earlier

Question 17

Postmature

Answer 17

Fetuses born later

Question 18

Placenta

Answer 18

The organ that facilitates nutrient and gas exchange between the maternal and fetal compartments

Question 19

When does the major changes in the placenta occure?

Answer 19

As it begins the 9th week

Question 20

Where does the fetal components of the placenta derive from?

Answer 20

• Derive from the trophoplast and extraembryonic mesoderm (The chorionic plate).
• from the summary: Derive from chorion frondosum or villous chorion

Question 21

Where does the maternal components of the placenta derive from?

Answer 21

• uterine endometrium

- From the summary: the maternal portion derive from decidua basalis

Question 22

Where is the intervillous lakes of maternal blood?

Answer 22

It is in the space between the chorionic and decidual plates

Question 23

Where can we find the villous tree(fetal tissue)?

Answer 23

They grow into the maternal blood lakes and are bathed in them

Question 24

Is the fetal circulation separated from the maternal circulation and how?

Answer 24

Yes, by:

1. A syncytial membrane (a chorion derivate)
2. Endothelial cells form fetal capillaries

Question 25

The human placenta is of the…

Answer 25

hemochorial type

Question 26

How much maternal blood is it in the intervillous lake?

Answer 26

150mL = 0,150L

Question 27

How often is the maternal blood renewed?

Answer 27

3-4 times a minute

Question 28

Main functions of the placenta:

Answer 28

1. Exchange of gases
2. Exchange of nutrients and electrolytes
3. Transmission of maternal antibodies, providing the fetus with passive immunity
4. Production of hormones, such as progesterone, estradiol, and estrogen. in addition: hCG and somatomammotropin.
5. Detoxification of some drugs

Question 29

The amnion

Answer 29

• Large sac containing amniotic fluid, produced by amniotic cells but is derived primarly from maternal blood.
• The fetus is suspended in it by its umbilical cord.
• The fetus swallows amniotic fluid, which is absorbed through its gut and cleared by the placenta.
• The fetus adds urine to the amniotic fluid, but this is mostly water.

Question 30

The fluid in the amnion

Answer 30

1. Absorbs jolts
2. Allows for fetal movements
3. Prevents adherence of the embryo to surrounding tissues.

Question 31

An excessive amount of amniotic fluid (hydramnios) is associated with..

Answer 31

Anencephaly and esophageal atresia

Question 32

An insufficient amount (oligohydramnios) is related to….

Answer 32

Renal agenesis

Question 33

The umbilical cord, surrounded by the amnion, contains:

Answer 33

1. Two umbilical arteries
2. One umbilical vein
3. Wharton’s jelly, which serves as a protective cushion for the vessels.

Question 34

Dizygotic, or fraternal, twins

Answer 34

Two thirds of twins are dizygotic, or fraternal; they have two amnions, two chorions, and two placentas, which sometimes are fused.

Question 35

Monozygotic twins

Answer 35

Monozygotic twins usually have two amnions, one chorion, and one placenta.

Question 36

Conjoined twins

Answer 36

In cases of conjoined twins, in which the fetuses are not entirely split from each other, there is one amnion, one chorion, and one placenta.

Question 37

Signals initiating parturition (birth) are not clear, but preparation for labor usually begins between 34 and 38 weeks.
Labor itself consists of three stages:

Answer 37

1. Effacement and dilatation of the cervix
2. Delivery of the fetus
3. Delivery of the placenta and fetal membranes.

Question 38

What characterize the trophoblast by the second month?

Answer 38

Great number of secondary and tertiary villi