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General Embryology:PLACENTA

The placenta is a discoid, organ which connects the

fetus with the uterine wall of the mother. It is a site of

nutrient and gas exchange between the fetus and

mother. Umbilical cord is attached to its center.

It develops By the end of the third month and it has

two components: fetal part formed of Chorionic villi

& maternal part formed by decidua basalis.

Its Weight at full term is about 500 – 600 gms

Surfaces: It has 2 surfaces:

1- fetal surface: which is

smooth because it is covered by

an amniotic membrane. The

umbilical cord is attached

centrally to this surface.

2- maternal surface: which is

rough, reddish and is

characterized by presence of 15-

20 lobules or cotyledons

Full-term placenta

Fetal part: Chorionic villi

They are numerous finger like processes called villi.

There is a space between villi called intervillous space

and is filled with maternal blood.

Placental circulation:

Maternal blood in the intervillous space-

Foetal Blood in the villi of the Placenta

Placental barrier:-These are layers separating the fetal blood in the villi

from maternal blood in the intervillous space.

-They prevent mixing of fetal and maternal blood but

they allow passage of certain substances throw it.

Functions Of The Placenta1. Exchange of gases O2 and CO2 (Respiratory).

2. Exchange of Nutrients and Electrolytes such as,

water, carbohydrates, proteins, lipids, and vitamins

(Nutrition).

3. Excretion of waste products as urea and uric acid

(kidney).

4. Transmission of Maternal antibodies resulting in

passive immunity of the fetus (Protective).

Estrogen (for uterine growth and development of

the mammary gland).

HCG (maintains the corpus luteum so prevents

other ovulations and prevents menses during

pregnancy. It is excreted by mother in the urine

early in pregnancy, their presence is used as an

indicator of pregnancy (pregnancy test).

5- Hormone Production (Endocrine) as: Progesterone (to maintain pregnancy).

Relaxin hormone to soften the uterine ligaments

to help delivery.

Somatomammotropin leads to development of

mammary glands.

6- Functions of placental barrier:

1. It prevents most organisms from passing to the

fetus, so it acts as a protective mechanism but, many

viruses such as German measles and poliomylitis

virus traverse the placenta. These viruses may result

in congenital malformations.

2. Most of the drugs in addition to cocaine, heroin

cross the placenta and cause serious damage.

Abnormalities of placenta

1- According to site: Placenta Praeviathe placenta is attached to the lower uterine segment (due to low level of implantation of the blastocyst). It causes severe antepartum haemorrhage. There are three types:

2- Abnormalities according to number: 1- Double placenta (bilobed or bidiscoid placenta).

2- Triple placenta (trilobed).

3- Accessory placenta (accessory one or more lobes). It may cause severe postpartum hemorrhage if the accessory lobe is retained in the uterus after labor.

Umbilical CordLength: about 50 cm

Diameter: 1-2 cm

Contains two arteries and one vein, surrounded

by mucoid connective tissue (Wharton jelly)

Abnormalities of the umbilical cord

very short cord - 20-30 cm - it brings problems during delivery

very long cord - 80-90 cm - it tends to entwine around the neck or extremity of the fetus

true knots - occur in about 1% of pregnancies, they form during labor as a result the fetus passing through a loop of the cord - it causes of fetal anoxia

The Amniotic Fluid It is clear and watery. The source of the fluid still remains unsettled. It may be fetal, maternal or both.

Functions of the amniotic fluid1- protection of the embryo against shock, blows or pressure. 2- maintaining a uniform pressure for the proper growth and differentiation of the delicate tissues of the embryo.3- It allows fetal movements and maintains a constant environmental temperature.

Abnormalities of the Amniotic fluid

1.Polyhydramnios This is a condition when the

volume of the amniotic fluid exceeds two liters.

2.Oligohydramnios: In this condition the fluid is scanty

in amount.