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Placenta

The placenta is the The placenta is the site of nutrient and site of nutrient and gas exchange gas exchange between the fetus between the fetus and motherand mother..

ShapeShape:: The full term placenta The full term placenta is discoid in shape. is discoid in shape. Diameter = 15-25 cm, Diameter = 15-25 cm, 2-3 cm thick, 2-3 cm thick, Weight = 0.5 kg.Weight = 0.5 kg. Umbilical cord is Umbilical cord is attached to its center. attached to its center.

Surfaces: -It has 2 surfaces:

1- fetal surface: which is smooth and shinny 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 has 15 – 20 elevated areas called cotyledons with deep grooves in between made by the decidual septa.

Development:Maternal part: decidua basalis.Maternal part: decidua basalis.Fetal part: chorion frondosumFetal part: chorion frondosum..

Villi:-primary chorionic villi.-secondary chorionic villi.-Tertiary chorionic villi.

A- Villi opposite decidua basalis proliferate chorion frondosum.Villi of chorion frundosum are divided into: 1- Anchoring villi: reach decidua basalis. They are used for fixation of the fetus to the uterus. 2- Free villi ( nourishing): do not reach decidua basalis. They are used for nutrition of the fetus. B- Villi opposite decidua capsularis degenerate chorion laeve.

Tertiary chorionic villiTertiary chorionic villi contain contain embryonic blood vesselsembryonic blood vessels that develop in that develop in loose connective tissue core. These blood loose connective tissue core. These blood vessels connect up with vessels that vessels connect up with vessels that develop in the chorion and connecting develop in the chorion and connecting stalk.stalk.

Maternal blood is derived to the placenta by 80 – 100 Maternal blood is derived to the placenta by 80 – 100 spiral arteries in the uterus.spiral arteries in the uterus.

Erosion of these maternal vessels to release blood Erosion of these maternal vessels to release blood into the intervillous spaces is done by trophoblast into the intervillous spaces is done by trophoblast cells which invade the terminal ends of spiral arteries.cells which invade the terminal ends of spiral arteries.

During the 4During the 4thth and 5 and 5thth month, the decidua forms a month, the decidua forms a number of decidual septa, which project into the number of decidual septa, which project into the intervillous space.intervillous space.

As a result of this septum formation, the placenta is As a result of this septum formation, the placenta is divided into a number of compartments (cotyledons).divided into a number of compartments (cotyledons).

Sructure of placentaSructure of placenta

Placental CirculationPlacental Circulation::1. Fetal circulation.1. Fetal circulation.2. Maternal circulation.2. Maternal circulation.Maternal circulationMaternal circulation- Uterine artery → Spiral - Uterine artery → Spiral

artery → intervillous artery → intervillous space (where space (where exchange of oxygen exchange of oxygen and CO2 between and CO2 between mother and fetus mother and fetus occurs through the occurs through the placental barrier) placental barrier)

- The venous blood will - The venous blood will collect in the marginal collect in the marginal vein → uterine vein.vein → uterine vein.

Fetal circulationFetal circulation- The CO2 and wast - The CO2 and wast

products of the products of the embryo reaches to embryo reaches to the placenta the placenta through 2 umbilical through 2 umbilical arteries. These 2 arteries. These 2 arteries end by arteries end by capillaries inside the capillaries inside the tertiary villi where tertiary villi where exchange of CO2 exchange of CO2 and O2 will occur and O2 will occur through placental through placental barrier. barrier.

- The oxygen reaches - The oxygen reaches the embryo through the embryo through the umbilical vein.the umbilical vein.

Fetal Circulation

10 weeks

full term

(placental membrane)

Placental (membranes) Placental (membranes) barrierbarrier::

-These are layers separating -These are layers separating the fetal blood in the villi the fetal blood in the villi from maternal blood in the from maternal blood in the intervillous space. intervillous space. -These layers prevent mixing -These layers prevent mixing of the fetal and maternal of the fetal and maternal blood but they allow blood but they allow passage of certain passage of certain substances throw it.substances throw it.-It is not a true barrier -It is not a true barrier because only few because only few substances are unable to substances are unable to cross it. Most drugs in the cross it. Most drugs in the maternal blood can pass maternal blood can pass through it to the fetal through it to the fetal circulation and cause major circulation and cause major fetal congenital anomalies. fetal congenital anomalies.

- Early in pregnancy (till about 20 week gestation), it is formed of four layers (Fig. 56):a. The endothelial lining the fetal vessels.b. The connective tissue (mesoderm) of the villus.c. The cytotrophoblast layer.d. The syncytiotrophoblast.- After 20 weeks the cytotrophoblasts degenerate so increases the permeability of the placenta.

- Towards the end of pregnancy, a fibrinoid material made of fibrin is formed on the surface of the villi to decrease the permeability, so the placental barrier is formed of this fibrinoid material, the syncytiotrophoblasts, and the endothelium of the fetal blood vessels.

Functions Of The Placenta Exchange of gases (lung).Exchange of gases (lung).

Exchange of Nutrients and Electrolytes Exchange of Nutrients and Electrolytes (GIT).(GIT).

Excretion of waste products (kidney).Excretion of waste products (kidney). Transmission of Maternal antibodies Transmission of Maternal antibodies

resulting in passive immunity of the fetus.resulting in passive immunity of the fetus. Hormone Production as Hormone Production as Progesterone Progesterone

(maintains the corpus luteum so prevents other (maintains the corpus luteum so prevents other ovulations and prevents menses during ovulations and prevents menses during pregnancy), estrogenic hormones (estriol), HCG, pregnancy), estrogenic hormones (estriol), HCG, relaxin hormone to soften the uterine ligaments relaxin hormone to soften the uterine ligaments to help delivery and Somatomammotropin.to help delivery and Somatomammotropin.

Functions of placental Functions of placental barrierbarrier::

1.1. It prevents most organisms from passing It prevents most organisms from passing to the fetus, so it acts as a protective to the fetus, so it acts as a protective mechanism against damaging factors, mechanism against damaging factors, many viruses such as Rubella, Coxackie many viruses such as Rubella, Coxackie virus, German measles and poliomylitis virus, German measles and poliomylitis virus traverse the placenta. These viruses virus traverse the placenta. These viruses may result in congenital malformations.may result in congenital malformations.

2.2. Most of the drugs in addition to cocaine, Most of the drugs in addition to cocaine, heroin cross the placenta and cause heroin cross the placenta and cause serious damage. serious damage.

Abnormalities of placenta

1- According to site: 1- According to site: Placenta Placenta PraeviaPraeviathe 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:

1- Placenta accreta: due to abnormal adhesion between the chorionic villi and the uterine wall.2- Placenta percreta: The chorionic villi penetrate the myometrium all the way to the perimetrium.- the placenta fails to separate from the uterus after birth and may cause severe postpartum hemorrhage.

2- Abnormal penetration into the uterus:

3- Abnormal attachment of umbilical 3- Abnormal attachment of umbilical cord:cord:a- Velamentous attachment:a- Velamentous attachment:The cord does not reach the placenta itself but is attached to amniotic membrane over the fetal surface of placenta. The umbilical vessels pass in the membrane to reach the placenta. It is easly torn.B- Battle- dore placenta (marginal attachment of the cord

4- Abnormalities according 4- Abnormalities according to the number:to the 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.

5- Shape abnormalities: bi- or trilobed or horsehoe placenta

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