THE PLACENTA AT TERM

�PLACENTA AT TERM�

• SITUATION –It is usually situated in the upper uterine segment.
• SHAPE - It is a round flat mass.
• SIZE - Approximately 22cm in diameter and 2.5cm thick at its centre.
• WEIGHT- Approximately 1/6th of Babies weight.

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SITUATION

STRUCTURE

MATERNAL SURFACE

• It is dark red in colour.
• The surface arranged in approximately 18-20 lobes /cotyledon separated by grooves called sulci (furrows).

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 FETAL SURFACE

• Its appearance is smooth, shinny with bluish grey in colour.
• The umbilical cord is inserted into this surface.
• The amniotic membrane covers the fetal surface and can be stripped back from the chorion as far as the insertion of the umbilical cord.
• The inner membrane is the amnion (Liquor amnii) which contain the amniotic fluid.
• The outer membrane is the chorion.

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THE AMNION

• It is a tough transparent membrane, very difficult to tear. It lines the amniotic cavity and secretes amniotic fluid.
• THE CHORION - It is an opaque, thin, friable membrane. It appears to be thicker than the amnion. It is easily get torn which can lead to haemorrhage.

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AMNIOTIC FLUID

• Amniotic fluid or liquor amnii is the fluid contained in the amniotic sac and surrounds the fetus during pregnancy.
• COLOUR- Clear alkaline and slightly yellowish /straw coloured liquid inside the amniotic sac.

VOLUME- 1liter at 38 weeks and about 800mls at term.

SPECIFIC GRAVITY- 1006-1010

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�AMNOITIC FLUIDS CONT’D�

• The fluid is derived from exudates of maternal vessels in the decidua and from fetal vessels. Secretion of the amnion, and fetal urine.

COMPOSITION

• Amniotic fluids consists of 99% of water.
• 1% dissolved substances eg food substances eg proteins, lipids, sodium chlorides, carbohydrates fats,enzymes etc. fetus shared skin cells,
• Desquamated pigments.
• Fetal epithelial cells
• vernix caseosa
• lanugo.

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FUNCTIONS OF THE AMNIOTIC FLUID

DURING PREGNANCY

• The fluid distends the amniotic sac and allow symmetrical external growth of the embryo.
• Allows free movement of the fetus aiding musculoskeletal development.
• It equallizes pressure and protects the fetus from jarring and injury(cushions).
• The fluid maintains a constant temperature around the fetus.
• It provide small amount of nutrients for the fetus.
• It prevents adhesions between the fetus and the amnion.
• It permit normal fetal lung development.

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DURING LABOUR

• It protects the fetus ffrom infections as long as the membranes remain intact.
• Protect the placenta and umbilical cord from the pressure of the uterine contractions.
• It aids effacement and dilatation of the cervix particularly where the presenting part is poorly applied to the cervix.
• Prevent pressure on the presenting part.
• It flushes the birth canal when membranes rupture and offers the fetus a clean canal to pass through.

ABNORMALITIES OF THE LIQUOR AMNII

• Abnormalities of the liquor amnii may either be colour or quantity.

ABNORMALITIES IN QUANTITY

1.POLYHYDRAMNIOS

Excess amount of liquor amnii. About 2000mls. It is due to fetal malformations eg oesophageal artesia where the feyus cannot swallow the fluid .CNS abnormalities eg anencephaly,diabetes mellitus, multiple gestation.

2.OLIGOHYDRAMNIOS

Due to marked reduction inthe liquor amnii less than 300mls in the 3^rd trimester,causesmay include placental insufficiency with diminish blood flow, renal disorders, prematurely rupture of membranes.

ABNORMALITIES IN COLOUR

• Greenish liquor- it may be meconium passed by fetus due to fetal distress.
• Yellowish colour-due to excessive bilirubin associated with haemolytic disease(severe jaundice of the new bone).
• Milky appearance-when there is excessive amount of vernix caseosa in the liquor amnii.

�MATURED PLACENTA�

• Placenta is complete and are functioning by the 10^th week of fertilization.
• By the 12^th - 20^th week of gestation the weight is bigger than the fetus.

FUNCTIONS

1. Respiration-gas exchange
2. Nutrition – water vitamins, amino acids, minerals etc
3. Storage-glycogen, iron, fat soluble vitamins etc

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FUNCTIONS CONT’D

4.Storage-glycogen, iron, fat soluble vitamins etc

5. Excretion – Carbon dioxide, bilirubin, small amount of urea, uric acid.

6. Protection- limited barrier to infection ,alcohol , some chemicals, several viruses can pass through placenta.

7. Antibodies- eg Immunoglobulins G (IgG) can be transferred to the fetus and these will confer immunity on the baby for the first three months after birth.

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�PLACENTA PRODUCE THE FOLLOWING HORMONES�

• Human chorionic hormones (HCG)- produced by cytotrophoblastic layer of the chorionic villi, form the bases of pregnancy. It can be seen in the mothers urine.
• Oestrogen
• Progesterone
• Human placental lactogen (HpL) has a role in glucose metabolism in pregnancy .Its activities relate to human growth hormone.

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� UMBILICAL CORD�

• Its formed by the 5^th week of gestation. It extends from the fetal surface to the placenta to the umbilical area of the fetus.
• SIZE- At term it measures 40-50cm at length and diameter is 1-2cm.
• SHAPE - like a cord with about 40 spiral twist in it.
• Cord is short if less than 40cm.

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STRUCTURE

• Contains 2 arteries and one vein.
• The blood vessels are enclosed and protected by Wharton’s jelly a gelatinous substance formed by Mesoderm .
• The whole cord is covered in a layer of amnion.
• There are no nerves in the umbilical cord so cutting it following birth is not painful.

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�FUNCTIONS�

• Transport oxygen and nutrients to the developing fetus and removes waste products.
• It links the foetus to the placenta.
• Whartons jelly prevents kinking of the cord which may interfere with circulation.
• Protects the fetal vessels in the cord (by the jelly like substance).

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ABNORMALITIES OF THE UMBILICAL CORD

TOO SHORT CORD(LESS THAN 40CM)

• This causes delay or descent of the fetal head. The weight of the fetus may pull on the cord and this may cause premature separation of the placenta.

TOO LONG CORD (ABOUT 60-100CM)

• This may give rise to prolapse of cord when membranes rupture and cord around neck during vigorious turning movement of the fetus.

ABNORMALITIES OF THE UMBILICAL CORD CONT’D

TRUE KNOT

• Occasionally a very long cord may wrap around the neck or body of the fetus. It may become knotted during turning movements.These could be dangerous and can cause obstruction to fetal circulation when pulled tight.

FALSE KNOT

• It may be due to lumps of wharton’s jelly on the side of the cord.

ABSENCE OF A VESSELS

This may be due to fetal abnormalities of the cardiovascular system and absence of a kidney. It could be 1 in 200 newborns.

�VARIATIONS OF THE PLACENTA AND CORD�

SUCCENTUARIATE LOBE OF PLACENTA

• Has small extra lobe separated from the main placenta join to it by blood vessels that runs through the membranes.

COMPLICATION

• The small lobe may be retained in utero and lead to infection and haemorrhage.
• A hole is made in the membranes with vessels running to it (means to identification)

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 �CIRCUMVALLATE PLACENTA�

• Opaque ring is seen on the fetal surface of the placenta.
• There is doubling back of the chorion and amnion
• Often associated with prematurity, prenatal bleeding abruption, and multiparity

BIPARTITE PLACENTA

• Two complete separate placenta each with a cord and the cords are joined a short distance from the two.

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�TRIPARTITE PLACENTA�

• Has three complete separate placenta.

ABNORMALITIES OF THE CORD

• Normally the cord is centrally inserted but sometimes it could be laterally inserted.
• BATTLEDORE INSERTION OF THE CORD: The cord is attached to the edge of the placenta
• VELAMENTOUS INSERTION OF THE CORD: The cord is inserted into the membranes.

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COMPLICATIONS

• When the blood vessels run in front of the presenting part the blood vessels would tear when the membranes rupture giving rise to haemorrhage.
• The cord is likely to become detached upon applying traction.
• If the cord is low lying may pass across the uterine os when membranes rupture bleeding may cause fetal death.
• A term applied to blood vessels lying in front of the presenting part is called vasa praevia.

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