The placenta is circular organ in mammals that is developed during pregnancy to transfer nutrient and waste products between mother and fetus . The placenta is attached to uterine wall and establishes connection between mother and fetus through umbilical cord .
The Placenta is developed from Two Surfaces : The fetal part which develops from chorion frondosum and maternal component consists of decidua basalis . It begins at 6th week and is completed by 12th week of pregnancy.
Functions of placenta :
- Transfer of nutrients and waste product b/w Mother and fetus
2. Respiratory Function :
3. Excretory Function :
4. Nutritive Function :
Glucose :
It is principal source of energy is transferred to the fetus by Facilitated diffusion . There are transporter proteins ( GLUT 1) for facilitated diffusion.
Lipids :
Lipids for fetal growth and development are transferred across the fetal membrane or synthesizedin the fetus. Triglycerides and fatty acids are directly transported from the mother to the fetus in early pregnancy
Amino acids :
Amino acids are transferred by active transport through enzymatic mechanism (ATPase). Amino acid concentration is higher in the fetal blood than in the maternal blood.
Hormones :
.
5. Enzymatic Function :
2. Oxytocinase which neutralizes the oxytocin,
(3) phospholipase A2 which synthesizes arachidonic acid .
6. Barrier Function :
Antibody and antigens in immunological quantities can traverse across the placental barrier in both directions. The transfer of the larger molecule is probably facilitated by pinocytosis. The race of drug transfer is increased in late pregnancy.
Structure of Placenta :
AMNIOTIC MEMBRANE:
It consists of single layer of cubical epithelium loosely attached to the adjacent chorionic plate. It takes no part in formation of the placenta.
CHORIONIC PLATE:
From within outward, it consists of
(i) primitive mesenchymal tissue containing branches of umbilical vessels
(ii) a layer of cytotrophoblast and
(iii) syncytiotrophoblast. The stem villi arise from the plate.
BASAL PLATE:
It consists of the following structures from outside inwards.
(1) Part of the compact and spongy layer of the decidua basalis
(2) Nitabuch’s layer of fibrinoid degeneration of the outer syncytiotrophoblast at the junction of the cytotrophoblastic shell and decidua.
(3) Cytotrophoblastic shell
(4) Syncytiotrophoblast
INTERVILLOUS SPACE:
It is bounded on the inner side by the chorionic plate and the outer side by the basal plate, limited on the periphery by the fusion of the two plates. It is lined internally on all sides by the syncytiotrophoblast and is filled with slow flowing maternal blood. Numerous branching villi which arise from the stem villi project into the space and constitute chief content of the intervillous space.
STEM VILLI:
These arise from the chorionic plate and extends to the basal plate. With the progressive development — primary, secondary and tertiary villi are formed .
Functional unit of the placenta is called a fetal cotyledon or placentome, which is derived from a major primary stem villus. These major stem villi pass down through the intervillous space to anchor onto the basal plate.
Functional subunit is called a lobule, which is derived from a tertiary stem villi. About 60 stem villi persist in human placenta. Thus, each cotyledon (total 15–29) contains 3–4 major stem villi. The villi are the functional unit of the placenta. The total villi surface, for exchange, approximately varies between 10 square meters and 14 square meters.
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