" PLACENTATION 👇🏻

 " What is Placentation "👇🏻

A fully formed human placenta in situ :

Placenta is defined as a temporary intimate mechanical and physiological connection between foetal and maternal tissues for the nutrition, respiration, excretion, etc., of the foigitate into corresponding depressions, called crypts, in the wall of the uterus. Finally, the chorionic villi fuse with the eroded uterine mucosa to form a true placenta called placenta vera. Initially the chorionic villi are distributed on the whole surface of blastocyst but later the major part of blastocyst is exposed and chorionic villi disappear from the exposed part and remain only on a disc-like area to form metadiscoidal placenta. The placenta is fully formed in 10 weeks and lasts throughout pregnancy. The placenta is connected to the embryo through an umbilical cord. The part of placenta contributed by the foetus (e.g., chorionic villi) is called foetal placenta, while the part formed by the mother is called maternal placenta (mainly formed of decidua basalis) called decidua. A decidua (Fig. 3.30) is formed of three zones Outer decidua basalis (part of endometrium where blastocyst is embedded), middle decidua parietalis and inner decidua capsularies (separates blastocyst and uterine cavity).

On the histological basis, the human placenta is haemochorial placenta in which all three maternal tissues of placenta have been digested by the trophoblast of the chorionic placenta. So the chorionic villi, are bathed directly in the maternal blood sinuses.

On the basis of degree of intimacy of foetal and maternal tissues, human placenta is called deciduate placenta. It is so because at the end of pregnancy, the uterine wall is no longer intact and when the parturition occurs, then some maternal tissue called decidua or afterbirth is expelled. So the human placenta is haemochorial, metadiscoidal, chorionic and deciduate .

Function of placenta: -

1.Placenta helps in the nutrition of the embryo as the nutrients like amino acids ,monosugars,vitamins ,pass from the maternal blood into foetal blood through placenta. 

2. It also helps in respiration of the embryo as O of the maternal blood and CO, of the foetal blood are exchanged through placenta.

3. It also helps in excretion of the embryo as nitrogenous wastes of foetal blood like urea pass into maternal blood through placenta.

4. It also acts as an endocrine gland as it secretes certain hormones like estrogens, progesterone, human chorionic gonadotrophin (HCG) and human placental lactogen (HPL). HCG maintains the corpus luteum for the continued secretion of progesterone to maintain the pregnancy. At the end of gestation period, it also secretes relaxin which helps in softening of pubic symphysis and child birth. It also secretes small amounts of chorionic thyrotropin, chorionic corticotropin and chorionic somatomammotropin.

5. Antibodies (especially immunoglobulin-G) against diphtheria, smallpox, scarlet fever, measles, etc., pass from maternal blood to foetal blood through placenta and provide passive immunity.

6. It stores the glycogen till the formation of liver.

7. Though the placenta acts as an effective barrier for certain toxic chemicals like histamine but certain germs like AIDS virus, syphilis bacteria, viruses of German measles, etc, intoxicants like nicotine of cigarette smoke; and addictive drugs like heroin and cocain can pass through the placenta and cause the developmental defects.

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