PLACENTA By Prof Saeed Makarem 1 PLACENTA This

PLACENTA By • Prof. Saeed Makarem 1

PLACENTA • • This is a fetomaternal organ. It has two components: – Fetal part – develops from the chorionic sac – Maternal part – derived from the endometrium The placenta and the umbilical cord are a transport system for substances between the mother and the fetus. Function Of The Placenta: 1. Protection. 2. Nutrition. 3. Respiration. 4. Excretion. 5. Hormone production, (progesterone, estrogen, Gonadotrophins 2

DECIDUA • DEFINITION: 1. It is the functional layer of endometrium of the gravid (pregnant) uterus. 2. It includes the endometrium of fundus & body of uterus 3. The endometrium of the cervix does not form a part of decidua.

DECIDUA CAUSE OF FORMATION: 1. Trophoblast secretes chorionic gonadotrophins which prolong the life of corpus luteum 2. The corpus luteum of pregnancy continues to secrete progesterone till the 20 th week 3. The increasing level of progesterone in maternal blood induces changes in the endometrial into decidua

DECIDUA STEPS OF FORMATION (DECIDUAL REACTION): 1. The endometrium becomes thicker & more vascular 2. The endometrial glands become full of secretion 3. The connective tissue cells enlarge due to accumulation of lipid & glycogen. 4. They are called “decidual cells”

DECIDUA – Decidua basalis: It lies at the site of implantation , it forms the maternal part of the placenta – Decidua capsularis: it covers the conceptus – Decidua parietalis: the rest of the endometrium that lines the body & the fundus. 6

DEVELOPMENT OF PLACENTA • Until the beginning of the 8 th week, the entire chorionic sac is covered with villi, (C). • As the chorionic sac grows, only the part that is associated with Decidua basalis retain its villi, (D). • Villi of Decidua capsularis compressed by the developing sac. • Thus, two types of chorion are formed: – Chorion frondosum (villous chorion) – Chorion laeve – bare (smooth) chorion 7

DEVELOPMENT OF PLACENTA • The villous chorion will form the fetal part of the placenta. • The decidua basalis will form the maternal part of the placenta. • The placenta will grow rapidly. • By the end of the 4 th month, the decidua basalis is almost entirely replaced by the cotyledons. 8

DEVELOPMENT OF PLACENTA 1. FETAL PART: VILLOUS CHORION 2. MATERNAL PART: DECIDUA BASALIS

PRIMARY CHORIONIC VILLI At the end of 2 nd week, finger-like processes formed of outer syncytiotrophoblast & inner cytotrophoblast appear

SECONDARY CHORIONIC VILLI Early in 3 rd week, extraembryonic mesoderm extends inside the villi

TERTIARY CHORIONIC VILLI During 3 rd week, arterioles, venules & capillaries develop in the mesenchyme of villi & join umbilical vessels By the end of 3 rd week, embryonic blood begins to flow slowly through capillaries in chorionic villi

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A) MATERNAL SURFACE Irregular, divided into convex areas (cotyledons) B) FETAL SURFACE: smooth, transparent, covered by amnion with umbilical cord attached near its center & umbilical vessels radiating from it PLACENTA

FULL-TERM PLACENTA Maternal side • Cotyledons –about 15 to 20 slightly bulging villous areas. Their surface is covered by shreds of decidua basalis from the uterine wall. • After birth, the placenta is always carefully inspected for missing cotyledons. • Cotyledons remaining attached to the uterine wall after birth may cause severe bleeding. 15

• Fetal surface: FULL-TERM PLACENTA • This side is smooth (500 -600 gm- Diameter 15 -20 cm) and shiny. It is covered by amnion. • The umbilical cord is attached close to the center of the placenta. • The umbilical vessels radiate from the umbilical cord. • They branch on the fetal surface to form chorionic vessels. • They enter the chorionic villi to form Fetal side arteriocapillaryvenous system. 16

PLACENTAL CIRCULATION 17

STRUCTURE OF STEM CHORIONIC VILLUS 18

PLACENTAL MEMBRANE • This is a composite structure that separating the fetal blood from the maternal blood. • It has four layers: – Syncytiotrophoblast – Cytotrophoblast – Connective tissue of villus – Endothelium of fetal capillaries • After the 20 th week, the cytotrophoblastic cells disappear and the placental membrane consists only of three layers. 19

It separates fetal from maternal blood. It prevents mixing of them. It is an incomplete barrier as it only prevents large molecules to pass ( heparin & bacteria) But cannot prevents passage of viruses(e. g. rubella), micro-organisms(toxoplama, treponema pallidum) drugs and hormones. 20

TRANSFER ACROSS THE PLACENTAL MEMBRANE 21

Anomalies of Placenta 22

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BATTLEDORE PLACENTA VELAMENTOUS INSERTION OF CORD

FULL-TERM UMBILICAL CORD • Usually it is attached near the center of the fetal surface of placenta. • Length: about 50 cm • Diameter: 1 -2 cm • Contains two arteries and one vein, surrounded by mucoid connective tissue (Wharton jelly) • The vessels are longer than the cord and may have loops (false knots). 27