1. PLACENTA
Dr. Ahmed Fathalla Ibrahim

2. DECIDUA
DEFINITION:
It is the functional layer of endometrium in a pregnant women
It includes the endometrium of fundus & body of uterus
The endometrium of the cervix does not form a part of decidua. The cervix is closed by mucous plug during pregnancy

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

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

5. PARTS OF DECIDUA

6. DECIDUA PARTS OF DECIDUA:
Decidua basalis: between chorionic sac & muscle wall of uterus
Decidua capsularis: between chorionic sac & cavity of uterus
Decidua parietalis: remaining part

7. DECIDUA
FATE OF DECIDUA: The chorionic sac expands towards the cavity of the uterus due to the growth of fetus & enlargement of amniotic cavity:
The cavity of uterus is obliterated due to fusion of chorion & amnion
The decidua parietalis & capsularis disappear gradually
The decidua basalis persists to form a part of placenta

8. CHORION & CHORIONIC VILLI
DEVELOPMENT: During implantation, the trophoblast thickens at region of contact with endometrium & differentiates into:
Outer syncytiotrophoblast: a layer containing multiple nuclei in a common cytoplasm with no cell boundaries (secretes HCG)
Inner cytotrophoblast: a layer of mononucleated cells

9. PRIMARY CHORIONIC VILLI

10. SECONDARY CHORIONIC VILLI

11. TERTIARY CHORIONIC VILLI

12. STAGES OF CHORIONIC VILLI
PRIMARY: At the end of 2nd week, finger-like processes formed of outer syncytiotrophoblast & inner cytotrophoblast appear
SECONDARY: Early in 3rd week, extraembryonic mesoderm extends inside the villi
TERTIARY: During 3rd week, arterioles, venules & capillaries develop in the mesenchyme of villi & join umbilical vessels
By the end of 3rd week, embryonic blood begins to flow slowly through capillaries in chorionic villi

13. CHORIONIC VILLI
Chorionic villi invade & erode endometrium, maternal blood leaks & collects in spaces between villi (intervillous spaces)
Cytotrophoblast penetrates syncytiotrophoblast & extends to form a cytotrophoblastic shell that surrounds the chorionic sac & attaches it to endometrium. It prevent further penetration of decidua by syncytiotrophoblast

14. TYPES OF CHORIONIC VILLI
STEM (ANCHORING) VILLI: attach the chorionic sac to decidua through cytotrophoblastic shell
BRANCH (TERMINAL) VILLI: grow from the sides of stem villi, increase surface area for exchange between fetal & maternal blood

15. PLACENTA

16. FATE OF CHORIONIC VILLI
Until the beginning of 8th week, chorionic villi surround the whole chorionic sac, then differentiate into:
Smooth chorion (chorion laeve): villi in contact with decidua capsularis, degenerate & become avascular due to compression & disappearance of decidua capsularis
Villous chorion (chorion frondosum): large villi in contact with decidua basalis, form part of placenta

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

18. PLACENTA
MATERNAL SURFACE
B) FETAL SURFACE

19. PLACENTA SHAPE: circular disc
WEIGHT: about one-sixth that of fetus ( gm)
DIAMETER: cm
THICKNESS: 2-3 cm
SURFACES:
Fetal surface: smooth, transparent, covered by amnion with umbilical cord attached near its center & umbilical vessels radiating from it
Maternal surface: irregular, divided into convex areas (cotyledons)

20. PLACENTA
The fetal part of placenta is divided into cotyledons by projections from decidua basalis (placental septa)
Each cotyledon contains 2 or more stem villi with their branch villi
By the end of 4th month, decidua basalis is almost entirely replaced by cotyledons

21. PLACENTAL CIRCULATION

22. PLACENTAL CIRCULATION
Poorly oxygenaed blood leaves the fetus & passes through the 2 umbilical arteries to the placenta
Umbilical arteries divide into several chorionic arteries that enter chorionic villi
An arterio-capillary-venous network is formed in chorionic villi
Exchange of materials between fetal & maternal blood (in intervillous spaces) occurs across placental membrane (barrier)
Oxygenated blood returns to fetus by umbilical vein

23. PLACENTAL MEMBRANE
It separates fetal from maternal blood & prevents mixing of them
It is an incomplete barrier because it only prevents large molecules to pass (heparin, bacteria), but cannot prevent passage of viruses (e.g. rubella), microorganisms (e.g. toxoplasma gondii, treponema pallidum), drugs, hormones

24. PLACENTAL MEMBRANE COMPONENTS:
Until 20th week: it is formed of 4 layers:
Syncytiotrophoblast
Cytotrophoblast
Extraembryonic mesoderm
Endothelium of fetal blood vessels
After 20th week: it is more permeable to meet increased demand of fetus & is formed of 2 layers :

25. FUNCTIONS OF PLACENTA
METABOLISM: synthesis of glycogen, cholesterol & fatty acids: source of nutrition & energy for embryo or fetus during early pregnancy

26. FUNCTIONS OF PLACENTA
TRANSFER: transport of substances in both directions between placenta & maternal blood:
Gases: oxygen, carbon dioxide
Nutritional substances: glucose, aminoacids, vitamins
Hormones: steroid hormones (e.g. testosterone)
Electrolytes: Na+, K+, Cl-
Maternal antibodies: antibodies against diphteria, smallpox, measles

27. FUNCTIONS OF PLACENTA SECRETION OF HORMONES: Protein hormones:
Human chorionic gonadotropin (early pregnancy tests)
Human placental lactogen
Human chorionic thyrotropin
Human chorionic corticotropin
Relaxin
Steroid hormones:
Progesterone
Estrogen

28. ANOMALIES OF PLACENTA
ANOMALIES IN SIZE & SHAPE: normally chorionic villi persist only at site of decidual basalis:
Placenta membranacea: a large placenta due to persistence of on the entire surface of chorionic sac
Accessory placenta: a patch of chorionic villi persisted a short distance from main placenta

29. ACCESSORY PLACENTA

30. PLACENTA PREVIA, ACCRETA & PERCRETA

31. ANOMALIES OF PLACENTA ANOMALIES IN POSITION:
Placenta previa: when blastocyst implants close to or overlying internal os of uterus late pregnancy bleeding
ANOMALIES IN EXTENSION:
Placenta accreta: chorionic villi extend to the myometrium
Placenta percreta: chorionic villi penetrate the whole thickness of myometrium & extend to perimetrium

32. VELAMENTOUS INSERTION OF CORD
BATTLEDORE PLACENTA
VELAMENTOUS INSERTION OF CORD

33. ANOMALIES OF PLACENTA ANOMALIES IN ATTACHMENT OF UMBILICAL CORD:
Battledore placenta: the cord is attached to the margin of placenta
Velamentous insertion of cord: the cord is attached to the membranes surrounding placenta, umbilical vessels are liable to be ruptured