10 Placenta by lNR8170

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									Dr. Ahmed Fathalla Ibrahim
            DECIDUA
• DEFINITION:
1. It is the functional layer of
   endometrium in a pregnant
   women
2. It includes the endometrium of
   fundus & body of uterus
3. The endometrium of the cervix
   does not form a part of decidua.
   The cervix is closed by mucous
   plug during pregnancy
            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
3.The increasing level of
  progesterone in maternal blood
  induces endometrial changes into
  decidua
             DECIDUA
•  STEPS OF FORMATION (DECIDUAL
   REACTION):       IMPORTANT IN
   DIAGNOSIS OF EARLY PREGNANCY
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. They are called “decidual
   cells”
PARTS OF DECIDUA
             DECIDUA
• PARTS OF DECIDUA:
1. Decidua basalis: between chorionic
   sac & muscle wall of uterus
2. Decidua capsularis: between
   chorionic sac & cavity of uterus
3. Decidua parietalis: remaining part
              DECIDUA
•  FATE OF DECIDUA: The chorionic sac
   expands towards the cavity of the
   uterus due to the growth of fetus &
   enlargement of amniotic cavity:
1. The cavity of uterus is obliterated due
   to fusion of chorion & amnion
2. The decidua parietalis & capsularis
   disappear gradually
3. The decidua basalis persists to form a
   part of placenta
    CHORION & CHORIONIC VILLI
•  DEVELOPMENT: During implantation,
   the trophoblast thickens at region of
   contact with endometrium &
   differentiates into:
1. Outer syncytiotrophoblast: a layer
   containing multiple nuclei in a
   common cytoplasm with no cell
   boundaries (secretes HCG)
2. Inner cytotrophoblast: a layer of
   mononucleated cells
PRIMARY CHORIONIC VILLI
SECONDARY CHORIONIC VILLI
TERTIARY CHORIONIC VILLI
  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
       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
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
PLACENTA
    FATE OF CHORIONIC VILLI
•  Until the beginning of 8th week,
   chorionic villi surround the whole
   chorionic sac, then differentiate into:
1. Smooth chorion (chorion laeve): villi
   in contact with decidua capsularis,
   degenerate & become avascular due
   to compression & disappearance of
   decidua capsularis
2. Villous chorion (chorion frondosum):
   large villi in contact with decidua
   basalis, form part of placenta
DEVELOPMENT OF PLACENTA

1. FETAL PART: VILLOUS CHORION
2. MATERNAL PART: DECIDUA
   BASALIS
             PLACENTA
A) MATERNAL SURFACE




B) FETAL SURFACE
              PLACENTA
•  SHAPE: circular disc
•  WEIGHT: about one-sixth that of fetus (500-
   600 gm)
• DIAMETER: 15-20 cm
• THICKNESS: 2-3 cm
• SURFACES:
1. Fetal surface: smooth, transparent, covered
   by amnion with umbilical cord attached
   near its center & umbilical vessels radiating
   from it
2. Maternal surface: irregular, divided into
   convex areas (cotyledons)
            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
PLACENTAL CIRCULATION
 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
  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
   PLACENTAL MEMBRANE
COMPONENTS:
• Until 20th week: it is formed of 4 layers:
1. Syncytiotrophoblast
2. Cytotrophoblast
3. Extraembryonic mesoderm
4. Endothelium of fetal blood vessels
• After 20th week: it is more permeable to meet
   increased demand of fetus & is formed of 2
   layers :
1. Syncytiotrophoblast
2. Endothelium of fetal blood vessels
 FUNCTIONS OF PLACENTA
• METABOLISM: synthesis of
  glycogen, cholesterol & fatty acids:
  source of nutrition & energy for
  embryo or fetus during early
  pregnancy
 FUNCTIONS OF PLACENTA
• TRANSFER: transport of substances
     in both directions between placenta &
     maternal blood:
1.   Gases: oxygen, carbon dioxide
2.   Nutritional substances: glucose,
     aminoacids, vitamins
3.   Hormones: steroid hormones (e.g.
     testosterone)
4.   Electrolytes: Na+, K+, Cl-
5.   Maternal antibodies: antibodies
     against diphteria, smallpox, measles
 FUNCTIONS OF PLACENTA
• SECRETION OF HORMONES:
• Protein hormones:
1. Human chorionic gonadotropin (early
   pregnancy tests)
2. Human placental lactogen
3. Human chorionic thyrotropin
4. Human chorionic corticotropin
5. Relaxin
• Steroid hormones:
1. Progesterone
2. Estrogen
    ANOMALIES OF PLACENTA
•  ANOMALIES IN SIZE & SHAPE:
   normally chorionic villi persist only at
   site of decidual basalis:
1. Placenta membranacea: a large
   placenta due to persistence of on the
   entire surface of chorionic sac
2. Accessory placenta: a patch of
   chorionic villi persisted a short
   distance from main placenta
ACCESSORY PLACENTA
PLACENTA PREVIA, ACCRETA
      & PERCRETA
    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:
1. Placenta accreta: chorionic villi
   extend to the myometrium
2. Placenta percreta: chorionic villi
   penetrate the whole thickness of
   myometrium & extend to perimetrium
BATTLEDORE
 PLACENTA




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

								
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