Download 10.Placenta

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 (500600 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
1.
2.
3.
4.
5.
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+, ClMaternal 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