Fetal Membranes 2
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Transcript of Fetal Membranes 2
FETAL MEMBRANES 2
Dr Rania Gabr
OBJECTIVESBy the end of this lecture, the student should be able to: Describe the structure, functions, anomalies
of the placenta Describe the structure, functions, anomalies
of the umbilical cord
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 it2. Maternal surface: irregular, divided into convex areas (cotyledons)
PLACENTAThe maternal 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 Poorly oxygenated 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
FUNCTIONS OF THE PLACENTAExchange of metabolic & gaseous
products between maternal & fetal bloodstreamsRespiratory function: Exchange of gases – Nutritive function: Exchange of nutrients &
electrolytes – Transmission of maternal antibodies –Excretory function: Co2 and other stuff
Barrier function: prevents passage of some bacteria and some drugs from maternal to fetal blood.
Endocrine function: Production of hormones
Protein hormones:1. Human chorionic gonadotropin (early
pregnancy tests)2. Human placental lactogen3. Human chorionic thyrotropin4. Human chorionic corticotropin5. Relaxin
Steroid hormones:1. Progesterone2. Estrogen
ANOMALIES OF PLACENTA ANOMALIES IN SIZE & SHAPE:
Normally chorionic villi persist only at site of decidual basalis:
1. Placenta membranacea: a large thin membranous placenta due to persistence of functioning villi 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 myometrium2. Placenta percreta: chorionic villi penetrate
the whole thickness of myometrium & extend to perimetrium
ANOMALIES OF PLACENTA ANOMALIES IN ATTACHMENT OF
UMBILICAL CORD:1. Battledore placenta: the cord is
attached to the margin of placenta2. Velamentous insertion of cord: the
cord is attached to the membranes surrounding placenta, umbilical vessels are liable to be ruptured
Battledore placenta
Velamentous insertion of cord
UMBILICAL CORD Cord like structure Connects fetus to
the placenta Attached to the
ventral surface of the fetal body and to the smooth chorionic plate of the placenta
UMBILICAL CORD: FORMATION Develops from the connecting
stalk The connecting stalk initially
attached to the caudal end of the embryonic disc, after folding, becomes attached to the ventral surface of the curved embryonic disc, at the umbilical region
The umbilical region wider initially, becomes narrower as the folding progresses
The underlying structures are compressed together and form a cord like structure, the umbilical cord
UMBILICAL CORD: FORMATION CONT’D
Initial contents: Connecting
stalk Umbilical
vessels Allantois Yolk sac Extraembryoni
c celome Intestinal loop
(during 6-10 weeks)
UMBILICAL CORD: AT TERM
At term, the typical umbilical cord:
Is 55-60 cm in length, with a diameter of 2-2.5 cm
Has knotty appearance Usually contains two
arteries and one vein Is surrounded by a jelly
like substance called the Wharton's jelly
Is enclosed in amnionamnion
UMBILICAL CORD: PLACENTAL ATTACHMENTTypically attaches to the placenta near its center- Eccentric attachment
May attach to the placenta near its margin- Marginal attachment
May attach to the membranes around the placenta- Membranous (Velamentous ) attachment
placenta
UMBILICAL CORD CONT’D After delivery of the
placenta the umbilical cord is usually clamped and severed
The site of its attachment leaves a scar, the navel (belly button), on the anterior wall of the abdomen
ABNORMALITIES RELATED TO UMBILICAL CORD Omphalocele: Failure of
returning of intestinal loops back into the abdominal cavity
Long cord may prolapse or coil around the fetus thus cause difficulty in labour
Short cord may result in premature pull and separation of placenta causing severe bleeding during birth
True knots
True knot
Prolapsed cord