FETAL MEMBRANES 2

Dr Rania Gabr

OBJECTIVES

By 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)

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

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 PLACENTA

Exchange 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 placenta

2. 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 amnion

amnion

UMBILICAL CORD: PLACENTAL ATTACHMENT

Typically 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