Placenta at term for nursing students

The human placenta is discoid,

haemochorial and deciduate

The placenta is attached to the uterine

wall and establishes connection between

the mother and fetus through the

umbilical cord

Gross Anatomy: The placenta at term is:a circular disc with diameter of 15-20cmthickness : 2.5cm

Thin off towards the edgeFeels spongyweighs: 500gm

Choronic plate

Decidua basalisIntervillious space

Amniotic Membrane

Tertiary stem villi

Syncytiotrophoblast

Cyt otrophoblast

Chorion

laeve

Decidua parietalis

& capsularis

fused

It presents two surface

fetal & maternal peripheral margin

surface surface

Fetal surface:

Covered by smooth and glistening amnion with

the umbilical cord attached at or near its

centre

At term about four fifth of the placenta is of

fetal origin

Maternal surface :

Rough and spongy

Maternal blood gives it a dull red color

Thin greyish layer: remnant of decidua basalis

Is mapped out into 15-20 lobes or cotyledons

Numerous small greyish spots are visible: due

deposition of calcium in the degenerated areas

Only decidua basalis and the blood in the

intervillious space are of maternal origin

PERIPHERAL MARGIN

It is limited by the fused basal and chorionic plates

and is continuous with the chorion laeve and

amnion. Essentially, the chorion and the placenta

are one structure but the placenta is specialised

part of the chorion

Attachment:

Attached to the upper part of

body of the uterus

encroaching to the fundus

adjacent to the anterior or

posterior wall

The attachment to the

uterine wall is effective due

to the anchoring villi

Separation

Placenta separates

after the birth of the

baby and the line of

separation is through

the decidua

spongiosum

Amnion :

It consists of single layer of cubical epithelium

loosely attached to the adjacent chorionic plate.

It takes no part in formation of the placenta

Helps in formation of amniotic fluid.

Facilitate dilation of the cervix during

labour.

Rich source of glycerophospholipids

containing arachidonic acid precursor of

prostaglandin.

CHORION

It is thicker than amnion friable and shaggy

on both side.

Internally it is attached to the amnion by

loose areolar tissue and remnant of

primitive mesenchyme.

Externally it is covered by vestiges of

trophoblastic layer and the decidual cells of

the fused decidua capsularis and parietalis

which can be distinguished microscopically.

The term chorion contains no vessels and

nerves.

The umbilical cord or funis forms the connecting link between the fetus and the placenta.

Characteristics Its about 50 cm in length an usual

variation of 30-100cm.

Its diameter average 1.5cm with variation of 1 – 2.5cm.

cont

Its thickness is not uniform but presents

nodes or swelling at places, these

swelling are false knots may be due to

dilatation of the umbilical veins or local

collection of Wharton's jelly.

It shows a spiral twist from the left to

right from as early as 12th wk due to

spiral turn taken by the vessels vein

around the arteries.

Maternal circulation or utero placental

circulation:- The blood is deliverd to the

placental bed in the decidua by spiral arteries

and flow into the blood spaces surrounding the

villi. Its direction of flow is similar to fountain.

fetal circulation:-fetal blood low in oxygen is

pumped by the fetal heart toward the placenta

along the umbilical arteries and transported

along their branches to the capillaries of the

chorionic villi. yielded up Co2 & absorbed

oxygen, the blood is returned to fetus via

umbilical vein.

Dutta D.C. ‘text book of Obstetrics’, sixth

edition,Pp:28 to34 and 218 to 220

Ostrzenski adam; gynaecology; Lippincott ;

Second edition ; pg no - 209-216 ,193

www.sciencedirect.com/science/journal

www.en. Wikipedia.org/wik/placenta

www.placentajournal.org/