Placenta

• - discoid in shape
• It is hemochorial and deciduate.
• Placenta attached to uterine wall and
establishes connections between the mother
and fetus through umbilical cord
 Blastocyst
• Morula enters the uterine cavity and fluid begins to
penetrate the inter cellular space of the inner cell
mass. These space eventually coalesce to form the
blastocoele and embryo is called as blastocyst
• While morula remains free in the uterine cavity on
the 4th day and 5th day
• Implantation occurs in the edometrium of the
anterior or post. Wall of the body near the fundus
 Formation&development
• Developed from 2 sources
• 1-chorion frondosum(fetal)
• 2-decidua basalis(maternal)
• This two forms the discreete placenta. It
begins at 6th week and completed by 12th
week.
 Decidua
• Interstitial implantation completes on 11th day
• With this implantation cells of endometrium
become polyhydral filled with glycogen and
lipids and becomes more vascular.
• Theses decidual changes initially limited to
implantation site and soon occur through out
the endometrium
• Endometrium of pregnancy is decidua.
 Structures
• Placenta consists of 2 plates-chorionic &basal
plate
• Chorionic plate lies internally lined by amniotic
membrane and umbilical cord is attached to
this plate
• Basal plate lies to the maternal aspect
• Between these 2 plates lie the intervillious
space containing stem villi with their branches
the space being filled with maternal blood
 villi
On 13th day onwards the trophoblast starts
forming the villi which connect the chorionic
plate and basal plate
Primary, secondary and tertiary vili are
developed from the stem villi
Arise from the chorionic plate and extends to
the basal plate. With progressive development
primary,secondary and tertiary villi are
formed
• Primary villi – cells of trophoblast starts penetrating the
syncytiotrophoblast(epithelial covering of the embryonic
villi) raising finger like projections surrounded by
syncytium.a cytoplasmic mass contaiing several nuceli
• 2nd dry villi- mesodermal cells penetrate the inner core of
the primary villi to form 2nd villi. The mesodermal cells will
form blood vessels there by forming the villious capillary
system
• Tertiary villi- once vasculature has formed within the vilus
core it is termed as tetiary villi or defnitive placental villus
 Placenta
• At term is almost a circular disk with a
diameter of 15-20 cm and thickness of about
3cm at its center
• It has got 2 surfaces
• Fetal surface and maternal surface
Fetal surface Maternal surface
• Covered with smooth and • Is rough and spongy
glistening amnion with • Dull red in colour due to
umbilical cord attached at maternal blood
or near its center. • Cotyledons are present
• Branches of umbilical
vessels are visible beneath
the amnion as they radiate
from the insertion of the
cord
 Function
• Respiratory ,excretory and nutritive
• Endocrine function
• Barrier function
• Immunological function
 Mechanism involved
• Simple diffusion-
• Facillitated diffusion-(transporter mediated)
using transporter protein
• Active transfer- against concentration gradient
ATP mediated
• Endocytosis and exocytosis
• Leakage- break in placental membrane
• Respiratory function-intake of oxygen and
output of carbondioxide takes place by simple
diffusion
• Excretory function- waste products from the
fetus such as urea uric acid creatinine are
excreted in the maternal blood through simple
diffusion
• Nutritive function- get nutrients from maternal
blood
• Glucose- principal source of energy transferred by
facilitated diffusion
• Lipids- for fetal growth and development are
transferred across the fetal membrane
• Amino acids – active transport
• Water & electrolytes- Na,K and Cl cross through the
fetal membrane by simple diffusion where as Ca, P
and iron by active transport
• Enzyatic function- numerous enzymes are
mentioned
• Barrier function – fetal membrane act as a
protective barrier to the fetus against noxious
agents circulating in the maternal blood
• Immunological function- the fetus and
placenta contains paternally determined
antigens which are foreign to mother. Placenta
offers immunuological protection against this
 Anomalies of placenta
• Placenta succenturiata- is an accessoary lobe from
the main placental margin and connected to it by
membranes containing branches of umbilical vessel
• In the absence of communicating blood vessels it is
called placenta spuria
• Diagnosis- inspection of placenta after the
expulsion
• Treatment – exploration of uterus and removal of
lobe
 Placenta extrachorialis
• 2 types are there
• Circumvallate placenta
• Placenta marginata
• Circumvalate placenta- the chorionic plate of
the fetal side of the placenta is smaller than the
basal plate
• Placenta marginata- a thin fibrous ring is
present at the margin of the chorionic plate and
the fetal vessels originate from the ring