Fatel Circulation Placenta

 Placenta. 

1) Placenta is a temporary organ derived from the tissues of the fetus as well as the mother. 

 2) Human placenta is called chorionic placenta as it is made up of chorion which is an extra-embryonic membrane.Only 

(3) Blood vessels from the allantois vascularize the placenta. Branching villi emerge from the chorior and penetrate into the corresponding pits which are located in the uterine wall. 

 4) There are two parts of placenta, viz. fetal placenta and maternal placenta. 

 5) Foetal placenta is formed of chorionic villi. 

 (6) Maternal placenta is formed of uterine wall which is in intimate contact with the chorionic villi. 

 (7) Chorionic villi receive the blood from the embryo by the umbilical umbilical vein returns the blood back to the embryo. 

(8 ) Human placenta is said to be haemochorial because a part of placenta is from fetus which has chorionic villi. The other highly vascularized part is from uterine wall of mother. Thus fetal and maternal placenta together is called haemocorial placenta.

The Fetal Circulation

The circulatory system of a fetus, called the fetal circulation,exists only in the fetus and contains special structures that allow the developing fetus to exchange materials with its mother . It differs from the postnatal (after birth) circulation because the lungs, kidneys, and gastrointestinal organs do not

begin to function until birth. The fetus obtains O2 and nutrients from the maternal blood and eliminates CO2 and other wastes into it.

 The exchange of materials between fetal and maternal circulations occurs through the placenta (pla-SEN-ta), which forms inside the mother’s uterus and attaches to the umbilicus (navel) of

the fetus by the umbilical cord (um-BIL-i-kal). The placenta communicates with the mother’s cardiovascular system through many small blood vessels that emerge from the uterine wall. The

umbilical cord contains blood vessels that branch into capillaries

in the placenta. Wastes from the fetal blood diffuse out of the capillaries, into spaces containing maternal blood (intervillous spaces) in the placenta, and finally into the mother’s uterine veins.

Nutrients travel the opposite route—from the maternal blood ves-

sels to the intervillous spaces to the fetal capillaries. Normally,

there is no direct mixing of maternal and fetal blood because all

exchanges occur by diffusion through capillary walls.

Blood passes from the fetus to the placenta via two umbilical

arteries in the umbilical cord. These branches of the internal iliac (hypogastric) arteries are within the umbilical cord. At the placenta, fetal blood picks up O2 and nutrients and

eliminates CO2 and wastes. The oxygenated blood returns from

the placenta via a single umbilical vein in the umbilical cord.

This vein ascends to the liver of the fetus, where it divides into

two branches. Some blood flows through the branch that joins the

hepatic portal vein and enters the liver, but most of the blood

flows into the second branch, the ductus venosus (DUK-tus ve-NO¯-sus), which drains into the inferior vena cava.

 Deoxygenated blood returning from lower body regions of the

fetus mingles with oxygenated blood from the ductus venosus in the

inferior vena cava. This mixed blood then enters the right atrium.

Deoxygenated blood returning from upper body regions of the fetus enters the superior vena cava and also passes into the right atrium.

 Most of the fetal blood does not pass from the right ventricle to

the lungs, as it does in postnatal circulation, because an opening

called the foramen ovale (foˉ-RAˉ-men oˉ-VAL-e¯) exists in the sep-

tum between the right and left atria. Most of the blood that enters

the right atrium passes through the foramen ovale into the left

atrium and joins the systemic circulation. The blood that does

pass into the right ventricle is pumped into the pulmonary trunk,

but little of this blood reaches the nonfunctioning fetal lungs. Instead, most is sent through the ductus arteriosus (ar-te¯-re¯-O¯-sus),

a vessel that connects the pulmonary trunk with the aorta. The

blood in the aorta is carried to all fetal tissues through the systemic circulation. When the common iliac arteries branch into the external and internal iliacs, part of the blood flows into the internal iliacs, into the umbilical arteries, and back to the placenta for another exchange of materials.

 After birth, when pulmonary (lung), renal (kidney), and digestive functions begin, the following vascular changes occur

1. When the umbilical cord is tied off, blood no longer flows

through the umbilical arteries, they fill with connective tissue, 

and the distal portions of the umbilical arteries become fibrous

cords called the medial umbilical ligaments. Although the

arteries are closed functionally only a few minutes after birth,

complete obliteration of the lumens may take 2 to 3 months.

2. The umbilical vein collapses but remains as the ligamentum

teres (TE-re¯z) (round ligament), a structure that attaches the

umbilicus to the liver.

3. The ductus venosus collapses but remains as the ligamentum

venosum (ve-NO¯-sum), a fibrous cord on the inferior surface

of the liver.

4. The placenta is expelled as the afterbirth.

5. The foramen ovale normally closes shortly after birth to be-

come the fossa ovalis, a depression in the interatrial septum.

When an infant takes its first breath, the lungs expand and

blood flow to the lungs increases. Blood returning from the

lungs to the heart increases pressure in the left atrium. This

closes the foramen ovale by pushing the valve that guards it

against the interatrial septum. Permanent closure occurs in

about a year.

6. The ductus arteriosus closes by vasoconstriction almost im-

mediately after birth and becomes the ligamentum arterio-

sum (ar-te¯-re¯-O¯-sum). Complete anatomical obliteration of the lumen takes 1 to 3 months.