FETAL AND PORTAL CIRCULATIONS- ENGLISH
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FETAL AND
PORTAL CIRCULATIONS-
• The
blood circulation is defined as flow of blood
through blood vessels to
different parts of body. There are four types of blood circulations we study in anatomy and
physiology-
• Pulmonary
circulation.
• Systemic
circulation
• Fetal circulation (only in fetus)
• Portal
circulation.
FETAL CIRCULATION-
The lungs of developing fetus are
inactive. Fetus obtains its oxygen and nutrients, and excretes its
waste, via the mother’s blood. this exchange take place in the placenta. The
blood flow from placenta to fetus tissues and back to placenta is know as fetal
circulation
PLACENTA- This is a temporary structure that allows exchange of substances between circulatory systems of mother and fetus. The
placenta is firmly attached to the uterine wall and consists of an extensive
network of fetal capillaries bathed in maternal blood. Although the fetal
capillaries are in very close proximity to the maternal blood supply yet the
two circulations are completely separate.
VENOUS BLOOD FLOW TO FETUS
One umbilical vein collects oxygenated blood from placenta and travel to infant through
umbilical cord. There is a special vein (Ductus venosus) which is a
continuation of the umbilical vein that returns blood directly into the fetal
inferior vena cava, and most blood, therefore, bypasses the non-functional
fetal liver. Fetal inferior vena cava pour oxygenated blood into right atrium
of fetal heart.
There are two special adaptations in fetal heart to bypass
the lungs as it is already oxygenated blood.
• Foramen
ovale- This forms a valve-like opening
allowing blood to flow from right
atrium to the left atrium to bypass lungs.
• Ductus
arteriosus- This small vessel connects the pulmonary artery to the descending
thoracic aorta and diverts more blood into the systemic circulation, meaning
that very little blood passes through the fetal lungs. Oxygenated blood is pumped into fetal systemic circulation
RETURN OF BLOOD TO PLACENTA
Two placental arteries arises from internal iliac artery
and carry less oxygenated blood to placenta through umbilical cord . In this
way the fetal circulation is completed.
CHANGES AT BIRTH
When the baby takes its first breath the lungs inflate
for the first time, increasing pulmonary blood flow. Blood returning from the
lungs increases the pressure in the left atrium, closing the flap over the foramen
ovale and preventing blood flow between the atria. Blood entering the right
atrium is therefore diverted into the right ventricle and into the pulmonary
circulation through the pulmonary veins.
As the pulmonary circulation is established blood oxygen levels increase, causing constriction
and closure of the ductus arteriosus. When the placental circulation ceases, soon
after birth, the umbilical vein, ductus venosus and umbilical arteries
collapse, as they are no longer required.
PORTAL CIRCULATION-
• Portal
circulation can be defined as a part of the systemic circulation, in
which blood draining from the capillary bed of one structure flows through
larger vessels to supply the capillary bed of another structure, before
returning to the heart. In simple words
we can say that a system of blood vessels that begins and ends in capillaries
is called portal system.
• There
are many portal circulations in humen body such as hypophyseal portal
circulation, pancreatic portal system hepatic portal system etc.
HEPATIC PORTAL CIRCULATION-
The hepatic portal system is important it is defiend as
flow of blood from the intestine to
the liver, where
secondary capillary network is formed before entering the general circulation.
Hepatic portal vein receives
blood from
• The
splenic vein (from the spleen, the pancreas and part of the stomach.)
• The
inferior mesenteric vein ( blood from the rectum and a part of large intestine.
• The
superior mesenteric vein ( blood from the small intestine and a parts of the
large intestine)
• The
gastric veins ( blood from the stomach and the distal end of the oesophagus)
• The
cystic vein, (blood from the gall bladder)
The hepatic portal vein supplies about 75% of the blood
the liver requires, with the other 25% supplied by the hepatic artery. Blood
from the hepatic artery is oxygenated but nutrient-poor compared to that
supplied by the hepatic portal vein. Blood from either source passes into cavities
between the hepatocytes of the liver called sinusoids, which feature a
fenestrated, discontinuous endothelium allowing for the effecient transfer and
processing of nutrients in the liver .
Since blood received from the hepatic portal vein may be
contaminated with pathogens such as bacteria, the liver is rich in specialized
immune cells called Kupffer cells that detect and destroy foreign organisms.
Following processing, blood collects in a central vein that drains into the
hepatic vein and finally the inferior vena cava>>> right atrium
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