BLOOD VESSELS :
Blood circulates through the blood vessels.
They are arteries-which carries oxygenated (or) pure blood
,except the pulmonary arteries which carry de-oxygenated blood.
The veins carries de-oxygenated or impure blood except the
pulmonary veins which carries pure blood from lungs to left atrium of the
heart.
The arteries and veins are consists of three layers. They
are
1.
TUNICA ELASTICA, outer elastic layer made up of areolar connective tissue.it
is thicker in veins than the arteries.
2.
TUNICA MEDIA is made up of smooth muscle fibres, it is thicker in
artery then the vein.
3.
TUNICA INTIMA , is made up of endothelial cells ,and separated from
middle layer by a membrane called elastic lamina.
The lumen in vein is narrower,
while it is wide open in artery.
The veins are formed from smaller
veins called venules and venous capillaries.
The veins collects the
deoxygenated blood from lower limbs and other parts of the body and forms the
inferior venacava , and they collect the impure blood from the upper limbs and
head of the body and forms superior venacava and pour their contents into the
right atrium of the heart.
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