Download Pulmonary Circulation

There is a specific anatomic structure of fetal circulation:
1-Blood returning from the placenta through the umbilical vein
passes through the ducts venosus by-passing the liver into inferior
vena cava.
2-Then most of the blood (oxygenated) entering the right atrium
from the inferior vena cava is directed in a straight pathway
through the foramen ovale directly into the left atrium and then
into the left ventricle.
3-Other blood (deoxygenated) entering the right atrium from
superior vena cava is directed into the right ventricle then into
pulmonary artery then into the descending aorta through the ducts
arteriosus.
4-Blood is returned through the two umbilical arteries into the
placenta thus the deoxygenated blood becomes oxygenated again.
*At birth, when lungs, renal, digestive and liver functions are
established, the followings changes occur:
1-The umbilical arteries vasoconstrict shut and atrophy to become
the medial umbilical ligaments.
2-The umbilical vein vasoconstricts shut and become the round
ligament of the liver.
3-The placenta is delivered by the mother as the after birth.
4-The ducts venosus vasoconstricts shut and becomes the
ligamentum venosum (a fibrous cord in the liver).
5-the foramen ovale normally closes shortly after birth to become
the fossa ovalis (a depression in the internal septum).
6-The ductus arterious closes by vasoconstriction and atrophies
and become the ligamentum arteriosus.
Pulmonary Circulation :
Pulmonary circulation defined as the flow of deoxygenated
blood from the ventricle to the air sacs of the lungs and the return
of oxygenated blood from the air sacs of the lungs to the left
atrium.
Pulmonary trunk emerge from the right ventricle and passes
upward, then divide into right and left pulmonary arteries to the
right and left lungs respectively.On entering the lungs, these
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arteries divide and subdivide until they from capillaries around
the alveoli (air sacs) in the lungs. CO2 is passed from the blood
into the alveoli and O2 is passed from the alveoli into the blood.
The capillaries unite, venules and veins are formed and eventually
two pulmonary veins exit from each lung and transport the
oxygenated blood to the left atrium.
Blood flow through the lungs differs from systemic circulation
in several ways:
1-The pulmonary arteries have lager diameter, thinner wall and
less elastic tissue than their counterpart systemic arteries. As a
result there is little resistance to blood flow. This means that less
pressure is required to move blood through the lungs.
2-There is an auto regulation mechanism in response to levels of
oxygen. In systemic circulation, blood vessels dilate in response
to low oxygen concentration. In pulmonary circulation, blood
vessels constricts in response to low oxygen concentration. This
mechanism is very important in the distribution of blood in the
lungs who it is needed most.
3-There is a different between pulmonary and systemic
circulation relates to capillary hydrostatic pressure. In systemic,
the capillary hydrostatic pressure=25 mmHg but in pulmonary,
the capillary hydrostatic pressure= 15mmHg because the colloid
osmotic pressure in the interstitial fluid of the lungs is high. This
difference is to prevent pulmonary oedema.
*Pulmonary oedema may develop from:
a-increased capillary blood pressure due to increased left atrial
pressure (e.g. in case of mitral valve stenosis).
b-increased capillary permeability due to some bacterial toxin.
*Pulmonary oedema lead to decrease diffusion rate of O2 and
CO2 which lead to inhibits the exchange of gases in the lungs.
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Hepato-Portal Circulation:
Define as the flow of venous blood from the gastrointestinal
organs and spleen to the liver before returning to the heart. (which
can be summarized as following:
Coronary Circulation:
The left and right coronary arteries and their branches supply
blood to the heart muscle. These arteries branch from the base of
the ascending aorta as it leaves the heart.They traverse the
anterior surface of the heart in the grooves and pass to the
posterior surface, where their branches anastomose or join
together.(This anastomoses is for maintaining a blood supply to
the cells of the heart when a vessel becomes blocked). Numerous
branches from the main arteries carry blood to the capillary
networks among the muscle cells.
After passing through the capillaries, blood enters the cardiac
veins.
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Many of these veins unit to form a large vessel called the coronary
sinus which carries blood into the right atrium.
Other veins(from the wall of the right ventricle) return blood
return blood ‫جيبانيات‬directly to the right ventricle.Sinusoids
from the myocardium directly into the cavities of the ventricles.
Blood flow in heart muscle vessels only when the heart is
relaxed (contraction compresses the vessels and prevents the fl
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