Circulation
(Notes)
Portal
System:
A vein carrying
deoxygenated blood from a system of capillaries divides again to form a second
capillary system in tissues before returning to the heart. Such a vein is
called a portal vein.
Portal vein + Capillary
System -----à
Portal System.
Eg: Hepatic Portal Vein
returns blood from the intestine and breaks into a portal system of capillaries
in the liver (hepatic portal system). This allows the liver cells to take up
the nutrients from the portal blood brought from the small intestine.
ECG
The recording of
electric potential generated by the spread of Cardiac Impulse is called ECG. It
is the graphic record of the electric current produced by the excitation of the
cardiac muscles. A normal ECG consists of a P wave, a QRS complex and a T wave.
P
Wave : Small upward wave that indicates the depolarization of
atria. (Spread of impulse from sinus node throughout the atria).
QRS
Complex: Ventricular depolarization.
T
Wave : Return of ventricles from excited to normal state.
(repolarisation).
Importance
of Hepatic Portal Circulation :
Blood
which comes from alimentary canal contains absorbed food like glucose and amino
acids. Excess of glucose is converted into glycogen which is stored in the
liver for later use.
When an individual
feels the deficiency of food, the glycogen is converted into glucose and
transferred to blood stream via hepatic veins.
Also,
liver produces proteins which are put into blood circulation.
Rh (Rhesus) Blood
Group:
A
protein named Rhesus Antigen is present on the surface of the RBCs in
many persons. It was first discovered in the blood of the Rhesus Monkey.
People
who have this antigen --à Rh+
Those
who do not have -à Rh-
Formation
of Rh protein is controlled by a dominant gene, called R.
Incompatibility during blood
Transfusion:
Q:
First blood transfusion of Rh+ blood to Rh- person causes
no harm. Why?
A:
Rh- person develops anti Rh factors or antibodies in his/her blood. In
the second transfusion, anti Rh
factors of Rh- person attacks and destroys the RBCs of the donor.
Incompatibility during Pregnancy
If
the father’s blood is Rh+ and the mother’s blood is Rh-,
the foetus’s blood will be Rh+. If the Rh- blood of the mother has
not earlier come in contact with the Rh+ blood through transfusion, her first
child does not suffer. But, the Rh+ blood of the foetus stimulates the
formation of anti Rh factors (enough anti Rh factors are not produced in
the mother’s blood to harm the foetus).
But,
in the subsequent Rh+ fetuses, anti Rh factors of the mother may destroy the
foetal RBCs.
This
results in the Haemolytic Disease of the
Newborn (HDN)- Erythroblastosis foetalis