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.
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