Transportation in human beings

Date: December 09, 2014

Transportation in Human Being

In human beings, various substance, such as digested food, oxygen, hormones excretory products, are transported to relevant organs and tissues through blood and lymph. The blood circulatory system comprises heart, the organ wich pumps and receives blood and the blood vessels.

Composition and Functions of Blood– Circulation of blood is responsible for transportation of : (1) Nutrients (2), Respiratory Gases, (3) Waste products, (4) Hormones and enzymes, and (5) Ions from one part of the body to the other. Blood also plays a role in temperature regulation and protection of the body from the attack of foreign bodies and disease causing pathogens.

What is blood? It is a connective tissue blood has a fluid matrix called plasma, and three kinds of cells. These cells are (1) Erythrocytes (red blood corpuscles), (2) leucocytes (while blood corpuscles) and (3) blood platelets.

Plasma is colourles and contains a lot of water and many proteins. Blood looks red because of the red coloured pigment haemoglobin present in the red blood cells. Normal mature red blood cells are circular in shape and do not contain nuclei. Haemoglobin performs a very important function of carrying oxygen from lungs to tissues and carbon dioxide from tissues to lungs.

Red blood cells have a life span of about 120 days. It is estimated that about three million red blood corpuscles die everyday, but four times as many are produced in the bone marrow.

White blood cells are lesser in number than the red boold cells. They protect the body from infections. They are capable of squeezing themselves out of capillaries to destroy foreign matter. White blood cells also manufacture antibodies which are responsible for Immunity. Blood platelets are fragments of cells. They do not possess nuclei. They participate in the coagulation of blood. Blood cells are manufactured in the bone marrow from cells called stem cells.

Blood Clotting– An injury which ruptures a blood vessel may cause immense blood loss, which may even lead to death. Body has its own mechanism of preventing this loss by forming a blood clot which plugs the injury to stop bleeding.

Clotting or coagulation of blood is a complex process which required several factores. The major step in blood coagulation is described below.

As blood flows out of a damaged blood vessel blood platelets release a substance called Thromboplastin. In the presence of calcium and thromboplastin, Prothrombin present in blood gets converted into thrombin. Thrombin then catalyses the conversion of fibrinogen present in plasma into Fibrin. Fibrin is the ultimate product which forms a mesh, into which red blood corpuscles get entangled and form a Blood Clot. Plugs the ruptured blood vessel. So, no more blood can flow out. After the clot dries up, a yellow fluid remains on the cell. This is called serum. It is plasma without its fibrinogen.

Blood Groups and Blood Transfusion

Transfer of blood from a healthy individual (donor) to another individual (recipient), is known as blood transfusion. When the practice of blood transfusion began, it was noticed that the blood transfusion may not always match the blood of the patient who receives it. As a result, the blood of the patient clumps or agglutinates, proving fatal to the life of the patients. Landsteiner discovered theat mismatching of blood was due to a reaction between antigens present in the red blood cells of the donor and antibodies present in the plasma of receiver or recipient. Two different antigens were discouved and named A and B. Their corresponding antibodies which react and clump the blood were termed ‘a’ and ‘b’.  In human beings, four different blood groups are foundA, B, AB and O. Blood group are inderited from parents. Successful transfusion is possible between the same gourp or cetain gourps, as shown in the foffowing table

You can see from the table below that O group can give blood to all the groups, and hence, a person having this blood group is called universal donor. Interestingly, a person with AB group can receive blood of all other group, but cannot donate ot other group. Hence, AB group is the universal recipient.


Blood Group

Antigen present in RBC

Antibody present in Plasma

Possibility of blood donation




Can donate blood to A and AB




Can donate blood to B and AB




Can receive from all but donate to AB



a, b

Can donate to all but receive only from O.AB

Another factor in blood, called Rh factor, is alos genetically determined. Most people are Rh positive (Rh+). A few are Rh negative (Rh-). An Rh negative mother may lose her baby if the baby has Rh+ blood.

Blood reaches all the parts through the circulatory system, which consists of a central pumping organ, the hear and blood vessels.

Blood Vessels

Blood vessels are of three kinds (1) Arteries, which are thick- walled and carry blood from the heart to different organs; (2) Veins, which are thin-walled, have valves and carry blood from different organs to the hear; and (3) Capillaries, which are blood vessels occurring at the terminals of artery and vein. Capillaries are thin-walled and extremely narrow. Exchange of food material, gases and waste takes place through capillaries.

The Human Heart

Heart is four chambered: two upper chambers are called atria (singular, atrium) and they receive blood from large veins. The two lower chambers are the left and right ventricles. They transport blood to lungs and the entire body. These chambers are separated by partitions called septa. Between left atrium and left ventricle are valves, and so are valves between right atrium and right ventricle. Valves permit the flow of blood from atrium to ventricle and not in the reverse order. Heart is made of special muscle, cells called cardiac muscles.

The heart beats all the time throughout one’s life. Heart beat is due to rhythmic contraction and relaxation of heart muscles. When muscles of all four chambers of the heart are relaxed, bloods from large veins, called vena cava, pour into right atrium. This blood in the vena cava has very little amount of exyge, as it comes from tissues which have used up all oxygen. Pulmonary vein from lungs pours oxygenated blood into the left atrium. Next, the atria contract. During atrial contraction, right atrium pours deoxygenated blood into right ventricle and left atrium pours oxygenated blood into left ventricle. Next, the ventricle oxygenated blood is distributed to all the parts of the body through the largest artery, called aorta. From right ventricle, deoxygenated blood flows to the lungs through pulmonary artery. In this war, deoxygenated blood comes to the hear; it is oxygenated in the lungs and comes back to the heart. From the heart, oxygenated blood is distributed to all parts of the body. Since blood flows twice through the heart, it is called double circulation.

Detection of Normalcy of Heart Beat

The muscle fibres (or muscle cells) of the heart are specialized at certain parts of the heart, to generated electric currents that cause the normal rhythmic heart beats. An instrument called the electrocardiograph, can record the electrical changes during heart beat. This graphic recording is called ECG, or Electrocardiogram. A machine called the “pace maker” is inserterd in a heart patient whose heart does not beat normally. “Pace maker”, the machine takes the place of the specialized muscle cells that initiate heart beat and which in the patient have stopped functioning.

Lymphatic System

Lymph is also a circulatory fluid that drains into lymphatic capillaries, which join to form large lymph vessels. Lymph glands and lymph nodes are associated with lymph vessels.

Lymph is a light yellow fluid containing lymphocyte cells, which fight against infection. Lymph flows only in one direction that is from tissues to heart. As it bathes the cells and lies outside cells, lymph is also called edtracellular fluid.