The Circulatory System ICSE Class 10 Concise Biology

Class:- 10 ICSE {Selina Concise Biology}

Chapter:- 8 , THE CIRCULATORY SYSTEM

8.1 NEED FOR TRANSPORT INSIDE THE BODY

 Every organ in our body requires the involvement of the circulating body fluids. For example:

• The digestive system digests and absorbs nutrients that are needed to be transported to every cell of the body.

• The respiratory system draws in air, and the oxygen picked up from it in the lungs has to be transported to all parts of the body. Similarly, the CO, collected from the entire body has to be carried to the lungs to be exhaled out of the body.

 All the extra water, excess salts, and nitrogenous wastes such as urea have to be removed from different parts and have been sent to the excretory system to be thrown out of the body.

• Hormones secreted by the endocrine system have to be carried throughout the body by the circulating blood to act wherever required, and so on.

All such functions that need transport are performed by the two circulating fluids - the blood and the lymph. Besides transport, these fluids have some other functions also.

8.2 FLUIDS IN OUR BODY

There are three principal fluids in our body:

·     Blood, contained in the heart and in the blood vessels (arteries, veins, and capillaries) of the circulatory system.

·     Tissue fluid, occupying spaces between cells in the organs.

·     Lymph, which is contained within lymph vessels and lymphatic organs such as the spleen and the tonsils.

The above three principal fluids in our body are respectively described in section 8.3 (blood) and section 8.9.3 (tissue fluid and lymph1).

Fig. 8.1 shows a diagrammatic representation of the relationship between blood, tissue fluid, and lymph as they circulate in their respective vessels or spaces between the cells in different organs. It is clear from the diagram that blood in our body circulates in a closed manner i.e. all the time through blood vessels. Such a type of blood circulation is called a closed blood circulatory system. As against this, in certain animals such as insects, the blood mostly flows through open spaces in the body, called an open blood circulatory system. Their blood flows from the heart to body spaces without vessels.

8.3 PROPERTIES OF BLOOD: THE BLOOD

 

·     Never Stationary - Blood is always in motion from the heart to the arteries and back through the veins.

·     Colour - The blood is a somewhat thick fluid, bright red when taken from an artery or dark red when taken from a vein.

·     Volume- An average adult human has 5 to 6 liters of blood by volume in his body.

·     Taste - saltish Perhaps we have all "tasted" our blood as in the case when there is a cut in the tongue or bleeding from the gums. It tastes saltish. The blood is slightly alkaline with a pH of 7.3 to 7.45 (7 is neutral, neither acidic nor alkaline.

 8.5 FUNCTIONS OF BLOOD

 The main functions of the blood in our body can be treated under two broad headings: (A) Transport and (B) Protection.

 A. TRANSPORT BY BLOOD (Transport of digested food, oxygen, carbon dioxide, excretory substances, hormones, body heat).

 1. Transport of digested food from the alimentary canal to the tissues. These substances are simple sugars like glucose, amino acids, vitamins, mineral salts, etc.

2. Transport of oxygen from the lungs to the tissues. It occurs by means of red blood cells in combination with hemoglobin in the form of unstable compound oxyhemoglobin, which on reaching the tissues breaks up to deliver oxygen.

    ⟶Hb + 0₂      Hb.0₂

                  (Oxyhaemoglobin) 

3. Transport of carbon dioxide from the tissues to the lungs. It occurs partly in combination with hemoglobin and partly as a solution in blood plasma.

Hb + CO₂ ⟶  Hb.CO₂

                (Carbaminohaemoglobin)

4. Transport of excretory material from the tissues to the liver, kidney, or the skin for elimination or to render them harmless.

5. Distribution of hormones secreted by special glands (endocrine glands) directly into the blood.

6. Distribution of heat. The blood helps in keeping the temperature of the body uniform by distributing heat. 

B. PROTECTION BY BLOOD

 1. Blood forms a clot wherever there is a cut in a blood vessel. The clot serves to prevent

(i) further loss of blood and (ii) the entry of disease-causing germs.

2. Its white blood corpuscles protect the body from diseases by engulfing bacteria that may have entered the body.

3. It produces antitoxins and antibodies which neutralize the poisonous substances or kill the germs which enter the body.

 8.5 COMPOSITION OF BLOOD

 The blood consists of:

(i)     Plasma - fluid part, constitutes 55-60 percent of blood.

(ii) Cellular elements - red and white cells, and platelets, 40-45 percent of blood.

 8.5.1 PLASMA -The liquid portion of blood

 The plasma is a light yellow-colored, alkaline liquid. It mainly consists of:

The inorganic salts mainly include sodium glucose, chloride, and sodium bicarbonate. Among other substances contained in the plasma are amino acids, fibrinogen, hormones, urea, etc. The plasma from which the protein fibrinogen has been removed is called serum.

8.5.2 CELLULAR ELEMENTS (Fig. 8.2)

The formed or cellular elements of the blood (i.e. shaped structures visible under magnification) are of three categories :

·        Red Blood Cells (erythrocytes)

·        White Blood Cells (leukocytes)

·        Blood Platelets(thrombocytes)

(1) RED BLOOD CELLS (RBCs) - The oxygen carriers

 

Red blood cells are also called erythrocytes (erythros: red)

       ·     These are minute biconcave disc-like structures_ flat in the center and thick and rounded at the periphery.

·     These are very small about 7 microns in diameter (1-micron one=thousandth of a millimeter and is represented by the symbol "μ").

·     The small size plus the concavities on either side provide a large surface area which makes them very efficient in absorbing oxygen.

·     The small size enables the red blood cells to travel through very fine capillaries in the body where they have to travel in a single file.

(1) Red blood cells (erythrocytes) (2) White blood cells (leukocytes) (3) Blood platelets (thrombocytes)

 (1) RED BLOOD CELLS (RBCs)-The oxygen carriers

 Red blood cells are also called erythrocytes. (erythros: red)

 These are minute biconcave disc-like structures, flat in the center and thick and rounded at the periphery.

HAEMOGLOBIN is the effective chemical constituent of RBCs. The red blood cells have a colorless spongy body or stroma which contains respiratory pigment hemoglobin (Hb).

·          The hemoglobin is formed of an iron-containing part (haemin) and a protein (globin).

·          It has the ability to combine readily with oxygen from oxyhemoglobin, an unstable compound that readily gives up oxygen to needy tissues.

·          Haemoglobin can carry a very small quantity of carbon dioxide in the form of carbamino hemoglobin.

 Hemoglobin has a very strong affinity for carbon monoxide forming a stable compound carboxyhemoglobin (HbCO). This cuts down the capacity of the blood of transporting oxygen, sometimes resulting in death. This is known as carbon monoxide poisoning. For example, sleeping near burning furnaces in small rooms without ventilation can result in carbon monoxide poisoning and may even cause death.

 

Life and death of RBCs

·      In adults, the RBCs are produced in the marrow of long bones, especially in the ribs, breast bone, and ilium of the hip girdle.

·      In an embryo, they are produced in the liver and spleen.

·      In children, the RBCs are produced in the bone marrow of all bones until 5 years of age.

·      In children, the RBCs are produced in the bone marrow of all bones until 5 years of age.

·      The average life of an RBC is about 120 days.

·      The old and weak red blood cells are destroyed in the spleen, liver, and bone marrow, their iron part is retained in the liver while the rest is excreted as a bile pigment (bilirubin).

      ·      In a normal adult, approximately 2 million RBCs are destroyed every second. In other words, about I percent of the total erythrocytes in the body are destroyed every day. 

Based on the shape and other characteristics, the white blood cells are classified into two major categories (granular and non-granular) and five distinct types (Table 8.1 given on next page and Fig. 8.2) as follows:

Origin and life of WBCs :

The WBCs are produced in red bone marrow, lymph nodes, and sometimes even in the liver and the spleen. Their average life is about two weeks. The neutrophils live for only a few hours, and about 125 billion neutrophils are produced each day. The old and worn-out WBCs are destroyed in the same manner as the RBCs.

Leukemia is a cancer of the tissue forming WBCs whose number increases manifold at the cost of RBCs. It is usually a fatal disease. Currently, the treatment is only blood transfusion.

Leukopenia is the abnormal decrease in the number of WBCs.

Functions Of Leukocytes (WBCS) - Body defence

1. Phagocytosis: This is a process in which most WBCs and particularly the neutrophils engulf particle-like solid substances, especially bacteria. This is a defensive mechanism against disease germs. An abnormal increase in WBC count up to about 50,000 or more per cubic mm indicates some infection in the body.

2. Inflammation: Inflammation occurs due to the reaction of tissues to injury and to the localized invasion of germs. The inflamed spot has several characteristics: increased local heat, redness, swelling, pain, etc. Here the leucocytes (specially the monocytes and neutrophils) migrate through the walls of the blood vessels by diapedesis (Fig. 8.3) and fight against disease-causing germs. They also destroy the damaged cells by phagocytosis. Pus is mainly composed of the dead white blood cells together with the tissue cells destroyed by the bacteria.

3. Formation of antibodies: The WBCs (specially the lymphocytes) produce antibodies that kill or neutralize the germs or the poisons from them. Introducing weakened germs or germ substances (vaccines) during vaccination stimulates the formation of particular antibodies which, at a later period, would destroy the particular disease-causing germs if they enter into the body.

(3) BLOOD PLATELETS (Thrombocytes) (Initiators of clotting of blood)

Blood platelets are minute oval or round structures, non-nucleated, floating in the blood. These are about 200,000 to 400,000 per cu. mm. of blood in an adult. The platelets are derived from some giant cells called megakaryocytes in the red bone marrow. These are budded off from the megakaryocytes in a manner that each one is completely surrounded by a membrane. Their life span is 3 to 5 days and is destroyed mainly in the spleen (a lymphatic organ located in the abdomen). They are very important in the clotting of blood. At the site of injury, the platelets disintegrate to release a chemical substance thrombokinase which initiates the process of clotting of blood.

8.6 FUNCTIONS OF PLATELETS - CLOTTING OF BLOOD (COAGULATION)

When a blood vessel is cut, blood escapes. But soon a clot is formed on the wound (Fig. 8.4) and the flow of blood is stopped. If it were not so, the injured person would bleed to death. Clotting (also called coagulation) occurs in a series of steps as follows: 

1. The injured tissue cells and the platelets which disintegrate at the site of the wound release a substance thrombokinase (also called thromboplastin). (More recently it is called "Factor X" or Stuart factor).

2. The thrombokinase acts as an enzyme and with the help of the calcium ions present in the plasma, it converts the substance prothrombin (inactive) of the plasma, into thrombin (active). Vitamin K, a fat-soluble vitamin, is essential for the production of prothrombin.

3. Thrombin in the presence of calcium ions, reacts with the soluble fibrinogen of the plasma to convert it into insoluble fibrin. Fibrin is a solid substance that forms threads. These microscopic threads of fibrin are sticky and form a network (mesh) at the wound.

4. Blood cells are trapped in the network of the fibrin; the network then shrinks and squeezes out the rest of the plasma which is in the form of a clear liquid, the serum. The solid mass which is left behind is called a clot (or thrombus).

MAIN FUNCTION OF BLOOD CLOTTING

BLOOD CLOTTING

                                                                         THE FATE OF BLOOD IN BLOOD CLOTTING

BLOOD CLOTTING IN A TEST-TUBE

If some blood is taken in a test-tube, a clot will form in the usual way and the serum squeezed out from the clot will collect on the surface (Fig. 8.5).

It is a wrong notion that clotting is dependent on the exposure of blood to the air. In fact, clotting can be caused by the movement of blood over a rough surface as on cholesterol deposits on the inside of a blood vessel.

Haemophilia is a genetic disorder in which blood does not clot properly due to lack of blood-clotting proteins. Also in cases where the number of platelets falls to an abnormally low count, coagulation occurs very slowly and often leads to haemorrhage. Such a situation occurs in certain diseases as in the viral dengue fever which has taken hundreds of lives in Delhi and other states of India since 1996 till date.

8.7 BLOOD TRANSFUSION AND BLOOD GROUPS (ABO and Rh systems)

Sometimes it becomes necessary to inject blood into the body of patients undergoing surgical operations. This is called a blood transfusion. Blood taken from a healthy person (donor) is introduced through one of the patient's veins. But for doing so, it is necessary that the kind or the type of blood to be transfused should match (or be compatible) with the type of the blood of the receiving person (recipient).

The concept of blood grouping was discovered by Karl Landsteiner. RBCs of human beings have specific proteins on their surface. These proteins are called antigens. In humans, there are two types of antigens: 1. Antigen A 2. Antigen B. The plasma of the blood contains complementary proteins, called antibodies, with respect to the antigen that is present on the surface of RBCs. Depending on the presence or absence of the type of antigens, there are four blood groups as shown in the table.

There are several systems of blood grouping. But two of them, ABO system and Rh system are most important.

ABO System: According to the ABO system, the human blood is classified into four types A, B, AB, and O. Besides the transfusion of one's own type of blood (A to A, AB to AB, etc.), the other possible transfusions can be made as follows:

Accordingly, O-type blood can be given to persons of all types of blood i.e. to O, A, B & AB. Hence a person with O type is called a universal donor. A person with AB type of blood can receive blood from all types, i.e., from AB, A, B & O, and is, therefore, called a universal recipient. A person with A type can receive blood from A and O types and a person with B type from B and O types only.

The summary of matching (compatibility) and mismatching (incompatibility) in the ABO system is given in the table below:

Rh system: The blood of most people contains a substance called the Rh factor. (Rh stands for Rhesus, our common monkey, in which the factor was first discovered). When the blood of such an individual (Rh-positive) is transfused into persons lacking it (Rh negative), the blood of the recipient develops an antibody for Rh substance (gets sensitized) within about two weeks of transfusion. Now, if a second transfusion is given to such an Rh-negative person, the antibody produced by the first transfusion causes a reaction with the transfused blood, which may even lead to death. This is similar to the development of an allergy.

Rh factor in pregnancy: An Rh-negative woman may become sensitive if she carries an Rh-positive child in her uterus (when the husband is Rh-positive). The first Rh-positive child will be normal, but if it sensitizes the mother, the second positive child if conceived soon, may have a problem, sometimes leading to the death of foetus and abortion.

[Rh-positive may be written in short as Rh+ve or as Rh* and similarly, the Rh-negative may be written as Rh-ve or as Rh-]. People with Rh* blood group have D antigens on the surface of RBCs, while people with Rh blood group lack these antigens.

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