BODY FLUIDS AND CIRCULATION PART-1: BODY FLUIDS

In this post we are going to discuss about the Body Fluids. For the post of Exchange of Gases and Resporatory Disorders, click here

Different groups of animals have evolved different methods for this transport. Simple

organisms like sponges and coelenterates circulate water from their surroundings through their body cavities to facilitate the cells to exchange these substances. More complex organisms use special fluids within their bodies to transport such materials. Blood is the most commonly used body

fluid by most of the higher organisms including humans for this purpose. Another body fluid, lymph, also helps in the transport of certain substances. 

Blood:

Blood is a special connective tissue consisting of the following elements-

i) fluid matrix

ii) plasma

iii) Other elements.

Plasma:

•Plasma is a straw coloured, viscous fluid constituting nearly 55 per cent of the blood. 

•90-92 per cent of plasma is water and proteins contribute 6-8 per cent of it. 

•Fibrinogen, globulins and albumins are the major proteins.

•Fibrinogens are needed for clotting or coagulation of blood. 

•Globulins primarly are involved in defense mechanisms of the body and the albumins help in osmotic balance. 

•Plasma also contains small amounts of minerals like Na+, Ca++, Mg++, HCO3 –, Cl–, etc. Glucose, amino acids, lipids, etc., are also present in the plasma as they are always in transit in the body. 

•Factors for coagulation or clotting of blood are also present in the plasma in an

inactive form. 

•Plasma without the clotting factors is called serum.

For the post of Process of Digestion, Click here

Other Elements:

•Erythrocytes, leucocytes and platelets are collectively known as the other (formed) elements and they constitute nearly 45 per cent of the blood.

Erythrocytes:

•Erythrocytes or red blood cells (RBC) are the most abundant of all the cells in blood. 

•A healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs mm–3 of blood. 

•RBCs are formed in the red bone marrow in the adults. 

•RBCs are devoid of nucleus in most of the mammals and are biconcave in shape. 

•They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these

cells. 

•A healthy individual has 12-16 gms of haemoglobin in every

100 ml of blood. 

•These molecules play a significant role in transport of

respiratory gases. 

•RBCs have an average life span of 120 days after which they are destroyed in the spleen (graveyard of RBCs).

Other(Formed)Particles in Blood

For the post of Absorption of Food and Digestive Disorders, click here.

Leucocytes:

•Leucocytes are also known as white blood cells (WBC) as they are colourless due to the lack of haemoglobin. 

•They are nucleated and are

relatively lesser in number which averages 6000-8000 mm–3 of blood.

•Leucocytes are generally short lived. We have two main categories of WBCs-granulocytes and agranulocytes. 

•Neutrophils, eosinophils and basophils are different types of granulocytes, while lymphocytes and monocytes

are the agranulocytes. 

•Neutrophils are the most abundant cells (60-65 per cent) of the total WBCs and basophils are the least (0.5-1 per cent)

among them. 

•Neutrophils and monocytes (6-8 per cent) are phagocytic cells which destroy foreign organisms entering the body.

•Basophils secrete histamine, serotonin, heparin, etc., and are involved in inflammatory

reactions. 

•Eosinophils (2-3 per cent) resist infections and are also associated with allergic reactions. 

•Lymphocytes (20-25 per cent) are of two major types – ‘B’ and ‘T’ forms. Both B and T lymphocytes are responsible for immune responses of the body.

For the post of Anatomy of Digestive System, Click here.

Platelets:

•Platelets also called thrombocytes, are cell fragments produced from

megakaryocytes (special cells in the bone marrow). 

•Blood normally contains 1,500,00-3,500,00 platelets mm–3. 

•Platelets can release a variety

of substances most of which are involved in the coagulation or clotting of blood. 

•A reduction in their number can lead to clotting disorders which

will lead to excessive loss of blood from the body.

For the post related to Human Respiratory system, click here

Blood Grouping:

ABO Blood Grouping:

•ABO grouping is based on the presence or absence of two surface antigens (chemicals that can induce immune response) on the RBCs namely A and B. 

•Similarly, the plasma of different individuals contain two natural antibodies (proteins produced in response to antigens). 

•The distribution of antigens and antibodies in the four groups of blood, A, B, AB and O are given in the following table. 

•We know that during blood transfusion, any blood cannot be used; the blood of a donor has to be carefully matched with the blood of a recipient before any blood transfusion to avoid severe problems of clumping (destruction of RBC).

•From the above mentioned table it is evident that group ‘O’ blood can be donated to persons with any other blood group and hence ‘O’ group individuals are called ‘universal donors’. 

•Persons with ‘AB’ group can

accept blood from persons with AB as well as the other groups of blood; Therefore, such persons are called ‘universal recipients’.

Rh Blood Grouping:

•Another antigen, the Rh antigen similar to one present in Rhesus monkeys (hence Rh), is also observed on the surface of RBCs of majority (nearly 80 per cent) of humans. 

•Such individuals are called Rh positive (Rh+ve) and those in whom this antigen is absent are called Rh negative (Rh-ve).

•An Rh-ve person, if exposed to Rh+ve blood, will form specific antibodies against the Rh antigens. 

•Therefore, Rh group should also be matched before transfusions. 

•Erythroblastosis foetalis :

<> A special case of Rh incompatibility (mismatching)

has been observed between the Rh-ve blood of a pregnant mother with Rh+ve blood of the foetus. 

<> Rh antigens of the foetus do not get exposed to

the Rh-ve blood of the mother in the first pregnancy as the two bloods are well separated by the placenta. 

<> However, during the delivery of the first child, there is a possibility of exposure of the maternal blood to small

amounts of the Rh+ve blood from the foetus. 

<> In such cases, the mother starts preparing antibodies against Rh antigen in her blood. 

<> In case of her subsequent pregnancies, the Rh antibodies from the mother (Rh-ve) can leak into the blood of the foetus (Rh+ve) and destroy the foetal RBCs. 

<> This could be fatal to the foetus or could cause severe anaemia and jaundice to the baby. 

<> This condition is called erythroblastosis foetalis. 

<> This can be avoided by administering anti-Rh antibodies to the mother immediately after the delivery of the first child.

Blood Coagulation:

•Blood exhibits coagulation or clotting in response to an injury or trauma. This is a mechanism to prevent excessive loss of blood from the body. 

•We would have observed a dark

reddish brown scum formed at the site of a cut or an injury over a period of time. 

•It is a clot or coagulam formed mainly of a network of threads

called fibrins in which dead and damaged formed elements of blood are trapped. 

•Fibrins are formed by the conversion of inactive fibrinogens in the plasma by the enzyme thrombin. 

•Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin. 

•An enzyme complex, thrombokinase, is required for the above reaction. 

•Thrombokinase complex is formed by a series of linked enzymic reactions (cascade

process) involving a number of factors present in the plasma in an inactive state. 

•An injury or a trauma stimulates the platelets in the blood to release certain factors which activate the mechanism of coagulation. 

•Certain factors released by the tissues at the site of injury also can initiate coagulation. 

•Calcium ions play a very important role in clotting.

Lymph:

•As the blood passes through the capillaries in tissues, some water along with many small water soluble substances move out into the spaces between the cells of tissues leaving the larger proteins and most of the

formed elements in the blood vessels. This fluid released out is called the interstitial fluid or tissue fluid. 

•Tissue fluid has the same mineral distribution as

that in plasma. 

•Exchange of nutrients, gases, etc., between the blood and

the cells always occur through this fluid. An elaborate network of vessels called the lymphatic system collects this fluid and drains it back to the major veins. 

•The fluid present in the lymphatic system is called the lymph.

•Lymph is a colourless fluid containing specialised lymphocytes which are responsible for the immune responses of the body. 

•Lymph is also an important carrier for nutrients, hormones, etc. Fats are absorbed through

lymph in the lacteals present in the intestinal villi.