Download the Composition of blood PDF from the given link at the end of the topic. Genera Science is an essential topic for any competitive exams like SSC, WBCS, NTPC, UPSC, RAIL, Banking, and other state PSCs. Human blood is an important topic covered under General Science. In this topic, we provide a brief note on the composition of blood and its function of blood. In the next post, we will talk about blood group and blood circulation methods.
Table of Contents
Introduction
• All living cells in the animal body need to be provided with nutrients, O2, and other essential nutrients to keep them healthy and strong.
• Also, the waste or harmful substances produced, have to be removed continuously for the healthy functioning of tissues.
• Therefore, there must be an efficient process of getting these essential substances into the cell and removing the waste materials from the cell.
• Different groups of animals have evolved different mechanisms for this transport.
• To exchange these substances, simple organisms like sponges and coelenterates, use the water canal system and gastrovascular cavity respectively.
• More complex organisms such as humans use special fluids like blood 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.
• Substance transported by blood
* Nutrients – Glucose, Fatty acids, Vitamins
* Waste products of metabolism
* Respiratory gasses – O2 and CO2.
* Hormones
What is Blood?
• Blood is a special connective tissue consisting of plasma and formed elements (RBC, WBC, platelets).
Physical Properties of Blood
• Fresh blood has a unique smell.
• Venous blood is dark red or bluish because of the high concentration of carbon dioxide in the blood.
• Arterial blood is bright red due to the high oxygen content in the arterial blood.
• Blood tastes salty due to the presence of NaCl (0.97%).
• Blood is alkaline, with an average pH of 7.4.
• The Specific gravity of blood is 1.005-1.065
• The relative viscosity of blood is about 4-6.
Blood Volume in Man
• The amount of blood in the body of a healthy adult male (5 feet in height and 70 kg weight) is about 5000 ml or 5 liters, while in a female it is 4.5 liter.
Chemical composition of Blood
• Blood contains 55% plasma, 1% platelets, and white blood cells and 44% red blood cells.
• The ratio of plasma and blood cells (55: 45) is called the Haemocrite value of blood.
❒ Plasma
• Plasma is a straw-colored (Pale Yellow), viscous fluid of blood, in which the red blood cells, white blood cells, and platelets are suspended.
Composition of Plasma
• It constitutes more than half of the blood’s volume (55%) and consists mostly of water (90-92%) that contains dissolved salts (electrolytes) and proteins (6-8%).
❖ Nitrogenous waste
• Plasma contains some Nitrogenous wastes.
• Example ☞ Urea and Creatinine, Uric Acid
❖ Non-nitrogenous Waste
• Example ☞ Glucose, amino acids, lipids
❖ Amino Acids
• Example ☞ Alanine and Glutamine
❖ Electrolytes (0.9%)
• Plasma also contains small amounts of minerals.
• Example ☞ Na+, Ca++, Mg++, HCO3–, Cl– etc.
❖ Gases (1-2%)
• Example ☞ O2 and CO2
❖ Nutrients
• Plasma contains nutrients that nourish tissues.
• Example ☞ Amino acids, the building blocks of proteins and glucose.
❖ Proteins (6–8%)
• Example ☞ Fibrinogen, Globulins, and Albumins
• Fibrinogens are needed for clotting or coagulation of blood.
• Globulins primarily are involved in the defense mechanisms of the body.
• The albumins help in maintaining osmotic balance, also known as Oncotic pressure (standard value – 25 mmHg)
• 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.
• Fibinogens are essential for coagulation of blood.
• Fibinogen is the heaviest protein in blood plasma.
• Most abundant (80%) immunoglobulin in serum – IgG
• Albumin is a protein made by the liver (12 gm/Day)
• Albumin is the most abundant protein (60%) in blood plasma.
• Serum albumin levels are tested to detect any liver disease.
Plasma Proteins
| Albumin | Globulins | Fibrinogen | Prothrombin | |
|---|---|---|---|---|
| Produced by | Liver | Liver, Lymphoid tissue | Liver | Liver |
| Percentage | 3.5-5.0 % | 2.5-3.5 % | 0.3 % | 0.01% |
| Function | Maintaining osmotic pressure | Defense function | Blood clotting and Viscosity | Blood Clotting |
❖ Formed Elements
• Erythrocytes, leukocytes, and platelets are collectively called formed elements-
• They constitute nearly 45 percent of the blood
➣ Erythrocytes
• Erythrocytes are also known as red blood cells (RBC).
• They are the most abundant of all the cells in the blood.
• A healthy adult man has, on an average, 5 million to 5.5 million RBCs mm3 of blood.
• Red bone marrow in the adults produced the RBCs.
• Red blood cells do not have a nucleus.
• The RBC’s are biconcave in shape.
• They have got a red color, due to the presence of hemoglobin.
• hemoglobin is an iron-containing complex protein.
• A healthy individual has 12-16 gms hemoglobin in every 100 ml of blood.
• These molecules play a considerable role in transport of respiratory gases.
• The formation or production of red blood cells is known as Erythropoiesis.
• The average life span of RBCs is 120 days, after which they are destroyed in the spleen, also known as the graveyard of RBCs.
• The bone marrow produces 3 million red blood cells every second.
• Life span of RBC – 120 days
• RBC’s take 20 seconds to circulate the body one time.
• Each RBC contains 1 billion molecules of Oxygen.
• Each RBC contains 280 million Hemoglobin molecule.
• In a 70 Kg man there is 4gm of iron.
➣ Leukocytes
• Leukocytes are also known as white blood cells (WBC) as they are colourless due to the lack of hemoglobin.
• They are nucleated and are relatively lesser in number which averages 6000-8000 mm3 of blood.
• Leukocytes are generally short lived. Lifespan 13–20 days.
• WBCs are classified into major categories – granulocytes and agranulocytes.
• Granulocytes include neutrophils, eosinophils, and basophils.
• While lymphocytes and monocytes are the agranulocytes.
• Neutrophils are the most abundant cells (60-65 %) of the total WBCs and basophils are the least (0.5-1 %) among them..
• Neutrophils and monocytes (6-8 %) are phagocytic cells, which destroy foreign organisms entering the body.
• Basophil secrete histamine, serotonin, heparin, etc., and is involved in inflammatory reactions.
• Eosinophils (2-3 %) resist infections and are associated with allergic reactions.
• Lymphocytes (20-25 %) are of two major types – ‘B’ and ‘T’ forms.
• Both B and T lymphocytes are responsible for immune responses of the body.
➣ Platelets
• Platelets also called thrombocytes.
• Platelets are cell fragments produced from megakaryocytes (special cells in the bone marrow).
• Blood normally contains 1,500,00-3,500,00 platelets mm3.
• 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.
• Lifespan 3 days.
Formed Elements of Blood (45%)
| Cell Type | Number Per mm3 | Function |
|---|---|---|
| Erythrocytes (RBCs) | 5-6 million | Transport of Oxygen and Carbon dioxide |
| Leukocytes (WBCs) | 5k-10k | Defense and immunity |
| Platelets | 2.5-4 lakh | Blood Clotting |
Blood Clotting
• Blood Clotting is a mechanism to prevent excessive loss of blood from the body.
• A dark reddish brown serum formed at the site of a cut or an injury over a period of time.
• It is a clot or coagulum constituted mainly of a network of threads called fibrils in which dead and damaged formed elements that as Erythrocytes, leukocytes, and platelets 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 the other inactive substance present in the plasma called prothrombin.
• An enzyme complex, thrombokinase, is needed for the above reaction.
• This enzyme 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 triggered the platelets present 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 vital role in clotting.
Lymph
• Our heart pumps blood with some pressure. As a result of this pressure, when the blood passes through the capillaries into the tissue, some water, and many small water soluble substances move into the space between the tissue cells, large proteins, and most of the components formed in the blood vessels.
• This fluid released out into the intercellular space is called the interstitial fluid or tissue fluid.
• Interstitial fluid or 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 specialized 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.
More important info about Colour of Blood
• Not All Blood Is Red, the color of blood depends on the respiratory pigments used to transport oxygen. Due to the presence of the hemoglobin protein, the color of human blood is red. Hemoglobin is an iron-rich protein found in the red blood cells of humans.
• Other organisms have blood of varying colors. E.g Spiders, squid, octopuses, and some arthropods have blue blood. Some sorts of worms and leeches have green blood. Insects like Butterflies and Beetles have colourless or pale-yellowish blood. Some species of marine animals have yellow blood.
Various Colours of Blood
| Colour | Respiratory Pigments | Metal Presents | Species /Animals |
|---|---|---|---|
| Yellow | Haemovanabine | Vanadium | Beetles, Sea squirts, Sea cucumber. |
| Green | Chlorocruorin | Iron | Leeches and marine worms |
| Purple | Haemerythrin | Iron | Peanut worms (Sipuncula), Penis worm (Priapulida), Brachiopods |
| Blue | Haemocyanin | Copper | Horseshoe crab, Crustaceans |
| Red | Hemoglobin | Iron | red blood cells of all vertebrate animals |
Function of Blood
So far we have been discussing the composition of blood, now letting us know very briefly about the different functions of blood.
General Function of Blood
• Transport of Nutrients
• Transport of Respiratory Gases
• Drainage of waste products.
• Act as a medium of Transportes.
• Maintenance of water balance
• Maintenance of Acid-base equilibrium
• Maintenance of ion balance
• Regulation of body temperature
• Prevents Haemorrhage
• Defensive action
Function of Blood Corpuscles
Function of Red Blood cells
• Transport of Respiratory gases. E.g Oxygen and Carbon dioxide
• Acid-base balance
• Ion balance
• Viscosity of blood
• Sources of various pigments. E.g bilirubin, Biliverdin [see the image ‘fate of RBC’]
Function of White Blood cells
• Destruction of foreign particles by Phagocytosis method.
• Formation of Antibody
• Formation of Fibroblasts
• Manufacture of Trephones
• Secretion of Heparin
• Resistance of Allergy
• Destruction of Tumour cells
Function of Platelets
• Clotting of Blood
• Repair of the capillary endothelium
• Hasten clot retraction
Function of Plasma
• Transport of Nutrients.
• Drainage of waste products
• Maintenance of acid-base equilibrium
• Regulation of body temperature
• Maintenance of water balance
• Regulation of Blood Pressure
• Transport of Hormones
• Protect Haemorrhage
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File Name: Composition of Human Blood
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Primary Source – NCERT [Body Fluids and Circulation]
