Human Blood, Composition and Function Details Notes

Human Blood, Composition and Function Details Notes


• Connective tissue in fluid form
• Fluid of life – carries oxygen from lungs to all parts of body and carbon-di-oxide from all parts of the body to the lungs
• Fluid of growth – carries nutritive substances from the digestive system and hormones from endocrine gland to all the tissues.
• Fluid of health – protects the body against diseases and get rid of unwanted substances by transporting them into excretory organs like kidney.

Physical Characteristics of Blood

• Thicker than water 
• 8 % of total body weight
• Blood volume
70 mL/kg of body weight
5 - 6 liters in males
4 - 5 liters in females
• Temperature - 100.40F
• pH - 7.35 to 7.45

Blood Functions

• Respiratory
 Transport O2 from lungs to tissues
 Transport CO2 from tissues to lungs
• Nutrition
 Transport food from gut to tissues
• Excretory
 Transport waste from tissues to kidney (urea, uric acid)
• Protective
 White blood cells, antibodies, antitoxins.
• Regulatory
 regulate body temperature
 regulate pH through buffers
 coolant properties of water 
 vasodilatation of surface vessels dump heat
 regulate water content of cells by interactions with dissolved  ions and proteins
• Body Temperature
 Water- high heat capacity, thermal conductivity, heat of vaporization
 Typical heat generation is 3000 kcal/day

Blood composition

Suspension of cells in plasma (carrier fluid)
• 45% Cells 
• 55% Plasma 
• Red cells (erythrocytes) 5x106/mL                      99%
• White cells (leukocytes) 7x103/mL                      < 1%
• Platelets (thrombocytes) 3x105/mL
Composition of Blood
• Red blood cells (R.B.C.)
• White blood cells (W.B.C.)
 granular leukocytes
 neutrophils
 eosinophils
 basophils
 agranular leukocytes
 lymphocytes - T cells, B cells, natural killer cells (N.K.C)
 monocytes
• Platelets (special cell fragments)

Red blood cells (Erythrocytes)

• RBCs are the biconcave cells also known as erythrocytes. 
• RBCs contain the iron-rich protein called haemoglobin give blood its red colour. 
• RBCs are the most copious blood cells produced in bone marrow. 
• Their main function is to transport oxygen from and to various tissues and organs.

Functions of RBC

1. Transport oxygen from lungs to the tissues (oxyhemoglobin).
2. Transport carbon-di-oxide from tissues to lungs (carboxyhemoglobin)
3. Hemoglobin acts as a buffer and regulates the hydrogen ion concentration (acid base balance)
4. Carry the blood  group antigens and Rh factor

White blood cells (Leucocytes)

• Leucocytes are the colourless blood cells. 
• They are colorless because it is devoid of haemoglobin. 
• They are further classified as granulocytes and agranulocytes. 
• WBC mainly work as immunity and defence mechanism 

Types of White Blood Cells

There are five different types of White blood cells and are classified mainly based on the presence and absence of granules.
• Granulocytes – Eosinophils, Basophils, Neutrophils.
• Agranulocytes – Monocytes, Lymphocytes.


They are leukocytes, with the presence of granules in their cytoplasm. 
The granulated cells include- eosinophil, basophil, and neutrophil.


• They are the cells of leukocytes, which are present in the immune system.
• Responsible for combating infections in parasites of vertebrates and for controlling mechanisms associated with the allergy and asthma.
• Small granulocytes, which are produced in the bone marrow and make 2 to 4 percent of whole WBCs. 
• Present in high concentrations in the digestive tract.

Functions of eosinophils

Secrete lethal substances at the time of exposure to foreign proteins/parasites
1. Eosinophill peroxidase – destroy worms, bacteria and tumor cells.
2. Major basic protein – damage parasites
3. Eosinophill cationic protein (ECP) - destroys helminths.
4. Eosinophill derived neurotoxin – destroys nerve fibres (myelinated nerve fibres)
• They are the least common of the granulocytes, ranging from 0.01to 0.3 percent of WBCs.
• They contain large cytoplasmic granules, which plays a vital role in mounting a non-specific immune response to pathogens, allergic reactions by releasing histamine and dilates the blood vessels.
• Around 20 to 25 percent of basophils are present in WBCs.
• These white blood cells have the ability to be stained when exposed to basic dyes, hence referred to as basophil.
• These cells are best known for their role in asthma and their result in the inflammation and bronchoconstriction in the airways.

Functions of basophils

Basophill granules release some important substances like – 
1. Histamine – Acute hypersensitivity reaction- vascular changes, increase capillary permeability
2. Heparin – prevents intravascular blood clotting
3. Hyaluronic acid – necessary for deposition of ground substances in basement membrane
4. Proteases – exaggerate inflammation
       Basophill have IgE receptor – hypersensitivity reaction


• Normally found in the bloodstream, Predominant cells, which are present in pus.
• Around 60 to 70 per cent of WBCs are neutrophils with a diameter of 10 to 12 micrometres.
• Nucleus is 2 to 5 lobed and cytoplasm has very fine granules.
• Helps in the destruction of bacteria with lysosomes, and it acts as a strong oxidant.
• The lifespan of these WBCs extend for up to eight hours and are produced every day in the bone marrow.

Functions of neutrophils

1. First line of defense against invading micro-organisms.
2. Powerful and effective killer machine – contains enzymes like protease, elastase, metalloproteinase, NADPH oxidase; antibody like substances called defensins. 
          Defensins – antimicrobial peptides active against bacteria and fungi.
3. Secrete Platelet Aggregation Factor (PAF) – accelerates the aggregation of platelet during injury to the blood Vessels.


They are leukocytes, with the absence of granules in their cytoplasm. Agranulocytes are further classified into monocytes and lymphocytes.


• Usually have a large bilobed nucleus, with a diameter of 12 to 20 micrometres.
• The nucleus is generally half-moon shaped or kidney-shaped and it occupies 3 to 8 per cent of WBCs.
• These white blood cells have a single bean-shaped nucleus, hence referred to as Monocytes.

Function of Monocytes

1. To migrate into tissues and clean up dead cells, so called garbage trucks of the immune system.
2. Protect against the blood borne pathogens and they move very quickly to the sites of infections in the tissues.


• These white blood cells are colourless cells formed in lymphoid tissue, hence referred to as lymphocytes.
• There are two main types of lymphocytes – B lymphocytes and T lymphocytes.
• Size ranges from 8 to 10 micrometres.
• On average, a human body contains about 10 to 12 lymphocytes cells.

Function of Lymphocytes

1. Lymphocytes are very important in the immune systems and are responsible for humoral immunity.
2. Play a vital role in producing antibodies.
3. Commonly known as natural killer cells. Play an important role in body defence.

Platelets (Thrombocytes)

• Tiny disc-shaped cells that help regulate blood flow when any part of the body is damaged, 
• Thereby aiding in fast recovery through clotting of blood

Function of Platelets

1. Blood clotting
2. Clot retraction
3. Defence mechanism
4. Homeostasis
5. Repair and rupture of blood vessel

Blood Plasma

• Straw colored clear liquid 
• Contains 90% water
• 7% plasma proteins
 created in liver
 confined to bloodstream
 albumin
 maintain blood osmotic pressure
 immunoglobulin’s
 antibodies bind to foreign substances called antigens
 form antigen-antibody complexes
 fibrinogen
 for clotting 
• 2% other substances 
 Nutrients, electrolytes, gases, hormones, waste products

Functions of plasma proteins

1. Coagulation of blood – Fibrinogen to fibrin
2. Defense mechanism of blood – Immunoglobulin’s
3. Transport mechanism – α Albumin, β globulin transport hormones, gases, enzymes, etc.
4. Maintenance of osmotic pressure in blood
5. Acid-base balance
6. Provides viscosity to blood
7. Provides suspension stability of RBC
8. Reserve proteins

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