Blood: composition, properties and functions

July 15, 2017 Gaurab Karki Anatomy and Physiology, Class 12, Zoology 0




Blood: composition, properties and functions

  • Blood is a liquid connective tissue that contains cellular elements (blood cells) and fluid matrix (plasma).
  • Blood helps in the transportation of different substances throughout the body.
  • Study of blood and its disease is known as Hematology

Composition of Blood:

  1. Cellular substances (Blood cells) : 45% (44% RBC & 1% buffy coat containing platelets & WBC)
  2. Plasma: 55% (Of total: 91% liquid & Solid 9%).

Blood cells:

  • Erythrocytes or Red blood cells (RBC), Leucocytes or White blood cells (WBC) and Platelets or Thrombocytes

1. Erythrocytes or Red blood cells (RBC)

  • Biconcave, anucleate disc shaped of 7µm in size.
  • The normal count= 4.5-5.5 lakhs/mm3. It is measured by haemocytometer
  •  The life span of RBC is 120 days.
  • RBC contain blood pigment called Haemoglobin.
  • Total haemoglobin in our body is about 900 gm. It occupies about 1/3 of RBC.
  • RBC is produced in bone marrow by the process called Erythropoiesis
  • The immature nucleated RBC is called Reticulocyte.

 2. Leucocytes or White blood cells (WBC)

  • Large size, oval in shape, cell contain nuclei & some of them have granules.
  • Normal count-4000-11,000 per mm3.
  • 2 types-Granulocytes and Agranulocytes. These differ in size, shape, life span & functions.
  • Granulocytes includes- Neutrophils, Basophils & Eosinophils
  • Agranulocytes include –lymphocytes and monocytes

i. Neutrophils

  • It is most abundant WBC (40-70%) of total WBCs.
  • It is phagocytic in nature.
  • It is the first line of defense against bacteria.
  • Phagocytosis by Neutrophil is facilitates by Opsonization by antibody
  • The life span is 6 hrs.

 ii. Eosinophils

  • 1-4% of total WBCs
  • It destroys parasites & neutralize histamine released during allergic reaction. So, it is increased in parasitic infestation & in allergic reactions.
  • It is stained by acidic dye. Eg, eosin dye.

 iii. Basophils                                             

  • About 1% of total WBCs.
  • It contain basophilic granules.
  • It resembles mast cells in connective tissue.
  • It contains histamine, heparin & serotonin.
  • It is stained by basic dye

 iv. Lymphocytes                                      

  • 20-40% of total WBCs. It is the smallest WBC.
  • There are 2 types of lymphocytes.
  •  B-lymphocytes is concerned with humoral immunity.
  • T lymphocytes is concerned with cell mediated immunity.

v. Monocytes

  • 2-8 % of total WBCs, Have horse-shoe kidney shaped nucleus. It is the largest WBC.
  • It differentiates into Macrophages as it enters the tissues which express MHC (Major histocompatibility complex).
  • Macrophages in different parts of the body are given different names as follows
  • Kupffers cells= liver
  • Osteoclast cells= bone
  • Microglial cells= brain and spinal cord
  • Histiocytes =Connective tissue
  • Dust cells (alveolar macrophage)= Lungs
  • Hassal’s corpuscles= Thymus

3. Platelets or Thrombocytes

  • They are small non granulocytes disc
  • They are derived from pinching off the cytoplasm of the Giant cell megakaryotes in the red bone marrow.
  • Normal count is 1.5-4.5 lakh/mm3.
  • Life span 7-10 days.
  • Platelet is to help in coagulation. Thromboplastin is secreted by platelets during blood clotting.

 

Plasma

  • Plasma = (Blood- Blood cells)
  • It is the liquid part of blood and is composed of 90-92 % water, 7-8 % plasma protein and 1-2% other substances (glucose, amino acids, electrolytes, ammonia, enzymes, hormones, vitamins, etc).
  • Translucent, yellowish, little viscous when centrifuged.
  • Normal range: 60-80 gm/dl of blood.
  • Plasma proteins: Helps in maintaining osmotic pressure, coagulation of blood, viscosity, blood pressure, defensive action, transport of gases.
  • The solvent property of water helps in transport of nutrients as well as metabolic wastes from one part of body to another part
  • Liver produces about 30gm of plasma protein each day.
  • They are of three types:
  • Albumin: (58-60%) most abundant, main function is to maintain is to maintain plasma osmotic pressure (Oncotic pressure).
  • Globulin: (36-38%) – It is important for immunoglobulin. The most important globulin is gamma globulin.
  • Fibrinogen: (3-4%) – It helps in blood clotting.
  • Electrolytes- Na, K, Cl, Ca, HCO3
  • Nutrients- Glucose, amino acids, fatty acids, Vitamins & minerals.
  • Gases: Oxygen, Carbon dioxide, Nitrogen.
  • Waste products: Urea, Uric acid, Creatinine.

 

Properties of Blood:

  • Amount: : 7-9% of total body weight; 79ml/kg
  • Blood volume: 5-6 liters
  • Viscosity: (3.5-5.5) times more than water.
  • Specific Gravity:045-1.065
  • PH:3-7.4 (slightly alkaline)
  • Venous blood has low pH than the arterial blood as venous blood has more CO
  • Temperature- 380C (100.4F)
  • Osmotic pressure– 25 mm Hg.
  • Color: red, due to haemoglobin

Functions of Blood

i. Transportation:

  • transport of O2 from lungs to body tissue and CO2 from tissue to lungs
  • transport of wastes of cellular metabolism from body tissue to kidney, liver or sweat gland and eventually removal out of body
  • Transport of hormones, enzymes, other chemicals throughout the body.
  • Nutrients absorbed in the digestive tract, such as glucose, amino acids, vitamins, minerals etc and are circulated to all body tissues.
  • Waste products of the tissues, such as urea and creatinine, circulate through the kidneys and are excreted in urine.

ii. Regulation (Homeostasis):

  • regulate body temperature
  • distribution of heat throughout the body

iii. Balance

  • Maintaining electrolyte balance
  • Maintain acid base balance

iv. Protection:

  • protect body from harmful microorganisms, by WBCs, protein and antibody
  • develop immune response (plasma protein).

Blood: composition, properties and functions