Human Blood And Their Composition


Blood is a liquid connective tissue, human blood delivered some necessary substances like nutrients and oxygen to the cells. And transports waste products from cells to away from our body. It has two main Blood components: plasma & cells (Red blood cells, White blood cells, and Platelets). Plasma, which constitutes 55% of blood fluid, is mostly water (92%) and contains proteins, glucose, mineral ions, hormones, carbon dioxide. Albumin is the main protein in plasma(7%), and it functions to regulate the colloidal osmotic pressure of blood. The blood cells are mainly RBCs or erythrocytes 4.7 to 6.1 million (males) 4.2 to 5.4 million (females), WBCs or leukocytes 4000 – 11000 and platelets or thrombocytes 1,50,000 – 500,000.

Physical properties of blood

  • Blood is slightly alkaline fluid because Ph of blood is 7.35 to 7.45.
  • An average adult has a blood volume of approximately 5 liter, which composes about 8% of the total body weight.
  • Osmolarity of blood is 275 to 295 mmol/kg.
  • The specific gravity of blood is 1.052 to 1.062.
  • Blood temperature is 38°c or 100.°f.
  • Blood is made of 45% cells and 55% plasma.

Functions of blood in the body –

  • Supply of oxygen to tissues
  • Supply nutrients such as glucose, vitamins, amino acids, and fatty acids.
  • Removal of waste such as carbon dioxide, urea, and lactic acid etc.
  • Immunological functions, including circulation of white blood cells, and detection of foreign body material by antibodies.
  • Coagulation, the response to a broken blood vessel, the conversion of blood from a liquid to a semisolid gel to stop bleeding.
  • Messenger functions, including the transport of hormones and the signaling of tissue damage.
  • Regulation of core body temperature.
  • Hydraulic functions.

Components of blood

There are two components of blood.
(1) plasma (2) cells

Blood Plasma

plasma is the straw color liquid component of blood, in which blood cells are suspended, plasma made 55% part of blood.plasma is made of water, salts, and proteins. Proteins present in plasma called plasma protein, plasma proteins are responsible for osmotic pressure of blood.

blood transfusion complication precautions

composition of plasma

(1) 90% water (2) 8% protein (3) Inorganic salts (4) 1.1%organic salt

plasma proteins –

  • Albumin
  • Globulin
  • Fibrinogen

Inorganic Salts –

  • Sodium 135 to 146 mM
  • Potassium 3.5 to 5.2 mM
  • Calcium 2.1 to 2.7 mM
  • Carbonate 23 to 31 mM.
  • Phosphate 0.7 to 1.4

Blood Cells and its Functions –

There are three types of cells presents in blood. That are (1) RBC / ERYTHROCYTES (2) WBC / LEUKOCYTES (3) PLATELETS

RBC / ERYTHROCYTES 4.7 to 6.1 million (males) 4.2 to 5.4 million (females) –

  • RBC also called erythrocyte, the red color of blood is due to red blood cells because RBC contains hemoglobin, one RBC contains 280 million Hb molecule.
  • hemoglobin is a red iron-rich protein that binds oxygen. the red color of Hb is due to porphyrin pigment. 1 gm Hb contains 3.34 mg iron.
  • Mature RBC is small, round and biconcave in shape.
  • Nucleus absent in RBC.
  • RBC covered by a membrane composed of lipid and proteins.
  • The diameter of RBC is 7.2 µm.
  • The normal life span of RBC is 120 days.
  • RBC develops in bone marrow in adulthood and in embryonic life, RBC develops in the yolk sac and in fetal life RBC develops mainly in spleen, liver, and thymus.
  • It destroys in the spleen, so the spleen is called graveyard of RBC.
  • Normal RBC count is 4.7 to 6.1 mcl and normal count in children- 4.0 to 5.5 mcl.
  • Production of RBC is called erythropoiesis, kidney hormone erythropoietin helps in the production of RBC.

WBC / LEUKOCYTES  4000 – 11000 –

WBC is also called leukocyte. Nucleus present in WBC, dead WBC called pus. the life span of WBC is depended on their work and demand. WBC further divided into two groups. (1) Granular leukocyte (2)  Agranular leukocyte. WBCs concentration is decreased below the lower limit is called leukemia.

(1) Granular leukocyte –

Granules present in the cytoplasm of granulocytes, granules have an enzyme (ex. proteases) which destroy the microorganism. three granulocytes present in WBC are following.

  • Eosinophil – diameter of eosinophil is 10 to 14 µm. it seems red-orange color after staining with acidic dye (eosin), eosinophil plays important role in allergy and parasitic infection ex. malaria.
  • Basophil – Diameter of basophil is 8 to 10 µm, it seems blue-purple color after staining with basic dye (methylene blue). Play important role in healing process.
  • Neutrophil – Diameter of neutrophil is 10 to 12 µm, it seems violet color after staining with both dye (eosin+methylene blue=leishman’s stain). It provides first line defense. Old neutrophil called polymorphonuclear leukocyte, because its nucleus has 2-5 lobes and the young neutrophil called bands because its nucleus seems like a Rod.

(2) Agranular leukocytes –

Lymphocyte –

The diameter of lymphocyte is 7 to 12µm. Lymphocyte divided into two types according to work and formation. (i)T lymphocyte (ii)B lymphocyte.

(i)T lymphocyte – Its final maturation held in thymus gland so it called T lymphocyte. T-lymphocytes are responsible for cellular immunity. T lymphocyte divided into four cells these are following –

  • Helper T cells or CD4+ or inducer T cells– During any infection helper T cells stimulate other cells, normal count of CD4+ cells are 500 to 1500 cells/mm3 (average 950 mm3). if CD4+ count decrease below 200 mm3 than it indicates AIDS.
  • Cytotoxic T cells or killer cells or CD8+ cells– These cells attack directly to microorganism during infection.
  • Suppress T lymphocyte – These cells decreases the activity of killer cells.
  • Memory T lymphocyte – These cells present in lymphoid tissue, these cells prevents the same infection in the future.

(ii) B lymphocyte – Its final maturation held in Bone marrow (after birth) and during fetal life it matures in the liver so these cells called B lymphocyte. B lymphocyte responsible for Humoral immunity or B cells immunity. Humoral immunity means immunity that produces from antibody and immunoglobulin. B lymphocyte divided into two groups are-

A. Plasma cells- Plasma cells produce 5 types of immunoglobulin or antibody.

  • IgA – IgA presents in breast milk, sweat, tear, and saliva.
  • IgG – IgG is the most common type of immunoglobulin, it founds approximately 80%. IgG only can cross the placenta, it indicates chronic infection.
  • IgM – After any infection plasma cells secrets first IgM, it indicates acute infection.
  • IgE – It involves allergic and hypersensitivity.
  • IgD – it is less in numbers and less important.

Monocyte –

Its diameter is 14 to 18µm. It is largest WBC cells. Monocyte migrates blood to tissue and produces macrophage. Macrophages divided into two types.
Fixed Macrophage and Wandering Macrophage.

Fixed macrophage – Some macrophages stay fixed in any special tissue. Ex- kupffer cells in Liver and alveolar cells in the Lungs.
Wandering macrophage – These macrophages are movable in one to another organ, so-called wandering macrophage.

Platelets or Thrombocytes  1,50,000 – 500,000 –

  • Low platelet concentration is Thrombocytopenia.
  • Elevated platelet concentration is Thrombocytosis.
  • Thrombocytes are not complete cells, it develops from divination of a megakaryocyte into 2000 to 3000 parts.
  • Platelets are colorless and disc-shaped cells.
  • Platelet does not have Nucleus.
  • Diameter is 2 to 4µm and its volume is 7.5 cubic micron (µm3).
  • Platelets are responsible for control blood loss from damaged blood vessels. By formation of a clot within an intact vessel.
  • Thrombocytes have three important properties-1.Adhesiveness 2. Aggregation 3. Agglutination.
    Its life span is 5 to 9 days.
  • Dead platelets or thrombocytes are destroyed by fixed macrophages in Liver and Spleen.