Blood is a red liquid or a body fluid in humans and other animals that circulate in the arteries and veins. Blood transport some necessary substance such as oxygen, nutrients, heat, hormones, protective substance and clotting factors to the cells and carries away carbon dioxide and other waste products.

What is Blood and its types

Technically blood is a transport liquid pumped by the heart to all parts of the body after which it is returned to the heart to repeat the process.

Blood is both a tissue and a fluid it is a tissue because it is a collection of similar specialised cells that serve particular functions

Blood makes up about 7 to 8 percentages of body weight. This proportion is less in women and considerably greater in children,   gradually decreasing until the adult level is reached

These cells are suspended in a liquid matrix known as plasma which makes the blood a fluid. If blood flow ceases death will occur within minutes because of the effects of an unfavourable environment on highly susceptible cells

Blood Components

Our blood is made up of liquid and solids. The liquid part, called plasma and solids are made of cells


Plasma normally constitutes 55% of the blood volume

It is made up of water which is 90 to 92% and inorganic salt, plasma   proteins, gases, nutrients, waste materials and hormones

  • Water
  • solvent for carrying  other substances
  • Iron
  • also called blood electrolytes which are sodium, potassium, calcium, magnesium chloride,  Bicarbonates that mainly balance pH buffering and regulation of membrane permeability, muscle contraction and also transmission of nerve impulses
  • Nutrients
  • Together with mineral salts and vitamins they are used by body cells for energy, heat, repair and replacement, and for the synthesis of other blood components and body secretions.
  • Waste products
  • Urea, creatinine and uric acid are the waste products of protein metabolism. They are formed in the liver and carried in the blood to the kidneys for excretion.
  • Hormones
  • These are chemical messenger synthesized by endocrine glands. Hormones pass directly from the endocrine cells into the blood, which transports them to their target tissues and organs elsewhere in the body.
  • Gases
  •  Oxygen,  carbon dioxide and nitrogen are transported around  the body dissolved in plasma
  • Plasma proteins –  plasma proteins, which make up about 7% of plasma. Plasma viscosity (thickness) is due to plasma proteins, it’s mainly albumin, globulin and  

Albumins are the most abundant plasma proteins (about 60% of total) their main function is to maintain normal plasma osmotic pressure

Fibrinogens are responsible for clotting or coagulation of blood

Globulins also called immunoglobulin or antibodies. That’s mainly function as a defence from the foreign substance 

 Blood cells

 It constitutes 45% of blood

There are 3 types of cells

  • Erythrocyte also called red blood cells. It constitutes 44% of blood. These main functions are in gas transport, mainly of oxygen, but they also carry some carbon dioxide. Its normal  value is 5 to 6 million/mm3 and their lifespan is 120days 
  • Leukocyte (white blood cells) these cells have an important function in defence and immunity. They detect foreign or abnormal material and destroy it. Its normal value 5,000 to 10,000 mm3 of blood and Some white blood cells live less than a day, but others live much longer.
  • Thrombocytes known as a platelets. its lifespan is 8 to 12 days

Platelets help blood to clot when you have a cut or wound. Bone marrow, the spongy material inside your bones, makes new blood cells. Blood cells constantly die and your body makes new ones


  • Deliver oxygen ,nutrients to all body cell
  • Transport waste products from cells for elimination
  • Transport hormones
  • It maintains body temperature (distribute heat)
  • Maintain pH
  • Maintain fluid volume
  • Prevent blood loss (clotting )
  • Prevent infection  (WBC ,antibodies)


The blood and its types

There are important cells in our body that travel in the blood. They are involved in a gas exchange that is essential to human life. Commonly it’s called Red Blood Cells (RBCs), but another name is Erythrocytes. In medical terminology, Erythro- means Red, while-cyte means cell.   The reddish colour is due to the protein called hemoglobin, which contains red iron. This why our blood is red in colour. 99% of all blood cells are erythrocytes.  They are biconcave disc (round) with no nucleus.

Hemoglobin is responsible for the erythrocytes’ round shape. Their characteristic shape is suited to their purpose the biconcavity increases their surface area for gas exchange, and the thinness of the central portion allows fast entry and exit of gases. This shape is maintained by a cytoskeleton composed of several proteins.  Erythrocytes are very flexible like rubber, in that there are smooth and can easily bend and change shape when flowing through capillaries. Immature erythrocytes, called Reticulocyte, normally account for 1- 2 percent of red cells in the blood.

RBCs lifespan is about 120 days or 4months.


Because they have no nucleus, erythrocytes cannot divide and so need to be continually replaced by new cells Erythrocytes are created in the bone marrow which is present in the ends of long bones and in flat and irregular bones.  , before being released into the bloodstream RBCs pass through several stages of development before entering the blood.  The process of development of red blood cells from stem cells takes about 7days and is called erythropoiesis. The immature cells are released into the bloodstream as reticulocytes and mature into erythrocytes over a day or two within the circulation. During this time, they lose their nucleus and therefore become incapable of division.

Their lifespan in the circulation is about 120days. There are approximately 30 trillion red blood cells in the average human body, about 25% of the body’s total cell count, and around 1%. At the end of their life, they go to the spleen where they are broken down and older cells are cleared and destroyed daily.


  • Hemoglobin is an oxygen-carrying pigment and predominant protein of red blood cells that contains iron and carries oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs

  • It is made up of four protein molecules known as a globulin chain that is connected together. The normal adult hemoglobin molecule contains two alpha globulin chains and two beta globulin chains, but in fetus and infant, beta chains are not found, there another chain which is name gamma chains. These chains are gradually replaced by beta chains as an infant grows. Each globulin chain contains an important iron-containing porphyrin compound called Embedded within the heme compound is an iron atom that is vital in transporting oxygen and carbon dioxide in our blood. The iron contained in hemoglobin is also responsible for the red blood cells.


  • Newborns: 17 to 22 gm/dL
  • One (1) week of age: 15 to 20 gm/dL
  • One (1) month of age: 11 to 15 gm/dL
  • Children: 11 to 13 gm/dL
  • Adult males: 14 to 18 gm/dL
  • Adult women: 12 to 16 gm/dL
  • Men after middle age: 12.4 to 14.9 gm/dL
  • Women after middle age: 11.7 to 13.8 gm/dL


White blood cells are one of the cells the body makes to help fight against infectious disease and foreign material

Leukocytes are also called white blood cells. Since they do not possess any pigment, they appear colourless and called white blood cells

Gabriel Andral, a French professor of medicine and William Addison an English country practitioner, reported simultaneously the first description of leukocytes (1843). Leukocytes derived from Greek word Leuko means white while cyte means cell

There are several different types of WBC, they share commonalities but are distinction form and function. WBCs are produced in the bone marrow by hematopoietic stem cells ( it’s the process by which all mature blood cells are produced )   Based on the presence or absence of granules in the cell cytoplasm white blood cells are of two type.

  • Granulocytes
  • Agranulocytes   


Granulocytes include neutrophils, basophils and eosinophils, their granules contain the enzyme that damage or digest pathogens and release inflammation mediators into the bloodstream.

During their formation, granulopoiesis, they follow a common line of development through myeloblast to myelocyte before differentiating into the three types. All granulocytes have multilobed nuclei in their cytoplasm. Their names represent the dyes they take up when stained in the laboratory. Eosinophils take up the red acid dye, eosin; basophils take up alkaline methylene blue, and neutrophils are purple because they take up both dyes.

  1. NEUTROPHILS: a type of immune cells that is one of the first cell types to travel to the site of an infection. Neutrophils help fight infection by ingesting microorganism and releasing enzymes that kill the microorganisms.
  2. BASOPHILS: are types of white blood cells. Basophils are the least common of the granulocytes, representing about 0.5 to 1% of circulating white blood cells. They play role in allergic or responsible for inflammatory reactions
  3. EOSINOPHILS: is higher than normal level or eosinophils. Eosinophils are a type of disease-fighting white blood cell. This condition most often indicates a parasitic infection, an allergic reaction or cancer.


The monocytes and lymphocytes make up 25 to 50% of the total leukocyte count. They have a large nucleus and no cytoplasmic granules

Agranulocytes include monocytes and lymphocytes microphages and dendrites’ cells. This group is involved in both innate and adaptive immune system function

MONOCYTES: are types of white blood cell that fight off bacteria, viruses and fungi. Monocytes are the biggest type of white blood cell in the immune system. Originally formed in the bone marrow, they are released into our blood and tissues. When certain germs enter the body, they quickly rush to the site for attack.

LYMPHOCYTE: A small white blood cell that plays a large role in defending the body against disease. Lymphocytes are responsible for immune responses. Lymphocyte includes natural killer cells. There are two main types of lymphocytes: B cell and T cell. The B cells make antibodies that attack bacteria and toxins while the T cells attack body cells themselves when they have been taken over by viruses or have become cancerous.

The normal range of WBC

  • At birth (full-term infant): 10,000 to 25,000mm3 of blood
  • Infants up to 1year of age: 6,000 to 16,000 mm3 of blood
  • Adult : 4,000 to 11,000 mm3 of blood


  • Neutrophils: 2 to 5 days
  • Eosinophils: 7 to 12days
  • Basophils: 12 to 15days
  • Monocytes: 2 to 5 days
  • Lymphocytes: ½ to 1 day


Thrombocytes, also called platelets .thrombo means blood clot while cyte means cell. They have no nucleus. These are a component of blood whose function (along with the coagulation factors) is to stop bleeding by clumping and clotting blood vessel injuries

Thrombocytes make up less than 1% of blood’s volume (55% plasma, 45% blood cells those are 44% erythrocytes, 1% WBC and platelets)

The lifespan of platelets is 8 to 12 days

The normal value of platelet is between 2, 00,000 to 3, 50,000mm3

Platelets are formed from cells in the bone marrow called as megakaryocytes under the influence of thrombopoietin.