What is blood?

Blood is a fluid which transports oxygen, hormones, and nutrient to the cell and carries away carbon dioxide and other waste products from the cells or tissues.

it has two feature which are
1. Tissue
2.  Fluid

Blood is a tissue because of its composition. It consists of a collection of specialized cells that perform specific functions.

It is fluid because it shows all the properties of a fluid such as viscosity, drag force, turbulent flow, and streamline flow.

In the lungs of the human body blood cells bind with oxygen and releases carbon dioxide. The process of acquiring oxygen and releasing carbon dioxide depends on the partial pressure of oxygen and carbon dioxide.

The opposite process occurs at the tissue level.


What are the functions of blood?

The main functions are,

1.  Supply oxygen to cells
2.  Supply nutrients
3.  Removal of waste
4.  Immunological functions
5.  Coagulation
6.  Transport of hormones
7.  Signaling of tissue damage
8.  Hydraulic function
9.  Regulation of body temperature


Blood cells

1microliter of blood contains

4.7 to 6.1 million erythrocytes in male
4.2 to 5.4 million erythrocytes in the female

4000 to 11000 leukocytes

200000 to 500000 thrombocytes (platelets)

erythrocytes contain hemoglobin and lack the nucleus. WBC is part of the immune system of the body. Platelets take part in clotting.

erythrocytes contain hemoglobin which has the ability to carry oxygen and this hemoglobin is also responsible for the red color. Hemoglobin is a protein that contains a porphyrin ring and polypeptide chains there are four polypeptide chains in the hemoglobin. two of them are alpha chains and two are gamma chains in adults while in the child the chains are different.



About 55% of blood is plasma which makes the fluid and it is straw yellow in color.

Volume.  2.7 to 3 liters in adult

Plasma contains 92 % water and 8% plasma proteins.

The function of plasma is to circulate nutrients and remove waste products.

Plasma also contains other substances which are

Serum albumin
clotting factors


What is the PH of this fluid?

The PH  ranges from 7. 35 to 7.45. The PH of the blood is strictly regulated by homeostatic mechanisms.



Blood flow plays a major role in thermoregulation. For example in warm weather flow to the surface increases which warm the skin and result in faster heat loss.


The rate of flow

The rate of flow varies greatly in different organs.

For example
The rate of flow in the liver is 1350 ml/min which is the highest rate of flow in the body.

The rate of flow in the kidney is 1100 ml/min.

The rate of flow in the brain is 700 ml/min.


The Colour

The color depends on the type of protein that transports oxygen.

For example

The color of human blood is red due to hemoglobin.

The blood of mollusks is dark blue due to hemocyanin.

Annelid’s vascular fluid is green in color due to chlorocruorin.


1.  Injury
2.  Internal bleeding
3.  Shock
4.  Dehydration
5.  Atherosclerosis
6.  High blood pressure
7.  Diabetes Mellitus

The above-discussed disorders can greatly impact the blood, its flow, and its composition.


hematological disorders

Anemia is a disorder in which the body has insufficient erythrocytes. Anemia may occur due to thalassemia or nutritional deficiencies.

Genetics disorder may also be the cause of anemia.

This disorder can be confirmed by a blood test.

Other disorders are



There are eight different types of blood in humans and this classification depends on the presence of special proteins.

These types are named A, B, and O.

The types are
A positive
B positive
O positive
AB positive
A negative
B negative
O negative
AB negative

The positive and negative sign shows the presence or absence of the protein on the basis of which these types are described.

Rh system is another type  grouping system on the basis of which blood is divided into two types which are,

This system is also important as much as the ABO system because it can also create incompatibilities such as erythroblastosis fetalis.



Giving one person blood to another person is known as a transfusion.