Body Fluids and Circulation

“Body fluids are the fluids such as blood, lymph, milk and saliva which are produced in the body and then either circulated within the body or secreted outside it.”

Table of Contents

Body Fluids

Blood and lymph are the two most important body fluids in the human body. Blood comprises plasma, white blood cells, red blood cells, and platelets.

Lymph is a colourless fluid that circulates inside the lymphatic vessels.

The body fluids and circulation of these body fluids are described below in complete detail.

Types of Body Fluids

The different types of body fluids include:


The main components of blood include:

  1. Plasma: Plasma is the liquid component of blood. It is a thick fluid which makes up 55% of the total blood volume with the rest of the volume made by blood components such as RBC, WBC and Platelets. Plasma is 91% water and the rest of the total volume is made up of dissolved ions, suspended proteins, dissolved gases, nutrient molecules and waste products. . Albumin is the major protein in plasma. Other proteins include immunoglobulins and clotting factors.

  2. Red Blood Cells: 40% of the blood contains red blood cells. RBCs contain protein haemoglobin that gives a red colour to the blood.

  3. White Blood Cells: The white blood cells are very few in number. The WBC to RBC ratio is 1:600. They mainly protect the body against infections. Many WBCs cross the walls of the vessels and penetrate other tissues.

  4. Platelets: These are fewer in number than the red blood cells. The platelets help in the clotting of blood at the site of a wound.


Lymph is a colourless fluid present in the interstitial tissues. It circulates throughout the lymphatic system. It can be defined as blood without RBCs. The exchange of nutrients, hormones, and gases occurs through this fluid. It consists of lymphocytes that play a major function in the immune responses of the body.

Composition of Body Fluids

The composition of the body fluids is explained below:

Body Fluids


Intracellular Body Fluids

70% water, ions, and molecules

Extracellular Body Fluids

Cations and Anions

Transcellular Fluid

Electrolytes such as sodium, bicarbonate and chloride ions.

Functions of Body Fluids

The important functions of body fluids include:

  1. The body fluids facilitate the transportation of oxygen and nutrients throughout the body and remove waste from the body.
  2. They help in regulating body temperature.
  3. They maintain an efficient metabolism of the body.


“Circulation is the movement of blood through the vessels of the body that carries nutrients and gases along with it to and removes waste from the different parts of the body.”

The transportation of nutrients, wastes, gases, and other substances is carried out by the blood. This process is termed circulation. The human circulatory system serves the following functions:

  1. Transport of respiratory gases.

  2. Transport of nutrients to the cells.

  3. Transport of hormones from the endocrine glands to the respective organs.

  4. Destruction of pathogens.

  5. Transport of metabolic waste to the excretory organs for removal.

Types of Circulatory Systems

The circulatory system is of two types:

  • Open Circulatory system

  • Closed circulatory system

Open Circulatory System- Blood flows through parts of the body cavity, and not in closed vessels. This system is commonly found in insects.

Closed Circulatory System- Blood flows through closed tube-like vessels under sufficiently high pressure. This system is found in all vertebrates.

Mechanism of Circulation

The heart is the main organ involved in blood circulation. The human heart consists of two upper chambers called atria or auricles and two lower chambers called ventricles.

Arteries carry oxygenated blood away from the heart to the body while the veins carry deoxygenated blood from different parts of the body to the heart for purification. The pulmonary artery and pulmonary veins are an exception. The pulmonary artery carries deoxygenated blood away from the heart, while the pulmonary vein carries oxygenated blood to the heart.

The right auricle and right ventricle are separated by a tricuspid valve while the left auricle and left ventricle are separated by a bicuspid or mitral valve. These valves prevent the blood from flowing back into the auricles.

Two semilunar valves are present, each between the right ventricle and pulmonary artery, and the left ventricle and aorta. These valves prevent the blood from flowing back into the heart.

  • The deoxygenated blood is pumped into the right ventricle through the superior vena cava (which carries deoxygenated blood from the upper regions of the body) and inferior vena cava (which carries deoxygenated blood from the lower parts of the body). The oxygenated blood is carried by the pulmonary veins from the lungs to the left auricle. This is called auricular circulation.

  • Most of the auricular blood passes into the ventricles during diastole and the process is known as diastasis.

  • The rest of the blood passes into the ventricles during auricular systole.

  • The blood from the left ventricle passes from the left ventricle into the systemic aorta and deoxygenated blood passes from the right ventricle into the pulmonary aorta during ventricular systole.

  • The oxygenated blood is distributed to all the body parts by the systemic arch while the pulmonary aorta carries deoxygenated blood to the lungs.

Some fluid is forced out of the bloodstream during circulation which gets filtered by the lymph nodes to remove any bacteria and other matter. The filtered fluid is transported back into the bloodstream via lymph vessels.

Circulatory Disorders

The circulatory system functions 24*7 to maintain a proper flow of blood to all parts of the body. But blockages in the blood vessels might affect the functioning of the heart. This leads to certain heart diseases and even stroke. Following are a few diseases that might affect the functioning of the heart.


High blood pressure does not show any symptoms. It damages the heart and important organs. With high blood pressure, the blood is pumped out with very high pressure.

Coronary Heart Disease

This affects the arteries primarily. The deposition of fats, cholesterol, cell debris, clotting agents hardens the arteries. After a period of time, the blow flow is completely blocked.

Heart Attack

Heart attacks are medically termed Myocardial Infarction. When the blood does not reach the heart due to blockages it causes a heart attack. This completely damages the heart muscles.

Obesity, stress, high blood pressure, high cholesterol and fats, and smoking are some of the risk factors that increase the chances of a heart attack.


Angina or chest pain occurs due to coronary heart disease. The blockage of the arteries reduces the blood flow to the heart. Pain and pressure are experienced in the centre of the chest.

Heart Failure

When the heart stops pumping enough blood to meet the requirements of the body, it is known as heart failure. Chest pain, rapid breathing, and fainting are the symptoms of heart failure.

Key Points on Body Fluids and Circulation

  • Blood and lymph are the two main body fluids in the human body.

  • Blood comprises plasma, white blood cells, red blood cells and platelets.

  • Lymph comprises lymphocytes.

  • The blood transports nutrients, wastes, and gases throughout the body.

  • Lymph transports nutrients hormones and gases.

  • The blood flows through the circulatory system either through body cavities or through closed tube-like vessels.

  • Lymph flows through the lymphatic system.

For more information on Body fluids, their types, composition, functions and circulation, keep visiting BYJU’S website or download BYJU’S app for further reference.

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