Body Fluids and Circulation Notes for NEET, Download PDF

By Noushin Chaudhary|Updated : January 1st, 2019

In this article, we are providing you with short notes on Body Fluids and Circulation for NEET 2019 examination. This is one of the important chapters to pay attention from the unit of Human Physiology. This chapter is also equally important for the students who are preparing for boards examination this year. Every year 2-3 questions have been asked from this chapter in various medical examination like NEET, AIIMS, JIPMER. So, let us begin with a brief introduction about what are body fluids.

Body Fluids and Circulation Notes


Blood falls in the category of fluid connective tissue. It makes up around 8% of human body weight. The blood performs the following essential function:

  1. Transport of respiratory gases
  2. Transport of nutrition
  3. Removal of metabolic wastes
  4. Immunological functions
  5. Maintenance of homeostasis

Components of blood

Being a connective tissue, a fluid matrix of blood is called the plasma in which the cellular components or the formed elements are suspended. Blood cells are termed as formed elements as they are made from the haematopoietic stem cells inside the bone marrow and are released on maturation in the bloodstream. These components are described below:


It makes 55% of blood. It has a pale-yellow coloured appearance. It is made up of around 91% water, 7% proteins, and rest is the composition of ions, salts, hormones etc. The proteins found in plasma are as follows:

  1. Immunoglobulins- These are the antibody proteins that serve the immunological functions.
  2. Albumins- They help in maintaining the osmotic balance.
  3. Fibrinogen- These are involved in the blood clotting process.

Plasma keeps the fluidity of the blood and provides the matrix to the cells. It carries hormones, metabolic wastes, nutrients etc.

Formed Elements or Cellular Components

These make 45% of blood. These are developed from the myeloid and lymphoid progenitor stem cells in bone marrow. There are following three types of cells:

Erythrocytes or Red Blood Cells (RBCs)

  • Biconcave in shape.
  • Live for approximate 120 days.
  • Lack of cell organelles upon maturity.
  • Rich in a respiratory pigment called haemoglobin.

Helps in the transport of oxygen to the tissues

Leucocytes or White Blood Cells (WBCs)

  • Circular or spherical in shape.
  • Have varying lifespan.

Play role in the defence mechanism

Platelets or Thrombocytes

  • Developed from megakaryocytes.
  • Megakaryocyte breaks into small fragments rich in clotting factors called platelets.
  • Do not contain the nucleus

Important for the blood clotting

The WBCs can be further divided into the following types according to their morphology and functions:


  • Rich in granules
  • Have polymorphic nuclei

Phagocytosis of the bacterial pathogen. The release of granules causes fever.


  • Rich in granules
  • Have a multilobed nucleus

Inflammation and vasodilation.


  • Rich in granules
  • Have a bilobed nucleus

Allergic reactions




Humoral and cellular immunity




Form macrophages in tissues


It is a colourless fluid (because of the absence of haemoglobin) that is accumulated as interstitial fluid. The difference in hydrostatic pressure in arterioles and osmotic pressure in venules cause a fraction of plasma to seep out of capillaries to form an interstitial fluid. This fluid has some proteins, WBCs and water. It is then transported across the body in lymphatic vessels and is called lymph. It is finally returned into the bloodstream.

It has immunological functions due to the presence of WBCs and immunoglobulins. It also absorbs fats from the small intestine.

Circulatory pathways

The circulatory system in human is of the closed type, that is, the blood flows within the blood vessels and it is not released into the coelom. The blood vessels form a network of the circulatory pathway. There are following three types of blood vessels:


  • Have thick elastic and muscular walls with the narrow lumen.
  • In tissues, they form arterioles.
  • Deep-seated and blood flow with high pressure.
  • Do not have valves.
  • Carry the blood away from the heart.
  • Generally, except for the pulmonary artery which carries deoxygenated blood, arteries carry oxygenated blood.


  • Have thinner elastic and muscular walls with the wider lumen.
  • In tissues, venules unite to form veins.
  • They are superficially situated as blood flows with a lesser pressure and to prevent backflow of blood have valves.
  • Carry blood towards the heart.
  • Generally, except for pulmonary vein which carries oxygenated blood, veins carry deoxygenated blood.


Made from a single layer of endothelium

They perform diffusion of substances across the blood and tissues

Double Circulation

The human heart is four-chambered with upper chambers called atria and lower chambers called ventricles. The right atrium and ventricle receive the deoxygenated blood from the body organs and pump it to the lungs. The left atria and ventricles receive the oxygenated blood from the lungs and pump it to the body organs. Hence, the blood flows through the heart two times and completes the two circulations called double circulation as described below:

Systemic Circulation (from the heart to body organs and then back to the heart)

  • The aorta arising from the left ventricle supplies oxygenated blood to the body organs via the arteries.
  • The diffusion of gases at capillaries makes the blood deoxygenated and is received via the veins.
  • These veins unite to form the vena cava that collectively accumulate the deoxygenated blood to the right atrium.
  • Blood moves to the right ventricle from the right atrium.

Pulmonary Circulation (from the heart to lungs and then back to the heart)

  • It begins when the right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery.
  • Oxygen is provided to the blood through the lungs. This oxygenated blood is received by the pulmonary vein and is deposited to the left atrium. It then further moves to the left ventricle.

Regulation of Cardiac Activity

The human heart is myogenic. It can auto-generate the signals for contraction and relaxation through the cardiac nodules called the sino-atrial node (SA node). However, the brain and hormones also regulate its activity as described below:

Neural control

The sympathetic nervous system increases the heart rate while the parasympathetic nervous system decreases the same. Medulla oblongata has the centre for heart regulation.

Hormonal Control

Adrenaline increases the heart rate during stressed conditions. Thyroxine also regulates the heart rate.

Disorders of the Circulatory System

  1. Hypertension: Increase in blood pressure from the normal range of 120/80. It can cause heart failure and organ haemorrhage
  2. Atherosclerosis: Deposition of calcium, cholesterol, and fats in the coronary arteries reduces its lumen and reduce blood supply to the heart. It is also termed as coronary artery disease (CAD).
  3. Angina Pectoris: It occurs due to cardiac muscle fatigue resulting due to an affected blood supply. It causes pain and discomfort in the chest.
  4. Myocardial Infarction: It is also called heart It occurs due to the sudden cut-off of oxygen to heart muscles.

Download Body Fluids and Circulation Notes PDF

Download BYJU'S Exam Prep, the best NEET Preparation App

All the best!
Team BYJU'S Exam Prep


write a comment
Load Previous Comments
Suruchi Kumari
Nishidha Manoharan
Thanks a lot. 😍
rajput shweta
Aarif Dar

Aarif DarFeb 6, 2019

I think basophils have S shaped nucleus...sorry for inconvenience..

KumarJul 7, 2019

Is it enough  notes for neet 😏preparation???
Sagar Chaudhary
Thanks for sharing the information.

Best Cardiologist Near me
Sanket Latad

Sanket LatadFeb 14, 2020

Thanks for sharing
Pragya Bhavini
Thank you so much gradeup for providing such a good notes
Kamala Penta
There is no topic about blood clotting

Follow us for latest updates

GradeStack Learning Pvt. Ltd.Windsor IT Park, Tower - A, 2nd Floor, Sector 125, Noida, Uttar Pradesh 201303