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:
- Transport of respiratory gases
- Transport of nutrition
- Removal of metabolic wastes
- Immunological functions
- 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:
- Immunoglobulins- These are the antibody proteins that serve the immunological functions.
- Albumins- They help in maintaining the osmotic balance.
- 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)
Helps in the transport of oxygen to the tissues
Leucocytes or White Blood Cells (WBCs)
Play role in the defence mechanism
Platelets or Thrombocytes
Important for the blood clotting
The WBCs can be further divided into the following types according to their morphology and functions:
Phagocytosis of the bacterial pathogen. The release of granules causes fever.
Inflammation and vasodilation.
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.
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:
Made from a single layer of endothelium
They perform diffusion of substances across the blood and tissues
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)
Pulmonary Circulation (from the heart to lungs and then back to the heart)
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:
The sympathetic nervous system increases the heart rate while the parasympathetic nervous system decreases the same. Medulla oblongata has the centre for heart regulation.
Adrenaline increases the heart rate during stressed conditions. Thyroxine also regulates the heart rate.
Disorders of the Circulatory System
- Hypertension: Increase in blood pressure from the normal range of 120/80. It can cause heart failure and organ haemorrhage
- 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).
- Angina Pectoris: It occurs due to cardiac muscle fatigue resulting due to an affected blood supply. It causes pain and discomfort in the chest.
- Myocardial Infarction: It is also called heart It occurs due to the sudden cut-off of oxygen to heart muscles.
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