Blood and Its Circulation


Blood and Its Circulation

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Blood is a body fluid in people and different animals that provides necessary materials including vitamins and oxygen to the cells and transports metabolic waste merchandise faraway from the ones identical cells.

In vertebrates, it’s far composed of blood cells suspended in blood plasma. Plasma, which constitutes fifty five% of blood fluid, is mostly water (ninety two% by using extent), and contains proteins, glucose, mineral ions, hormones, carbon dioxide (plasma being the primary medium for excretory product transportation), and blood cells themselves. Albumin is the primary protein in plasma, and it functions to adjust the colloidal osmotic pressure of blood. The blood cells are especially purple blood cells (also referred to as RBCs or erythrocytes), white blood cells (also referred to as WBCs or leukocytes) and platelets (additionally known as thrombocytes). The most ample cells in vertebrate blood are crimson blood cells. These incorporate hemoglobin, an iron-containing protein, which helps oxygen transport by reversibly binding to this respiratory gas and significantly increasing its solubility in blood. In evaluation, carbon dioxide is in the main transported extracellularly as bicarbonate ion transported in plasma.

Human Circulatory System

The circulatory device, also called the cardiovascular device or the vascular device, is an organ gadget that lets in blood to circulate and transport vitamins (including amino acids and electrolytes), oxygen, carbon dioxide, hormones, and blood cells to and from the cells inside the body to offer nourishment and assist in preventing illnesses, stabilize temperature and pH, and maintain homeostasis.


The muscular organ which is located near the chest slightly towards the left in the thoracic region. It is the very crucial organ of our body which works continuously throughout our life. The human heart is divided into four chambers which are involved in the transportation of oxygenated blood and deoxygenated  The upper two chambers are called as atria whereas the lower two chambers are called as ventricles.

The human circulatory system is more advanced than that of other animals like fish, reptiles, etc. In the human body, blood circulates through the heart twice. Hence, circulation in human beings is called doule circulation.

Layers Of Heart

It consists of three layers namely:

Myocardium– The myocardium includes heart muscle cells that make up the bulk of heart wall and the middle layer.

Epicardium – The outer layer of cells is known as epicardium and the second layer which is membranous surrounds and protects the heart.

Endocardium -The endocardium lines the inner wall of the heart.

  1. The Pericardium

It is a fiber kind of a covering around the heart and keeps it in place. This is a unique membrane and lubricates the heart in the pericardial space to avoid friction. Pericardium has two exclusive layers:

  • Visceral layer directly covers the heart.
  • Parietal layer forms a sac that contains the fluid in the pericardial cavity.

2. The Heart Walls

The heart wall consists of three layers:

Epicardium – This is the outermost layer of the heart and a thin layer of membrane that protects and lubricates the outer its section.

Myocardium – This is a muscular layer and consists of muscle tissue. It contributes to the thickness and responsible for the pumping action.

Endocardium – It is the innermost layer that lines within the heart and keeps blood from sticking and prevents the formation of harmful blood clots.

3. Chambers Of Heart

The four chambers are as mentioned below:

  • Left atrium
  • Right atrium
  • Left ventricle
  • Right ventricle

Atria are thin, less muscular walls and smaller than ventricles. These are the blood-receiving chambers that are carried to the heart by the large veins.

Ventricles are larger and more muscular chambers of pumping and push blood out to the circulation. These are connected to larger arteries that deliver blood for circulation.

The right ventricle and right atrium are smaller than left chambers. Their walls consist of fewer muscles compared to left portion and size difference is based on their functions. The blood from the right side flows through the pulmonary circulation while blood from the left chambers is pumped to the complete body.


The fluid connective tissue which plays a vital role in circulating food, hormones, water, air and other necessary products to different parts of the body. Blood flows through a specified set of pathways called blood vessels. The organ which is involved in pumping blood to different body parts is the heart.  Blood cells, blood plasma, proteins, and salts together constitute the human blood. The composition of blood are:

  • Plasma, the fluid part of the blood that is composed of  90%  of water.
  • Blood cells, the solid part of blood.

There are three types of blood cells.

  1. Red blood cells (RBC) / Erythrocytes: They are mainly involved in transporting oxygen, food, and other substances to various parts of the body. These blood cells also function by, removing the waste from the body.
  2. White blood cells (WBC) / Leukocytes: They are specialized in defense. They fight against foreign particles entering the body.
  3. Platelets /Thrombocytes: Platelets help in clotting of blood at the time of wound or cut.

Blood Vessels

Blood vessels are the pathways through which the blood travels from one part to different parts of the body.  Arteries and veins are two types of blood vessels in the circulatory system of the body.

  • Arteries are the blood vessels that transport oxygenated blood from the heart to various parts of the body. They are thick, elastic and are divided into a small network of blood vessels called capillaries.
  • Veins are the blood vessels, a carrier deoxygenated blood towards the heart from various parts of the body for purification.  They are thin, elastic and are present closer to the surface of the skin.
  • Capillaries It allows the switching of chemicals and water between the tissues and blood. They are very thin and tiny. Exchange of blood takes place between blood tissues and capillaries. This function takes place in capillary beds. Connective tissues are also found occasionally.
  • Sinusoids They are very small vessels located within the bone marrow, liver and spleen.


The human circulatory system consists of another body fluid called lymph. It is also known as tissue fluid. It is a colorless fluid consisting of salts, proteins, water, etc. which transport and circulates digested food and absorbed fat to intercellular spaces in the tissues.

Layers of Blood Vessels

Both arteries and veins consist of three layers.

  • Tunica Intima: It is one of the innermost and thinnest layers of arteries and veins. It comprises of endothelial cells. They are in direct contact with the flow of blood. It intern consists of three layers. I.e. Inner Layer, Middle Layer, and Outer Layer.
  • Tunica Media: It is one of the thickest layers of arteries. Its function is to control the caliber of the vessel.  It also consists of connective tissue and polysaccharide substances.
  • Tunica Adventitia: It controls the caliber of the vessel. It is surrounded by the tunica media. It comprises of collagen and also supported by the lamina.