Cardivascular System

Introduction

Heart and blood vessels with blood, form the cardiovascular system. In vertebrates, blood vessels are of closed type. Therefore, blood circulates from the heart back to the heart.

Blood Circulation in Vertebrates

Heart: Heart is composed of four chambers: two auricles and two ventricles.

Blood vessels: Blood vessels are composed of arteries, veins and blood capillaries.

Circulation: Blood starts from left ventricle, passes through aorta (main artery) and its branches to all parts of the body and into the blood capillaries. From here, blood enters into the veins, and run back to right auricle of the heart .From right auricle, blood passes into the right ventricle, then through the pulmonary artery to lungs. In lungs gaseous exchange of O2 and CO2 take place. From lungs, oxygenated blood goes back through the veins to the left auricle, thence to left ventricle. Thus a single circulation of blood completes.

Heart Beat: Heart is a pumping machine, which contracts and relax rhythmically to pump out the blood. This is called heart beat. A single heart beat consists of one contraction (systole) and one relaxation (diastole) of heart muscles.

Pace maker: The pace maker (made up of nerve cells) initiates the heart beat.

Blood pressure: The pressure exerted by the blood against the walls of blood vessels is called blood pressure.

Blood: Blood is a liquid tissue. It is composed of loose cells and plasma. Cells are mainly of three types: red blood cells (RBC), white blood cells (WBC) and blood platelets.

Function of Blood: Main functions of blood are-

• Transport of gases
• Transport of nutrients
• Transport of waste products
• Communication within the body
• Defensive mechanism against diseases
• Coagulation or Clotting of blood
• Regulation of body temperature
• Regulation of blood pressure