Organization of Circulatory System

Dr. Sumera Gul

Associate Professor

Department of Physiology

Learning Objectives

• At the end of the session, the students should be able to:

• Explain the general organization of circulatory system

• Describe the functions of various components of circulatory system

• Discuss the physical characteristics of circulation

What is the Circulatory System?

Circulatory System

• The Circulatory System is a transport system

• Transports materials through out the entire body.

• Transports nutrients, water, and oxygen to the billions of body cells

• Carries away wastes such as carbon dioxide that body cells produce.

Circulatory System

• Most of cells in body are not in direct contact with external environment

• However, they need to exchange nutrients, water, gases and waste products.

• They also need chemical messengers

• The achieve these long distance exchanges cells are linked with one another and with the external environment by vascular system.

• Blood flows in it and performs the said function.

Components of Circulatory System

Heart

Blood

Vessels

• Arteries

• Capillaries

• Veins

Circulation

• Systemic Circulation

• Pulmonary Circulation

Systemic Circulation

• Greater circulation or peripheral circulation

• Receives blood from left side of heart

• Takes blood from heart to all parts of body and back

• Works under higher pressures

• Holds more blood (84% of total blood volume)

Pulmonary Circulation

• Receives blood from right side of heart

• Takes blood from heart to lungs and back

• Lesser blood volume (9% of total blood volume)

• Lower working pressures

84% of total blood volume in systemic circulation

64% in veins

13% in arteries

7% in arterioles and capillaries

= = =

7% heart

= = =

9% pulmonary circulation

Vascular Tree

• Arteries

• Arterioles

• Capillaries

• Venules

• Veins

• Carry blood from heart and branch into smaller arteries

• A small artery when reaches an organ branches into many arterioles

• Arterioles branch further within the organ, smallest of vessels

• Capillaries rejoin to form venules inside the organ

• Venules merge to form veins. Smaller veins join to form larger veins which eventually drain into heart

Microcirculation

Arteries

• Rapid-transit passage for blood from heart to body

• Pressure-reservoir to provide driving force for blood when heart is relaxing

• Elastic arteries, large arteries near to heart

• Muscular arteries, less elastic and more muscular, medium sized vessels near organs

Arterioles• Smaller diameter

• Major resistance vessels

• Smallest vessels, narrowest and maximum in number

• Walls are only one cell thick

• Contain many capillary pores

• Site of exchange of gases and other material

Capillaries

Veins

• Blood leaving capillary bed enters the venous system

• Blood reservoir

• Contains valves to ensure blood flow in one direction

• Less resistance

• Thin walled

Cross sectional area of circulatory system:

Pressures in Circulatory system

Pressures (Systemic)

• 120mmHg during systole and 80mmHg during diastole (mean 100mmHg)

• 35mmHg on arteriolar end of capillaries and 10 mmHg on venous end (mean 17mmHg)

• Almost 0 in terminal end of vena cava

Pressures (Pulmonary)

• 25mmHg during systole and 8mmHg during diastole (mean 16mmHg)

• Mean pulmonary capillary pressure is 7 mmHg

Pressures in Circulatory system

Blood Flow

Task for you.

How is Cardiovascular system different from Circulatory system?