Lesson 9
The Human Cardiovascular and Lymphatic Systems

9.1 Introduction

NEED FOR CIRCULATORY SYSTEMS

The need for circulatory systems is based on two criteria:

(1) Number of cells. Multicellular animals are animals with a great number of cells.

(2) Size. In larger animals, most cells are too far away from sources of food and oxygen for simple diffusion to provide sufficient amounts. Also, distances are too great for simple removal of wastes.

Because of these criteria, we need a system (or systems) to carry materials to all cells. To get food and oxygen to the cells and to remove waste products, we need a transport system or circulatory system. Human circulatory systems are so effective that no cell is more than two cells away from a blood capillary.

BASIC COMPONENTS OF ANY CIRCULATORY SYSTEM

The four basic components of any circulatory system are a vehicle, conduits, a motive force, and exchange areas. The vehicle is the substance which actually carries the materials being transported. A conduit is a channel, pipe, or tube through which a vehicle travels. If we say that a force is motive, we mean that it produces movement. Systems providing a motive force are often known as pumps. Since the materials being transported must eventually be exchanged with a part of the body, special areas are developed for this purpose. They are called exchange areas.

CIRCULATORY SYSTEMS IN THE HUMAN BODY

The cardiovascular system is the circulatory system involving the heart and blood vessels. The lymphatic system is a drainage-type circulatory system involved with the clear fluid known as lymph. And then there are other minor circulatory systems in the human body, such as the one involved with cerebrospinal fluid.