Transport

This page - Introduction to Circulatory systems

Page 2 - The heart and blood vessels

Page 3 - Blood composition

Page 4 - Plant transport systems

Introduction

Living things constantly absorb useful substances which must be distrubuted throughout their bodies. They also continuously produce waste products which must be removed by the body before they become harmful.

In small organisms this can be done by a simple process known as diffusion, eg. in Amoeba. However, in larger multicellular organisms, diffusion is not fast enough in removing waste products from the organisms. They must rely on a transport system which can carry these substances fast enough round the body. Usually this consists of some form of pumping organ usually known as the heart which pushes forward a liquid known as blood around a system of blood vessels. The blood vessels pick oxygen from the respiratory organ and passes it to the rest of the body. Blood also picks up carbon dioxide and waste products from the cells and transports them to organs which remove them from the blood and excrete them from the body.

Transport systems in multicellular organisms

Components of the circulatory system include

• blood: a connective tissue of liquid plasma and cells
• heart: a muscular pump to move the blood
• blood vessels: arteries, capillaries and veins that deliver blood to all tissues
  

Vertebrates, and a few invertebrates, have a closed circulatory system. Closed circulatory systems have the blood closed at all times within vessels of different size and wall thickness. In this type of system, blood is pumped by a heart through vessels.

The human closed circulatory system is sometimes called the cardiovascular system.

Closed circulatory systems are of two types, depending on whether the blood passes through the heart once or twice in each circulation of the body.

Fish have a single circulation. The fish’s blood is pumped from the heart through the gills, and then on to the rest of the body before returning to the heart. Blood goes once through the heart in each circulation of the body.

Birds and mammals have a double circulation. Here the blood is first pumped from the heart to the lungs via the pulmonary circulation, and returns to the heart again; from there it is pumped to the to the body tissues via the systemic circulation. One side of the heart serves the pulmonary circulation and pumps deoxygenated blood. The other side of the heart serves the systemic system and pumps oxygenated blood.