Importance of the Circulatory System
Our body has a small surface area to volume ratio, therefore simple diffusion through body surfaces to take in their requirements of food and oxygen and to remove CO2 and wastes.
Large organisms have therefore developed transport systems to carry dissolved substances from specialized organs which absorb them to body cells and carry waste substances back to specialized organs which excrete them. The substances carried maybe:
Blood - the transport medium
Our blood is composed of three types of cells:
Plasma is a straw colored fluid composed of: 90% water and 10% dissolved substances . The dissolved substances consist of: dissolved food, waste products, plasma proteins, hormones, dissolved gases and mineral salts.
Components of the Circulatory System
Our circulatory system consists of:
1. a transport medium - the blood
2. tubes through which the medium can travel - blood vessels
3. a pump to push the medium through the tubes - the heart
Here is the PowerPoint which was done in class.
Blood vessels are the tubes by which blood is transported throughout the body. There are three main types of blood vessels and each one has a specific structure which enables it to efficiently carry out its function. The blood vessels are:
(See above for pictures of the blood vessels)
Arteries carry blood away from the heart. As blood leaves the heart, it is rushing out at a very high pressure. Therefore arteries have very thick walls to withstand this pressure. It also has a small lumen (space where blood passes through) and a very muscular and elastic walls. Blood does not flow through our arteries like the way water flows in a river, the movement is not smooth. In our arteries blood flows in pulses. There is evidence of this every time we feel our pulse! Smaller branches of arteries are called arterioles.
Capillaries link arteries to veins. They are also the site in the body where blood is allowed to interact with our cells. The capillaries are one cell thick, therefore they allow useful materials to be absorbed by the blood and unwanted substances from the body to be diffused into the blood. These unwanted substances are taken to the respective organs to be eliminated from the body e.g. urea to the kidney and alcohol to the liver. A network of collection of capillaries is known as a capillary bed.
Veins take blood to the heart. This blood is low in oxygen and is traveling at a very low pressure. The pressure is decreased as the blood speed slows as it enters and exits the capillaries. The veins are well suited to deal with this; they are the only vessels to contain valves. Valves are present in veins to prevent the back flow of blood. Veins have less muscular walls as there is no high pressure to deal with and they have a very large lumen when compared to arteries. This is to allow a greater amount of blood to get to the heart as the pressure is quite low.