2.1 The circulatory system and the heart
Large organisms need a transport system to move materials around the body.
Humans have a circulatory system which consists of blood vessels, blood and the heart.
The heart is a muscular organ that pumps blood around the body. It is actually two pumps held together.
The right pump forces deoxygenated blood to the lungs, where it picks up oxygen and loses carbon dioxide.
After returning to the heart, the oxygenated blood is then pumped to the rest of the body by the left pump.
The heart has four chambers. The upper ones called atria receive blood from the vena cava on the right and the pulmonary veins on the left.
More about the heart
The atria contract to move blood into the lower chambers, the ventricles. When the ventricles contract they force blood into the pulmonary artery from the right side and into the aorta on the left side.
Valves in the heart prevent blood from flowing in the wrong direction.
The heart muscle is supplied with oxygenated blood via the coronary arteries.
The action of the two sides of the heart results in double circulation.
veins ---> atria ---> ventricles ---> arteries
The structure of the heart
2.2 Keeping the blood flowing
Blood flows round the body in three main types of blood vessels:
- carry blood away from the heart
- have thick walls containing muscle and elastic tissue
- have thinner walls than arteries
- often have valves along their length to prevent back flow of blood
- are narrow, thin-walled vessels
- carry the blood through the organs and diffuse substances with all the living cells
If blood vessels are blocked or too narrow the blood will not flow efficiently. Then organs will be deprived of nutrients and oxygen.
Leaky valves mean the blood could flow in the wrong direction.
2.3 Transport in the blood
Blood is a tissue. The fluid plasma contains red blood cells, white blood cells and platelets.
Blood plasma transports:
- carbon dioxide from the organs to the lungs
- soluble products of digestion from the small intestine to other organs
- urea from the liver to the kidneys where urine is made
- are small fragments of cells
- do not have a nucleus
- help blood to clot at the site of the wound
More Transport in the blood
Red blood cells:
- are biconcave discs which do not have a nucleus, giving it a large surface area and space for more of the red pigment haemoglobin
- use their haemoglobin which combines with oxygen to form oxyhaemoglobin in the lungs
- carry the oxygen to all the organs where the oxyhaemoglobin splits into haemoglobin and oxygen
White blood cells:
- have a nucleus
- form part of the body's defence system against microorganisms
2.4 Artificial or Real?
Artificial blood - Advantages:
- always available, doesn't always need to be kept in the fridge
- doesn't contain cells so can get into any tissue and matches all blood groups
- expensive, doesn't carry as much oxygen as whole blood
- some artificial blood does not dissolve in water so doesn't mix easily with the blood
- broken down very quickly in the body, can cause unpleasant side effects
- no wait for a donor, no need to match tissue
- no need for immunosuppressant drugs
- BUT issues with size, problems with clotting, inconvient, expensive
2.5 Transport systems in plants
Flowering plants have separate transport systems.
Xylem tissue transports water and mineral ions from the roots to the stem, leaves and flowers.
The movement of water from the roots through the xylem and out of the leaves is called the transpiration stream.
Phloem tissue transports dissolved sugars from the leaves to the rest of the plant, including the growing regions and the storage organs.