3. Mass Transport Flashcards
The circulatory System is a mass transport system
Multi cellular organisms have a small surface area to volume ratio so they need a specialised transport system to transport raw materials from specialised exchange organs to their body cells
The circulatory system is made up of the heart and blood vessels
The human circulatory system
The heart pumps blood around the body. Blood transports respiratory gases, soluble food products, hormones and heat around the body. For every complete circuit of the body the blood passes through the heart twice. It is a double circulation.
What would happen if the blood supply to the cardiac muscle was restricted?
The coronary arteries supply the cardiac muscle
Name
Arteries, arterioles and veins have the same basic structure
Name it
A tough outer layer that resists pressure changes
Muscle layer that can contract and so control the flow of blood
Elastic layer that helps to maintain blood pressure by stretching and then springing back
Thin inner endothelium that is smooth to prevent friction
Lumen through which the blood flows
q
Arteries
carry blood away from the heart
The muscle layer is thick – so that they can control the volume of blood passing through them.
The elastic layer is thick- so that the vessel can stretch at systole and then spring back at diastole- this is called elastic recoil and helps to maintain high pressure and smooth pressure surges.
The overall thickness of the wall is large – resists vessel bursting under pressure
There are no valves- because the blood is under constant high pressure and does not tend to flow backwards
Arterioles
Arterioles carry blood under lower pressure from arteries to capillaries.
Muscle layer is relatively thicker than in arteries – contraction of these muscles controls the flow of blood into the capillaries that supply the tissues with blood
Elastic layer is relatively thinner –because the blood pressure is lower.
Veins
carry blood slowly under low pressure from tissues to the heart
Muscle layer is relatively thin compared to arteries because veins carry away from tissues and thus do not control the flow into the tissues.
Elastic layer is relatively thin because the low pressure of the blood will not cause them to burst and the pressure is too low to create an elastic recoil
Overall thickness is low because no risk of bursting
There are valves to ensure blood does not flow backwards
function of capillaries
The function of capillaries is to exchange metabolic materials such as oxygen, glucose and carbon dioxide between the blood and cells of the body.
Capillary and its Wall
consists only of the endothelium so they are extremely thin – short diffusion distance.
They are highly branched – provides a large surface area
No cell is far from a capillary
The lumen is narrow so red blood cells are squashed flat against the walls. This also reduces the diffusion distance
There are spaces between the endothelial cells that allow white blood cells to escape in order to deal with infections within tissues.
The Capillary Bed
Substances are exchanged between the blood and body tissues at the capillaries. These are the smallest blood vessels.
Measurements were taken in the renal artery, the renal vein, an arteriole, the aorta and the vena cava.
Suggest which letter represents each blood vessel. Explain your choices.
Relative blood pressure is highest in the aorta as it has just left the heart. Relative blood pressure in the other blood vessels decreases as they get further away from the heart. The vessel with the lowest relative blood pressure is the vena cava as it is the last blood vessel before blood returns to the heart.
