Circulatory system structure Flashcards
What is a closed circulatory system?
Contains a pump (heart), vessels (arteries, capillaries and veins) and a medium (blood) to transport substances around the body.
What is a double circulatory system?
Blood is confined to vessels and passes twice through the heart for each complete circuit of the body (to the lungs and tissues).
What are arteries?
Carry blood away from the heart and into arterioles. They have a thicker muscular layer, thicker elastic layer and overall thicker wall than veins.
What are arterioles?
Smaller arteries that control blood flow from arteries to capillaries. Their muscular layer is relatively thicker than in arteries and elastic layer is relatively thinner than in arteries.
What are capillaries?
Tiny vessels that link arterioles to venules. Their walls consist mostly of the lining layer making them extremely thin, they are numerous and highly branched, they have a narrow diameter and narrow lumen and there are spaces between the lining (endothelial) cells.
What are veins?
Carry blood from venules back to the heart. They have a thinner muscular layer, thinner elastic layer and overall thinner wall than arteries. They contain valves at intervals throughout to ensure that blood does not flow backwards.
Why do multicellular organisms require a transport system?
As they have a low SA:V and cannot rely on diffusion to supply all their cells and tissues with the substances they need or to remove waste substances such as CO2 and urea because the diffusion distance is too long. They require a specialised, efficient mass transport system to carry raw materials from specialised exchange organs to their body cells and carry waste substances away.
What is the single form of a circulatory system?
a heart with two chambers meaning the blood passes through the heart once for every circuit of the body
What is the double form of the circulatory system?
the heart has four chambers and blood passes through the heart twice for ever circuit of the body
Why is a double circulatory system more efficient?
it increases pressure and therefore speed of delivery of oxygenated blood to tissues
What happens when arterioles contract?
Blood flow is restricted
What do arterioles branch into?
capillaries which form networks in tissues called capillary beds
What does smooth muscle layer do?
contracts to control the flow of blood in arteries, arterioles and veins
What does the elastic layer do?
allows the vessel to stretch and recoil (spring back) in arteries, arterioles and veins
What does the endothelium do?
thin inner lining which is smooth to reduce friction in all vessels
What are features of the artery? (4 things)
- carry blood away from the heart
- narrower lumen to help maintain high pressure
- thick muscular walls and elastic layer allows stretch and recoil with each ventricular contraction to maintain high blood pressure
- endothelium is folded to allow stretching to help maintain high pressure
What are features of veins? (5 things)
- carry blood towards the heart
- wider lumen than arteries as blood is at low pressure
- thinner layers of muscle and elastic tissue
- valves to ensure that blood does not flow backwards
- when skeletal muscles contract they compress veins, helping to increase pressure and push blood along
What are features of capillaries? (6 things)
- smallest blood vessels diameter same as a red blood cell
- site of substance exchange with cells
- very close to cells so short diffusion pathway
- walls are only once cell thick for short diffusion pathway
- gaps called fenestrations between endothelial cells allow substances to diffuse out between
- large number of capillaries to increase surface area for gas exchange
Blood always flows from … to … pressure
high , low
What blood vessel has the lowest pressure?
the vena cava
Where is blood pressure highest and when?
in the aorta immediately after a ventricular contraction
Why are there fluctuations in the blood pressure of arteries and arterioles?
elastic tissue stretches when blood moves through at a high pressure then recoils as blood pressure drops. this helps to even out the pressure of blood flowing through the artery.
