Blood vessels and their functions Flashcards
What are the 4 different types of blood vessels?
- Arteries - carry blood away from the heart and into the arterioles.
- Arterioles - they are smaller arteries that control blood flow from arteries to capillaries.
- Capillaries - are tiny vessels that link arterioles to veins.
- Veins - carry blood from capillaries back to the heart.
- Arteries, arterioles and veins carry out transport, not exchange, only capillaries carry out the exchange.
What are the basic layered structure of arteries, arterioles and veins?
They all have the same basic structure:
- Tough fibrous outer layer - it resists pressure change from outside and inside.
- Muscle layer - so they can contract and control the flow of blood.
- Elastic layer - helps to maintain blood pressure by stretching and springing back (recoiling).
- Thin inner lining (endothelium) - this is smooth so it reduces friction and it’s thin to allow diffusion.
- Lumen - it’s the central cavity of the blood vessel which allows blood flow to go through.
What is the only difference between arteries and arterioles?
They are similar in structure but arterioles are smaller in diameter and have a larger muscle layer and lumen.
What is the role of arteries and how does its structure adapt to its function?
Its role is to transport blood rapidly under high pressure from the heart to the tissues.
- Walls are thick and muscular which resists the vessel bursting under pressure.
- Have elastic tissue to stretch and recoil as the heart beats which helps to maintain high pressure.
- Inner lining (endothelium) is folded, allowing the artery to stretch which again helps to maintain high pressure.
- All arteries carry oxygenated blood except for pulmonary arteries which take deoxygenated blood to the lungs.
- There are no valves (except the one in the heart) because blood is under constant high pressure as the heart pumps blood into the arteries so it does not cause backflows.
What is the role of arteriole and how does its structure adapt to its function?
Arteries divide into smaller valves called arteriole. It carries blood under lower pressure than the arteries, from arteries to the capillaries it also controls the blood flow between the 2.
- The muscle layer is thicker than the arteries - The contraction of the muscle layer allows constriction of the lumen which restricts the flow of blood and controls the movement into the capillaries.
- The elastic layer is thinner than the arteries - blood pressure is lower.
What is the role of the vein and how does its structure adapt to its function?
Veins transport blood slowly, under low pressure, from the capillaries into the heart.
- Muscle layer is quite thin in comparison to arteries - veins carry blood away from the tissues so their contraction doesn’t control the flow of blood to tissues.
- Elastic layer is quite thin in comparison to arteries - low pressure in the vein so it does not cause them to burst and pressure is too low to create a recoil action.
- Overall thickness of the wall is quite thin - low pressure so it doesn’t need thick walls to prevent it from bursting. It also allows them to be flattened easily so it helps the flow of blood within them.
- Contains valves - to ensure it does not backflow because the pressure is low.
- Wider lumen than the arteries.
What is the role of the capillaries and how does its structure adapt to its function?
Capillaries exchange metabolic materials e.g. oxygen, CO2 and glucose between the blood and cells. The flow of blood in the capillaries is much slower allowing the substances to be exchanged.
- Walls most just made up of lining layer - so they are very thin so diffusion distance is short which allows rapid diffusion of materials between the blood and the cells.
- Numerous and highly branched - provides a large SA for exchange.
- Narrow diameter - it means that no cells are that much far away from a capillary and there’s a short diffusion pathway.
- Lumen is very narrow - RBC is squeezed flat against the side of a capillary. This brings them closer to the cells to supply O2, reduces the diffusion distance.
- There are spaces inbetween the lining (endothelial) cells - allow WBC to escape in order to deal with infections within the tissues.
What is tissue fluid?
- Tissue fluid is a watery liquid which contains glucose, amino acids, fatty acids, ions and O2.
- It supplies all of those substances to the tissues and in return, it receives CO2 and other waste materials from the tissues.
- So tissue fluid is where materials are exchanged between blood and cells, it baths all the cells of the body.
Where and how is tissue fluid formed?
Formed from blood plasma.
Tissue fluid is formed because of the high hydrostatic pressure of arterial circulation when it reaches the capillaries and this is because of the strong pumping mechanism of the heart.
What is hydrostatic pressure?
Blood pumped by the heart passes along the arteries, then arterioles and eventually capillaries, the pressure created when it pumps by the heart is hydrostatic pressure.
How does the formation of tissue fluid work?
- The blood has high hydrostatic pressure, once it reaches the capillaries, at the arterial end of the capillary, due to the high hydrostatic pressure a lot of the small molecules e.g. O2 and nutrients are forced out through pores in the capillaries but larger cells e.g. proteins, RBC remain in the blood.
- The process of which fluid is forced out of the capillaries and forming tissue fluid is called ultrafiltration.
- Cells are able to take O2 and glucose from the tissue fluid and release CO2 and waste by diffusion.
- At the venule end of the capillary, the blood has low hydrostatic pressure due to the fluid lost from the arterial side so tissue fluid will diffuse back into the blood but now because it contains a lot of CO2 and waste product.
- Also as the plasma has lost water but still contain proteins. Therefore has a lower water potential than the tissue fluid. So water would leave the tissue by osmosis down a water potential gradient.
What factors might oppose the outward pressure of the movement of liquid?
- The hydrostatic pressure of the tissue fluid outside the capillaries is higher, which resist the outward movement of liquid.
- Lower water potential of the blood due to plasma proteins will cause water to move back into the blood.
What happens if not all tissue fluid can return to the capillaries?
The remainder is carried back by the lymphatic system. This is a system of vessels that begin in the tissues. These larger vessels drain all the contents back to the bloodstream by 2 ducts that join veins close to the heart.
How are the contents in the lymphatic system move into the bloodstream?
By 1) Hydrostatic pressure of the tissue fluid that left the capillaries.
2) Contraction of body muscles - squeezes the lymph vessels - valves in the lymph vessels ensure the fluid would move towards the heart.
