The circulatory system Flashcards
Why do multicellular organisms need specialised transport systems?
The have a low. S.A. to vol. ratio
- need a specialised transport system (the circulatory system)
- carry raw materials from specialised exchange organs to their body cells
What does the blood transport?
- respiratory gases
- products of digestion
- metabolic waste
- hormones
Describe the circulatory system.
- made up of heart and bood vessels
- Two circuits:
- heart to the lungs and v.v.
- other loop takes blood around the rest of the body
* Heart has its own blood supply - left and right coronary arteries.
What are the different types of blood vessels?
Arteries
Veins
arterioles
capillaries
What do arteries do?
Arteries carry oxygenated blood from the heart under high pressure.
How are arteries adapted?
- carry oxygenated blood from heart to body at high pressure
- walls thick and muscular with elastic tissue which stretches and recoils as the heart beats - helps maintain high pressure.
- Inner endothelium folded -allows it to stretch - maintain high pressure.
Which artery differes to the others and why?
All arteries carry oxygenated blood except for the pulmonary arteries - take deoxygenated blood to the lungs.
How do arterioles direct blood to areas of the body with a higher demand for it?
Muscles in the arterioles contract to restrict the blood flow or relax to allow full blood flow.
What do viens do?
Veins carry deoxygenated blood back to the heart under low pressure.
How are veins adapted?
- Wider lumen than arteries
- Have valves to prevent backflow
How does blood flow through the veins if it has a low presssure?
Blood flow through the veins is helped by contraction of the body muscles surrounding them.
Which vein differs from the rest?
All veins carry deoxygenated blood (because oxygen has been used up by the body cells)
They carry deoxygenated blood back to the heart from the body under low pressure.
Unlike other veins, pulmonary veins also carry oxygenated blood from the heart to the lungs.
Which blood vessels are responsible for taking blood to and from the lungs?
The pulmonary artery takes blood to the lungs and the pulmonary vein takes blood away from them.
What do the capillaries do?
Exchange substances between the blood and body tissues.
How are capillaries adapted for their function?
Adapted for effieient diffusion:
- found near cells in exchange tissues (e.g. alveoli in the lungs) so there’s a short diffusion pathway.
- walls one cell thick - also shortens diffusion pathway
- large no. of capillaries - to inc. s.a. for exchange
What is tissue fluid?
fluid that surrounds the cells that’s made up of small molecules that leave the blood plasma e.g. oxygen, water and nutrients (e.g. ions, glucose).
Why dosen’t the tissue fluid contain big molecules?
Tissue fluid doen’t contain big molecules like red blood cells or big proteins as they’re too large to be pushed through the capillary walls.
How do cells interact with the tissue fluid?
Cells take in oxygen and nutrients and release metabolic waste into the tissue fluid.
What is the process by which substances move out of the capillaries?
Pressure filtration
Explain pressure filtration.
At the arterial end of the capillary, the hydrostatic pressure is greater than the osmotic pressure. This difference in pressure forces fluid out of the capillaries (via the gaps in capillary endothelium).
At the venous end of the capillary (the end nearest the viens) the hydrostsic pressure is lower than the osmotic pressure and so the overall movement of fluid is into the capillary.
Some tissue fluid enters the lymph system and drains back into the blood.
Why does water re-enter the capillary from the tissue fluid at the venous end ef the capillary bed?
Due to fluid loss and an increasing concerntration of plasma proteins (which don’t leave the capillaries) towards the venule end of the capillary, the water potential at the venule end of the capillary is lower than in the tissue fluid. This causes water to re-enter by osmosis.
What happens to excess tissue fluid?
It is drained into the lymphatic system - a network of tubes which transport it back into the circulatory system.
Diagram of a capillary bed.
Diagram of the circulatory system
