More Exchange and Transport Systems - The Circulatory System Flashcards
Why do mammals have a circulatory system?
Because of the low surface area : volume ratio
What is the circulatory system made up of?
The heart and blood vessels
What is the heart’s own blood supply?
Coronary arteries
Where do arteries carry blood to and from?
What are their characteristics?
ARTERIES
Carry blood FROM the HEART to the rest of the BODY.
Their walls are THICK and MUSCULAR
and have elastic tissue to stretch and recoil as the heart beats,
which helps maintain the high pressure.
The inner lining (endothelium) is folded, allowing the artery to stretch
– this also helps it to maintain high pressure.
All arteries carry oxygenated blood except for the pulmonary arteries, which take deoxygenated blood to the lungs.
What are arterioles?
The divisions of arteries, which are smaller vessels.
These form a network throughout the body.
Blood is directed to different areas of demand
in the body by muscles inside the arterioles,
which contract to restrict the blood flow
or relax to allow full blood flow.
Where do veins carry blood to and from?
What are their characteristics?
Veins take blood back to the heart under low pressure.
They have a wider lumen than equivalent arteries, with very little elastic or muscle tissue.
Veins contain valvs to stop the blood flowing backwards.
Blood flow through the veins is helped by contraction of the body muscles surrounding them.
All veins carry deoxygenated blood (because ofygen has been used up by body cells),
except for the pulmonary veins, which cary oxygenated blood to the heart from the lungs.
- Elastic tissue in wall
- Thin muscle wall
- Smooth endothelium
- Large lumen
Where are substances exchanged between blood and body tissues?
At the capillaries
What do arterioles branch into?
Capillaries
What happens at the capillaries?
How are they adapted for this? (3)
Substances are exchanged between cells and capillaries, so they’re adapted for efficient diffusion:
1) They’re always found very near cells in exchange tissues (e.g. alveoli in the lungs), so there’s a short diffusion pathway.
2) Their walls are only one cell thick, which also shortens the diffusion pathway.
3) There are a large number of capillares, to increase the surface area for exchange. Networks of capillaries in tissue are called capillary beds.
1) What is tissue fluid?
2) What does it consist of?
3) What happens at the cells?
TISSUE FLUID:
1) The fluid that surrounds cells in tissues.
2) It consists of small molecules that leave the blood plasma, e.g. oxygen, water and nutrients.
It does NOT contain red blood cells or big proteins, as they’re too large to be pushed out through the capillary walls.
3) Cells take in oxygen and nutrients from the tissue fluid, and release metabolic waste into it.
At a capillary bed, how do substances move out of the capillaries and into the tissue fluid?
By pressure filtration:
1) At the start of the capillary bed, nearest the arteries, the hydrostatic (liquid) pressre inside the capillaries is greater than the hydrostatc pressure in the tissue fluid.
2) This difference in hydrostatic pressure means a overall outward pressure forces fluid out of the capillaries and intot he spaces around the cells, reforming tissue fluid.
3) As fluid leaves, the hydrostatic pressure reduces in the capillaries
- - so the hydrostatic pressure is much lower at the venule end of the capillary bed (the end that’s nearest to the veins).
4) Due to the fluid loss, and an increasing concentration of plasma proteins (which don’t leave the capillaries),
the water potential at the venule end of the capillary bed is lower than the water potential in the fluid.
5) This means that some water re-enters the capillaries from the tissue fluid at the venule end by osmosis.
Where is excess tissue fluid draned into?
The lymphatic system
