Topic 3.3 - Mass Transport in Mammals Flashcards
What is the function of the circulatory system?
Transports raw materials from specialised exchange organs to body cells
Describe the 2 circuits the circulatory system consists of
- 1 takes blood from heart to lungs, then back to heart
- Other loop takes blood around the rest of the body
What the function of a vein?
Take blood back to heart under low pressure
Describe the structure of a vein.
- Large lumen
- Very little elastic or muscle tissue = thin walls
- Contain valves to prevent blood flowing backwards
- Blood flow is helped by contraction of body muscles surrounding veins
What is the function of arteries?
Carry oxygenated blood from heart to rest of body
Describe the structure of arteries
- Walls are thick, smooth muscular & have elastic tissue
- Endothelium (inner lining) is folded
What do the walls of the arteries do and what does this help to do?
- Stretch under high pressure
- Recoil under low pressure (elastic recoil)
- Helps to maintain blood pressure
Arteries divide into smaller vessels called…
arterioles
What is the function of arterioles?
Control blood flow from arteries to capillaries
Describe how arterioles control blood flow
- Muscles contracts & arterioles narrow to restrict blood flow to capillaries or relax to allow full blood flow
Arterioles branch into…
capillaries
What is the function of capillaries?
Exchange substances between blood and body tissues
Name 4 adaptations of capillaries for efficient diffusion
- Found near cells in exchange tissues causes a short diffusion pathway
- Walls are a single layer of endothelium cells which also shortens diffusion pathway
- Large no. of capillaries & highly branched increases SA for exchange
- Narrow lumen so red blood cells are squeezed flat against capillary which reduces diffusion distance
What are capillary beds?
Network of capillaries in tissue
Capillaries have ___ between lining (endothelial) cells
gaps
Why do capillaries have gaps between lining (endothelial) cells?
They act as a sieve - controlling which molecules can leave the capillaries. This also allows white blood cells to escape
What is tissue fluid?
Fluid that surrounds cells
What is tissue fluid made from?
Small molecules that leave blood plasma (e.g. oxygen, water and nutrients)
Why doesn’t tissue fluid contain red blood cells or big proteins?
Because they’re too large to be pushed out through capillary walls
What do cells do with tissue fluid?
They take in oxygen and nutrients from tissue fluid & release metabolic waste into it
In capillary bed, substances move out of capillaries into tissue fluid, by ____ _____
pressure filtration
Describe how substances move out of capillaries into tissue fluid by pressure filtration
- At start/arterial end of capillary bed: hydrostatic (liquid) pressure inside capillaries is higher than hydrostatic pressure in tissue fluid
- Difference in hydrostatic pressure causes pressure which forces water/fluid + small molecules out of capillaries & into spaces around cells, forming tissue fluid
- Loss of water/fluid = hydrostatic pressure reduces in capillaries, therefore hydrostatic pressure is lower at venule end
- Also, there’s increasing conc. of plasma proteins , therefore the water potential at venule end is lower than water potential in tissue fluid
- Some water re-enters capillaries from tissue fluid at venule end by osmosis
If asked about a particular end of the capillary, what do you need to do?
Compare hydrostatic pressure and osmotic pressure
Explain how fluid leaves the capillary at the arterial end
Hydrostatic pressure is greater than osmotic effect which forces molecules/fluid out
What within the bloodstream can affect the water potential?
Proteins