Flashcards in Transport in Mammals (Chapter 8) Deck (112)
What is the mammalian circulation system?
A closed double circulation consisting of a heart, blood vessels and blood
What is the function of arteries?
To transport blood, swiftly and at high pressure, to the tissues, away from the heart
What are the three layers of muscle in the walls of arteries and veins?
Tunica intima (an inner endothelium)
Describe the tunica intima
Very smooth, minimising friction with the moving blood
It is made up of flat cells (squamous epithelium) fitting together like jigsaw pieces
What does the tunica media contain?
Smooth muscle, collagen and elastic fibres
What does the tunica externa contain?
Elastic fibres and collagen fibres
What are the distinctive characteristics of an artery wall?
Its strength and elasticity
Why must artery walls be very strong?
To withstand the very high blood pressure of the blood leaving the heart
How are artery walls strong?
They are thick
How does the composition of the artery wall provide strength and resilience?
- (Nearer the heart) the tunica media contains large amounts of elastic fibres, allowing the wall to stretch as pulses of blood surge through at high pressure
- (Further from the heart) tunica media has fewer elastic fibres but more muscle fibres
Why is the elasticity of artery walls important?
- It allows them to 'give', which reduces the likelihood that they will burst
- It allows artery walls to stretch as the high-pressure blood surges into them when the ventricles contract (reducing the pressure) and then recoil inwards as the pressure drops when the ventricles relax (giving the blood a little push)
What are arteries called when they branch into smaller vessels?
Describe the walls of arterioles
- Similar to arteries, but have a greater proportion of smooth muscle
- This muscle can contract, narrowing the diameter of the arteriole and so reducing blood flow, to help control the volume of blood flowing to different tissues at different times
What is the function of capillaries?
To take blood as close as possible to all cells, allowing rapid transfer of substances between cells and blood
What are capillary beds?
Networks of capillaries
What are adaptations of capillaries?
Small size (approx 7μm in diameter)
Extremely thin walls (one layer of endothelial cells)
Tiny gaps between endothelial cells
Why is the small size of capillaries important?
- Allows them to bring blood as close as possible to each group of cells in the body as they are approx the same diameter as an RBC
Why are the thin walls of capillaries important?
- RBCs are brought within 1μm of the cells outside the capillary, needing the oxygen
Why are the gaps between the cells in capillary walls important?
- They allow some components of the blood to seep through into the spaces between the cells in all the tissues of the body, forming tissue fluid
What is the function of veins?
To return blood to the heart
What does the low blood pressure inside a vein mean for the vein?
- That there is no need for veins to have thick walls
- Their tunica media is much thinner than in arteries and has far fewer elastic fibres and muscle fibres
How is blood returned to the heart if it has low blood pressure (e.g. from your legs) ?
- Many veins run within or close to several leg muscles, so when you tense these muscles, they squeeze inwards on the veins, temporarily raising the pressure
- Veins also contain semi lunar valves which allow blood to move towards the heart but not away, so the squeezing of muscles only squeezes it upwards
What is plasma?
A pale yellow liquid in blood consisting of mainly water with other substances dissolved in it
Give examples of solutes in blood plasma
Nutrients e.g. glucose
Waste products e.g. urea
Protein molecules - plasma proteins which always stay in the blood
What is tissue fluid?
Leaked plasma between the cells in tissues which has leaked through the gaps in the cells of the capillary wall
How is tissue fluid different from blood plasma?
- Far fewer protein molecules (too large to fit through gaps in capillary walls)
- No RBCs (but some WBCs)
Why does plasma move out into tissue fluid at the arterial end of the capillary bed?
- The blood pressure inside the capillary is enough to push fluid out into the tissue (down a pressure gradient) and there is no change in water potential as proteins remain in the capillary
- The hydrostatic pressure is greater than the difference in water potential between the blood and tissue fluid
Why does tissue fluid move back into capillaries at the venous end of the capillary bed?
- Water moves from high water potential to low water potential
- Since tissue fluid lacks the high concentrations of proteins that exist in plasma, and the pressure is lower, fluid moves into the capillaries from a higher water potential to a lower water potential
Overall, does more blood flow into or out of capillaries?