Mass flow Flashcards
Why do large multicellular organisms use mass flow
Their surface area to volume ratio is too small
Their diffusion pathway is too long
What do mammals have ?
Closed double circulatory system
Closed- blood is enclosed within blood vessels and pumped around by the heart
Double- blood passes through the heart twice in one
What is the role of each blood vessel ?
Arteries- take blood away from the heart Double
Veins- take blood to the heart
Capillaries- connect arteries and veins and are the site of gas exchange
What are the features of the artery ?
Thick wall helps withstand the high pressure
Endothelium is present but folded
Lumen is narrow so maintains high pressure
Elastic content is high so they can stretch and recoil
No valves apart from aorta and pulmonary artery
Pressure is high- pressure drops when ventricles relax but stays high due to elastic recoil of walls
Pressure decreases with distance from heart as there is resistance to blood flow due to friction
Walls- thick to withstand pressure
What are the features of veins ?
Walls are thin
Endothelium is present but not folded
Lumen is wide to reduce resistance
Elastic content is low
They have valves to prevent backflow of blood
Pressure is low due to large volume
Walls are thin due to low pressure
Wide lumen to fit large volume of blood
What are the features of capillaries ?
Small diameter but many- short diffusion distance, large total cross sectional area lowers pressure and slows blood flow enhancing exchange
Narrow lumen- blood cells just fit
Capillary pores reduce pressure
Features of arterioles:
Arteries branch into arterioles
Muscular walls so contract and relax
Contract so they constrict arterioles
Relax so they dilate the arterioles
Vasoconstriction and vasodilation
Tissue fluid formation
Hydrostatic pressure of blood high at arteriole end due to contraction of left ventricle
Water and small soluble molecules are forced out of the capillary
Reduces the volume of the blood so means the remaining blood has a greater volume of capillary to contain it
Red blood cells and large proteins remain
Tissue fluid returning to the circulatory system
This lowers the water potential of the blood
Water moves back into the venous end of capillary by osmosis
Lymph system collects any excess tissue fluid which returns to the blood
What is oedema ?
Build up of tissue fluid
What does the cardiac cycle do ?
Maintains unidirectional flow of blood in the heart
Systole- contract
Diastole- relax
