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Unicellular Multicellular
- high SA:V ratio = short distance for material to - low SA:V ratio = long distance for material to
travel travel
- low metabolic needs – slow transport sufficient - high metabolic needs – needs faster rate of
exchange
b. Open vs Closed
Insects: open circulatory system
blood has direct contact with tissues & organs
no respiratory gases/pigments in blood – via tracheal system
haemolymph (blood) pumped by dorsal tube-shaped heart (runs length of body) into haemocoel (cavity)
haemolymph then re-absorbed by dorsal vessel
Earthworm: closed circulatory system
blood vessels: higher pressure (conc grad) / circulate faster / transport longer distances
respiratory gases in blood – aided by pigment = concentration gradient
5 pseudoheart pairs pump blood
blood vessels – run length of body
- Ventral: distributes blood to body segments
- Dorsal: collects blood from body
c. Single vs Double
Fish: closed single circulatory system
through heart once
2 heart chambers
- heart ventricle pumps deoxygenated blood to gill capillaries – high pressure
- gill capillaries reduce pressure & oxygenate blood – slows blood flow to body tissues
o slower rate of delivery/removal – but efficient for metabolic activity (don’t maintain body temperature)
- deoxygenated blood flows back to heart atrium – then heart ventricle
Mammal: closed double circulatory system – 1 circulation = through heart twice
through heart twice: pulmonary circulation (heart & lungs) & systemic circulation (heart & body tissue)
4 heart chambers (more complex)
- high pressure sustained after oxygenation
o maintain concentration gradient
o fast flow rate – meet high metabolic needs (need to maintain body temperature)
- oxygenated/deoxygenated kept separated – improves oxygen distribution
, d. mammalian circulatory system
Heart (cardiac muscle): 4-chambered pump – for double circulation & separation of de/oxygenated blood
atria: receive blood – thin walls
atria-ventricular valves: prevent backflow from ventricles to atria
ventricles:
- thick walls: contraction generates high pressure – blood pumped great distance
- L>R – thicker muscular wall: generates higher pressure – blood must travel greater distance
semi-lunar valves: prevent backflow from arteries to ventricles
Vena cava (superior/inferior): deoxygenated blood from body (upper/lower regions)
Right atrium
Tricuspid – atrio-ventricular valve
Right ventricle
Pulmonary – semi-lunar valve
R/L pulmonary artery: deoxygenated blood to lungs
R/L pulmonary veins: oxygenated blood to left atrium
Left atrium
Bicuspid / mitral – atrio-ventricular valve
Left ventricle
Aortic – semi-lunar valve
Aorta: oxygenated blood to systemic circulation
Blood vessels: distribute blood
further from heart – decrease pressure & rate
- more branched = bigger total cross-sectional area
- smaller diameter = more friction
- tissue fluid formed
Arteries – away: pressure corresponds with ventricular systole
- Protective outer layer: tough collagen fibres – resists over-stretching (could cause loss in recoil)
- Thick muscular layer & many elastic fibres: withstand high pressure
smooth muscle contract/relax – adjust diameter of lumen = control blood flow
elastic recoil: allow stretching to accommodate changing blood flow
- Smooth endothelium – reduce friction
- Smaller lumen
Arterioles: connect arteries to capillaries
Capillaries: form networks within tissues – for exchange
Thin endothelium – single-cell: short diffusion pathway
Dense network: large cross-sectional area – reduces to low pressure
Narrow: red blood cells can lie flat against wall – reduces diffusion distance to Hb
Narrow lumen (small diameter) – friction: slow blood flow – more time for diffusion/exchange
Permeable to gas
Pores/fenestrations: tissue fluid formation & solute/water exchange
Venules: connect capillaries to veins
Veins – back
- Protective outer layer: tough collagen fibres
- Thin muscular layer & few elastic fibres – low pressure
- Smooth endothelium – reduce friction
- Bigger lumen: largest diameter – maximise flow
Skeletal muscle (surrounds vein) contracts: compresses vein – reduces volume & increases pressure inside
forces blood through semi-lunar valve & causes valve behind to close – ensures 1 direction flow
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