A concise and clear overview of the key concepts covered in chapter 8. These notes make biology easy to understand and are a good place to start your revision and boost your grades.
- supply oxygen and - high metabolic demands so diffusion alone isn’t sufficient
nutrients to the sites - SA:V ratio gets smaller in larger multicellular organisms (less for absorption)
where they are - enzymes/hormones made in one place and need to be transported to another
needed - food digested in one organ and needs to be transported to every cell
- remove waste from - waste products removed from every cell must be transporte to excretory
individual cells system
features of circulatory systems open circulatory system
- circulating fluid for transport - few vessels
- pumping device - pumped from heart into body cavity called the
- vessels to carry transport medium haemocoel
- - low pressure
permeable surfaces that enable substances to
enter or leave - direct contact with blood and cells
- mass flow - open ended vessel returns fluid to heart
- uni directional flow - haemolymph transports nutrients/waste (not
- two circuits (one to pick up O2 one to deliver) gas)
- heart in thorax and abdomen
- no steep conc. gradient (low pressure)
closed circulatory system - can’t meet changing demands of organisms
- eg. insects/molluscs
- blood enclosed in vessels
- no direct contact with cells of body
- heart pumps blood under pressure and quickly
and blood returns directly to heart
- substances enter and leave the blood by
diffusion through the walls of the blood vessels
- effective for animals which are active and
maintain body temp
single vs double circulatory system
blood travels once blood travels twice
through heart through heart
two sets of capillaries - 1. one capillary network
oxygen and carbon
dioxide
2. substances exchanged
between blood and cells
pressure is low as travels high pressure, very
far so inefficient efficient
, Blood vessels Blood vessels
made up of:
- elastic fibres - composed of elastin (prevent
tearing) and can stretch and recoil, providing vessel
walls with flexibility, made of collagen
- collagen fibres - high tensile strength and
structural support with some flexibility (fibrous
protein)
- smooth muscle - contracts/ relaxes to constrict/
dilate artery
- endothelium - inner lining of cells, can fold/
unfold, single layer of cells - smooth to reduce
friction
Arteries Histology of arteries
- diameter > 100um to 2.5cm - TUNICA INTIMA: endothelium which
- has a pulse when heart contracts and folds/unfolds + smooth to offer least
elastic fibres recoil to even out surges resistance
- carry blood AWAY from heart - TUNICA MEDIA: thick muscular walls to
- carry oxygen except the pulmonary and withstand and maintain high pressures
umbilical artery in foetus
- TUNICA ADVENTITIA: wall has smooth
- elastic arteries near heart - stretch and
muscle which contracts and constricts the
recoil to even out surges
- lumen
muscular arteries (peripheral) have more
muscle
Capillary bed
Arterioles - site of gas exchange
- endothelium has
- diameter < 100um - fenestration’s
- arise from an arteriole branch
- link arteries and veins
- lined with smooth muscle (less elastin),
allows diameter to be controlled by
nerves/ hormones
- constrict or dilate to control blood flow
- smooth muscle contracts - vasoconstriction
which increases resistance
Capillaries
- diameter: 7um
- thin walls
- large surface area
- leaky walls for blood plasma to exit
- blood flow is slower than in arterioles to allow
time for diffusion
- one cell thick - short diffusion path
- red blood cells squeeze to give up O2
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