Circulatory System Flashcards
Why is the circulatory system necessary?
- mammals are relatively large and highly organised; the interdependence of our specialised regions requires an efficient transport system
- mammals are too large to rely solely on diffusion for transport of substances
Mass flow
- bulk movement of substances from one area to another due to differences in pressure
- more efficient transport over long distances
Blood vascular system
Provides most important means of mass flow in mammals
Open circulatory system
- blood is not confined to vessels
- blood flow is slow, at a low pressure, and there is little control over its distribution
- e.g. through the haemocoel of arthropods
Closed circulatory system
- heart, arteries, artérioles, capillaires, venules, veins
- blood can be at much higher pressures
- much more control over distribution
- allows vasodilation and vasoconstriction by contraction of smooth muscle
Artérioles
Narrow, thin-walled arteries
Venules
Small veins
Double circulatory system
- in each complete circuit of the body, blood flows through the heart twice
- pulmonary + systemic circulation
- each organ has a major artery (supplies it with blood) and a major vein
Pulmonary circulation
Transports blood between the heart and the lungs
Systemic circulation
Transports blood between the heart and the rest of the body
Why don’t the stomach and small intestine have major veins?
- carried by hepatic portal veins to the liver, for digested food molecules to be processed
- blood is then transported back to the heart via hepatic vein
Single circulatory system in fish
- in each complete circuit of the body, blood flows through the heart once
- blood is pumped from the heart to the gills, then to the rest of the body
- pressure drops dramatically as blood leaves the gills- it reaches the body slower
- does not work for mammals, as the kidneys cannot function efficiently at low pressures
Pressure gradients
• blood is pumped from a high pressure to a low pressure through
i) the heart pumping
ii) contractions of skeletal muscles squeezing blood through veins
iii) inspiration reduces thoracic cavity pressure, helping to draw blood back to the heart
• valves prevent backflow and ensure unidirectional blood flow
Heart tissue under a microscope
- pink -> muscle tissue
* purple -> elastic tissue
Arteries
- thick muscular wall
- lots of smooth muscle
- more elastic than fibrous tissue
- relatively small lumen
- blood under high pressure
- no valves (except aorta and pulmonary artery)
- layers of endothelium + collagen fibres
- e.g. aorta
