WJEC AS Biology Unit 2 Topic 3 Vascular Systems - Basic Revision Notes

Vascular Systems of Animal Groups

• Common features of a transport system are

  • Suitable medium to carry materials

  • A pump for moving the blood

  • Valves to maintain unidirectional flow

In addition some have

• • Respiratory pigment to increase volume of oxygen that can be transported

  • A system of vessels with a branching network to distribute the transport medium all over the body.

• In open systems blood doesn't move around in vessel, it bathes in tissue directly whilst held in a cavity called the haemocoel.

• In closed systems blood moves in vessels, and can be either

  • Single - blood moves through heart once in passage around the body.

  • Double -  blood moves through heart twice in passage around the body.

• Fish - Ventricle of heart pumps deoxygenated blood to gills where its pressure falls.  Oxygenated blood is carried to tissue from there.  Deoxygenated blood moves back to atrium then the ventricle and the process starts again.

• Mammals  - Have a closed double system.  Blood is pumped by the muscular heart at high pressure with two ventricles and two atria.

• Earthworm - Have a closed single system.  Blood moves forward in the dorsal vessel and back in the ventral vessel.  5 pairs of pseudohearts (thickened muscular blood vessels) pump blood from the dorsal vessel to the ventral vessel and keep it moving.

• Insects - Have an open blood system.  They have long dorsal tube shaped heart running the length of the body.  It pumps blood out at low pressure into the haemocoel, where materials are exchanged between blood and body cells.  The blood returns slowly to the heart and the system starts again.  There is no oxygen in blood so therefore no respiratory pigment.  

The Heart

• The heart acts as two pumps to get blood pumped around the body.

Blood

• Capillaries have thin walls, one layer of endothelium.  They are permeable to water and solutes.  Their small diameter allows them to slow the rate of blood flow, leaving plenty of time for diffusion.  There are lots of them, providing a large surface area/exchange surface.

• Veins have a larger diameter lumen.  They have thinner walls with less muscle than arteries.  The blood pressure in veins is lower than arteries, so therefore the flow rate is lower than arteries.  The blood either returns to the heart by gravity or by pressure from surrounding muscle.  They have semilunar valves to prevent backflow.  They are 6mm in diameter.  They split into smaller venules.  

• Arteries carry blood away from the heart.  They branch into arterioles.  Thick, muscular walls withstand high pressure from the heart.  Elastic fibres allow stretching to accommodate changes in blood flow and blood pressure.  They recoil and push blood through.  This is the pulse, and it regulates blood pressure.  Contractions of smooth muscle regulate flow and blood pressure. They are 10mm diameter.

• Arteries and Veins have a similar structure.

  • Lumen, is the hole in the centre.

  • Innermost layer is endothelium, it is one cell thick and surrounded by a tunica intima, a smooth lining…