blood vessels and functions

what do arteries do?

• carry blood AWAY from the heart and into the arterioles

what are the common features in arteries and veins?

• tough, fibrous outer layer - resists pressure changes

• muscle layer - can contract to control flow of blood

• elastic layer - stretch and recoil which helps to maintain pressure

• thin inner lining (endothelium) - smooth to reduce friction and thin to allow diffusion

• lumen - central cavity through which blood flows

characteristics of arteries?

• thicker muscle layer

• thicker elastic layer

• overall thickness of wall is greater

• there are no valves

• small diameter lumen

• blood flows faster

• high pressure blood

characteristics of arterioles?

• muscle layer is thicken than arteries - because of vasoconstriction

• elastic layer is thinner than arteries - because pressure is lower

characteristics of veins?

• muscle layer is thinner

• thinner elastic layer

• overall thickness of wall is smaller

• contains valves

• large diameter lumen

• low pressure blood

characteristics of capilaries?

• arterioles branch into capillaries

• walls consist of the endothelium only

• numerous and highly branched

• narrow diameter

• lumen is narrow

• spaces between lining cells

adaptations of capillaries?

• always found very near cells in exchange tissues, so there’s a short diffusion pathways

• their walls are only one cell thick, also shortening diffusion pathway

• there are a large number of capillaries, to increase surface area for exchange

• networks of capillaries in tissue are called capillary beds

what are capillary beds?

• networks of many tiny capillaries that connect arterioles to venules within tissues

arterioles and venules?

• arterioles- brings blood to the capillaries

• venules- takes blood away from capillaries

importance of capillary beds as an exchange surface?

• large sa- forming a dense network which increases diffusion

• thin walls- made of endothelial cells only, creating short diffusion distance

• permeable walls- gaps between cells, which allows substances and tissue fluid to move out

• narrow lumen- very small diameter, so red blood cells can pass close to wall

• slow blood flow- more time for exchange

• close to cells- right next to body cells for short diffusion distance

• maintains conc. gradient- constant blood flow

  • brings O2/glucose & removes CO2 and waste

what is tissue fluid?

• the fluid that surrounds cells in tissues

• it is made from blood plasma, that contains glucose, amino acids, fatty acids, ions in solution and oxgen

• it is needed for exchanging materials between blood and cells

what does tissue fluid do?

• supplies these important substances to the tissues

• it removes carbon dioxide and other waste materials from the tissues

  • it is the link between capillaries and cells- it allows substances to move easily between blood and cells

how do substances move out of capillaries?

• they move into the tissue fluid (in a capillary bed) by pressure filtration

pressure filtration?

• in order for substances carried in the bloodstream to diffuse into the cells, they must first move out from the capillaries

• substances move into the tissue fluid from the capillaries in a process called pressure filtration

pressure gradient?

• there is a high pressure in the capillaries at the entrance to a capillary bed

• the high pressure creates a pressure gradient between the inside of the capillaries and the outside

movement of tissue fluid?

• the fluid in the capillaries flows down the pressure gradient into the surrounding space

  • this is pressure filtration

• the fluid that has moved out of the capillaries created the tissue fluid

• substances in the tissue fluid can now diffuse or be transported into the cells

decreasing pressure?

• the movement of fluid out of the capillaries causes the pressure inside the capillaries to decrease

• this means that the pressure in the capillaries at the exit of the capillary bed is low than the pressure at the entrance of the capillary bed

water potential gradient?

• when fluid moves out of the capillaries, plasma proteins remain inside the capillaries

• the plasma protein concentration inside the capillaries increases and the water potential decreases

• a water potential gradient is established and water diffuses via osmosis back into he capillaries from the tissue fluid

lymphatic system?

• excess tissue fluid flows into the lymphatic system

• the lymphatic system recycles the excess tissue fluid into the blood stream