Biology AQA 3.2.7 The blood system

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circulatory system in mammals

coronary artey

Coronary vein

aorta

aorta

renal artey- to the kidneys

herpatic artery

hepatic portal vein

Artery: They carry blood away from the heart. the walls are thick and muscular, they have elastic tissue which helps them to cope under the high pressure.

The endothelium is folded to allow stretch.

Artery:

Cell wall

Muscle

Folded epithelium

Medium lumen

Vein:

Cell wall

Smaller muscle layer

epithlium

Large lumen

Capillary:

Thin epithelium

Small lumen

Arterioles:

divide off from arteries. these form a network through the body. this causes blood to be directed to different areas of demand.

Veins:

take blood back to the heart at a low pressure. They have a wider lumen and they also contain valves to stop backflow. the muscle contractions help the blood to be carried

Capillaries:

Found near cells in exchange tissues, they create a shorter diffusion pathway. they are only one cell thick to allow efficient gas exchange. they increase the surface area

At the start of the cappilary, near the arteriole, the tissue fluid pressure is greater- this causes fluid to be forced out of the capillaries into the cell, causing the fluid

->

As the fluid leaves, the pressure in the capillaries reduces.- so the pressure is lower at the vein end.

->

Due to fluid loss, the water potential near the veins is lower- so the fluid renters the cappilary by osmosis.

THE

THE LYMPH:

Tissue fluid doesnt contain proteins or big molecules.

any excess fluid is drained through the lymph, which dumps the excess fluid back into the circulatory system.

the blood system

structure

Tissue fluid