2.3.1 blood circulatory system  (Page 7/8)

Figure showing capillaries as the transition between arteries and veins

http://en.wikipedia.org/wiki/File:Illu_capillary.jpg

Interactive diagram illustrating arterial and venous structure.

http://www.phschool.com/science/biology_place/biocoach/cardio2/structure.html

Figure

Shows the how valves cause blood to only flow one way though veins

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Venous_valve.svg /2000px-Venous_valve.svg.png

Capillaries

• Capillaries are little more than a single layer or endothelial cells.
• Capillaries form intricate networks throughout the tissues.
• They allow water, nutrients and gasses to diffuse out of the blood and waste materials to diffuse into the blood.
• This exchange occurs between the blood and the interstitial fluid.
• The interstitial fluid is the fluid surrounding the cells.
• The blood never comes into contact with the cells.
• The blood and interstitial fluid exchange material, and the interstitial fluid then exchanges material with the cells.

Veins

• The intricate networks formed by the capillaries eventually converge to form venules, (small veins)
• The venules then converge to form veins which return the blood to the heart.
• Veins only consist of two layers.

1. The outer layer is made up of connective tissue
2. The inner layer is made up of endothelial cells.

Valves

• Once the blood has passed through the capillaries very little blood pressure remains to return blood to the heart.
• Instead of pressure from the heart veins use a series of valves to force blood to return to the heart.
• Contraction of the muscles squeezes the veins, pushing the blood through them.
• The valves cause the blood to flow in only one direction, back to the heart.

Figure showing capillaries as the transition between arteries and veins

http://en.wikipedia.org/wiki/File:Illu_capillary.jpg

Interactive diagram illustrating arterial and venous structure.

http://www.phschool.com/science/biology_place/biocoach/cardio2/structure.html

Figure

Shows the how valves cause blood to only flow one way though veins

http://upload.wikimedia.org/wikipedia/commons/thumb/4/4a/Venous_valve.svg /2000px-Venous_valve.svg.png

Veins

• The intricate networks formed by the capillaries eventually converge to form venules, (small veins)
• The venules then converge to form veins which return the blood to the heart.
• Veins only consist of two layers.

1. The outer layer is made up of connective tissue
2. The inner layer is made up of endothelial cells.

Valves

• Once the blood has passed through the capillaries very little blood pressure remains to return blood to the heart.
• Instead of pressure from the heart veins use a series of valves to force blood to return to the heart.
• Contraction of the muscles squeezes the veins, pushing the blood through them.
• The valves cause the blood to flow in only one direction, back to the heart.

Figure showing capillaries as the transition between arteries and veins

http://en.wikipedia.org/wiki/File:Illu_capillary.jpg

Interactive diagram illustrating arterial and venous structure.

http://www.phschool.com/science/biology_place/biocoach/cardio2/structure.html