Understanding the Types of Blood Vessels in the Human Circulatory System

1. Biology 12 Circulatory System – Part 2

2. Types of Blood Vessels • There are 5 main types of blood vessels • Arteries • Arterioles • Capillaries • Venules • Veins

3. The aorta, the largest artery in the body is almost the diameter of a garden hose • The aorta in a blue whale is so big, you could swim down it • Capillaries, on the other hand, are so small that it takes ten of them to equal the thickness of a human hair • One pound of excess fat adds approximately 200 miles of extra capillaries. This increases BP! • If you stretched your veins out, and hooked them all together, they would go around the world 2 times!!

5. Arteries • Function • Transport blood away from the heart • Structure • Thick, elastic walls • Location • Usually deep, along bones • This protects them from injury and temperature loss • Notes • Walls can expand • Arteries have very high blood pressure • Expansion is the “pulse” we feel

6. Arteries of the Human Body

7. Arterioles • Function • Control blood flow into capillaries • Structure • Smaller in diameter than arteries, thinner walls • Have pre-capillary sphincters • Location • Leading towards all capillaries • Notes • Blood Pressure > Osmotic Pressure • Regulate blood pressure with pre-capillary sphincter muscles • Can dilate or constrict to constrict to increase or decrease blood flow to a particular capillary bed

9. Capillaries • Function • Connect arteries to veins • Structure • Very thin walls (1 cell thick) • Location • Everywhere; within a few cells of each other • Site of “capillary-fluid exchange” CO2 O2

10. Capillary-Fluid Exchange Arteriole Side • Blood pressure at arteriole side = 40 mmHg • Osmotic pressure = 25 mmHg • Net blood pressure (15 mmHg) forces water out of the blood into the interstitial fluid • Water carries with it the O2 and nutrients • Because there is more O2 and nutrients in interstitial fluid, it diffuses into body cells

11. Capillary-Fluid Exchange Arteriole Side

12. Capillary-Fluid Exchange • The large things (ex. RBC, WBC, platelets, blood proteins) stay in the capillary because they are too big to leave • Because most of the water has left, the blood becomes very hyperosmotic (concentrated) • The venule side of the capillary is therefore under great osmotic pressure to draw water back into the blood

13. Capillary-Fluid Exchange Venule Side • Osmotic pressure at venule side = 25 mmHg • Blood pressure = 10 mmHg • Blood very concentrated (has little water) • Net osmotic pressure (15 mmHg) forces water back into the blood • Water carries with it CO2 and metabolic wastes (urea) • These are carried to the kidneys and other excretory organs to be removed

14. Capillary-Fluid Exchange Venule Side

16. Venules • Function • Drain blood from capillaries • Structure • Thinner walls than veins • Location • Often near the surface • Notes • Join to form veins • Osmotic Pressure > Blood Pressure • The end result is no change in blood volume (no volume is lost in the exchange)

17. Veins • Function • Transport blood towards the heart • Structure • Inelastic walls, contain one way valves • Location • Often near to surface • Notes • Blood pressure & velocity is much lower than in arteries • Valves prevent blood from flowing backwards • Surrounded by skeletal muscle, “squeezes” blood along

21. Veins of the Human Body

22. How Does It All Fit Together? Arteries: • Carry blood away from the heart • Elastic Capillaries: • Very thin tubes • Connect arteries to veins • Can close down or open up to regulate blood flow • Gas exchange Veins: • Bring blood towards the heart • Have valves to stop blood from moving backwards