The Blood Vessels Arteries arterioles capillaries venules veins

The Blood Vessels Arteries, arterioles, capillaries, venules, veins

Structure of Arteries • Four Layers: • 1. Inner endothelium layer • 2. Thick elastic connective tissue layer • 3. Thick smooth muscle layer • 4. Connective tissue layer

• Arteries carry blood away from the heart • Elastic and muscular middle layers help arteries to keep blood flowing. • Steady pressure and flow is maintained through the arterioles

• Blood pressure highest in the arteries • Aorta is biggest in the body • Branches of aorta: • 1 Coronary artery 2. Innominate arteries; subclavian branch, carotid branches

Capillaries • Microscopic vessels allowing exchange of materials • Vessel walls are one cell thick • One red blood cell fits inside diameter

• Pressure inside capillaries causes fluid to leak into interstitial fluid • Capillaries are very numerous, no body cell is more than 100 micrometers from one

Structure of Veins • Same layers as arteries but different proportions: • 1. • 2. • 3. • 4. Inner endothelium layer Thin elastic connective tissue layer Thin smooth muscle layer Connective tissue layer

• Capillary blood drains into venules, which empty into veins • Veins carry blood back to the heart. • Pressure is lowest in the veins • Skeletal muscle help return blood to the heart • Veins have valves that prevent backflow

• Varicose veins lose their ability to recoil and remain permanently swollen • Superior vena cava is the largest. It returns blood from the shoulders and head. • Inferior vena cava returns blood from the lower body