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. Inner endothelium layer 2. Thin elastic connective tissue layer 3. Thin smooth muscle layer 4. 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