Blood Vessels The roads around the body Some

Blood Vessels The roads around the body

• • • Some basics Closed circuit of tubes that carries blood from the heart to the cells and back again The force of the heart beat (blood pressure) pushes blood through the first two types of blood vessels. Muscle contraction brings it back. 3 main types – Arteries – carries blood away from heart – Capillaries – delivers nutrients and other materials to the cells – Veins – carries blood to the heart

Arteries • Arteries have strong elastic walls adapted to high pressure – 3 layers • Inner layer ( tunica interna) made of endothelium like the heart – smooth to help prevent blood clots • Middle layer (tunica media) smooth muscle fibers and a thick layer of elastic connective tissue, nerves connect here to help control vasodilation and vasoconstriction • Outer layer (tunica externa) thin, connective tissue, attached artery to surrounding area. • Branch into thinner vessels called arterioles

Capillaries • • Start at the end of the smallest arterioles and end at the venules Are the smallest diameter blood vessels – • Are semipermeable due to small slits where the endothelial cells overlap – • Composed of the endothelium that is the inner lining of the arterioles Size of the opening depends on the tissue, muscles less, organs more Precapillary sphincters control the blood flow into the capillary.

Veins • • Veins carries blood back to the artria. Venules are little veins that connect the capillaries to the veins. 3 layer walls once again, but this time the middle layer is not as developed. – • Therefore less elastic and muscular Many veins have valves – – 2 leaflets that close if the blood moves away from the heart Typically found in the limbs

Neat trick veins. . . • • Veins are the blood reservoirs If the blood pressure drops significantly due to blood loss, the veins will constrict and return more blood to the heart. – Help to maintain normal blood pressure even loss is 25% of blood volume

Blood Pressure • The force the blood exerts on the inner walls of the blood vessels – • Maximum pressure during ventricular constriction is called Systolic pressure – • Typically referring to the pressure in the arteries (Arterial blood pressure) 120 is average Lowest pressure when the ventricles relax is the Diastolic pressure – 80 is average

Two pathways • • Systemic circuit – left ventricle to the rest of the body and then to the right atrium Pulmonary circuit – Right ventricle to the lungs and then to the left atrium

Increased pressure • Varicose veins – veins with abnormal dilations – • Results from increased blood pressure in the saphenous veins (found in the legs) due to gravity. Hypertension – persistently elevated arterial pressure – Can contribute to atherosclerosis