Blood Vessels  Arteries: vessels that carry blood away from heart, surrounded by thick layer of smooth muscle, high levels of BP  Capillaries: microscopic thin walled vessels connect to the smallest veins and arteries  Veins: vessels that carry blood to heart surrounded by thin layer of smooth muscle and are flaccid, low levels of BP

Vessel Wall Layers  Tunica interna: inner of vessel, direct contact with blood, secretes chemicals for dilation and constriction of the vessel  Tunica media: middle layer, made of smooth muscle and elastic fibers to prevent rupture from BP and to aid in vasomotion  Tunica externa: covers vessel and anchors it to tissue and other vessels

Arteries  Conducting arteries: biggest in the body i.e. aorta, carotid. Large amounts of elastic fibers allow expansion and contraction with each HB normalizing BP  Distributing arteries: smaller branches that deliver blood to specific organs  Resistance arteries: very little elastic fiber, funnel blood to capillaries, smallest called arterioles

Veins  Postcapillary venules: smallest veins, more porous than capillaries allowing fluid exchange  Muscular venules: have a thin layer of smooth muscle  Medium veins: have venous valves acting in the skeletal muscle pump that resists retrograde flow caused by gravity

Veins  Venous sinuses: large thin walled vessels found in the heart and brain not capable of vasomotion  Large veins: thin tunica media with thick tunica externa made of bundles of smooth muscle, (venae cavae, pulmonary veins)

Blood Pressure  Flow: amount of blood flowing in an organ, tissue or vessel in a given time  Perfusion: volume of blood over time per gram of tissue  Blood pressure: the pressure exerted on the wall of a vessel (120/80)  Pulse pressure: the difference between systolic and diastolic pressures

Blood Pressure  Hypertension: chronic high BP of 140/90 or higher  Hypotension: chronic low BP can be caused by blood loss, dehydration, anemia

Resistance  Blood viscosity: the thickness of blood can increase or decrease blood flow  Vessel length: friction develops with length  Vasoconstriction: narrowing vessel ↑ BP  Vasodilation: widening of vessel ↓ BP  Laminar flow: blood in center of vessel travels faster than blood along vessel wall