BLOOD VESSELS Arteries Away from the heart Oxygen

BLOOD VESSELS Arteries Away from the heart Oxygen rich Elasticity and contractility (ANS, sympathetic) Divide into smaller vessels- arterioles Which divide to single cell layer thick capillaries

Arterial walls § 3 layers around an opening: lumen § Endothelium-Inner layer is made of simple squamous epithelium § Middle layer: made of smooth muscle and elastic fibers § Outer layer: elastic and collagen fibers

Blood vessels § Veins § Oxygen poor blood § Carry blood to the heart § Similar to arteries but the smooth muscle layer is thinner § Branch into smaller vessels : venules § Venules branch into capillaries § Contains folds in the inner layer called: valves § Lumen is wider than in corresponding arteries

Veins

Varicose veins

Capillaries § Connect arterioles to venules § Primary function: exchange nutrients and waste between blood and tissue cells. § Certain tissue with more metabolic activity (muscle, nerve, kidney, liver) require more caplillaries. § Composed of a single layer of endothelium and a basement membrane § Flow of blood in capillaries is regulated by smooth muscle fibers + precaplillary sphincters: rings of smooth muscle at their origin.

Blood reservoirs § Veins- 60%, referred to as blood reservoirs (also liver + spleen) § Arteries-15% § Pulmonary Vessels-12% § Heart-8% § Capillaries-5%

PHYSIOLOGY OF CIRCULATION § Blood flow: amount of blood that passes thru a vessel in a given period of time. § Determined by: § Blood pressure § Resistance § Blood pressure: pressure exerted on the wall of a vessel § Resistance: opposition to blood flow from friction between blood + vessel walls related to: § Viscosity-adhesiveness § Blood vessel length- the longer the more resistance

3 Factors Affecting Blood Pressure 1. Cardiac Output: amount of blood leaving the lt. ventricle each minute. Stroke volume x heart rate a. chemicals: epinephrine, K, Na, Ca: increase CO, which increases BP b. temperature, emotions, gender, age

Factors continued § 2. Blood Volume: Normal = 5 liters or quarts Anything that decreases blood volume decreases blood pressure Ex: Trauma like a hemorrhage, diuretics Anything that increases blood volume increases blood pressure Ex: Salt intake

Factors continued 3. Peripheral resistance: resistance to blood flow as it moves away from the heart. a. mostly in arterioles, capillaries, + venules b. arterioles control blood pressure + flow by changing their diameter. Vasoconstriction + Vasodialation This process is controlled by the vasomotor center in the medulla oblongata

Factors continued

Vasomotor Center § Located in the Medulla Oblongata § Maintains peripheral resistance in the arterioles( especially skin, abdominal viscera) § Increased sympathetic impulse=increase vasoconstriction and decreases in impulses=vasodilatation § Is modified by: baroreceptors, chemoreceptors, brain, and hormones

Baroreceptors § Same as in the control of heart rate: § Parasympathetic stimulation slows things down and thus lowers Blood Pressure (BP) § Sympathetic speeds things up thus Increasing BP § Special note: blood vessels are controlled by sympathetic only.

Capillary Exchange § Filtration- fluid goes from arteriole end capillaries into surrounding interstitial tissue. § Reabsorbtion-fluid returns to into the venous end capillaries § About 85% of filtered fluid reabsorbs, the rest is returned to the cardiovascular system by the lymphatic system

Pulse + Blood Pressure § Pulse- alternate expansion and recoil of an artery with each contraction of the lt. ventricle. § Tachycardia- rapid pulse over 100/min § Bradycardia- slow pulse under 60/min § Measured by a sphygmomanometer § 120/80=systolic/diastolic § Systolic=pressure against arterial wall during vent. Contraction. § Diastolic=pressure against arterial wall during vent. relaxation

Circulatory Routes § § § Pulmonary-lungs Systemic- rest of the body Cerebral – brain Hepatic Portal- liver Fetal – see ch. 24 Renal- kidney

3 functional adaptations for venous return § Respiratory pump-changes in abdominal and thoracic pressure during breathing § Muscular pump-milking of skeletal muscle § Smooth muscle contraction under sympathetic control

§ Orthostatic Hypotension § Old people –sympathetic system can not respond fast enough when they stand up § Hypertension – high blood pressure over 140 (systolic) § Hypotension- low blood pressure below 90