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 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 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 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