Blood Vessels-CH 19

Structure of Blood Vessels

Lumen: blood containing space  Anastomosis: union of vessels supplying blood to same body tissue Collateral circulation: if vessel has an issue, the anastomosis work together as a backup for blood to reach tissue. Three tunic layers Tunica intima: endothelium, intimate contact w/blood and lumen Tunica Media: smooth muscle and elastin (to stretch/recoil) Tunica Externa: collagen fibers Three groups of arteries: Elastic: closest to heart, takes greatest pressure of blood from heart, greatest # elastin, when heart relaxes the recoil to propel blood onward during diastole. Store mechanical nrg during ventricular systole then transmit energy to keep blood moving after aortic and pulm valves close. Muscular: deliver blood to organs, more smooth muscle less elastin, actively constrict and relax Arteriole: Smallest. Tunica media is mostly smooth muscles to constrict and relax. Vasomotor fibers regulate activity of smooth muscle. Small changes in diameter greatly influence blood pressure and flow.

: Arteriosclerosis: artery walls thicker and stiffer resulting in hypertension Atherosclerosis: an arteriosclerosis, all patchy thickenings called atheroma form intruding into vessel lumen, making it easy for arterial spasms or blood clot,

Arteries, Capillaries, and Veins

Arteries: carry blood away from heart. Thickest tunica media, closest to heart, exposed to higher pressure.  Three groups of arteries: Elastic: closest to heart, takes greatest pressure of blood from heart, greatest # elastin, when heart relaxes the recoil to propel blood onward during diastole. Muscular: deliver blood to organs, more smooth muscle less elastin in media, actively constrict and relax. Thickest tunica media. More active in constricting than stretching. Arteriole: Smallest. Tunica media is mostly smooth muscles to constrict and relax. Vasomotor fibers regulate activity of smooth muscle. Small changes in diameter greatly influence blood pressure and flow (THE RESISTANCE VESSEL).  Metarteriole: end of arteriole that goes to capillary junction. Veins: farthest from heart, least pressure. Lumens larger. Tunica media smaller, Tunica externa thicker. Have valves to keep  Venule: forms when capillaries unite, larger ones have sparse media and thin external. Small ones drain capillaries, contain endothelium where few fibroblasts congregate. Forms veins! Capillaries: Smallest vessel, link between artery and vein. Walls have thin tunica intima, good for exchange of blood/fluids. Intercellular cleft: gaps of unjoined membrane allowing limited passage of membrane and small solutes. Capillary bed: blood flow regulation occurs here. pre capillary sphincter: smooth muscle fibers surrounding root of capillary, regulating blood flow. Capillary types: Continuous: most common with endothelial cells forming continuous tube interrupted by intercellular clefts. Fenestrated: in kidneys, villi of small intestine, and endocrine glands. Has pores Sinusoids: form real porous channels through which blood can percolatein liver and spleen.

Systemic pathway of blood

Aorta/elastic arteries: take most pressure.  Muscular: pressure starts dropping Arteriole: steepest drop, greatest resistance to blood flow. blood flow no longer pulses by time it gets through arteriole Capillaries: low, high would rupture them forcing out fluids continuous fenestrated sinusoid Veins: can be thinner walled without burning since low pressure. Requires adaptations to bring blood to heart. Venous valves, muscular and pulmonary pump venous valve: more in veins of limbs, which is needed for upward flow. Prevent back flow and moves it to heart muscular pump: contracting muscle pump on veins. forces blood upward respiratory pump: pressure decreases in thoracic cavity and increases in abdominal cavity which squeeze abdominal veins

Diseases

 Arteriosclerosis: artery walls thicker and stiffer resulting in hypertension Atherosclerosis: an arteriosclerosis, all patchy thickenings called atheroma form intruding into vessel lumen, making it easy for arterial spasms or blood clot, Varicose veins: When exposed to higher than normal pressure d becomes incompetent.

Fluid Exchange

Pressures for reabsorption Blood colloid osmotic pressure (BCOP): result of presence of plasma proteins too large to cross capillary (36 mmHg) Interstitial fluid hydrostatic pressure (IFHP): close to zero, significant factor during state of edema.

Starling Forces There is nearly as much fluid reabsorbed as flitered. Arterial end pressure: outward 10mmHg and fluid leaves capillary. (filtration) Venous end: inward -9mmHg (reabsorbed) Fluid not reabsorbed: (3L) a day, enters the lymphatic vessels to be eventually returned to blood. 

Gas and nutrient exchange passive diffusion process move into or out of capillary down concentration gradient.

Venous reserve veins and venules contain large percentage of blood volume, 64% at rest. They function as blood reservoirs. IF BP DROPS: stimulation of sympathetic NS will cause venoconstriction allow a great volume of blood to flow to skeltal muscle. Venous return Volume of blood returning to veins to right atrium=same amount of blood pumped into arteries of left ventricle. aided by venous valves, skeletal muscle pump, and breathing Pumps: Skeletal muscle: use action of muscles to milk blood in 1 direction (valves) respiratory pump: use negative pressures in thoracic and abdominal cavities generated during inspiration to pull venous blood to heart.

Pressure, flow, resistance

Blood pressure: measure (mmHg) of force exerted in lumen of blood vessels. blood flow: # of blood which is reaching end organs (tissues) Resistance: sum of many opposing factors to flow of blood Peripheral resistance: viscocity of blood, length of bv in body, and diameter (only changable factor) OHMS LAW= BP=FLOW X RESISTANCE........BLOOD FLOW= BP/RESISTANCE To increase blood flow: increase BP, decrease systemic vascular resistance in BV.  Our body does this during exercise blood flow to organ is proportional to resistance in organ's capillary bed, which is proportional to 4th power of blood vessel's lumen When bv dialates, it decreases resistance by a power of 4. if the diameter of a blood vessel decreases by one-half, its resistance to blood flow increases 16 times! Cardiac Output (CO)= Mean arteriole blood pressure/Systemic vascular resistance  measure of blood ejected by ventricles over time product of heart rate and stroke volume influenced by venous return, contractile strength of heart, metabolic demands

Autoregulation maintenence of adequate blood flow to organs by adjustment of pressure and resistance. controlled by negative feedback involves vascular, nervous, and endocrine hormones and orgs like adrenal and kidney, heart. Vascular system: senses changed in BP and blood flow and signals cardiovascular centers in brain.  Heart modifies rate and force of contraction . Arterioles/precap sphincters of metarterioles adjust resistance at specific tissue beds.