topic 8

• types of blood vessels

  elastic artery

  muscular artery

  arteriole

  capillaries

  venules

  veins
• elastic (conduction) arteries


  smooth but large blood pressure fluctuations
• Muscular (distrubuting) arteries


  more active in vasoconstriction
• arterioles


  critically important in regulating blood flow and blood pressure
• capillaries (smallest blood vessels)


  allow only a single red blood cell to pass at a time
• venules


  are formed when capillary beds unite
• veins


  capacitance vessels that contain 65% of the blood supply

  special adaptations: large diameter lumens; low resistance to flow, valves; prevent back flow of blood
• blood flow


  actual volume of blood flowing through a vessel, an organ, or the entire circulation in a given period
• total blood flow =

  cardiac output
• blood flow is relatively constant when

  at rest
• blood pressure


  force per unit area exerted on the wall of a blood vessel by its contained blood
• blood pressure is measured

  in reference to systemic arterial blood pressure in large arteries near the heart
• blood pressure differences within the vascular system provide


  the driving force that keeps blood moving from higher to lower pressure areas
• peripheral resistance


  opposition to flow, the amount of friction that blood encounters as it passes through vessels, generally encountered in the systemic circulation
• the three important sources of resistance are

  blood viscosity, total blood vessel length, and blood vessel diameter
• increased body temperature reduces

  blood viscosity
• decreased body temperature increases

  blood viscosity
• blood viscosity


  thickness or stickiness of the blood, 1.8x more viscous than water
• blood vessel length


  the longer the vessel, the greater the resistance encountered
• blood vessel diameter


  resistance varies inversely with the vessel radius; small diameter arterioles are the major determinants if peripheral resistance
• Fatty plaques from atherosclerosis

  Cause turbulent blood flow

  Dramatically increase resistance due to turbulence
• arterial blood pressure is a measure of 2 factors

  compliance/distensibility and pulsatility
• compliance/distensibility


  the ability of the elastic arteries to stretch
• pulsatility


  the volume of blood forced into these vessels at any time; pressure fluctuations; reflect the volume changes
• during systole blood is forced

  forward because pressure in the aorta is higher then in the distal vessels
• during diastole aortic pressure


  drops as the elastic arteries of the aorta recoil and blood moves forward
• differences in systolic and diastolic pressure =

  pulse pressure
• pulse pressure


  temporarily raised by increased stroke volume and faster blood ejection

  chronically elevated by atherosclerosis; arteries are less stretchy

  changes with each heart beat; map is a more reliable measure of the pressure level delivering blood to tissues

  map and pulse pressure decrease with distance from the heart
• MAP =


  [(2 x diastolic) + systolic] / 3
• there are two basic mechanisms for regulating blood pressure

  long term mechanisms and short term mechanisms
• long term mechanisms


  kidneys regulate blood volume
• short term mechanisms


  recruit both neural and chemical control

  regulate vessel diameter, heart rate, and heart contractility

  rising and falling blood pressure
• short term regulation of rising blood pressure

  rising blood pressure causes stretching of arterial walls which stimulates the baroreceptors in the carotid sinus, the aortic arch, and other large arteries of the neck and thorax, which increases impulses to the brain and decreases sympathetic activity and increases parasympathetic activity
• decreased sympathetic activity in rising blood pressure

  regulation of vascular smooth muscule increases arteriolar diamater and lowers blood pressure
• increased parasympathetic activity in rising blood pressure

  lowers cardiac output which reduces heart rate and contractility and lowers blood pressure
• short term regulation of falling blood pressure

  no stretching of arterial walls inhibits baroreceptors and decreases impulses to the brain which increases sympathetic activity and decreases parasympathetic activity
• increased sympathetic activity in falling blood pressure

  contraction of vascular smooth muscles decreases arteriolar diameter and raises blood pressure
• decreased parasympathetic activity in falling blood pressure

  higher cardiac output and increases heart rate and contractility and raises blood pressure
• short term regulation of blood pressure: hormonal control of rising blood pressure

  decreased sympathetic activity decreases impulses to adrenal glands which decreases release of epinephrine and norepinephrine into the blood and decreases heart rate, contractility and vasoconstriction which lowers blood pressure
• short term regulation of blood pressure: hormonal control of falling blood pressure


  increases sympathetic activity which increases impulses to adrenal glands and increases the release of epinephrine and norepinephrine which increases heart rate, contractility, and vasoconstriction which increases blood pressure