circulation

• blood flow

  volume of blood flowing through vessel, organ, or entire circulation

  • measured in mL/min
  • like cardiac output for entire vascular system
  • relatively constant when at rest but is different for each organ levels and it's needs
• blood pressure

  force per unit area exerted on wall of blood vessel by blood

  • measured in mmHg
  • measured as systemic arterial BP in large arteries near heart
  • pressure keeps blood flowing from higher to lower pressure areas
• resistance(peripheral resistance)

  • opposition to flow
  • amount of friction blood encounters with vessel walls, generally in systemic circulation
• blood viscosity

  • thickness or stickiness of blood due to formed elements and plasma proteins
  • greater the viscosity the harder it is for molecules to slide past each other
  • increase viscosity means increases resistance
• total blood vessel length

  longer the vessel the greater the resistance encountered
• blood vessel diameterif resistance increases, resistance decreases, fourht power of vessel radius

  • greatest influence on resistance
  • frequent changes alter peripheral resistance
  • fluid close to the walls moves slower than in middle of the tube
• small-diameter arterioles are big determinants of peripheral resistance

  • radius changes frequently in smaller vessels
• sudden changes in vessel diameter or obstacles dramatically increase resistance

  • things like fatty plaques from atherosclerosis
  • laminar flow is disrupted and becomes turbulent flow, irregular flow that increased resistance
• blood flow is directly proportional to blood pressure gradient

  • if blood pressure gradient increases then blood flow speeds up
• blood flow is inversely proportional to peripheral resistance 


  if peripheral resistance increases then blood flow decreases

  
• peripheral resistance is easily changed by altering blood vessel diameter so it is more important influencing blood flow
• pumping action of heart makes blood flow
• pressure results when flows is opposed by resistance
• • Systemic pressure is highest in aorta and declines throughout pathway
  • Steepest drop occurs in arterioles
• Pulse locations

  A) branchial

  B) carotid

  C) facial

  D) radial

  E) femoral

  F) popliteal

  G) tibial

  H) pedis

  I) temporal

  
• Arterial Blood Pressure


  determined by: elasticity of arteries close to heart and volume of blood pushed in them
• Blood pressure near heart is pulsatile 


  meaning that it rises and falls with each heartbeat
• Systolic pressure

  pressure forced in aorta during ventricular contraction

  • averages 120 mm Hg
  • left ventricle pushes blood into aorta
• Diastolic pressure


  lowest level of aortic pressure when heart is at rest
• Pulse pressure


  difference between systolic and diastolic pressure
• Pulse


  throbbing of arteries due to difference in pulse pressures, which can be felt under skin
• Mean arterial pressure (MAP)


  pressure that propels blood to tissues

  • Pulse pressure phases out near end of arterial tree
  • Flow is nonpulsatile with a steady MAP pressure
• Heart spends more time in diastole, so not just a simple average of diastole and systole
• MAP is calculated by adding diastolic pressure + 1/3 pulse pressure

  • Pulse pressure and MAP both decline with increasing distance from heart
• Radial pulse


  • (taken at the wrist)
  • most routinely used, but there are other clinically important pulse points
• Pressure points


  areas where arteries are close to body surface

  • Can be compressed to stop blood flow in event of hemorrhaging
• Systemic arterial BP is measured indirectly by auscultatory methods using a sphygmomanometer

  1. wrap around arm over elbow
  2. increase pressure until it exceeds systolic pressure in brachial artery
  3. realse pressure slowly and listen for sounds of Korotkoff
• systolic pressure

  normally less than 120 mm Hg

  • pressure of when the blood starts to spurt through artery
• Diastolic pressure

  normally less than 80 mm Hg

  • pressure of when sound disappears because blood is flowing
• Goal of blood pressure regulation is to keep blood pressure high enough to do its job but not so high that blood vessels are damaged

  Example:

  • If BP to brain is too low, perfusion is inadequate, and person loses consciousness
  • If BP to brain is too high, person could have stroke
• Blood pressure changes due to posture, physical exertion, emotional upset, fever

  • Age, sex, weight, race, mood, and posture can also play a role
• Tissue perfusion: blood flow through body tissues; involved in:

  Delivery of O2 and nutrients to, and removal of wastes from, tissue cells

  Gas exchange (lungs)

  Absorption of nutrients (digestive tract)

  Urine formation (kidneys)
• Rate of flow is precisely right amount to provide proper function to that tissue or organ
• Extrinsic control

  sympathetic nervous system and hormones control blood flow through whole body

  • direct blood in arteriolar smooth muscle to take it to where it goes
• Intrinsic control: Autoregulation (local) control of blood flow:


  Blood flow is adjusted locally to meet specific tissue's requirements

  • local arterioles that feed into capillaries can change their diameters
  • organs regulate their own blood flow by varying resistance of their own arterioles
• Autoregulation


  local (intrinsic) conditions that regulate blood flow to that area
• Reactive hyperemia


  increased blood flow to an area due to intrinsic factors
• Myogenic responses

  Smooth muscle changes in accordance to MAP to avoid tissue damage
• passive stretch

  increased blood pressure stretches blood vessel walls more than normal

  • smooth muscle responds by constricting and slowing flow to tissue
• reduced stretch

  decreased MAP causes not enough stretch

  • smooth muscle responds by dilating increasing blood flow