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Lecture 9

BIO271 2014 Lecture 9.pdf

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Christopher Garside

  Lecture  9:  Circulatory  Systems  Part  2  –  Physics;  the  Heart   Physics  of  Blood  Flow   -­‐ Law  of  Bulk  Flow:Q=  ΔP/R   o Q  =  flow   o ΔP  =  pressure  drop   o R  =  resistance  (due  to  friction)   § R=  8Lη/πr4   • L  =  length  of  the  tube   • η  =  viscosity  of  the  fluid  à  increase  in  viscosity  increases  resistance  =  decrease  flow   • r  =  radius  of  the  tube  (greatest  effect)  à  think  effects  of  vasoconstriction  or  vasodilation     o half  the  radius  =  change  in  resistance  by  16X   o flow  is  directly  proportional  to  the  pressure  difference/drop  from  one  point  to  another;  inversely   proportional  to  resistance   -­‐ Poiseuille’s  equation:   Q=  ΔPπr /8Lη4  à  more  detailed  version  of  Law  of  Bulk  Flow   -­‐ Thickness  of  blood  vessel  walls  does  not  really  have  an  effect  unless  diameter  changes  too       Modeling  Circulatory  Systems   -­‐ compare  Law  of  Bulk  Flow  with  Ohm’s  Law  àQ=  ΔP/R   and  I=  ΔV/R     -­‐ like  electrical  resistors,  blood  vessels  can  be  arranged  in  series  or  parallel   -­‐ resistors  in  series   o R T  = 1 R 2 +  R  …..   § R T  increases   § The  more  resistors,  the  greater  the  resistance   -­‐ resistors  in  parallel   o 1/R T  =  1/R1  +  2/R   § R T  decreases   § Inverse  of  resistance  of  each  resistor   -­‐ Because  of  the  law  of  conservation  of  mass,  the  flow  through  each  segment   of  the  system  must  be  equal   -­‐ Allows  fresh  blood  to  tissues   -­‐ Blood  flows  in  series   o heart  à  arteries  à  smaller  arteries  à  arterioles  à  capillaries  à   venules  à  veins  =  adding  resistors  in  s eries     o Also  within  each  types  of  blood  vessels,  have  vessels  in  parallel  (especially  capillaries)  =  reduces  overall   resistance   o Flow  is  identical  at  each  position  (A,  B,  C,  D,  E)  =  same  volume  of  fluid  has  to  go  through  all  of  them   § but  when  you  have  vessels  in  parallel,  you  can  control  how  much  of  that  volume  of  fluid  is  going   through  each  vessel,  but  changing  the  radius  (by  vasoconstriction/vasodilation)   o we  have  both  resistors  in  series,  and  resistors  in  parallel   o parallel  =  control  and  reduction  of  resistan ce     Blood  Velocity   -­‐ flow  (Q)   o volume  of  fluid  transferred/unit  time  (a  rate)   -­‐ velocity   o distance  transferred/unit  time   o the  fact  that  something  goes  faster  does  not  mean  more/less  is  flowing   -­‐ blood  velocity  =  Q/A   o velocity  is  proportional  to  flow;  inversely  propo rtional  to  the  cross-­‐sectional  area  (of  what  the  vessels  are   within  the  circulatory  system)   o A  =  cross-­‐sectional  area  of  the  vessels   o Therefore,  V  is  inversely  related  to  the  total  X -­‐sectional  area   § Ex.  Total  cross-­‐sectional  area  of  capillaries  is  very  large   =  velocity  is  slow  =  long  time  for  diffusion   • Blood  flow  decreases  as  it  moves  through  capillary  beds  in  the  tissues  (what  we  want!  =   need  diffusion  of  oxygen  out  into  tissues,  and  diffusion  of  CO2  out  into  the  blood)   • Need  some  time  or  else  there  wont  be  ti me  for  diffusion  if  blood  rushes   • Significant  increase  of  cross -­‐sectional  area  across  capillary  bed  =  exchange  of  gases         Transmural  Pressure   -­‐ Gradient  across  the  walls   -­‐ High  pressure  within  vessel,  lower  pressure  outside  the  vessel   o Push  out  on  walls  of  vessel  =  stress/tension  in  the  wall   -­‐ pressure  exerts  a  force  across  vessel  wall   -­‐ law  of  LaPlace   o σ  (T)  =  Pr/w   § σ  =  wall  stress/tension   § T=  tension  within  walls  of  vessel/chamber   § P  =  transmural  pressure   • Difference  between  internal  and   external  pressure   § r  =  vessel  radiu   § w  =  vessel  wall  thickness   o increase  radius  =  increase  in  tension   o increase  in  radius  +  increase  pressure  =  same  tension  in  the  walls   o tension  is  inversely  proportional  to  the  thickness  of  the  wall  of  the  vessel/chamber   o shows  us  what’s  happening  within  a   vessel  or  chamber   -­‐ right  ventricle  <  left  ventricle   -­‐ right  ventricle  pumps  blood  to  the  pulmonary  circuit ;  left  side  pumps  blood  to  the  whole  systemic  system   o right  walls  do  not  have  to  be  as  thick  on  the  right  side  to  create  the  same  tension  required  to  pump  blood   -­‐ arteries  and  veins  have  the  same  diameter,  but  arteries  have  thicker  walls  because  of  the  greater  pressure  in   arteries   -­‐ aorta  à  large  radius  à  large  tension  (large  stress)  =  thick  wall  to  reduce  tension   o too  much  tension  =  dangerous   -­‐ compare  to  vena  cava?   -­‐ Small  radius  =  create  a  greater  pressure  to  create  the  same  tension       Aneurysm  and  LaPlace   -­‐ Aneurysm  =  lethal  =  stretching  of  a  blood  vessel  (often  in  brain  and  abdomen)   -­‐ Expansion  of  a  specific  region  of  a  blood  vessel  =  increased  radius  =  decreased  thi ckness   o Sometimes  stress  is  too  great  =  burst  of  blood  vessels   § Deadly  in  brain  Aneurysm   -­‐ localized,  pathological,  blood-­‐filled  dilatation  of  a  blood  vessel  caused  by  a  disease  or   weakening  of  the  vessel’s  wall   o σ  (T)  =  Pr/w   Hearts   -­‐ cardiac  cycle  –  pumping  action  and  relaxation  phases  of  the  heart   o two  phases   1) systole   • contraction  and  emptying   • spread  of  excitation  across  chambers  of  the  heart   • blood  is  forced  out  into  the  circulation s  (pulmonary  and   systemic  in  humans,  fish  has  one)   2) diastole   • relaxation  and  filling   • follows  repolarization  of  the  heart   • blood  enters  the  heart   -­‐ chambered  hearts  evolved  from  simple  pulsatile  blood  vessels  or  tubular   peristaltic  hearts  (ex.  Insects)     Arthropod  Heart  –  Neurogenic     • neurogenic:  to  contract  they  need  a  signal  from  the  CNS/NS   o myogenic:  within  muscles  itself   • opened  circulatory  system  with  a  chambered  heart,  has  blood  vessels  (arteries)   • Heart  pumps  hemolymph  out  via  arteries         o Hemolymph  returns  to  the  heart  via  ostia  (holes  in  the  walls  of  the  heart)  during  diastole   § Ostial  valves  open  and  close  to  regulate  flow   § The  heart  is  suspended  by  a  series  of  ligaments    (attached  to  exoskeleton)   • Neurons  of  cardiac  ganglion  undergo  spontaneous   rhythmic  depolarization   o Cardiac  ganglion  sits  on  top  of  heart,  or  some  of  the  neurons  can  even  be  inte grated  into  heart  cells   (depends  on  arthropod)     § External  to  muscle  tissue  itself   à  sends  signal  to  start  contraction   1. Signal  is  sent  by  neurons  of  the  cardiac  ganglion   2. valves  in  ostia  close   3. cardiomyocytes  contract     o only  one  exit  for  the  blood  =  out  the  arte ries,  not  ostia   o neural  signal  closed  the  ostia  +  contraction  of  muscle  cells  within  the  heart   o functions  as  a  pressure-­‐suction  pump   -­‐ Pressure-­‐suction  pump:     v As  heart  contracts:  Volume  ↓;  pressure  ↑     o Pressure  inversely  proportional  to  volume   • Hemolymph  ‘squirts’  out  arteries     • Stretched  ligaments  pull  apart  walls  of  heart     o As  heart  contracts,  it  gets  smaller  =  stretches  suspensory  ligaments   v Heart  relaxes:  Volume  of  heart  ↑;  pressure  ↓     • Elastic  recoil  of  ligaments   à  ligaments  pull  the  heart  back  open  (increase  in  heart  volume,  decreasing  pressure)   • Ostial  valves  open  à  blood  flows  back  into  the  heart  (suction)   • Hemolymph  suctioned  into  heart       Vertebrate  Hearts   -­‐ Complex  walls  with  four  main  layers   1) Pericardium   o Sac  filled  with  fluid  à  reduces  friction   between  walls   o Space  between  layers  filled  with   lubricating   fluid   § Outer  (parietal)  and  inner  (visceral)   layers   § Visceral  pericardium:  connected   directly  to  the  heart,  continuous   with  the  epicardium  (outer  layer  of   the  heart)   § Partial:  outer  region  of  the  sac   surrounding  the  heart   o Sac  of  connective  tissue  that  surrounds  heart   o Anchors  it  to  the  thoracic  cavity   o In  most  species,  its  compliant  and  stretches   easily   § Contracts  with  the  heart  mostly   o In  elasmobranchs  à  very  tough  structure   2) Epicardium   o Outer  layer  of  heart,  continuous  with  visceral  pericardium     o Contains  blood  vessels,  and  nerves  that  regulate  heart  and  coronary  arteries  (extend  into  myocardium)   o Some  continue  into  myocardium,  many  do  not   à  remain  within  epicardium   3) Myocardium   o Bulk  of  heart  tissue   o Cardio  myocytes  and  muscle  cells   o Layer  of  heart  muscle  cells  (cardiomyocytes/cardiac  muscle  cells)   o 2  types  of  myocardium:   1) compact  myocardium       § tightly  packed  cells   § regular  pattern   § highly  vascularized   2) spongy  myocardium   § loosely  connected  cells   § some  not  vascularized   o relative  proportions  very  among  species   • mammals   § mostly  compact,  little  spongy  in  our   hearts   § nicely  organized,  contract  together   § lots  of  blood  vessels  to  supply  most   cells   • fish  and  amphibians   § mostly  spongy   § few  blood  vessels,  little  supply  of  oxygen  via  blood  vessels   § arranged  as  trabeculae  (muscular  ridges)  that  extends  into  chambers   4) Endocardium   o Innermost  layer  of  connective  tissue  covered  by  epitheli al  cells  (called  endothelium)     o These  cells  line  the  heart  –  creates  a  smooth  layer  so  blood  doesn’t  have  much  resistance   o Important  for  flow  of  blood   o Blood  Heart  Barrier??     § These  cells  can  secrete  hormones/paracrines,  and  can  also  control  ionic  concentrations  within  the   extracellular  fluids  (ex  what  the  blood  brain  barrier  does)   § Blood  heart  barrier  controlled  by  endothelial  cells  within  the  endocardium     Fish   -­‐ 4  chambers  arranged  in  series   o 2  primary  (atrium  and  ventricle)  and  2  auxillary  (sinus  vneoses  and  bulbus  arteriosus)   o 1  atria/1  ventricle   o contract  in  sequence  -­‐  one  way  valves  à  only  open  in  a  single  direction   § valves  are  important  for  unidirectional  flow   o sinus  venosus:  no  valves  out  to  body  tissues   § very  thin  wall,  doesn’t  contract  very  well   § if  it  did,  some  of  the  blood  may  flow  in  atrium,  but  can  also   flow  back  out  to  the  circulatory   systems   § important  in  fish  for  initiating  the  heartbeat   o once  pressure  in  ventricles  increases,  the  valve  to  the  atrium  closes,  but  cant  open  to  the  atrium   § valve  to  the  bulbus  arteriosus  will  open,  and  blood  flows  in   o bulbus  arteriosus  is  somewhat  compliant,  accepts  a  large  volume  of  blood   § serves  as  a  pressure  reservoir  (similar  to  our  aorta)   à  reduces  variations  in  blood  pressure   § slowly  pushes  blood  to  rest  of  the  system  (as  it  recoils)   à  In  a  relatively  constant  flow   § doesn’t  contract,  accepts  pressure,  increases  in  volume,  and  recoils  to  send  out  to  circulation   o but  there  is  a  valve  between  the  atrium  and  sinus  venosus   § a  valve  between  the  atrium  and  ventricle   § and  a  valve  between  the  ventricle  and  bulbus  arteriosus     Amphibian  Hearts   -­‐ three-­‐chambered  hearts   o 2  atria,  1  ventricle   -­‐ have  a  spongy  myocardium   o 2  supplies  of  blood  are  sent  into  1  ventricle   o oxygenated  from  the  pulmonary,  and  deoxygenated  blood  from  the  systemic  circuit   o not  highly  vascularized  -­‐  oxygenated  blood  finds  its  way  into  entire  ventricle  can  supply  oxygen  to   myocytes  (spongy  myocardial  myocytes)   -­‐ trabeculae  in  ventricle   o helps  prevent  mixing  of  oxygenated  and  deoxygenated  blood  in  ventricle   -­‐ spiral  folds  in  conus  arteriosus   o helps  direct  deoxygenated  blood  to  pulmocutane ous  circuit  and  oxygenated  blood  to  systemic  circuit       o as  pressure  increase  in  ventricle,  this  spiral  fold  stands  up  and  directs   blood   o mechanism  of  spiral  fold  function  not  well  understoo d     Reptile  Hearts  (non-­‐crocodilian)   -­‐ 2  atria  +  1  ventricle  (subdivided  into  3  compartments)   o ventricle  is  incompletely  separated  into  3  compartments   o separation  of  oxygenated  and  deoxygenated  blood  nearly  complete   o conus  arteriosus  divided  to  form  base  of  3  large  arteries     -­‐ flow  of  blood:   o from  system  circulation  –  flows  in  from  vena  cava  à  right  atrium  à   into  heart  à  cavum  venosum  à  falls  over  muscular  ridge  into  the   cavum  pulmonale  (deoxygenated  blood)   o from  pulmonary  vein:  directly  into  the  cavum  arteriosum  (oxygenated   blood)     Shunting  in  Reptile  Hearts   -­‐ under  non-­‐shunting  conditions:  blood  flows  from  right  atrium  to  the  pulmonary   artery,  and  from  the  left  atrium  to  the  right  and  left  aortas   -­‐ can  shunt  in  blood  to  bypass  pulmonary  or  systemic  circuit   -­‐ right-­‐to-­‐left  shunt  (R-­‐L)   o deoxygenated  blood  bypass  pulmonary  circuit  and  enters   systemic  circuits   o during  breath-­‐holding   o when  they  are  under  water  =  lungs  are  useless   o some  blood  from  the  right  atrium  enters  the  aortas,  bypassing  the  lungs   -­‐ left-­‐to-­‐right  shunt  (L-­‐R)   o some  blood  from  the  left  atrium   enters  the  pulmonary  artery,   bypassing  the  tissues   o oxygenated  blood  reenters   pulmonary  circuit     o thermoregulation  à  when  reptiles   heat  up,  they  need  to  lose  some  of   their  body  heat,  they  can  send  the   blood  through  pulmonary  circuit  to   cool  it  down  (cool  down  body  water)   § gives  animal  flexibility  to   dive   o from  cavum  arteriosum  to  caven  venosum,  out  the  left  and  right  aorta  to  body  tissues   o although  incompletely  separated  chambers,  can  function  just  as  well   -­‐ 3  chambers  à  amphibians  and  reptiles  often  go  underwater   o allows  them  to  divert  blood  away  from  t he  lungs  (cant  use  lungs  to  get  oxygen  underwater)   à  allows  for   recirculation  without  lungs   o when  blood  returns  to  the  heart  at  rest,  it  is  still  saturated  with  75%  hemoglobin       Hearts  of  Birds  and  Mammal     -­‐ Fourchambers   o Two  atria   o Two  ventricles   § separated  by  intraventricular  septum  (where  conducting  pathways  are)   -­‐ Valves   o Atrioventricular  (AV)  valves   § Between  atria  and  ventricles   • Tricuspid  (Right  hand  side)  and  Bicuspid  (Left  hand  side)   § Have  extensions/tendons:  chordae  tendineae   • Extend  into  ventricles  and  mainta in  unidirectional  flow   • Constantly  pulling  down  onto  atrioventricular  valves  so  that  they  cannot  open  into  the       atria   • Unidirectional  flow  of  blood   -­‐ Semilunar  valves   o Between  ventricles  and  arteries   § Aortic  and  Pulmonary   o No  chordae  tendineae;  3  flaps  of  tissue   called  semilunar   (half  moon  shaped  bits  of  tissue  that  came  together  to   form  a  valve)   o Excellent  at  providing  one  way  flow,  or  maintaining  one   way  flow  –  doesn’t  not  allow  backflow  of  blood  into   ventricles   o Snaps  shut  when  the  pressure  is  greater  in  the  arte ry  than   the  atria  à  pressure  shuts  the  valve     Cardiac  Cycle  –  High  Coordinated   -­‐ fish  hearts   o serial  contractions  of  chambers   o sinus  venosus  –  not  a  contractile  chamber  in  most  fishes   o valves  are  passive   §
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