5.3 Volumes & stuff

Question 1

what is stroke volume

Answer 1

amount of blood pumped out by one ventricle with each beat

*after contracting -> still some fluid in heart

SV = EDV - ESV

ex: =120 ml/beat – 50 ml/beat -> =70 ml/beat

Question 2

what is ejection fraction

Answer 2

percent of total ventricular volume ejected in one contraction

EF = SV/EDV

EF will INC with exercise

Question 3

what is cardiac output

Answer 3

• volume of blood pumped by each ventricle in one minute

CO = HR x SV

Question 4

what is cardiac reserve

Answer 4

difference between resting & maximal CO

Question 5

how can you estimate maximla CO

Answer 5

4-5x the resting CO in non athletic poeple

• maximal CO may reach 35L/min in trained athletes

Question 6

how is stroke volume regulated?

Answer 6

• Preload
  
  • degree of stretch of cardiac muscle cells before they contract
    
    • more muscle stretches the more forcefult he cotnraction
    • INC venus return -> INC EDV -> INV SV -> INC CO
• Frank Starling law of heart
  
  • slow HB & excercise INC venus return
  • INC venous return distends ventricles which INC contraction force
  • keeps equal output between both ventricles

Question 7

how does contractility influence stroke volume

what increases and decreases contractility

Answer 7

• contractility = contractile strength at a given muscle length, independent of muscle stretch & EDV
• INC contractility
  
  • positive inotropic agents
  • INC Ca influx due to SNS stimulation
  • hormones (thyoxine, glucagon and epinephrine)
• DEC contractiltiy
  
  • Negative inotropic agents
  • acidosis (excess H+)
  • INC extracellular K+
  • calcium channel blockers

Question 8

how do catecholamines modulate cardiac contraction

Answer 8

• Epinaphrine & norephinephrine released
• binds to B1 receptors -> activavte cAMP second messanger -> phosphorylates
  
  • Voltage gates Ca channels
    
    • open time increases
    • inc Ca entry from ECF
      
      • INC Ca stoes in SR and inc Ca release -> MORE forceful contraction
  • Phospholamban
    
    • INC Ca-ATPase on SR
      
      • INC Ca stoes in SR and inc Ca release -> MORE forceful contraction
      • Ca removes from cytosol faster -> shortens Ca-troponin bidnign time -> shorter duration of contraciton

Question 9

how does afterload influence stroke volume

Answer 9

afterload: pressure that must overcome from ventricles to eject blood
- more pressure -> more blood reamining in heart

*If INC ESV then DEC SV

*this is how much force you need to poen the valve (opening door example)

Question 10

what si the impact of the SNS on the heart

Answer 10

SNS is activated by emotional or physical stressors

• > NE causes pacemaker to fire mroe rapidly & inc contractility
• initaties the atrial (Bainrbidge) reflex

Question 11

what is the brainbridge reflex

Answer 11

aka atiral reflex

• SNS relfex initiated by INC venous return
• stretch of atrial walls stimulates SA node to ↑ heart rate

*extra blood coming back -> when atria stretches more HR inc

Question 12

how does the PSNS effect the heart

Answer 12

• Ach hyperpolarizes pacemaker cells by opening K+ channels
• at rest, heart exhibits vagal tone

Question 13

how do hormones regulate the heart

Answer 13

• epinephrine from adrenal meducally INC HR and contractility
• Thyroxine INC HR and enhances effects of NE & E

Question 14

How do intra and extra cellular ion concentrations regulat HR

Answer 14

ex Ca and K

• must be maining for normal heart function-> changing ion conc can later contractility and HR

Question 15

Factors that alter HR

Answer 15

• INC HR
  
  • SNS stimulation
  • Inc in body temp
  • epinephrine and thyroxine
• DEC HR
  
  • PSNS
  • dec body temp

Question 16

who main variables that INC SV and decrease SV

Answer 16

increasing EDV will inc SV

Increasing ESV will dec SV

* SO increase: INC EDV, DEC ESV ( you want lots of blood at the end of filling, and barely any at end of contraction)

Question 17

what influcences EDV

Answer 17

* in general when INC venous return SV INC

• Inc venous return
  
  • inc ventricular filling time
  • muscle contractions (compress veins and assist valves in directing vanous blood twd atrium)
• Dec venous return
  
  • large bc in blood volume (bleeding/dehydration)
• changes in peripheral blood patterns can do either

Question 18

how does EDV influence ESV

Answer 18

• determines myocardial preload (amount sacromere stretches at the end of diasotle)
• amount of preload affects ESV by influencing efficinecy of contractions

Question 19

what influences ESV

Answer 19

• Increases
  
  • inc in filling time
  • PSNS stimulation Dec contractility (larger ESV)
  • vasoconstriction: increases afterload, harder to pump blood out to more blood left at end of contraction
• decreases
  
  • greater contractility (caused by SNS stimulation)
  • variosu hormones
  • decrease in afterload (vasodilation) -> harder to pump blood out

Question 20

what other factors affect heart rate

Answer 20

Age: Inc age = dec HR

gender: slghtler faster in females (72-80bpm vs. 64-72bpm in males)

Long term exercise: inc fitness, dec resting HR

Question 21

what are congential heart defects

Answer 21

– Lead to mixing of systemic & pulmonary blood
– Involve narrowed valves or vessels that increase the workload on the heart