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18B  

Heart  Physiology    

Heart  Valves  

•  Ensure  unidirec=onal  blood  flow  through  the  heart  •  Atrioventricular  (______)  valves  

–  Prevent  backflow  into  the  atria  when  ventricles  contract  –  Tricuspid  valve  (_____________)  – Mitral  valve  (____________)  

•  Chordae  tendineae  anchor  AV  valve  cusps  to  papillary  muscles  

Heart  Valves  

•  Semilunar  (SL)  valves  – Prevent  backflow  into  the  ___________________  when  they  relax  

– Aor=c  semilunar  valve  – Pulmonary  semilunar  valve  

Figure 18.8a

Pulmonary valve Aortic valve Area of cutaway

Mitral valve Tricuspid valve

Myocardium

Tricuspid (right atrioventricular) valve Mitral (left atrioventricular) valve Aortic valve

Pulmonary valve

(b)

Pulmonary valve Aortic valve Area of cutaway

Mitral valve Tricuspid valve

Myocardium

Tricuspid (right atrioventricular) valve

(a)

Mitral (left atrioventricular) valve Aortic valve

Pulmonary valve Fibrous

skeleton

Anterior

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Figure 18.8b

Pulmonary valve Aortic valve Area of cutaway

Mitral valve Tricuspid valve

Myocardium

Tricuspid (right atrioventricular) valve Mitral (left atrioventricular) valve Aortic valve

Pulmonary valve

(b)

Figure 18.8c

Pulmonary valve

Aortic valve Area of cutaway Mitral valve

Tricuspid valve

Chordae tendineae attached to tricuspid valve flap

Papillary muscle

(c)

Figure 18.8d

Pulmonary valve Aortic valve Area of cutaway Mitral valve Tricuspid valve

Mitral valve Chordae tendineae

Interventricular septum

Myocardium of left ventricle

Opening of inferior vena cava

Tricuspid valve

Papillary muscles

Myocardium of right ventricle

(d)

Figure 18.9

1 Blood returning to the heart fills atria, putting pressure against atrioventricular valves; atrioventricular valves are forced open.

1 Ventricles contract, forcing blood against atrioventricular valve cusps.

2 As ventricles fill, atrioventricular valve flaps hang limply into ventricles.

2 Atrioventricular valves close.

3 Atria contract, forcing additional blood into ventricles.

3 Papillary muscles contract and chordae tendineae tighten, preventing valve flaps from everting into atria.

(a) AV valves open; atrial pressure greater than ventricular pressure

(b) AV valves closed; atrial pressure less than ventricular pressure

Direction of blood flow Atrium

Ventricle

Cusp of atrioventricular valve (open)

Chordae tendineae Papillary muscle

Atrium

Blood in ventricle

Cusps of atrioventricular valve (closed)

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Figure 18.10

As ventricles contract and intraventricular pressure rises, blood is pushed up against semilunar valves, forcing them open.

As ventricles relax and intraventricular pressure falls, blood flows back from arteries, filling the cusps of semilunar valves and forcing them to close.

(a) Semilunar valves open

(b) Semilunar valves closed

Aorta Pulmonary trunk

Heart  Physiology:  Sequence  of  Excita=on  

1.  Sinoatrial  (SA)  node  (___________________)  –  Generates  impulses  about  75  =mes/minute  (sinus  

rhythm)  –  Depolarizes  faster  than  any  other  part  of  the  

myocardium  

Heart  Physiology:  Sequence  of  Excita=on  

2.  Atrioventricular  (_____)  node  –  Smaller  diameter  fibers;  fewer  gap  junc=ons  –  Delays  impulses  approximately  0.1  second  –  Depolarizes  50  =mes  per  minute  in  absence  of  

SA  node  input  

Heart  Physiology:  Sequence  of  Excita=on  

3.  Atrioventricular  (AV)  bundle  (_______________________)  

–  Only  electrical  connec=on  between  the  atria  and  ventricles  

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Heart  Physiology:  Sequence  of  Excita=on  

4.  Right  and  le]  bundle  branches  –  Two  pathways  in  the  interventricular  septum  

that  carry  the  impulses  toward  the  __________  of  the  heart  

Heart  Physiology:  Sequence  of  Excita=on  

5.  __________________  fibers  –  Complete  the  pathway  into  the  apex  and  

ventricular  walls  –  AV  bundle  and  Purkinje  fibers  depolarize  only  

30  =mes  per  minute  in  absence  of  AV  node  input  

Figure 18.14a

(a) Anatomy of the intrinsic conduction system showing the sequence of electrical excitation

Internodal pathway

Superior vena cava Right atrium

Left atrium

Purkinje fibers

Inter- ventricular septum

1 The sinoatrial (SA) node (pacemaker) generates impulses.

2 The impulses pause (0.1 s) at the atrioventricular (AV) node. The atrioventricular (AV) bundle connects the atria to the ventricles. 4 The bundle branches conduct the impulses through the interventricular septum.

3

The Purkinje fibers depolarize the contractile cells of both ventricles.

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 Extrinsic  Innerva=on  of  the  Heart  

•  Heartbeat  is  modified  by  the  ANS    •  Cardiac  centers  are  located  in  the  ______________  ____________________  – Cardioacceleratory  center  innervates  SA  and  AV  nodes,  heart  muscle,  and  coronary  arteries  through  sympathe=c  neurons  

– Cardioinhibitory  center  inhibits  SA  and  AV  nodes  through  parasympathe=c  fibers  in  the  vagus  nerves  

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Figure 18.15

Thoracic spinal cord

The vagus nerve (parasympathetic) decreases heart rate.

Cardioinhibitory center

Cardio- acceleratory center

Sympathetic cardiac nerves increase heart rate and force of contraction.

Medulla oblongata

Sympathetic trunk ganglion

Dorsal motor nucleus of vagus

Sympathetic trunk

AV node SA node

Parasympathetic fibers Sympathetic fibers Interneurons

Electrocardiography  

•  Electrocardiogram  (___________________):  a  composite  of  all  the  ac=on  poten=als  generated  by  nodal  and  contrac=le  cells  at  a  given  =me  

•  Three  waves  1.  ___  wave:  depolariza=on  of  SA  node  2.  _________  complex:  ventricular  depolariza=on  3.  ___  wave:  ventricular  repolariza=on  

Figure 18.16

Sinoatrial node

Atrioventricular node

Atrial depolarization

QRS complex

Ventricular depolarization

Ventricular repolarization

P-Q Interval

S-T Segment

Q-T Interval

Figure 18.17

Atrial depolarization, initiated by the SA node, causes the P wave.

P

R

T

Q S

SA node

AV node

With atrial depolarization complete, the impulse is delayed at the AV node.

Ventricular depolarization begins at apex, causing the QRS complex. Atrial repolarization occurs.

P

R

T

Q S

P

R

T

Q S

Ventricular depolarization is complete.

Ventricular repolarization begins at apex, causing the T wave.

Ventricular repolarization is complete.

P

R

T

Q S

P

R

T

Q S

P

R

T

Q S

Depolarization Repolarization

1

2

3

4

5

6

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Figure 18.18

(a) Normal sinus rhythm.

(c) Second-degree heart block. Some P waves are not conducted through the AV node; hence more P than QRS waves are seen. In this tracing, the ratio of P waves to QRS waves is mostly 2:1.

(d) Ventricular fibrillation. These chaotic, grossly irregular ECG deflections are seen in acute heart attack and electrical shock.

(b) Junctional rhythm. The SA node is nonfunctional, P waves are absent, and heart is paced by the AV node at 40 - 60 beats/min.

Heart  Sounds  

•  Two  sounds  (lub-­‐dup)  associated  with  __________________  of  heart  valves  – First  sound  occurs  as  AV  valves  close  and  signifies  beginning  of  _________________  

– Second  sound  occurs  when  SL  valves  close  at  the  beginning  of  ventricular  ________________    

•  Heart  murmurs:  abnormal  heart  sounds  most  o]en  indica=ve  of  valve  problems  

Figure 18.19

Tricuspid valve sounds typically heard in right sternal margin of 5th intercostal space

Aortic valve sounds heard in 2nd intercostal space at right sternal margin

Pulmonary valve sounds heard in 2nd intercostal space at left sternal margin

Mitral valve sounds heard over heart apex (in 5th intercostal space) in line with middle of clavicle

Mechanical  Events:  The  Cardiac  Cycle  

•  Cardiac  cycle:  all  events  associated  with  blood  flow  through  the  heart  during  one  complete  heartbeat  – Systole—_________________    – Diastole—___________________    

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Phases  of  the  Cardiac  Cycle  

1.  ____________________  filling—takes  place  in  mid-­‐to-­‐late  diastole  

–  AV  valves  are  open    –  80%  of  blood  passively  flows  into  ventricles  –  Atrial  systole  occurs,  delivering  the  remaining  

20%  –  End  diastolic  volume  (EDV):  volume  of  blood  in  

each  ventricle  at  the  end  of  ventricular  diastole  

Phases  of  the  Cardiac  Cycle  2.  Ventricular  systole  

–  Atria  relax  and  ventricles  begin  to  _________________  –  Rising  ventricular  pressure  results  in  closing  of  AV  valves  –  Isovolumetric  contrac=on  phase  (all  valves  are  closed)  –  In  ejec=on  phase,  ventricular  pressure  exceeds  pressure  in  

the  large  arteries,  forcing  the  SL  valves  open  –  End  systolic  volume  (______):  volume  of  blood  remaining  

in  each  ventricle    

Phases  of  the  Cardiac  Cycle  

3.  Isovolumetric  relaxa=on  occurs  in  early  ______________________  

–  Ventricles  relax  –  Backflow  of  blood  in  aorta  and  pulmonary  trunk  

closes  SL  valves  and  causes  dicro=c  notch  (brief  rise  in  aor=c  pressure)  

Cardiac  Output  (CO)  

•  _________________  of  blood  pumped  by  each  ventricle  in  one  minute  

•  CO  =  heart  rate  (HR)  x  stroke  volume  (SV)  – HR  =  number  of  beats  per  minute  – SV  =  volume  of  blood  pumped  out  by  a  ventricle  with  each  beat  

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Autonomic  Nervous  System  Regula=on  

•  _____________________  nervous  system  is  ac=vated  by  emo=onal  or  physical  stressors  – Norepinephrine  causes  the  pacemaker  to  fire  more  rapidly  (and  at  the  same  =me  increases  contrac=lity)    

Autonomic  Nervous  System  Regula=on  

•  ______________________  nervous  system  opposes  sympathe=c  effects    – Acetylcholine  hyperpolarizes  pacemaker  cells  by  opening  K+  channels  

•  The  heart  at  rest  exhibits  vagal  tone  (parasympathe=c)    

Chemical  Regula=on  of  Heart  Rate    

1.  ____________________  –  Epinephrine  from  adrenal  medulla  enhances  

heart  rate  and  contrac=lity  –  Thyroxine  increases  heart  rate  and  enhances  the  

effects  of  norepinephrine  and  epinephrine  

2.  Intra-­‐  and  extracellular  _______  concentra=ons  (e.g.,  Ca2+  and  K+)  must  be  maintained  for  normal  heart  func=on  

Other  Factors  that  Influence  Heart  Rate  

•  _________________________  

•  _________________________  

•  _________________________  

•  _________________________  

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Age-­‐Related  Changes  Affec=ng  the  Heart  

•  Sclerosis  and  thickening  of  valve  flaps  •  Decline  in  cardiac  reserve  •  Fibrosis  of  ____________  muscle  •  Atherosclerosis