Ch 11 Heart
Heart Physiology
(PPT 2)
Cardiac muscle characteristics:
irritability
contractility
self-exciting
rhythmic
Control of the Heart
Medulla oblongata (of brainstem) & the
autonomic nervous system control heart rate
SA node (intrinsic control)- cardiac muscle
cells in RA, stimulated by neurons, stimulate
other cardiac muscle cells to contract (i.e.
starts the heartbeat!)
SA node (in RA)- “pacemaker” of cardiac
cycle, sends impulses in atria to stimulate AV
node. Starts the heartbeat!
AV node- (in RA) stimulates AV bundle
(between ventricles), Purkinje fibers and
ventricles
Conduction system of the
heart
Starts the
Heartbeat!
“Pacemaker”
video- conduction system of the heart
Cardiac Cycle
Cardiac cycle= 1 complete heartbeat = .8 sec
Systole- contraction
Diastole- relaxation
“Atrial systole with simultaneous ventricular
diastole, then atrial diastole with simultaneous
ventricular systole”
Cardiac Cycle
Heart sounds = “LUBB DUPP”
“LUBB”- AV valves
(tricuspid and bicuspid)
closing after atrial
systole
“DUPP”- semilunar
valves (pulmonary and
aortic) closing after
ventricular systole
Diagnostic technique
EKG/ECG
(Think back to nerve
impulses and
polarization,
depolarization,
repolarization)
P wave  (signals depolarization of atria…right before they contract)
QRS complex  (signals depolarization of ventricles, before they contract!)
T wave  (results from currents flowing during repolarization of the
ventricles)
EKG/ECG
flatlining
Practical applications
Artificial pacemaker
If SA node is defective, then electronic device called a
pacemaker is implanted into heart to take SA node’s
place.
Practical applications
Cardiac output
(def.) volume of blood pumped by LV per minute (ml/min)
CO= stroke volume (SV) x heart rate (HR)
SV= volume of blood pumped from LV per beat
(ml/beat)
HR= heart beats per minute
(b/min)
Cardiac output sample
problem
CO= amt of blood in body, (because each drop of
blood takes 1 minute to circulate through body)
Approx. 5 Liters= 5000ml
Average fitness CO= SV x HR
5000ml/min = 67 ml/beat x 75 b/min
Always stays the same
Average SV
Average HR
Cardiac output sample
problems
If a person is a couch potato…..
then resting CO =
5000 ml/min= 50 ml/beat x 100 b/min
But If they begin to exercise and are now of
average fitness……
then resting CO=
5000ml/min = 67 ml/min x 75 b/min
Cardiac output sample
problems
If they become even more fit or active
resting CO= 5000ml/min
5000ml/min= 83 ml/beat x 60 b/min
TAKE HOME MESSAGE: As person becomes more
fit- heart becomes more fit at rest, pumps less beats
per min., but more blood per beat!
Cardiac Output
Regulation of SV and HR- can be
affected by exercise and fitness level
TAKE HOME MESSAGE: As a person’s
fitness level increases, their HR decreases, SV
increases, but resting CO stays the same.
Fitness =
HR
SV
Homeostatic Imbalances
Angina pectoris- crushing chest pain, can be symptom
of MI
Heart attack (myocardial infarction, AKA MI):
Caused by blocked coronary artery due to either clot
or atherosclerotic plaque, can lead to myocardial
(muscle cell) death
Myocardial infarction
anticoagulants
Homeostatic Imbalances
Murmurs- occurs if
valves don’t close
correctly or if they
leak
Fibrillation- if
atrial or ventricular
chambers don’t
contract
simultaneously,
ventricular
fibrillation can be
deadly
Atrial Fibrillation
Ventricular fibrillation
Can lead to death
because ventricles
tremble, but don’t
contract (so no blood
flow)
Defibrillator
Shocks heart to “reset” it
Defibrillator
Homeostatic Imbalances
MVP- bicuspid valve leaks, blood flows backwards
Pericarditis- inflammation of pericardium around heart
Homeostatic Imbalances
Cardiac arrhythmia- irregular heart beat, due to
fibrillation or SA node problems
CAD (Coronary Artery Disease):
plaque/cholesterol in coronary arteries
Coronary Artery Disease
HDL’s- good cholesterol
LDL’s- bad cholesterolclogs arteries
Catheterization is a treatment,
not a cure, because if one
doesn’t change eating habits
then it will just happen again
Homeostatic Imbalances
CHF- (Congestive Heart Failure)- heart weakening,
not necessarily stoppage
Due to:
MI
Atherosclerosis
Hypertension
CAD
Other heart diseases