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Circulatory system
Pressure gradients move
blood through the heart
and vessels.
Pulmonary circulation vs.
systemic circulation
head
and arms
aorta
(to pulmonary
circuit)
(from
pulmonary
circuit)
heart
other organs
diaphragm
liver
“Double pump” both
ventricles pump an
equal volume of
blood into systemic
and pulmonary
circuits
Higher resistance
through the systemic
circuit
intestines
legs
Pressure - force exerted by pumped blood
on a vessel wall
Resistance - opposition to blood flow
from friction
vena
cava
Right atrium
Tricuspid
valve
Right ventricle
vena cava
Right pulmonary
artery
Left pulmonary
artery
Pulmonary
semilunar
valve
Right atrium
Tricuspid
valve
Right ventricle
Aorta
Left pulmonary
vein
Right
pulmonary
vein
Left atrium
Bicuspid
valve
Left ventricle
Aorta
Left pulmonary
vein
Right
pulmonary
vein
Aortic
semilunar
Left atrium
valve Bicuspid
valve
Left ventricle
Valves ensure one-way flow
When pressure is
greater behind the
valve, it opens.
When pressure is
greater in front of
the valve, it closes
Leakproof
“seams”
semilunar valve
Shape of the AV valves is maintained by
chordae tendineae
Right atrium
Tricuspid valve
Chordae tendineae
Papillary muscle
contracts with ventricle
Septum
Right ventricle
Ventricular
Systole
Ventricular
Diastole
Blood pressure variation
Heart
myocardium
Cardiac muscle fibers
are interconnected by
intercalated discs.
Junctions between cardiac muscle cells
Desmosome
Gap junction
Action
potential
Intercalated disc
Pacemaker activity
Slow depolarizations set off action potentials in a cycle
Pacemaker cells only!
These cells do not contract
Cardiac muscle
Self-excitable muscles - action potential gradually
depolarizes, then repolarizes
Spontaneous action potential
Pacemaker cell
Gap junctions
Action potential spread
to other cells
Gap junctions
No gap junctions between
atria and ventricles
Fibrous insulating tissue
prevents AP from directly
spreading from atria to
ventricles
Conduction of contraction
Pacemaker locations:
SA node
AV node
Sinoatrial
(SA) node Atrioventricular
(AV) node
Bundle of His
Purkinje fibers
Bundle of His
Purkinje
fibers
Problems with heart rhythm
AV node rhythm is slower - bradycardia
Problems with heart rhythm
Heart block – a type of bradycardia.
Ventricles pump slowly and out of rhythm
of atria
Ventricular fibrillation
Problems with heart rhythm
Atrial fibrillation
Ventricular fibrillation
Action potential in cardiac muscle
These are contractile cells
not pacemaker cells
Plateau
phase
Threshold
potential
Long refractory
period ensures no
summation of
twitches
Relaxation of
cardiac muscles is
essential
Electrocardiogram
Currents from heart spread to body tissues and
fluid
Sum of all electrical activity spread to electrodes
and recorded
R
T
P
P
Q
PR
S
ST
TP interval

Cardiac cycle
Ventricular and atrial diastole
Cardiac cycle
Atrial contraction
Cardiac cycle
Isovolumetric ventricular contraction
“Lub”
End diastolic volume
is in the ventricles
Cardiac cycle
Ventricular ejection
Cardiac cycle
Isovolumetric ventricular relaxation
“Dub”
End systolic volume
is in ventricles
Heart murmurs
Systolic or diastolic murmurs
Often due to stenosis or regurgitation at a valve
(“whistle” vs. “swish”)
Normal heart
“lub-dup”
Diastolic mitral stenosis
“lub-dup-whistle”
Diastolic aortic regurgitation
“lub-dup-swish”
Systolic aortic stenosis
“lub-whistle-dup”
Systolic tricuspid regurgitation
“lub-swish-dup”
Diastolic patent ductus arteriosus
Sympathetic signals increase stroke volume
Extrinsically:
conduction speed
contraction strength
Recall: muscle length and force
Frank Starling law
Stroke volume (SV) (ml)
(intrinsic increase in stroke volume)
Optimal length
Increase
in SV
B1
A1
Normal resting length
(Cardiac muscle does
not normally operate
within the descending
limb of the length–
tension curve.)
Increase
in EDV
End-diastolic volume (EDV) (ml)