Metabolism and properties of the
myocardium, arterial and venous
haemodynamics, blood pressure
Romana Šlamberová, M.D. Ph.D.
Department of Normal, Pathological and
Clinical Physiology
Myocardium - morphology
• Intercalated disks = the fibers are connected to each
other in Z lines
– Provide strong union between fibers
– Maintain cell-to-cell cohesion – so the pull of one contractile
unit is transmitted to the next one
– Along the sides of the muscle fibers = „Gap junction“ –
provide low-resistant bridges for the spread of excitation =
myocardium is functioning as a „syncytium“
• Actin, myosin, tropomyosin, troponin
• Large amount of mitochondrias in tight contact with
fibrils
Myocardium – contractil
response
• Contraction – begins just after the start of
depolarization and lasts about 1.5 x longer than
the action potential
• Absolute refractory period – cardiac muscle
cannot be excited again = therefore tetanus (as
in the skeletal muscle) cannot accur
• Vulnerable period = period at the end of the
action potential during which the fibrilation of
the heart may accur
Myocardum – correlation length
x tension
• Starling’s law = initial length of the fibers is
determined by the degree of diastolic filling of the
heart, and the pressure developed in the ventricle is
proportionate to the total tension developed
The developed tension
increases as the diastolic
volume increases until it
reaches a maximum, then
tends to decrease.
Myocardium – metabolism
• Abundant blood supply, numerous
mitochondria, high content of myoglobin (a
muscle pigment) as a storage of O2
• Metabolism mostly aerobic, only about 1%
anaerobic (during hypoxia possible up to 10%
anaerobic, if more – not enough energy for
contractions)
• Utilization of substrates depending on the
nutrition – 60% fats (mostly FA), 35%
carbohydrates, 5% ketones and AAs
Haemodynamics - arteries
• Role of arteries in the systemic circulatory
system is to transport the blood under the
pressure from the left ventricle to separate
tissues and organs.
• Arteries – strong, flexible, elastic wall is
responsible for the fast flow of the blood (from
lungs – periphery in 10 s = circulatory speed)
• Arterioles – strong wall consisted mostly by
smooth muscles that is adjustable based of the
needs of the body
Blood flow in arteries
• Ascending aorta
– During the ejection phase of systole is the speed up
to 100 cm/s = turbulent flow
– Average speed is only around 20 cm/s
– At the beginning of diastole the flow may be even
reversed = semilunar valves closure
= nárazové proudění aortou
• Other arteries
– Constant continual flow of lower speed
Role of flexibility
• Systole = transformation of
kinetic energy of blood to
elastic energy of aorta wall
• Diastole = transformation of
elastic energy of aorta wall to
kinetic energy of blood
• Progression of blood the way of
the lowest resistance, i.e. from
the heart to the periphery
Blood pressure in arteries
• Pressure puls = ejection of blood from the left ventricle induces temporary
increase of blood pressure in the aorta
– Increase of blood pressure is followed by decrease = primary wave
– At the beginning of diastole is low increase = dicrotic wave (based of
relaxation of ventricle and retrograde blow of blood that closes the aortal
valve)
– Steady decrease up to the beginning of next ejection phase.
• Blood pressure never reaches zero level – elasticity of arteries and
peripheral resistance
Blood pressure
• Systolic pressure = the highest value of pressure
during the systole
– 120 mm Hg = 16 kPa
• Diastolic pressure = the lowest value of pressure
during the diastole
– 80 mm Hg = 12 kPa
• Puls pressure (pressure amplitude) = difference
between the systolic and diastolic pressure
(dependent on pulse volume and flexibility of
arteries)
– 50 mm Hg = 6,6 kPa
• Mean pressure = average value of pressure during
the entire heard action (diastole is longer than systole)
– 90 mm Hg = 12 kPa
Haemodynamics - veins
• Role of veins in the systemic circulatory system is to
transport the blood from separate tissues and organs
to the right atrium.
• Venules and small veins
– Blood flow is continual
• Large veins
– Pulsation that is induced by retrograde function of the right
atrium = venous pulse (phlebogram from jugular vein)
• Speed of the blood flow increases from venules to the
heart
• Middle linear speed of the blood flow = 10-16 cm/s
Phlebogram – venous pulse
a – increase in filling of central
veins based of the systole of
right atrium
c – movement of cuspidal
valves in the direction to the
atriums at the beginning of
isovolumic contraction
s – relaxation of atriums and
movement of heart basis
and cuspidal valves in the
direction to the apex at the
beginning of ejection of
ventricles
v – filling of atriums during the
isovolumic relaxation
y – emptying of atriums during
the filling phase
Blood flow in veins
•
•
•
•
Gravity – positive and negative (dependent on location)
Muscle pump – skeletal muscles
Veins valves – against the retrograde blood flow
Respiration – during inspiration the intrathoracal pressure
decreases and the blood is sucked into the caval veins and the
right atrium
• Sucking function of the heart – decrease of the pressure in
atriums durint the ejection phase of the heart
• Vein pump – spiral muscle fibers in media
• Arterial pulse wave – pressure to veins (thanks to valves the
flow is also in the direction to the heart)
Blood pressure in veins
Depends on gravitation and on flexibility of veins
• Gravity – Pressure in the head (-10 mmHg) <
central blood pressure (0 mmHg) < pressure in
legs (90 mmHg)
• Width of veins – venules (10-15 mmHg), larger
veins (5 mmHg)
• Flexibility of veins – Physiologically affected
by sympathetic system – contraction of smooth
vein muscles results in lower flexibility and in
final in increased blood pressure and blood
comeback
Blood pressure
• Systolic blood pressure depends on:
– Systolic blood volume
– Elasticity of arterial walls
• Diastolic blood pressure depends on the
resistance of periphery (resistance is induced
mostly by arterioles)
• Normal blood pressure: 120 mmHg (16 kPa) / 80
mmHg (12 kPa)
• Mean blood pressure: pm = 1/3 ps + 2/3 pd
• Increased blood pressure: 145 mmHg (19,4 kPa)
/ 95 mmHg (12,7 kPa)
1 mmHg = 0,133 kPa