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Cardiovascular System
Heart
Electrocardiogram
• A device that records the electrical activity
of the heart.
• Measuring the relative electrical activity of
one heart cycle.
• A complete contraction and relaxation.
Electrocardiogram
• 3 ways to measure electrical activity:
– Left wing, + right wing, right leg = Lead I
– Left leg, + right wing, right leg = Lead II
– Left leg, + Left wing, right leg = Lead III
• Each create a triangle around heart
– Einthoven’s Triangle (based on Einthoven’s
law)
Electrocardiogram
dI
I
I
)
a
e
(L
Heart
(-)
(+)
(L
e
a
0°
I)
I
d
(+)
(+)
(-)
(-)
Right wing =
- .20 mV
(Lead I)
Left leg = +1.00 mV
Left wing =
+ .30 mV
180°
Electrocardiogram
• Lead I – Lead II + Lead III = 0
• Lead I – Lead II = Lead III
• Einthoven’s Law:
– Lead I = left wing – right wing
(+ .30 mV) – (- .20 mV) = + .50 mV
– Lead II = left leg – right wing
(+ 1.00 mV) – (- .20 mV) = + 1.20 mV
– Lead III = left leg – left wing
(+ 1.00 mV) – (+.30 mV) = + .70 mV
Electrocardiogram
• Lead I - Lead II + Lead III = 0
(+ .50 mV) – (+ 1.20 mV) + (+ .70 mV) = 0
• Lead I - Lead II = Lead III
(+ .50 mV) – (+ 1.20 mV) = (+ .70 mV)
Electrocardiogram
Electrocardiogram
Electrocardiogram
Heart Output
• Stroke Volume
– volume of blood ejected from heart
during a single systolic contraction
– Only about 2/3 of volume of ventricle is
pumped out with one contraction.
– = End diastolic volume – End systolic
volume
Heart Output
• Cardiac Output
– amount of blood ejected from both
ventricles per unit time
– = Heart rate X Stroke volume
• Heart rate and stroke volume negatively
correlate
Starling’s Law of the Heart
• The more the ventricle is filled with blood
during diastole (end-diastolic volume), the
greater the volume of blood ejected during
the systolic contraction (stroke volume).
• Note - the force of contraction increases as
the heart is filled with more blood.
Heart contraction and
Blood Pressure
• More blood to ventricle with higher venous
blood pressure = higher stroke volume
• Higher arterial blood pressure - reduces
stroke volume as semilunar valves close
prematurely
Blood Pressure
• Blood Pressure =
– Systolic over diastolic
– Contracted over relaxed
• Chicken blood pressure = 180 mm Hg/100 mm Hg
• Turkey blood pressure = 300/250
• Human blood pressure = 120/80
Blood Pressure
• Arterial pressure - Simplification “Closed
system (arteries to arterioles to capillaries) Heart contracts put blood in arteries under
pressure
• Venous pressure due to skeletal muscles
contracts - squeezing veins, gravity, “pull”
of heart contractions, closed system
Arterial Blood Pressure
• Arteries have “elastic’ inner walls providing
RESISTANCE to expansion (This is
PERIPHERAL RESISTANCE)
Arterial Blood Pressure
• Arterial walls surrounded by smooth muscle
– if muscles contract, arterial diameter ↓,
arteries/arterioles constrict
(VASOCONSTRICTION), resistance and B.P. ↑
– if muscles relax, arterial diameter ↑,
arteries/arterioles dilate (VASODILATION),
resistance and B.P. ↓
– Muscles normally do not completely relax Vascular tone
Arterial Blood Pressure II
• When blood is forced out of the ventricle,
arterial B.P. up - Systolic B.P.
• When valves close - Diastolic B.P.
Arterial Blood Pressure II
• Dilation/relaxation of blood vessel smooth muscles
under the control of autonomic nervous system (+
hormones)
– Parasympathetic nerve (part of vagus)
• More nervous activity - more Acetyl choline –
vasodilation
– Sympathetic nerve
• More nervous activity - more Norepinephrine
–vasocontriction in arterioles of skin and gut,
but vasodilation in arterioles of muscle.
Hormones and Arterial B.P.
• Renin – Angiotensin
– Kidney releases renin (enzyme)
– Converts Angiotensinogen (precursor produced
by the liver) into Angiotensin I
– ACE (lung & renal enzyme) converts
Angiotensin I into Angiotensin II
– Angiotensin II (I just a little) is a powerful
vasoconstrictor
Hormones and Arterial B.P.
• Norepinephrine/Epinephrine (adrenal medulla) –
at higher levels ↑ B.P.
• Arginine vasotocin and Mesotocin - increase
B.P. at physiological concentrations probably via
increased water retention + vasoconstrictor?
• Histamine (not a hormone) from basophilsvasodilator (released with inflammation) also a
bronchoconstrictor (allergic reaction)
Nervous Regulation of Blood
Pressure
• Neural receptors (largely peripheral) detect
changes in arterial and venous blood
pressure and blood composition (pH, CO2,
02 - hypoxia)
• Brain integration of data
• If Blood pressure too high - cardiac output
reduced to compensate
• If hemorrhage - B.P. falls - Cardiac output
increased to compensate.