Download Physiology Lec.(2) Dr.Rafah Sami

Physiology
Lec.(2)
Dr.Rafah Sami
-----------------------------------------------------------Cardiac cycle
The events that occur at the beginning of a heart beat and last until the
beginning of the next heart beat is called cardiac cycle
Each beat of the heart begins with a spontaneous action potential that is
initiated in SA node
This figure shows the events of cardiac cycle:-
The ventricle fill with blood during diastole and contract during systole. The
top three curves of this diagram show the aortic pressure, left ventricular
pressure and left atrial pressure. the curves below show Ventricular volume
,ECG
The atria function as primary pumps for the ventricles about(75%)of
ventricular filling occurs during diastole before the contraction of atria, which
cause the remaining 25% of ventricular filling, when the atria fail to function
properly, such as in atria fibrillation, pressure waves include:1-the(a)wave which is caused by a trial contraction.
2-The (c)wave which occurs during ventricular contraction due to slight back
flow and bulging of (A-V) valves toward the atria.
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3-The (v)wave which is caused by filling of atria from the venous return.
the ventricles fill with blood during diastole and the following events occur
just before and during diastole.
during systole the(A-V)valves are closed and the atria fill with blood
At the beginning of diastole when ventricular pressure decrease below that of
atria, the A-V valves open the high pressure in atria pushes blood into the
ventricles during diastole
The period of rapid filling of ventricles occur during the first third diastole and
provide most of ventricular filling
A trial contraction occurs during the last third of diastole and contributes
about 25%of the filling of the ventricle
out flow of blood from ventricles occur during systole
the following events occur during systole:1-At the beginning of systole ,ventricular contraction occurs, the A-V valves
close, and pressure begins to build up in the ventricle, no out flow of blood
occurs ,the first(0.2-0.3)second of ventricular contraction
2-When left ventricular pressure exceeds the aortic pressure of about
80mmHg,and right ventricular pressure exceeds the pulmonary artery
pressure of 8mmHg
,the aortic and pulmonary valves open ,ventricular out flow occurs and this is
called period of ejection
most of ejection occurs during the first part of this period then followed by a
period of slow ejection. the last period of systole is called a period of
isovolumic relaxation and is caused by ventricular relaxation ,causes the
ventricular pressure to fall below the aortic and pulmonary artery pressure
,thus ,the semi lunar valves close at this time
ventricular ejection increase pressure in the aorta to 120mmHg(systolic
pressure).when ventricular pressure exceeds the diastolic pressure in the
aorta, the aortic valves opens and blood is ejected into the aorta. pressure in
the aorta increases to about 120mmHg and distends the elastic aorta and
other arteries
when the aortic valves closes at the end of ventricular ejection, there is a
slight back flow of blood followed by sudden cessation of flow and this causes
(incisura)or a slight increase in aortic pressure .During diastole , blood
continues to flow into peripheral circulation and arterial pressure decreases
to80mmHg(diastolic pressure)
Atrioventricular Valves (AV Valves)
They permit the blood flow from the atria into the ventricle. The tricuspid
valve is situated between the right atrium and the right ventricle, while the
mitral valve (bicuspid) is located between the left atrium and the left
ventricle. When ventricles contract, these valves close and prevent the
regurgitation of blood into the atrium.
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Semilunar Valves
They are situated at the base of the aorta and pulmonary artery. During
ventricular contraction, they open and blood flows into the peripheral
circulation. However, when ventricles relax, the regurgitation of blood is
prevented by the closure of these valves.
HEART SOUNDS
During each cardiac cycle four heart sounds are produced, but only the 1st
and2nd heart sounds are heard clearly. The3rd heart sound can be heard in
some individuals but the 4th sound is inaudible. All the four heart sounds can
be recorded graphically with the help of a phonocardiograph.
(lup)First Heart Sound
It is produced at the beginning of the ventricular systole and is also known as
the systolic sound. It is better heard in the 5th left intercostals space, 3 1/2.
inches from the mid clavicular line. It is dull (Low pitched) and prolonged .
The following factors contribute to the production of 1st sound:
• Closure of AV valves
• Contraction of ventricular muscle
Second Heart Sound(Dup)
It is also known as the diastolic sound and is produced after the protodiastolic period of cardiac cycle. It is auscultated in the second intercostals
space on either side of the sternum, is sharp (high pitched) . The second
sound is due to the sudden closure of semi lunar valve.
ELECTROCARDIOGRAM-------------(E.C.G.)
Our knowledge of electricity from the living tissues dates back to 1853 Kolliker
demonstrated that electrical changes can be recorded from tissues during
activity. These changes have a very low voltage and exhibit rapid fluctuations
providing difficulty in their recording. Einthoven (1903) recorded the electrical
activity of cardiac muscle by a sensitive string galvanometer. The present day
appliances used for this purpose are an improvement of this early device. A
record of the electrical activity of heart muscle is known as electrocardiogram.
It gives information about the rate, rhythm and conductivity of myocardium.
Clinically the ECG has become an essential investigation for the diagnosis
arrhythmias, conduction defect, myocardial infarction and various other
conditions. Recording of ECG can be obtained by connecting two points from
the body surface to the electrocardiograph. In recent years there has been
considerable improvement in the recording technique, which provides better
information about the myocardial activity.
Bipolar limb leads The potential difference between the two limbs is recorded
by connecting them to the electrocardiograph.
Lead I Right arm and left arm
Lead II
Right arm and left leg
Lead III
Left arm and left leg
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Einthovens Triangle
It is an imaginary equivalent triangle obtained by connecting the three points
used for recording limb leads i.e. right arm, left arm and left leg. The heart is
situated in the middle of this triangle and the ends of the axis indicate the
direction in which electrical activity spreads. Einthoven's law enunciates that
the sum total of voltage from leads I and III is equal to the voltage of lead II.
Unipolar Limb Lead
ِAugmented unipolar limb lead
Augmented leads are of three types, depending on the exploring electrode i.e.
aVR, aVL, aVF.
Precordial Leads
The exploring electrode is placed directly on the chest wall over the heart.
They constitute precordial leads and the electrical activity can be recorded
from six different sites over the chest.(V1,V2,V3,V4,V5,V6).
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Normal electrocardiograph
EGG shows five deflections, out of which three are conventional positive
waves (upward) and two deflections are called negative wave typical EGG
record from limb lead II is given up in figure.
PWave
It is a positive wave and has a duration of 0.1 sec. Its gradual rise indicate
Slow a trial depolarization. A trial repolarization is not recorded in ECG. Since
It blends with the QRS complex.
An inverted 'P' wave is seen in conditions where electrical activity does not
commence at the SA node. This wave may be absent in a trial fibrillation
QRS Waves (Ventricular Complex)
These are due to depolarization of different regions of the ventricular muscle
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They follow P'"wave after an isoelectric period
Q wave is a small negative wave
due to the septal depolarization, it is absent in patent interventricular septum
and may become more prominent in old myocardial infarction
R and S waves indicate the depolarization of ventricular wall. the duration of
QRS complex is about 0.08 sec and it increases .if there is a conduction delay
.in myocardial weakness. these waves are of low voltage
T wave is due to repolarization of ventricular muscle. alteration in T wave
indicate reduced coronary blood flow and infarction
PR interval it is the interval from the commencement of P to the R wave and
indicates the conduction from atria to the ventricle through the bundle of His.
Any prolongation beyond 0.2second indicates first degree heart block
ST segment:-this is an isoelectric period between the end of S wave and the
beginning of T wave. Elevation of ST segment is seen immediately after
myocardial infarction but after a few days the deviation is corrected and
typical T wave abnormality is observed
Echocardiography:-is the use of ultrasound waves to investigate and display
the action of the heart as it beats used in diagnosis and assessment of
congenital and acquired heart disease, it is safe, painless and reliable and
reduces the need for cardiac catheterization
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