Download Cardiac Muscle

The Heart
• THE HEART IS RESPONSIBLE FOR THE CIRCULATION OF
THE BLOOD.
• The heart is actually two pumps in one:
• 1. one propels blood through the pulmonary
circulation (to the lungs where the blood releases
carbon dioxide and receives oxygen)
• 2. the second propels blood through the systemic
circulation (to all remaining tissues of the body).
ANATOMY OF THE HEART
• Located in the thoracic cavity
between the lungs in a space
within the mediastinum called the
pericardial cavity
• The blunt end of the cone is the
apex
• The flat top is the base.
• The heart is a muscular pump
consisting of four chambers: two
atria and two ventricles
Base
Apex
•
Pericardium
The pericardium or pericardial sac, is a doublelayered closed sac that surrounds the heart
• fibrous pericardium tough, fibrous connective tissue
outer layer prevents over-distention of the heart and
anchors the heart in the mediastinum
• serous pericardium. a thin, transparent inner layer
of simple squamous epithelium
• parietal pericardium The portion of the serous
pericardium lining the fibrous pericardium
• visceral pericardium or epicardium that portion
covering the heart surface
• (The parietal and visceral portions of the serous
pericardium are continuous with each other where
the great vessels enter or leave the heart)
• pericardial cavity between the visceral and parietal
pericardia is filled with a thin layer of serous
pericardial fluid that helps reduce friction
Cardiac Muscle
• Intercalated disks- has cell to cell special
contacts
• Desmosomes- hold cells close together
• Gap Junctions- low electric Resistance between
cells…greater conductivity
• Therefore cardiac cells act as a single unit
electrically
Conducting System Process
1.
SA Sinoatrial Node- pacemaker of heart (generates action potentials
greater frequency)
–
.04 faster than to surrounding muscle
2.
AV Atrioventricular Node- Slow to transmit action potential and
allows completion of atrial contraction
3.
AV Bundle of His
–
Fast
4.
Bundle branches- right and left
1.
2.
3.
5.
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IV Septum
Rt Ventrical apex
Lt Ventrical apex
Perkinje Fibers- large diameter cardiac muscle
–
Transmits signal to apex of ventricles
–
A lot of intercalated disks
Myocardium in apex contracts in a wringing action
Autorhymicity of Cardiac Muscle
•
Action potentials in heart without external stimuli
1.
2.
3.
4.
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After each action potential the membrane potential returns to its
resting membrane potential
Unstable slow ion channels open and cause depolarization
This causes fast channels to open and increase depolarization
When depolarization reaches threshold--action potential happens
more often in SA Node because more slow channels
Plateau Phase- Prolonged period of depolarization,
separates contractions in the heart
Heart has long action potential so the heart will rest
between contractions and not tetanic contractions
Absolute refractory period – CM insensitive to further
stimuli
EKG
• Electrokardiogram- device to record the action potential of cardiac
muscle summation
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Cannot detect force of contraction
Cannot detect Blood Pressure
Can detect abnormal heart rates/ rhythems
Can detect abnormal conduction pathways
Can detect hypertrophy and atrophy and relative position of damage
• P Wave- Action potential depolarization of atrial myocardium
– Causes Atrial contraction
• QRS Complex- Ventricular depolarization
– Causes onset of ventricular contraction
– Also atrial repolarization masked by QRS signal
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T Wave- repolarization before ventricular relaxation
PQ/PR Interval- .16 sec- atria contract and relax
QT Interval- .3 sec- ventricles contract and relax
1 Cardiac Cycle- from onset muscle contraction to next
Heart Sounds
• First heart sound
– “Lubb”- ventricles contact and both AV valves
close
• Second heart sound
– “Dupp”- semilunar valves close at end of
ventricular systole
• Systole is between first and second sounds.
• Diasole is between second and first sounds.
Blood Pressure
•
•
•
•
Systolic- to contract
Diastolic- to dialate
Refers to ventricles
120 systolic / 80 Diastolic
Normal
72 beats/min
X 70 ml/beat
5040 ml/min=5 L/min
Exercise
120 beats/min
X 200 ml/beat
24,000 ml/min=24 L/min
Systole
1.
2.
3.
4.
Isometric Contraction – Contraction of the ventricle
causes A-V valves to close and pressure to build in
heart.
Ejection – Ventricular pressure exceeds the pressure
in the pulmonary trunk and aorta and the semilunar
valves open to expel the blood.
At around 80mm Hg pressure aortic SLV opens and
goes up to 120mm Hg.
At end of systole ventricular volume dropw because
the heart runs out of blood.
Diastole
•
Isometric Relaxations
1.Back flow of blood closes semilunar valves.
2.Pressure drops and AV values open
3.Blood rushes into ventricles from atria.
4.Cardiac Reserve- difference between cardiac
output at rest and exercise.
Blood Pressure
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Procedure
Center the bladder over the Brachial Artery just medial to the
biceps tendon. Apply snugly and securely
Check the palpatory systolic pressure first
Inflate to 20 to 30 mm Hg above the palpatory systolic
Place bell of stethoscope over the brachial artery
Deflate the cuff slowly (2 to 3 mm Hg per sec.) and note the points
where the following occurs:
Two consecutive beats are heard typically crisps sounding
(indicates systolic pressure)…recorded as auscultatory systolic
pressure
A muffling of the pulse sounds recorded as mid-diastolic point.
The point at which the sounds begin to fade away.
The sound disappears- (indicates peripheral resistance of
arteries)…recorded as end-diastolic pressure.
• Ischemia (is-ke'me-ah), - lack of an adequate
blood supply to the heart may lead to
fibrillation—
MYOCARDIAL INFARCTION
• A myocardial infarct is an area of heart tissue
in which the cardiac cells have died
• it is generally a result of ischemia.
• Ischemia (is-ke'me-ah), is lack of an adequate
blood supply to the heart
• Abnormalities in the shape of the waves and changes
in their timing send signals that something may be
wrong with the intrinsic conduction system or may
indicate a myocardial infarct (present or past).
HEART BLOCK
• any damage to the AV node can partially or totally
release the ventricles from the control of the SA
node.
• the ventricles begin to beat at their own rate, which is
much slower, some or all of the time
• Sn: depolarization waves can reach the ventricles
only by traveling through the AV node.
HEART RATE ANOMALIES
• Tachycardia is a rapid heart rate (over 100
beats per minute).
• Bradycardia is a heart rate that is substantially
slower than normal (less than 60 beats per
minute).
• Neither condition is pathological, but prolonged
tachycardia may progress to fibrillation.
FIBRILLATION
• fibrillation—a rapid uncoordinated shuddering of the
heart muscle
• makes the heart totally useless as a pump and is a
major cause of death from heart attacks in adults.
• During fibrillation, the normal pattern of the ECG is
totally lost, and the heart ceases to act as a
functioning pump.
• Abnormalities in the shape of the waves and changes in their timing send
signals that something may be wrong with the intrinsic conduction system or
may indicate a myocardial infarct (present or past).
• A myocardial infarct is an area of heart tissue in which the cardiac cells have
died; it is generally a result of ischemia.
• During fibrillation, the normal pattern of the ECG is totally lost, and the heart
ceases to act as a functioning pump.
• Because the atria and ventricles are separated from one another by
"insulating" connective tissue, which is part of the fibrous skeleton of the
heart, depolarization waves can reach the ventricles only by traveling
through the AV node. Thus, any damage to the AV node can partially or
totally release the ventricles from the control of the SA node. When this
occurs, the ventricles begin to beat at their own rate, which is much slower,
some or all of the time. This condition is called heart block,
• damage to the SA node results in a slower heart rate. When this is a
problem, artificial pacemakers are usually installed surgically.
• Ischemia (is-ke'me-ah), or lack of an adequate blood supply to the heart
may lead to fibrillation—a rapid uncoordinated shuddering of the heart
muscle makes the heart totally useless as a pump and is a major cause of
death from heart attacks in adults.
• Tachycardia is a rapid heart rate (over 100 beats per minute).
• Bradycardia is a heart rate that is substantially slower than normal (less
than 60 beats per minute).
• Neither condition is pathological, but prolonged tachycardia may progress to
fibrillation.