Physio Heart

7/28/2019 Physio Heart

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Heart Muscle

Right Heart

pumps the blood

through the lungs

Left Heart pumps

the blood through

the peripheral

organs


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Basic Anatomy

Interatrial septum

Interventricular septum

Tricuspid valve

Bicuspid valveSemilunar valves

What happens when the

right or left ventricle

weakens?

What causes the

characteristic lub-dub

sound?


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Pulmonary Circuit

involves the rightventricle which pumps

deoxygenated blood to

the lungs

Systemic Circuit

involves the left ventricle

and the remainder of the

arteries, capillaries and

veins of the body

Coronary circulationsupplies blood to the

myocardium (right and

left coronary arteries)


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Embolusclot

Ischemia - blood

deficiency in myocardial

cells

Angina pectoris - chest

pain that accompanies

ischemia

Myocardial infarction

heart attack


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Sinoatrial node or pacemaker

typically depolarizes

spontaneously at the rate of70-80 times per minute,

causing the atria to contract

Impulses from SA Node pass

to the Atrioventricular Node,Atrioventricular bundle and

finally to the conduction

myofibers or Purkinje fibers


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Innervation of the Heart

Sympathetic impulses

accelerate heart action

Parasympathetic

impulses decelerate

heart action


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Cardiac CycleDiastole phase of

relaxation

Systole phase of

contraction

LATE DIASTOLE. Atria and ventricles are relaxed. AV valves are open, and the

semilunar valves are closed. Blood is flowing from the atria to the ventricles,

with 65% to 75% of ventricular filling occurring before the end of this phase.


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relaxation

Systole phase of

contraction

ATRIAL SYSTOLE. The atria contract and pump the additional 25% to 35% of

the blood into the ventricles.


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relaxation

Systole phase of

contraction

VENTRICULAR SYSTOLE. At the beginning of the ventricular contraction, the

AV valves close, causing the first lub sound. Semilunar valves open and

ventricular ejection begins. (70-90 mL/beat = stroke volume)


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relaxation

Systole phase of

contraction

EARLY DIASTOLE. As the ventricles begin to relax, the pressure drops rapidly.

The semilunar valves close, preventing the backflow into the ventricles

causing the second dub sound. Then, AV valves open and blood begins toflow from atria to the ventricles.


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CARDIAC OUTPUT = stroke volume X heart rate

Note:

Normal heart rate is 55 to 90 beats per minute


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SITES OF CARDIAC

AUSCULTATION


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Electrocardiogram (ECG)

Depolarization of the atria

Ventricular repolarization


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P atrial depolarization

QRS ventricular depolarization

T ventricular repolarization


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ARRHYTHMIA refers to deviations from normal heart rate or from

normal electrical activity of the conduction system.

a. Rate Arrhythmia

Bradycardia slow heart rate of fewer than 55 bpm which may

be caused by excessive vagal (parasympathetic) stimulation,

decreased body temperature or certain drug

Tachycardia a rapid heart rate of more than 90 bpm, may be

caused by excessive sympathetic stimulation, increased body

temperature or drugs such as caffeine

b. Conduction Arrhythmia

Abnormal rhythmicity of the SA node

Shift of pacemaking function from the SA node to another part

of the heart (ectopic pacemaker or ectopic focus) may be

caused by ischemia or localized heart damage, dilation of atriadue to hypertension, toxic irritants like nicotine, caffeine,

alcohol; lack of sleep, anxiety, extremes in body temperature,

departures from normal body pH

Abnormal pathway or blockage of impulses in the conduction

system


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Physiology of Cardiac MuscleTHREE TYPES OF CARDIAC MUSCLE

1. Atrial Muscle

2. Ventricular Muscle

3. Specialized excitatory and conductive muscle fibers. Contract only

weakly because they contain few contractile fibers, instead, they

exhibit rhythmicity and varying rates of conduction, providing anexcitatory system for the heart

Contract in much the same way as skeletal

muscle except that the duration of contraction

is much longer


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Physiologic Anatomy of Cardiac Muscle

Figure 1. Structure of the heart and course of blood flow

through the heart chambers

Cardiac Muscles are

striated muscles

Cardiac Muscles have

typical myofibrils that

contain actin and myosin

filaments almost identical

to those found in skeletal

muscles

Filaments in cardiac

muscles interdigitate and

slide along each otherduring contraction in the

same manner as occurs in

skeletal muscle


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Physiologic Anatomy of Cardiac Muscle

Figure 2. (a) micrograph of heart muscle tissue (b) cardiac

muscle tissue showing intercalated disks

CARDIAC MUSCLE AS A SYNCYTIUM

Intercalated discs cell membranethat separate individual cardiac

muscle cells from one another

Cell membranes fuse with one

another in such a way that they form

permeable communicatingjunctions (gap junctions) that allow

relatively free diffusion of ions

ATRIAL SYNCYTIUM

[action potentials can be conductedfrom AS to VS by way of the

atrioventricular (A-V) bundle]

VENTRICULAR SYNCYTIUM


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Action Potential in Cardiac Muscle


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EVENT ASSOCIATED IN ACTION POTENTIALGENERATION

a. Stimulus (chemical-electrical-mechanical) is sufficientto alter the resting membrane potential of a particularregion of the membrane

b. The membranes permeability to sodium ions increasesat the point of stimulation

c. Sodium ions rapidly move into the cell through themembraned. As sodium ions move into the cell, the transmembrane

potential reaches zero (the membrane becomes locallydepolarized)

e. Sodium ions continue to move inward, and the inside ofthe membrane becomes positively charged relative tothe outside (reverse polarization)

f. Reverse polarization at the original site of stimulationresults in a local current that acts as a stimulus to theadjacent region of the membrane.


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g. At the point originally stimulated, the membranespermeability to sodium decreases, and its permeabilityto potassium increases.

h. Potassium ions rapidly move outward, again makingthe outside of the membrane positive in relation to the

inside (repolarization)i. Sodium and potassium pumps transport sodium ionsback out of, and potassium ions back into, the cell.


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g. At the point originally stimulated, the membranespermeability to sodium decreases, and its permeabilityto potassium increases.

h. Potassium ions rapidly move outward, again makingthe outside of the membrane positive in relation to the

inside (repolarization)i. Sodium and potassium pumps transport sodium ionsback out of, and potassium ions back into, the cell.

(RESTING MEMBRANE POTENTIAL)Note: the resting membrane potential of normalcardiac muscle is about -85 to -95 mV and about -90 to -100 mV in the specialized conductive fibers

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