Download Document

Chapter 12
The Heart
Location, Size, and
Position of the Heart
 In mediastinum
 2/3 to the left of the body midline
 Apex = point

Most inferior portion
 Shape and size of a closed fist
 Septum divides right and left sides
(internally)
Pericardium
 Two-layered fibrous sac

Inner layer = visceral pericardium or epicardium

Outer layer = parietal pericardium
 Pericardial cavity is filled with pericardial fluid

Approximately 15-30 ml pericardial fluid present
Three layers of the Heart Wall

Epicardium
Outer layer
 Connective tissue


Myocardium
Middle layer
 Thick
 Muscle


Endocardium
Inner layer (lining)
 Very thin, smooth

Summary of layers
 Outside (external) to Inside (internal)
Parietal Pericardium
 Pericardial cavity (filled with fluid)
 Visceral Pericardium/Epicardium
 Myocardium
 Endocardium

Anatomy of the Heart
 Heart chambers
 Two upper chambers are
Right and left atria (atrium)
 Small chambers
 Receive blood


Two lower chambers called ventricles
Right and left ventricles
 Larger chambers
 Pump blood out of heart

Vessels
 Pulmonary Arteries
 Carry blood from R ventricle to lungs
 R pulmonary artery to R lung
 L pulmonary artery to L lung
 Pulmonary Veins
 Carry blood from lungs to L atria
 R pulmonary veins from R lung
 L pulmonary veins from L lung
Vessels cont.
 Vena Cava
 Inferior and superior
 Empties blood into heart from body
Valves

Cuspid valves
Tricuspid: between right atrium and ventricle
 Bicuspid (mitral): between left atrium and ventricle
 Open and close from chordae tendineae


Semilunar valves
Pulmonary Semilunar: base of pulmonary arteries
 Aortic Semilunar: base of aorta
 Open and close from pressure within heart

The 4 valves
The heart is where
pulmonary
circulation starts
and ends.
The valves support
1-way movement
through the heart.
The heart
acts as two
pumps
Right atrium and
ventricle pump
deoxygenated
blood to the lungs
Left atrium and
ventricle pump
oxygenated blood
to the body
Sequence of
Blood Flow
Heart Sounds
 Two distinct heart sounds in every heartbeat or
cycle—“lubb-dupp”
 First (lubb) sound is caused by the vibration and
closure of AV valves during contraction of the
ventricles
 Second (dupp) sound is caused by the closure of
the semilunar valves during relaxation of the
ventricles
Heart Actions
 Contraction is called systole
 Relaxation is called diastole
 These actions create Blood Pressure
Practical Application
 Supposed an individual was injured by falling off a
roof and he severely damaged his right arm with
copious blood loss. His blood pressure steadily
dropped to dangerous levels. How would you
explain the drop in his blood pressure?
Continued
 In response to the drop in blood pressure, the heart
begins beating more rapidly. The increase in HR
increases overall blood flow and thus causes even
more rapid blood loss from a wound. The more
blood lost, the faster the heart beats and the faster
blood volume is lost. How can you explain this?
What type of feedback is this?
Cardiac Cycle
 Heart beat is regular and rhythmic—each complete
beat called a cardiac cycle—average is about 72
beats per minute
 Each cycle, about 0.8 seconds long, subdivided into
systole (contraction phase) and diastole (relaxation
phase)
Cardiac Cycle
 Stroke volume is the volume of blood ejected from
one ventricle with each beat
 Cardiac output is amount of blood that one
ventricle can pump each minute—average is about
5 L per minute at rest
 Benefit of exercise!
Conduction System of the Heart

SA (sinoatrial) node
The pacemaker
 In wall of right atrium near superior vena cava


AV (atrioventricular) node


AV bundle (bundle of His)


In the floor of right atrium near septum
Located in the septum of the ventricle
Purkinje fibers—
Located in the walls of the ventricles
 Cause contraction of myocardium

Conduction System of the Heart
 Electrocardiography
 Measures the electrical impulses that result in contraction of
the heart
 Impulses transformed into visible tracings by a machine called
an electrocardiograph
 The visible tracing of these electrical signals is called an
electrocardiogram or ECG
Conduction System of the Heart

The normal ECG has three deflections or waves called the P
wave, the QRS complex, and the T wave
 P wave—associated with depolarization of the atria
 QRS
complex—associated with depolarization of the
ventricles
 T wave—associated with repolarization of the ventricles
Issues with the heart’s conduction system





Bradycardia—slow heart rate (under 60 beats/min)
Tachycardia—rapid heart rate (over 100 beats/min)
Sinus dysrhythmia—variation in heart rate during breathing
cycle
Premature contraction (extrasystole)—contraction that occurs
sooner than expected in a normal rhythm
Fibrillation—condition in which cardiac muscle fibers are “out
of step,” producing no effective pumping action
Chronic diseases of the heart
Coronary Circulation and Coronary Heart
Disease
 Blood, which supplies oxygen and nutrients to the
myocardium of the heart, flows through the right and
left coronary arteries
 Blockage of blood flow through the coronary arteries
can cause myocardial infarction
CHD
 Atherosclerosis (type of “hardening of arteries” in
which lipids build up on the inside wall of blood
vessels) can partially or totally block coronary blood
flow
 Angina pectoris—chest pain caused by inadequate
oxygen to the heart
Heart Failure
 Heart failure—inability to pump enough returned
blood to sustain life; it can be caused by many
different heart diseases
 Right-sided heart failure—failure of the right side of
the heart to pump blood, usually because the left side
of the heart is not pumping effectively
Heart Failure
 Left-sided heart failure (congestive heart failure)—
inability of the left ventricle to pump effectively,
resulting in congestion of the systemic and
pulmonary circulations
 Diseased hearts can be replaced by donated living
hearts (transplants) or by artificial hearts (implants),
although both procedures have yet to be perfected