A

1
A PTHE HEART

• CHAPTER 12

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THE HEART

• BEGINS TO BEAT IN THE EMBRYO AT 4 WEEKS
• BEATS AN AVERAGE OF 100,000 TIMES EACH DAY
• IMAGINE SQUEEZING A TENNIS BALL 70 X A MINUTE!
• ITS FUNCTION IS TO PUMP BLOOD THROUGH THE
  ARTERIES, CAPILLARIES VEINS

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STRUCTURE OF THE HEART

• Located in the thoracic cavity between the lungs
  - mediastinum
• Fig 12-1
• Enclosed by the 3 layered pericardial membranes
• outer pericardium
• parietal pericardium
• visceral pericardium
• Serous fluid in middle

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LAYERS OF THE HEART

• ENDOCARDIUM
• lines the chambers of the heart, very smooth
  to prevent blood clotting
• MYOCARDIUM
• the thickest, middle layer that makes up the
  walls of the chambers
• EPICARDIUM
• outer layer next to the pericardial membranes

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HEART STRUCTURE

• Divided into four chambers
• Right and left upper chambers are called ATRIA
• Right and left lower chambers are called the
  VENTRICLES

• The atria are separated by the interatrial septum
• The ventricles are separated by the
  interventricular septum

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RIGHT ATRIUMfig 12-2

• Receives deoxygenated blood from the superior and
  inferior vena cava.
• Blood flows from right atrium through the
  atrioventricular valve or tricuspid valve into
  the right ventricle

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RIGHT VENTRICLE

• Receives blood from the right atrium
• When this ventricle contracts it sends blood to
  the lungs through the pulmonary semilunar valve,
  into the pulmonary artery
• While in the lungs co2 is exchanged for 02

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LEFT ATRIUM

• Receives oxygenated blood from the lungs via the
  4 pulmonary veins
• Blood flows from the left atrium into the left
  ventricle through the left atrioventricular valve
  also called the mitral valve or the bicuspid valve

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LEFT VENTRICLE

• Walls are thicker than in the right ventricle
• Pumps more forcefully
• The blood goes through the aortic semilunar valve
  and then enters the aorta
• The aorta which is the largest artery of the
  body then sends blood throughout the body

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FOUR VALVES

• Valves of the heart prevent backflow of blood
  into the previous chamber or the lungs
• In the right ventricle there are special muscles
  called papillary muscles

• Right ventricle also has fibrous connective
  tissue called chordae tendineae that prevent the
  tricuspid valve from inverting allowing a
  backflow of blood

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CORONARY VESSELS fig 12-4

• Right left coronary arteries supply blood to
  the heart 1st before blood goes anywhere else in
  the body
• If one of these arteries becomes clogged it
  deprives blood from the heart muscle or it
  becomes ischemic

• Prolonged ischemia can cause an area of necrotic
  tissue called an infarct
• another name for this is a myocardial infarction
  or MI

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CARDIAC CYCLE-fig 12-5

• The sequence of events in one heartbeat is called
  the cardiac cycle
• Systole is when the chamber contracts
• Diastole is when the chamber relaxes

• Atrial systole or contraction is followed by
  ventricular systole and vice versa
• These mechanical events keep blood moving from
  the veins through the heart into the arteries
• Blood flows passively from the atria to the
  ventricles but all blood must be actively pumped
  by the ventricles

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HEART SOUNDS

• Two sounds per heart beat lub-dup
• Lub sound created by closure of the AV valves
  during ventricular systole
• Dup sound created by closure of the aortic
  pulmonary semilunar valves
• Murmurs- improper closing of a valve produces a
  murmur

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CONDUCTION SYSTEM-fig 12-6

• Sinoatrial (SA) node is the natural pacemaker of
  the heart with a rate of 60-80 beats/min
• The stimulus moves into the atrioventricular or
  AV node with a natural beat of 50-60 beats/min

• Next the impulse moves to the Bundle of His,
  which if it initiates the heart beat would be
  only 15-40 beats/minute
• Goes to the right and left bundle branches then
  into the
• Purkinje fibers
• An EKG depicts the electrical activity of the
  heart

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CONDUCTION

• Arrhythmias are irregular heartbeats which can be
  harmless or life threatening
• Palpitations are an irregular heart beat that a
  person can actually feel. It is usually due to
  too much caffeine, nicotine, alcohol, or
  emotion/panic attacks
• Ventricular fibrillation is when the ventricles
  are beating very rapidly uncoordinated. no
  blood can be pumped when they do this

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HEART RATE table 12-2

• Normal heart rhythm is called a sinus rhythm
• Rate of lt 60 is bradycardia
• Rate of gt 100 is tachycardia
• Normal heart rate varies with age physical
  condition

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CARDIAC OUTPUT Table 12-2

• The amount of blood pumped by a ventricle in one
  minute
• Stroke volume-amount of blood pumped by a
  ventricle per beat average is 60-80ml
• Cardiac output stroke volume x pulse average
  resting is 5-6 liters per minute
• Starlings law of the heart the more cardiac
  muscle fibers are stretched, the more forcefully
  they contract like a rubberband that is
  stretched let go. It retracts with more force
  the further out it is stretched
• Ejection fraction - the percentage of its total
  blood that a ventricle pumps during systole
  average is 60 to 70

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REGULATION OF THE HEART RATE

• Heart muscle generates its own beat
• Medulla contains 2 cardiac centers accelerator
  inhibitory centers
• Pressoreceptors in the carotid aortic sinuses
  detect changes in BP
• Chemoreceptors in the carotid aortic bodies
  detect changes in the oxygen content of the blood
• They cause the heart to speed up or slow down,
  depending on the bodys needs at the time

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THE HEART OF THE ELDERLY

• Cardiac muscle becomes less efficient
• Decrease in strength of contraction
• Blood supply may be compromised by
  atherosclerosis of the coronary arteries
• Abnormal rhythms may occur
• HTN may cause enlargement of the left ventricle