Chapter 20: The Heart

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Chapter 20 The Heart
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How are the cardiovascular system and heart
organized?
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• The Pulmonary Circuit
• Carries blood to and from gas exchange surfaces
  of lungs
• The Systemic Circuit
• Carries blood to and from the body

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3 Types of Blood Vessels

• Arteries
• carry blood away from heart
• Veins
• carry blood to heart
• Capillaries
• networks between arteries and veins

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4 Chambers of the Heart

• Right atrium
• collects blood from systemic circuit
• Right ventricle
• pumps blood to pulmonary circuit
• Left atrium
• collects blood from pulmonary circuit
• Left ventricle
• pumps blood to systemic circuit

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Figure 201
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Where is the heart located and what are its
general features?
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• Located directly behind sternum in mediastinum
• Between 2 pleural cavities
• Surrounded by pericardial sac

Figure 202a
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Figure 202b
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• Great vessels at base
• Pointed tip is apex
• atria
• superior receiving chambers
• ventricles
• inferior pumping chambers
• Internal partitions separate chambers
• Interatrial septum
• Interventricular septum

Figure 203
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What is the structure and function of the
pericardium?
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2 Layers of Pericardium

• Parietal pericardium
• outer layer
• forms inner layer of pericardial sac
• fibrous tissue that surrounds and stabilizes
  heart
• Visceral pericardium
• inner layer of pericardium
• called epicardium

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• Pericardial cavity
• Is between parietal and visceral layers
• contains pericardial fluid
• Pericarditis
• An infection of the pericardium

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Figure 202c
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What are the layers of the heart wall?
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3 Layers of the Heart Wall

• Epicardium
• outer layer
• Myocardium
• middle layer
• Endocardium
• inner layer

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Figure 204
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What is the path of blood flow through the heart,
and what are the major blood vessels, chambers,
and heart valves?
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Atria

• receiving chambers
• push blood to ventricles
• relatively small, thin walled
• when empty, atria have wrinkled flap
• auricle
• inside the atria ridges of muscles on wall
• pectinate muscles
• on inner wall
• fossa ovalis

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• Blood enters right atrium through three veins
• Superior vena cava
• Inferior vena cava
• Coronary sinus
• Blood enters the left atrium through four
  pulmonary veins

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Ventricles

• pumping chambers of the heart
• right ventricle pumps blood into pulmonary trunk
• left ventricle pumps blood into aorta
• Right ventricle wall is thinner, develops less
  pressure than left ventricle

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Left and Right Ventricles

• Left ventricle has a greater workload
• more massive but the two chambers pump equal
  amounts of blood

Figure 207
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• internal walls of the ventricles have irregular
  muscle ridges
• Trabeculae Carneae
• papillary bundles
• stalk-like muscle bundles that play a role in
  valve function

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• One-way valves prevent backflow during
  ventricular contraction
• Two pairs of valves
• Atrioventricular valves
• Semilunar valves
• Valves open and close depending on blood pressure

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Cusps

• Fibrous flaps that form bicuspid (2) and
  tricuspid (3) valves
• Free edges attach to chordae tendineae extending
  from papillary muscles of ventricle
• Prevent valve from opening backward

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Right Atrioventricular (AV) Valve

• Also called tricuspid valve
• Opening from right atrium to right ventricle
• Has 3 cusps
• Prevents backflow of blood during ventricular
  contraction

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Left Atrioventricular (AV) Valve

• Also called mitral or bicuspid valve
• Opening from left atrium to left ventricle
• Has 2 cusps
• Prevents backflow of blood during ventricular
  contraction

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Semilunar Valves

• Pulmonary and aortic tricuspid valves
• Prevent backflow from pulmonary trunk and aorta
  into ventricles
• Have no muscular support
• 3 cusps support like tripod

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Figure 208
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Internal Anatomy
Figure 206a
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Pathway of blood through heart

• The Pulmonary Circuit
• Carries blood to and from gas exchange surfaces
  of lungs
• The Systemic Circuit
• Carries blood to and from the body

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• Oxygen poor blood enters the right atrium via the
  vena cavae
• Blood flows from right atrium to right ventricle
  through the right (AV) valve
• Blood flows from right ventricle to pulmonary
  trunk through pulmonary valve
• Pulmonary trunk divides into left and right
  pulmonary arteries leading to the lungs

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• Oxygen rich blood returns from lungs through left
  and right pulmonary veins
• Pulmonary veins deliver to left atrium
• Blood from left atrium passes to left ventricle
  through left atrioventricular (AV) valve
• Left ventricle contracts pushing blood into the
  aorta through the aortic semilunar valve

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How is the heart supplied with blood?
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Blood Supply to the Heart

• Coronary circulation

Figure 209
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• Coronary arteries and cardiac veins
• Supply blood to muscle tissue of heart
• Right Coronary Artery
• Supplies blood to
• right atrium and portions of both ventricles
• Left Coronary Artery
• Supplies blood to
• left ventricle, left atrium, interventricular
  septum

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Cardiac Muscle Cells
Figure 205
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Characteristics of Cardiac Muscle Cells

• Striated
• Small size
• Single, central nucleus
• Interconnections between cells
• Intercalated discs

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• Intercalated discs
• interconnect cardiac muscle cells
• secured by desmosomes
• linked by gap junctions
• convey force of contraction
• propagate action potentials