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13.0 HEART
Upon completion of this lecture, students will be able to:
a)
Define and use properly the following words: Heart, Endocardium, Endothelium,
Subendocardium, Myocardium, Epicardium, Pericardium, Atria, Ventricle, Mesothelium,
Fibroelastic, Cardiac skeleton, Fibrous rings, annulus fibrosi, Trigone, Cardiac valves,
Cardiac conduction, Chordae tendinea, Purkinje fibers, Glycogen, Intercalated discs,
Sinoatrial node, Atrioventricular node, Atrioventricular bundle, Bundle of His.
a)
Describe and associate basic structure/function for the following: all structures listed
above; why Purkinje fibers appear as they do in histology sections, the cardiac
conduction system, compare endocardium and myocardium in the atria versus the
ventricles
b)
Identify by microscopy: Heart, Endocardium, Endothelium, Subendocardium,
Myocardium, Epicardium, Pericardium, Atria, Ventricle, Mesothelium, Fibroelastic,
Cardiac skeleton, Fibrous rings, annulus fibrosi, Trigone, Cardiac valves, Chordae
tendinea, Purkinje fibers, Glycogen, Intercalated discs.
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HEART
I.
LAYERS OF THE HEART (T.intima; T. media; T. adventitia)
A. ENDOCARDIUM (T. intima)
1. Location: Inner surface
2. Structure: Endothelium + dense connective tissue (CT) (fibroelastic)
3. Relative thickness: thinner than myocardium; Thicker in atria than ventricles
4. Subendocardium: blood & lymph vessels, nerves, conducting system
B. MYOCARDIUM (T. media)
1. Structure: Cardiac muscle + CT
2. Relative thickness: Thickest layer but thinner in atria
C. EPICARDIUM (T. adventitia)
1. Visceral pericardium:
2. Structure: Mesothelium + fibroelastic CT
3. blood vessels, autonomic nerves, fat
II.
CARDIAC SKELETON
A. The fibrous connective tissue base onto which the atrial and ventricular musculature and
the cardiac valves insert.
B. Consists of: Four dense FIBROUS RINGS
1. CT (annulus fibrosi)
2. surrounding the atrioventricular openings
3. and the origins of the aorta and pulmonary artery
4. The interventricular septum consists of collagen fibers
C. TRIGONE
1. dense connective tissue between the AV opening and the base of the aorta
2. continuous with the fibrous rings.
D. Species variation
1.
2.
3.
4.
III.
Pig & cat: dense irregular CT
Dog: fibrocartilage
Horse: hyaline cartilage
Young Ruminants: bone
CARDIAC VALVES
A. Structure:
1. fold of endocardium;
2. core of dense CT (with elastin);
3. continuous with fibrous rings
B. Chordae tendinea continuous with the endocardium of the cardiac valves
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IV.
CARDIAC CONDUCTION SYSTEM (Modified cardiac muscle fibers)
A. PURKINJE FIBERS
1. Subendocardial connective tissue area
2. fewer myofibrils (more space within each cell)
3. glycogen & mitochondria numerous
4. no intercalated discs; but desmosomes and gap junctions
5. can be bi-nucleate
B. Sinoatrial node (SA node)
1. normal pacemaker (Atria to ventricles)
C. Atrioventricular node (AV node)
1. receives the impulse from the SA node and sends to ventricles through AV
bundles
D. Atrioventricular bundle (fibers merge to form "Bundle of His")
1. "Bundle of His" branches to form left & right bundles (Purkinje fibers) along the
septum
2. Purkinje fibers are found in subendocardium & extend into the myocardium
V.
BLOOD SUPPLY
A. Coronary arteries
1. thick, often with longitudinal bundles of muscle
2. supply dense capillary network
3. originate with the aortic arch
B. Capillary Network
1. supplies myocardium, epicardium, heart skeleton, valves
C. Venules and Veins
1. collect blood from capillaries
2. open into the right atrium
D. Heart Lymph vessels
1. capillaries in connective tissue (can become very prominent & appear engorged)
2. usually parallel with blood vessels
3. more lymph vessels in epicardium
VI.
NERVE SUPPLY
A. Extensive plexuses in the sinoatrial and atrioventricular nodes
B. Sensory fibers in myocardium and epicardium
C. Autonomic innervation
1. Parasympathetic supplies only the SA node, atria, & AV node
2. Sympathetic innervation supplies the entire heart
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