Download lecture outline: the heart

LECTURE OUTLINES & REVIEW QUESTIONS
LECTURE OUTLINE: THE HEART
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
CIRCULATORY SYSTEM: HEART
ANATOMY 25 - GUTHRIE
OVERVIEW
Heart divided into four chambers
Two atria (sing. = atrium)
Right & left
Separated by interatrial septum
Receiving chambers
Two ventricles
Right & left
Separated by inteventricular septum
Pumping chambers
Two pumps in series
Right heart
Pulmonary circuit pump
Atrium
Receives systemic venous blood
Low in oxygen; high in carbon dioxide
SVC (superior vena cava)
Capillary beds above diaphragm
IVC
Capillary beds below diaphragm
Coronary Sinus
Capillary beds in heart wall
Ventricle
Pumps blood through lungs
Pulmonary trunk  arteries  capillaries  veins
Left heart
Systemic circuit pump
Atrium
Receives pulmonary venous blood
High in oxygen; low in carbon dioxide
Pulmonary veins (four)
Ventricle
Pumps blood through systemic circuit
Aorta  arteries  capillaries  veins
Valves ensure one way flow through system.
A-V (atrioventricular) valves: atria  ventricles
Semilunar valves: ventricles  arteries
page 1 of 10
LECTURE OUTLINES & REVIEW QUESTIONS
HEART LOCATION & ORIENTATION
Thoracic cavity:
Between lungs
Rests on central tendon of diaphragm.
Most of heart situated to left of midline.
Conical in shape
Apex: 4th or 5th left intercostal space
Base: great vessels
Occupies pericardial cavity; flanked by pleural cavities
THE MEDIASTINUM (middle wall )
“Space” between lungs in pleural cavities
Boundaries:
Anterior: sternum
Posterior T1-T12
Superior: thoracic inlet
Inferior: diaphragm
Divisions:
Superior, anterior, middle, posterior
Major contents:
Superior: great vessels, trachea, esophagus
Anterior: thymus
Middle: Heart & Pericardial cavity
Posterior: esophagus, trachea & bronchi, descending aorta,
pulmonary arteries & veins
PERICARDIA & PERICARDIAL CAVITY
Fibrous pericardium:
Dense ct, adherent to central tendon of diaphragm
Parietal pericardium:
Mesothelium + loose ct. = serous membrane (serosa)
Visceral pericardium (also called epicardium)
Mesothelium + loose ct = serous membrane (serosa)
Pericardial cavity:
Between visceral & parietal pericardia
Contains serous fluid
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
CIRCULATORY SYSTEM: HEART
ANATOMY 25 - GUTHRIE
THE HEART WALL
Superficial to deep:
Epicardium: visceral pericardium
Variable amounts of subepicardial fat
Myocardium: cardiac muscle
Endocardium & subendocardium: endothelium + loose ct
HEART EXTERNAL ANATOMY
Surfaces & Margins:
Surfaces:
Base
Pulmonary (right & left)
Diaphragmatic
Anterior
Margins:
Inferior (acute) & obtuse.
Meet at apex
Anterior Aspect of Heart
In general: ventricles down and to left; atria up and to right
More of right heart visible than left heart
Auricles = ear-shaped parts of the atria.
Anterior interventricular sulcus
Separates ventricles.
Contains coronary vessels and variable fat
Coronary sulcus
Separates ventricles from atria;
Contains coronary vessels and variable fat
Interrupted by pulmonary trunk
Great Vessels (right to left):
SVC (superior vena cava)  top of right atrium
IVC (inferior vena cava)  bottom of right atrium
Ascending aorta leaves left ventricle  aortic arch
Branches of arch:
Brachiocephalic trunk (artery)
Left common carotid
Left subclavian a.
page 2 of 10
LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
Pulmonary trunk leaves right ventricle  pulmonary arteries.
Right pulmonary artery passes under aortic arch
Ligamentum arteriosum:
Band of ct between pulmonary trunk & aortic arch.
Remnant of fetal ductus arteriosus.
Posterior Aspect of Heart
More of left heart visible than right
Long axes of atria oriented at nearly right angles
Right: superior – inferior; left = transverse
Posterior interventricular sulcus
Separates ventricles.
Contains coronary vessels and variable fat
Continuous with anterior interventricular sulcus near apex
Coronary sulcus
Separates ventricles from atria;
Contains coronary vessels and variable fat
Coronary sinus
Expanded vein in part of sulcus below left atrium
Collects blood from cardiac veins.
Empties into right atrium
Great vessels:
SVC & IVC  right atrium
Two left & two right pulmonary veins  left atrium
Pulmonary trunk divides into pulmonary arteries
Right artery passes under arch of aorta on way to right lung
HEART INTERNAL ANATOMY
Ventricles
Separated by interventricular septum
Myocardium much thicker than atrial
Both have same basic structural characteristics
Right Ventricle
Right A-V (atrioventricular, tricuspid) valve
Controls atrioventricular opening (orifice)
Three cusps
Chordae tendineae
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
ANATOMY 25 - GUTHRIE
Connective tissue cords attached to free edges of A-V valve
Papillary muscles
Three nipple-like extensions of myocardium
Chordae tendineae attach to their tips
Trabeculae carneae
Interlacing ridges of myocardium
Pulmonary semilunar valve
Controls ventricular – pulmonary trunk opening
Three crescent-shaped cusps
Moderator band
Band of myocardium in lower part of ventricle.
Stretches between septum and outer wall.
Present in right ventricle only.
U-shaped blood flow through ventricle
Entrance (A-V orifice) and Exit (pulmonary trunk)
at the same level.
Left ventricle
Left A-V (atrioventricular, bicuspid, mitral) valve
Controls atrioventricular opening (orifice)
Twocusps
Chordae tendineae
Connective tissue cords attached to free edges of A-V valve
Papillary muscles
Two nipple-like extensions of myocardium
Chordae tendineae attach to their tips
Trabeculae carneae
Interlacing ridges of myocardium
Aortic semilunar valve
Controls ventricular – ascending aorta opening
U-shaped blood flow
Entrance (A-V orifice) and Exit (ascending aorta)
at the same level.
Myocardium much thicker than right ventricle
No moderator band
page 3 of 10
LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
ANATOMY 25 - GUTHRIE
Atria
Separated by interatrial septum (hard to see in most diagrams)
Myocardium much thinner than in ventricles
Both have same basic structural characteristics
Valve flaps or folds are usually called cusps.
Composition: connective tissue core covered with endocardium
A-V valve cusps are flat sheets with irregular free edges.
Semilunar valve cusps resemble half a tea cup
Right Atrium
Openings:
SVC
IVC + “valve”
“Valve” = crescent-shaped fold of endocardium + ct.
Does not open and close.
Coronary sinus + “valve”
“Valve” = crescent-shaped fold of endocardium + ct.
Does not open and close.
Atrioventricular orifice + right A-V valve
A-V valve cusps
Free edges attached to papillary muscles by chordae tendineae
Three papillary muscles in right ventricle
Two papillary muscles in left ventricle
Left are bigger than right
Fossa ovalis (oval depression)
Oval depression in interatrial septum.
Scar left by closure of foramen ovale, a fetal opening between
the atria
Pectinate muscles
Feather-like ridges of myocardium in auricle and adjacent
part of atrial wall.
Rest of atrial wall is smooth
Left Atrium
Openings:
Pulmonary veins (2 right + 2 left)
Atrioventricular orifice + left A-V valve
No fossa ovalis
Pectinate muscles
Feather-like ridges of myocardium in auricle only.
Rest of atrial wall is smooth
HEART VALVES: A CLOSER LOOK
A-V valves guard openings between atria and ventricles
Semilunar valves guard openings between ventricles and arteries
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
Semilunar valves
Both valves have three cusps.
Dense ct “beak” on free edge
Small depressions in arterial wall just above cusps.
Facilitates closure.
Aortic valve:
Openings of coronary arteries above two of the cusps.
Fibrous skeleton of heart
Connective tissue between atria & ventricles
Somewhat resembles interlocking figure 8’s
Attachment site for valves + myocardium
Valve Function
Ensure one-way flow of blood through heart.
A-V valves
Open:
Allows blood flow from atrium to ventricle
Closed:
Mechanism:
Ventricular myocardium contracts.
Ventricular pressure increases.
Blood pushes on undersides of cusps.
Cusps forcesd together.
Prevents reflux of blood from ventricles to atria during
ventricular pumping phase.
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LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
Prevention of “overclosure” or “blow-back:” Papillary muscles
 chordae tendineae  free edges of cusps
Semilunar valves
Open:
Mechanism:
Ventricular myocardium contracts.
Ventricular pressure increases.
Blood flattens cusps against wall.
Allows blood flow from ventricle into artery
Closed:
Mechanism:
Ventricular myocardium relaxes.
Ventricular pressure decreases.
Ventricular pressure < arterial pressure.
Arterial blood  ventricle.
Valve cusps trap blood, balloon out, make contact.
Prevents backflow from arteries to ventricles.
FIRST & SECOND HEART SOUNDS
First Heart Sound:
Often written as “lubb.” Low pitched; softer
Closure of A-V valves
Second Heart Sound:
Often written as “dupp.” High pitched; louder.
Closure of semilunar valves
Listening to valve sounds on chest wall
Aortic: 2nd intercostal space to right of sternum
Pulmonic: 2nd intercostal space to left of sternum
Tricuspid: 5th intercostal space to right of sternum
Bicuspid: 5th intercostal space to left of sternum
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
ANATOMY 25 - GUTHRIE
CORONARY CIRCULATION
Part of Systemic Circulation
Coronary Arteries: right and left
Only branches of ascending aorta
First branches of systemic circulation (heart takes care of itself)
Run to right or left in coronary sulcus between atria & ventricles
In general:
Right coronary artery branches supply right heart
Left coronary artery branches supply left heart
But variable amounts of overlap
Major Named Branches (most common pattern; variations occur)
Right Coronary Artery:
SA Nodal (right atrium toward SVC and S-A node),
Right marginal (inferior or acute margin)
AV Nodal
Posterior interventricular (posterior interventricular sulcus)
Left Coronary Artery:
Short; divides into:
Circumflex (coronary sulcus to back of heart)
Left marginal (left or obtuse margin)
Posterior left ventricular
Anterior interventricular (toward apex in anterior sulcus)
Diagonal
Cardiac veins:
Most empty into coronary sinus  right atrium
Major Veins:
Small (runs with right marginal a.)
Middle (runs with posterior interventricular a.)
Great (runs with anterior interventricular and circumflex aa.)
Posterior vein of left ventricle (runs with posterior left
ventricular a.)
Anterior cardiac veins  right atrium
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LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
Myocardial Infarction
Collateral Circulation
Alternate circulatory routes
Terminal or end arteries
Sole supply routes
No collateral pathways
Functional end arteries
Potential collateral routes
Not sufficient to compensate for sudden blockage
Coronary arteries = functional end arteries
Blockage  myocardial infarction
CARDIAC MUSCLE: A Quick Review
Branching cells.
Connected end to end by intercalated discs.
One or two nuclei/ cell.
Striations or bands: A, I, Z.
“Myofibrils:” arrays of myofilaments.
Lots of mitochondria.
Intercalated discs look like projecting interlocking fingers.
Transverse parts:
Desmosomes
Fasciae adherentes (elongated tight junctions)
Longitudinal parts: gap junctions (cell to cell communication).
EM:
Thick & thin myofilaments.
Arranged to produce A, I, H, M, Z bands
Sarcoplasmic reticulum around myofibrils.
More tubular than in skeletal muscle.
Meets t-tubules at Z lines.
ANATOMY 25 - GUTHRIE
Anatomy:
S-A (sinu-atrial) node: cluster of cells in right atrial wall adjacent
to SVC termination.
A-V node: cluster of cells at junction of interatrial and
interventricular septa.
A-V bundle:
Bundle of cells leaving A-V node in upper part of
interventricular septum.
Splits into:
Right and left bundle branches.
Travel down interventricular septum to apex, then up outer
ventricular walls towards coronary sulcus.
(In right ventricle, some bundle branch cells run in moderator
band from the interventricular septum to outer wall.)
Purkinje fibers branch off and contact some cardiac muscle
cells.
Function:
All parts of system periodically and automatically fire action
potentials.
But S-A node = “pacemaker”
Fires most frequently and drives rest of system.
S-A node  atrial myocardium (contraction / relaxation)  AV
node  AV bundle  right & left bundle branches:
purkinje fibers  ventricular myocardium (contraction / relaxation)
Not necessary to contact all myocardial cells.
Gap junctions relay action potential from cell to cell
Takes time: Atrial myocardium…interventricular septum to
apex… outer ventricular walls to coronary sulcus.
Heart contraction ~ wringing out a dishrag.
Right heart slightly ahead of left heart.
CONDUCTION SYSTEM
Specialized heart muscle cells.
Assure synchronization of atrial & ventricular filling and pumping.
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
page 6 of 10
LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
CARDIAC CYCLE: PUMPING SEQUENCE & BLOOD
FLOW
Diastole and Systole
Terms usually refer to ventricular activity
Diastole = myocardial relaxation
Systole = myocardial contraction
The Cycle
Diastole: ventricular filling.
Atrial & ventricular myocardium relaxed.
AV valves open. Semilunar valves closed.
Pressure in heart low.
Blood flow:
SVC, IVC, Coronary sinus  right atrium  AV orifice past
open right AV valve  right ventricle
Pulmonary veins  left atrium  AV orifice past open left
AV valve  left ventricle
S-A Node fires  atrial myocardium  atrial contraction (weak)
 final volume of blood forced into ventricles  atrial relaxation
Systole: ventricular contraction
AV node: slight delay, then fires  AV bundle  bundle
branches  purkinje fibers  ventricular myocardia starts to
contract  ventricular volume starts to decrease
intraventricular pressure starts to increase  AV valves close
(first heart sound; prevent reflux into atria)
Action potential continues to spread through ventricular
myocardium  ventricular volume continues to decrease 
intraventricular pressure continues to increase  semilunar valves
open  blood forced into pulmonary trunk and ascending aorta
(arterial walls expand to take blood; elastic tissue stretched).
ANATOMY 25 - GUTHRIE
Ventricular myocardium relaxes  ventricular volume increases
 intraventricular pressure decreases  arterial pressure higher
than ventricular pressure  elastic tissue in arterial walls recoils:
blood forced toward ventricles  semilunar valves close. (2nd heart
sound). AV valves open… Cycle repeats.
HEART INNERVATION
Autonomic Nerves
Sympathetic and Parasympathetic
Match cardiac rate and output to need.
Not necessary for myocardial contraction or synchronization.
Myocardial & conduction system automaticity
Parasympathetic (“decelerator fibers”)
Effects: Decreased heart rate (minor decrease in contractile force +
some coronary arterial constriction)
Pathway:
Medulla: inhibition center neurons  dorsal motor nucleus of
vagus n. vagus nerves (cranial nerves X)  second order
neurons  S-A and A-V node cells
Sympathetic (“accelerator fibers”):
Effects: Increased: heart rate, contractile force, cardiac output.
Pathway: Medulla: excitatory center neurons  first order
sympathetic neurons in lateral grey column of thoracic spinal cord
 thoracic spinal nerves (preganglionic fibers)  second order
neurons in sympathetic chains  sympathetic cardiac nerves
(postganglionic fibers)  S-A and A-V node cells + myocardial
cells
Diastole: ventricular relaxation
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
page 7 of 10
LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
DEVELOPMENT & CONGENITAL DEFECTS
Development:
“Blood islands” develop in mesoderm (18 day embryo)  blood
vessels start to form.
Two endothelial tubes fuse.
Fused tube develops two expansions + arterial and venous ends
Heart folds & rotates.
Interatrial and interventricular septa form.
Great vessels separate
Defects:
Ventricular septal defect
Frequency: ~ 1/500 births
Problem: Upper septal deficiency.
Result: Blood mixes between ventricles.
Transposition of great vessels
Frequency: ~ 1/1000 births
Problem: Aorta from right ventricle & pulmonary trunk from left
ventricle. (Bulbus cordis does not divide properly.)
Result: Unoxygenated blood repeats systemic circuit; oxygenated
repeats pulmonary circuit.
Coarctation of aorta
Frequency: ~ 1/1500 births
Problem: Part of descending aorta narrowed
Result: Increased work load on left ventricle.
Tetralogy of Fallot
Frequency: ~ 1/2000 births
Problem: pulmonary trunk narrowed + pulmonic stenosis +
ventricular septal defect + aorta opens connected to both
ventricles + right ventricular myocardial thickening (due to
overload)
Result: ????
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
ANATOMY 25 - GUTHRIE
Pulmonary stenosis
Frequency: ~ 1/2800 births
Problem: pulmonic valve narrowed.
Result: Decreased blood flow to lungs.
REVIEW QUESTIONS: THE HEART
1.
The anatomical “wall” between the lungs is called the __?__. (a)
pleural cavity (b) peritoneal cavity (c) mediastinum (d)
pericardial cavity (e) none of these
2. The heart occupies the __?__ mediastinum. (a) superior (b)
anterior (c) posterior (d) middle (e) lateral
3. In its normal position, the apex of the heart is located __?__. (a)
to the left of the midline (b) in the fourth or fifth intercostal
space (c) in the cardiac notch of the left lung (d) all of these (e)
none of these
4. The pericardial cavity is located between the __?__ . (a)
myocardium and endocardium (b) parietal and fibrous
pericardia (c) epicardium and parietal pericardium (d)
myocardium and epicardium (e) none of these
5. The muscle of the heart wall is referred to as __?__. (a)
endocardium (b) myoepithelium (c) endothelium (d)
myocardium (e) epicardium
6. The heart is lined with __?__. (a) epicardium (b) visceral
pericardium (c) endocardium (d) myocardium (e) none of these
7. The coronary sulcus is the external boundary between the __?__ .
(a) right and left atria (b) right and left ventricles (c) atria and
ventricles (d) right and left auricles (e) none of these
page 8 of 10
LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
8. The anterior and posterior interventricular sulci of the heart
__?__. (a) mark the external boundaries between the ventricles
(b) overlie the interventricular septum (c) are continuous with
each other near the apex of the heart (d) all of these (e) none of
these
9. Which of the following is not located in the right atrium ? (a)
valve and orifice of the coronary sinus (b) valve and orifice of the
IVC (c) openings of the pulmonary veins (d) orifice of the SVC
(e) fossa ovalis
10. Pectinate muscles __?__. (a) are interlacing ridges of
myocardium (b) are located in the left auricle (c) are located in
the right auricle and adjacent atrial wall (d) all of these (e) none
of these
11. Blood enters the left atrium through the __?__. (a) pulmonary
trunk (b) pulmonary veins (c) inferior vena cava (d) superior
vena cava (e) coronary sinus
ANATOMY 25 - GUTHRIE
17. Papillary muscles are __?__. (a) projections of myocardium (b)
connected to chordae tendineae (c) located in the ventricles (d)
contract during systole to control the A-V valves (e) all of these
18. __?__ are interlacing ridges of myocardium located in the
ventricles. (a) pectinate muscles (b) papillary muscles (c)
trabeculae carneae (d) chordae tendineae (e) none of these
19. Which of the following can be found only in the right ventricle ?
(a) papillary muscles (b) trabeculae carneae (c) chordae
tendineae (d) moderator band (e) myocardium
20. The aortic semilunar valve is located between the __?__ and the
__?__. (a) left ventricle, ascending aorta (b) right ventricle,
pulmonary trunk (c) right ventricle, conus arteriosus (d) left
ventricle, aortic arch (e) left atrium, left ventricle
12. The right atrium receives blood from the __?__. (a) IVC (b)
SVC (c) coronary sinus (d) all of these (e) none of these
21. The pulmonary semilunar valve is located between the __?__ and
the __?__. (a) left ventricle, ascending aorta (b) right ventricle,
pulmonary trunk (c) right ventricle, conus arteriosus (d) left
ventricle, aortic arch (e) left atrium, left ventricle
13. The tricuspid valve is located between the __?__ and the __?__.
(a) pulmonary trunk, right ventricle (b) ascending aorta, left
ventricle (c) right ventricle, right atrium (d) left ventricle, left
atrium (e) right atrium, left atrium
22. During ventricular diastole, the semilunar valves prevent the
backflow of blood from the __?__. (a) atria to ventricles (b)
ventricles to atria (c) aorta and pulmonary trunk to the ventricles
(d) ventricles to the aorta and pulmonary trunk (e) none of these
14. The valve between the left atrium and the left ventricle is called
the __?__ . (a) left A-V (b) mitral (c) bicuspid (d) all of these
(e) none of these
23. The semilunar valves consist of __?__ cusps. (a) 2 (b) 3 (c) 4
15. The left A-V valve has __?__ cusps (= flaps) and the right A-V
valve has __?__. (a) 2, 2 (b) 3, 3 (c) 2, 3 (d) 3, 2 (e) none of
these
16. Chordae tendineae __?__. (a) are attached to the free edges of
the A-V valves (b) are attached to papillary muscles (c) are
located in the ventricles (d) all of these (e) none of these
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
24. The fibrous skeleton of the heart is __?__. (a) located between
the atria and the ventricles (b) an attachment site for the
semilunar and atrioventricular valves (c) is an attachment site for
the myocardium (d) all of these (e) none of these
25. Which heart chamber has the thickest myocardium ? (a) left
ventricle (b) right ventricle (c) left atrium (d) right atrium
page 9 of 10
LECTURE OUTLINES & REVIEW QUESTIONS
CIRCULATORY SYSTEM: HEART
26. The right ventricle pumps blood into the __?__. (a) pulmonary
trunk (b) pulmonary veins (c) IVC (d) SVC (e) ascending
aorta
27. Blood leaves the left ventricle through the __?__. (a) thoracic
aorta (b) aortic arch (c) pulmonary trunk (d) ascending aorta
(e) abdominal aorta
28. If you traced a volume of blood through the circulatory system
beginning at the IVC, through which heart chamber would it
pass thirdly ? (a) right ventricle (b) left atrium (c) left ventricle
(d) right atrium
29. The first heart sound is caused by the __?__. (a) closure of the
semilunar valves (b) opening of the semilunar valves (c) closure
of the A-V valves (d) opening of the A-V valves (e) contact of
the heart apex with the rib cage
30. The second heart sound is caused by the __?__. (a) closure of the
semilunar valves (b) opening of the semilunar valves (c) closure
of the A-V valves (d) opening of the A-V valves (e) contact of
the heart apex with the rib cage
31. The left coronary artery branches into __?__ arteries. (a) anterior
and posterior descending (b) circumflex and posterior
descending (c) marginal and circumflex (d) circumflex and
anterior descending (e) none of these
32. The right coronary artery terminates as the __?__ artery. (a)
marginal (b) anterior interventricular (c) posterior
interventricular (d) circumflex (e) nodal
33. The __?__ cardiac vein runs with the posterior interventricular
branch of the right coronary artery. (a) small (b) middle (c)
great (d) none of these
ANATOMY 25 - GUTHRIE
35. Nearly all of the veins draining the heart wall empty into the
__?__. (a) SVC (b) IVC (c) coronary sulcus (d) coronary sinus
(e) anterior cardiac veins
36. If you traced a volume of blood from the ascending aorta
through the right coronary artery, which artery would it be least
likely to go through ? (a) circumflex (b) posterior
interventricular (c) marginal (d) superior venal caval (nodal)
37. The S-A node of the heart's conduction system __?__. (a) is
located in the right atrium (b) is the normal pacemaker of the
heart (c) is located near the SVC (d) is connected to the A-V
node by internodal tracts (e) all of these
38. The A-V node of the heart's conduction system __?__. (a) is
located at the junction of the interatrial and interventricular
septa (b) sends impulses into the common A-V bundle (c) is
driven by impulses from the S-A node (d) all of these (e) none
of these
39. Purkinje fibers __?__. (a) are modified cardiac muscle cells in
the heart's conduction system (b) are also called pectinate
muscles (c) are also called trabeculae carneae (d) are the same as
papillary muscles (e) none of these
40. If you traced an impulse through the heart's conduction system,
through which of the following listed structures would it pass
thirdly ? (a) Purkinje fibers (b) common A-V bundle (c) S-A
node (d) A-V node (e) right and left bundle branches
41. If you traced an impulse through the heart's conduction system,
through which of the following listed structures would it pass
last ? (a) Purkinje fibers (b) common A-V bundle (c) S-A node
(d) A-V node (e) right and left bundle branches
34. The __?__ cardiac vein runs with the anterior interventricular
and circumflex branches of the left coronary artery. (a) small (b)
middle (c) great (d) none of these
Anat25.LORQ.CirculatorySystem:Heart.mguthrie
page 10 of 10