Heart Lab

Front 1

The heart is an approximately cone shaped organ about the size of a person's ------

Back 1

fist

Front 2

The heart is located in the +++++++ which is the region of the thoracic cavity between the 2 _______. It is surrounded and protected by the ______

Back 2

mediastinum
lungs
Pericardium

Front 3

The sternum is +++++ to the heart and the thoracic vertebrae are _____.

Back 3

anterior
posterior

Front 4

The pointed ___ of the heart tilts slightly to the left side of the body and touches the ______

Back 4

apex
diaphragm

Front 5

The broad base of the heart is located beneath the 2nd ____

Back 5

rib

Front 6

The pericardium is composed of an outer fibrous membrane and a double walled serous membranous sac, The fibrous pericardial membrane is attached to the ______ and to the large blood vessels that are attached to the heart.

Back 6

diaphragm

Front 7

The pericardial serous membrane is composed of an outer parietal and an inner ____layer. The cavity between the two pericardial serous membranes is called the ---------cavity and it is filled with serous fluid. Both the fibrous membrane and the parietal serous membrane of the pericardium are attached to each other and they form the _____ pericardium. However, the visceral peridcardial membrane is visceral pericardium that covers cardiac muscle and is regarded as the outermost region of the heart.

Back 7

visceral
pericardial
parietal

Front 8

The heart chambers are the right and left ++++ that are superior to the right and left ventricles. Each atrium has a sac=like extension known as an ______ that increases its internal volume. The two atria form the base of the heart and the tip of the left ventricle forms the ____

Back 8

atria
auricle
apex

Front 9

A coronary sulcus or groove exists between the atria and the ++++++ of the heart. This sulcus accomodates fat and branches of blood vessels that serve the heart ____. These blood vessels are the coronary ++++ that drains the heart wall and branches of the coronary artery that supply the heart wall with ______

Back 9

ventricles
wall
blood

Front 10

An anterior interventricular sulcus and a posterior interventricular sulcus indicate the exterior lines of demarcation between the left and right ++++++. These sulci contain fat as well as branches of the coronary arteries and cardiac veins.

Back 10

ventricles

Front 11

The base of the heart is associated with the great blood vessels of the pulmonary and systemic circulatory systems. These great vessels are the: aorta, pulmonary +++++, inferior vena cava, superior vena cava, as ell as two left and two right pulmonary veins.

Back 11

trunk

Front 12

The aorta conducts ______ blood away from the left ventricle. The pulmonary trunk leads deoxygenated blood away from the right +++++

Back 12

oxyegenated
ventricle

Front 13

The inferior and superior vena cavae allow deoxygenated blood from all the systems of the body to flow into the right ++++. The pulmonary veins allow oxygenated blood from the left and right lungs to flow into the left ____

Back 13

atrium
atrium

Front 14

The aorta has 3 notable sections : the ascending aorta, through which oxygenated blood flows +++++, the aortic arch that curves towards the posterior region of the +++++, and the descending aorta that runs downwards along the posterior body wall. Arteries that supply the upper regions of the body with blood branch from the aortic ____

Back 14

upwards
thorax
arch

Front 15

A short band of connective tissue know as the ligamentum arteriosum connects the pulmonary ____ to the ____.

Back 15

trunk
aorta

Front 16

The ligamenutum +++++++ is a vestigial structure that was derived after birth from a fetal blood vessel known at the ductus arteriosus.

Back 16

arteriosum

Front 17

The ductus arteriosus allows blood to bypass the dysfunctional developing lungs of the ____

Back 17

fetus

Front 18

The heart has cavities of the right and left ___ that are superior to cavities of the right and left ventricles.

Back 18

atria

Front 19

A wall that is composed of ____layers forms the outer boundary of each cavity in the heart. Epicardium is the outtermost layer. _____ is the middle muscular layer. _____ is the cardiac muscle that forms most of the heart. Epicardium is the inner most layer of heart wall and visceral ++++++. Endocardium is the endothelium that lines the chambers and valves of the heart.

Back 19

3<BR>myocardium<BR>myocardium<BR>pericardium

Front 20

Myocardium is the muscular middle layter and ______ is the inner most layter of the heart's wall. Epicardium is visceral pericardium. Myocardium is the cardiac muscle that forms most of the heart. Endocardium is the _____that lines the chambers and valves of the heart.

Back 20

endocardium
endothelium

Front 21

Valves in the heart ensure one-way flow of blood thru the atria and _____. Each AV valve is attached by tendinous cords called ______ tenineae to papillary muscles on the floor of the ventricles.

Back 21

ventricles
chordae

Front 22

The tricuspid valve exists between the right atrium and right ventricle. While the mitral or _____ valve lies between the left atrium and left ventricle.

Back 22

bicuspid

Front 23

Pulmonary and aortic ______ valves respectively located at the entrance ot the pulmonary trunk and the entrance to the aorta. The pulmonary trunk is attached to the left ventricle and it transports blood to all the systems of the body.

Back 23

semilunar

Front 24

The right and left atria are separated by the ______ septum. The anterior surface of the interior wall of the right atrium has ridged pectinate muscles and the interior wall of the right atrium of an adult heart has a slight oval depression known as the ____ _____.

Back 24

interatrial
fossa ovalis

Front 25

An opening called the fossa ovalis occupies a similar position in the herat of the _____. This opening allows blood to shunt between the right and left ____ in order to bypass the developing fetal lungs.The foramen ovale usually reduces its diameter as a newborn baby gasps and it eventually becomes occluded with connective tissue. The inner walls of the ventricles contain prominent ridges of cardiac muscle that are known as trabeculae _____.

Back 25

fetus
atria
carnae

Front 26

There are 2 pathways of pumping blood: the systemic and pulmonary ______

Back 26

circuits

Front 27

The heart beats rhythmically throughout a person's lifetime and it pumps blood thru ___ pathways in the body: the systemic and _____ circuit. The left ventricle of the heart pumps ______ blood thru the aorta and other arteries of the systemic circuit to organs in each system of the body. Unlike arteries of the pulmonry circuit, the systemic ____ conduct deoxygenated blood away from organs of each system of the body to the right atrium.

Back 27

2
pulmonary
oxygenated
veins

Front 28

In contrast to the left ventricle, the right ventricle pumps deoxygenated blood through the ______ circuit to the lungs. Specifically, the right ventricle pumps deoxygenated blood through the ______ trunk into left and right pulmonary +++++ that conducts blood to the left and right lungs. Unlike pulmonary arteries, the pulmonary veins channel ______ blood away from the left and right lungs to the left atrium of the heart.

Back 28

pulmonary
pulmonary
arteries
oxygenated

Front 29

Systemic circulation of the blood occurs when the myocardium in the walls of the ____ ventricle contract pumping oxygenated blood into the aorta and through the branching arteries that channel blood to tissues and all organs except the _____. It is important to note that systemic circulation includes coronary circulation by which blood flows to and from the _____ in the heart wall.

Back 29

left
lungs
myocardium

Front 30

Systemic arteries eventually branch into microscopic ______ that allow exchange of food, respiratory gases, and excretory substances to occur between blood and tissues. Capillaries merge into the systemic veins that conduct ______ blood to the right atrium. Contraction of myocardium in the walls of the right atrium pump deoxygenated blood thru the right AV valve or _______ valve into the left ventricle so that systemic circulation can occur.

Back 30

capillaries
oxygenated
tricuspid

Front 31

Pulmonary circulation of blood occurs when the myocardium in the walls of the ____ ____ contract and pump _____ blood thru the pulmonary _____ valve into the pulmonary trunk and thru the pulmonary arteries that lead blood directly to the 2 lungs. Pulmonary arteries eventually branch into microscopic capillaries that surround alveoli or thin=walled air sacs, in the lungs. These capillaries allow gaseous exhange to occurr between blood and _____. At the venous end, pulmonary capillaries merge into pulmonary veins that allow oxygenated blood to flow into the left atrium. Contractions of the myocardium in the walls of the left atrium pump the oxygenated blood thru the left AV valve or biscuspid or mitral valve into the left ventricle so that systemic circulation can occur.

Back 31

right ventricle
deoxygenated
semilunar
alveoli

Front 32

Coronary circulation occurs thru the coronary arteries and cardiac ++++. Right and left coronary arteries branches channel oxygenated blood to the posterior aspect of the ventricles and lateral regions of the heart. The main branches of the right coronary artery are the posterior interventricular artery and the _____ artery. The left coronary artery has branches that supply the anterior side of the ventricles and the lateral aspect of the psterior region on the left side of the heart with +++++ blood. The principal branches of the left coronary artery are the _____ interventricular artery and the circumflex artery. The great cardiac vein, middle cardiac vein, and small cardiac vein drain blood from the myocardium into the coronary sinus. Blood that flows thru the coronary sinus eventually empties blood into the right atrium.

Back 32

veins
marginal
oxygenated
anterior interventricular

Front 33

The 2 layers of the heart are the visceral and _____. The visceral is attached to the heart and = the epicardium.

Back 33

parietal

Front 34

The wall of the heart = epicardium, the outter layer, the +++++, and the inner layer or _______.

Back 34

myocardium
endocardium

Front 35

The r and L atria are the receiving chambers and teh r and L ventricles are the _____ chambers.

Back 35

ejecting

Front 36

Valves between the atrium and ventricles are called atrioventricular valves or tricuspid (right) and _____ (left) valves.

Back 36

bicuspid

Front 37

The tricuspid and bicuspid AV valves are attached to tendons called the chordae tendineae, which are attached to triangular muscles called _____ muscles.

Back 37

papillary

Front 38

The _____ tendineae pull the valves open from right atrium to left ventricle

Back 38

chordae

Front 39

The chordae tendineae anchor the cusps of the ____ valves to the ventricular walls. Holds the positions of the flaps from the valves. Helps prevent _____ flow of blood.

Back 39

backward

Front 40

The ______ septum divides the right and left sides of the heart. The right side contains +++++ blood, and the left side contains oxygenated blood.

Back 40

interatrial
deoxygenated

Front 41

Difference between artery and vein: Artery is _____ and vein _____. The only exception is the pulmonary artery and vein.

Back 41

oxygenated
deoxygenated

Front 42

Both the ____ _____ ____and the Inferior Vena Cava bring impure blood to the heart.

Back 42

Superior Vena Cava

Front 43

Artery away from the heart and _____ toward the heart except pulmonary.

Back 43

vein

Front 44

The superior vena cava is above the diaphragm and the inferior vena cava is below the ++++++

Back 44

diaphragm

Front 45

The right atrium carries deoxygenated blood. R atrium contracts and blood goes to the right ventricle. This blood will eject to the pulmonary ______. The pulmonary trunk is actually the pulmonary artery.

Back 45

trunk

Front 46

The pulmonary trunk or artery carries ________ blood wihch is purified in the lungs. Right sides carries impure blood.

Back 46

deoxygenated

Front 47

Blood purified in _______veins. From pulmonary vein go to L atrium. Then to Left ventricle. Main artery of L ventricle is the Aorta.

Back 47

pulmonary

Front 48

The Pulmonary Circuit Right ventricle to pulmonary trunk to pulmonary _____ to lobar arteries to _____ capillary beds to venules to pulmonary veins to left atrium

Back 48

arteries
alveolar

Front 49

The systemic circulation begins with the ascending aorta. The head and neck receive blood from the common _____ and vertebral arteries. The upper limbs receive blood from the _______ arteries.

Back 49

carotid
subclavian

Front 50

Blood goes from lungs to pulmonary artery. R pulmonary and R ____ and L pulmonary and L +++++

Back 50

lung
lung

Front 51

Semilunar valves are located at the beginning of pulmonary artery and aorta. They close in diastole due to back pressure of the blood in the corresponding arteries, once the systolic _____ force from the ventricle stops.

Back 51

ejection

Front 52

The AV valves separate the atria and _____. They close in systole with the force generated by the blood of the ventricle due to ______ of the ventricle.

Back 52

ventricles
contraction

Front 53

The muscle of the left ventricle is 2-3 times thicker than that of the right, although the size of the ____ is about the same as the right.

Back 53

cavity

Front 54

The tricuspid and bicuspid valves stop the back ___ from the ventricles to the ___. On the left bicuspid and the right is ______.

Back 54

flow
atria
tricuspid

Front 55

The functions of the heart valves is to prevent backflow of blood into the heart during the period of time where the heart doesn't beat (_____) and to segment the heart into chambers.

Back 55

diastole

Front 56

The tricuspid valve is located between the right ++++ and the right ventricle.

Back 56

atrium

Front 57

The pulmonary valve is located between the right ventricle and the ______ artery.

Back 57

pulmonary

Front 58

The mitral or ______ valve is located between the left atrium and the left ventricle.

Back 58

bicuspid

Front 59

The aortic valve is located between the left _____ and the aorta.

Back 59

ventricle

Front 60

The semi lunar valve is located between the right ventricle and the pulmonary artery. It opens in a ventricular systole, when the pressure in the right ventricle falls rapidly, the pressure in the pulmonary artery will close the pulmonary valve. Prevents backflow of blood from right +++++ to pulmonary artery.

Back 60

ventricle

Front 61

The pulmonary and aortic semi lunar valves regulate blood flow between the ventricles and the great +++++

Back 61

arteries

Front 62

The AV valves, the tricuspid and mitral valves, regulate opening between the atria and ______

Back 62

ventricles

Front 63

The pulmonary semi lunar valve is involved with the _____ ventricle, and the aortic semi lunar valve and the ____ ventricle.

Back 63

Right
Left

Front 64

The AV valves open when atrial pressure is less than _______ pressure.

Back 64

ventricular

Front 65

The AV valves are forced to close by blood in the ventricles when the ventricular pressure rises above the ____pressure.

Back 65

atrial

Front 66

The pulmonary semilunar valves are forced to ____ and blood ejected when the ventricular pressure is _____than the pressure in the arteries.

Back 66

open
greater

Front 67

Semilunar valves{ When the ventricular pressure is less than the arterial pressure, the blood holds the valve _____.

Back 67

closed

Front 68

When the atrial pressure is greater than the ventricular pressure, the AV valve will ++++

Back 68

opens

Front 69

When the ventricular pressure is greater than the atrial pressure, the AV valve will ____

Back 69

close

Front 70

When the ventricular pressure is greater than the arterial pressure, the semilunar valve will _____

Back 70

open

Front 71

When the arterial pressure is greater than the ventricular pressure, the semilunar valve will ++++

Back 71

close

Front 72

The heart is enclosed in a double-walled sac called the +++++. The outer wall or pericardial sac is also the ++++ pericardium. The parietal pericardium has a deep, fibrous layer of irregular connective tissue and a deep, thin serous layer. The serous layer forms the epicardium or _____ pericardium

Back 72

pericardium
parietal
visceral

Front 73

Between the parietal and visceral membranes is a space called the ______ cavity. It contains the pericardial fluid which allows the heart to beat with minimal friction of the membranes.

Back 73

pericardial

Front 74

The 3 layers of the heart wall are: epicardium, ++++++++, and endocardium. The epicardium is simple squamous over ______ tissue. The endocardium lines the interior of the _____ chambers. Its simple squamous over areolar.

Back 74

myocardium
areolar
heart

Front 75

The myocardium is the ++++++ layer of the heart wall and performs the most work.

Back 75

thickest

Front 76

Cardiac muscle cells are known as cardiac ______

Back 76

myocytes

Front 77

The superior chambers are the right and left _____ or receiving chambers. Each atrium has a small earlike extension called an _______

Back 77

atria
auricle

Front 78

The two inferior chambers eject blood into the arteries or
_______. The right ventricle is the most anterior part of the heart. The left ventricle forms the _____ and interior posterior aspect.

Back 78

apex

Front 79

The atria are separated by the +++++++ septum. The interventricular septum is a more muscular wall between the +++++++

Back 79

interatrial
ventricles

Front 80

The internal ridges of the ventricles are the trabeculae ++++++

Back 80

carneae

Front 81

The ends of the cell are slightly branched and through the branches, each cardiocyte contacts several others to form a network.
b. One network is in the ____and another network is in the ventricles.

Back 81

atria

Front 82

The nucleus is centrally located; the sarcoplasmic _____ is less developed than in skeletal muscle and lacks terminal cisternae.

Back 82

reticulum

Front 83

The sarcoplasmic reticulum does have footlike sacs associated with the T tubules, which are much larger than in skeletal muscle.
ii. These T tubules admit calcium ions to activate muscle _______.

Back 83

contraction

Front 84

Cardiocytes have especially large _______

Back 84

mitochondria

Front 85

Cardiocytes are joined end to end by thick connections called i_______discs, which are complex steplike structures with three distinctive features compared to skeletal muscle.

Back 85

intercalated

Front 86

The heartbeat is coordinated by a cardiac ______system composed of an internal pacemaker and nervelike conduction pathways through the myocardium. (pp. 732–733)

Back 86

conduction

Front 87

a. (1) The sinoatrial (SA) node, a patch of modified cardiocytes in the right atrium, initiates each ______t and determines the heart rate.

Back 87

heartbeat

Front 88

(2) Signals from the SA node spread throughout the ____

Back 88

atria

Front 89

The atrioventricular ____ node, located near the right AV valve at the lower end of the interatrial septum, acts as an electrical gateway to the ventricles; the fibrous skeleton prevents currents from getting to ventricles by any other route.

Back 89

AV

Front 90

d. (4) The atrioventricular (AV) ______ (bundle of His) is the pathway by which signals leave the AV node; it forks into the right and left bundle branches that enter the interventricular septum and descend toward the apex.

Back 90

bundle

Front 91

(5) Purkinje fibers, nervelike processes, spread upward throughout the ventricular myocardium and distribute the electrical ______ to cardiocytes of the ventricles.

Back 91

excitation

Front 92

When the Purkinje fibers have delivered the signals, the cardiocytes themselves perpetuate it by passing ion flows from cell to cell via _____junctions.

Back 92

gap

Front 93

The heart does receive both _______ and parasympathetic nerves that modify heart rate and contraction strength. (p. 733)

Back 93

sympathetic

Front 94

The sympathetic pathway to the heart originates in the lower cervical to upper thoracic segments of the spinal _____

Back 94

cord

Front 95

Cardiocytes are joined end to end by thick connections called intercalated discs, which are complex steplike structures with three distinctive features compared to skeletal ______

Back 95

muscle

Front 96

Interdigitating folds. The plasma membrane is folded somewhat like the bottom of an egg carton, and the folds interlock with those of ______ cells.

Back 96

adjoining

Front 97

Mechanical junctions. The cells are tightly joined by two types of junctions: the fascia _______ and desmosomes.

Back 97

adhesions

Front 98

The fascia adherens is the most extensive and is a band in which actin of thin myofilaments is anchored to the plasma membrane and the cells are linked via transmembrane ______

Back 98

protein

Front 99

Desmosomes interrupt the fascia ______ here and there; these are weldlike mechanical junctions between cells.

Back 99

adherens

Front 100

Electrical junctions. The intercalated discs contain gap junctions that allow the flow of ions between cardiocytes, enabling coordinated contraction of each network of _______

Back 100

cardiocyts

Front 101

______ muscle contains satellite cells that can divide, but cardiac muscle does not; the repair of damaged cardiac muscle is almost entirely by fibrosis (scarring).
a. A limited capacity for myocardial mitosis and regeneration was discovered in 2001.

Back 101

skeletal

Front 102

In terms of ________cardiac muscle depends almost exclusively on aerobic respiration to make ATP. (p. 732)
1. Cardiac muscle is rich in myoglobin, a short-term source of stored oxygen.
2. Its huge mitochondria fill about 25% of the cell, compared to 2% of skeletal muscle fibers that have smaller mitochondria.

Back 102

metabolism

Front 103

_____ muscle is adaptable to fuel source, getting about 60% of its energy from fatty acids, 35% from glucose, and 5% from other fuels such as ketones, lactic acid, and amino acids.
4. It makes little use of anaerobic fermentation and is not prone to fatigue, but it is vulnerable to oxygen deficiency.

Back 103

cardiac

Front 104

The ______t is coordinated by a cardiac conduction system composed of an internal pacemaker and nervelike conduction pathways through the myocardium. (pp. 732–733)

Back 104

heartbeat

Front 105

The cardiac conduction system generates rhythmic electrical signals in the following order. (Fig. 19.12)
a. (1) The sinoatrial (SA) node, a patch of modified cardiocytes in the right atrium, initiates each heartbeat and determines the ______.

Back 105

heart rate

Front 106

The cardiac conduction system generates rhythmic electrical signals in the following order. (Fig. 19.12)
a. (1) The sinoatrial (SA) node, a patch of modified cardiocytes in the right atrium, initiates each heartbeat and determines the ______.
2) ______ from the SA node spread throughout the atria.
c. (3) The atrioventricular (AV) node, located near the right AV valve at the lower end of the interatrial septum, acts as an electrical gateway to the ventricles; the fibrous skeleton prevents currents from getting to ventricles by any other route.
d. (4) The atrioventricular (AV) bundle (bundle of His) is the pathway by which signals leave the AV node; it forks into the right and left bundle branches that enter the interventricular septum and descend toward the apex.
e. (5) Purkinje fibers, nervelike processes, spread upward throughout the ventricular myocardium and distribute the electrical excitation to cardiocytes of the ventricles.
3. When the Purkinje fibers have delivered the signals, the cardiocytes themselves perpetuate it by passing ion flows from cell to cell via gap junctions.

Back 106

signals

Front 107

Contraction of the heart is called ______ and relaxation is diastole.
B. The sinus rhythm, triggered by the SA node, is a cycle of 70–80 bpm in adults, although rates of 60–100 bpm are not unusual. (pp. 733–734)

Back 107

systole

Front 108

3. Any abnormal cardiac rhythm is called ______a. One cause of arrhythmia is a heart block, the failure of any part of the cardiac conduction system to transmit signals.
b. It is usually a result of disease and degeneration of conduction system fibers.
i. A bundle branch block is due to damage to one or both bundle branches.
ii. Damage to the AV node causes total heart block, in which signals from the atria fail to reach the ventricles, which then beat at their intrinsic rhythm of 10 to 40 bpm.

Back 108

arrhythmia

Front 109

C. The cells of the SA node do not have a stable resting _____; instead their membrane potential starts at about –60 mV and drifts upward in a gradual depolarization called the pacemaker potential. (p. 734) (Fig. 19.13)
1. The slow drift results from a slow inflow of Na+ without a compensating outflow of K+.
2. When the pacemaker potential reaches –40 mV, voltage regulated fast calcium–sodium channels open, and both ions flow in from the extracellular fluid.
a. This produces the rising phase of the action potential, which peaks at slightly above 0 mV.
b. At this point, K+ channels open and K+ leaves the cell, bringing about repolarization.
c. K+ channels then close and the cycle begins again.

Back 109

potenitial

Front 110

3. Each depolarization of the SA node sets off ____heartbeat; at rest, the SA node typically fires every 0.8 second or so, or 75 bpm.
D. Impulse conduction to the myocardium begins when the SA node fires. (pp. 734–735)
1. Firing of the SA node excites atrial cardiocytes, stimulating atrial contraction.
2. The signal travels at 1 m/sec through the atrial myocardium and reaches the AV node in about 50 msec.
3. In the AV node, the signal slows down to about 0.05 m/sec.
a. The slowing is primarily due to fewer gap junctions in cardiocytes in this region.
b. The signal is delayed for about 100 msec, which allows the ventricles to fill.
4. The ventricular myocardium has a conduction speed of only 0.3 to 0.5 m/sec, but signals travel through the AV bundle and Purkinje fibers at a speed of 4 m/sec.

Back 110

one

Front 111

5. As a result, the entire ventricular myocardium _______ within 200 msec after the SA node fires, causes contraction of the ventricles in near unison.
6. Signals reach the papillary muscles before the rest of the myocardium, so that these take up slack in the tendinous cords an instant before ventricular contraction.
7. Ventricular systole begins at the apex of the heart and moves upward, pushing blood toward the semilunar valves.

Back 111

depolarized

Front 112

7. Ventricular systole begins at the ____of the heart and moves upward, pushing blood toward the semilunar valves.
E. The action potentials of cardiocytes are significantly different from those of neurons and skeletal muscle fibers. (pp. 735–736) (Fig. 19.14)
1. Cardiocytes have a stable resting potential of –90 mV and normally depolarize only when stimulated, unlike SA node cells.
2. A stimulus opens voltage-regulated sodium gates, allowing Na+ inflow and depolarization of the cell to threshold.
3. The threshold voltage opens more Na+ gates and triggers a positive feedback cycle.
4. The action potential peaks at nearly +30 mV, at which point the Na+ gates close quickly.
5. As action potentials spread over the membrane, they open voltage-regulated slow calcium channels that admit Ca2+.
a. The Ca2+ binds to ligand-regulated calcium channels on the sarcoplasmic reticulum (SR), opening them and releasing Ca2+ from the SR.
b. This second wave of Ca2+ binds to troponin and triggers contraction just as in skeletal muscle.
c. The SR provides 90% to 98% of the Ca2+ needed for myocardial contraction.
6. In cardiac muscle the depolarization is prolonged for 200 to 250 msec, as compared to 2 msec in skeletal muscle and neurons.
a. This long plateau in the action potential may result because Ca2+ channels are slow to close, or because SR is slow to remove Ca2+.
7. As long as the action potential is in its plateau, the cardiocytes contract.
a. Cardiac muscle does not have the brief twitch of skeletal muscle, but a more sustained contraction for blood expulsion.
b. Both atrial and ventricular cardiocytes exhibit plateaus, but they are more pronounced in the ventricles.
8. At the end of the plateau, Ca2+ channels close and K+ channels open; membrane voltage drops rapidly and muscle tension declines soon afterward.
9. Cardiac muscle has an absolute refractory period of 250 msec, compared with 1 to 2 msec in skeletal muscle, preventing wave summation and tetanus.

Back 112

apex

Front 113

A cardiac cycle consists of ____ complete contraction and relaxation of all four heart chambers. (p. 739)
B. Certain principles of pressure and flow apply to movement of a fluid. (pp. 740–741)
1. A fluid is a state of matter that can flow in bulk from place to place, including both liquids and gases.
2. Fluid dynamics is the term for principles that govern flow.
3. The main variables are pressure, which impels a fluid to move, and resistance, which opposes flow.
4. Pressure is measured by a device called a manometer.
a. Typically this is a J-shaped glass tube partially filled with mercury.
b. The sealed end, above the mercury, contains a vacuum, and the lower end is open.
c. Pressure applied at the lower end is measured in terms of how high it can push the mercury column up the tube.
d. Thus pressures are expressed in millimeters of mercury (mm Hg).
5. Blood pressure is usually measured with a sphygmomanometer, which has its open end attached to an inflatable pressure cuff that is wrapped around the arm.. (Fig. 18

Back 113

one

Front 114

Blood pressure is usually ______ with a sphygmomanometer, which has its open end attached to an inflatable pressure cuff that is wrapped around the arm.. (Fig. 18.20a)
6. Flow occurs when a fluid is subjected to more pressure at one point than at another, which creates a pressure gradient.
a. Fluids always flow down their pressure gradients.

Back 114

measured