Modul Dyspneu

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COMPLETE REPORT

MODUL Dypsnoe

Scenario 1

System Cardiovaskular

1A Group

Maria Ulfah (1102090049) Irfan Thamrin (1102090056) Rizki Rahmadhan (1102090063) Akhmad Edwin Indra Pratama (1102090064) Fakhrurrazi (1102090065) Muh. Fadly Aditya (1102090070)

Muhammad Assadul Malik (1102090072) Inna Mthmainnah Musa (1102090084) Andi Firman Mubarak (1102090088) Ainun Martoni (1102090093) Andi Fajar Apriani (1102090106) Dzul Ikram (1102090108) Zarah Alifani Dzulhijjah (1102090115) Sigit Dwi Pramono (1102090133) Andi Anugrah Suci (1102090142)Nur Sabriany Lihawa (1102090156)

FAKULTAS KEDOKTERAN

UNIVERSITAS MUSLIM INDONESIA

2010


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A. SCENARIOB. ANATOMY

Position

Left : linea medioclavicularis

sinistra

Right : linea parasternalis

dextraTop : intercostal II

Bottom : intercostal V


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Morphology

ApexA part of left ventricle

Position :

-intercostalis space 5 kiri

- 9 cm from left mediana line

- 2 fingers left medioclavicularis line in medial site

BasisTop : craniodorsal in the left orientationBuilt by:

- some parts of left and right atrium

- proximal part of large blood vessels

sternocostalis facies sinister diaphragmatica facies

Walls layers :

Epicardium (outher)


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Myocardium (middle) Endocardium (inner)

Chembers of the heart:

Right atriumThe right atrium receives the superior vena cava in its upper and posterior part, the

inferior vena cava and coronary sinus in its lower part, and the anterior cardiac vein

(draining much of the front of the heart) anteriorly.Running more or less vertically

downwards between the venae cavae is a distinct muscular ridge, the crista

terminalis (indicated on the outer surface of the atrium by a shallow groovethe

sulcus terminalis). This ridge separates the smooth-walled posterior part of the

atrium, derived from the sinus venosus, from the rough-walled anterior portion

which is prolonged into the auricular appendage and which is derived from the true

fetal\atrium. The openings of the inferior vena cava and the coronary sinus are

guarded by rudimentary valves; that of the inferior vena cava being continuous withthe annulus ovalis around the shallow depression on the atrial

Right ventricle

The right ventricle is joined to the right atrium by the way of the vertically disposed

tricuspid valve, and with the pulmonary trunk through the pulmonary valve. A

muscular ridge, the infundibuloventricular crest, between the atrioventricular and

pulmonary orifices, separates the inflow and outflow tracts of the ventricle. The

inner aspect of the inflow tract path is marked in the presence of a number of

irregular muscular elevations (trabeculaecarneae) from some of which the papillary

muscles project into the lumen of the ventricle and find attachment to the freeborders of the cusps of the tricuspid valve by way of the chordae tendineae. The

moderator band is a muscular bundle crossing the ventricular cavity from the

interventricular septum to the anterior wall and is of some importance since it

conveys the right branch of the atrioventricular bundle to the ventricular muscle.

The outflow tract of the ventricle or infundibulum is smooth-walled and is directed

upwards and to the right towards the pulmonary trunk. The pulmonary orifice is

guarded by thepulmonary valves, comprising three semilunar cusps.

Left atrium

The left atrium is rather smaller than the right but has somewhat thicker walls. On

the upper part of its posterior wall it presents the openings of the four pulmonary

veins and on its septal surface there is a shallow depression corresponding to the

fossa ovalis of the right atrium. As on the right side, the main part of the cavity is

smooth-walled but the surface of the auricle is marked by a number of ridges due to

the underlying pectinate muscles.

Left ventricle

The left ventricle communicates with the left atrium by way of the mitral (so-called

because it vaguely resembles a bishops mitre), which possessesa large anterior and

a smaller posterior cusp attached to papillarymuscles by chordae tendineae. With

the exception of the fibrous vestibule immediately below the aortic orifice, the wall


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of the left ventricle is marked by thick trabeculae carneae. The aortic orifice is

guarded by the three semilunar cusps of the aortic valve, immediately above which

are the dilated aortic sinuses. The mouths ofthe right and left coronary arteries are

seen in the anterior and left posteriorsinus respectively.

The conducting system of the heart

This consists of specialized cardiac muscle found in the sinuatrial node and in the

atrioventricular node and bundle. The heart-beat is initiated in the sinuatrial node (the

pacemaker of the heart), situated in the upper part of the crista terminalis just to the

right of the opening of the superior vena cava into the right atrium. From there the

cardiac impulse spreads the atrial septum immediately above the opening of the

coronary sinus. The impulse is then conducted to the ventricles by way of the

specialized tissue of the atrioventricular bundle (of His). This bundle divides at the

junction of the membranous and muscular parts of the interventricular septum into its

right and left branches which run immediately beneath the endocardium to activateall parts of the ventricular musculature

The blood supply to the heart

The hearts blood supply is derived from the right and left coronary arteries whose

main branches lie in the interventricular and atrioventricular grooves. The right

coronary arteryarises from the anterior aortic sinus and passes forwards between the

pulmonary trunk and the right atrium to descend in the right part of the

atrioventricular groove. At the inferior border of the heart it continues along the

atrioventricular groove to anastomose with the left coronary at the posterior

interventricular groove. It gives off a marginalbranch along the lower border of theheart and the posterior interventricular branch which runs forward in the inferior

interventricular groove and to anastomose near the apex of the heart with the

corresponding branch of the left coronary artery. The left coronary artery, which is

larger than the right, rises from the left posterior aortic sinus. Passing first behind and

then to the left of the pulmonary trunk, it reaches the left part of atrioventricular

groove in which it runs laterally round the left border of the heart as the circumflex

arteryto reach the posterior interatrial groove. Its most important branch, given off

about 2 cm from its origin, is the anterior interventricular artery which supplies the

anterior aspect of both ventricles and passes around the apex of the heart to

anastomose with the posterior interventricular branch of the right coronary. Note thatthe sinuatrial node is usually supplied by the right coronary artery, although the left

coronary artery takes over this duty in about one-third of subjects. Although

anastomoses occur between the terminations of the right and left coronary arteries,

these are usually inefficient. Thrombosis in one or other of these vessels leads to

death of the area of heart muscle supplied (a myocardial infarction).

The venous drainage of the heart

The bulk of the venous drainage of the heart is achieved by veins which accompany

the coronary arteries and which open into the right atrium. The rest of the blood

drains by means of small veins (venae cordis minimae) directly into the cardiac cavity.


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The coronary sinus lies in the posterior atrioventricular groove and opens into the

right atrium just to the left of the mouth of the inferior vena cava.

It receives:

1the great cardiac vein in the anterior interventricular groove;

2the middle cardiac vein the inferior interventricular groove;

3the small cardiac vein accompanying the marginal artery along the lower border

of the heart;

4the oblique vein descends obliquely on the posterior aspect of the left

atrium.

The anterior cardiac veins (up to three or four in number) cross the anterior

atrioventricular groove, drain much of the anterior surface of the heart and open

directly into the right atrium.

Nerve supply

The nerve supply of the heart is derived from the vagus (cardio-inhibitor) and the

cervical and upper 5 thoracic sympathetic ganglia (cardioaccelerator) by way ofsuperficial and deep cardiac plexuses.

C. FISIOLOGIHeart Cycle


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The cardiac events that occur from the beginning of one heartbeat to the beginningof the next are called the cardiac cycle. Each cycle is initiated by spontaneous

generation of an action potential in the sinus node. This node is located in the

superior lateral wall of the right atrium near the opening of the superior vena cava,

and the action potential travels from here rapidly through both atria and then

through the A-V bundle into the ventricles. Because of this special arrangement of

the conducting system from the atria into the ventricles, there is a delay of more

than 0.1 second during passage of the cardiac impulse from the atria into the

ventricles.This allows the atria to contract ahead of ventricular contraction, thereby

pumping blood into the ventricles before the strong ventricular contraction

begins.Thus, the atria act as primer pumps for the ventricles, and the ventricles inturn provide the major source of power for moving blood through the bodys

vascular system. The cardiac cycle consists of a period of relaxation called diastole,

during which the heart fills with blood, followed by a period of contraction called

systole.

Function of the Atria as Primer Pumps

Blood normally flows continually from the great veins into the atria; about 80 per

cent of the blood flows directly through the atria into the ventricles even before the

atria contract. Then, atrial contraction usually causes an additional 20 per cent fillingof the ventricles. Therefore, the atria simply function as primer pumps that increase


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the ventricular pumping effectiveness as much as 20 per cent. However, the heart

can continue to operate under most conditions even without this extra 20 per cent

effectiveness because it normally has the capability of pumping 300 to 400 per cent

more blood than is required by the resting body.Therefore, when the atria fail to

function, the difference is unlikely to be noticed unless a person exercises; then

acute signs of heart failure occasionally develop, especially shortness of breath.

Function of the Ventricles as Pumps

Filling of the Ventricles. During ventricular systole, large amounts of blood

accumulate in the right and left atria because of the closed A-V valves. Therefore, as

soon as systole is over and the ventricular pressures fall again to their low diastolic

values, the moderately increased pressures that have developed in the atria during

ventricular systole immediately push the A-V valves open and allow blood to flow

rapidly into the ventricles, as shown by the rise of the left ventricularvolume curve inThis is called the period of rapid filling of the ventricles. The period of rapid filling

lasts for about the first third of diastole. During the middle third of diastole, only a

small amount of blood normally flows into the ventricles; this is blood that continues

to empty into the atria from the veins and passes through the atria directly into the

ventricles. During the last third of diastole, the atria contract and give an additional

thrust to the inflow of blood into the ventricles; this accounts for about 20 per cent

of the filling of the ventricles during each heart cycle.

Emptying of the Ventricles During Systole

Period of Isovolumic (Isometric) Contraction. Immediately after ventricularcontraction begins, the ventricular pressure rises abruptly. Then an additional 0.02 to

0.03 second is required for the ventricle to build up sufficient pressure to push the

semilunar (aortic and pulmonary) valves open against the pressures in the aorta and

pulmonary artery.Therefore, during this period, contraction is occurring in the

ventricles, but there is no emptying. This is called the period of isovolumic or

isometric contraction, meaning that tension is increasing in the muscle but little or

no shortening of the muscle fibers is occurring.

Period of Ejection. When the left ventricular pressure rises slightly above 80 mm Hg

(and the right ventricular pressure slightly above 8 mm Hg), the ventricular pressures

push the semilunar valves open. Immediately, blood begins to pour out of the

ventricles, with about 70 per cent of the blood emptying occurring during the first

third of the period of ejection and the remaining 30 per cent emptying during the

next two thirds. Therefore, the first third is called the period ofrapid ejection, and

the last two thirds, theperiod ofslow ejection.

Period of Isovolumic (Isometric) Relaxation. At the end of systole, ventricular

relaxation begins suddenly, allowing both the right and left intraventricular pressures

to decrease rapidly. The elevated pressures in the distended large arteries that have

just been filled with blood from the contracted ventricles immediately push blood

back toward the ventricles, which snaps the aortic and pulmonary valves closed. For

another 0.03 to 0.06 second, the ventricular muscle continues to relax, even though


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the ventricular volume does notchange, giving rise to the period of isovolumic or

isometricrelaxation. During this period, the intraventricular

pressures decrease rapidly back to their low diastolic levels. Then the A-V valves

open to begin a new cycle of ventricular pumping.

End-Diastolic Volume, End-Systolic Volume, and Stroke Volume

Output. During diastole, normal filling of the ventricles increases the volume of each

ventricle to about 110 to 120 milliliters. This volume is called the end-diastolic

volume. Then, as the ventricles empty during systole, the volume decreases about 70

milliliters, which is called the stroke volume output.The remaining volume

in each ventricle, about 40 to 50 milliliters, is called the end-systolic volume. The

fraction of the end-diastolic volume that is ejected is called the ejection fraction

usually equal to about 60 per cent. When the heart contracts strongly, the end-

systolic volume can be decreased to as little as 10 to 20 milliliters. Conversely, when

large amounts of blood flow into the ventricles during diastole, the ventricular end

diastolic volumes can become as great as 150 to 180 milliliters in the healthy heart.

By both increasing the end-diastolic volume and decreasing the end-systolic volume,the stroke volume output can be increased to more than double normal.

Function of the Valves

Atrioventricular Valves. The A-V valves (the tricuspid and mitral valves) prevent

backflow of blood from the ventricles to the atria during systole, and the semilunar

valves (the aortic andpulmonary arteryvalves) prevent backflow from the aorta and

pulmonary arteries into the ventricles during diastole. These valves, for the left

ventricle, close and open passively. That is, they close when a backward pressure

gradient pushes blood backward, and they open when a forward pressure gradient

forces blood in the forward direction. For anatomical reasons, the thin, filmy A-Vvalves require almost no backflow to cause closure, whereas the much heavier

semilunar valves require rather rapid backflow for a few milliseconds.

Aortic and Pulmonary Artery Valves.

The aortic and pulmonary artery semilunar valves function quite differently from the

A-V valves. First, the high pressures in the arteries at the end of systole cause the

semilunar valves to snap to the closed position, in contrast to the much softer

closure of the A-V valves. Second, because of smaller openings, the velocity of blood

ejection through the aortic and pulmonary valves is far greater than that through the

much larger A-V valves. Also, because of the rapid closure and rapid ejection, the

edges of the aortic and pulmonary valves are subjected to much greater mechanicalabrasion than are the A-V valves. Finally, the A-V valves are supported by the

chordae tendineae, which is not true for the semilunarvalves. It is obvious from the

anatomy of the aortic and pulmonary valves that they must be constructed with an

especially strong yet very pliable fibrous tissue base to withstand the extra physical

stresses.


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Conducting System

Origin and Spread of Excitation within the Heart

The heart consists of two kinds of muscle cells: contractile cells and conducting cells.

Contractile cells constitute the majority of atrial and ventricular tissues and are the

working cells of the heart. Action potentials in contractile cells lead to contraction and

generation of force or pressure. Conducting cells constitute the tissues of the SA node,the atrial internodal tracts, the AV node, the bundle of His, and the Purkinje system.

Conducting cells are specialized muscle cells that do not contribute significantly to

generation of force; instead, they function to rapidly spread action potentials over the

entire myocardium. Another feature of the specialized conducting tissues is their

capacity to generate action potentials spontaneously. Except for the SA node, however,

this capacity normally is suppressed.

The action potential spreads throughout the myocardium in the following sequence:

1. SA node. Normally, the action potential of the heart is initiated in the specializedtissue of the SA node, which serves as the pacemaker. After the action potential isinitiated in the SA node, there is a very specific sequence and timing for the


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conduction of action potentials to the rest of the heart.

2. Atrial internodal tracts and atria. The action potential spreads from the SA node tothe right and left atria via the atrial internodal tracts. Simultaneously, the action

potential is conducted to the AV node.

3. AV node. Conduction velocity through the AV node is considerably slower than inthe other cardiac tissues. Slow conduction through the AV node ensures that theventricles have sufficient time to fill with blood before they are activated and contract.

Increases in conduction velocity of the AV node can lead to decreased ventricular

filling and decreased stroke volume and cardiac output.

4. Bundle of His, Purkinje system, and ventricles. From the AV node, the actionpotential enters the specialized conducting system of the ventricles. The action

potential is first conducted to the bundle of His through the common bundle. It then

invades the left and right bundle branches and then the smaller bundles of the Purkinje

system. Conduction through the His-Purkinje system is extremely fast, and it rapidly

distributes the action potential to the ventricles. The action potential also spreads from

one ventricular muscle cell to the next, via low-resistance pathways between the cells.

Rapid conduction of the action potential throughout the ventricles is essential andallows for efficient contraction and ejection of blood.

Action Potential of the Heart

1. Phase 0, upstroke. In ventricular, atrial, and Purkinje fibers, the action potential


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begins with a phase of rapid depolarization, called the upstroke. As in nerve and

skeletal muscle, the upstroke is caused by a transient increase in Na+

conductance

(gNa), produced by depolarization-induced opening of activation gates on the Na+

channels. When gNa increases, there is an inward Na+

current (influx of Na+

into the

cell), or INa, which drives the membrane potential toward the Na+

equilibrium

potential of approximately +65 mV. The membrane potential does not quite reach

the Na+

equilibrium potential because, as in nerve, the inactivation gates on the Na+

channels close in response to depolarization (albeit more slowly than the activation

gates open). Thus, the Na+

channels open briefly and then close. At the peak of the

upstroke, the membrane potential is depolarized to a value of about +20 mV.

The rate of rise of the upstroke is called dV/dT. dV/dT is the rate of change of the

membrane potential as a function of time, and its units are volts per second (V/sec).

dV/dT varies, depending on the value of the resting membrane potential. This

dependence is called the responsiveness relationship. Thus, dV/dT is greatest (the

rate of rise of the upstroke is fastest) when the resting membrane potential is most

negative, or hyperpolarized (e.g., -90 mV), and dV/dT is lowest (the rate of rise of theupstroke is slowest) when the resting membrane potential is less negative, or

depolarized (e.g., -60 mV). This correlation is based on the relationship between

membrane potential and the position of the inactivation gates on the Na+

channel

When the resting membrane potential is relatively hyperpolarized (e.g., -90 mV), the

voltage-dependent inactivation gates are open, and many Na+

channels are available

for the upstroke. When the resting membrane potential is relatively depolarized

(e.g., -60 mV), the inactivation gates on the Na+

channels tend to be closed, and

fewer Na+

channels are available to open during the upstroke. dV/dT also correlates

with the size of the inward current (i.e., in ventricular, atrial, and Purkinje fibers, the

size of the inward Na+

current).2. Phase 2, plateau. During the plateau, there is a long period (150 to 200 msec) of

relatively stable, depolarized membrane potential, particularly in ventricular and

Purkinje fibers. (In atrial fibers, the plateau is shorter than in ventricular fibers.)

Recall that for the membrane potential to be stable, inward and outward currents

must be equal such that there is no net current flow across the membrane.

How is such a balance of inward and outward currents achieved during the plateau?

There is an increase in Ca2+

conductance (gCa), which results in an inward Ca2+

current. Inward Ca2+

current is also called slow inward current, reflecting the slower

kinetics of these channels (compared with the fast Na+

channels of the upstroke).

The Ca2+

channels that open during the plateau are L-type channels ("L," for long-lasting) and are inhibited by the Ca

2+channel blockers nifedipine , diltiazem, and

verapamil. To balance the inward Ca2+

current, there is an outward K+

current,

driven by the electrochemical driving force on K+

ions (as described for phase 1).

Thus, during the plateau, the inward Ca2+

current is balanced by the outward K+

current, the net current is zero, and the membrane potential remains at a stable

depolarized value.The significance of the inward Ca2+

current extends beyond its

effect on membrane potential. This Ca2+

entry during the plateau of the action

potential initiates the release of more Ca2+

from intracellular stores for excitation-

contraction coupling. This process of so-called Ca2+

-induced Ca2+

release will be

discussed in the section on cardiac muscle contraction.3. Phase 3, repolarization. Repolarization begins gradually at the end of phase 2, and


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then there is rapid repolarization to the resting membrane potential during phase 3.

Recall that repolarization is produced when outward currents are greater than

inward currents. During phase 3, repolarization results from a combination of a

decrease in gCa (previously increased during the plateau) and an increase in g K (to

even higher levels than at rest). The reduction in gCa results in a decrease in the

inward Ca2+ current, and the increase in gK results in an increase in the outward K+

current (IK), with K+

moving down a steep electrochemical gradient (as described for

phase 1). At the end of phase 3, the outward K+

current is reduced because

repolarization brings the membrane potential closer to the K+

equilibrium potential,

thus decreasing the driving force on K+.

CIRCUITRY

The left heart and right heart have different functions. The left heart and the

systemic arteries, capillaries, and veins are collectively called the systemic

circulation. The left ventricle pumps blood to all organs of the body except the lungs.

The right heart and the pulmonary arteries, capillaries, and veins are collectively

called the pulmonary circulation. The right ventricle pumps blood to the lungs. The


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left heart and right heart function in series so that blood is pumped sequentially

from the left heart to the systemic circulation, to the right heart, to the pulmonary

circulation, and then back to the left. The rate at which blood is pumped from either

ventricle is called the cardiac output. Because the two sides of the heart operate in

series, the cardiac output of the left ventricle equals the cardiac output of the rightventricle in the steady state. The rate at which blood is returned to the atria from

the veins is called the venous return. Again, because the left heart and the right

heart operate in series, venous return to the left heart equals venous return to the

right heart in the steady state. Finally, in the steady state, cardiac output from the

heart equals venous return to the heart.

Step of the circuicity:

1. Oxygenated blood fills the left ventricle. Blood that has been oxygenated in thelungs returns to the left atrium via the pulmonary vein. This blood then flows fromthe left atrium to the left ventricle through the mitral valve (the AV valve of the left

heart).

2. Blood is ejected from the left ventricle into the aorta. Blood leaves the left ventriclethrough the aortic valve (the semilunar valve of the left side of the heart), which is

located between the left ventricle and the aorta. When the left ventricle contracts,

the pressure in the ventricle increases, causing the aortic valve to open and blood to

be ejected forcefully into the aorta. (As noted previously, the amount of blood

ejected from the left ventricle per unit time is called the cardiac output.) Blood then

flows through the arterial system, driven by the pressure created by contraction ofthe left ventricle.

3. Cardiac output is distributed among various organs. The total cardiac output of theleft heart is distributed among the organ systems via sets of parallel arteries. Thus,

simultaneously, 15% of the cardiac output is delivered to the brain via the cerebral

arteries, 5% is delivered to the heart via the coronary arteries, 25% is delivered to

the kidneys via the renal arteries, and so forth. Given this parallel arrangement of

the organ systems, it follows that the total systemic blood flow must equal the

cardiac output.

The percentage distribution of cardiac output among the various organ systems is

not fixed, however. For example, during strenuous exercise, the percentage of thecardiac output going to skeletal muscle increases, compared with the percentage at

rest. There are three major mechanisms for achieving such a change in blood flow to

an organ system. In the firstmechanism, the cardiac output remains constant, but

the blood flow is redistributed among the organ systems by the selective alteration

of arteriolar resistance. In this scenario, blood flow to one organ can be increased at

the expense of blood flow to other organs. In the second mechanism, the cardiac

output increases or decreases, but the percentage distribution of blood flow among

the organ systems is kept constant. Finally, in a thirdmechanism, a combination of

the first two mechanisms occurs in which both cardiac output and the percentage

distribution of blood flow are altered. This third mechanism is used, for example, in

the response to strenuous exercise: Blood flow to skeletal muscle increases to meet


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the increased metabolic demand by a combination of increased cardiac output and

increased percentage distribution to skeletal muscle.

4. Blood flow from the organs is collected in the veins. The blood leaving the organs isvenous blood and contains waste products from metabolism, such as carbon dioxide

(CO2). This mixed venous blood is collected in veins of increasing size and finally in

the largest vein, the vena cava. The vena cava carries blood to the right heart.

5. Venous return to the right atrium. Because the pressure in the vena cava is higherthan in the right atrium, the right atrium fills with blood, the venous return. In the

steady state, venous return to the right atrium equals cardiac output from the left

ventricle.

6. Mixed venous blood fills the right ventricle. Mixed venous blood flows from theright atrium to the right ventricle through the AV valve in the right heart, the

tricuspid valve.

7. Blood is ejected from the right ventricle into the pulmonary artery. When the rightventricle contracts, blood is ejected through the pulmonic valve (the semilunar valve

of the right side of the heart) into the pulmonary artery, which carries blood to thelungs. Note that the cardiac output ejected from the right ventricle is identical to the

cardiac output that was ejected from the left ventricle. In the capillary beds of the

lungs, oxygen (O2) is added to the blood from alveolar gas, and CO2 is removed from

the blood and added to the alveolar gas. Thus, the blood leaving the lungs has more

O2 and less CO2 than the blood that entered the lungs.

8. Blood flow from the lungs is returned to the heart via the pulmonary vein. Oxygenated blood is returned to the left atrium via the pulmonary vein to begin a

new cycle.

D. HISTOLOGYArteries

General considerations_ Carry blood away from the heart and toward capillary beds

_ Have thicker walls and smaller lumens than veins of similar size

_ Tunica media is the predominate tunic.

_ Cross-sectional outlines are more circular in arteries than in veins.

Types Elastic (large) arteries (aorta, pulmonary arteries)

_ Internal elastic lamina is present but difficult to distinguish.

_ Tunica media is composed of fenestrated sheets of elastic tissue (elastic lamellae)

and smooth muscle.

_ Passively maintain blood pressure by distension and recoil of the elastic sheets

Muscular (medium, distributing)_ Tunica media is composed of smooth muscle.

_ Internal elastic lamina. Single, fenestrated, elastic sheet; lies internal to the

smooth muscle of the tunica media.

_ External elastic laminae. Multiple elastic sheets; lie external to the smooth

muscle of the tunica media


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_ Regulate blood pressure and blood distribution by contraction and relaxation of

smooth muscle in the tunica media

Small arteries and arterioles_ Less than 200 microns in diameter

_ Small arteries have an internal elastic lamina and up to eight layers of smooth

muscle in the tunica media.

_ Arterioles usually lack an internal elastic lamina and have one to two layers of

smooth muscle in the tunica media.

_ Arterioles are the vessels that regulate blood pressure and deliver blood under

low pressure to capillaries.

Capillaries

General considerations_ Function to exchange oxygen and carbon dioxide and nutrients and metabolic

wastes between blood and cells

_ Lumen is approximately 8 microns in diameter, thus only largeenough for RBCsto move through in a single row.

_ Composed of the endothelium (simple squamous epithelium) and its

underlying basal lamina

TypesContinuous capillaries

_ Most common

_ Endothelium is continuous (i.e., has no pores)

Fenestrated capillaries_ Endothelium contains pores that may or may not be spanned by a

diaphragm. If present, the diaphragm is thinner than two apposed plasma

membranes.

_ Pores with diaphragms are common in capillaries in the endocrine organs

and portions of the digestive tract. Pores lacking diaphragms are uniquely

present in the glomerular capillaries of the kidney.

_ Pores facilitate diffusion across the endothelium

Discontinuous sinusoidal capillaries_ Larger diameter and slower blood flow than in other capillaries

_ Endothelium has large pores that are not closed by a diaphragm.

_ Gaps are present between adjacent endothelial cells.

_ Partial or no basal lamina present.

_ Prominent in spleen and liver


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Veins General considerations

_ Return blood from capillary beds to the heart

_ Have thinner walls and larger lumens than arteries of similar size; cross-

sectional outlines are more irregular

_ Tunica adventitia is the predominate tunic.

_ Larger veins possess valves, that are extensions of the tunica intima

that serve to prevent back-flow of blood.

TypesVenules and small veins_ Tunica media is absent in venules. Smooth muscle fibers appear in the tunica

media as venules progress to small veins.

_ High endothelial venules. Venules in which the endothelium is simple

cuboidal; facilitate movement of cells from the blood into the surrounding

tissues (diapedesis). This type of venule is found in many of the lymphatic

tissues.

Medium veins. Smooth muscle forms a more definitive and continuous tunicamedia; most named veins are in this category

Large veins, includes superior and inferior venae cavae; have well-developed,longitudinally oriented smooth muscle in the tunica adventitia in addition tothe smooth muscle in the tunica media.


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Heart

Develops by a vessel folding back on itself to produce four chambers

in the adult. Two upper chambers, atria (singular, atrium), receiveblood from the body and lungs; two ventricles pump blood out of the

heart.

Impulse conducting system. Formed of specialized cardiac muscle

fibers that initiate and coordinate the contraction of the heart

_ Sinoatrial (SA) node in the right atrium is the electricalpacemakerthat initiates

the impuse.

_ Fibers spread the impulse throughout the atria as well as transferring it to the

atrioventricular node.

_ The atrioventricular (AV) node is located in the interatrial septum.

_ An atrioventricular bundle extends from the AV node in the septummembranaceum and bifurcates into right and left bundle branches that lie

beneath the endocardium on both sides of the interventricular septum.

_ Purkinje fibers, modified, enlarged cardiac muscle fibers leave the bundle

branches to innervate the myocardium.

Tunics

Endocardium_ Homologous to the tunica intima of vessels Consists of an endothelium

(simple squamous epithelium) plus underlying connective tissue

_ Cardiac valves. Folds of the endocardium

_ Semilunar valves at the base of the aortic and pulmonary trunks preventbackflow of blood into the heart.


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_ Atrioventricular valves (bicuspid and tricuspid) prevent backflow of blood

from the ventricles into the atria.

Myocardium_ Composed of cardiac muscle

_ Fibers insert on components of the cardiac skeleton.

_ Thickest layer of the heart

_ Variation in thickness depends on the function of each chamber; thicker in

ventricles than atria and thicker in left ventricle than right ventricle

Epicardium (visceral pericardium)_ Serous membrane on the surface of the myocardium

_ Consists of a simple squamous epithelium and a loose connective tissue, with

adipocytes, adjacent to the myocardium.

_ Coronary blood vessels are located in the connective tissue.

Cardiac skeleton. Thickened regions of dense connective tissue thatprovide support for heart valves and serve as insertion of cardiac

muscle fibers

_ Annuli fibrosi are connective tissue rings that surround and stabilize each

valve.

_ Septum membranceum is a connective tissue partition forming the upper

portion of the interventricular septum; this connective tissue also separates

the left ventricle from the right atrium.

E. PATOFISIOLOGIF. DD

Modul Dyspneu

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