Basic Anatomy & Physiology II Dr. L. Bacha Chapter Outline (Marieb & Hoehn 6th ed)

17.1 The heart has four chambers and pumps blood through the pulmonary & systemic circuits

Size, Location, and Orientation of the Heart (p. 580)

the heart is about the size of what? a fist it is enclosed in the medial cavity of the thorax called what? mediastinum about 2/3 of the heart lies to the left of the midline

the heart is cone shaped:- the broad superior base is at the level of the second rib- its rounded inferior tip called the apex is at the level of the fifth intercostal space

Coverings of the Heart the heart is enclosed in a double-walled sac called what? the pericardium

fibrous pericardium ◦ the superficial part of the pericardium; it is fused to the parietal layer of the serous pericardium

◦ it is a layer composed of what type of tissue? tough, dense CT◦ lists its three functions:

(1) protects the heart (2) anchors it to surrounding structures (3) prevents overfilling of the heart with blood

serous pericardium ◦ describe the serous pericardium:

a thin, slippery, two-layer serous membrane that forms a closed sac around the heart

1. parietal layer of the serous pericardium- the outer lining of the pericardial cavity; fused to the fibrous pericardium

2. visceral layer of the serous pericardium

- what is it also called? epicardium- it covers the surface of the heart and is the outermost layer of the heart wall

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pericardial cavity

- the slit-like potential space between the visceral and parietal layers of the serous pericardium- the pericardial cavity contains a thin film of serous fluid called pericardial fluid

pericardial fluid = a serous (watery) fluid produced by the serous membranes

lubricates the serous membranes so that they glide smoothly past one another, without friction, during the activity of the heart

Layers of the Heart Wall list the three layers of the heart wall:

epicardium; myocardium; endocardium1. Epicardium

- made of delicate connective tissue and an epithelium; it is often infiltrated with adipose tissue

- also called the visceral layer of the serous pericardium

2. Myocardium

- thick middle layer that is formed mainly of what type of muscle tissue? cardiac muscle

- the cardiac muscle tissue consists of interlacing bundles of branching cardiac muscle cells joined end to end by intercalated discs

3. Endocardium- made of an endothelium (simple squamous epithelium) and a thin layer of connective tissue - it provides a smooth lining of the chambers and covers the valves - the endocardium is continuous with what?

the endothelial lining of the blood vessels leaving and entering the heart

Chambers and Associated Great Vessels

name the two superior chambers: atria name the two inferior chambers: ventricles name the internal partition that separates the two atria:

the interatrial septum name the internal partition that separates the two ventricles:

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the interventricular septum grooves (sulci) on the heart surface mark the boundaries between certain chambers and carry blood vessels, supplying what?

the myocardium- coronary sulcus (atrioventricular groove) encircles what?

the junction of the atria with the ventricles like a crown

- anterior interventricular sulcus - the groove between the right and left ventricles on the anterior surface of the heart

- posterior interventricular sulcus - the groove between the right and left ventricles on the posterior surface of the heart

Atria: The Receiving Chambers◦ each atrium has a wrinkled extension visible externally called an auricle

- what is the function of the auricles?

increase the atrial volume somewhat◦ functionally, the atria are receiving chambers for what?

blood returning to the heart from the circulation

◦ blood enters the RIGHT ATRIUM via three veins:the superior vena cava - returns blood from body regions superior to the diaphragmthe inferior vena cava - returns blood from body areas below the diaphragmthe coronary sinus - collects blood draining from the myocardium

◦ blood enters the LEFT ATRIUM by way of what veins? four pulmonary veins Ventricles: The Discharging Chambers

◦ the RIGHT VENTRICLE pumps blood into what large artery? pulmonary trunk◦ the LEFT VENTRICLE ejects blood into what large artery? aorta

17.2 Heart valves make blood flow in one directionThe valves open and close in response to pressure changes as the heart contracts & relaxes. The valves prevent the backflow of blood

Atrioventricular (AV) Valves- there are two atrioventricular valves, one between each atrium and ventricle:

a. Tricuspid valve (right AV valve) – between the right atrium and right ventricleb. Bicuspid valve (mitral valve; left AV valve) – between the left atrium and left ventricle

Structure of AV valves

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Atrioventricular valves have the following three components: 1. cusps - tongue-like flaps 2. chordae tendineae

- are tendon-like fibrous cords of collagen that connect the cusps to papillary muscles - function: anchor the cusps to papillary muscles to prevent them from flipping up

into the atria when the ventricles contract 3. papillary muscles

- projections of cardiac muscle of the ventricles; chordae tendineae attach to them

- describe the AV valve cusps (flaps) and blood flow when the heart is completely relaxed:

- the AV valve flaps hang limply into the ventricular chambers below.

- During this time blood flows into the atria and then through the open AV valves into the ventricles

when the ventricles contract, compressing the blood in their chambers, the intraventricular pressure rises, forcing the blood superiorly against the valve flaps. As a result, what happens?

the flap edges meet, closing the valveSemilunar (SL) Valves- there is a semilunar valve at the base of each large artery where it arises from a ventricle; the semilunar valves prevent backflow of blood into the ventricles:

a. Pulmonary semilunar valve - between the pulmonary trunk and right ventricleb. Aortic semilunar valve - between the aorta and left ventricle

Structure of semilunar valves: each semilunar valve is formed by three half-moon shaped, pocket-like cusps when the ventricles contract and intraventricular pressure rises above the pressure in the aorta and

pulmonary trunk, what happens to the semilunar valve cusps and blood flow?

- the SL valves are forced open and their cusps flatten against the arterial walls as blood rushes past them

what happens to the semilunar valves when the ventricles relax and the blood (in the aorta and pulmonary trunk) flows backward toward the heart?

the blood fills the cusps and closes the valves

17.3 Blood flows from atrium to ventricle, and then to either the lungs or the rest of the body

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The Pulmonary and Systemic Circuits page 579

Return to page 579 and read the information under The Pulmonary and Systemic Circuitsto answer these questions:◦ the heart pumps blood into two circuits:pulmonary circuit - consists of blood vessels that carry blood to and from what?

the lungssystemic circuit - consists of blood vessels that carry blood to and from what?

all body tissuesCarefully follow Focus Fig. 17.1 on page 590 and the diagram below!

☆ Draw a long solid arrow to connect the words “RIGHT ATRIUM” to “RIGHT VENTRICLE”. Draw a long open arrow to connect the words “LEFT ATRIUM” to “LEFT VENTRICLE”.This should help you realize that these two circuits are continuous with each other! If we traced the pathway of a single red blood cell, its path would alternate between the two circuits.

Another way to look at the same information as above:

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= vessel or chamber with deoxygenated blood (low O2; high CO2) = vessel or chamber with oxygenated blood (highO2; low CO2)Pulmonary circuit: Systemic circuit:

LEFT VENTRICLE

AORTA and OTHER SYSTEMIC ARTERIESthroughout the body

SYSTEMIC CAPILLARIES

(gas exchange takes place here between the blood in systemic capillaries and cells of

tissues throughout the body))

SYSTEMIC VEINS(from throughout the body)

SUPERIOR & INFERIOR VENA CAVA

(AND CORONARY SINUS)

RIGHT ATRIUM

RIGHT VENTRICLE

PULMONARY TRUNK

PULMONARY ARTERIES

PULMONARY CAPILLARIES in the lungs(gas exchange takes place here

between the blood in the pulmonary capillaries and

air in the alveoli of the lungs)

PULMONARY VEINS

LEFT ATRIUM

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◦ define ductus arteriosus:

◦ define ligamentum arteriosum:

Myocardial Thickness and Function ◦ the atria are relatively small, thin walled chambers because:

- functionally, they are receiving chambers for blood returning to the heart from the circulation- they need to contract only minimally to force blood into the ventricles below

◦ the ventricles are larger and the walls of the ventricles are thicker than the atria because:- the ventricles are discharging chambers, the actual pumps of the heart- they need to contract to propel blood out of the heart into the circulation

◦ the walls of the left ventricle are 3 times thicker than the right ventricle because:- equal volumes of blood are pumped by the ventricles at any moment, but the two ventricles have unequal workloads: the right ventricle needs to generate pressure to force blood through the pulmonary circuit (to the lungs and back to the left side of the heart)

the left ventricle needs to generate pressure to force blood through the entire systemic circuit (through the entire body and back to the right side of the heart)

A word about blood flow related to the fetal heart:In the heart of the fetus, there are structures that allow much of the blood to bypass the lungs, because the fetus does not depend on pulmonary gas exchange to receive oxygen and get rid of carbon dioxide:

foramen ovale - an opening between the right atrium and left atrium in the heart of the fetusfossa ovalis - a membrane covered depression after birth that marks the location of the foramen ovale

ductus arteriosus - a vessel that joins the pulmonary trunk with the aorta in the fetusligamentum arteriosum - the CT remnant, after birth, that was the ductus arteriosus

Coronary Circulation (page 589)The wall of the heart requires oxygenated blood, like other organs. It is supplied by blood vessels of the systemic circuit that form the coronary circulation; see Figs 17.10 (a) and (b). (In other words, the coronary circulation is the part of the systemic circuit that supplies the cells of the wall of the heart itself with oxygen, etc.)

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right and left coronary arteries(which arise from the aorta just beyond the aortic semilunar valve)

branch and lead into capillaries in the myocardium

(where exchange of gases, nutrients, and waste products takes place)

coronary veins

coronary sinus

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17.4 Intercalated discs connect cardiac muscle fibers (cells) into a functional syncytium

Microscopic Anatomy (of Cardiac Muscle Cells)

does cardiac muscle tissue contract by the sliding filament mechanism? yes cardiac muscle cells are short, branched, interconnected cells with 1 or 2 central nuclei cardiac muscle tissue is well vascularized

the ends of cardiac muscle cells connect to adjacent cardiac muscle cells by special junctions called intercalated discs, which consist of desmosomes and gap junctions:

- the desmosomes in the intercalated discs prevent what?

adjacent cells from separating during contraction- the gap junctions of the intercalated discs allow what?

ions to pass from cell to cell, transmitting current across the entire heart

because the gap junctions electrically couple cardiac muscle cells, how does the myocardium ∙behave?

as a single coordinated unit or functional syncytium

the heart relies on aerobic respiration; it has large (and numerous) mitochondria that make the cardiac

muscle cells highly resistance to what? fatigue

17.5 Pacemaker cells trigger action potentials throughout the heart

Setting the Basic Rhythm: The Intrinsic Conduction System

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right and left coronary arteries(which arise from the aorta just beyond the aortic semilunar valve)

branch and lead into capillaries in the myocardium

(where exchange of gases, nutrients, and waste products takes place)

coronary veins

coronary sinus

= deoxygenated blood = oxygenated blood

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the independent, but coordinated, activity of the heart is a function of what two factors:

(1) the presence of gap junctions(2) the activity of the heart’s “in house” conduction system

there are two categories of cardiac muscle cells:1. almost all of the cardiac muscle cells (99%) are contractile cardiac muscle cells that are responsible

for the heart’s pumping action

2. the intrinsic conduction system of the heart consists of noncontractile cardiac muscle cells specialized to initiate and distribute impulses throughout the heart, so that it depolarizes and contracts in an orderly, sequential manner

Sequence of ExcitationTrace the sequence of electrical excitation through the intrinsic conduction system of the heart in Fig. 17.13:

① Sinoatrial node (SA node)◦ the sinoatrial node is located where?

right atrial wall, just inferior to entrance of the superior vena cava

◦ noncontractile cardiac muscle cells of the sinoatrial node are self-excitable or “autorhythmic”, meaning that they have the special ability to depolarize spontaneously

◦ its cells typically generate impulses (“fire”) about how often?

75 times per min. ◦ explain why the SA node sets the pace for the heart as a whole?

because no other region of the conduction system or the myocardium has a faster depolarization rate

- for this reason, it is the “pacemaker” for the heart

- its characteristic rhythm that determines heart rate is called what? sinus rhythm◦ the sinoatrial node initiates impulses that spread via gap junctions through the atria, causing the contractile cardiac muscle cells of the atria to depolarize and contract then the impulses spread to the atrioventricular node

② Atrioventricular node (AV node)◦ from the SA node, the impulse spreads throughout the atria◦ where is the AV node located?

inferior portion of interatrial septum

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③ Atrioventricular bundle (AV bundle; bundle of His)◦ where is the atrioventricular bundle located?

in the superior part of the interventricular septum◦ is the only electrical connection between the atria and ventricles!

④ Right and left bundle branches◦ two pathways that course from the AV bundle along the interventricular septum toward what?

the heart apex⑤ Subendocardial conducting network (Purkinje fibers)

◦ conducts the impulse into the myocardium of the ventricles, which causes the contractile cardiac muscle cells of the ventricles to depolarize and contract

Defects in the intrinsic conduction system can cause irregular heart rhythms called what?

arrhythmiasModifying the Basic Rhythm: Extrinsic Innervation of the Heart although the heart rate is set by the intrinsic conduction system, it is modified by the autonomic nervous system (and hormones)

do you think that the sympathetic nervous system increases or decreases heart rate and the force of

contraction of the heart? increases do you think that the parasympathetic nervous system increases or decreases heart rate?

decreases the cardiac centers are located in what part of the brainstem?

the medulla oblongata1. what type of neurons project from the cardioacceleratory center?

sympathetic neurons in T1 – T3 level of the spinal cord

the sympathetic neurons of the cardioacceleratory center run to the heart where they innervate what structures?

the SA and AV nodes, heart muscle, and coronary arteries

the effect of the cardioacceleratory center is that it increases heart rate and force of contraction

2. parasympathetic neurons of the cardioinhibitory center run in the vagus nerve and innervate the SA and AV nodes the effect of the cardioinhibitory center is that it decreases the rate of heartbeat

Electrocardiography

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what can be detected with an electrocardiograph?

the electrical currents generated in and transmitted

through the heart and spread throughout the body

define electrocardiogram (ECG) ( from the glossary in the back of the book!):

a graphic record of the electrical activity of the heart waves of an ECG:P wave the P wave results from spreading of the depolarization wave from the SA node through the atria, and leads to atrial systole

QRS complex the QRS complex results from ventricular depolarization, and leads to ventricular systole it also results from atrial repolarization, and leads to atrial diastole

T wave: the T wave results from ventricular repolarization, and leads to ventricular diastole

examine the three waves on the ECG Fig. 17.16 17.6 The cardiac cycle describes the mechanical events associated with blood flow through

the heart Phases of the Cardiac Cycle what do the following two terms refer to?

systole - periods of contractiondiastole - periods of relaxation

what does the cardiac cycle include?

all events associated with the blood flow through the heart during one complete heartbeat

- these mechanical events of the cardiac cycle always follow the electrical events seen in the ECG

assuming the average heart rate is 75 beats per minute (at rest), each cardiac cycle lasts about 0.8 s

During a cardiac cycle, not only is there contraction and relaxation of the myocardium of the heart chambers, but there is also opening and closing of the valves and changes in blood pressure within the chambers and the major arteries.

Summary of the 2 step pumping action of the heart:

1. Atrial Systole - The RA and LA contract almost simultaneously

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An ECG is also called an EKG. Why the “K” in EKG? “Kardio” is Greek for heart!

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2. Ventricular Systole - 0.1 to 0.2 s later the RV and LV contract while the atria relax3. Relaxation Period -all chambers are relaxed for a moment

Remember, this is a cycle, and even though we study it as three steps, step 3 continues to step 1, to step 2, to step 3, to step 1, etc., as long as the heart continues to beat!

1. Atrial Systole - the walls of the atria contract- the sudden increase in blood pressure within the atria forces the final 20% of the blood into the ventricles

- the atrioventricular valves are open- the semilunar valves are closed

2. Ventricular Systole

- the walls of the ventricles contract while the atria relax- the AV valves close due to the increase in blood pressure in the ventricles as they begin to

contract- the semilunar valves open (when the blood pressure in the ventricles is greater than in the aorta

and pulmonary trunk)- the result is that about 2/3 of the volume of blood in the ventricles is forced into the aorta and

pulmonary trunk this volume of blood ejected by the each ventricle per heart beat is called the stroke volume

3. Relaxation: Atrial and Ventricular Diastole - both atria and both ventricles relax- the semilunar valves close- the AV valves open- venous return (blood returning to the heart) fills the atria and, because the AV valves are open, it fills the ventricles to about 80% of their final volume of blood

Heart Sounds the heart sounds often described as “lup dup”; what are they associated with heart valves closing

the first heart sound occurs when what valves close? the AV valves the second heart sound occurs when?

- as the semilunar valves snap at the beginning of ventricular relaxation

define heart murmurs: abnormal heart sounds 17.7 Stroke volume and heart rate are regulated to alter cardiac output Cardiac output (CO)◦ define cardiac output –

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amount of blood pumped out by each ventricle in 1 minute◦ define stroke volume -

the volume of blood pumped out by one ventricle with each beat

◦ in general, stroke volume correlates with what?

the force of ventricular contraction◦ what is the normal resting value for heart rate (HR)? 75 beats/min◦ what is the normal resting value for stroke volume (SV)? 70 ml/beat◦ the following equation shows the relationship between cardiac output, heart rate and stroke volume:

CO = HR x SV◦ write the equation that shows how the average adult cardiac output (at rest) can be computed:

CO = 75 beats/min x 70 ml/beat = 5250 ml/min (5.25 L/min)◦ define cardiac reserve:

the difference between resting and maximal CO the average person: cardiac reserve is 4 to 5 times resting CO (20 to 25 L/min) in top athletes: cardiac reserve can be up to 7 to 8 times resting CO (35 to 40 L/min)

Regulation of Stroke Volume

• Name the three most important factors that affect stoke volume (and therefore CO) by causing changes in EDV or ESV:

preload, contractility, and afterload1. Preload: Degree of Stretch of Heart Muscle

• what is preload?

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First, time out for some review info about SV:Stroke volume is the difference between end diastolic volume (EDV) and end systolic volume (ESV).

SV = EDV – ESV 120 ml/beat – 50 ml/beat = 70 ml/beat

End diastolic volume (EDV) = the volume of blood in a ventricle at the end of atrial systole/just before the ventricle contracts; a normal EDV is 120 ml/beat

End systolic volume (ESV) = the volume of blood that remains in each ventricle at the end of ventricular systole; a normal ESV is 50 ml/beat

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the degree to which cardiac muscle cells are stretched just before they contract

• the Frank-Starling law of the heart expresses the relationship between preload and stroke volume

• the higher the preload (stretch) on cardiac muscle fibers prior to contraction, the greater the force of contraction a greater force of contraction causes an increase in SV, which causes an increase in CO

• preload can be compared to the stretching of a rubber band; the more the rubber band is stretched, the more forcefully it will snap back!

• the most important factor stretching cardiac muscle is venous return

- define venous return:

= the amount of blood returning to the heart and distending its ventricles

• anything that increases venous return increases EDV and, consequently, SV and contraction force; Both exercise and increased filling time (such as due to a slow heart rate) increase venous return, which increases EDV:

read about why ∙ exercise increases venous return2. Contractility

• contractility = strength of contraction; it is independent of muscle stretch and EDV• contractility rises when what happens?

more Ca2+ enters the cytoplasm from the extracellular fluid and the SR

- enhanced contractility means what?

more blood is ejected from the heart (greater SV), hence a lower ESV

• does increased sympathetic stimulation increase or decrease contractility of the heart? increases

• define positive inotropic agents:

substances that increase contractility

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- list examples of positive inotropic agents:

epinephrine, thryroxine, glucagon; the drug digitalis; high levels of extracell Ca2+

• define negative inotropic agents:

impair or decrease contractility- list examples of negative inotropic agents:

acidosis (excess H+); rising extracell K+ levels; drugs called calcium channel blockers

3. Afterload: Back Pressure Exerted by Arterial Blood• to eject blood, the pressure that is generated by contraction of the ventricles must be greater than the back pressure exerted on the aortic and pulmonary semilunar valves by the blood in the aorta and pulmonary trunk

• define afterload:

= the pressure that the ventricles must overcome to eject blood

- it is essentially what?

the back pressure that arterial blood exerts on the aortic and pulmonary valves

• in healthy people, why is afterload not a major determinant of stroke volume?

because it is relatively constant• describe how an increase in afterload in people with hypertension (high blood pressure) affects SV and ESV:

afterload reduces the ability of the ventricles to eject blood. Consequently, more blood remains in the heart after systole, increasing ESV and reducing SV

Regulation of Heart Rate◦ in a healthy cardiovascular system, SV tends to remain relatively constant. However, when blood volume drops sharply or the heart is seriously weakened, what happens?

SV declines

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and CO is maintained by increasing HR and contractility

◦ factors that regulate heart rate also regulate cardiac output

◦ although the sinoatrial node initiates cardiac action potentials, the autonomic nervous system and chemicals influence the initiation of impulses from the SA node, and therefore influence HR:

1. Autonomic Nervous System Regulation of Heart Rate• the autonomic nervous system exerts the most important extrinsic controls affecting heart rate!

• when the sympathetic nervous system is activated, sympathetic nerve fibers release what neurotransmitter at their cardiac synapses?

norepinephrine at the cardiac synapses- norepinephrine causes the SA node fires more rapidly and the heart responds by beating faster

• what is the effect of acetylcholine, released by nerve fibers of the parasympathetic nervous system, on heart rate?

- reduces heart rate• under resting conditions, both autonomic divisions continuously do what?

- continuously send impulses to the SA node of the heart- but the dominant effect on the SA node is inhibitory; so what division, sympathetic or parasympathetic, do you think predominates?

parasympathetic for this reason, the heart is said to exhibit what? ∙

- vagal tone, and heart rate is generally slower than it would be if the vagal nerves were not innervating it

2. Chemical Regulation of Heart Rate • Hormones

∙ epinephrine is released when and by what organ?

- liberated by the adrenal medulla during sympathetic nervous system activation

- what is the effect of epinephrine on heart rate and contractility?

- enhances heart rate and contractility

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∙ thyroxine is a thyroid hormone that increases metabolic rate and production of body heat. When released in large quantities, it causes what effect on the heart?

causes a sustained increase in heart rate• Ions

- increase in calcium ions in the blood (hypercalcemia) - increases heart rate- hypocalcemia - decreases heart rate- high blood levels of potassium ions in the blood (hyperkalemia) - decreases heart rate

3. Other Factor That Regulate Heart Rate:• list other factors that influence heart rate:

age, gender, exercise, body temp

The End!

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Define:

tachycardia: = an abnormally fast heart rate >100 beats/minbradycardia: = a heart rate slower than 60 beats/min

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