Chapter 17: The Cardiovascular System I: The Heart

Ejection Fraction

% of blood ejected with each ventricular systole: SV/EDV; normal ejection fraction is 60%

Pacemaker cells

(1%) display the property of autorhythmicity, meaning they sets their own rhythm without a need for input from the nervous system; spontaneously generate action potentials that coordinate cardiac electrical activity

Myocardium (2 components)

(1) cardiac muscle (2) fibrous skeleton - composed of dense irregular connective tissue which gives structural support acting as an insulator for heart's electrical activity

Describe the 2 factors that influence EDV

(1) length of time ventricle spends in diastole (2) amount of blood returning to right ventricle from systemic circuit (venous return) - EDV increases when ventricles spend more time in diastole, because of more filling time; also ruses when left ventricle pumps blood more forcefully into systemic circuit, because additional blood returns to right atrium more rapidly, increasing venous return - Relationship between preload and stroke volume is explained by Frank-Starling law: States that increased ventricular muscle cells stretch leads to more forceful contraction; When is this important? - utilized when we exercise - Direct relationship between Preload and EDV

Contractile cells

(99%) contract in response to electrical excitation in the form of action potentials that spread from one cell to the next through gas junction

Pacemaker potential

(much different from that of a contractile cell) - Depolarization in a pacemaker cell occurs much more slowly; due in part to lack of voltage-gated sodium ion channels in pacemaker sarcolemma -Pacemaker cell action potentials lack a plateau phase and membrane potential oscillates- that is, it never remains at resting level and instead occurs in a cycle with last even triggering first - Occurs because of HCN (nonspecific cation channels) that are unique to pacemaker cells

Differentiate between right and left ventricular hypertrophy.

- Long-standing increases in preload and afterload are associated with enlargement of ventricles (ventricular hypertrophy) - Right ventricular hypertrophy most often results from respiratory disease or high blood pressure in pulmonary circuit; left ventricular hypertrophy generally results from high blood pressure in systemic circuit - Leads to heart failure (left and right)

Summary of the 3 influences over Stroke Volume (SV)

1.) The preload of the left heart is determined by the volume of blood coming in from the pulmonary circuit 2). The contractility is determined by the heart's intrinsic ability 3). The afterload of the left heart is determined by the pressure in the systemic circuit

Define Heart Rate (HR)

60-80 cardiac cycles or beats per minute (bpm)

Endocrine systems effect on cardiac output in detail

Adrenal medulla is activated by sympathetic nervous system, and in response it secretes hormones epinephrine and norepinephrine into bloodstream - Hormones have same effects as sympathetic nervous system neurotransmitters- they are positive inotropic and chronotropic agents- but effect is longer-lasting than sympathetic stimulation - Other hormones that also have positive ion-tropic and chronotropic effects include thyroid hormone and glucagon produced by pancreas - Amount of water in blood (blood volume) plays a significant role in determining heart's preload and therefore its strength of contraction a. Hormone such as aldosterone and antidiuretic hormone increase blood volume and preload, and so raise cardiac output (secreted while exercising) b. Atrial natriuretic peptide, decreases blood volume and preload, and therefore reduces cardiac output

Age and Physical Fitness

Age and physical fitness influence heart rate and cardiac output; younger children and elderly often have a higher resting heart rate, whereas trained athletes often have a much lower resting heart rate.

Afterload

Amount of Back Pressure: afterload refers to the force that the right and left ventricles must overcome in order to eject blood into their respective arteries. - Determined by blood pressure in arteries of both pulmonary and systemic circuits - As afterload increases, ventricular pressure must be greater to exceed pressur ein arterial pulmonary and systemic vessels and open semilunar valves - An increase in afterload therefore generally causes a decrease in stroke volume and increase in the ESV of ventricles; (conversely, a decrease in afterload generally corresponds to a higher stroke volume and a lower ESV)

Why must blood flow through the heart occur in only one direction?

Blood flow through the heart must occur in only one direction so that deoxygenated blood goes to the pulmonary circuit and oxygenated blood goes to the systemic circuit.

Body Temperature

Body temperature influences CO; SA node fires more rapidly at higher body temperature and more slowly at lower body temperature.

What regulates cardiac output?

Cardiac output is regulated primarily by the nervous and endocrine systems, which influence both heart rate and stroke volume

Causes of heart failure

Cause include MI, cardiomyopathy, valvular disease

Preload

Degree of Cardiac Muscle Cell Stretch: preload refers to the length or degree of stretch of the sarcomeres in the ventricular cells before they contract and is largely determined by the EDV.

Equation for Stroke Volume (SV)

EDV - ESV = SV - In an average heart, the resting stroke volume is equal to about 70 ml. - 120 ml (EDV) - 50 ml (ESV) = 70 ml (SV)

Electrolytes

Electrolytes in extracellular fluid plays a large role in determining length and magnitude of an action potential and cardiac output.

Exercise

Exercise increases stroke volume, so for body to maintain a constant cardiac output, heart rate must decrease.

chronotropic agents

Factors that influence rate at which SA node depolarizes - Anything that increases rate at which this node fires is called a positive chronotropic agent; include sympathetic nervous system, E and NE, and elevated body temperature - One with opposite effect is known as a negative chronotropic agent; include parasympathetic nervous system and decreased body temperature

Equation for Cardiac Output (CO)

HR x SV = CO - To find the cardiac output, multiply the heart rate by the stroke volume: 72 beats/min (HR) × 70 ml/beat (SV) = 5040 ml/min, or ~5 liters/min (CO) - Resting cardiac output averages about. 5 liters/min; the right ventricle pumps about 5 liters into the pulmonary circuit and the left ventricle pumps the same amount into the systemic circuit in 1 minute.

Cardiac Regulation by the Endocrine System

Hormonal regulation of cardiac output occurs in various forms, such as epinephrine and norepinephrine, thyroid hormone, glucagon, aldosterone, antidiuretic hormone, and atrial natriuretic peptide.

Cardiac Innervation and Regulation by the Autonomic Nervous System: Parasympathetic Nervous System

Parasympathetic nervous system exerts essentially the opposite effects on the heart. It innervates the heart by the left and right vagus. nerves (CN X). The nerves of the parasympathetic division of the ANS release the neurotransmitter acetylcholine , which primarily affects the SA node, decreasing its rate of action potential generation. - These nerves release acetylcholine; primarily affects SA node, decreasing its rate of action potential generation - Negative chronotropic effect slows heart rate

What 3 factors influence stroke volume?

Preload, Contractility, Afterload

Relaxed ventricle

Pressure from the left ___atrium_____ pushes blood against the ___mitral___ valve ___opening______ it. Pressure from the backflow of blood in the ____aorta___ closes the ____aortic____ valve.

Tricuspid valve

Right AV valve between right Atrium and right Ventricle

Sinus rhythms

SA node is the normal pacemaker of the entire heart; electrical rhythms generated and maintained by the SA node are known as sinus rhythms.

What are the great vessels?

Superior vena cava, Inferior vena cava, Pulmonary trunk, Pulmonary veins, Pulmonary arteries, and Aorta

Cardiac Innervation and Regulation by the Autonomic Nervous System: Sympathetic Nervous System

Sympathetic nerves that release the neurotransmitter norepinephrine. , which increases cardiac output with both positive chronotropic and inotropic effects. - Neurons release neurotransmitter norepinephrine; increases cardiac output with both positive chronotropic and inotropic effects; increases entry of calcium ions into cardiac muscle cells

Other Factors that Influence Cardiac Output

The following factors influence CO: electrolyte concentration in the extracellular fluid, body temperature, age, physical fitness, and exercise.

The cardiovascular system consists of what components

The heart, blood vessels, and blood

Describe the events occurring in the 4 Phases of the Cardiac Cycle

Ventricular Filling - blood drains from atria intro ventricles; A-V valves open; 120 ml of blood kn own as end-diastolic volume (EDV); 80% passively and 20% actively with atrial systole Passive Active Isovolumetric contraction - pressure in ventricles rises rapidly as ventricles begin to contract; all valves closed and volume does not change Ventricular ejection - pressure in ventricles rises to push semilunar valves open; rapid outflow of blood from ventricles; 70 ml of blood (stroke volume) pumped from each ventricle; 50 ml of blood remains in each ventricle known as end-systolic volume (ESV) Isovolumetric relaxation - occurs as ventricular diastole begins and pressure declines in ventricles; all valves closed

Other functions of the heart

a. Maintains blood pressure homeostasis due to Rate and Force of heart's contraction b. Secretes ANP (atrial natriuretic peptide) - ANP lowers blood pressure by decreasing sodium ion retention in kidneys and therefore increasing water in urine

Fibrillation

abnormal, rapid contractions of different parts of the heart that prevent the heart muscle from contracting as a single unit. - In fibrillation, electrical activity in heart causes parts of heart to depolarize and contract while others are repolarizing and not contracting

ionotropic agents

agents that affect contractility and force of contraction; Ex: sympathetic nervous system - When heart rate is too high, contractility decreases, as does preload; as heart is beating too rapidly to develop significant tension during each contraction a decrease in both stroke volume and cardiac output occurs

End Diastolic Volume (EDV)

amount of blood in ventricle after it has filled during relaxation (ml/beat)

End Systolic Volume (ESV)

amount of blood in ventricle at end of a contraction (ml/beat)

Stroke Volume (SV)

amount of blood pumped in one heartbeat (ml/beat)

Define Cardiac Output (CO)

amount of blood pumped into pulmonary and systemic circuits in 1 minute (ml/min)

Chordae tendineae

attach papillary muscles to valves located between atria and ventricles

The Atrioventricular Valves

backward flow is prevented by valves between atria and ventricles, consist of flaps, called cusps; composed of endocardium overlying a core of collagenous connective tissue

Left Ventricular Heart Failure

blood often backs up within pulmonary circuit; known as pulmonary congestion; increases pressure in these vessels, driving fluid out of pulmonary capillaries and into lungs, a condition called pulmonary edema

Right Ventricular Heart Failure

blood often backs up within systemic circuit; known as systemic congestion; increases pressure in these vessels, driving fluid out of systemic capillaries and into tissues, a condition called peripheral edema

Pulmonary Arteries

bring deoxygenated blood to right and left lungs

Purkinje fiber system

depolarize at 20 times/minute; (1) Atrioventricular bundle (AV bundle) penetrates heart's fibrous skeleton though septum (2) Right and left bundle branches course along right and left sides of inter ventricular septum (3) Terminal branches penetrate ventricle and finally come into contact with contractile cardiac muscle cells

Inferior vena cava (IVC)

drains deoxygenated blood from veins inferior to diaphragm

Superior vena cava (SVC)

drains deoxygenated blood from veins superior to diaphragm

Base

flattened base is posterior side (not inferior) facing posterior rib cage is point of attachment of the great vessels

Parietal pericardium

fused to fibrous pericardium to form pericardial sac

S4

heard just before S1; typically results from blood being forced into a stiff or enlarged ventricle; pathologic; congestive heart failure

Pericarditis

inflammation of pericardium

Endocardium

inner layer that lines lumen composed of simple squamous epithelium and layers of connective tissue called endothelium; covers heart valves and is continuous with lining of blood vessels

Serous pericardium

inner serous membrane that produces serous fluid:

Visceral pericardium or epicardium

innermost layer or epicardium; superficial layer of heart wall

Tachycardia

is a heart rate over 100 beats permute; sinus tachycardia is a regular, fast rhythm

Bradycardia

is a heart rate under 60 beats per minute

Atrial fibrillation

is generally not life threatening because atrial contraction isn't necessary for ventricular filling; manifests on an ECG tracing as an "irregularly irregular" rhythm (one that has no discernible pattern) and lacks P waves

Ventricular fibrillation

is immediately life-threatening and manifests on ECG with chaotic activity; - Treated with defibrillation (an electric shock to heart); depolarizes all ventricular muscle cells simultaneously and throws cells into their refractory periods - Ideally, SA node will resume pacing heart after shock is delivered

Right atrium

larger, thinner-walled, and more anterior

Systemic side of heart

left side of heart is systemic pump; receives oxygenated blood from pulmonary veins and pumps it into blood vessels that serve body called systemic circuit; - Arteries deliver oxygenated blood to smallest blood vessels systemic capillaries - Gas exchange in reverse: O2 diffuses from blood into tissue, and CO2 diffuses from tissues into blood - Veins return deoxygenated blood back to right side of heart, to be pumped into pulmonary circuit

Atrioventricular (AV) node

located in lower right atrium; slower with an intrinsic rate of 40 action potentials per minute

Sinoatrial (SA) node

located in upper right atrium; fastest intrinsic rate of depolarization—60-80 times per minute, a rate that is subject to influence from sympathetic and parasympathetic nervous systems

Coronary Artery Bypass Grafting (CABG)

other vessels are grafted onto heart (come from saphenous vein in the leg)

Fibrous pericardium

outer layer; composed of collagen bundles that make it tough; Low distensibility - resists stretching to prevent chambers of heart from overfilling with blood

P-R interval

period from beginning of P wave to beginning of R wave; represents time it takes for depolarization generated by SA node to spread through atria to ventricles; includes AV node delay

Apex

points toward left hip

Pulmonary trunk

receives deoxygenated blood pumped from right ventricle

S-T segment

recorded during plateau phase of ventricles, and no net changes occur in electrical activity (flat); Elevation or depression of S-T segment is seen with many clinical conditions, most notably myocardial ischemia and myocardial infarction

Mechanical physiology

refers to the actual processes by which blood fills the cardiac chambers and is pumped out of them. Pressure changes caused by contractions drive blood flow through the heart, with valves preventing backflow.

P wave

represents atrial depolarization except SA node; registers as an upward deflection on ECG

R-R interval

represents entire duration of generation and spread of an action potential through heart; can be measured to determine heart rate

QRS complex

represents ventricular depolarization; actually three separate waves; Q wave is first downward deflection; R is large upward deflection; S is following downward deflection

Describe the ventricles

right and left ventricles are asymmetrical; right ventricle is wider with thinner walls than left ventricle because of pressure differences in pulmonary and systemic circuits - Right ventricle has little resistance against which to pump; left ventricle pumps against much greater resistance - Left ventricle works harder than right ventricle and has greater muscle mass; walls of left ventricle are about three times thicker than those of right ventricle; example of Structure-Function Core Principle

Pulmonary side of heart

right side of heart is pulmonary pump; pumps blood into vessels to lungs called pulmonary circuit; • Pulmonary arteries deliver oxygen-poor and carbon dioxide-rich, or deoxygenated, blood to lungs •Gas exchange between lung alveoli and pulmonary capillaries; O2 diffuses in while CO2 diffuses out •Pulmonary veins deliver oxygen-rich (oxygenated) blood to left side of heart

Explain the significance of the fossa ovalis.

small indentation in septum of atria; remnant of a hole known as foramen ovale present in fetal heart

Angiography

small tube is fed through femoral artery in ascending aorta, and into coronary arteries; special dye is injected into arteries, and examined by x-ray

The Semilunar Valves

stop blood from flowing back into ventricles; half-moon shape with three cusps; also composed of endocardium and a central collagenous core

Aorta

supplies entire systemic circuit with oxygenated blood

Contractility

the heart's intrinsic pumping ability, or ability to generate tension. - Increasing contractility will increase stroke volume and therefore decrease ESV - Decreasing contractility will do opposite: decreasing stroke volume and increasing ESV (assuming that preload and after load remain constant)

Interventricular septum

thick, muscular wall separates right and left ventricles; contracts with rest of ventricular muscle; helps to expel blood into pulmonary trunk and aorta

Left atrium

thicker-walled, smaller, and located mostly on posterior side at base

Q-T interval

time from beginning of QRS complex to the end of the T wave; action potentials spread through ventricular cells

Papillary muscles

ventricles contain finger-like projections of muscle

Myocardial Infarction (MI)

"heart attack", clot or plaque obstructs flow; hear tissue dies and is replace by scar tissue

Explain the function of the auricles.

- Atria have a muscular pouch called an auricle; expand to give atria more space in which to hold blood - Auricle of right atrium much larger than left atrium

Compare the pressure changes in the right and left ventricle during the cardiac cycle

- Right ventricle: Pressure in the right. s trifle must be more than the luk monarch trunk to push blood through the pulmonary valve - Left ventricle: Pressure in the left ventricle must be more than in the aorta to push blood through the aortic valve

Explain the significance of the plateau phase.

- Sequence of events of a contractile cell action potential resembles that if a skeletal muscle fiber action potential with one important exception: plateau phase - Plateau phase lengthens cardiac action potential to about 200-300 msec; slows heart rate, providing time required for heart to fill with blood - Plateau phase also increases strength of heart's contraction; prolonged action potential makes muscle twitch last a long time, so it can develop more force; allows more calcium ions to enter cell; needed for cell's contraction via sliding-filament mechanism - Plateau phase also effectively prevents tetany (sustained contraction) in heart by lengthening refractory period (time during which an excitable cell cannot be stimulated to contract again); allows heart to relax and ventricles to refill with blood before cardiac muscle cells are stimulated to contract again

State how valves ensure blood flow in one direction

- Two types of valves ensure this by preventing blood from flowing backward; flaps of valves oriented to open and close depending on the pressures in chambers - Backflow of blood doesn't occur in veins draining into atria, as atria are under very low pressure and blood mostly flows into atria when help of gravity and pressure in veins

3 types of gated ion channels

- Voltage-gated Na+ ion channels - open in response to voltage changes across membrane - Ca2+ ion channels - demonstrate voltage-gated opening but time-gated closing, meaning that they close after a certain period regardless of voltage - K+ ion channels; some of these channels are ligand-gated, whereas others are voltage-gated

Pacemaker Cells and the Cardiac Conduction System:

1% of cardiac muscle cells capable of spontaneously generating action potentials, thereby setting the pace of the heart. - There are three populations of these cells in heart that are capable of spontaneously generating action potentials, thereby setting pace of heart - These three cell populations are collectively called the cardiac conduction system - Pacemaker cells undergo rhythmic, spontaneous depolarizations that lead to action potentials; spread quickly through heart by cardiac conduction system (group of interconnected pacemaker cells

Connecting the Electrical and Mechanical Events in the Heart: Wigger's diagram

1) Ventricular filling phase: Ventricular diastole followed by Atrial systole - AV valves open semilunar valves closed; (up arrow) pressure in atria and slight (up arrow) pressure in ventricles; ECG: generation of P-wave and beginning of QRS complex (2) Isovolumetric Contraction phase: Ventricular systole - AV and semilunar valves closed; increasing (bigger arrow) pressure in ventricles; ECG: completion of QRS complex; S1 (lub) heart sound. (3) Ventricular Ejection phase: Ventricular systole - AV valves close and semilunar valves open; (up arrow) increasing pressure in ventricles; ECG: beginning of T-wave. stroke volume occurs here (4) Isovolumetric Relaxation phase: Ventricular diastole - AV and semilunar valves close; dicrotic notch- rapidly decreasing pressure in ventricles; ECG: completion of __________________; S2 (dub) heart sound.

The Coronary Circulation

1. Coronary Arteries - Ascending Aorta emerges from left ventricle, two branches arise: Right (supplies rt. atrium and ventricle) and Left (supplies lt. atrium and ventricle) Coronary arteries; Coronary arterial supply forms anastomoses (systems of channels formed between blood vessels) 2. Cardiac Veins - three major veins: Great, middle and small cardiac veins drain the four chambers; all drain into.... 3. Coronary Sinus - receives blood from cardiac veins; empties into right Atrium

Pulmonary veins

2 from each lung—drain oxygenated blood into left atrium

Identify the 4 chambers of the heart and the vessels that empty blood into them.

4 Chambers - superior right and left atria (singular atrium) and inferior right and left ventricles - Both right and left atria receive blood from veins (blood vessels that bring blood to heart) - Blood drains from atria to ventricles; - Ventricles pump blood into blood vessels called arteries (carry blood away from heart) - Main veins and arteries that bring blood to and from heart are known as great vessels

Coronary Artery Disease (CAD)

A buildup of fatty material called plaques in coronary arteries results in Coronary Artery Disease, or CAD; leading cause of death worldwide; - CAD decreases blood flow to myocardium; results in inadequate oxygenation of myocardium, a condition known as myocardial ischemia - When present, symptoms generally come in form of chest paint; preferred to as angina pectoris - Most dangerous potential consequence of CAD is a myocardial infarction (MI)

Define heartbeat.

Cardiac muscle cells contract as a unit to produce one coordinated contraction; muscle cells are arranged in a spiral pattern

Contractile Cell Action Potentials

Contractile cells make up the great majority (99%) of cardiac muscle cells. Resting Membrane Potential is set at -85 mV. - An action potential in a contractile cardiac muscle cell results from a reversal in membrane potential—inside of plasma membrane swings from negative (about -85 mV) to momentarily positive (ranging from 0 to +20 mV) - These changes happen because of voltage-gated ion channels in sarcolemma and because of unequal concentrations of sodium and potassium ions on either side of membrane that drives those ions in or out of cell through channels

heart block

Disturbances in conduction pathways - normal conduction pathway may be disrupted or a blockage along conduction system, called a heart block; Often found at AV node; P-R interval is longer than normal; extra P waves are present as some are not being conducted through AV node - Block is along right or left bundle branch; generally widen QRS complex, as depolarization takes longer to spread through ventricles

Describe diastole and systole as they occur in the cardiac cycle

Each cardiac cycle consists of one period of relaxation called diastole and one period of contraction called systole for each chamber of the heart - Atrial and ventricular diastoles and systoles occur at different times as a result of AV node delay; both sides of heart are working to pump blood into their respective circuits simuealtanously - Cycle is divided into four main phases that are defined by actions of ventricles and positions of valves: filling, contraction, ejection, and relaxation

Contracted ventricle

High pressure in the left ventricle pushes blood against the mitral valve _________ it and against the aortic valve __________ it.

Bicuspid valve (mitral valve)

Left AV valve between left Atrium and left Ventricle

What are the two types of cardiac muscle cells?

Pacemaker cells and Contractile cells

Cardiac Tamponade

Pericardial cavity becomes filled with excess fluid - excess fluid squeezes heart; ventricles can't fill up with as much blood; less blood pumped with each beat - Pericardiocentesis: excess fluid is removed via a needle inserted into the pericardial cavity

Pulmonary circuit is [ ] pressure; Systemic circuit is [ ].

Pulmonary circuit is low-pressure because it pumps blood only to lungs; systemic circuit is high-pressure because it has to pump blood to entire rest of body

Differences between cardiac muscle and skeletal muscle in contractions

SR of cardiac muscle less extensive than skeletal muscle; concentration of calcium ions in cardiac extracellular fluid plays a significant role in determining strength of contraction (also no triad)

Define the Cardiac Cycle.

Sequence of events that take place within heart fin one heartbeat ti the next is known as cardiac cycle

What are the 3 groups of pacemaker cells?

Sinoatrial (SA) node, Atrioventricular (AV) node, Purkinje fiber system

4 Steps in contractile cell action potential

a. Rapid depolarization phase. fast Voltage-gated sodium ion channels in the sarcolemma are activated. Rapid and massive influx of sodium ions occurs, leading to depolarization b. Initial repolarization phase. Due to the abrupt inactivation of the sodium ion channels and very small outflow (eflux) of potassium ions through potassium (voltage-gated) ion channels that are open briefly. c. Plateau phase. The depolarization is sustained at about 0 mV, known as the plateau phase. Due to the opening of slow voltage-gated calcium ion channels and the influx of calcium ions. d. Repolarization phase. Both the sodium and calcium ion channels return to their resting states and potassium ion channels open. Positively-charged potassium ions exit the cardiac muscle cell and the membrane potential returns to its resting value of about -85 mV.

State the sequence of Conduction Pathway through the Heart and the time for each:

a. SA node generates an action potential; spreads rapidly via gap junctions to surrounding atrial cells and conducted by atrial conducting fibers to AV node: 0.03 second b. Conduction slows at AV node because of low number of gap junctions between AV nodal cells and presence of nonconducting fibrous skeleton that surrounds AV node; known as AV node delay: 0.13 second; allows atria to depolarize (and contract) before ventricles, giving ventricles time to fill with blood c. Action potential is then conducted from AV bundle to Right and Left bundle branches to Purkinje fibers to contractile cardiac muscle cells of ventricles: 0.06 sec

Mechanism of Contractile Cell Contraction: Excitation-Contraction Coupling:

a. Sliding filament mechanism-similar to skeletal muscle. b. Depolarization propagates through the sarcolemma down the t-tubule which causes the sarcoplasmic reticulum to release calcium ions. These ions bind to troponin exposing active sites on actin and cross bridge cycling occurs as myosin binds to active sites.

4 Steps in generation of pacemaker potential

a. Slow initial depolarization phase. Plasma membrane in a hyperpolarized state. Opens HCN (nonspecific cation) channels in the membrane which allow more positive ions to leak into the cell than positive ions to leak out, which results in an overall slow depolarization to threshold. b. Full depolarization phase. At threshold, calcium ion channels open, allowing these ions to enter the cell and thereby causing the membrane to fully depolarize. c. Repolarization phase. Calcium ion channels close while voltage-gated potassium ion channels begin to open, allowing these ions to leave the cell and the membrane to repolarize. d. Minimum potential phase. potassium ion channels remain open and the membrane is hyperpolarized, which opens the HCN (nonspecific cation) channels, and the cycle begins again.

Describe the Histology of Cardiac Muscle Tissue and Cells

a. Typically branched cells with a single nucleus (uninucleate); shorter and wider than skeletal muscle fibers b. Contain Myoglobin (protein that carries oxygen); many mitochondria; reflect their high energy demands - Striations- alternating light and dark bands due to arrangement of contractile proteins (actin and myosin) within cardiac muscle cells - Intercalated discs- join cardiac muscle cells; contain desmosomes to hold cardiac muscle cells together and gap junctions to allow ions to flow from one cell to another - Sarcoplasmic reticulum- smooth ER; calcium storage

Coronary Angioplasty

balloon inflated in blocked artery and wire-mesh tubing called a stent inserted into artery

Aortic valve

between left ventricle and aorta

Pericardial cavity

between parietal and visceral layers; contains watery serous fluid (pericardial fluid); acts as a lubricant, decreasing friction as heart moves

Pulmonary valve

between right ventricle and pulmonary trunk

Electrocardiogram (ECG)

graphic recording of electrical activity occurring in all cardiac muscle cells over a period of time; - Electrical changes are shown on ECG as deflections, or waves that show changes in electrical activity—if there is no net difference, there is no deflection shown - May reveal disturbance in electrical rhythm known as a dysrhythmia or arrhythmia

S3

heard right after S2; results from recoil of ventricular walls as they are stretched and fulled; normal in young

Lub (S1)

heard when AV valves close

Dub (S2)

heard when semilunar valves close

T wave

represents ventricular repolarization; T wave is an upward deflection