Chapter 19: Heart Powerpoint Flashcards
The right side of the heart is known as the ______ circuit.
pulmonary
What does the pulmonary circuit do?
Carries blood to lungs for gas exchange and back to heart
The left side of the heart is known as the ______ circuit.
systemic
What does the systemic circuit do?
Supplies oxygenated blood to all tissues of the body and returns it to the heart
The pulmonary circuit is on the ____ side of the heart
right
Where does blood enter and leave the systemic circuit?
Oxygenated blood enters via the pulmonary veins and leave via the aorta
Where does blood enter and leave the pulmonary circuit?
Oxygen-poor blood enter via inferior & superior venae cavae
Leave via pulmonary trunk
At any age, the heart is the size of your ______
fist
What are the two layers of the sac protecting the heart?
Pericardial sac (outer) Visceral pericardium/ epicardium (inner)
What are the two layers of the pericardium?
1) Superficial fibrous layer of connective tissue
2) Deep, thin serous layer (parietal pericardium)
Describe the visceral pericardium (epicardium)
Serous membrane covering heart
What fills the pericardial cavity?
5 to 30 mL of pericardial fluid
What are the 3 functions of the pericardium?
1) Protects and anchors the heart
2) Allows heart to beat without friction
3) Prevents overfilling of the heart with blood
What are the 3 layers of the heart?
Epicardium, myocardium and endocardium
Describe the epicardium (visceral pericardium)
- Serous membrane covering heart
- Adipose in thick layer in some places
- Coronary blood vessels travel through this layer
Describe the endocardium
- Smooth inner lining of heart and blood vessels
- Covers the valve surfaces and is continuous with endothelium of blood vessels
Describe the myocardium
- Layer of cardiac muscle proportional to work load; left side has more muscle.
- Muscle spirals around heart (produces wringing motion)
- Fibrous skeleton framework of collagenous and elastic fibers
What is the purpose of the fibrous skeleton framework of the myocardium?
- Provides structural support and attachment for muscle and valves
- Electrical insulation between atria and ventricles (limits spread of action potentials)
Describe the atria of the heart
- Receiving chambers of heart
- Each atrium has an auricle (seen on surface) to enlarge chamber
- Pectinate muscles: internal ridges of atria and auricles
Describe the ventricles of the heart
- Discharging chambers of heart
- Trabeculae carneae: internal ridges in both ventricles
What are the two external sulci of the heart?
Atrioventricular sulcus and interventricular sulcus
What does the atrioventricular sulcus do?
Separates atria and ventricles
What does the interventricular sulcus do?
Overlies interventricular septum that divides the right ventricle from the left
What are the two internal septums of the heart?
Interatrial septum and interventricular septum
What does the interatrial septum do?
- Wall that separates atria
- There’s a hole in this septum in fetuses
What does the interventricular septum do?
Muscular wall that separates ventricles
What do the valves of the heart do?
ensure one-way flow of blood
What do the atrioventricular (AV) valves do?
Control blood flow between atria and ventricles
The right AV valve is called the _____ valve, and the left AV valve is called the _____ valve (formerly the _____ valve).
Tricuspid valve; mitral valve; (bicuspid)
What do the chordae tendineae do?
- Cords connect AV valves to papillary muscles
- Prevent AV valves from flipping (eversion) or bulging into atria when ventricles contract
Describe the semilunar valves
- Located at exit of ventricles (controls flow into great arteries)
- Open and close because of blood flow and pressure
Pulmonary semilunar valve: ____ side
Aortic semilunar valve: ____side
right; left
What happens when the ventricles of the heart contract?
- AV valves close as blood attempts to back up into the atria
- Pressure rises inside of the ventricles
- Semilunar valves open and blood flows into great vessels
What happens when the ventricles of the heart relax?
- Pressure drops inside the ventricles
- Semilunar valves close as blood attempts to back up into the ventricles from the vessels
- AV valves open
- Blood flows from atria to ventricles
Describe the flow of blood through the heart (11 steps)
1) Blood enters right atrium from superior and inferior venae cavae.
2) Blood in right atrium flows through right AV valve into right ventricle.
3) Contraction of right ventricle forces pulmonary valve open.
4) Blood flows through pulmonary valve into pulmonary trunk.
5) Blood is distributed by right and left pulmonary arteries to the lungs, where it unloads CO2 and loads O2.
6) Blood returns from lungs via pulmonary veins to left atrium.
7) Blood in left atrium flows through left AV valve into left ventricle.
8) Contraction of left ventricle (simultaneous with step 3) forces aortic valve open.
9) Blood flows through aortic valve into ascending aorta.
10) Blood in aorta is distributed to every organ in the body, where it unloads O_2 and loads CO_2
11) Blood returns to right atrium via venae cavae.
_% of blood pumped by heart is pumped to the heart muscle
5
Is most blood delivered to the heart muscles when it’s relaxed or contracted?
Relaxed
Define the arterial supply
right & left coronary arteries branch from the ascending aorta
Define and describe angina pectoris
- Chest pain from partial obstruction of coronary blood flow (ischemia)
- Obstruction partially blocks blood flow
- Myocardium shifts to anaerobic respiration/fermentation, producing lactate and thus stimulating pain
Define and describe myocardial infarction (MI)
- Also known as a heart attack
- Sudden death of a patch of myocardium resulting from long-term obstruction of coronary circulation
- Obstruction often blood clot or fatty deposit (atheroma)
- Some protection from MI is provided by arterial anastomoses which provide alternative routes of blood flow (collateral circulation) within the myocardium
Describe cardiomyocytes
striated, short, thick, branched cells
Repair of damage of cardiac muscle is almost entirely by what?
Fibrosis (scarring)
What do the intercalated discs (cell junctions) of the heart contain?
- Interdigitating folds
- Desmosomes and fascia adherens
- Gap junctions (electrical junctions)
Cardiomyocytes have a smaller sarcoplasmic reticulum, which means they must depend on the influx of what?
Calcium ions (**)
The heart depends almost exclusively on what kind of respiration to make ATP? Why?
- Aerobic
- Because the heart is rich in myoglobin and glycogen and has huge mitochondria
True or false: The heart is adaptable to different organic fuels
True; the heart is more vulnerable to oxygen deficiency than lack of a specific fuel
True or false: cardiac muscle is fatigue resistant
True
Describe autorhythmic cells
- Composed of an internal pacemaker and nerve-like conduction pathways through myocardium
- Initiate and distribute action potentials through the heart
- Leads to depolarization and contraction of the rest of myocardium
Describe the sinoatrial (SA) node
- Modified cardiomyocytes
- Pacemaker (determines heart rate)
Describe the atrioventricular (AV) node
Electrical gateway to the ventricles
Describe the atrioventricular (AV) bundle (bundle of His)
Bundle forks into right and left bundle branches
Describe the subendocardial conducting networks (Purkinje fibers)
- Nerve-like processes spread throughout ventricular myocardium
- Cardiomyocytes then pass signal from cell to cell through gap junctions
List the 5 steps of the heart’s conduction system
1) SA node fires.
2) Excitation spreads through atrial myocardium.
3) AV node fires.
4) Excitation spreads down AV bundle.
5) Subendocardial conducting network distributes excitation through ventricular myocardium.
________ nerves increase heart rate and contraction strength
Sympathetic
________ nerves slow the heart rate; little or no vagal stimulation of the myocardium
Parasympathetic
Define systole and diastole
Systole: contraction
Diastole: relaxation
Systole and diastole usually refer to what?
The action of the ventricles
Define sinus rhythm
Normal heartbeat triggered by the SA node
SA node actually about 100 bpm but vagus nerve slows it to ~75 bpm (vagal tone)
Define ectopic focus
A region firing other than the SA node; may set heart rhythm if SA node is damaged
Give an example of ectopic focus
Nodal rhythm: if SA node is damaged, heart rate is set by AV node, 40 to 50 bpm
Why can ectopic focus typically not sustain life?
Other ectopic focal rhythms (excluding nodal rhythm) are 20 to 40 bpm and too slow to sustain life – requires artificial pacemaker
True or false: SA node does not have a stable resting membrane potential
True
Describe the steps of an action potential of the SA node
1) Starts at −60 mV and gradually depolarizes due to slow Na^+ inflow; this is called pacemaker potential
2) When it reaches threshold of −40 mV, voltage-gated fast Ca^(2+) and Na^+ channels open, which causes faster depolarization
3) K^+ channels then open and K^+ leaves the cell, causing repolarization
4) Once K^+ channels close, pacemaker potential starts over
Signal from SA node stimulates what?
Two atria to contract almost simultaneously
Signal from the SA node slows when it reaches what part of the heart? Why?
- Signal slows down through AV node
- This is because it has thin cardiomyocytes with fewer gap junctions
- This delays signal 100 ms which allows the ventricles time to fill
Signals travel very quickly through what two places (after the SA node)?
AV bundle and subendocardial conducting network (Purkinje fibers)
When signal reaches the AV bundle and subendocardial conducting network (Purkinje fibers), what happens?
- Entire ventricular myocardium depolarizes and contracts in near unison
- Then ventricular systole progresses up from the apex of the heart, twisting the heart
Cardiomyocytes have a stable resting potential of ____ mV, and depolarize only when stimulated
−90
What are the 3 phases of electrical stimulation (in general)?
Depolarization, plateau, repolarization
Describe the depolarization phase of myocardium
- Very brief
- Stimulus opens voltage-regulated Na^+ gates (Na^+ rushes in)
- Na^+ gates close quickly
Describe the plateau phase of myocardium
- Lasts 200 to 250 ms, sustains contraction for expulsion of blood from heart
- Ca(2+) channels open allowing Ca(2+) to flow in from the ECF
- This causes Ca(2+) to be released from the SR to trigger contraction
Describe the repolarization phase of myocardium
Ca^(2+) channels close, K^+ channels open, rapid diffusion of K^+ out of cell returns it to resting potential
Describe the refractory period of myocardium after an action potential. What does this prevent?
- Has a long absolute refractory period of 250 ms (compared to 1 to 2 ms in skeletal muscle)
- Prevents wave summation and tetanus which would stop the pumping action of the heart
List the 5 steps of myocardium conducting an action potential
1) Voltage-gated Na^+ channels open.
2) Na^+ inflow depolarizes the membrane and triggers the opening of still more Na^+ channels, creating a positive feedback cycle and a rapidly rising membrane voltage.
3) Na^+ channels close when the cell depolarizes, and the voltage peaks at nearly +30 mV.
4) Ca^(2+) entering through slow Ca^(2+) channels prolongs depolarization of membrane, creating a plateau. Plateau falls slightly because of some K^+ leakage, but most K^+ channels remain closed until end of plateau.
5) Ca^(2+) channels close and Ca^(2+) is transported out of cell. K+ channels open, and rapid K^+ outflow returns membrane to its resting potential.
Compare and contrast the conduction of an electrical signal in skeletal and cardiac muscle
1) Skeletal:
- Requires motor neuron to release ACh.
- Binding of ACh causes depolarization of motor end plate.
- This leads to action potential across sarcolemma of muscle cell.
- Depolarization (Na+ rushes in) leads to contraction of muscle.
- Repolarization (K+ rushes out) “resets” sarcolemma
- Action potential: 1-2ms
- Contraction: 15-100ms
2) Cardiac:
- Have slow depolarization to threshold
- At threshold, have fast depolarization.
- This leads to action potential of rest of conduction system AND any muscle cell connected by gap junctions.
- Depolarization (Na+ rushes in) leads to contraction of muscle.
- Plateau (Ca+ flows in) allows ____(**)
- Repolarization (K+ rushes out) “resets” sarcolemma
- Action potential: 200-250ms
- Contraction: 200ms
Define an Electrocardiogram (ECG or EKG)
Composite of all action potentials of nodal and myocardial cells detected, amplified and recorded by electrodes on arms, legs, and chest
What happens during the P wave of an ECG?
- SA node fires, atria depolarize and contract
- Atrial systole begins 100 ms after SA signal
What happens during the QRS complex of an ECG?
- Ventricular depolarization
- Complex shape of spike due to different thickness and shape of the two ventricles
What happens during the ST segment of an ECG?
- Ventricular systole
- Corresponds to plateau in myocardial action potential
What happens during the T wave of an ECG?
Ventricular repolarization and relaxation
Deviations of ECG from normal can indicate what?
1) Myocardial infarction (MI)
2) Abnormalities in conduction pathways
3) Heart enlargement
4) Electrolyte and hormone imbalances
Describe ventricular fibrillation
- Serious arrhythmia caused by electrical signals traveling randomly
- Heart cannot pump blood; no coronary perfusion
- Hallmark of heart attack (MI)
- Kills quickly if not stopped
Define the cardiac cycle
One complete contraction and relaxation of all four chambers of the heart
What are the two main variables that govern fluid movement?
Pressure causes flow and resistance opposes it
Fluid will only flow if there is a ______ ________
pressure gradient (pressure difference)
Fluid flows from ____-pressure point to ____-pressure point
high; low
What unit is pressure measured with, and with what instrument?
Pressure is measured in mmHg with a manometer (sphygmomanometer for BP)
Increasing volume, ______ pressure
Decreasing volume, _______ pressure
Increasing volume, decreases pressure
Decreasing volume, increases pressure
Describe how pressure gradients and flow allow the heart to function
1) When ventricle relaxes and expands, its internal pressure falls
- This allows AV valves open, blood flows into ventricle
2) When ventricle contracts, internal pressure rises
- This causes AV valves to close; semilunar valves are pushed open and blood flows out of ventricles
Define valvular insufficiency and give 3 examples of valvular insufficiency disorders
-Defined as any failure of a valve to prevent reflux (regurgitation), the backward flow of blood
Examples:
1) Valvular stenosis: cusps are stiffened and opening is constricted by scar tissue (such as from rheumatic fever)
2) Mitral valve prolapse
3) Heart murmur: abnormal heart sound
Define auscultation
Listening to sounds made by the body
Describe the first heart sound (S1) and the second heart sound (S2)
1) First heart sound (𝐒𝟏): louder and longer “lubb,” occurs with closure of AV valves
2) Second heart sound (𝑺𝟐), softer and sharper “dupp,” occurs with closure of semilunar valves
List the 4 phases of the cardiac cycle
1) Ventricular filling (during diastole)
2) Isovolumetric contraction (during systole)
3) Ventricular ejection (during systole)
4) Isovolumetric relaxation (during diastole)
The entire cardiac cycle (all four of these phases) is ___ sec in a heart beating 75 bpm
0.8
Describe ventricular filling (during diastole)
- Ventricles relax and expand, pressure decreases.
- Blood flows from atria to ventricles
- At end of phase, atria contract to finish filling ventricles
- AV valves are open; semilunar valves are closed
Describe the 2 things that happen during ventricular systole (atria in diastole)
1) Isovolumetric contraction: ventricles start contracting and AV valves close
2) Ventricular ejection: semilunar valves forced open
Describe the 2 things that happen during early diastole
1) Isovolumetric relaxation: Both atria and ventricles are relaxed; semilunar valves close
The cycle starts over!
2) Ventricular filling: AV valves now open
True or false: Both ventricles must eject same amount of blood
True
Define congestive heart failure (CHF) and describe its causes
- Results from the failure of either ventricle to eject blood effectively
- Usually due to a heart weakened by myocardial infarction, chronic hypertension, valvular insufficiency, or congenital defects in heart structure
Define left ventricular failure and describe its symptoms
- Blood backs up into the lungs causing pulmonary edema
- Symptoms: Shortness of breath or sense of suffocation
Define right ventricular failure and describe its symptoms
- Blood backs up in the vena cava causing systemic or generalized edema
- Symptoms: Enlargement of the liver, ascites (pooling of fluid in abdominal cavity), distension of jugular veins, swelling of the fingers, ankles, and feet
- Eventually leads to total heart failure
Describe the steps of a pulmonary edema
1) Right ventricular output exceeds left ventricular output.
2) Pressure backs up.
3) Fluid accumulates in pulmonary tissue.
Describe the steps of a systemic edma
1) Left ventricular output exceeds right ventricular output.
2) Pressure backs up.
3) Fluid accumulates in systemic tissue.
Define cardiac output
- Amount ejected by each ventricle in 1 minute
- Cardiac output = heart rate x stroke volume
What is normal cardiac output at rest? What about during vigorous exercise?
- About 4 to 6 L/min at rest
- Vigorous exercise increases CO to 21 L/min for a fit person and up to 35 L/min for a world-class athlete
Define cardiac reserve and state what it’s correlated with
- The difference between a person’s maximum and resting CO
- Increases with fitness, decreases with disease
Define heart rate and stroke volume
Heart Rate: beats per minute
Stroke Volume: amount of blood pumped out by a ventricle with each contraction
Infants have HR of ___ bpm or more
Young adult females average __ to __ bpm
Young adult males average __ to __ bpm
Heart rate rises again in the elderly
Infants have HR of 120 bpm or more
Young adult females average 72 to 80 bpm
Young adult males average 64 to 72 bpm
Heart rate rises again in the elderly
Define positive and negative chronotropic agents
Positive chronotropic agents—factors that raise the heart rate
Negative chronotropic agents—factors that lower the heart rate
What does the cardiovascular center of the medulla do, and what influences it?
-Sends out sympathetic or parasympathetic signals based on input from cerebral cortex or limbic system
What 3 variables affect stroke volume?
1) Preload
2) Contractility
3) Afterload
1) Increased preload or contractility ______ stroke volume
2) Increased afterload _____ stroke volume
1) Increased preload or contractility increases stroke volume
2) Increased afterload decreases stroke volume
Define and describe preload
- Defined as the amount of tension in ventricular myocardium immediately before it begins to contract
- Increased preload causes increased force of contraction
- Exercise increases venous return and stretches myocardium
What does the Frank–Starling law of the heart say?
- Stroke volume is proportional to the end diastolic volume
- Ventricles eject almost as much blood as they receive
- The more they are stretched, the harder they contract
Define contractility in the context of the heart
It refers to how hard the myocardium contracts for a given preload
Positive inotropic agents increase __________
contractility
Give 4 examples of things that are positive inotropic agents
1) Hypercalcemia
2) Catecholamines
3) Glucagon
4) Digitalis
Give 4 examples of negative inotropic agents
1) Hypocalcemia
2) Hyperkalemia
3) Acidosis
4) Drugs such as calcium channel blockers
Define and describe afterload
- Defined as the sum of all forces opposing ejection of blood from ventricle
- Afterload mostly is the blood pressure in aorta and pulmonary trunk
- Opposes the opening of semilunar valves
- Limits stroke volume
What increases afterload?
- _______(**) increases afterload and opposes ventricular ejection
- Anything that impedes arterial circulation can also increase afterload
- Lung diseases that restrict pulmonary circulation (Cor pulmonale) such as: emphysema, chronic bronchitis, and black lung disease
