CH. 18 The Heart Flashcards
What are the 3 parts of the circulatory system and their functions?
Heart - serves as the pump that imparts pressure to move the blood to the tissue
Blood Vessels - the conveyance through which blood travels (perfusion)
Blood - medium used to transport materials long distances in the body
What makes up the blood vessels and their functions?
Arteries - carry blood away from the heart
Capillaries - serves as the vessels of exchange (between blood & air/blood & cells)
Veins - carry blood towards the heart
What is the heart and its 3 anatomic features?
It is a hollow, 4-chambered organ
Features:
-Two-pump structure
-Great vessels that deliver and propel blood
-Two pairs of valves
What makes up the two-pump structure of the heart?
Right Pump - receives deoxygenated blood from body and propels it to lungs
Left Pump - receives oxygenated blood from lungs and propels it to body returning to circulation
Two Chambers on each pump:
-Atrium: receiving, superior chambers that contractions contribute very little to the propulsion of blood from the heart
-Ventricle: propelling, inferior chambers to return the blood to circulation
What are the two large arteries and their features?
Pulmonary Trunk - receives deoxygenated blood from right ventricle and splits into pulmonary arteries
Aorta - receives oxygenated blood from left ventricle
Both are found on the superior border of the ventricles
What are the large veins of the heart and their features?
Superior & Inferior Vena Cava - deliver deoxygenated blood from body to right atrium
Pulmonary Veins - deliver oxygenated blood from lungs to left atrium
Both are found on the posterior aspect of the heart
What are the two pairs of valves and their features?
Atrioventricular (AV) Valves: lies between atrium and ventricles, prevent backflow from ventricle to atria, and edges of the valves are cord-like to prevent papillary muscles being exerted by ventricular pressure
-Right AV Valve = tricuspid valve
-Left AV Valve = mitral (bicuspid) valve
Semilunar Valves: lie at the junction between the arteries & ventricles, possessing 3 cusps to prevent backflow into the ventricle
-Pulmonary Valve = lies between right ventricle and pulmonary trunk
-Aortic Valve = lies between left ventricle and aorta
Feature: Serve a unidirectional blood flow into the heart and prevent backflow
What are the two types of circuits and their features?
Pulmonary Circuit (right side):
-delivers deoxygenated blood from the heart to lungs
gas exchange occurs in lungs
-returns oxygenated blood from lungs to heart
Systemic Circuit (left side):
-delivers oxygenated blood from heart to tissues
-material and gas exchange occurs in tissues
-returns deoxygenated blood from tissues to heart
Both feature: equal amount of blood are pumped by both ventricles (ventricular balance)
What are the colors of veins and arteries? What does this indicate?
Veins = blue for deoxygenated blood
Arteries = red for oxygenated blood
Where is the location of the heart?
Within the mediastinum where the apex (point) of the heart points towards the left hip
2/3rd’s of the mass of the heart lies to the left of mid-sternal line
What are the pericardium and its features?
Double-walled sac (pericardial sac) covering the heart that is composed of two layers:
Fibrous Pericardium (outermost layer)
-tough, dense layer of connective tissue
-functions to protect the heart, anchor it to the surrounding structures and protect it from overfilling
Serous Pericardium (innermost layer)
-thin, two-layer membrane: parietal (outermost) and visceral (inner) layers
Pericardial Cavity = space between the fibrous and serous pericardium filled with serous fluid pericardium (allow two serous layers to slide without friction)
What are the layers of the heart wall?
Epicardium - the visceral layer of the serous pericardium
Myocardium - cardiac muscle bundles (circumference of the heart) and fibrous connective tissue network (fibrous skeleton)
Endocardium - thin sheet of squamous epithelium and is continuous with endothelium of blood vessels
What is the fibrous skeleton of the heart and its features?
Dense connective tissue that serves as a skeletal framework within the heart
Functions:
-structural support between atria and ventricles
-provide a base for attachment of the heart valves
-provide a framework for attachment of the cardiac muscle
-acts as an electrical insulator for the prevention of atria and ventricles contracting simultaneously
Fribous Skeleton of the Heart Framework:
-Atrial muscle anchored above the rings
-Ventricular muscle anchored below the rings
-Cardiac muscles are arranged in spiral bundles (pushes blood upward to arteries by wringing effect)
What is the difference between the ventricular wall thickness?
Right ventricle is for the pulmonary side for low resistance and low pressure to overcome where it does not generate much force
Left ventricle is for the systemic side for high resistance and high pressure to overcome where it needs to generate a lot more force. Therefore, the walls are thicker having to push out more blood
What are the septa?
Interatrial atrium that is a thin wall to separate the right and left atrium
What parts is the atrium consist of (both sides)?
Pectinate Muscles = muscular ridges in right auricle
Fossa Ovalis = oval depression
Opening for Coronary Sinus (right side) = vessel through which blood returns to heart from coronary circulation
Openings for superior and inferior vena cava or pulmonary veins openings
AV valves
What parts are the ventricles consist of (both sides)?
Trabecular Carneae = irregular muscle ridges on inner walls
Papillary Muscle = serves as anchors for chordae tendineae
Chordae Tendineae = collagen fibers attached to the ends of the both of the AV valves
Semilunar valves
What is a factoid?
The shortest circulation in the body
What is the purpose of coronary circulation?
The heart cannot receive nutrients from the blood being pumped. Therefore, it has its own blood supply
Blood flow is intermittent due to heart pumping
What are the features of the arteries in coronary circulation?
Left Coronary Artery:
-Anterior Interventricular Artery = supplies the anterior walls of both ventricles
-Circumflex Artery = supplies the left atrium and the posterior wall of the left ventricle
Right Coronary Artery:
-Right Marginal Artery = supplies the lateral right side of the heart
-Posterior Interventricular Artery = supplies the posterior wall of both ventricles
What are the features of the veins in coronary circulation?
They collect the blood from the capillaries of the myocardium to join together to form the Coronary sinus. It returns deoxygenated blood back to the right atrium
Coronary Sinus:
-Great Cardiac Vein = serves the anterior heart
-Middle Cardiac Vein = serves the posterior heart
-Small Cardiac Vein = serves the right inferior portion of the heart
Posterior Cardiac Vein = returns blood from the circumflex artery
Anterior Cardiac Vein = empty directly into the right atrium
What is the difference between skeletal & cardiac muscle?
Skeletal:
-long, cylindrical
-multinucleate
-unbranched
-not interconnected
Cardiac:
-short, fat
-uninucleate
-branched
-interconnected (for signal sending)
What is the structure of the cardiac muscle?
Possesses
-T-tubules
-Sarcoplasmic reticulum
-Myofilaments organized into the sarcomere
Intercalated discs link cardiac muscle cells together mechanically and electrically through:
-Desmosomes (anchor the cells together)
-Gap Junctions (allow ions to pass between cells ensuring electrical currents passed across the heart)
Mitochondria account for 25-35% of cell volume providing high resistance to fatigue (due to generating ATP/energy)
What is the electrical activity in the heart?
The heart beats rhythmically as a result of AP spread across the muscle membranes. There are two types of muscle cells:
Contractile Cells = 99% of the muscle cells that do mechanical work of pumping
Nodal (Autorhythmic) Cells = specialized cells that initiate & conduct APs and display pacemaker activity
What are the action potentials of the cardiac contractile cells?
Resting Membrane Potential
-open K channels
Depolarization (rising)
-rapid rising phase
-voltage-gated Na channels open to allow Na influx
Plateau
-opening of K channels to start repolarization
-opening of “slow” L-type Ca channels prolongs depolarization
-ions flow opposes the other
Repolarization (falling)
-rapid falling phase
-inactivation of Ca channel and K channels remain open
What are refractory periods of action potentials and their features?
The time wherein a new AP can not be initiated by normal events in a region that has just undergone an AP until an excitable membrane has recovered
Prevents tetany from occurring
Protects the heart to ensure alternating periods of contraction & relaxation
What are the ions and their functions in nodal pacemaker activity?
Establish and maintain resting membrane potential: Na/K ATPase, Na leak channels, K channels
Voltage-Gated Channels that Produce AP:
-I(f) Na channels (“funny current”)
-K channels
-T-type Ca channels (“transient”)
-L-type Ca channels (“long-lasting”)
What are the action potentials in the nodal (autorhythymic) pacemaker?
Resting Membrane
-is around -60 mV for the purpose of pacemaker channels to become activated in subsequent steps
-function of ion movement through Na/K ATPase, Na leak channels, K channel
Reaching Threshold
-Na Leak channels has constant, passive influx into the cells
-I(f) Na Channels open in response to passive influx of NA into cell
-T-type Ca channels open in response to depolarization to allow Ca into the cell
Depolarization (the spike)
-L-type Ca channels open at threshold (-40 mV) allowing rapid influx of Ca into the cell
Repolarization (falling phase)
-L-type Ca channels closes at 0 mV to stop influx of Ca
-K channels open for K effux and begin to close at the RMP
What makes up the heart’s conduction system?
-SA Node (Sinoatrial Node)
-AV Node (Atrioventricular Node)
-Bundle of His (Atrioventricular Bundles)
-Purkinje Fibers
What is the SA node?
It is the pacemaker of the heart. It sets the rate for the rest of the heart such as for the other nodes, initiating an action potential spreading to the rest of the heart
If damaged, the next fastest node sets the pace
What is atrial excitation?
Action potential is set off in the SA node and spreads throughout both atria via gap junctions
What are the two conduction pathways in the heart?
Interatrial Pathway
-Rapidly transmit the actional potential from the SA node to the left atrium, so that both atria depolarize to contract simultaneously
Internodal Pathway
-From the SA node to the AV node to ensure sequential contracting of the ventricles following atrial contraction. Only point of electrical contact between atria and ventricles
What is the AV node?
It is conducted slowly to allow the atria to completely depolarize and contract before the ventricles do (causing a delay)
What is the process of conduction through the heart?
1) Atrial excitation is initiated and goes through the interatrial and internodal pathways to speed it up
2) It goes through the AV node
3) Impulse travels rapidly down Bundles of His & Purkinje fibers to the ventricular myocardium for the ventricles to contract as a unit and ensure a coordinated contraction to eject blood into the pulmonary & system circulation
What is the electrocardiogram (ECG)?
It is a recording of the electrical currents generated by the cardiac muscle to provide a comprehensive assessment of the electrical changes in the heart
It represents:
-Electrical activity in the body fluids by the cardiac muscle
-Overall spread of activity of the heart during depolarization and hyperpolarization
-Comparison in voltage detected by electrodes at different points
It DOES NOT represent:
-A direct recording of the electrical activity of the heart
-A recording of a single action potential
What are the 3 waveforms of the ECG and their meaning?
P Wave (atrial depolarization): Starts in the beginning where approximately 0.1s after it begins, the atria contract. It is typically small and generates less electrical activity. THE FIRING OF THE SA NODE IS NOT DETECTABLE
QRS Wave (ventricular depolarization): Middle, and is an odd shape (down-up-down) as a result of the convoluted path the wave takes through the ventricular walls
T Wave (ventricular repolarization)
What are the 3 periods of no current net flow in the ECG?
PR Interval: AV nodal delay
QT Interval: Plateau phase of ventricular contractile cells
TP Interval: Heart is at rest & ventricular filling is taking place
What is the difference between systole and diastole?
Systole: contraction and emptying; spread of excitation
Diastole: relaxation and filling; subsequent repolarization
What are the 2 heart sounds?
“Lub-Dub”:
1st heart sound (S1) - closure of the AV valves (“Lub”)
2nd heart sound (S2) - closure of the semilunar valve (“Dup”)
Alternative gallop rhythms heart sounds are rare (S3 & S4)
Provide clinically important information about heart acitivity
Does blood make sounds when flowing?
No, it is usually in a laminar fashion. However, when it is turbulent, it produces a sound
What are murmurs of the heart?
Sound resulting from abnormal vibrations due to valve malfunctions
-Valvular Stenosis: stiff valve doesn’t open completely causing a whistling noise
-Valvular Insufficiency (Valvular Incompetence): valves do not close completely due to valve edges do not fit properly together producing a swishing noise
-Systolic Murmur: between S1 & S2
-Diastolic Murmur: between S2 & S1
What are the phases of the cardiac cycle?
1) Atrial Systole
2) Early Ventricular Systole
3) Late Ventricular Systole
4) Early Ventricular Diastole
5) Late Ventricular Diastole
What happens in atrial systole?
Coincides with the PR interval
Atria contracting and ventricles are relaxing
Ventricular Pressure is less than atrial and arterial trunk pressures
AV valves are open and semilunar valves are closed
Blood volume is filled to the maximum in the ventricles (end-diastolic volume, EDV)
What happens in early ventricular systole?
Coincides with QRS complex
Atria relaxing and ventricles contracting
Ventricular pressure is greater than atrial pressure and less than arterial trunk pressure
AV valves are closed and semilunar valves are closed
Blood volume in ventricles is filled to maximum (end-diastolic volume, EDV) and stays constant
What happens in the late ventricular systole?
Coincides with QT interval
Atria are relaxing and ventricles are contracting
Ventricular pressure is greater than atrial and arterial trunk pressure
AV valves are closed and semilunar valvaes are open
Blood exiting to arterial trunks reaching minimum volume (end-systolic volume, ESV)
What happens in the early ventricular diastole?
Coincides with T wave
Atria and ventricles are relaxing
Ventricular pressure is greater than atrial pressure but less than arterial trunk pressure
AV valves and semilunar valves are closed
Blood volume in ventricles remains at minimum volumes (end-systolic volume, ESV) where no blood enters/exits
What happens in the late ventricular diastole?
Coincides with TP interval
Atria and ventricles are relaxing
Ventricular pressure is less than atrial and arterial trunk pressure
AV valves are opened and semilunar valves are closed
Blood volume in the ventricles is increasing. Blood accumulated in atria rushes into ventricle then slows down as atrial pressure falls
What is cardiac output?
The amount of blood pumped by a single ventricle in 1 min (L/min)
Is determined by heart rate (bpm) and stroke volume (ml/beat)
CO = HR * SV
What factors affect heart rate?
Collectively known as CHRONOTROPIC AGENTS. External factors that act on the SA and Av node such as autonomic innervation, varying levels of hormones, and other chemicals and drugs
What is cardiovascular innervation?
It is the heart rate and strength of contraction regulated by the autonomic nervous system. It is reflexively controlled by responding to chemo- & barostimulation to maintain homeostasis, and the atrial reflex prevents the heart from overfilling
These cardiac centers extend from the medulla (kidney) to the heart to modulate cardiac activity. The medulla consists of both cardioacceleratory and cardioinhibitory centers
What is the cardioacceleratory center?
-Sympathetic
-Projects through T1-T5 of the spinal cord, extending to the SA node, AV node, and myocardium
-Increases heart rate and force of contraction
-Induce dilation and greater blood flow to the myocardium in the coronary arteries
What is the cardioinhibitory center?
-Parasympathetic
-Projects via left (innervates AV node) and right (innervates SA node) vagus nerves
-Decrease heart rate but generally has no effect on the force of contraction
What are positive chronotropic agents?
They are factors that increase heart rate
Sympathetic fibers release NorE which binds to the beta1-adrenergic receptors activating a cAMP-dependent 2nd messenger:
-increased Na and Ca permeability
-decreased K permeability
-increases conductive velocity and contractile strength
Thyroid hormone causes nodal cells to be more responsive to Epi and NorE by increasing the number of beta1-adrenergic
Certain chemicals and drugs such caffeine invents cAMP breakdown, and nicotine stimulates the release of NorE
What are negative chronotropic agents?
They are factors that decrease heart rate
Parasympathetic fibers release ACh which binds to and modulates voltage-gated K channels causing:
-decreased in Na and Ca permeability which reduces contractile strength
-increased K permeability
-prolongs transmission of excitation
It is with certain chemicals and drugs where beta blockers interfere with Epi and NorE binding to beta1-adrenergic receptors
What factors affect stroke volume?
-Preload or venous return
-External ionotropic agents that alter contractility
-Afterload or the degree of resistance in the arteries
What is venous return?
It is the volume of blood that is returned to the heart via the veins and is directly related to stroke volume. It determines the amount of blood in the ventricle at the end of rest immediately prior to contraction (EDV)
Explained by the Frank-Starling law
Increase in venous return = increase EDV = increase SV
What is the Frank-Starling law?
The amount of blood the heart pumps out during systole is the same amount that it is returned to it during diastole
What are ionotropic agents?
External factors (ex. autonomic innervation & varying levels of hormones) alter the contractility (the force of contraction at a given stretch of the cardiac cells)
Positive ionotropes increases Ca availability and the number of crossbridges formed (strong contractions)
Negative ionotropes decreases Ca availability and the number of crossbridges formed (weaker contractions)
What is afterload?
The back pressure exerted by the arterial blood that must be overcome for the ventricles to eject blood
If afterload increases, then ventricles have a reduced ability to eject blood (resulting in increased ESV and lower SV)
