Heart Study Guide Flashcards
(45 cards)
What are the two major divisions of the cardiovascular system and what do they do?
The two major divisions of the cardiovascular system are the heart and blood vessels. The heart acts as a pump while the blood vessels act as a delivery system.
What is the general function of the cardiovascular system? Define perfusion.
The general function of the cardiovascular system is to transport blood throughout the body to allow exchange of substances (E.g respiratory gases, nutrients, and waste products) between the blood of capillaries and the body’s cells. Perfusion- delivery of blood per time per gram of tissue (in mL/min/g); it is the goal of the cardiovascular system.
Describe the mediastinum.
Mediastinum- (medius= middle) it’s of the thoracic cavity; where the heart is located; between the lungs.
Define the pericardium: fibrous, visceral and parietal layers, pericardial cavity and pericardial fluid.
Pericardium- the three layers the heart is enclosed in
Fibrous Pericardium- outermost covering; dense irregular ct; attaches to diaphragm and base of aorta, pulmonary trunk; anchors heart and prevents it from overfilling
Visceral layer of Serous Pericardium- Simple squamous epithelium and areolar ct; attaches directly to heart
Parietal layer of serous Pericardium- Simple squamous epithelium and areolar ct; attaches directly to heart
Pericardial cavity- space that separates the parietal and visceral layer of pericardium
Pericardial fluid- released by the 2 layers of the serous pericardium; released into the pericardial cavity; the oily mixture that lubricates the serous membranes to decrease
friction with every heart beat.
Review pulmonary and systemic circulation
- R. Atrium
- Tricuspid valve
- R. Ventricle
- Pulmonary valve
- Pulmonary trunk
- R., L Pulmonary arteries
- Capillaries (O₂ is loaded CO₂ unloaded)
- Pulmonary Veins (Red now)
- Pulmonary veins
- L. Atrium
- Bicuspid (mitral valve)
- L. Ventricle
- Aortic Valve
- Aorta
- Systemic arteries
- Tissue Capillaries (O₂ is unloaded, CO₂ is loaded)
- Systemic Veins
- Vena Cava
- R. Atrium
Describe the general structure of cardiac muscle.
The general structure of cardiac muscle is striated, short, thick, branched cells, one central nucleus surrounded by light staining mass of glycogen. Includes sarcolemma (plasma membrane), myofibrils.
Describe intercalated discs, desmosomes, gap junctions.
Intercalated discs- join cardiocytes end to end with 3 features:
- interdigitating folds
- mechanical junctions= desmosome
- electrical junctions= gap junctions
Desmosomes- protein filaments that anchor into a protein plaque located on the internal surface of the sarcolemma. Acts as mechanical junctions to prevent cardiac muscle cells from pulling apart.
Gap junctions- protein pores between the sarcolemma of adjacent cardiac muscle cells. Provides a low resistance pathway for flow of ions between cardiac cells; allow action action potential to move continuously along sarcolemma of cardiac muscle cells, resulting in synchronous contraction of that chamber.
Describe the metabolism of cardiac muscle.
The metabolism of cardiac muscle depends almost exclusively on aerobic respiration to make ATP, is rich in myoglobin and glycogen, has huge mitochondria: fills 25% of the cell.
The metabolism is adaptable to different types of fuels for molecules which includes fatty acids (60%); glucose (35%), ketones, lactic acid, and amino acids (5%).
The metabolism is more vulnerable to O₂ deficiency than lack of a specific fuel.
The metabolism is fatigue resistant because it makes little use of anaerobic fermentation or oxygen debt mechanisms.
Locate the 4 valves in the heart. What is the function of valves? How do they open and close? Look at Figure 19.10.
Right Atrioventricular (AV) valve- covers the right av opening and has 3 cusps (tricuspid valve); prevents blood flow from right ventricle to right atrium.
Left Atrioventricular (AV) valve- has only two cusps (bicuspid, mitral); prevents backflow of blood to left atrium
-the function of the valves, when open, allow blood to flow through the heart and when closed it prevents back flow.
Ensures one-way flow of blood through heart.
- When open, cusps of valves extend into ventricles which allows blood to move from atrium to move into ventricles.
- When ventricles are contracting, blood is forced superiorly which causes AV valves to close.
Pulmonary Semilunar valve- located between right ventricle and pulmonary trunk; prevents blood flow from pulmonary trunk into right ventricle.
Aortic Semilunar Valve- located between left ventricle and the ascending aorta; prevents blood flow from aorta into left ventricle.
- Semilunar valves open when ventricles contract and the force of blood pushes the semilunar valves open and blood enters the arterial trunks.
- the semilunar valves close when the ventricles relax and the pressure in the ventricle becomes less than the pressure in an arterial trunk; closure of semilunar valves prevents blood flow back into the ventricle.
*When AV valves are open, SL are closed (Diastole), When SL are open, AV valves are closed (Systole)
What is the fibrous skeleton? What are its 4 functions?
Fibrous Skeleton of heart- framework of collagenous and elastic fibers
The fibrous skeleton provides: Structural support, attachment for cardiac muscles, anchors valve tissue, *electrical insulation between atria and ventricles; important in timing and coordination of contractile activity.
Coronary circulation will be covered in the lab. Think about this. Do the coronary arteries fill with blood when the heart is contracting or relaxing?
Coronary arteries fill with blood when the heart is relaxing. (Doesn’t flow when the heart is contracting because the vessels are compressed.)
Describe the conduction system in the heart: SA node, AV node, AV bundle, left and right bundle branches, Purkinje fibers
Sinoatrial (SA) node- located in the posterior wall of the right atrium, adjacent to the entrance of the superior vena cava. The cells here initiate heartbeat and are commonly referred to as the pacemaker of the heart.
Atrioventricular (AV) node- located in the floor of the right atrium between the right AV valve and the opening for the coronary sinus.
Atrioventricular (AV) bundle/ bundle of His- extends from the AV node into and through the interventricular septum. It divides into left and right bundles.
Purkinje fibers- extend from the left and right bundles beginning at the apex of the heart and continue through the walls of the ventricles.
SA node fires
- Excitation spreads through atrial myocardium
- AV node fires
- Excitation spreads down AV bundle
- Purkinje fibers distribute excitation through ventricular myocardium.
Briefly describe the cardiac center and the autonomic nerve supply to the heart.
The heart doesn’t need a stimulus to beat and is autorhythmic (self-start)
-The cardiac center houses both the cardioinhibitory and cardioaccelerator centers.
-modifies cardiac activity including both heart rate and its force of contraction.
-The cardioinhibitory center is parasympathetic
-the cardioacceleratory center is sympathetic
The autonomic nervous system (ANS) controls rate and force; adjusts SA node
Vagus is parasympathetic
Parasympathetic shows your heart rate
Sympathetic innervates muscle and force of contraction.
What physiologic processes are involved in heart contraction?
The conduction system and cardiac muscle cells are involved in heart contraction.
Conduction-
Initiation- SA node initiates action potential.
Spread of Action Potential- an action potential is propagated throughout the atria and the conduction system
Cardiac Muscle Cells-
The action potential- the action potential is propagated across the sarcolemma of cardiac muscle cells.
Muscle contraction- thin filaments slide past thick filaments and sarcomeres shorten within cardiac muscle cells.
Why does the SA node spontaneously fire at regular intervals?
Nodal cells have an unstable resting membrane of -60mV.
Reference off of the ECG and understand the process.
Define resting potential. Remember this from BIO 111?
Resting potential- leaky channels, more negative
Use Fig. 19.15 and 19.16 to explain autorhythmicity and the electrical behavior of the SA node(pacemaker).
Autorhythmic- cardiocytes (cardiac nodal cells) are self-excitatory; they require no nerve stimulus for contraction
SA node Reaching threshold- Slow voltage-gated Na+ channels open. Inflow of Na+ changes membrane potential from -60 mV to -40 mV.
Depolarization of SA node- Fast voltage-gated Ca+ channels open. Inflow of Ca2+ channels open. Inflow of Ca2+changes membrane potential from -40 mV to just above 0 mV.
Fast voltage-gated Ca2+ channels close. Voltage-gated K+ channels open allowing K+ outflow. Membrane potential returns to RMP -60 mV, and K+ channels close.
Reference off of the pacemaker physiology.
What is vagal tone?
Vagal tone- the normal resting heart rate of 75 beats per minute is due to continuous parasympathetic stimulation of the SA node by the vagus nerve; slowing of heart rate.
Describe the spread of the action potential through the heart’s conduction system.
An action potential is generated at the SA node. It spreads via gap junctions between cardiac muscle cells throughout the atria to AV node.
The action potential is delayed at the AV node before it passes to the AV bundle within the interventricular septum.
The Av bundle conducts the action potential to the left and right bundle branches and then to the Purkinje fibers.
The action potential is spread via gap junctions between cardiac muscle cells throughout ventricles.
What 2 events occur within cardiac muscle cells after stimulation by the conduction system?
Propagation of action potential at sarcolemma and contraction of sarcomeres within cardiac muscle cells.
The action potential is initiated in the conduction system and is propagated across the sarcolemma of cardiac muscle cells.
In Muscle contraction, thin filaments slide past thick filaments and sarcomeres shorten within cardiac muscle cells.
Describe the feature of the sarcolemma of cardiac muscle cells.
In cardiac muscle, sodium channels are fast channels, Ca channels are slow, K is normal; resting membrane potential is -90 mV.
List the electrical events of an action potential that occur at the sarcolemma.
Depolarization- fast voltage -gated Na+ channels open and Na+ rapidly enters the cell, reversing the polarity from negative to positive (-90 mV to +30 mV). These channels then close.
Plateau- Voltage-gated K+ channels open and K+ flows out of the cardiac cells. Slow voltage-gated Ca2+ channels open and Ca2+ enters the cell, with no electrical damage and the depolarized state is maintained.
Repolarization- Voltage gated Ca2+channels close, voltage gated K+ channels remain open, and K+ moves out of the cardiac muscle cell, and polarity is reversed from positive to negative(+30 mV to 90mV).
Describe the mechanical events of cardiac muscle cell contraction.
Ca2+ enters sarcoplasm from interstitial fluid and SR leading to contraction.
As in skeletal muscle, it binds to troponin and initiates crossbridge cycling
Ca2+ levels decrease leading to relaxation; channels close and move pumps it into SR and out of cell.
How do cardiac muscle cells differ from skeletal muscle cells? Define refractory period.
Cardiac muscle cells- cannot exhibit tetany, have a long refractory period.
- cell cannot fire a new impulse during refractory period
- cardiac muscle cell’s plateau phase leads to refractory period of 250 ms
- the heart cell contracts and relaxes before it can be stimulated again
- makes sustained (tetanic) contraction impossible
Skeletal muscle cells- can exhibit tetany; have a short refractory period; doesn’t have enough time to relax.
Refractory period- non-responsive
