Chapter 17 - Cardiac Function Flashcards
What causes variations in heart size and position?
Age, body size, shape, weight, or pathological conditions of the heart or nearby structures.
What is the role of the mitral valve (bicuspid)?
Direct blood flow from the left atrium to the left ventricle.
What is the role of the tricuspid valve?
Direct blood flow from right atrium to right ventricle.
What are chordae tendineae?
Tether the valve leaflets to the papillary muscles of the ventricular chambers.
Chordae tendineae are connective tissue.
What are papillary muscles function?
Attached to the ventricular walls, prevent the valve leaflets from bending backward into the atria during systole.
Which valves are the semilunar valves?
The pulmonic valve that lies between the right ventricle and pulmonary artery.
The aortic valve, between the left ventricle and aorta.
What are the four different types of cardiac muscles and their functions?
Myocardium - produces contractile forced to eject blood from heart
Endocardium - Squamous epithelial cells of the cardiac chambers and valves, providing smooth surface to prevent clotting and minimize trauma to RBCs
Epicardium - Outer surface of the heart covered by epithelial cells, which is part of the protective covering called the Pericardium
Pericardium - Protective covering of the heart that envelopes the heart like a sac. Inner layer (visceral pericardium or epicardium) is attached to the heart’s outer surface, whereas the outer layer of the pericardium (or parietal pericardium) forms a sac around the heart and is composed of an epithelial layer and a tough fibrous layer.
Describe isovolumic contraction:
All four cardiac valves close immediately following the end of atrial systole causing intraventricular pressure to rise rapidly, which is when the S1 sound is heard.
Volume remains constant during this phase.
What is inotropy?
Commonly used interchangeably with contractility and is reflected by the velocity and degree of cardiac muscle shortening during systole.
Discuss ventricular ejection:
A rapid rise in ventricular pressure due to ventricular pressure exceeding aortic/pulmonic pressure, which forces the valves open for a period of rapid ejection. As the rapid ejection phase ends, there is a period of reduced ejection as aortic and pulmonic pressure rises and ventricular pressures and volumes fall.
Discuss Stroke Volume (SV), End-Diastolic Volume (EDV), and End-Systolic volume (ESV):
Stroke volume (SV) is the amount of blood ejected with each contraction from the ventricles.
EDV is the volume of blood that remains in the ventricle before ejection.
ESV is the volume of blood that remains in the ventricle after ejection.
How is Stroke volume calculated?
How is ejection fraction (EF) calculated AND what is a normal EF?
What is the EF in patients with systolic heart failure?
Stroke volume (SV) = EDV - ESV
EF = SV/EDV
A normal EF is 60% to 80%
Patient’s with systolic heart failure have an EF less than 40%
Discuss Isovolumic Relaxation:
Isovolumic relaxation phase beings with the closure of the semilunar valves in response to falling ventricular pressure; (S2 sound) and ends when the AV valves open for ventricular filling.
What is lusitropy?
The rate and degree of ventricular relaxation during Isovolumic relaxation and is an energy-requiring process that reflects the efficiency of calcium removal from the cytoplasm.
Impaired relaxation (lusitropic dysfunction) is common in those with heart failure and contributes to symptoms of congestion. Due to lusitropy being an energy-requiring processs, isovolumic relaxation may be impaired when flood flow and oxygen to the heart are inadequate.
How does aortic stiffness effect blood pressure?
Aortic stiffness results in greater differences between systolic and diastolic BPs; raising the systolic and lowering diastolic.
What doe the right coronary artery supply?
Right atrium (50% of persons) Right ventricle Intraventricular septum Sinus node (50% of persons) Atrioventricular node Bundle of His
What does the left anterior defending coronary artery supply?
Right atrium (45% of persons) Right ventricle (minor) Left ventricle (anterior, apex) Anterior papillary muscles Right and left bundle branches Intraventricular septum
What does the Left Circumflex coronary artery supply?
Left Atrium Left Ventricle (posterior, anterior) Sinus Node (45% of persons)
Where do the right and left coronary arteries originate from?
Within the sinuses of Valsalva.
In most people, what does the right coronary artery supply?
Right ventricle
AV Node
Sinoatrial (SA) node
Right atrium
How is coronary blood flow regulated?
Coronary artery blood flow is regulated centrally by the autonomic nervous system and locally by autoregulation.
What is the amount of coronary flow dependent on?
Coronary blood flow depends on driving pressure and coronary resistance.
What is coronary resistance dependent on?
Coronary resistance is dependent on vessel diameter.
What are two important vasodilation chemicals, how are they produced, and what is their function?
Adenosine and Nitric oxide are produced in response to inadequate oxygen delivery to the heart and help to increase blood flow and to meet metabolic demand.
When does the left ventricle receive blood flow and why does this happen?
Driving pressure is highest during systole, which actually causes little blood flow to the left ventricle due to vessel compression by the contracting myocardium. Most coronary blood flow to endocardial areas of the ventricles occurs during diastole.
What are Myocytes composed of?
Thin filaments: Actin protein and two regulatory proteins (troponin and tropomyosin)
Thick filaments: Myosin proteins
Titin: A flexible proteins that attaches the thick filament to the Z disk.
What is unique about myosin proteins (thick filaments) compared to actin proteins (thin filaments)?
Myosin has enzymatic activity and splits ATP to release energy needed for movement of the filaments.
What roles to Troponin and Tropomyosin play in the heart?
At rest, tropomyosin inhibits myosin-binding sites on actin.
The position of tropomyosin is regulated by the calcium-binding protein troponin.
What is Nebulette?
Nebulette is another actin-associated protein that helps regulate thin filaments length.
What is Ohm’s law?
An increase in driving pressures increases flow; an increases in resistance reduces flow.
What happens at rest when calcium is absent from the cytoplasm?
What happens when calcium enters the cardiac cell?
When calcium is absent, troponin induces tropomyosin to inhibit the actin-binding sites.
When calcium is present, calcium binds to troponin C, the troponin complex induces tropomyosin to move and expose binding sites for the myosin head.
What is an immediately available form of energy for cardiac energy metabolism When ATP levels drop?
Creative Phosphate (CP)
What intracellular proteins help to diagnose myocardial cell damage?
Creative Kinase (CK or CPK)
The MB form of CK
Troponin
Myoglobin
What are the primary energy substrates for the heart to produce energy?
Fatty acids and Glucose
Related to cardiac electrophysiology, what does rhythmicity and automaticity refer to?
Rhythmicity and automaticity refer to an intermittent, regular, spontaneous generation of action potentials.
What determines the rate of rhythmicity?
Rate of rhythmic discharge is determined by the relative influx of sodium and calcium, versus the efflux of potassium.
What is the path of heart’s conduction system?
SA Node Atrial internodal pathways AV Node Bundle of His Ventricular bundle branches Purkinje fibers
What is the rate of depolarization for the AV node?
40 to 60 times per minute
What nerve(s) innervate The SA node and the AV node.
Sympathetic nerves supply all areas.
Localized to the SA node is the Right vagus nerve.
Localized to the AV node is the Left vagus nerve
Define the following terms:
Chronotropic effect:
Dromotropic effect:
Inotropic effect:
Lusitropic effect:
How do they work?
Chronotropic effect - increases heart rate
Dromotropic = increasing speed of conduction
Inotropic = increase contractility
Lusitropic = relax more quickly
All are controlled by Sympathetic nerve endings releasing NE to bind to beta receptors on the heart to increase cAMP, which regulates membrane channels, and increases depolarizing currents.
What does an ECG analyze?
Irregularities in initiation of impulses,
conduction rates,
Conduction pathways.
What are the major deflections of the ECG?
P wave: atrial depolarization
PR interval: atrial, AV node, and Purkinje depolarization
Q wave: Septal depolarization
R wave: apical depolarization
S wave: depolarization of lateral walls (base)
T wave: ventricular repolarization
What three characteristics contribute to cardiac contractility?
- The amount of contractile proteins in the muscle cells
- Availability of ATP
- Availability of free calcium ions in the cytoplasm
Given that contractility is defined by “independent of fiber end-diastolic length”, what does not affect contractility?
Preload does not affect contractility.
What are the agents that increase and decrease contractility.
Give examples of each:
Positive inotropes increase contractility. Positive inotropes include: sympathetic neurotransmitters norepinephrine and epinephrine, thyroid hormone, caffeine, digitalis.
Negative inotropes decrease contractility by reducing intracellular calcium levels; such as: L-Type calcium channel blockers, parasympathomimetics, and sympathetic blocking drugs.
What will an increase in after load result in?
An increase in after load will result in a decreased stroke volume (unless contractility, preload, or both adjust to compensate.
What will a decrease in after load result in?
A decrease in after load will allow a larger than normal volume of blood to be ejected from the heart.
What percent of ejection fraction indicates significant myocardial impairment?
Ejection fraction of less than 40% where normal is 60% to 70%
What is the formula for Cardiac Output (CO)?
CO = HR X SV
What is the difference between Atrial Natriuretic peptide (ANP) and B-type natriuretic peptide?
ANP is released by Myocytes in response to atrial stretch.
BNP are released due to chronic overdistension
—BNP is a marker for congestive heart failure.
What does ANP and BNP cause to occur related to the kidneys?
ANP and BNP cause enhanced excretion of sodium and water by the kidneys.
Where is the heart located?
Mediastinum, suspended between the lungs, behind the sternum, and in front of the vertebral column, thoracic aorta, and esophagus.
