Exam 1: heart Objectives
13. Contrast the way action potentials are generated in cardiac pacemaker cells, in cardiac contractile cells and in skeletal muscle cells.
Contractile cells make up 99% of all cardiac muscle cells they have no threshold but instead receive an action potential via gap junctions their RMP is -90mV Autorhythmic cells aka pacemaker cells make up 1% or less of cardiac muscle cells but are very important. Autorhythmic cells do not have a stable resting membrane potential but do have threshold.
27. Explain the significance of the Frank-Starling Law of the heart.
Frank Starling Law of the heart = amount of stretch in cardiac muscle increases the amount of tension; so...increase stretch = increase force of contraction stretch can be increased by filling the ventricles more, this is quantified by EDV
18. Describe the role of the autonomic nervous system in the regulation of cardiac function.
In addition to exogenous things such as drugs, the Autonomic Nervous System acts to adjust heart rate: Sympathetic Nervous System increases heart rate Parasympathetic Nervous System decreases heart rate
26. Define venous return, preload and afterload, and explain the factors that affect them as well as how each of them affects EDV, ESV and SV
Preload - is the amount of tension (stretch) in the ventricular myocardium immediately before it contracts; this is summarized by the Frank Starling Law (SV is proportional to EDV), meaning more blood = more stretched = greater next contraction Afterload - is the sum of all forces that must be overcome before a ventricle can eject blood; most significantly is resistance on semilunar valves (blood pressure in aorta and pulmonary trunk)
9. Define systemic and pulmonary circulation.
Pulmonary circuit - carries blood to and away from lungs; is supplied by right side of the heart Systemic circuit - carries blood to and from all organs of the body; is supplied by the left side of the heart
19. Define cardiac cycle, systole, and diastole, explaining the phases of ventricular filling and ventricular ejection.
Systole = contraction Diastole = relaxation The Cardiac Cycle is one complete contraction and relaxation of all four heart chambers • Ventricular and Atrial diastole In this phase everything is relaxed (there are no APs and the muscles are repolarizing) The atria are filling from the veins; The AV valves are open, ventricles are also filling * Volume in atria and ventricles is increasing with no change in pressure * SA node fires in this step and begins depolarizing the atria 80% of ventricular fill volume happens passively
17. Explain how the cardiac conduction system produces efficient pumping of blood
The Cardiac Conduction System is composed of an internal pacemaker and conducation system that controls the myocardium. It is how the autorhythmic cells are distributed through the heart. These "structures" are embedded in the myocardium.
1. Describe the size and shape of the heart and indicate its position in the thoracic cavity
The heart is a 4-chambered pump that lies in the thoracic cavity within the mediastinum.The Base is the wide, superior portion of heart, large vessels attach here Apex is the tapered inferior end, tilts to the left • In adult: weighs 10 ounces, 3.5 in. wide at base, 5 in. from base to apex • At any age, heart is size of fist
3. Describe the layers of the pericardium and the location of the pericardial cavity.
The pericardial sac encloses the heart: • Pericardium (aka pericardial sac) is a double walled sac that encloses the heart; consists of fibrous and serous layers • Pericardial Cavity between parietal and visceral layers contains pericardial fluid
14. Compare and contrast cardiac muscle contraction and skeletal muscle contraction.
The size of contraction in a cardiac muscle cell can change (different from skeletal muscle) by changing the amount of Ca that comes in from the ECF. This can be regulated by the ANS.
7. Compare and contrast the structure and function of the atrioventricular and the semilunar valves.
• AV Valves (aka atrioventricular valves) control blood flow between the atria and ventricles: Semilunar Valves prevent backflow from the ventricles to the great arteries :
25. Define end diastolic volume (EDV) and end systolic volume (ESV) and calculate stroke volume (SV) given values for EDV & ESV
* (max amount of blood has entered = End diastolic volume) * (End systolic volume = amt of blood left over after ventricular contraction is completed) Stroke Volume is the total volume of blood pumped by one ventricle in one cardiac cycle and can change based on nervous input.
10. Describe blood flow through the heart naming all chambers and valves passed.
1 deoxygenated blood enters the right atrium via the superior/inferior vena cava 2 after a sodium and potassium exchange occurs in the sa node an electrical impulse shocks the right atrium causing atrial depolarization/contraction. deoxygenated blood then passes through the tricuspid valve and enters the right ventricle 3 after ventricular depolarization/contraction deoxygenated passes through the pulmonic valve into the pulmonary arteries where it travels to the lungs and becomes oxygenated 4 oxygenated blood then enters the left atrium via the pulmonary veins 5 after atrial depolarization/contraction oxygenated blood passes through the bicuspid valve/mitral valve and enters the left ventricle 6 after ventricular depolarization/contraction oxygenated blood then passes through the aortic valve and enters the aortic arch where it begins it's journey through body and organs
24. Calculate cardiac output, given stroke volume and heart rate
Cardiac Output (mL/min) = Stroke Volume (mL/beat) x Heart Rate (beats/min)
23. Define cardiac output, and state its units of measurement
Cardiac Output tells you how much blood is pumping through your body in a set amount of time (usually minutes) Cardiac Output (mL/min) = Stroke Volume (mL/beat) x Heart Rate (beats/min)
11. Identify the right and left coronary arteries and their branches, the cardiac veins, and the coronary sinus.
Left Coronary Artery - small opening in ascending aorta anterior interventricular branch - travels in anterior interventricular sulcus circumflex branch - travels in coronary sulcus Right Coronary Artery - small opening in ascending aorta right marginal branch - runs towards apex of the heart posterior interventricular branch - travels in posterior interventricular sulcus Coronary Sinus (is fed by cardiac veins) is a small hole found in the R atrium that drains deoxygenated blood from the heart itself Cardiac veins Great Cardiac Vein Middle Cariac Vein Small Cardiac Vein Anterior Cardiac Vein
28. Discuss the influence of positive and negative inotropic agents on SV
Negatively inotropic agents weaken the force of muscular contractions. Positively inotropic agents increase the strength of muscular contraction.
8. Identify the major blood vessels entering and leaving the heart and classify them as either an artery or a vein and as containing either oxygenated or deoxygenated blood.
The Great Vessels are blood vessels that enter and exit the heart itself: Superior Vena Cava receives deoxygenated blood from the head and upper trunk and extremities and delivers it to the right atrium. Inferior Vena Cava receives deoxygenated blood from the lower trunk and extremities and delivers it to the right atrium. Pulmonary Trunk and Arteries take deoxygenated blood from the right ventricle and deliver it to the lungs Pulmonary Veins (four of them, two from each lung) receive oxygenated blood from the lungs and deliver it to the left atrium Aorta takes oxygenated blood from the left ventricle to all organs of the body
15. List the parts of the conduction system and explain how the system functions (SAN, AVN, AVBundle, AVBundle Branches, Perkinje Fibers).
The Sinoatrial Node is the pacemaker. The SA node is located in the Right Atrium (near the superior vena cava) The SA node fires first and the fastest the SA node is connencted to the internodal pathway which distributes the information to all of the atrial muscle (R and L) The Atrioventricular node gathers information from the internodal pathway The AV node is located in the R atrium (near the AV valve) This is the electrical gateway to the ventricles The Atrioventricular bundle is the pathway out of the AV node and the bundle forks into right and left bundle branches The AV bundle and bundle branches are located in the interventricular septum The Purkinje fibers arise from lower bundle branches and turn up and spread through ventricular myocardium
6. Identify and describe the function of the primary internal structures of the heart, including chambers, septa, valves, papillary muscles, chordae tendineae, and venous and arterial openings.
Within the heart the four chambers are separated by walls called septa (septum = singular): • Interatrial Septum found between the two atria • Interventricular septum separates the ventricles • Atrioventricular septum divides the atria from the ventricles. Valves are critical anatomical structures that ensure one-way flow of blood in the heart: • AV Valves (aka atrioventricular valves) control blood flow between the atria and ventricles: Right AV Valve (aka Tricuspid Valve) is between right atria and right ventricle Left AV Valve (aka Bicuspid Valve aka Mitral Valve) is between left atria and ventricle Chordae Tendonae - connect AV valves to the papillary muscles to keep valves from being "floppy" Semilunar Valves prevent backflow from the ventricles to the great arteries : Pulmonary semilunar valve - opening between right ventricle and pulmonary trunk Aortic semilunar valve - opening between left ventricle and aorta Veins also have valves that prevent the backflow of blood (more later)
16. Define automaticity (autorhythmicity) and explain why the SA node normally paces the heart.
the SA node is connencted to the internodal pathway which distributes the information to all of the atrial muscle (R and L)
21. Relate the heart sounds to the events of the cardiac cycle
• Early ventricular systole In this phase the ventricles begin to contract Because blood is pushing up the AV valve snaps shut "Lub" • Ventricular diastole (T wave) Ventricles relax and repolarize Because blood is trying to rush back in, Semilunar Valves snap shut "Dub"
5. Discuss the structure and significance of the endocardium.
• Endocardium Smooth inner lining of the heart and blood vessels simple squamous epithelium and thin areolar tissue Covers the valve surfaces and is continuous with endothelium of vessels
29. Discuss the influence of positive and negative chronotropic agents on HR.
• Factors that raise the heart rate are called positive chronotropic agents, and factors that lower it are negative chronotropic agents
4. Identify myocardium and describe its histological structure, including the significance of intercalated discs.
• Myocardium the thickest middle layer cardiac muscle performs the work of the heart
22. Identify the waveforms in a normal EKG. Relate the waveforms to atrial and ventricular depolarization and repolarization and to the activity of the conduction system. Relate the EKG waveforms to the normal mechanical events of the cardiac cycle.
• P Wave - signal travels through and depolarizes atria; atrial contraction • QRS Complex - signal from AV node spreads to ventricular myocardium; ventricular contraction • T Wave - ventricular repolarization; ventricle relaxes • PR Interval - Time it takes for depolarization to spread from atria to ventricles • QT interval - is the length of time it takes for the ventricles to depolarize and repolarize
2. On the external heart identify the location of the four chambers as well as the coronary sulcus, anterior interventricular sulcus and posterior interventricular sulcus.
• Right and Left Atria superior chambers receive blood returning to the heart via great vessels (see below) have earlike extensions to increase volume known as auricles • Right and Left Ventricles inferior chambers pump blood into arteries The heart "sits on its side" and rests on the diaphragmatic surface. The right atrium and right ventricle face anteriorly and the left atrium and left ventricle are posterior. • These sulci mark the boundaries between the four chambers and are largely filled with fat and coronary blood vessels. • Anterior intraventricular sulcus separate the R and L ventricles anteriorly • Posterior intraventricular sulcus separate the R and L ventricles posteriorly • Coronary atrioventricular sulcus encircles heart and separates atria from ventricles
12. List the phases of the cardiac muscle action potential and explain the ion movements that occur in each phase.
• Ventricular and Atrial diastole In this phase everything is relaxed (there are no APs and the muscles are repolarizing) The atria are filling from the veins; The AV valves are open, ventricles are also filling * Volume in atria and ventricles is increasing with no change in pressure * SA node fires in this step and begins depolarizing the atria 80% of ventricular fill volume happens passively • Atrial systole (the P wave) In this phase atrial contraction is forcing blood into the ventricles * volume of the atria are decreasing * Pressure is increasing, as is the volume in the ventricles 20% of ventricular fill volume happens actively. • Early ventricular systole In this phase the ventricles begin to contract Because blood is pushing up the AV valve snaps shut "Lub" * No change in volume of the ventricles * (max amount of blood has entered = End diastolic volume) * Pressure is increasing • Atrial diastole / Ventricular Systole (QRS wave) Eventually blood overcomes semilunar valves and pushes out to aorta or pulmonary trunk * Pressure continues to increase; Volume in ventricle decreases * (End systolic volume = amt of blood left over after ventricular contraction is completed) • Ventricular diastole (T wave) Ventricles relax and repolarize Because blood is trying to rush back in, Semilunar Valves snap shut "Dub" All valves are closed in this stage * Decrease in pressure as ventricles relax * Volume stays the same
