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40 Cards in this Set
- Front
- Back
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SA Node
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(Sino Atrial Node): It is located in right atrium near the opening of cranial vena cava. It is also called the pacemaker because it initiates the nerve impulses, that spread throughout the atrial muscles leading to contraction or atrial systole. |
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AV Node
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(Atrio Ventricular Node): It is located in the inter-atrial septum. It picks up the electrical impulses from atrial muscles and transmits them to Bundle of His.
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Bundle of His
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It is located in the inter-ventricular septum and divides into two branches - left and right bundle branches. These branches enter the left and right walls of ventricles.
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Purkinje Fibers
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These originate from the right and left bundle branches and innervate the ventricular muscles. These fibers transmit the electrical impulses to the ventricular muscles leading to the contraction (ventricular systole).
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The pathway of conduction of an electric impulse in heart
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SA node → Atria → AV node → Bundle of His → Purkinje Fibers → Ventricles
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Atrial Diastole
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When both left and right atria are relaxed and receiving blood. The left atrium receives blood from pulmonary veins, while right atrium is receiving blood from cranial and caudal vena cavae. During this period AV valves are open, therefore, ventricles are also receiving blood during this period. Ventricles are also in a state of diastole.
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Ventricular Diastole
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Ventricles are relaxed during this stage and receiving blood from both left and right atrium. The 70% of the ventricles are already filled up during the atrial diastole as AV valves are open. Rest 30% filling is completed during atrial systole. That means atrial contraction helps in emptying remaining 30% blood from atria to ventricles.
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Atrial Systole
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The atrial muscles contract to push 30% of remaining blood into ventricles. During this period the AV valves are open but semilunar valves are closed.
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Ventricular Systole
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The first event during this period is - the increased pressure in ventricles shut close the AV valves to prevent back flow of blood into atria. Now the semilunar valves are opened due to high pressure in ventricles. The ventricular muscles contract and push the blood into the aorta and pulmonary artery. At the end of the ventricular systole, the semilunar valve shut close to prevent back flow of blood into ventricles
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1st Heart Sound (Lub)
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It is produced by closer of AV valves. This sound is louder and of longer duration. This sound indicates the beginning of the ventricular systole.
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2nd Heart Sound (Dub)
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It is produced due to the closer of semilunar valves and vibrations of blood vessels. This sound indicates the beginning of the diastole.
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Heart murmur
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Abnormal heart sound, that is produced due to abnormal blood flow in the heart. This abnormal blood flow may occur due to a problem in heart valves or other heart disorders.
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Valvular Insufficiency
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It is the leakage of AV valves when these valves fail to close completely. Mitral valve or bicuspid valve leakage may lead to left side congestive heart failure. The tricuspid valve leakage may lead to the right side congestive heart failure.
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Valvular Stenosis
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It is the condition when semilunar valves fail to open completely. It makes the restricted blood flow in aorta and pulmonary artery due to narrowing of these openings. The narrowing of the valvular opening may occur due to thickening of the valve leaflets. In such cases, ventricles have to work harder and faster to meet the body blood requirement, leading to hypertrophy of the ventricular muscles.
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Cardiac Output
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It is the volume of the blood pumped by each ventricle per minute. It is expressed in liters/min. The cardiac output depends on the heart rate and stroke volume (volume of blood pumped /beat).
Cardiac Output (CO) = Heart Rate X Stroke Volume.(liters/min.) (beats/min) (liter /beat) |
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Stimulation of parasympathetic fibers slows down
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The heart rate (bradycardia) by decreasing the force of contraction of heart muscles and also decreases the blood flow to the coronary arteries.
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Sympathetic stimulation speeds up
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The heart rate (tachycardia) and blood flow to the coronary arteries. The sympathetic stimulation causes contraction and relaxation to occur quicker and more efficiently, so the heart rate increases. At rest, the parasympathetic system dominates over the sympathetic system.
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Control of Stroke Volume
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It depends on the contractibility of heart and ventricular filling. The main determinant of the stroke volume is the force of contraction of heart muscles. This contractibility of heart muscles depends on the stretching of heart muscles or the degree of diastolic blood volume (End Diastolic Volume). The more-distended or stretched are the heart muscles, the ventricles will respond with more forceful contraction.
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Starling Law of the Heart
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States that greater the diastolic filling, greater will be the cardiac output. That means heart will pump the amount of blood presented to it, within the physiological limit. More the stretching of cardiac muscles more will be the contraction.The ventricular filling or End Diastolic Volume (EDV).
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Ventricular Compliance
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The ability of ventricles to distend easily during the filling. If the ventricles are diseased or non-compliance, the stroke volume will be reduced with the fact that the ventricles did not accept as much blood volume. |
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Venous return to atria
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Depends on blood pressure in veins and constriction of smooth muscles in veins. |
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Bainbridge Reflex |
The increased right atrium blood pressure (or increased blood pressure in vena cavae returning the blood to right atrium) would increase the heart rate and therefore stroke volume. There are some special receptor cells in the right atrium, that respond to increased blood pressure in the right atrium and send this message to the brain. The brain, in turn, stimulates the sympathetic system and increases the heart rate. (e.g. during exercise, the heart rate increases because the greater amount of blood is returning to the heart).
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Why is it important to measure the cardiac output?
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It helps to assess the state of the circulatory system of the animal. Also, helps in measuring the response of the patient to various therapeutical drugs used to treat heart problems.
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Blood Pressure
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It is defined as the pressure, that the blood exerts on the vessel wall. It is a dynamic measurement that corresponds to cardiac output. Blood pressure is measured in mmHg. The device used to measure the blood pressure is called sphygmomanometer.
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Systolic pressure
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Peak pressure obtained during ventricular systole with each cardiac ejection.
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Diastolic pressure
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The lowest pressure reached in the arteries during ventricular relaxation.
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Pulse Pressure
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Difference between systolic and diastolic pressure. (Systolic - Diastolic)
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Mean Pulse Pressure
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Average pressure (Average of systolic and diastolic pressure)
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Pressures in dogs |
Normal systolic pressure in dogs: 150 +/- 30 m.m. Hg
Normal diastolic pressure in dogs: 75 +/- 15 m.m. Hg |
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Hypertension
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It is the stage when systolic pressure is above 180 mm Hg or diastolic pressure above 95 mm Hg. Hypertension is usually associated with renal diseases, hyperadrenocorticism (cushing's disease), diabetes mellitus, hyperthyroidism.
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Pulse
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It is the wave of systolic pressure, that starts at the ventricles and spreads throughout the arterial network.
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How is the pressure maintained within the arterial system, so that blood continues to flow to the vital organs even during diastole?
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-The initial blood pressure is due to the contraction of the ventricles.
-This pressure is maintained throughout the ventricular diastole by the elasticity of aorta and large arteries. -The arterioles at the end of arterial network regulate the flow of blood into capillaries. (Arterioles are narrow, thick walled tubes at the terminal end of arteries. The thick layer of smooth muscles in the arterioles are innervated by sympathetic and parasympathetic fibers, which control the diameter of the lumen of the arteriole. Blood flows into capillaries from these arterioles). -The volume of blood also affects the blood pressure (decreased blood volume will decrease the blood pressure, as noticed in the case of severe hemorrhages). |
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Electrocardiography (ECG or EKG)
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The EKG measures the electrical activity of the heart. As the heart muscles undergo depolarization, the electric current spreads throughout the body and can be recorded at the body surface. The impulses that start from SA node and spread throughout the heart muscles are recorded on a chart in form of P, QRS and T deflections.
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P wave
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Indicates atrial depolarization: As the impulses originate from SA node and spread throughout the atrial muscles, these impulses depolarize the atrial muscles, that is recorded as P-wave on the chart and leading to atrial systole.
The normal P-wave in dog is 0.04 sec. by 0.4 mV (2 boxes wide and 4 boxes tall). |
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QRS complex
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Indicates ventricular depolarization: From atrial muscles, the impulses are transmitted to AV node. This AV node transmits these impulses throughout the heart muscles via Bundle of His, therefore depolarizing the ventricular muscles leading to ventricular systole.
Normal value in dogs is 0.06 sec. (3 boxes) |
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T-wave
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Indicates ventricular repolarization or ventricular diastole. It is usually longer in duration as compared to the depolarization.
Can be positive or negative |
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PR Interval
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Measured from beginning of P wave to beginning of QRS complex. Normal PR interval is 0.06-0.13 sec. (3-6 boxes wide).
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QRS Complex
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Normal value in dogs is 0.06 sec. (3 boxes)
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ST Segment
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Between the end of S wave and beginning of T wave. Not more than 0.2 mV (2 boxes below baseline). Normally it lies on the baseline and then dips into T wave.
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QT Interval
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Between beginning of QRS complex to end of T wave. Normal value is 0.14 -0.22 sec. (7-11 boxes wide).
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