Physiology Lab quiz 3
What is a myogenic response?
Change in vascular resistance in response to stretch of blood vessels in absence of any external factors
Why is an ectopic beat followed by a "skipped beat"?
The ventricle will not depolarize or contract, resulting in a skipped beat. The ventricle must wait for the next SA node depolarization to arrive.
Why is ventricular fibrillation such a serious condition?
The ventricles are not contracting as a unit. Pumping ability is near zero, and CO and MAP fall to near zero.
Why doesn't atrial failure result in death?
The ventricles fill 80% full with blood. The atrial contractions contribute about 20% of the blood in the ventricle. Not necessary for life, but important for exercise
What is an isovolumetric ventricular contraction?
Ventricle contracts - increases pressure. AV and Semilunar Valves closed. No blood entering or exiting ventricle.
What is an isovolumetric ventricular relaxation?
Ventricle relaxes - decreases pressure. AV and Semilunar valves closed. No blood entering or exiting ventricle.
Describe the effect of stimulating the vague nerve, including the NT, receptor, effect on ion channels, and membrane potential.
1. Apply high stimulus voltage to the vague nerve which increases action potentials. An excess of Ach is released by the muscarinic receptors of SA node. Membrane becomes hyperpolarized that threshold is not met. 2. Once stimulation is stopped, contractions resume after delay. Ach must first be broken down be acetylcholinesterase. 3. 1st contraction after break is stronger than usual. Blood entered and stretch ventricle closer to optimal length. This leads to stronger next beat./
What are the 7 steps of excitation-contraction coupling?
1. Depolarization of cardiac Contractile cell to threshold via gap junction 2. Opening of calcium channels in plasma membrane. 3. AP travels down T Tubule 4. Calcium is released from ST by calcium-induced calcium release. AP in T tubule 5. Calcium binds to troponin causing shift in tropomyosin 6. Binding sites for Myosin on actin are exposed 7. Cross bridge cycle occurs
List the 4 responses of increased sympathetic nervous system regarding MAP
1. Inc. HR --> Inc. CO --> Inc. MAP 2. Inc. TPR --> Inc. MAP 3. Inc. Venous Vasoconstriction --> Inc. VR --> Inc. EDV --> Inc. SV --> Inc. CO --> Inc. MAP 4. Inc. Contractility --> Inc. SV --> Inc. CO --> Inc. MAP
List the sequence of events initiated by the cardiovascular center, to correct the decrease in MAP.
1. Increase HR, Increase CO, Increase MAP 2. Increase TPR, Increase MAP 3. Increase Vasoconstriction, Increase VR, Increase EDV, Increase SV, Increase CO, Increase MAP 4. Increase Contractility, Increase SV, Increase CO, Increase MAP
How does the respiratory pump work?
1. Inspiration: decrease pressure in thoracic cavity, increase pressure in abdominal cavity 2. Pressure on veins in abdominal cavity creates gradient that factors blood movement to thoracic cavity: Increases central venous pressure and venous return
How does the skeletal muscle pump work?
1. One-way valves in peripheral veins 2. Skeletal muscle contracts, squeezing on veins to increase pressure, blood moves toward the heart, blood cannot move backwards due to valves 3. Skeletal muscle relaxes, blood flows into veins between muscles
What are the factors affecting resistance to flow?
1. Radius of vessel 2. Length of vessel 3. Viscosity of fluid
How is PPP amplitude related to TPR?
1. The pulse wave gets TALLER if MORE blood enters the capillary due to a vasedilation or decreased TPR 2. The pulse wave gets shorter if less blood enters the capillary due to Vasoconstriction or increased TPR.
What are the local factors that control vascular resistance?
1. Vascular resistance regulated through changes in radius of arterials 2. Depends on Contractile state of smooth muscles in walls of the vessel 3. Local factors regulate radius to regulate blood flow
Which has the same contraction rate in the ventricle as in the atria? (AV Block)
1st degree AV node block
Signal delay from SA node to AV node is called...
1st degree Heart Block
Which has (have) a slower ventricular rate than atrial beat? (AV Block)
2nd and 3rd degree AV node block
What is Einthoven's triangle?
3 leads on the skin to measure the electrical activity of the heart
Which has a very slow, but regular ventricular beat? (AV Block)
3rd degree AV node block
Which of the following conditions may occur when the AV node does not conduct atrial depolarization to the ventricle
3rd degree heart block
What is the value of conduction velocity?
4 m/sec
What is the average CO?
5 liters/min at rest
What is the average blood volume?
5.5 liters
What is the MAP for a BP of 120/70?
70 x (1/3) 50 = 86.67
When the depolarization of the atria occurs in an abnormal direction, the P wave appears inverted. This indicates that.....
A place other than the SA node gets to threshold before the SA node (Ectopic beat)
What happens if the SA node fails? What area usually takes over as the pacemaker?
AV node
What disorder might result in a prolonged PR interval?
AV node disease
9. What is an AV block? Compare first, second, and third degree AV node block.
AV node disease that results in conduction problems between the atria and ventricles. 1st: Longer depolarization 2nd: Some depolarization 3rd: Most severe- no depolarization
What valve closes during the first heart sound?
AV valves close
Is the T wave normal or abnormal? (PVCs)
Abnormal
Why doesn't the heart experience recruitment?
All cells participate in each contraction
Why doesn't the heart experience recruitment? (what characteristic of heart cells prevents recruitment?)
All the cells participate in each contraction, the heart cannot undergo recruitment.
What is an ectopic beat?
An ectopic beat is any contraction that occurs following a depolarization that originates outside the SA node.
What is an ectopic beat?
Any contraction that occurs following a depolarization that originates outside the SA node
Where are the arterial baroreceptors located?
Aortic arch and carotid sinuses
What are relatively large, branching vessels that conduct blood away from the heart?
Arteries
What are small branching vessels with high resistance?
Arterioles
What is the difference between atrial flutter and atrial fibrillation?
Atrial Flutter: Some of the depolarization are NOT CONDUCTED into the ventricle because they arrive at the AV node while it is still in refraction Atrial Fibrillation: The atrial depolarization circles randomly around and around the atria, no longer depolarizing the atria as a unit.
P-wave represents...
Atrial depolarization
What prevents summation or tetany from occurring in the heart? Why is this important in heart function?
Because cardiac muscle cannot be stimulated to contract again during contraction and most of relaxation, the heart cannot undergo summation and/or tetany. This insures that the heart can relax and fill between contractions.
When does the depolarization in the ventricle occur in relationship to ventricular contraction?
Before
Describe the pulmonary circulation
Begins in the right ventricle, flows through the lungs, and ends in the left atrium
Describe the systemic circulation
Beings in the left ventricle, flows through the body tissues, and ends in the right atrium
After a period of no heart beat, why might the next contraction be stronger than usual?
Blood continues to enter the ventricle, stretching the muscle to a more optimal length.
What causes the sounds of Korotkoff?
Blood spurts through the vessel with each heart beat, this creates a turbulent flow (noisy flow)
How would an increase in blood viscosity affect MAP?
Blood viscosity may increase in certain disease states, increasing resistance, which would increase MAP
What is the site of exchange between blood and tissue?
Capillaries
What are platelets and what do they do?
Cell fragments, important in blood clotting
Why is mean arterial pressure closer to diastolic pressure than to systolic pressure? How is it calculated?
Closer to diastolic pressure, the heart spends more time in Diastole than in Systole. MAP = Diastole + 1/3 (pulse pressure)
What is total peripheral resistance?
Combined resistance of all blood vessels within the systemic circuit.
If the heart cannot experience summation/tetany or recruitment, by which two mechanisms does the heart increase its strength of contraction?
Contractility and strength-tension
Predict what happens to PPP when standing up from a sitting position. Be sure to determine, the change in MAP caused by standing up, and the cardiovascular center's corrective response that alters MAP.
Decreased VR --> Decreased EDV --> Decreased SV --> Decreased CO --> Decreased MAP --> Increased PPP
What effect does stimulating the vague nerve have on the heart? Which branch of the autonomic nervous system is involved? Name the NT released. What is the receptor?
Decreased heart rate. Parasympathetic. Acetylcholine. muscarinic.
What does the QRS complex mean?
Depolarization spreading through the ventricles
What are the components of baroreceptor reflex? (detectors, afferents, integration center, efferents, effectors).
Detectors = baroreceptors Afferents = visceral afferents Integration center = cardiovascular control center Efferent = autonomic nervous system Effectors = heart, arterioles, and veins
What is different about the strength of the next ventricular contraction immediately following the skipped beat? Explain.
During the compensatory pause, blood continues to flow into the ventricle, stretching the heart closer to optimal length.
The acronym ECG stands for...
Electrocardiogram
What might cause a prolonged QRS complex?
Enlargement of the ventricles or with damage to the conduction fibers (bundle branch block)
What are the hormonal controls of MAP?
Epinephrine, Vasopressin, Angiotensin II
What is an electrocardiogram?
External measure of electrical activity of the heart
Atrial fibrillation is more deadly than ventricular fibrillation. True or false?
False
Tachycardia is slow heart rate and bradycardia is fast heart rate. True or false?
False
What are the sounds of Korotkoff- relate them to systolic and diastolic pressure.
First appearance of sound: systolic pressure 2nd sound (when it disappears): diastolic pressure
What is contained in the plasma?
Fluid and solutes
Cardiac muscle cells are connected together electrically by...
Gap junctions
Untreated hypertension can increase the risk for the following....
Heart failure Stroke Blindness due to detachment of the retina Renal failure
What are the 3 determinants of mean arterial pressure?
Heart rate, stroke volume, and total peripheral resistance
What is hypertension?
High blood pressure >140/>90
What happens if the SA node fails? What area usually takes over as pacemaker?
If the SA node fails, the next fastest area takes over as pacemaker, usually the AV node
List the one response of increased Parasympathetic nervous system regarding MAP
Inc. HR --> Inc. CO --> Inc. MAP
When a person lies down from a standing position, what is the first change in the cardiovascular system. How does the cardiovascular center (baroreceptor reflex) respond to correct this change?
Increase VR, Increase EDV, Increase SV, Increase CO, and Increase MAP
How can the ventricle contract with more force, without stretch? How is this different from skeletal muscle? What is this called?
Increase contraction strength by increasing available Ca2+. Unlike a single skeletal muscle cell, cardiac muscle SR does not release an exact amount of calcium. Called Contractility.
What are the effects of Parasympathetic activity on heart rate
Increased Parasympathetic activity (vague nerve) muscarinic Cholinergic Receptors in SA node: Increase open state of K+ channels and closed state of calcium channels Decrease heart rate
What effect does increased sympathetic nervous system stimulation have on the PPP? Why?
Increased Sympathetic will decrease PPP because there is decreased blood flow into the capillaries.
What are the effects of sympathetic activity on heart rate?
Increased sympathetic activity (nerves or epinephrine) Beta 1 receptors in SA node Increase open state of it and calcium channels Increase rate of spontaneous depolarization Increase heart rate
What does glucagon do to the heart rate?
Increases heart rate
How can the ventricle contract with more force, without stretch.
It can contract with more force if there is an increase in calcium released.
Why is an ectopic contraction usually weaker than a normal contraction?
It did not originate in the SA node
Describe the effect on the K+ channels in the pacemaker cell.
K+ channels hyperpolarize the SA node cell. Heart rate is slowed
What is laminar blood flow? How is it related to the measurement of blood pressure?
Laminar: The outer layers of blood in a vessel flow more slowly than the inner layers No sound
What are fenestrated capillaries?
Large gaps between endothelial cells forming pores or fenestrations. Allow proteins and in some cases blood cells to move through.
What is high compliance?
Large increase in blood volume required to produce large increase in pressure
How does Contractility increase in force of contraction affect stroke volume? Cardiac output?
Larger stroke volume and increased cardiac output
How is cardiac output related to MAP?
MAP = CO x TPR
What is the relationship between total peripheral resistance (TPR) and mean arterial pressure (MAP)?
MAP = CO x TPR
What is compliance?
Measure of how the pressure of a vessel will change with a change in volume
What is the long term regulation of MAP?
Minutes to days. Regulate blood volume. Involves kidneys. Primarily hormonal control.
What problem can shift the ST segment off the baseline?
Myocardial Infarction
Why is no sound heard when the sphygmomanometer is inflated?
No flow occurs through the vessel, so no sound is heard
What is laminar flow?
No sound
How did we record the depolarization wave in the ventricle (R-wave)? Where does ventricular contraction occur in relationship to this wave?
Notice how the R-wave occurs right before the onset of ventricular Systole (Contraction).
Which of the following is the most closely associated with transit of the depolarization wave through the AV node?
P-R segment
What are premature ventricular contractions (PVCs)? Why is there no P-wave preceding this beat?
PVC results from an ectopic source in the ventricle reach threshold before the SA node depolarization reaches the ventricle. The P-wave is not visible due to the large depolarization and repolarization that occurs during the PVC.
Which branch of the autonomic nervous system is involved when we stimulate the vague nerve?
Parasympathetic
Which nervous system lowers heart rate?
Parasympathetic
What is central venous pressure?
Pressure in the large veins of the thoracic cavity that lead into the heart
What is turbulent flow?
Produces korotkoff sound
What are erythrocytes and what do they do?
Red blood cells, transports oxygen and carbon dioxide
What does the T wave mean?
Repolarization of the ventricles
What does the P-wave mean?
Result of the depolarization spr3eading through the atria.
Why is the SA node the pacemaker of the heart, even though other areas are capable of automaticity?
SA node has the fastest beat.
What is the intrinsic depolarization rate of the SA node? The AV node? The Purkinje system?
SA: 60-100 AV: 40-60 Purkinje: 20:40
What is the short-term regulation of MAP?
Seconds to minutes. Regulate Cardiac output and total peripheral resistance, involves heart and blood vessels, primarily neural control.
What valve closes during the second heart sound?
Semilunar valves close
What are the 4 factors that influence central venous pressure and venous return?
Skeletal muscle pump Respiratory pump Blood volume Venomotor tone
What 4 things can increase VR?
Skeletal muscle pump Respiratory pump Increased blood volume Increased venomotor tone
What is low compliance?
Small increase in blood volume causes a large increase in pressure
How is blood pressure measured?
Sphygmomanometer
What is the systemic circuit?
Supplied by left heart. Blood vessels from heart to systemic tissues and tissues to heart.
What is the pulmonary circuit?
Supplied by right heart. Blood vessels from heart to lungs and lungs to heart
Which autonomic nervous system and NT increases contraction strength by Contractility?
Sympathetic
Which nervous system speeds the heart?
Sympathetic
What are the two parts of the cardiac cycle? Which lasts longer?
Systole and Diastole (longer, 2/3 of the time)
Relate the sounds of Korotkoff to: Systolic arterial blood pressure, Diastolic arterial blood pressure
Systolic arterial blood pressure: First appearance of a sound Diastolic arterial blood pressure: Disappearance of the sound
What is pulse pressure?
Systolic pressure - diastolic pressure
How is TPR related to MAP
TPR = MAP / CO
Why is it beneficial for the AV node to slow conduction between the atria and ventricle?
The AV node slows conduction that allows the atria to contract before the ventricles.
Describe the effect on the "Funny" Na+ channels in the pacemaker cells.
The Na+ channels open increasing the time to depolarize to threshold. Slows the heart rate
During the PR interval, where is the depolarization wave in the heart?
The P-R interval is most closely associated with transit of the depolarization wave through the AV node
What is cardiac output? How is it calculated?
The amount of blood pumped by each ventricle per minute. CO = SV x HR
In a grade III AV block, where is the atrial rate set? Where is the ventricular rate set?
The atria continue to contract at the SA node rate, but the ventricles contract at the Purkinje rate
How do the pacemaker cells of the heart get to threshold? What type of channel is involved? How is this channel different from other channels we have studied?
The cells depolarize to threshold on their own through the opening of "funny" sodium channels that are stimulated when the cell depolarized. "Funny" channels have Na+ and then Ca2+ enter the cell and brings the membrane to threshold
What is the first change in the cardiovascular system that occurs as a result of hemorrhage?
The change is decreased blood volume
List the sequence of events beginning with hemorrhage and ending with a decrease in MAP.
The change is decreased blood volume, which decreases venous return, which decreases stroke volume, which decreases cardiac output, which decreases mean arterial pressure
Why might this contraction be weak? (PVCs)
The contraction strength is weak, due to little filling time and a small EDV.
How is the excitation-contraction mechanism of the cardiac cell similar to that of skeletal muscle? How is it different from skeletal muscle?
The cross-bridge steps are identical to skeletal muscle Different because the cardiac muscle undergoes calcium-induced-calcium release
What is ventricular tachycardia?
The ectopic source in the ventricle depolarized repeatedly at a rate FASTER than the SA node, the new area takes over as ventricular pacemaker.
What is the Starling Law of the Heart? How was this illustrated in our turtle demonstration?
The heart pumps out whatever comes in. The heart will be artificially stretched by pulling on a hook in the ventricle and observing the change in contraction strength.
Why would the contraction that follows this beat be stronger than usual? (PVCs)
The next contraction is often extra strong, due to increased filling time and a large EDV.
Why is this beat followed by a COMPENSATORY PAUSE? (PVCs)
The pause occurs because the SA node reached threshold sometime during the PVC, but the depolarization arrived at the ventricle when it was still in refraction from the PVC.
Explain why this property does not occur in skeletal muscle.
The skeletal muscle does not experience calcium-induced-calcium release.
When stimulating the vagus nerve on the heart, what happens to resting or baseline membrane potential? How does this slow/stop the heart? What happens to the acetylcholine after it is released?
There are a high frequency of APs. The node membrane becomes so hyperpolarized that threshold is not reached during this time period. The acetylcholine is broken down by acetylcholinesterase.
Why does an increase in TPR cause a small amplitude PPP?
There is a decrease in blood flow
What is different about the QRS complex? (PVCs)
There is a wide QRS
What is TPR?
Total peripheral Resistance: Pressure of a vessel
How does Vasoconstriction affect capillary blood flow?
Vasoconstriction causes less blood to enter the capillaries decreases capillary blood flow.
How does Vasoconstriction affect peripheral pulse pressure (PPP) amplitude?
Vasoconstriction decreases PPP
How does Vasoconstriction affect TPR?
Vasoconstriction increases TPR.
How does Vasoconstriction affect MAP?
Vasoconstriction raises MAP
What are relatively large converging vessels that conduct blood to the heart?
Veins
What are the 3 primary factors affecting Stroke Volume?
Ventricular contractility, End-diastolic volume, Afterload
QRS complex represents....
Ventricular depolarization
What are small converging vessels?
Venules
What are leukocytes and what do they do?
White blood cells, defend body against pathogens
Explain how an increase in VR will affect MAP
inc. VR --> Inc. EDV --> Inc. SV --> Inc. CO --> inc. MAP