Ch 14 study notes

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Simon Fraser University
Biomedical Physio & Kines
BPK 205
Parveen Bawa

Chapter 14 1.What purpose does the cardiovascular system serve? Deliver oxygen and nutrients and remove waste 2. Draw the heart and label its atria, ventricles, two nodes, valves, arteries, and veins. 3. Why does blood flow? Why does blood flow faster through smaller vessels? All fluids flow down pressure gradients. From high pressure to low pressure. There is high pressure created in heart chambers during contraction, and lower pressure in blood vessels. Lowest pressure is at the Vena cava just before blood enters the right atrium. Blood flow is faster through smaller vessels because Flow Velocity = Flow rate/Cross- sectional Area. A smaller vessel will have a smaller Cross-sectional area, and since Flow velocity is inversely proportional to Cross-sectional are, then the Flow Velocity will be greater. 4. Explain the similarities and differences between cardiac, smooth, and skeletal muscle. • Skeletal: o Striated (fibers are parallel) o Have Sacromeres o Need motoneuron for excitation o Need APs o Ca++ for contraction targets thin filaments o Have T-tubules • Smooth: o Not Striated o No sacromeres o Can be autorythm or excited by neurotransmitters o May or may not have APs o Ca++ for contraction targets thick filaments o Other facts:  Hormones and Paracrines  Maintains force over longer period of time. In many organs, it’s even tonic. Ex. Sphincter of bladder  No T-tubules  Instead of z-lines, it has dense bodies or protein plaques (the latter attaches it to cell membrane) • Cardiac: o Striated o Have sacromeres o Need depolarization from autorythmic cardiac cells for excitation o Have APs o Ca++ for contraction targets thin filaments o Have T-tubules, but they’re larger than in skeletal muscle  Depolarization of cell from an adjacent cell activates voltage gated Ca++ channels for Ca++ intake.  Release of Ca++ from SR is initiated by incoming Ca++ from outside the cell, not by depolarization of T-tubule o Have Intercalated disks that contain demosomes that transfer force between cells o Gap junctions transfer electrical activity between cells 5. How do autorhythmic cells generate their rhythm (mentions channels/currents)? • SA node composed of nodal tissue that has characteristics of both muscle and nervous tissue • SA node generates impulses that travel through the heart causing both atria to contract • When impulses reach the AV node, there is about a tenth of a second delay from when it started in the SA node. This allows the atria to empty blood into the ventricles. Ventricles contract when impulses reach AV node. • Impulse travels down to the atrioventricular bundle, and branches down to the base of the heart where they divide into the purkinje fibers. These purkinje fibers contract • Refractory period much longer than in skeletal muscle fibers. This is to avoid tetanus • The HCN channels that slowly activate control pacemaker potential and, the rhythm. 1. Hyperpolarization of autorythmic cells activates HCN gated channels (gated by either cAMP or cGMP). Channel open to K+ and Na+. 2. More Na+ flows in than K+ flows out slowly causing depolarization. This starts the pacemaker potential 3. Eventually threshold for voltage gated L-type Ca++ channels is reached. Ca++ flows in starting the action potential depolarization 4. At maximum depolarization, voltage gated K+ channels open, and Ca++ channels close, causing repolarization to occur. 6. Describe the Cardiac cycle including the conduction of electrical signals within the heart and the contraction/relaxation of the muscles. How do these events relate to the PQRST waves measured using ECG? [ I do not want the pressure-volume diagram or the Wiggers diagram here--want just the sequence of events including depolarizations, contractions,opening or closing or valves] When does the atrium go through diastole, and when is the ventricle in diastolic condition? 1. Blood passively flows from inferior and superior vena cava to right atrium 2. SA node pulses causing both atria to contract. Tricuspid Atrio-ventriocular valve opens allowing blood to flow into the right ventricle 3. Tricuspid valve closes blocking backflow 4. Impulse reaches to AV node, depolarizing it which causes ventricles to contract. Pulmonary semilunar valve opens allowing blood transfer via pulmonary arteries to the lungs. When pressure in Pulmonary arteries is greater than pressure in the right ventricle, then the valve will close to prevent backflow 5. Blood returns to heart via pulmonary veins. Blood enters left atrium passively. 6. Another impulse begins at SA node to contract atria. Blood enters left ventricle via bicuspid valve. Once blood pressure is greater in left ventricle than left atrium, the bicuspid valve shuts 7. Depolarization of AV node contracts Ventricles. Blood flows through atrial semilunar valve to aorta where blood is distributed to various areas that require blood in the body. Atrium goes through diastole after the blood has been transferred to the ventricles, before AV valves were shut Ventricles at diastole after blood has finished ejecting into the aorta/pulmonary vein. Occurs when pressure in aorta/pulmonary vein exceeds pressure in ventricle. At this same moment, SL valves shut. 7. Draw atrial chamber, connect it to ventricular chamber, connect it to the aorta. Take each curve of Wigger's diagram( aortic pressure, ventricular pressure, ventricular volume) along with ECG curve, and describe what different parts of heart are going through during a complete cardiac cycle. DREW IT 8. What is the difference between the action potentials of autorhythmic cells of the heart, APs of contractile cells of the heart, and APs of a skeletal muscle fibre [mention channels, time duration, and what initiates the action potential] APs of Autorhthmic cells: 1. HCN gated channels (gated by cAMP or cGMP) are opened due to hyperpolarization, allowing K+ and Na+ to flow through. More Na+ flows in than K+ flows out causing pace-maker potential (slow depolarization) 2. Eventually pace-maker potential reaches threshold and voltage-gated L-Type Ca+ + channels open gradually but rapidly. At this point the HCN gated channels close. Ca++ rushes in causing massive depolarization. 3. At greatest depolarization, voltage gated K+ channels are opened to allow repolarization. Ca++ channels are closed to stop depolarization. 4. Cell repolarizes APs of Contractile Heart Muscle Cells: 1. Action potential originating from Autorhythmic cells opens voltage gated Na+ channels. Na+ flows in causing depolarization rapidly. 2. This activates voltage-gated L-Type Ca++ channels SLOWLY. Ca++ flows in. At maximum depolarization Na+ channels inactivate. 3. Ca++ flowing in via L-Type Ca++ channels activates release of Ca++ from SR via Ryanodine receptors (SLOW). 4. Fast voltage gated K+ channels open to start initial polarization. 5. Fast voltage gated K+ channels close. Membrane potential remains relatively constant because of decreased K+ flowing out, and Ca++ flowing in via L-Type channels and from the SR (they’ve finished opening now). 6. Both types of Ca++ channels close, and Slow Voltage gated K+ channels open, allowing K+ to flow out and repolarize the cell Differences with Skeletal Muscle action potential: • Time duration: o Contractile Heart Muscle APs last longer so that the refractory period is longer and there cannot be tetanus. Heart cannot function if there’s tetanus, it needs time for chambers to relax • Channels: o Both types of Heart muscle APs use L-Type voltage gated Ca++ channels. o Autorhytmic cell APs are initiated by HCN gated channels (gated by cAMP or cGMP). o In Contractile Heart muscle cells, there is a plateau in the membrane poten
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