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You Gotta Circulation!! Quick Outline • • • • • Glossary Blood Flow Heart Sounds Heart Rate and how it changes Blood Pressure and how it changes 1 Terms (of Endearment?) The Heart Its Electricity • • • • • • • • • • • • • • • • • • • • Vena Cava Right Atrium Right AV Valve Right Ventricle Pulmonary Valve Pulmonary Artery Pulmonary Vein Left Atrium Left AV Valve Left Ventricle Aortic Valve Aorta Arterioles And Controls Intercalated Disks •Sympathetic Desmosomes •Excites the Heart Gap Junctions •Uses NE SA Node AV Node •Acts on SA node and arterioles Bundle of His Left and Right Bundle •Parasympathetic Branches •Relaxes the Heart • Terminal Purkinje Fibers •Uses Ach •Acts on SA node Basics of Flow ZOOM!! RA RV LA LV So we have Vena CavaRARV Pulmonary ArteryLung Pulmonary VeinLALVAorta Body Arterioles 2 Heart Sounds • Lub: the closing of the AV Valve – This happens just after the ventricles start contracting. (Contraction increases the pressure in the ventricle above the pressure in the atria, causing the valves to close.) • Dub: the closing of the Pulmonary and Aortic Valves – This happens just after blood is finished ejecting from the ventricle. (The ventricle relaxes, decreasing its pressure below the pressure in the pulmonary artery or the aorta, so the pulmonary or aortic valves close.) Valves close passively as a result of a pressure difference on each side of the valve. Electrical Statement • Electrical Synapses: – Faster than Chemical – Can transmit information in either direction – Travel through gap junctions—don’t diffuse through synapses •Gap Junctions Look Like: •Desmosomes Look Like: Cell 1 Cell 1 Cell 2 Gap Junction Cell 2 3 Conduction SA Node Depolarization of R and L atria AV Node Bundle of His Left and Right Bundle Branches Terminal Purkinje Fibers It’s Got Rhythm • Each part of the heart has inherent rhythm, but some parts are faster than others • The SA Node is the fastest--so it paces the heart • Its Action Potential Looks like • Ion Channels: – F Channels • Permeable to Na+ and K+ at membrane voltages below 40mV – V-gated Ca++ channels – K+ channels 4 Sympathetic Stimulation and SA Node Action Potentials Recall that this occurs when norepinephrine binds to betaadrenergic receptors on the SA Node Thank you to U. Rochester for this image Actions of Parasympathetic Stimulation on SA Node Action Potentials Recall that this happens when acetylcholine binds to muscarinic acetylcholine receptors on the SA Node Again, props to U. Rochester for the image 5 Ventricular Muscle Cell Action Potential Key: 1st Fast increase in membrane potential due to V-gated Na+ channels 2nd The Na+ channels close, and Vgated Ca++ channels and K+ channels open. The K channels are acting to decrease the membrane voltage and the Ca++ are acting to increase it. Result? Plateau. 3rd The v-gated Ca++ close. 4th Resting membrane voltage is set by the high permeability of K+. Equations to Scribble in the Margins • CO=HR x SV • BP= CO x TPR • Blood pressure can be changed by changes in CO or in TPR. You saw how CO could be changed 2-3 slides ago. Altering heart rateChange in COChange in BP. • So an increase in sympathetic stimulation increases the amount of NE bound to _-adrenergic receptors in the SA node, which increases the HR, which increases the CO and the BP. • An increases in parasympathetic stimulation increases the amount of ACh bound to muscarinic ACh receptors, which decreases the HR, which decreases the CO and the BP. 6 But what about TPR? What changes it? – TPR is influenced by the resistance to flow in the arterioles, which is controlled the arterioles’ radii, which are controlled by the contraction or relaxation of the smooth muscle around the arteriole. – Arterioles have SNS innervation but not PSNS • When norepinephrine binds to _-adrenergic receptors on the smooth muscle cells, the smooth muscle contracts, which decreases the radius of the arteriole. This causes an increase in TPR, and because BP=CO x TPR, it lead to an increase in BP. • When less norepinephrine binds, the smooth muscle relaxes, which causes an increase in the radius of the arteriole. This leads to a decrease in TPR, and because BP=CO x TPR, it leads to a decrease in BP. Baroreceptors • Baroreceptors serve as the sensor in the blood pressure negative feedback loop. They are located in the carotid artery and have mechanosensitive neurons that sense blood pressure. They send action potentials into the brain stem, where the comparator is. The brain then changes the relative amount of sympathetic and parasympathetic amounts of innervation if necessary. 7 Baroreceptors • If baroreceptors are cut, then the axon terminal (in the brain stem) and the peripheral terminal (in the carotid artery) are not communicating. • If the barorecptor is cut and then the axon stump (which is still connected to the brain stem) is stimulated at a high rate, the brain stem is “sensing” high blood pressure. So it will take action to decrease the blood pressure. • Meanwhile, the peripheral terminals will sense a decrease in BP, but won’t be able to get this information to the brain stem. Ok take a deep breath It’s time for respiration 8