Biology 2313 Week 5 Notes
Biology 2313 Week 5 Notes Biology 2313
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This 7 page Class Notes was uploaded by Ednjon Parilla on Saturday September 24, 2016. The Class Notes belongs to Biology 2313 at University of Texas at El Paso taught by Dr. Zaineb Al-Dahwi in Fall 2016. Since its upload, it has received 17 views. For similar materials see Human Anatomy & Physiology II in Science at University of Texas at El Paso.
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Date Created: 09/24/16
Chapter 18: The Heart – Cardiac Output Difference of Circulations Pulmonary Circuit o Shorter o Low resistance; lower pressure o Associated with the right side Systemic Circuit o Longer o 3x to 5x higher resistance than PC (due to the length); higher pressure o Associated with the left side o Workload is much greater than PC; thickness of myocardium in the left shows this Heart Valves: Function Valves are going to be opening and closing according to the differences in blood pressure o Which is the driving force of moving the blood to different chambers; blood flow depends on difference in pressure 80% of blood is returned into atrium How the valves work (using valve between ventricle + artery in left as example): 1) Blood is returned into atrium Blood pressing against the AV values causes them to open 2) Blood moves into ventricle As the ventricles fill, AV valve flaps hang limply into ventricles 3) Atria contract Forces additional blood into ventricles 4) AV valve close Closes due to the contraction of ventricles and blood pressure against the AV cusps Papillary muscles contract an chordae tendineae tighten o Prevents valve flaps from everting into artia 5) Ventricle contract and increases the pressure Moves the AV flaps upward to close the valve Intraventricular pressure rises and blood is pushed up against semilunar valves 6) Semilunar Valves open Pressure in the ventricle exceeds pressure in the artery o Blood is pushed against the wall causing the opening of the valve and the moving of the blood into the artery 7) Relaxation (from contraction) Blood pressure goes down Pressure in aorta (artery) is greater in the ventricle 8) Backflow Caused by the higher pressure in artery than ventricle Cusps are filled at the base of the artery 9) Ballooning Caused by filled artery base Closes the semilunar valve (between ventricle and aorta) 10) Papillary muscles contract to keep the valve closed Also prevents backflow of blood into atrium ↳ Important to Note: Difference in blood pressure causes contraction and relaxation Atrio-Ventricular Valve is CLOSED at ventricular contraction Cardiac Muscle Cells Cardiac Muscle Cells VS Skeletal Muscle Cells: Anatomic Features Similarities o Striation; both are striated Arrangement of I and A bands in myofibrils (specifically in the sarcomere) are the same o Way of Contraction Both contract by the sliding of actin and myosin = Sliding Filament Model Differences o Skeletal Muscle Cells: 1) Long muscle fiber, no branching, multinucleated 2) Do not contract as a single unit 3) Cytoplasmic Reticulum provides feedback control required to balance the processes of calcium storage, release, and reuptake 4) Contain more T-tubules than cardiac muscle cells o Cardiac Muscle Cells: 1) Shorter muscle fiber, branching, single-nucleated Connective tissue (Endomysium) connected to the fibrous cardiac skeleton (between the branches) 2) Contracts as a single unit All cardiac muscles are inter-dependent between other cells Connected by intercalated discs o Contain 2 Types of Cellular Junctions Desmosomes: linkage; prevents separation during contraction of heart Gap Junctions: protein channels that connect 2 cardiac muscle cells Work as a bridge where ions can go from one cell to another Reflective electrical impulses are sent (ions moving) and jh cause contraction as a single unit Functions as a Functional Syncytium 3) Cytoplasmic Reticulum is modified to store calcium extracellular space 2+ Ca activates channels 4) Less T-tubles than skeletal muscles Communication is through gap junctions Physiological Differences between Cardiac + Skeletal Muscle Cells #1 Activation Cardiac Muscle Cells (Myocytes) o 2 Major Types Self-Excitable Cells (aka Auto-rhythmic Cells): same anatomical features as other cardiac muscle cells, difference in _______ Capable of generating own depolarization “Pace maker cells” 1% of cells in the heart NOT CONTRACTILE Only job is to generate depolarization for the heart o The heart has its own in-house nervous system DOESN’T NEED the nervous system outside of heart! Proven by heart transplants Skeletal Muscle Cells needs the nervous system in order to become activated (to contract) o No contraction leads to paralysis #2 Contraction Cardiac Muscle Cells o Contracts as a single unit → functional syncytium Gap junctions are the reason for electrical coupling + single beating of the heart Skeletal Muscle Cells o Use motor units; muscles can contract at different times Your muscles will contract when you want it to; not automatic! #3 Source of Calcium Cardiac Muscle Cells o From extracellular space o For CONTRACTILE cardiac muscle cells Plasma Membrane has sodium + calcium channels (specifically Slow Calcium Channels) Depolarization will cause the calcium channels to open 20% of calcium is provided; needed for contraction Calcium Sensitive Channels (on cytoplasmic reticulum) will release the rest of calcium needed for contraction #4 Length of Absolute Refractory Period nd o Absolute Refractory Period = the amount of time in which a 2 action potential cannot be generated Skeletal Muscle Cells o Brief refractory period Allows 2 ndaction potential if repolarization (before relaxation) is FULLY COMPLETE, but relaxation is NOT COMPLETE (Partial Relaxation) Cardiac Muscle Cells o Absolute refractory period is almost as long as the entire contraction- relaxation cycle of the skeletal muscle cells o THE HEART NEEDS TO GO BACK TO COMPLETE RELAXATION! During relaxation the heart is filled with blood If it doesn’t reach complete relaxation, there is less blood being pumped; therefore, decreasing efficiency of the heart #5 Respiratory Mechanisms Cardiac Muscle Cells o The Heart is FULLY DEPENDENT on aerobic respiratory mechanisms (uses oxygen) Skeletal Muscle Cells o Uses anaerobic mechanisms + is capable of switching to aerobic mechanisms Action Potential in Pacemaker Cells Pacemaker Cells = cardiac muscle cells that are non-contractile Self-excitable; generate own depolarization (do not require stimulation from nervous system) Unstable Resting Membrane Potential is what allows depolarization o Have a particular sodium channel = Funny Channel Action Potential Review 1. Depolarization = sodium enters 2. Repolarization = exit of potassium 3. Hyperpolarization = continuous potassium exit; causes a negative membrane ↳ Important to note: CONTRACTION follows DEPOLARIZATION RELAXATION follows REPOLARIZATION ↳ The electrical function happens BEFORE mechanical End of Hyperpolarization Sodium channel opens and sodium enters; slowly drifts membrane into the threshold (depolarization) Makes the membrane more positive Pacemaker Potential = time period when the membrane is slowly drifting the membrane back into the threshold Reaching the threshold leads to the uprising of depolarization Causes the opening of calcium channels and inactivation Continues the cycle: ▫ Pacemaker Potential → Depolarization → Repolarization Intrinsic Conductive System Sequence of Excitation 1) SA Node = Sinoatrial Node ↳ Node: collection of non-contractile cardiac muscle cells Has the fastest beating rate: 75 beats per min. Known as pacemaker of the heart Location: Right Atrium Electrical impulse is transmitted into both atria trough gap junction This transmission is through the Internodal Pathway; sends the electrical impulse from SA node to AV node 2) AV Node = Atrioventricular Node Has a beating rate of 50 beats per min. Located: at the center of the heart; in the floor of the right atrium, between the atria and ventricles Delay in passage of electrical impulse Muscle fibers in the AV node have a smaller diameter Promotes increase in resistance; slower passage of electrical impulse (depolarization) This ensures that contraction of the ventricle doesn’t match the contraction of the atrium! 3) AV Bundle = Atrioventricular Bundle Beating rate of 30 beats per min. Location: between atria and ventricles Divides into right and left bundle branches Sends impulses from the AV node to the ventricles 4) Bundle Branches Responsible for excitation in septum between the ventricles Location: along the interventricular septum 5) Purkinje Fibers (or called Subendocardial Conducting Network) Most important portion responsible for excitation of septum cells Location: AV Bundle Function - to send nerve impulses to the ventricles and cause them to contract and pump blood either to the lungs or the rest of the body. Left Purkinje fibers start at the apex of the heart and move upward Right Purkinje fibers start from the bundle branches and move upward ↳ Important to note! If the SA node becomes infected; AV node becomes the pacemaker If AV node becomes infected; AV Bundle + Bundle Branches take over but DO NOT provide jjj a sufficient rate to become the pacemaker In this case an artificial pacemaker should be provided Innervation of the Heart Made possible by the Parasympathetic branch under the Autonomic Nervous System MODIFIES the activity of the heart o Nerves will lower or increase the heart rate NOT generate the heart rate Medulla Oblagata (in Brainstem) Collection of nerve cells 3 Centers o Cardiovascular center o Respiratory center o Vasomotor center Cardiovascular Center Cardio-excitatory Center (or the Cardio-acceleratory Center) o Project to the sympathetic NS with interneurons o From sympathetic NS to the heart through sympathetic cardiac nerves Sympathetic cardiac nerves increase heart rate + force of contraction At the heat the impulse innervates the SA + AV nodes, heart muscles, and coronary arteries Cardio-inhibitory Center o Sends impulses through the Vagus Nerve (parasympathetic) used by the cardio-acceleratory center Goes straight to the SA + AV Node in the heart ↳ Important to note: the conduction system is made of cardiac contractile cells (allowed by lk gap junctions) Action Potential in Cardiac Muscle Cells 1) Depolarization = Excitation Excitation passes through the sarcolemma (plasma membrane of muscle cells) Opening of Na channels (voltage-gated) o Allows entrance + generates depolarization o Slow Ca 2+channels are also opening at the same time! + Inactivation of Na channels o Slow Ca 2+channels will be completely opened at this time Increase in Ca 2+intake = maintains and prolongs depolarization 2) Plateau Phase Prolonged depolarization Prolonged depolarization = prolonged contraction (Sustained Contraction) 2+ Provides efficiency in the pumping action of the heart Ca channels inactivated; leads to repolarization Opening of K channels 3) Repolarization ↳ REMINDER!! Depolarization THEN Contraction Repolarization THEN Relaxation Length of Refractory Period (in skeletal muscle) almost = Contraction and Relaxation Cycle (in cardiac muscles) Refractory Period = the period when a 2 ndaction potential cannot be generated Prevents summation (tetanic contraction; which can lead to heart fatigue) EKG or ECG (represents electrical makers) Electrical activity of the heart throughout the body (of both contractile and nodes) Nodal refers to the Conductive (electrical) System NOT representing a SINGLE action potential Defelection Waves represent contractile + nodal cells that represent certain portions of the heart P Wave QRS Complex T Wave 1) Atrial Depolarization (P Wave) o Electrical activity due to passage of depolarization through ventricles (QRS) o Repolarization wave through ventricle (T) Cannot be seen due to the strength of the QRS depolarization which is occurring at the same time EKGs can differ Aspects of EKG 1) P-Q Interval: beginning at atrial depolarization to ventricular depolarization
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