Cardiovascular Physiology 2024.pdf

CARDIOVASCULAR PHYSIOLOGY VP 2024 Clara Camargo, DVM Study guide 1. Define the different terms from the Cardiovascular Terminology 2. Name and explain the different parts and functions of the Cardiovascular System 3. Define hemodynamics 4. Explain the different types of blood vessels and their chara...

CARDIOVASCULAR PHYSIOLOGY VP 2024 Clara Camargo, DVM Study guide 1. Define the different terms from the Cardiovascular Terminology 2. Name and explain the different parts and functions of the Cardiovascular System 3. Define hemodynamics 4. Explain the different types of blood vessels and their characteristics 5. Understand hemodynamic concepts of blood flow, blood pressure, resistance and compliance. Correlate blood vessel types with the hemodynamic concepts. 6. Explain the different types of cardiac cells, their functions and locations 7. List and explain the specific properties of cardiac muscle cells (compare to skeletal muscle cells) 8. Explain the role of the intercalated discs and where they can be found 9. Explain the conduction system of the heart (pacemakers, action potentials,and prevention of abnormal impulse conduction) Cardiovascular physiology - overview Cardiovascular physiology: The study of  heart  blood vessels  blood https://www.youtube.com/watch?v=3V8YMnIcpkI Pulmonary vs Systemic Circuit 1. Pulmonary → Right Side of Heart Pumps blood thru the lungs → RBC picks up O2 and drops off CO2 2. Systemic → Left Side of Heart Pumps blood thru the body’s tissues → supplies O2 and nutrients and removes CO2 C AR D I O VA S C U L A R TERMINOLOGY SYSTOLE: Contraction and emptying of the heart TACHYCARDIA: Increase in heart rate DIASTOLE: Relaxation and filling of the heart BRADYCARDIA: Decrease in heart rate CARDIAC OUTPUT: The total volume of blood pumped by the heart per unit time (mL/min) HEART RATE : Number of heartbeats per minute CARDIOVASCULAR SYSTEM The cardiovascular system is formed by the heart & blood vessels Primary function of cardiovascular system: TRANSPORT The bloodstream is a transportation system: Distributes O2 & nutrients to tissues Removes CO2 & other wastes from metabolically active cells & delivers them to the lungs, kidneys, or liver, where they are excreted Major role to maintain homeostasis HEMODYNAMICS Describes the principles that control blood flow in the cardiovascular system  Based on basic principles of physics applied to blood flow to and from the heart, and within the blood vessels  Depends greatly on the different characteristics of the different blood vessels Diameter (related to resistance) Elasticity (related to compliance)  Blood vessels will actively participate in regulation of blood flow to organs HEMODYNAMICS AND BLOOD VESSELS Arteries: aorta is largest artery; deliver oxygenated blood to the organs; thick-walled with lots of elastic tissue, smooth muscle and connective tissue; under highest blood pressure Arterioles: smallest branches of arteries; extensive smooth muscle; highest resistance to blood flow; highly innervated and can be contracted or relaxed in response to sympathetic nerve stimulation or vasoactive substances Capillaries: thin-walled with single layer of endothelial cells surrounded by basal lamina; sites of exchange of nutrients, gases, water and solutes between blood and tissues. Can be selectively perfused with blood Venules and veins: thin-walled, contain endothelial cell layer and some elastic tissue, smooth muscle and connective tissue; ↓elastic tissue = ↑capacitance; veins contain largest percentage of blood in cardiovascular system; ↑ blood volume under low pressure HEMODYNAMICS Blood flow (Q): requires a driving force → pressure difference  Blood flows from higher pressure to lower Blood pressure: pressure of circulating blood against the walls of blood vessels (resulting from the heart pumping blood through the circulatory system) pressure area  The pressure differences that exist between the heart and blood vessels are the driving force for blood to flow ↑ Pressure → ↓ Pressure The greatest decrease in pressure occurs in the arterioles because they contribute the largest portion of the resistance. HEMODYNAMICS Resistance is a force that opposes the flow of a fluid (an impediment to flow). In blood vessels, most of the resistance is due to vessel diameter. ↓ vessel diameter → ↑ resistance → ↓ blood flow Capacitance (or compliance) ability to increase the volume of blood it holds without a large increase in blood pressure. High capacitance → high blood volume and low pressure (i.e., veins) HEMODYNAMICS - summary From aorta To vena cava HEMODYNAMICS - summary Area and volume contained in systemic blood vessels Identify:  Type of blood vessel area and blood volume  Arteries vs capillaries vs Small volume of blood under higher pressure High volume of blood under low pressure veins  % of blood volume contained in each type of vessel https://doctorlib.info/physiology/physiology-2/29.html TYPES OF MUSCLE CELLS C AR D I O VA S C U L A R SIMILARITIES that cardiac muscle and skeletal muscle share Fibers are striated Myofibrils are made up from actin & myosin filaments Similar sarcomere arrangement Contains Sarcoplasmic Reticulum and T-tubules DIFFERENCES between cardiac and skeletal muscle cells CARDIAC MUSCLE CELLS Are ONLY found in the heart Involuntary contractions Fibers are short & branched Usually uninucleated (possibly up to 4 nuclei) High mitochondria density Interconnected by intercalated disks  Allows the muscle cell to contract in a wave like pattern Distribution of mitochondria in cardiomyocytes Colored SEM Image of Mitochondria in Cardiomyocytes Credit: Steve Gschmeissner/Science photo library Alexander V Panov and Sergey I Dikalov. “Mitochondrial Metabolism and the Age-Associated Cardiovascular Diseases”. EC Cardiology 5.11 (2018) CARDIAC MUSCLE is a functional syncytium Greek: Syn = together + Kytos = cell A functional syncytium consists of a group of cells that function as a single unit while still maintaining their individual cellular role Cardiac muscle cell → Do not fuse into a single multinucleated fiber during embryonic development Cardiac myocytes branch during development and bind to other myocytes Fibers remain separated as distinct cells with their sarcolemma but are electrically connected to each other through intercalated disks (desmosomes + GAP junctions) Skeletal muscle cells fuse into multinucleated fibers → characterising a morphological syncytium INTERCALATED DISK It is a dark, dense cross-band found at the end of each myocardial cell Part of the sarcolemma (plasma membrane) Contains 2 important cell-cell junctions  GAP JUNCTIONS Forms channels Allow rapid transport of ions Action potential travel easily from one cell to the next  DESMOSOMES Provide mechanical strength Anchors the cardiac muscle fibers together CARDIAC MUSCLE - 2 different cell types 1. CONTRACTILE CELLS - CARDIOMYOCYTES/ MYOCARDIUM Constitute most of atrial and ventricular tissues and are the working cells of the heart Responsible for contraction and generation of force/pressure 2. CONDUCTING CELLS Specialized muscle cells that do not contribute significantly to generation of force They function to generate and rapidly spread action potentials over the entire myocardium Found in SA node, AV node, AV Bundle, Purkinge Fibers Receive and respond to modulating effects of the autonomic nervous system PACEMAKER CELLS (AUTORHYTHMIC CELLS) → cells that exhibit automatic rhythmical electrical discharge, responsible for the cardiac action potentials CONDUCTION SYSTEM OF THE HEART Cardiac electrophysiology includes all processes involved in the electrical activation of the heart:  Cardiac action potentials  Conduction of action potentials along specialized conducting tissues  Excitability and the refractory periods  Modulating effects of the autonomic nervous system on heart rate/contractility CONDUCTION SYSTEM OF THE HEART  The action potentials initiated in the SA node are conducted to the entire myocardium in a specific, timed sequence.  Contraction follows a specific sequence “sequence” is critical because the atria must be activated and contract before the ventricles, and the ventricles must contract from apex to base for efficient ejection of blood CARDIAC MUSCLE ACTION POTENTIAL The normal/natural/primary pacemaker of the heart is the SINOATRIAL (SA) node or sinus node  SA node starts the action potential that is conducted throughout the heart  Slower pacemakers are located in the AV node and Bundle of His-Purkinje system  May adjust the heart’s rhythm when: SA node fires faster than normal SA node fires slowler than normal Impulses generated in the SA node are blocked SINOATRIAL NODE OR SINUS NODE (SA node) It is a small strip of specialized conducting cardiac muscle cells (pacemaker cells) Located in the right atrium Immediately below and slightly lateral to the opening of the cranial (superior) vena cava The SA node fibers have almost no contractile muscle filaments The action potential spreads from the SA node to the right and left atria via the atrial internodal tracts Action potential moves from SA node to → atrial walls (Bachmann’s bundle, internodal pathways) and to the AV node Simultaneously, the action potential is conducted to the AV node ATRIOVENTRICULAR NODE (AV-NODE) The AV-NODE delays impulse conduction from the atria to the ventricles Located in the posterior wall of the right atrium immediately behind the tricuspid valve Slow conduction through the AV node ensures that the ventricles have sufficient time to fill with blood before they are activated and contract  Increases in conduction velocity of the AV node can lead to decreased ventricular filling and decreased stroke volume and cardiac output AV node fibers have small quantity of GAP junctions → (slower ion movement between cells) BUNDLE OF HIS or AV BUNDLE AV-Bundle passes downward in the ventricular septum (commom bundle) and divides into left and right bundle branches  The branches lie beneath the endocardium From the AV node, the action potential enters the specialized conducting system of the ventricles  The action potential is first conducted to the common AV bundle, then right and left branches, then to Purkinje system Atrio Ventricular insulation The AV-BUNDLE (Bundle of His) allows only forward electrical conduction from the atria to the ventricles Atrial muscle is separated from ventricular muscle by a continuous fibrous skeleton Acts as an insulator to prevent passage of cardiac impulse between atrial and ventricular muscle through abnormal routes PURKINJE FIBERS SYSTEM Conduction through the His-Purkinje system is extremely fast, and it rapidly distributes the action potential to the ventricles The action potential also spreads from one ventricular muscle cell to the next (GAP junctions) Rapid conduction of the action potential throughout the ventricles is essential and allows for efficient contraction and ejection of blood ventricles must contract from apex to base for efficient ejection of blood PURKINJE FIBERS SYSTEM Each AV bundle branch (left and right) spreads downward toward the apex of the ventricle, progressively dividing into smaller branches These branches turn sideways around each ventricular chamber and back toward the base of the heart (Purkinje system) The ends of the Purkinje fibers penetrate the muscle mass and become continuous with the cardiac fibers Supplemental videos FYI: How SA node cells generate action potential https://www.youtube.com/watch?v=v7Q9BrNfIpQ Cardiac Conduction System https://www.youtube.com/watch?v=RYZ4daFwMa8 (Up to 1:38min) https://www.youtube.com/watch?v=9e_YeNveR5M FYI https://www.youtube.com/watch?v=_4rv7O2ji6o&t=125s Comparative anatomy HAPPY STUDYING CLARA CAMARGO, DVM [email protected] ©2021 Ross University School of Veterinary Medicine. All rights reserved.