Cardiovascular System PDF

- Cardiovascular System - Components of the Cardiovascular System - The Heart: Biological Pump - Generates force to move blood through the body - Two main events per beat: electrical (action potential) and mechanical (contraction)...

- Cardiovascular System - Components of the Cardiovascular System - The Heart: Biological Pump - Generates force to move blood through the body - Two main events per beat: electrical (action potential) and mechanical (contraction) - Left and right sides differ in structure and function - Left Ventricle (LV) vs Right Ventricle (RV) - LV has thicker myocardium to generate higher pressure - Higher pressure necessary for systemic circulation compared to pulmonary circulation - Blood: Transport Medium - Composed of plasma (55-58% of total volume) and cellular components - Total blood volume averages 5.5 liters - Hematocrit (red blood cell volume) averages 42-45% - Buffy coat contains leukocytes and platelets - Vasculature: Blood Vessels - Not passive in blood movement - Divided into pulmonary and systemic circuits - Arranged in parallel (systemic) and series (pulmonary) configurations - Importance of Vessel Arrangement - Parallel arrangement allows for better regulation of blood flow - Requires less pressure than series arrangement - Ensures same quality of blood to all tissues - Cardiovascular System Roles in Homeostasis - Nutrient and Waste Transport - Delivers nutrients and removes waste products from cells. - Most cells within 10 um of a capillary for efficient exchange - Hormone and Signaling Molecule Distribution - Facilitates communication between different parts of the body - Enables rapid response to physiological changes - Temperature Regulation - Helps maintain body temperature through blood circulation - Allows for heat distribution and dissipation - Pressure, Flow, and Resistance in the Cardiovascular System - Ohm\'s Law Application - Flow (F or Q) = Pressure difference (ΔP)/Resistance (R) - Pressure gradient, not absolute pressure, drives blood flow - Factors Affecting Resistance - Vessel length (L) - Blood viscosity (η) - Vessel radius (r) - most significant factor (raised to 4th power) - Impact of Vessel Radius - Small changes in radius can dramatically affect resistance and flow - Key mechanism for regulating blood flow to different organs - Heart Structure and Function - Heart Valves - Ensure one-way blood flow through the hear - Two types: Atrioventricular (AV) and Semilunar (SL) valves - Atrioventricular Valves - Right AV (tricuspid) and Left AV (bicuspid/mitral) - Prevent backflow from ventricles to atria - Semilunar Valves - Pulmonary and Aortic semilunar valves - Prevent back flow from arteries to ventricles - Heart Tissue Layers - Endocardium: innermost layer, separates chambers from myocardium - Myocardium: thick layer of cardiac muscle - Epicardium: outer protective layer - Pericardium: fluid-filled sac surrounding the heart - Cardiac Muscle Cells and Electrical Activity - Cardiac Myocyte Characteristics - Striated appearance - Mostly mononucleated - Branched ends for interconnection - Electrical Connections - Gap junctions allow rapid communication between cells - Forms a functional syncytium for coordinated contraction - Comparison with Skeletal and Smooth Muscle - Similarities to Skeletal Muscle - Presence of sarcomeres and striations - Contains troponin for calcium-mediated contraction - Presence of T-tubules - Similarites to Smooth Muscle - Presence of pacemaker cells - Gap junctions forming a syncytium - Calcium entry from extracellular fluid - Modulation by autonomic nervous system and hormones - Cardiovascular System Regulation - Autonomic Nervous System Control - Sympathetic and parasympathetic influences on heart rate and contractility - Receptor Types in Cardiovascular Regulation - Cholinergic Receptors - Nicotinic acetylcholine receptors (nAChR) at autonomic ganglia - Muscarinic acetylcholine receptors (mAChR) on target tissues - Adrenergic Receptors - Beta (β) receptors, particularly β1 and β2 - Alpha (α) receptors, focusing of α1 - Important targets for therapeutic interventions in cardiovascular diseases - Conduction Pathway of the Heart - Sequence of Electrical Events - Begins with the SA node, the primary pacemaker. - Atrial contractile cells facilitate the atrial kick - The AV node introduces a delay for proper timing. - Components of the Conduction System - Bundle of His conducts impulse to the ventricles - Bundle branches distribute signals to the ventricles - Purkinje fibers ensure rapid contraction of ventricular muscle. - Importance of Electrical Connections - Cardiac muscle cells are connected via gap junctions. - This allows for rapid communication and synchronization. - Functional syncytium ensures coordinated heartbeats. - Cardiac Action Potentials - Phases of Action Potentials - Phase 0: Rapid depolarization due to Na+ influx - Phase 1: Initial repolarization as Na+ channel close. - Phase 2: Plateau phase maintained by Ca2+ influx - Phase 3: Rapid repolarization as Ca2+ channel close and K+ channels open. - Phase 4: Resting membrane potential is established - Differences Among Cell Types - Nodal cells exhibit pacemaker potentials. - Conducting cells have unique ion channel profiles. - Contractile cells lack spontaneous action potential generation. - Ion Channels Involved - Fast Na+ channels are crucial for rapid depolarization. - L-type Ca2+ channels contribute to the plateau phase - K+ channels are essential for repolarization - Excitation-Contraction Coupling - Mechanism Overview - Calcium-induced calcium release (CICR) is key - Trigger Ca2+ enters through L-type channels. - Ryanodine receptors release more Ca2+ from the SR - Steps in Contraction - Ca2+ binds to troponin, exposing actin binding sites. - Cross-bridge cycling occurs, generating force. - Ca2+ is pumped back into the SR and ECF for relaxation. - Role of Calcium - Essential for initiating contraction in cardiac muscle. - Regulates the strength and duration of muscle contraction. - Involves both extracellular and intracellular calcium sources. - Vascular Arrangement - Parallel vs Series Circulation - Parallel arrangement allows equal blood quality to tissues. - Series arrangement in the pulmonary circuit ensures proper gas exchange. - Total resistance is lower in parallel systems, enhancing blood flow. - Sequence of Blood Vessels - Blood flow from arteries to arterioles, then capillaries. - Venules collect blood before it returns through veins - Refractory Periods in Cardiac Muscle - Absolute Refractory Period (ARP) - No new action potential can be initiated. - Fast Na+ channels are inactive during this phase. - Prevents tetanic contractions in cardiac muscle. - Relative Refractory Period (RRP) - Some Na+ channels recover, allowing potential for new action potentials - Occurs as the cell membrane approaches full repolarization. - Important for maintaining rhythmic heart contractions. - Physiological Significance - Refractory periods ensure proper heart function. - Allow time for the heart to refill with blood. - Critical for preventing arrhythmias and maintaining cardiac output. - The Cardiac Cycle - Overview of the Cardiac Cycle - The cardiac cycle consists of two main phases: diastole (relaxation) and systole (contraction). - Diastole occupies about 2/3 of the cycle, while systole takes up 1/3. - Four Phases of the Cardiac Cycle - Ventricular Filling (Diastole): Blood flows passively from atria to ventricles, followed by the atrial kick. - Isovolumetric Contraction (Systole): Ventricles contract with all valves closed, leading to pressure build-up. - Ejection (Systole): Ventricles eject blood into the aorta and pulmonary artery as valves open. - Isovolumetric Relaxation (Diastole): Ventricles relax with all valves closed, preparing for the next cycle. - Stroke Volume (SV) - Defined as the volume of blood ejected from each ventricle per beat. - Calculated as SV = End-Diastolic Volume (EDV) - End-Systolic Volume (ESV). - Average stroke volume is approximately 70 mL at rest. - Cardiac Output and Its Regulation - Definition of Cardiac Output (CO) - Cardiac output is the volume of blood ejected from each ventricle per minute. - Calculated as CO = Heart Rate (HR) x Stroke Volume (SV). - Average Values - Typical resting values are around 70 beats/min and 70 mL/beat, resulting in approximately 5 L/min of cardiac output. - CO can increase significantly during intense exercise, reaching 25-30 L/min. - Regulation of Cardiac Output - Cardiac output can be influenced by factors such as autonomic nervous system activity, blood volume, and heart contractility. - Most beta-adrenergic receptors in the heart are β1 receptors, which significantly regulate heart function. - Ejection Fractions and Heart Failures - Types of Heart Failure - Heart Failure with Preserved Ejection Fraction (HFpEF): Characterized by a stiff ventricle that struggles to relax, indicating diastolic dysfunction. - Heart Failure with Reduced Ejection Fraction (HFrEF): Traditionally recognized as heart failure, indicating systolic dysfunction. - Ejection Fraction (EF) - Ejection fraction measures the heart\'s efficiency, typically calculated from the left ventricle. - Typical EF values range from 55-70%, with lower values indicating potential heart failure. - Clinical Relevance - Understanding the cardiac cycle, stroke volume, and ejection fraction is crucial for effectively diagnosing and managing heart conditions. - Autonomic Innervation of the Heart - Parasympathetic Effects - Slow heart rate and weakens atrial contraction. - Reduces conduction speed through the AV node. - Sympathetic Effects - Increases heart rate and enhances ventricular contraction strength. - Norepinephrine (NE) acts immediately, while epinephrine (Epi) supports NE effects. - Control of Heart Rate - Resting State - At rest, parasympathetic input dominates, keeping heart rate around 70 bpm. - Sympathetic input is minimal, allowing for a lower heart rate. - Increased Physical Activity - Physical activity decreases parasympathetic input and increases sympathetic input. - The intrinsic firing rate of SA nodal cells is 100 bpm, but resting heart rate is slower due to parasympathetic tone. - Control of Stroke Volume - Preload and End-Diastolic Volume (EDV) - Stroke volume is influenced by changes in EDV, also known as preload. - Increased EDV enhances filament overlap, leading to stronger contraction. - Frank-Starling Law - The Frank-Starling mechanism ensure that the output of the right and left ventricles is matched. - It prevents blood from backing up into veins and capillaries, maintaining venous pressure. - Sympathetic Stimulation - Sympathetic stimulation increases stroke volume without changing EDV. - Norepinephrine and epinephrine enhance calcium availability, leading to stronger contractions - Afterload and Mean Arterial Pressure (MAP) - Increased afterload, or MAP, can decrease stroke volume by making it harder for ventricles to contract. - Healthy hearts are less affected by afterload compared to failing hearts, where wall stress is significant factor. - Distribution of Cardiac Output - At Rest vs. During Exercise - At rest, cardiac output is distributed to maintain vital organ function. - During strenuous exercise, cardiac output increases, with heart rate rising linearly while stroke volume plateaus after a certain point. - Implications for Exercise - Increased heart rate and stroke volume work together to support elevated cardiac output during physical activity. - Understanding these dynamics is crucial for assessing cardiovascular health and performance.