Cardiovascular Physiology for 290 (1)

Functions of the Cardiovascular System

• Primary Roles: 3 main functions

  • pumps-blood - transportation

  • thermoregulation

  • hemostasis

• Closed System: Blood circulates through a closed system, maintaining pressure.

  • stays in the body, via blood vessels and is regulated by heart rate

• Total Blood Volume: Approximately 4.5 liters in an adult.

• Circulatory Types:

  • Pulmonary Circulation: Transports deoxygenated blood from the heart to the lungs and returns oxygenated blood to the heart.

  • Systemic Circulation: Delivers oxygenated blood from the heart to the rest of the body and returns deoxygenated blood back to the heart.

Hemodynamics

• Definition: Study of blood flow and its mechanics.

• Pressure Gradient: Blood flows from areas of higher to lower pressure.

• Blood Pressure: Pulsatile in the aorta and arteries, fluctuating with heartbeats.

Ohm’s Law and Poiseuille’s Law

• Hydrostatic Pressure: Consideration of pressure exerted by fluids at rest.

• Pressure vs. Flow: They are interrelated but regulated independently.

• Velocity: Depends on flow rate and cross-sectional area of blood vessels.

• Vasoconstriction and Dilation: Alter resistance in the circulatory system to regulate blood flow.

Cardiac Action Potenitals:

Cardiac Action Potentials: these are electrical impulses that triggger heart contractions, influenicng heart rate and the strength of contraction, ultimately affecting cardiac output and ensuring efficient blood circulation throughout the body.

• Phases of Contractile Cell Action Potential (AP):

  • Long Refractory Period: Prevents tetanus, allowing the heart to relax.

  • Funny Current (If) and HCN Channels: Contribute to spontaneous depolarization in pacemaker cells.

  • CCAP- action potential comes from the pacemaker cells

    • Phase 0- the sodium channel is open and sits at -40mV, causing rapid depolarization as sodium ions rush into the cell, leading to a sharp increase in membrane potential.

    • Phase 1: the sodium channel closes, at +20 mV, and potassium channels open, allowing potassium ions to flow out of the cell, which causes a partial repolarization of the membrane potential.

    • Phase 2: potassium channels close, calcium channels open, allowing calcium ions to enter the cell, which balances the outflow of potassium and maintains a plateau phase in the action potential, crucial for sustaining contraction. so it stays around near 10mV

    • Phase 3: the cell repolarizes to -40mV from the influx of calcium. Potassium will reopen, and the calcium channel will close, and the cell drops back to its resting membrane potential of approximately -90 mV, completing the cycle of the action potential.

    • Phase 4: the resting state is re-established as ion pumps actively transport sodium out of the cell and potassium back in, ensuring the membrane is ready for the next action potential.

• Phases of Pacemaker Cell Action Potential

  • autorhythmicity- have ability to create their own action potential, SA node starts the signal ,initiating contraction and setting the rhythm for the heartbeat.

  • slow depolarization without the use of outside signal

Cardiac Conduction Pathway( just the anatomy)

• Sinoatrial (SA) Node: The primary pacemaker of the heart located in the right atrium.

• Atrioventricular (AV) Node: The secondary pacemaker located at the junction of the atria and ventricles, responsible for delaying the impulse before it passes to the ventricles.

• Bundle of His: A collection of heart muscle cells that transmit impulses from the AV node to the ventricles.

• Right and Left Bundle Branches: Pathways that carry impulses down the interventricular septum to the Purkinje fibers.

• Purkinje Fibers: Specialized fibers that distribute the electrical impulse throughout the ventricles, causing them to contract.

• Electrical Signaling: Begins in the SA node (sinoatrial node).

• Components:

  • SA node: Natural pacemaker that initiates contraction.

  • Internodal Pathways: Conduct signal rapidly to AV node.

  • AV node: Delays signal to allow atria time to contract before ventricles.

  • AV Bundle, Bundle Branches, Purkinje Fibers: Conduct electrical impulse rapidly through ventricles.

  • Depolarization Wave: Moves upwards from the apex of the heart, ensures efficient contraction.

    Pathway goes:

    • Sinoatrial Node (SA Node): Initiates the electrical impulse, setting the pace for the heart rhythm.

    • Atrioventricular Node (AV Node): Acts as a gatekeeper, controlling the signal flow from the atria to the ventricles.

    • Bundle of His: Connects the atrial and ventricular systems, transmitting impulses to the Bundle Branches.

Electrocardiography (ECG)

• ECG Waves:

  • P wave: Atrial depolarization

  • P-R segment: Conduction through AV node and bundle

  • QRS complex: Ventricular depolarization

  • T wave: Ventricular repolarization

• Segments/Intervals: Includes P-R and QT intervals, which reflect both electrical activity and heart performance.

P-V Loops

• Left Ventricular Pressure-Volume Changes: Demonstrates the changes during the cardiac cycle.

  • Key Points:

    • Movement around the curve (A-B-C-D-A): Represents filling, contraction, and emptying of the heart.

    • EDV (End-Diastolic Volume): Volume of blood in the ventricle at end of filling.

    • ESV (End-Systolic Volume): Volume remaining in the ventricle after contraction.

    • Stroke Volume: Volume of blood pumped out of the ventricle during one contraction.

Wiggers Diagram

• Overview: Illustrates pressure changes in the left heart, volume changes in the left ventricle, and corresponding ECG throughout the cardiac cycle.

• Phases:

  • Atrial and Ventricular Systole: Heart contracting and pumping blood.

  • Isovolumetric Contraction: All valves closed, pressure in ventricles raises.

  • Dicrotic Notch: Brief increase in aortic pressure following closure of the aortic valve.

Cardiac Output

• Formula: CO = HR (Heart Rate) x SV (Stroke Volume)

• Relation: CO also equates to VR (Venous Return).

• Intrinsic Regulation: Governed by Starling’s Law and Bainbridge Reflex.

Extrinsic Regulation of Heart Rate

• Parasympathetic Stimulation: Decreases heart rate through ACh released on muscarinic receptors.

• Sympathetic Stimulation: Increases heart rate via norepinephrine acting on beta-1 receptors.

• Mechanisms:

  • Hyperpolarization: Slows depolarization via parasympathetic activity.

  • Increased Depolarization: Speeded up by sympathetic activity and epinephrine.

Extrinsic Regulation of Contractility

• Phospholamban: Regulatory protein affecting Ca2+ handling in cardiac muscle.

• Catecholamines: Epinephrine and norepinephrine increase Ca2+ entry and enhance contraction force and duration.

Skeletal Muscle Pump and Respiratory Muscle Pump

• Role in Venous Return: Skeletal muscle contractions and diaphragm movements assist in returning venous blood to the heart.

Ejection Fraction, Preload, and Afterload

• Ejection Fraction: Ratio of stroke volume to end-diastolic volume, an indicator of heart performance.

• Preload and Afterload: Factors affecting stroke volume and cardiac output.

Blood Vessels of the Body

• Path of Blood Flow: From arteries to arterioles to capillaries to veins.

• Tunics: Blood vessels consist of three layers (tunica intima, tunica media, and tunica externa).

• Vasoconstriction vs. Vasodilation: Processes that adjust vessel diameter to regulate blood flow and pressure.

Microcirculation

• Components: Microcirculation includes arterioles, capillaries, and venules.

• Precapillary Sphincters: Control blood flow into capillary beds depending on local needs.

  • Relaxed: Allows full blood flow through capillaries.

  • Constricted: Redirects blood flow via metarterioles, bypassing capillary beds.

Blood Pressure

• Measurement: Systolic Blood Pressure (SBP) and Diastolic Blood Pressure (DBP).

• Mean Arterial Pressure (MAP): Calculated as MAP = DBP + 1/3 Pulse Pressure (PP).

• Hydrostatic Pressure: Plays critical role in blood filtration and absorption within capillaries.

Acute Regulation of Blood Pressure via Baroreceptors

• System Regulation: Controlled by the cardiovascular control center in the medulla, which modulates heart rate and vessel tone through sympathetic and parasympathetic inputs.

• Baroreceptor Reflex: Detects changes in arterial pressure and adjusts heart and vessel activity accordingly.

Chronic Regulation of Blood Pressure via Kidneys

• Role of Kidneys: Influence blood volume and pressure long-term through mechanisms such as renin-angiotensin system and fluid balance.

Distribution of Blood in the Body

• Autoregulation of Blood Flow: Body tissues regulate their own blood supply based on local demands.

• Mechanisms: Includes myogenic response and metabolic autoregulation facilitated by various vasodilators and vasoconstrictors.

Capillaries: Site of Nutrient and Waste Exchange

• Types of Capillaries:

  • Continuous Capillaries: Have tight junctions; allow small solutes and fluids to pass.

  • Fenestrated Capillaries: Have pores for rapid exchange of larger molecules, found in areas like the kidneys.

Starling's Forces

• Net Filtration/Absorption: Determined by hydrostatic and osmotic pressures across capillary walls, affecting fluid movement between blood and interstitium.

  • Hydrostatic Pressure (PH): Forces fluid out.

  • Colloid Osmotic Pressure (TT): Pulls fluid into the capillary.

  • Net Average: Approximately 3 L/day of fluid filtered out, returned by lymphatic drainage.

Lymphatics

• Function of Lymphatic System: Transport lymph fluid back into venous circulation, removing excess fluids and waste from tissues.

Hemostasis

• Definition: Process that prevents and stops bleeding (hemorrhage).

• Normal Clotting Time: Involves three primary phases:

  1. Vasoconstriction: Immediate narrowing of blood vessels to reduce blood loss.

  2. Platelet Plug Formation: Platelets aggregate at the injury site to form a temporary plug.

  3. Blood Coagulation Cascade: Series of reactions follow to stabilize the plug and form a fibrin clot.

Pacemaker Cells- pacers that set the heart rhyrythm, which are primarily located in the sinoatrial (SA) node, play a crucial role in initiating electrical impulses that regulate heartbeats.