Cardiovascular System Overview

Cardiovascular System Function

• Transports oxygen, nutrients, hormones, and removes waste products like carbon dioxide
• Delivers essential substances to target cells
• Heart acts as a pump converting chemical energy into mechanical energy

Heart Structure

• Two pumps: right side – low pressure, left side – high pressure
• Each pump has an atrium and ventricle
• Atria “prime” the ventricles to expel cardiac output into either the pulmonary or systemic circulation

Electrical Activity of the Heart

• Myocardial contraction is coordinated by nerve fibers to create a wave-like pumping action
• Depolarization (change in voltage across the cell membrane) triggers contraction
• Heart is innervated by the parasympathetic (slows heart rate) and sympathetic (increases heart rate and force) nervous systems
• Both nerve supplies originate in cardiovascular control centers in the medulla
• Parasympathetic supply is through the right (slows SA node depolarization) and left (slows AV node conduction) vagus nerves
• Cardiac muscle functions like a syncytium due to low-resistance connections between cells, enabling coordinated contraction
• Nerve action potentials (1 ms) are produced by changes in sodium and potassium permeability
• Cardiac action potentials are longer (250 ms) due to calcium ion flow during plateau phase

Types of Action Potentials

• Fast response tissues: include atria, ventricles, and specialized conduction system (bundle of His, fascicles, bundle branches, Purkinje fibers) – depolarization initiated by sodium channels
• Slow response tissues: SA and AV nodes – depolarization initiated by calcium ions through L-type channels

Cardiac Conduction System

• Sino-atrial (SA) node: the natural pacemaker of the heart
• Atrio-ventricular (AV) node: delays conduction to allow ventricular filling
• Bundle of His: conducts impulses to ventricles
• Left and right bundle branches: distribute impulses to ventricular walls
• Purkinje fibers: transmit signals to ventricular muscle

Electrical Events of a Heartbeat

• Each SA node stimulus depolarizes the atria, creating a wave of contraction
• Depolarization is the release of an electrical stimulus, repolarization is recharging
• Three stages:
  • Atrial depolarization
  • Ventricular depolarization
  • Atrial and ventricular repolarization

Excitation-Contraction Coupling

• Action potentials trigger a cascade of events leading to myofibril contraction
• Calcium concentration in the extracellular fluid is crucial for contraction strength
• Calcium is actively pumped back into the sarcoplasmic reticulum during repolarization

Heart Properties

• Automaticity: ability to spontaneously depolarize
• Rhythmicity: ability to maintain a regular discharge rate
• Chronotropic: rhythm of automaticity
• Bathmotropy: cellular excitability
• Dromotropy: impulse conduction

Basic Terms and Concepts

• Membrane potential: difference in electrical charge across the cell membrane, influenced by ion permeability and forces
• Conductance: ease of ion flow across the membrane through pumps or channels
• Resting membrane potential (RMP): electrical potential during diastole, around -90 mV
• Threshold potential (TP): membrane potential where depolarization becomes self-sustained, initiating action potential
• Excitability: ability to depolarize to a stimulus, influenced by RMP-TP difference
• Refractoriness: period during depolarization and early repolarization where another action potential cannot be triggered, regardless of stimulus strength

Explore the functions, structure, and electrical activity of the cardiovascular system. This quiz covers how the heart pumps blood, the role of its chambers, and the nervous system's influence on heart rate. Test your knowledge on the essential concepts of cardiovascular physiology.