Lecture Notes: Heart Function and Anatomy

Overview

• Brief review of heart anatomy and conductile components:
  • SA node, AV node, conductile fibers
• Relation to EKG readings and electrodes
• Heart's functionality under varying oxygen demands

Types of Heart Cells

1. Work Cardiomyocytes

   • Also known as contractile cells
   • Make up 99% of heart cells
   • Function: Contract and generate force to pressurize blood for movement
   • Striated cells with similarities to skeletal muscle

2. Pacemaker Cells

   • Comprise 1% of heart cells
   • Location: Primarily in the SA node
   • Function: Generate action potentials through spontaneous depolarization
   • Unique characteristic: Clear appearance due to lack of sarcomeres

Pacemaker Cells Functionality

• SA node as the primary pacemaker
• AV node as the secondary pacemaker if SA node is damaged
• Potential for ectopic heartbeats if proper conduction is disrupted

Heart Wall Structure

• Three Layers of the Heart Wall:
  1. Endocardium: Inner lining of simple squamous epithelium
  2. Myocardium: Middle muscular layer, contains cardiomyocytes
  3. Epicardium: Surface layer of mesothelium (specialized epithelium)
• Importance of smooth lining for reducing blood turbulence
• Myocardium supplied by extensive blood vessels

Blood Flow and Heart Health

• Blood vessels nourish myocardium during diastole
• Heart attack (myocardial infarction) caused by blockage in these vessels
• Significance of slower heart rates in enhancing myocardial perfusion

Work Cardiomyocytes Details

• Function as a syncytium, working together to generate force
• Frank-Starling Law: Cells generate more force when stretched
• Structure specifics:
  • Short, thick, and branched cells
  • Centrally located nuclei
  • Intercalated discs with gap junctions for electrical synapse
• Obligate aerobic cells requiring constant oxygen supply

Pacemaker Cells and the SA Node

• Role as the heart's primary pacemaker, setting heart rate
• SA node location: Superior, lateral wall of the right atrium
• Structure:
  • Crescent-shaped cluster
  • Composed of modified cardiomyocytes without sarcomeres
  • Connected by gap junctions, lead to transitional cells and conductile fibers

Autonomic Control of Heart Rate

• SA node's natural firing rate: 100-110 bpm
• Resting heart rate lowered to ~72 bpm due to parasympathetic (vagal) tone
• Parasympathetic/Sympathetic balance affects heart rate

These notes cover the key points discussed in the lecture on heart function, focusing on the anatomy and functionality of different cell types within the heart, the structure of the heart wall, blood flow, and the influence of autonomic nervous system on heart rate. This summary is intended to assist with studying and understanding the heart's physiology.