Human Physiology II: Cardiovascular System

Study Notes

Myocardium and Gap Junctions

Gap junctions in the myocardium account for about 30% of the resistance of the outside membrane, facilitating cell communication and electrical conduction.

Pericardium

The main function of the pericardium is to protect the heart by providing a fixed position within the thoracic cavity, preventing overexpansion, and reducing friction during heartbeats.

Atrioventricular Node

The atrioventricular (AV) node serves as a critical electrical relay between the atria and ventricles, ensuring proper timing for contraction by delaying the electrical signal before it passes to the ventricles.

Main Circulations

The human heart has two main circulations: the pulmonary circulation, which carries deoxygenated blood to the lungs, and the systemic circulation, which delivers oxygenated blood to the body.

Conductive Fibers

The conductive system of the heart includes specialized fibers known as Purkinje fibers, which assist in the rapid conduction of electrical impulses throughout the myocardium.

Heartbeat Frequency

The heart beats approximately 100,000 times in one day, averaging around 70 to 75 beats per minute under resting conditions.

Sinoatrial Node Function

The primary function of the sinoatrial (SA) node is to act as the natural pacemaker of the heart, initiating electrical impulses that regulate heart rate and rhythm.

Cardiac Action Potential - Phase 0

During Phase 0 of the cardiac action potential, sodium ions (Na+) are primarily responsible for the rapid depolarization, leading to the initiation of the action potential.

Parasympathetic Nervous System Effect

The parasympathetic nervous system decreases heart rate by releasing acetylcholine, which slows down the electrical conduction through the heart.

Absolute Refractory Period Duration

The duration of the absolute refractory period in cardiac muscle is approximately 200 to 300 milliseconds, during which the heart cannot be stimulated to contract again.

Plateau Phase - Phase 2

Calcium ions (Ca2+) are primarily responsible for the plateau phase (Phase 2) of the cardiac action potential, maintaining depolarization and contributing to the contraction of cardiac muscle.

Norepinephrine Effect

Norepinephrine increases heart rate and cardiac output by stimulating beta-adrenergic receptors, enhancing the heart's contractility and overall function.

Description

Learn about the functional anatomy of the heart, types of circulations, specialized cardiac tissues, and the action potentials of the heart. Understand the differences between cardiac and skeletal muscles and the refractory periods of the heart.