Anatomy & Physiology: The Heart – Structure, Function, and Regulation

The Heart: Structure, Function, and Regulation

Overview

This study guide covers the anatomy and physiology of the heart, focusing on its structure, the flow of blood, the conduction system, and regulatory mechanisms. It is designed to help students understand the key concepts and terminology necessary for mastering this topic in a college-level Anatomy & Physiology course.

Learning Objectives

• Describe the size, shape, location, and orientation of the heart in the thorax.

• Name the coverings of the heart.

• Describe the structure and function of each of the three layers of the heart wall.

• Describe the structure and functions of the four heart chambers. Name each chamber and provide the name and general route of its associated great vessels. Explain the functional and anatomical differences between the right and left sides, and describe their location, function, and mechanism of operation.

• Trace the pathway of blood through the heart and explain how the anatomy of the heart relates to its function as a pump.

• Name the major branches and describe the distribution of the coronary arteries.

• Compare the microscopic anatomy and functional properties of cardiac muscle and explain how it differs from skeletal muscle.

• Briefly describe the events of excitation-contraction coupling in cardiac muscle cells. Explain the complete action potential in cardiac pacemaker and contractile cells.

• Name the components of the conduction system of the heart and trace the conduction pathway.

• Draw a diagram of a normal electrocardiogram tracing. Name the individual waves and intervals, and indicate what each represents. State one possible cause for changes that can be detected on an ECG tracing.

• Describe normal heart sounds and explain how heart murmurs differ.

• Define cardiac output, stroke volume, and heart rate.

• Explain the effects of various factors regulating stroke volume and heart rate.

• Explain the role of the autonomic nervous system in regulating cardiac output.

Key Anatomical Structures of the Heart

Students should be able to identify the following structures under a microscope or via images:

• External Structures: Anterior interventricular artery, anterior interventricular sulcus, aortic arch, aortic semilunar valve, apex of the heart, auricle of left/right atrium, atrioventricular valve (mitral, tricuspid), brachiocephalic trunk, chordae tendineae, circumflex artery, coronary arteries, coronary sinus, endocardium, epicardium, fibrous skeleton, fossa ovalis, interventricular septum, left atrium, left ventricle, left common carotid artery, left coronary artery, left pulmonary artery/veins, left subclavian artery, myocardium, papillary muscles, pectinate muscles, pulmonary trunk/artery/veins, right atrium, right ventricle, right coronary artery, right marginal artery, right pulmonary artery/veins, superior/inferior vena cava, trabeculae carneae, tricuspid valve, ventricular septum.

• Microscopic Structures: Cardiac muscle tissue, intercalated discs, T tubules, sarcoplasmic reticulum.

Key Terms and Definitions

• Pulmo-: lung

• Peri-: around

• Endo-: within

• Epi-: over, above

• My(o)-: muscle

• Cardio-: heart

• Vents-: underside

• Cornu-: horn

• Ventr-: belly

• Semi-: half, moon

• Cyte-: cell

• Intercal-: insert

• Iso-: same

• Tachy-: fast

• Brady-: slow

Major Topics and Subtopics

Heart Anatomy

• Location and Orientation: The heart is located in the mediastinum of the thoracic cavity, between the lungs, and is oriented with the apex pointing down and to the left.

• Coverings: The heart is enclosed by the pericardium, which consists of a fibrous pericardium and a serous pericardium (parietal and visceral layers).

• Heart Wall Layers:

  • Epicardium: Outer layer, also known as the visceral pericardium.

  • Myocardium: Middle, muscular layer responsible for contraction.

  • Endocardium: Inner lining of the heart chambers and valves.

• Chambers and Valves: The heart has four chambers (right/left atria, right/left ventricles) and four main valves (tricuspid, pulmonary, mitral, aortic) that ensure unidirectional blood flow.

• Major Vessels: Include the aorta, pulmonary arteries and veins, superior and inferior vena cava.

Blood Flow Through the Heart

• Deoxygenated blood enters the right atrium via the superior and inferior vena cava, passes through the tricuspid valve to the right ventricle, and is pumped through the pulmonary valve to the pulmonary arteries and lungs.

• Oxygenated blood returns via pulmonary veins to the left atrium, passes through the mitral valve to the left ventricle, and is pumped through the aortic valve to the systemic circulation.

Coronary Circulation

• The heart receives its own blood supply via the right and left coronary arteries, which branch from the aorta.

• Major branches include the circumflex artery, anterior interventricular artery, and right marginal artery.

• Venous blood is collected by the coronary sinus and returned to the right atrium.

Microscopic Anatomy of Cardiac Muscle

• Cardiac muscle cells are striated, branched, and interconnected by intercalated discs, which contain gap junctions and desmosomes for synchronized contraction.

• Cardiac muscle differs from skeletal muscle in that it is involuntary, has a single nucleus per cell, and relies on both intracellular and extracellular calcium for contraction.

Excitation-Contraction Coupling

• Action potentials in cardiac muscle cells trigger calcium influx, leading to contraction.

• Pacemaker cells in the sinoatrial (SA) node initiate the heartbeat and set the pace for the heart.

Conduction System of the Heart

• The conduction system includes the SA node, atrioventricular (AV) node, bundle of His, right and left bundle branches, and Purkinje fibers.

• This system ensures coordinated contraction of the atria and ventricles.

Electrocardiogram (ECG/EKG)

• An ECG records the electrical activity of the heart.

• Key components: P wave (atrial depolarization), QRS complex (ventricular depolarization), T wave (ventricular repolarization).

• Abnormalities in the ECG can indicate arrhythmias, myocardial infarction, or conduction blocks.

Heart Sounds and Murmurs

• Normal heart sounds ("lub-dub") are produced by the closing of heart valves.

• Heart murmurs are abnormal sounds caused by turbulent blood flow, often due to valve defects.

Cardiac Output, Stroke Volume, and Heart Rate

• Cardiac Output (CO): The volume of blood pumped by each ventricle per minute.

• Stroke Volume (SV): The amount of blood ejected by a ventricle with each beat.

• Heart Rate (HR): The number of heartbeats per minute.

Formula:

$\text{Cardiac Output} = \text{Stroke Volume} \times \text{Heart Rate}$

Regulation of Cardiac Output

• Cardiac output is regulated by intrinsic and extrinsic factors, including preload, afterload, contractility, and autonomic nervous system input.

• Sympathetic stimulation increases heart rate and contractility; parasympathetic stimulation decreases heart rate.

Autonomic Nervous System and the Heart

• The autonomic nervous system modulates heart rate and force of contraction via sympathetic and parasympathetic pathways.

• Neurotransmitters such as norepinephrine and acetylcholine play key roles in this regulation.

Sample Table: Comparison of Cardiac and Skeletal Muscle

Feature	Cardiac Muscle	Skeletal Muscle
Control	Involuntary	Voluntary
Cell Shape	Branched, single nucleus	Long, cylindrical, multinucleate
Intercalated Discs	Present	Absent
Contraction Initiation	Pacemaker cells (SA node)	Motor neuron stimulation
Calcium Source	Extracellular and sarcoplasmic reticulum	Sarcoplasmic reticulum only

Additional info:

• Students are expected to be able to identify anatomical structures on models, diagrams, or microscope slides, even if not identical to those seen in class.

• Understanding the terminology and word roots will aid in mastering more complex anatomical and physiological concepts.