Flashcards for Heart Anatomy and Physiology

Lecture Overview

Course Title: BIO 111C - Fundamentals in Anatomy & Physiology IProfessor: Dr. Michael Ha, M.D.Institution: University of District of Columbia

Recap of Previous Lectures

• Erythrocytes: Focus on the structure and function of red blood cells in oxygen transport through hemoglobin, which binds oxygen in the lungs and releases it in tissues.

• Hematopoiesis: The process of blood formation occurring in the bone marrow, producing various blood cells including erythrocytes, leukocytes, and platelets.

• Anemias: Conditions resulting from insufficient red blood cells or hemoglobin, leading to fatigue, weakness, and other symptoms due to inadequate oxygen delivery to tissues.

Heart Anatomy

Structure of the Heart

Function: The heart serves as a muscular pump creating pressure gradients essential for driving blood through both the pulmonary (lungs) and systemic (body) circulatory systems, efficiently supplying oxygen and nutrients.Size: Approximately the size of a human fist, embodying a complex structure that facilitates its vital functions, with a significant role in maintaining homeostasis.Dimensions: Approximate measurements: Length: 12 cm, Width: 9 cm, Thickness: 6 cm.Weight: The heart weighs between 280-340 grams in males and 230-280 grams in females, reflecting variations in individual size, lifestyle, and physiological needs.

Heart Location

The heart is primarily located in the mediastinum, which houses the heart and other midline structures; it occupies a position primarily on the left side of the midline.Position relative to surrounding organs:

• Medial to the lungs

• Posterior to the sternum

• Anterior to the esophagusBase: The base is the wide top of the heart, lying between the T5-T8 vertebrae.Apex: The pointed end, or apex, is located in the 5th intercostal space, approximately 9 cm to the left of the midline, critical for the pumping function and sound of heartbeats.

Pericardium

Overview

Definition: The pericardium is a double-walled sac enveloping the heart, vital for providing protection, limiting heart movement, and supporting heart function.Fibrous Pericardium:

• Description: The exterior layer consists of dense irregular connective tissue, offering a robust protective layer against trauma and infection.

• Functions:

  • Protects the heart from infections and trauma (bacterial, viral, and traumatic injuries).

  • Anchors the heart to surrounding structures, including the diaphragm and great vessels, ensuring it remains in place.

  • Prevents overfilling of the heart by limiting its stretching during filling cycles, providing structural integrity.

Serous Pericardium:

• Structure: Made of areolar connective tissue and a layer of mesothelium, this inner layer is more delicate than the fibrous pericardium.

• Components:

  • Parietal Layer: Lines the internal surface of the fibrous pericardium.

  • Visceral Layer (Epicardium): Covers the external surface of the heart, providing lubrication.

  • Pericardial Cavity: The space between these two layers contains pericardial fluid, acting as a lubricant to reduce friction during the heart's contractions and relaxations.

Heart Wall

Layers of the Heart Wall

• Epicardium (Visceral pericardium): The outermost layer that provides a protective barrier and contains blood vessels leading to the heart as well as nerve fibers.

• Myocardium:

  • Description: Composed predominantly of cardiac muscle cells (myocytes), which are specialized for continuous contraction and relaxation cycles.

  • Functions:

    • Contracts powerfully to eject blood from the heart chambers during ventricular systole.

    • Stabilizes heart valves and myocytes for efficient functioning.

    • Efficient contraction distribution ensures the force is evenly spread, adding strength and preventing overdistention during fills.

• Endocardium:

• Description: This inner layer lines the heart ventricles and covers the heart valves, ensuring smooth blood flow and minimizing turbulence during blood movement.

• Function: Composed of simple squamous epithelium, facilitating optimal blood flow within the heart chambers.

Heart as a Pump

Pump Pathway

The pathway of blood flow through the heart is as follows:

1. Head and Upper Body → Superior Vena Cava → Right Atrium

2. Right Ventricle → Pulmonary Trunk → Lungs (for gas exchange)

3. Pulmonary Veins → Left Atrium → Left Ventricle

4. Aorta → Rest of the Body (supplying oxygenated blood)

Chambers of the Heart

Four Chambers

• Right and Left Atria:

• Function: The upper chambers receive deoxygenated blood returning from the body to the heart (right atrium) or oxygenated blood from the lungs (left atrium).

• Separation: Separated by the interatrial septum, which maintains functional specificity between oxygenated and deoxygenated blood.

• Right and Left Ventricles:

• Function: The lower chambers pump blood into the pulmonary arteries (right ventricle) or the aorta (left ventricle), vital for distributing blood.

• Separation: Separated by the interventricular septum, critical for preventing mixing of oxygen-rich and oxygen-poor blood.

Great Vessels of the Heart

• Superior & Inferior Vena Cava: Bring deoxygenated venous blood to the right atrium from systemic circulation, facilitating double circulation.

• Aorta: The largest artery in the body, carries oxygen-rich blood from the left ventricle to systemic circulation, supplying all body tissues.

• Pulmonary Trunk: Transports deoxygenated blood from the right ventricle to the lungs for gas exchange where carbon dioxide is removed and oxygen is absorbed.

• Pulmonary Veins: Return oxygenated blood from the lungs to the left atrium, completing the pulmonary circuit before it is distributed to the body.

Atria Structure

Important Structures

• Auricle: An ear-like projection from each atrium that increases its capacity, aiding in accommodating varying volumes of returning blood.

• Pectinate Muscles: Found in the anterior wall of the atria, enhancing contraction strength through parallel ridges that improve functional efficiency.

• Crista Terminalis: A ridge marking the junction where the smooth surface of the atrium meets the rough pectinate muscles, essential for proper conduction system function.

• Fossa Ovalis: A depression in the interatrial septum representing the remnant of the foramen ovale from fetal circulation, allowing blood to bypass pulmonary circulation in utero.

Ventricles Structure

Key Features

• Left Ventricular Wall: Significantly thicker than the right wall, due to the increased muscular strength required to pump blood throughout the entire body, overcoming greater resistance.

• Apex Location: Found at the floor of the left ventricle, crucial for maximizing efficient blood ejection into the systemic circuit.

Important Structures

• Trabeculae Carneae: These irregular muscle columns in the ventricles enhance contraction efficiency and prevent collapse of the ventricular walls during systole.

• Papillary Muscles: Located in the ventricles, they attach to heart valves via chordae tendineae, crucial for preventing valve prolapse and regurgitation (backflow of blood).

Heart Valves

Overview

Function: Heart valves ensure unidirectional blood flow, preventing backflow and maintaining efficiency in systemic and pulmonary circulation.

• Atrioventricular (AV) Valves: Regulate blood flow between the atria and ventricles, ensuring coordinated flow.

• Right AV Valve: Known as the tricuspid valve, comprising three cusps, crucial for effective separation of oxygenated and deoxygenated blood.

• Left AV Valve: Also known as the mitral valve or bicuspid valve, consisting of two cusps that help to prevent backflow into the atria.

• Semilunar Valves: Control blood flow from the ventricles into the major arteries.

• Pulmonary Semilunar Valve: Positioned between the right ventricle and pulmonary trunk, ensuring efficient blood flow to the lungs.

• Aortic Semilunar Valve: Located between the left ventricle and aorta, regulating flow into systemic circulation.

Electrical Conduction System

Nodes and Pathways

• Sinoatrial Node (SA Node): The heart's primary pacemaker, located in the right atrium, initiating the electrical impulse crucial for heartbeat regulation and setting the rhythm of the heart.

• Atrioventricular Node (AV Node): Located at the junction of the atria and ventricles, it delays the impulse, allowing the atria to contract fully before ventricles respond, ensuring synchrony in heart contractions.

• Bundle of His: Transmits impulses from the AV node to the ventricles through the interventricular septum, critical for coordinated contraction.

• Purkinje Fibers: Distribute the electrical impulse throughout the ventricular myocardium, stimulating contraction efficiently.

Speed of Conduction

• SA Node Speed: 0.8-1.0 m/s, facilitating initiation of contraction ensuring quick response in heart rate changes.

• AV Node Delay: 0.03-0.05 m/s, allowing optimal ventricular filling before contraction, enhancing stroke volume.

• Purkinje Fibers Speed: Fast at 5 m/s, ensuring rapid contraction of the ventricles for effective blood ejection.

Nervous System Influence

• Sympathetic Nervous System: Increases heart rate and the strength of contractions during stress or physical activity by releasing norepinephrine, preparing the body for fight or flight responses.

• Parasympathetic Nervous System: Decreases heart rate and contraction strength through the Vagus Nerve (X), promoting restorative functions during rest states.

Electrocardiogram (ECG)

Purpose and Function

A vital diagnostic tool that measures the electrical depolarization and repolarization cycles of cardiac muscle, reflecting heart health and rhythm.

Waves and Intervals:

• P Wave: Represents atrial depolarization, indicating atrial contraction.

• QRS Complex: Indicates ventricular depolarization, reflecting electrical activation of the ventricles (and hence their contraction).

• T Wave: Reflects ventricular repolarization, essential for the heart returning to a resting state.

• P-Q Interval: The duration during which atrial depolarization occurs and the impulse travels through the AV node.

• S-T Segment: Indicates the duration of ventricular systole, reflecting the plateau phase of action potentials during contraction.

Important Intervals:

• P-R Interval: A critical interval measuring approximately 0.16 seconds, assessing effective electrical conduction through the AV node.

• Q-T Interval: A graphical representation of the entire electrical activity of the heart during one cardiac cycle, assisting medical professionals in diagnosing various heart conditions and arrhythmias.