Cardiovascular System - Heart Overview

Cardiovascular System - Heart

• Heart is the central pumping organ of the cardiovascular system, including heart, blood vessels, and blood.
• The heart functions as a "double pump," encompassing systemic and pulmonary circuits (and coronary circulation).
• The heart undergoes ~75 contractions per minute, resulting in ~108,000 contractions per day.
• Each contraction pumps approximately 70 mL of blood, totaling ~14,000 liters per day (~3,698 gallons).
• The heart is situated within the mediastinum, encased by the pericardium (pericardial sac), with a surrounding pericardial cavity.
• The base of the heart rests on the superior and inferior vena cavae and the aorta and pulmonary trunk.
• The apex of the heart points towards the left, resting against the lower part of the left lung.

Heart Shape and Size

• The heart is roughly cone-shaped and fist-sized.
• Average female heart: 250-300 grams (9-11 oz)
• Average male heart: 300-500 grams (11-12 oz)
• The heart has four chambers: two atria and two ventricles, responsible for receiving and pumping blood.
• The pulmonary circuit carries deoxygenated blood to the lungs, where it becomes oxygenated.
• Systemic circuit circulates oxygenated blood throughout the body, picking up carbon dioxide.

Blood Circulation

• Right ventricle → pulmonary trunk → L & R pulmonary arteries → L & R lungs → pulmonary capillaries (gas exchange) → pulmonary veins → left ventricle → aorta → systemic circuit (gas exchange) → superior/inferior vena cavae → right atrium → right ventricle.

Heart Membranes, Surface Features, & Layers

• The pericardium encloses the heart, consisting of dense irregular connective tissue (fibrous pericardium) and a double-layered serous membrane.
• This serous membrane (serous pericardium) has the parietal layer lining the fibrous pericardium and the visceral layer covering the heart's surface (epicardium).
• A serous fluid fills the pericardial cavity between these layers.
• The heart wall has distinct layers: epicardium, myocardium (cardiac muscle), and endocardium (endothelial tissue).
• Atria have ear-like extensions called auricles.
• Coronary sulcus surrounds the heart between atria and ventricles.
• Inter ventricular sulci separate the ventricles.
• The myocardium, composed of cardiac muscle, is thicker in the left ventricle due to its role in systemic circulation.

Internal Structures of the Heart

• Septa separate the atria and ventricles (interatrial & interventricular septa), including the fossa ovalis.
• Atrioventricular (AV) valves (tricuspid and mitral) and semilunar valves (pulmonary and aortic) regulate blood flow.

Cardiac Skeleton

• Cardiac skeleton − dense irregular connective tissue that reinforces the atrioventricular septum, provides attachment points for heart valves, and insulates the heart's electrical conducting system.

Heart Chambers

• The right atrium receives deoxygenated blood from the body (except the lungs) via superior and inferior vena cavae and the coronary sinus.
• The right ventricle pumps blood into the pulmonary circuit via the pulmonary trunk then pulmonary arteries, to the lungs.
• The left atrium receives oxygenated blood from the lungs through the pulmonary veins.
• The left ventricle pumps oxygenated blood to the systemic circulation via the aorta.
• The atrioventricular valves regulate blood flow between the atria and ventricles.
• The semilunar valves regulate flow between the ventricles and major arteries.
• Heart chambers contain muscular ridges, and/or tendinous attachments, to ensure efficient blood flow.

Cardiac Cycle

• Systole refers to chamber contraction, while diastole refers to chamber relaxation.
• The cardiac cycle encompasses the entire period between one ventricular contraction and the next.
• The cycle involves atrial and ventricular systole and diastole, regulated by electrical signals and pressure changes within each chamber.

Heart Valves Structure & Function

• Heart valves ensure one-way blood flow, preventing backflow.
• Atrioventricular (AV) valves regulate blood from atria to ventricles.
• Semilunar valves regulate blood flow from ventricles to major arteries.

Heart Sounds

• Heart sounds arise from valve closure during the cardiac cycle, enabling auscultation
• S₁ (lub): closure of AV valves.
• S₂ (dub): closure of semilunar valves.
• Murmurs indicate abnormal blood flow.

Cardiac Muscle & Electrical Activity

• Cardiac muscle cells, also known as cardiomyocytes, have branched structures with intercalated discs that contain specialized gap junctions and desmosomes for rapid signal transmission and strong attachment.
• Cardiac muscle cells have autorhythmicity, meaning they can initiate their own electrical signals.
• Specialized myocardial conducting cells initiate and spread the electrical signals that trigger contractions, and control the heart rate.

Conduction System of the Heart

• The heart's conduction system comprises nodes and specialized pathways that coordinate the rhythmic atrial and ventricular contractions.
• The sinoatrial node (SA node) acts as the heart's pacemaker.
• The atrioventricular node (AV node) delays the signal, allowing the atria to contract before the ventricles.
• The AV bundle (Bundle of His), bundle branches, and Purkinje fibers rapidly conduct the signal through the ventricles.

Spread of Conducting Signal

• Steps in the cardiac cycle showing electrical and mechanical events
• The conduction sequence ensures coordinated contractions of the atria and ventricles.

Electrocardiogram (ECG)

• An ECG records the electrical activity of the heart through electrodes placed on the body surface.
• Different waves (P, QRS, and T) on the ECG correspond to different parts of the cardiac conduction system.

Disorders of the Conducting System

• Heart blocks represent disruptions in the heart's electrical conduction pathway.
• First-degree, second-degree, and third-degree blocks reflect varying degrees of conduction delays or interruptions.
• Arrhythmias are irregular heart rhythms and can be treated with artificial pacemakers.

Heart Rates

• Heart rate varies based on factors like age, fitness level, and activity.
• The autonomic nervous system (ANS) controls heart rate through sympathetic (speeds up) and parasympathetic (slows down) pathways.

Coronary Circulation

• Coronary arteries supply oxygenated blood to the heart muscle (myocardium).
• Coronary veins drain deoxygenated blood from the heart muscle.
• Coronary vessels follow branching patterns to ensure adequate coverage of the myocardium.

Development of the Heart

• The heart develops from a series of embryonic steps.

Explore the anatomy and functions of the heart as part of the cardiovascular system. This quiz covers the structure, size, and unique characteristics of the heart that allow it to effectively pump blood throughout the body. Test your knowledge on the heart's functioning and its importance in human physiology.