By Meera Shanmugam
Photo by Robina Weermeijer on Unsplash
Introduction:
The human heart is an amazing organ that tirelessly pumps blood throughout the body, ensuring every cell and system is working. Understanding the anatomy and functions of the heart is essential to understanding the complexities of cardiovascular health.
Structure of the Heart:
The heart is a muscular organ around the size of a fist on the left side of your chest inside the pericardial sac. It is divided into four chambers: two atria and two ventricles. These chambers work to receive and pump blood, making sure it flows continuously through the body.
Atria: The upper chambers of the heart, the right and left atria, receive blood returning to the heart. The right atrium receives deoxygenated blood from the body from the superior and inferior vena cavae, and the left atrium receives oxygenated blood from the lungs through the pulmonary veins.
Ventricles: The lower chambers of the heart, the right and left ventricles, are responsible for pumping blood out of the heart. The right ventricle pumps deoxygenated blood to the lungs for oxygenation, while the left ventricle pumps oxygen-containing blood to the rest of the body using the aorta.
Valves of the Heart:
To ensure blood flows in the correct direction within the heart, four valves are important in preventing backflow:
Tricuspid Valve: Located between the right atrium and right ventricle, the tricuspid valve prevents the backflow of blood from the right ventricle to the right atrium during ventricular contraction.
Pulmonary Valve: Located between the right ventricle and the pulmonary artery, the pulmonary valve prevents blood from flowing back into the right ventricle after being pumped into the pulmonary artery.
Mitral Valve: Located between the left atrium and left ventricle, the mitral valve prevents the backflow of blood from the left ventricle to the left atrium during ventricular contraction.
Aortic Valve: Located between the left ventricle and the aorta, the aortic valve prevents blood from flowing back into the left ventricle after coming into the aorta.
Blood Supply to the Heart:
The heart itself needs a constant supply of oxygenated blood to function properly and pump blood to the rest of the body. This supply is given by the coronary arteries, which branch off the aorta and are around the heart, delivering oxygen and nutrients to its muscle tissue.
Heart Physiology: The Cardiac Cycle
The cardiac cycle is a sequence of events that happen during one complete heartbeat, including both the systole (contraction) and diastole (relaxation) phases of the heart.
Systole: During systole, the ventricles contract, making a pressure that propels blood into the pulmonary artery and aorta. This phase starts when atrioventricular valves close, preventing blood from flowing back into the atria, and the opening of the semilunar valves, allowing blood to be pushed into the pulmonary arteries and aorta.
Diastole: Diastole happens after systole and is the relaxation phase of the heart chambers. During diastole, the ventricles relax, allowing them to fill with blood from the atria. The semilunar valves close to prevent backflow into the ventricles, while the atrioventricular valves open, allowing for the blood to flow from the atria into the ventricles.
Regulation of Heart Rate and Rhythm
The rate and rhythm of heartbeats are controlled by electrical signals that are created by specialized cells inside the heart’s conduction system.
Sinoatrial (SA) Node: Located in the right atrium, the SA node serves as the heart’s natural pacemaker, starting each heartbeat by generating electrical impulses that spread through the atria, causing them to contract.
Atrioventricular (AV) Node: Located between the atria and ventricles, the AV node acts like a relay station, delaying the electrical impulse slightly to allow the atria to contract completely before transmitting the signal to the ventricles.
Purkinje Fibers: These are fibers that transmit the electrical impulse through the ventricles, making sure ventricular contraction is smooth.
Factors Affecting Heart Function:
Several factors influence heart function, including:
Autonomic Nervous System: The autonomic nervous system’s sympathetic and parasympathetic branches control heart rate and how it contracts. Sympathetic stimulation increases heart rate and contractility, while parasympathetic stimulation decreases it.
Hormonal Influence: Hormones like adrenaline (epinephrine) and noradrenaline (norepinephrine) that are released during times like stress or exercise can increase heart rate and contractility, increasing the cardiac output to meet increased metabolic requirements.
Ion Concentrations: The balance of ions such as calcium, potassium, and sodium within cardiac muscle cells is important to regulate the electrical activity and contractility of the heart.
Conclusion:
Understanding the heart’s structure and function is important for keeping the heart healthy. From its chambers and valves to how it pumps blood throughout the body, the heart’s job is very important to keep the body well. The cardiac cycle, controlled by electrical signals, makes sure the heart contracts at a steady rhythm. Factors like the nervous system, hormones, and ion levels also influence heart function. Recognizing these complexities and information about the heart can help to appreciate the importance of caring for our hearts to stay healthy.
MCR Committee: Physiology
Citations:
Professional, C. C. M. (n.d.). Heart. Cleveland Clinic. https://my.clevelandclinic.org/health/body/21704-heart
Heart Anatomy | The Texas Heart Institute. (2022, March 31). The Texas Heart Institute. https://www.texasheart.org/heart-health/heart-information-center/topics/heart-anatomy/
Heart | Structure, Function, Diagram, Anatomy, & Facts. (2024, April 13). Encyclopedia Britannica. https://www.britannica.com/science/heart
Heart explained. (n.d.). Better Health Channel. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/heart