Tuesday, March 9, 2021

Human Anatomy:The Heart

A free Educational Medical Resource from Medika Life

The primary function of human heart is to pump blood into the arteries that carries oxygen and nutrients to all the tissues of the body. The heart is located in the center of the chest with its apex toward the left. It is the hardest working muscle in the body as it beats non-stop. If we want to understand how the heart performs its vital role, we will first have to look at its structure, i.e., cardiac anatomy.

Layers of the Heart Wall

Three layers of tissue form the heart wall. The outer layer of the heart wall is the epicardium, the middle layer is the myocardium, and the inner layer is the endocardium.

Chambers of the Heart

The internal cavity of the heart is divided into four chambers:

  • Right atrium
  • Right ventricle
  • Left atrium
  • Left ventricle

The two atria are thin-walled chambers that receive blood from the veins. The two ventricles are thick-walled chambers that forcefully pump blood out of the heart. Differences in thickness of the heart chamber walls are due to variations in the amount of myocardium present, which reflects the amount of force each chamber is required to generate.

The right atrium receives deoxygenated blood from systemic veins; the left atrium receives oxygenated blood from the pulmonary veins.

Valves of the Heart

Pumps need a set of valves to keep the fluid flowing in one direction and the heart is no exception. The heart has two types of valves that keep the blood flowing in the correct direction. The valves between the atria and ventricles are called atrioventricular valves (also called cuspid valves), while those at the bases of the large vessels leaving the ventricles are called semilunar valves.

The right atrioventricular valve is the tricuspid valve. The left atrioventricular valve is the bicuspid, or mitral, valve. The valve between the right ventricle and pulmonary trunk is the pulmonary semilunar valve. The valve between the left ventricle and the aorta is the aortic semilunar valve.

When the ventricles contract, atrioventricular valves close to prevent blood from flowing back into the atria. When the ventricles relax, semilunar valves close to prevent blood from flowing back into the ventricles.

Pathway of Blood through the Heart

While it is convenient to describe the flow of blood through the right side of the heart and then through the left side, it is important to realize that both atria and ventricles contract at the same time. The heart works as two pumps, one on the right and one on the left, working simultaneously. Blood flows from the right atrium to the right ventricle, and then is pumped to the lungs to receive oxygen. From the lungs, the blood flows to the left atrium, then to the left ventricle. From there it is pumped to the systemic circulation.

Blood Supply to the Myocardium

The myocardium of the heart wall is a working muscle that needs a continuous supply of oxygen and nutrients to function efficiently. For this reason, cardiac muscle has an extensive network of blood vessels to bring oxygen to the contracting cells and to remove waste products.

The right and left coronary arteries, branches of the ascending aorta, supply blood to the walls of the myocardium. After blood passes through the capillaries in the myocardium, it enters a system of cardiac (coronary) veins. Most of the cardiac veins drain into the coronary sinus, which opens into the right atrium.

Physiology of the Heart

The conduction system includes several components. The first part of the conduction system is the sinoatrial node . Without any neural stimulation, the sinoatrial node rhythmically initiates impulses 70 to 80 times per minute. Because it establishes the basic rhythm of the heartbeat, it is called the pacemaker of the heart. Other parts of the conduction system include the atrioventricular node, atrioventricular bundle, bundle branches, and conduction myofibers. All of these components coordinate the contraction and relaxation of the heart chambers.

Cardiac Cycle

The cardiac cycle refers to the alternating contraction and relaxation of the myocardium in the walls of the heart chambers, coordinated by the conduction system, during one heartbeat. Systole is the contraction phase of the cardiac cycle, and diastole is the relaxation phase. At a normal heart rate, one cardiac cycle lasts for 0.8 second.

Heart Sounds

The sounds associated with the heartbeat are due to vibrations in the tissues and blood caused by closure of the valves. Abnormal heart sounds are called murmurs.

Heart Rate

The sinoatrial node, acting alone, produces a constant rhythmic heart rate. Regulating factors are reliant on the atrioventricular node to increase or decrease the heart rate to adjust cardiac output to meet the changing needs of the body. Most changes in the heart rate are mediated through the cardiac center in the medulla oblongata of the brain. The center has both sympathetic and parasympathetic components that adjust the heart rate to meet the changing needs of the body.

Peripheral factors such as emotions, ion concentrations, and body temperature may affect heart rate. These are usually mediated through the cardiac center.

Reproducing this material

Medika Life has provided this material as a free resource for patients. The content on this page may be reproduced for non-commercial purposes under a Creative Commons License CC BY-NC-ND, subject to acknowledgement of the source. Consult our Copyright page for additional information.

Medika Lifehttps://medika.life
Medika Life is a digital Health Publication for both the medical profession and the public. Make informed decisions about your health and stay up to date with the latest developments and technological advances in the fields of medicine.

LEARN MORE

More from this Author

Vitaccess is Reshaping Digital Health in the U.K.

Medika has identified Vitaccess for our Healthcare Innovation watch list. This UK based Digital Startup offers innovative and exciting approaches to data management that directly benefit patient outcomes.

HealthTap Introduces Virtual Primary Care that Prioritizes Uninsured and Underinsured Populations in the U.S.

Because HealthTap connects patients with doctors using their dynamic matching technology, it’s extremely efficient and therefore low-cost virtual care

Texas Food Relief with NCS Group and #BStrong Initiative Deliver Food Aid Across Texas

Each NCS Group Unlimited Carrier Fleet Vehicle brings a total of $180K+ worth of supplies and aid, and a total of six trucks are arriving in Texas

Global Empowerment Mission in Partnership with Bethenny Frankel’s BStrong Initiative Align with NCS Group for Texas Aid Relief During The State of Emergency

The LATEST mission is bringing three relief trucks to Texas with the first truck en route from Miami to Denton (The Cross Timbers Hope Center In Denton, TX) followed by Houston, TX on Tuesday (February 23)
%d bloggers like this: