It is a muscular organ about the size of a closed fist. It was in the chest, slightly to the left of the center.
Our heart beats 100,000 times a day, pushing 5,000 gallons of blood through our body every 24 hours. It provides blood rich in oxygen and nutrients to our tissues and eliminates waste.
As the heart contracts, it pumps blood throughout the body. It carries deoxygenated blood to the lungs where it is loaded with oxygen and discharges carbon dioxide, a waste product of metabolism.
The heart, blood and blood vessels combined are known as the circulatory system. An average human has about 5 liters of blood, which is pumped constantly throughout the body.
In this article, we will explain the structure of the heart, how it pumps blood around the body and the electrical system that controls it.
Basic Anatomy of the Heart
The heart is made up of four cameras:
Atria : the two upper chambers (they receive blood).
Ventricles : the two lower chambers (they discharge blood).
The left atrium and the left ventricle are separated from the right atrium and the right ventricle by a wall of muscle called the septum.
The heart wall is made up of three layers of tissue:
Epicardium : protective layer made mainly of connective tissue.
Myocardium : the muscles of the heart.
Endocardium : covers the inside of the heart and protects the valves and the chambers.
These layers are covered by a thin protective coating called the pericardium.
Structure and Functions of the Heart
The moderate size and weight of the heart give little indication of its incredible strength.
Weight : about the size of a person’s fist, the hollow, cone-shaped heart weighs less than one pound.
Mediastinum : comfortably enclosed within the inferior mediastinum, the medial cavity of the thorax, the heart is flanked on each side by the lungs.
Appendix : its sharpest vertex is directed towards the left hip and rests on the diaphragm, approximately at the level of the fifth intercostal space.
Base : its posterosuperior broad aspect, or base, from where the great vessels of the body emerge, points towards the right shoulder and is below the second rib.
Pericardium : the heart is enclosed in a double-walled sac called the pericardium and is the outermost layer of the heart.
Fibrous pericardium: the loose-fitting superficial part of this sac is known as the fibrous pericardium, which helps protect the heart and anchors it to surrounding structures such as the diaphragm and sternum.
Serous pericardium: deep in the fibrous pericardium is the slippery two-layer serous pericardium, where its parietal layer covers the inside of the fibrous pericardium.
Chambers of the Heart
The heart has four hollow chambers, or cavities: two atria and two ventricles.
Receptors of cameras : the two upper atria are mainly the receiving chambers, they play a lighter role in the pumping activity of the heart.
Discharge chambers : the two lower-walled, thick-walled ventricles are the discharge chambers, or actual pumps of the heart, where when they contract, the blood is expelled from the heart into the circulation.
Pulp : the septum that divides the heart longitudinally is known as the interventricular septum or interatrial septum, depending on the chamber that separates.
Large Associated Ships
The large blood vessels provide a way for all of the cardiac circulation to continue.
Upper and lower vena cava : the heart receives relatively poor oxygen blood from the veins of the body through the large superior and inferior vena cava and pumps it through the pulmonary trunk.
Pulmonary arteries : the pulmonary trunk is divided into the right and left pulmonary arteries, which carry blood to the lungs, where oxygen is collected and carbon dioxide is discharged.
Pulmonary veins : oxygen-rich blood drains from the lungs and returns to the left side of the heart through the four pulmonary veins.
Aorta : the blood that comes back to the left side of the heart is pumped from the heart to the aorta, from where the systemic arteries branch out to supply essentially all of the body’s tissues.
The heart is equipped with four valves, which allow blood to flow in only one direction through the chambers of the heart.
Atrioventricular valves : the atrioventricular valves or AV are located between the atrial and ventricular chambers on each side, and prevent reflux into the atria when the ventricles contract.
Bicuspid valves : the left AV valve, the bicuspid or mitral valve, consists of two fins or cusps of the endocardium.
Tricuspid valve : the right AV valve, the tricuspid valve, has three fins.
Semi-lunar valve : the second set of valves, the semilunar valves, protect the bases of the two large arteries that leave the ventricular chambers, which is why they are known as the pulmonary and aortic semilunar valves.
Cardiac Circulation Vessels
Although the chambers of the heart are bathed in blood almost continuously, the blood contained in the heart does not nourish the myocardium.
Coronary artery : the coronary arteries branch out from the base of the aorta and surround the heart in the coronary groove (atrioventricular groove) at the junction of the atria and the ventricles, and these arteries become compressed when the ventricles contract and fill when the heart is relaxed.
Cardiac veins : the myocardium is drained by several cardiac veins, which flow into an enlarged vessel in the back of the heart called the coronary sinus .
Blood circulates within the blood vessels, which form a closed transport system, the so-called vascular system.
Arteries : As the heart beats, blood is propelled into large arteries that leave the heart.
Arterioles : then it moves successively in smaller and smaller arteries and then in arterioles, which feed the capillary beds in the tissues.
Veins : the capillary beds are drained by venules, which in turn empty into veins that finally empty into the large veins that enter the heart.
Except for the microscopic capillaries, the walls of the blood vessels have three layers or tunics.
Intimate tunic: the intimate tunic, which covers the light, or the interior of the vessels, is a thin layer of endothelium that rests on a basement membrane and decreases friction as blood flows through the lumen of the vessel.
Tunica media : The tunica media is the voluminous intermediate layer consisting mainly of smooth and elastic muscle fibers that contract or dilate, which causes blood pressure to increase or decrease.
External tunic: the external tunic is the outermost tunic composed largely of fibrous connective tissue, and its function is basically to support and protect the vessels.
Major Veins of Systemic Circulation
The main veins converge in the vena cava, which enter the right atrium of the heart.
Veins Draining in the Vena Cava Superior
The veins that drain into the superior vena cava are named in a distal to proximal direction; that is, in the same direction, blood flows into the superior vena cava.
Radial and ulnar veins: the radial and ulnar veins are deep veins that drain the forearm; they join to form the deep brachial vein, which drains the arm and empties into the axillary vein in the axillary region.
Cephalic vein: the cephalic vein provides superficial drainage of the lateral aspect of the arm and empties into the axillary vein.
Basilic vein: the basilic vein is a superficial vein that drains the medial aspect of the arm and empties into the brachial vein proximally.
Median cubital vein : the basilic and cephalic veins are joined at the anterior aspect of the elbow by the median ulnar vein, often chosen as the site for blood collection in order to perform blood tests.
Subclavian vein: the subclavian vein receives venous blood from the arm through the axillary vein and from the skin and muscles of the head through the external jugular vein.
Vertebral vein: the vertebral vein drains the back of the head.
Internal jugular vein: the internal jugular vein drains the dural sinuses of the brain.
Brachiocephalic veins : the right and left brachiocephalic veins are large veins that receive venous drainage from the subclavian, vertebral, and internal jugular veins on their respective sides.
Vena Azygos : the azygos vein is a unique vein that drains the thorax and enters the superior vena cava just before joining the heart.
Physiology of the Heart
As the heart beats or contracts, the blood makes continuous circular trips, in and out of the heart, through the rest of the body and then into the heart, only to be sent again.
System of Intrinsic Conduction of the Heart
Spontaneous contractions of the heart muscle cells occur regularly and continuously, giving rhythm to the heart.
Heart muscle cells: Heart muscle cells can and do contract spontaneously and independently, even if all nerve connections are cut.
Rhythms : Although the heart muscles can beat independently, the muscle cells in different areas of the heart have different rhythms.
Intrinsic conduction system: the intrinsic conduction system, or the nodal system, which is integrated into the heart tissue establishes the basic rhythm.
Composition : the intrinsic driving system is composed of a special tissue that is not found anywhere else in the body; It is like a cross between a muscle and nervous tissue.
Function : this system causes the depolarization of the cardiac muscle in only one direction, from the atrium to the ventricles; it imposes a contraction rate of approximately 75 beats per minute in the heart, so that the heart beats as a coordinated unit.
Synatrial node (SA) : the SA node has the highest depolarization rate in the whole system, so you can start the rhythm and set the rhythm for the whole heart; therefore, the term ” pacemaker “.
Atrial contraction : from the SA node, the impulse propagates through the atria to the AV node, and then the atria contract.
Ventricular contraction : it then passes through the AV bundle, bundle branches and Purkinje fibers, producing a “twisted” contraction of the ventricles that starts at the apex of the heart and moves to the atria.
Expulsion : this contraction expels the blood effectively to the large arteries that leave the heart.
How does the heart work?
The heart contracts at different speeds depending on many factors. At rest, it may beat around 60 times per minute, but may increase to 100 beats per minute or more.
Exercise, emotions, fever, diseases and some medications can influence heart rate.
The left side and the right side of the heart work in unison. The right side of the heart receives deoxygenated blood and sends it to the lungs; The left side of the heart receives blood from the lungs and pumps it to the rest of the body.
The atria and ventricles contract and relax in turn, producing a rhythmic heart rhythm.
The right atrium receives deoxygenated blood from the body through veins called the superior and inferior vena cava (the largest veins in the body).
The right atrium contracts and the blood passes to the right ventricle. Once the right ventricle is full, it contracts and pumps blood to the lungs through the pulmonary artery, where it captures oxygen and discharges carbon dioxide.
The newly oxygenated blood returns to the left atrium through the pulmonary vein. The left atrium contracts, pushing the blood into the left ventricle. Once the left ventricle is full, it contracts and pushes the blood into the body through the aorta.
Each beat can be divided into two parts:
Diastole : the atria and ventricles relax and fill with blood.
Systole : the atrium contracts (atrial systole) and pushes the blood to the ventricles; Then, when the atria begin to relax, the ventricles contract (ventricular systole) and expel blood from the heart.
When blood is sent through the pulmonary artery to the lungs, it travels through small capillaries on the surface of the pulmonary alveoli (air sacs).
Oxygen travels to the capillaries and carbon dioxide travels from the capillaries to the alveoli, where it is exhaled into the atmosphere.
The muscles of the heart also need to receive oxygenated blood. They are fed by the coronary arteries on the surface of the heart.
When the blood passes near the surface of the body, as in the wrist or neck, it is possible to feel the pulse; This is the rush of blood as the heart pumps it through the body.
The heart has four valves that help ensure that blood flows in one direction only:
- Aortic valve : between the left ventricle and the aorta.
- Mitral valve : between the left atrium and the left ventricle.
- Pulmonary valve : between the right ventricle and the pulmonary artery.
- Tricuspid valve : between the right atrium and the right ventricle.
Most people are familiar with the sound of a human heartbeat.
It is often described as a “lub-DUB” sound. The “lub” sound is produced by the closing of the mitral and tricuspid valves, and the “DUB” sound is caused by the closing of the pulmonary and aortic valves.
The Electrical System of the Heart
To pump blood throughout the body, the heart muscles must coordinate perfectly, squeezing the blood in the right direction, at the right time, at the correct pressure. The activity of the heart is coordinated by electrical impulses.
The electrical signal begins at the sinoatrial node (or sinus, SA), the heart pacemaker, located in the upper part of the right atrium. This signal causes the atria to contract, pushing the blood into the ventricles.
The electrical impulse travels to an area of cells in the lower part of the right atrium called the atrioventricular (AV) node. These cells act like a door, slow down the signal so that the atria and ventricles do not contract at the same time; It is necessary that there be a slight delay.
From here, the signal is transported along special fibers called Purkinje fibers within the walls of the ventricle; They pass the impulse to the heart muscle, which causes the ventricles to contract.
There are three types of blood vessels:
Arteries : carries oxygenated blood from the heart to the rest of the body. The arteries are strong and elastic, which helps to drive blood through the circulatory system.
Its elastic walls help keep blood pressure constant. The arteries branch out into smaller arterioles.
Veins : these carry the deoxygenated blood to the heart and increase in size as they approach the heart. The veins have thinner walls than the arteries.
Capillaries : connect the smaller arteries with the smaller veins. They have very thin walls, which allows them to exchange compounds with surrounding tissues, such as carbon dioxide, water, oxygen, waste and nutrients.
Although we rarely consider it, the heart is an essential and powerful organ. It pumps oxygen and nutrients around our body constantly, never stopping. Powered by muscles and perfectly synchronized by electrical signals, it is one of the best engineering feats of nature.