What Is The Structure Of The Heart?

What Is The Structure Of The Heart
Heart chambers – Your heart is divided into four chambers. You have two chambers on the top (atrium, plural atria) and two on the bottom (ventricles), one on each side of the heart.

Right atrium: Two large veins deliver oxygen-poor blood to your right atrium. The superior vena cava carries blood from your upper body. The inferior vena cava brings blood from the lower body. Then the right atrium pumps the blood to your right ventricle. Right ventricle: The lower right chamber pumps the oxygen-poor blood to your lungs through the pulmonary artery. The lungs reload blood with oxygen. Left atrium: After the lungs fill blood with oxygen, the pulmonary veins carry the blood to the left atrium. This upper chamber pumps the blood to your left ventricle. Left ventricle: The left ventricle is slightly larger than the right. It pumps oxygen-rich blood to the rest of your body.


What type of structure is the heart?

The human heart is a four-chambered muscular organ, shaped and sized roughly like a man’s closed fist with two-thirds of the mass to the left of midline. The heart is enclosed in a pericardial sac that is lined with the parietal layers of a serous membrane, The visceral layer of the serous membrane forms the epicardium,

What is the main function of the heart answer?

Types of Circulation –

Pulmonary circulation is a portion of circulation responsible for carrying deoxygenated blood away from the heart, to the lungs and then bringing oxygenated blood back to the heart. Systemic circulation is another portion of circulation where the oxygenated blood is pumped from the heart to every organ and tissue in the body, and deoxygenated blood comes back again to the heart.

Now, the heart itself is a muscle and therefore, it needs a constant supply of oxygenated blood. This is where another type of circulation comes into play, the coronary circulation.

Coronary circulation is an essential portion of the circulation, where oxygenated blood is supplied to the heart. This is important as the heart is responsible for supplying blood throughout the body. Moreover, organs like the brain need a steady flow of fresh, oxygenated blood to ensure functionality.

In a nutshell, the plays a vital role in supplying oxygen, and nutrients and removing carbon dioxide and other wastes from the body. Let us gain a deeper insight into the various anatomical structures of the heart:

What is the structure of the heart muscle?

Structure and Function – Rapid, involuntary contraction and relaxation of the cardiac muscle are vital for pumping blood throughout the cardiovascular system. To accomplish this, the structure of cardiac muscle has distinct features that allow it to contract in a coordinated fashion and resist fatigue.

  • The individual cardiac muscle cell (cardiomyocyte) is a tubular structure composed of chains of myofibrils, which are rod-like units within the cell.
  • The myofibrils consist of repeating sections of sarcomeres, which are the fundamental contractile units of the muscle cells.
  • Sarcomeres are composed of long proteins that organize into thick and thin filaments, called myofilaments.

Thin myofilaments contain the protein actin, and thick myofilaments contain the protein myosin. The myofilaments slide past each other as the muscle contracts and relaxes. This process activates from the release of calcium from the sarcoplasmic reticulum (SR) when delivering an action potential to the muscle, in a process called excitation-contraction coupling.

  • The sliding of actin and myosin past each other produces the formation of “cross-bridges,” which causes contraction of the heart and generation of force.
  • Cardiomyocytes are rectangular, branching cells that typically contain only one centrally-located nucleus.
  • This arrangement contrasts with skeletal muscle cells, which often contain many nuclei.

Cardiomyocytes contain many mitochondria to produce large amounts of adenosine triphosphate (ATP) and myoglobin to store oxygen to meet the demands of muscle contraction. Like skeletal muscle, the organization of thin and thick myofilaments overlapping within the sarcomere of the cell produces a striated appearance when viewed on microscopy.

This characteristic appearance consists of thick dark-colored A-bands (mainly composed of myosin) with a relatively bright H-zone in the center, and lighter colored I-bands (mainly actin) with a dark central Z line (also known as Z disc) connecting the actin filaments. The outside of the cardiomyocyte is surrounded by a plasma membrane called the sarcolemma that acts as a barrier between extracellular and intracellular contents.

Invaginations of the sarcolemma into the cytoplasm of the cardiomyocyte are called T-tubules, and they contain numerous proteins like L-type calcium channels, sodium-calcium exchangers, calcium ATPases, and beta-adrenergic receptors that allow for the exchange of ions with extracellular fluid surrounding the cell.

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At the Z-line of the cardiomyocyte, T-tubules run adjacent to enlarged areas of the sarcoplasmic reticulum known as the terminal cisternae, and the combination of a single T-tubule with one terminal cisterna referred to as a diad. This configuration contrasts with skeletal muscle, which combines 2 terminal cisternae with 1 T-tubule to form “triads,” which appear at the A-I junction.

Neighboring cardiomyocytes are joined together at their ends by intercalated disks to create a syncytium of cardiac cells. Within the intercalated disc, there are three different types of cell junctions: fascia adherens, desmosomes, and gap junctions.

The transverse side of the intercalated discs runs perpendicular to the muscle fibers at the Z lines and provides a structural component via fascia adherens and desmosome connections. The lateral side of the discs contains gap junctions that permit intercellular communication by allowing ions from one cardiomyocyte to move to a neighboring cell without having to be excreted into the extracellular space first.

The low resistance of the gap junctions allows depolarization to spread quickly throughout the syncytium, which facilitates the rapid transmission of action potentials to produce a synchronized contraction of the cardiomyocytes in unison. One other distinct feature of cardiac muscle fibers is that they have their own auto rhythmicity.

  • Unlike smooth or skeletal muscle which require neural input for contraction, cardiac fibers have their own pacemaker cells like the sinoatrial (SA) node that spontaneously depolarizes.
  • These depolarizations occur at a consistent pace, but the pacemaker cells can also receive input from the autonomic nervous system to decrease or increase the heart rate depending on the requirements of the body.

The myocardial action potential occurs in five steps, beginning with rapid depolarization during Phase 0, followed by initial partial repolarization during Phase 1, a plateau period of Phase 2, then a rapid repolarization during Phase 3, leading to stabilization at the resting potential during Phase 4.

  1. Phase 2 plateau is a unique feature of the myocardial action potential that is not present in skeletal muscle.
  2. It is caused by balancing the effects of potassium efflux from the cell with an influx of calcium through voltage-gated L-type calcium channels (AKA dihydropyridine receptor) on the cell’s surface.

This influx of calcium is relatively small and insufficient to cause contraction by itself. Still, it triggers the sarcoplasmic reticulum to release its stores of calcium into the myoplasm of the myocyte in a process called calcium-triggered-calcium-release.

The calcium can then bind to troponin on the thin filament and begin the process of myocyte contraction seen with each heartbeat. The concentration of calcium in the myocyte is the critical factor that determines how much force is generated with each contraction. Cardiac muscle cells can increase contractility through beta-1 adrenergic receptors on the surface with a Gs G-protein.

When stimulated by either the sympathetic nervous system or beta-1 agonist drugs, the Gs activate the enzyme adenylyl cyclase, which converts ATP to cAMP. Intracellular cAMP increases the activity of protein kinase A (PKA), which then phosphorylate calcium channels permitting more calcium to enter the cell, leading to increased contraction.

  1. The cardiac muscle does not relax and prepare for the next heartbeat simply by ceasing contraction; it occurs in an active process called Lusitropy.
  2. During lusitropy, Sarco/endoplasmic reticulum Ca-ATPase (SERCA) pumps on the membrane of the sarcoplasmic reticulum use ATP hydrolysis to transfer calcium back into the sarcoplasmic reticulum ( SR) from the cytosol.
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The regulatory protein phospholamban can control the rate at which the SERCA pumps calcium into the SR. Phospholamban reduces the transfer of calcium by the SERCA (sarcoplasmic reticulum Ca2+ ATPase) when bound together. Just as it can increase contractility, the sympathetic nervous system can also increase lusitropy through beta-1 adrenergic stimulation by phosphorylation of phospholamban with cAMP-dependent protein kinase (PKA).

What is the structure around the heart called?

Heart Anatomy Your heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone (sternum). A double-layered membrane called the pericardium surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your heart’s major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body The heart weighs between 7 and 15 ounces (200 to 425 grams) and is a little larger than the size of your fist. Your heart is located between your lungs in the middle of your chest, behind and slightly to the left of your breastbone (sternum). A double-layered membrane called the pericardium surrounds your heart like a sac. The outer layer of the pericardium surrounds the roots of your heart’s major blood vessels and is attached by ligaments to your spinal column, diaphragm, and other parts of your body.

The inner layer of the pericardium is attached to the heart muscle. A coating of fluid separates the two layers of membrane, letting the heart move as it beats. Your heart has 4 chambers. The upper chambers are called the left and right atria, and the lower chambers are called the left and right ventricles.

A wall of muscle called the septum separates the left and right atria and the left and right ventricles. The left ventricle is the largest and strongest chamber in your heart. The left ventricle’s chamber walls are only about a half-inch thick, but they have enough force to push blood through the aortic valve and into your body.

What type of muscle is the heart?

Overview – The 3 types of muscle tissue are cardiac, smooth, and skeletal. Cardiac muscle cells are located in the walls of the heart, appear striped (striated), and are under involuntary control. Smooth muscle fibers are located in walls of hollow visceral organs (such as the liver, pancreas, and intestines), except the heart, appear spindle-shaped, and are also under involuntary control.

Skeletal muscle fibers occur in muscles which are attached to the skeleton. They are striated in appearance and are under voluntary control. Updated by: Diane M. Horowitz, MD, Rheumatology and Internal Medicine, Northwell Health, Great Neck, NY. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M.

Editorial team.

Is the heart a bone?

There is no bone in your heart. Your heart is an organ made of cardiac muscle.

How is human heart formed?

19.5 Development of the Heart – Anatomy and Physiology 2e By the end of this section, you will be able to:

Describe the embryological development of heart structures Identify five regions of the fetal heart Relate fetal heart structures to adult counterparts

The human heart is the first functional organ to develop. It begins beating and pumping blood around day 21 or 22, a mere three weeks after fertilization. This emphasizes the critical nature of the heart in distributing blood through the vessels and the vital exchange of nutrients, oxygen, and wastes both to and from the developing baby.

  • The critical early development of the heart is reflected by the prominent heart bulge that appears on the anterior surface of the embryo.
  • The heart forms from an embryonic tissue called mesoderm around 18 to 19 days after fertilization.
  • Mesoderm is one of the three primary germ layers that differentiates early in development that collectively gives rise to all subsequent tissues and organs.
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The heart begins to develop near the head of the embryo in a region known as the cardiogenic area, Following chemical signals called factors from the underlying endoderm (another of the three primary germ layers), the cardiogenic area begins to form two strands called the cardiogenic cords ().

  • As the cardiogenic cords develop, a lumen rapidly develops within them.
  • At this point, they are referred to as endocardial tubes,
  • The two tubes migrate together and fuse to form a single primitive heart tube,
  • The primitive heart tube quickly forms five distinct regions.
  • From head to tail, these include the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and the sinus venosus.

Initially, all venous blood flows into the sinus venosus, and contractions propel the blood from tail to head, or from the sinus venosus to the truncus arteriosus. This is a very different pattern from that of an adult. Figure 19.36 Development of the Human Heart This diagram outlines the embryological development of the human heart during the first eight weeks and the subsequent formation of the four heart chambers. The five regions of the primitive heart tube develop into recognizable structures in a fully developed heart.

  1. The truncus arteriosus will eventually divide and give rise to the ascending aorta and pulmonary trunk.
  2. The bulbus cordis develops into the right ventricle.
  3. The primitive ventricle forms the left ventricle.
  4. The primitive atrium becomes the anterior portions of both the right and left atria, and the two auricles.

The sinus venosus develops into the posterior portion of the right atrium, the SA node, and the coronary sinus. As the primitive heart tube elongates, it begins to fold within the pericardium, eventually forming an S shape, which places the chambers and major vessels into an alignment similar to the adult heart.

This process occurs between days 23 and 28. The remainder of the heart development pattern includes development of septa and valves, and remodeling of the actual chambers. Partitioning of the atria and ventricles by the interatrial septum, interventricular septum, and atrioventricular septum is complete by the end of the fifth week, although the fetal blood shunts remain until birth or shortly after.

The atrioventricular valves form between weeks five and eight, and the semilunar valves form between weeks five and nine. : 19.5 Development of the Heart – Anatomy and Physiology 2e

What are the 4 parts of the heart?

The heart has four chambers: two atria and two ventricles. The right atrium receives oxygen-poor blood from the body and pumps it to the right ventricle. The right ventricle pumps the oxygen-poor blood to the lungs. The left atrium receives oxygen-rich blood from the lungs and pumps it to the left ventricle.

Is the heart filled with blood?

What is the difference between pericardial effusion and cardiac tamponade? – The pericardium is a double-walled sac that surrounds the heart. Between the inner wall of the pericardium and your heart is a thin layer of fluid, which cushions and protects your heart from outside forces (much like bubble wrap around a fragile item inside a shipping box).

  • Under normal circumstances, the pericardium has just enough fluid to cushion your heart, but not so much fluid that your heart can’t expand and fill up with blood with every heartbeat.
  • Happens when there’s too much fluid inside the pericardium, which means your heart has no room to expand and fill up with blood.

Without quick treatment, it can cause your heart to stop, which is eventually fatal within minutes to hours.

Is the heart made of mesoderm?

Early development – The heart derives from embryonic mesodermal germ layer cells that differentiate after gastrulation into mesothelium, endothelium, and myocardium, Mesothelial pericardium forms the outer lining of the heart. The inner lining of the heart – the endocardium, lymphatic and blood vessels, develop from endothelium.