Human heart structure and function pdf
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- What Is the Heart? Anatomy, Function, Pathophysiology, and Misconceptions
- 40.3A: Structures of the Heart
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The current approach to understanding cardiac dynamics relies upon movements that adhere to the conventional topographical separation of cardiac muscle into the left ventricle, right ventricle, and septum. Functional analyses have addressed them independently, and this approach has resulted in many suppositions that this report will define and question. Alternatively, cardiac muscle mass is formed by the helix and surrounding circumferential wrap described by Lower in the s [ 1 ], Senac in the s [ 2 ], Krehl in the s [ 3 ], Mall in the s [ 4 ], and more recently by Torrent Guasp [ 5 ].
For example, the left ventricular free wall and septum are usually discussed separately, yet both are formed by the same muscle Figure 1 and their function cannot be separated unless isolated focal lesions exist. For this reason, the anterior descending and posterior descending coronary arteries are simply vascular highways perched upon the top or bottom of the helical muscle forming the septum and its adjacent LV free wall.
Upper left—intact heart. Upper right—circumferential or basal loop unfolding its right segment. Second layer—further circumferential or basal loop unfolding of its left segment and showing inner helix. Third layer—helix unfolding to display descending segment DS after ascending segment AS is separated.
The entire basal loop containing RS and LS is also shown. Bottom layer—HMVB unraveled to display its rope-like model appearance. Longitudinal fibers only exist within the two papillary muscles; b unfolding of HVMB model. Upper right—circumferential wrap or basal loop with transverse fibers and the inner helix. Lower right—unfolded helix showing the oblique fibers of the inner descending helical arm that is separated from the outer ascending helical arm.
Lower right—outer ascending helical arm. Marker arrow points to the left anterior descending artery pathway that bisects the helical muscles forming septum and left ventricular free wall. Treating disease requires restoration of normality, so decisions must be based upon an understanding of anatomic normality.
The helical ventricular myocardial band model of Torrent Guasp [ 5 ] appears in the two classical anatomy texts of Clemente [ 9 , 10 ], and Moore and Dally [ 11 ] and its mechanics explain each motion [ 6 , 8 , 12 ]. This knowledge answers the query about the heart by explaining the only valid definition of heart structure involves describing a mechanical architecture whose motion can account for all dynamic cardiac movements.
Misconceptions happen without it. For example, rather than focusing upon cardiac compression, the pivotal role of twisting for mechanical proficiency must be understood [ 13 ]. The background behind this misunderstanding started years ago when Erasistratus BC , then Galen AD and subsequently Borelli s [ 14 ] described twisting, which causes blood to have an ebb and flow motion. The newer three-dimensional imaging tools MRI and speckle tracking provide the spatial resolution that allowed re-emergence of the clockwise and counterclockwise twisting rotations Erasistratus described years ago.
A heart with two ventricles, separated by a midline muscular septum defines its classic morphologic description. Despite correct topography, no functional insight is provided to define what these three structures do.
A different structural guideline has existed for years, whereby heart architecture contains a helix formed by right- and left-handed fibers and a surrounding circumferential wrap [ 1 , 2 , 3 , 5 , 16 ]. His novel description of a helical ventricular myocardial band HVMB [ 17 ] identifies a vortex at the tip of the apex, which is formed by the overlapping of coiled helical arms.
Apical view of heart muscle showing the fibers clockwise and counterclockwise spiral formation. Images display common anatomy from Lower in left , and Torrent Guasp in right. Grant [ 18 ], Lev and Simkins [ 19 ], and Anderson [ 20 ] questioned his macroscopic findings because of concerns about the validity of his dissection planes in cadaver tissue.
Our analysis of the functional studies by Armour and Randall [ 21 ] also questioned the proper site for posterior papillary muscle, but their correct location is now displayed in subsequent HVMB dissections. Our report is a counterforce to this conclusion, since mechanically explaining cardiac function is the only hallmark for determining the creditability of structure. MacIver questions whether abrupt helical changes occur in a wrapped myocardium by using CT images, thereby taking a position that countermands their presence during gestation, with ongoing helical persistence during adulthood Figure 3.
His argument that a circumferential horizontal wrap exists in the septum would functionally erase the twisting motion, which is the most powerful force of cardiac efficiency. It would introduce a wedge that shall impair motion between the gliding helical arms, as shown in Supplementary Video S2 and Figure 4.
Moreover, adult DT-MRI images from the same laboratory that generated the prior gestation studies Figure 3 , further documents that circumferential fibers are absent in the septum [ 24 ].
Conversely, the mechanics of the myocardial band completely describes this pathophysiology during health and disease. Note absent circumferential fibers in septum. Doppler longitudinal strain imaging of septum right and left sides in apical four-chamber view. Longitudinal strain marked by red right and green left circles, showing deformation in opposite directions on right and left septum sides—relative to baseline zero value. Timing shows LV first and RV second.
Macroscopic analysis has the limitations of not addressing the microscopic display of the nests of layers and lamellae within individual myocytes that interact with cardiac ejection and filling. LeGrice found sarcomeres clustered in 1—12 groups within their connective tissue netting [ 27 , 28 ].
This need is emphasized in clinical heart failure where the normal conical heart shape develops a spherical configuration [ 29 ]. This geometric change transforms the fiber direction of helical arms into a more transverse architectural fiber orientation which impairs LV systolic and diastolic function [ 13 ]. The conceptual understanding of macroscopic cardiac structure is straight forward because only three components need be known.
There is a circumferential wrap of transverse fibers that surrounds both ventricles—called a basal loop—which compresses and rotates the global heart, and predominantly forms the RV free wall [ 25 ]. The second is the muscular helix that resides within an apical loop nestled within its surrounding circumferential wrap [ 30 ]. The same helix forms the septum and part of the LV free wall, whose movements are shortening, lengthening and twisting.
Functional balance exists between the structural wrap and helix, as the wrap causes counterclockwise motion before ejection, the helix produces twisting, and the wrap triggers clockwise recoil during post ejection interval that includes the isovolumic period [ 6 ]. State-of-the-art imaging reports do not recognize this dynamic balance because they do not address the fundamental role of the surrounding wrap [ 33 , 34 , 35 ]. This gap keynotes the hiatus between deduction and anatomic knowledge, especially since this large circumferential wrap muscle mass highlights the framework structural contributions of William Harvey [ 15 ], Krehl [ 3 ], Mall [ 4 ], Robb [ 16 ], and Torrent Guasp [ 5 ].
A common analogy explains such domination, as one could imagine a train heading south at 60 miles per hour, while its first car houses a runner who speeds northward toward the back car at 6 miles per hour; the power of the southern train always wins, as does the wrap over the helix. The anatomy documenting the location of the outer circumferential wrap becomes evident from echo studies showing the smooth reciprocal movement in different directions between the contracting inner and outer helical arms Supplementary Video S2.
Interposing a transverse band of compressing muscle between these gliding surfaces would interrupt this motion, as well as impair the smooth positive and negative septum strain displacement on longitudinal strain recordings Figure 4. Macroscopic interlocking of structure and function is aided by the comparison of their dynamic clockwise and counterclockwise helical motions in Supplementary Video S2 , with their anatomic configuration in post mortem CT images Figure 5. Computerized Ttomography of cardiac short axis, at mid ventricle level, following air insufflation to separate collagen scaffold netting.
Plane between the two septum muscle mass rims reflects the echogenic line in septum, and Supplementary Video S4 records motion between these post mortem rims. The plane identifying the mid ventricular overlapping between helical arms Supplementary Video S2 extends from apex to base and is called the hyperechogenic zone.
The smooth and efficient muscle movements, on either side of it, suggest this zone reflects is a glide path for helical arm motions. Working septum muscle fibers display different directionality on either side of septum line. This disappears, as does the echogenic line—when cardioplegia cardiac arrest stops contractile function. These dynamic findings differ from conclusions made from post mortem DT-MRI observations that suggest circumferential fibers exist within the septum mid myocardium due to observations of zero helix angles [ 42 ].
Yet physiologic testing exposes uncertainty about the anatomic validity of DT-MRI findings, because the micron thick echogenic zone disappears following cardioplegia, yet the dead heart septum MRI studies describe a circumferential muscle that occupies half of its muscle mass [ 43 , 44 ]. The most powerful or dominant muscle amongst these three architectural components governs the direction of movement, and their contraction takes place at different timing intervals [ 45 ].
For example, the wrap narrows and stretches the ventricle during the pre-ejection isovolumic phase, as it overcomes the simultaneously contracting inner descending helix that should make the ventricle shorten [ 6 , 7 ]. Conversely, shortening during ejection emphasizes the dominance of the inner descending helical arm. The outer helical coil cannot produce shortening because its longitudinal strain signal is positive showing elongation Figure 4. Despite this, both helical arms exert dominance during twisting because the inner descending coil causes shortening generating twice the longitudinal strain [ 47 ] while the outer ascending helical coil makes the apex turn counterclockwise [ 46 ].
Our imaging tools provide insight into this action via the echogenic septal line Figure 6 as the echo beam suggests their fiber orientation pathways by passing along or across the ascending and descending muscle masses [ 12 ].
The wrap [ 6 , 7 ] causes clockwise global recoil during the post ejection isovolumic phase, as it springs backward to reverse its pre-ejection counterclockwise motion [ 37 , 48 , 49 ]. Simultaneously, the ventricle lengthens from straightening of the contracting outer ascending helical coil that starts when the dominant inner descending helix contraction stops Figure 7 [ 7 ].
Upper left shows intact heart containing a basal loop circumferential wrap with right RS and left LS segments and helix dark color with descending DS and ascending AS segments. Lower left—diastole without contraction. Lower middle—displays shows torsion twisting with stronger contraction of descending helical arm tighter coils , and stretching of ascending helical arm. Lower right—recoil with global clockwise rotation; note lengthening due to ongoing contraction of ascending helical arm. Upper drawing—cobra shows similar elongation from its contracting muscle.
Global longitudinal strain measurements match those recorded by sonomicrometry [ 6 ] and the observed septum motion in opposite directions reflects the reciprocal fiber orientation of its helical muscles Figure 4. This timing hiatus between the end of contraction in the inner and outer helical arms provides a mechanical contradiction i. Mitral valve opening MVO is a term reflecting the Doppler based echocardiographic recording of initial transmitral inflow into the left ventricle.
This passage coincides with left ventricular pressure falling below atrial pressure, and the most rapid anterior mitral leaflet motion [ 51 ]. Its designation is universal and the term MVO appears in text books and journal reports Figure 8. Yet physical separation of the mitral leaflets is the only valid MVO requirement. Physiologic observations in all texts and medical journals, showing mitral valve opening MVO when LV pressure falls below left atrial pressure, and that the isovolumic relaxation phase exists between aortic valve closure and MVO.
MRI recordings quantify leaflet separation, and Supplementary Video S3 documents that mitral valve leaflets detach from each other at the end of systole—with an open aortic valve. Such MVO documentation exposes an enormous discrepancy between reality versus what has been deduced. The uncoiling process causes MVO, and introduces the muscular action that may trigger diastolic dysfunction. The functional dynamics of the wrap and helix establishes the mechanical insight to explain why MVO occurs during systole.
This geometric process focuses upon the architectural interaction between the mobile ventricle that uncoils—and the mitral annulus that is fixed. The circumferential wrap causes clockwise recoiling, which rotates the helix that contains the papillary muscles that connect with the mitral leaflets and annulus.
The dynamics of papillary motion are shown in Supplementary Video S4. Figure 9 a,b anatomically displays them at rest and during motion. The report of Mall [ 4 ], a renowned anatomist, demonstrates their clockwise and counterclockwise ventricular movements during twisting and uncoiling. Mitral valve inflow area opens during from its clockwise rotation during recoil. These cohesive actions of recoiling by the wrap and elongation by the outer helix arm reinforce why mechanical factors play such a vital role in mitral leaflet separation.
Our understanding of diastolic dysfunction is enhanced by a fuller understanding of MVO—since uncoiling cannot begin while torsion is ongoing. Prolonged torsion narrows this gap, so that thinking about the mechanical reasons for MVO may spawn some of the new treatments that will be subsequently considered [ 56 ]. MVO is due to anatomic changes that carry vast physiologic implications—as we suspect recoiling will become the centerpiece behind understanding diastolic dysfunction.
It signifies that part of the cardiac cycle between aortic valve closure and MVO, where the ventricle relaxes diastole without lengthening, and ventricular volume is unaltered.
What Is the Heart? Anatomy, Function, Pathophysiology, and Misconceptions
The cardiovascular system can be thought of as the transport system of the body. This system has three main components: the heart , the blood vessel and the blood itself. Blood can be thought of as a fluid which contains the oxygen and nutrients the body needs and carries the wastes which need to be removed. The following information describes the structure and function of the heart and the cardiovascular system as a whole. The heart is located in between the two lungs. It lies left of the middle of the chest.
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. 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.
40.3A: Structures of the Heart
The heart pumps blood through the body with the help of structures such as ventricles, atria, and valves. The heart is a complex muscle that pumps blood through the three divisions of the circulatory system: the coronary vessels that serve the heart , pulmonary heart and lungs , and systemic systems of the body. Coronary circulation intrinsic to the heart takes blood directly from the main artery aorta coming from the heart.
Your heart does a lot of work to keep the body going. Each day, the average human heart beats about , times, pumping 2, gallons of blood through the body. In fact, the heart does more physical work than any other muscle over a lifetime. Located between the lungs in the middle of the chest, the heart pumps blood through the network of arteries and veins known as the cardiovascular system. Blood delivers oxygen and nutrients to every cell and removes the carbon dioxide and other waste products made by those cells.
The cardiovascular system is a closed system if the heart and blood vessels. The heart pumps blood through a closed system of blood vessels. Blood vessels allow blood to circulate to all parts of the body.
The human heart is an organ that pumps blood throughout the body via the circulatory system, supplying oxygen and nutrients to the tissues and removing carbon dioxide and other wastes. In humans, the heart is roughly the size of a large fist and weighs between about 10 to 12 ounces to grams in men and 8 to 10 ounces to grams in women, according to Henry Gray's " Anatomy of the Human Body. The physiology of the heart basically comes down to "structure, electricity and plumbing," Phillips told Live Science. The right atrium and right ventricle together make up the "right heart," and the left atrium and left ventricle make up the "left heart. A double-walled sac called the pericardium encases the heart, which serves to protect the heart and anchor it inside the chest. Between the outer layer, the parietal pericardium, and the inner layer, the serous pericardium, runs pericardial fluid, which lubricates the heart during contractions and movements of the lungs and diaphragm. The heart's outer wall consists of three layers.
The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system.