Anatomy of the Human Heart: Difference between revisions

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=== Nerve Supply  ===
=== Nerve Supply  ===
The sympathetic and parasympathetic autonomic nervous supplies to the heart form the cardiac plexus which is located close to the arch of the aorta. The fibres from the cardiac plexus accompany the coronary arteries and reach the heart, with most of them terminating at the SA node, AV node and a much less dense supply to the atrial and ventricular myocardium [11].
In general,the parasympathetic vagal fibres are inhibitory and reduce the heart rate and stroke volume. The sympatheticnerves act as accelatory nerves increasing both the heart rate and stroke volume [11]. The afferent nerves run
along sympathetic pathways via both cardiac accelerator nerves and thoracic splanchnic nerves to reach the intermediolateral horn of T1–T4 of the spinal cord [11].
The noradrenergic or the sympathetic nervous system is mainly involved with increasing the heart rate (chronotropy),
contractility (ionotropy) and the speed of conduction (dromotropy) in the cardiac muscle fibres and the conduction tissue; and the transmitter involved is mainly nor-epinephrine [6]. The SA node receives most
of it nerve fibres from the right-sided thoracic sympathetic
ganglia and the right vagus [8]. The AV nodes
and ventricles receive their nerve supply form the leftsided
thoracic sympathetic ganglia and the left vagus,
which is mainly because SA node develops from the
structures on the right side of the embryo and the AV
node develops from the structures on the left side of the
embryo [8].
The sympathetic effects are mediated mainly by the
adrenergic receptors, which includes β-1 and β-2 adrenergic
receptors [2, 11]. β-1 receptors are found mainly
in the SA node and AV node, and the ventricular myocardium
acts via activation of adenylate cyclase and an
increase in cAMP (cyclic adenosine monophosphate)
concentration in the cell to mediate the above mentioned
sympathetic effects [2, 11]. β-2 receptors are
mainly found in the vascular smooth muscles in addition
to the bronchial smooth muscle and wall of the GI
tract and the bladder. The mechanism of action is same
as that of β-1 receptors, i.e., increase in cAMP levels but
they cause relaxation of the vascular smooth muscle and
are involved in regulation of blood flow and systemic
blood pressure [2, 11].
The cholinergic or the parasympathetic nervous system
effects in the heart are opposite to the ones mentioned
above and the transmitter involved is mainly
acetylcholine [8, 12, 13]. The vagi supply the parasympathetic
fibres to the heart via the cardiac plexuses. The
parasympathetic effects are mediated via the muscaranic
receptors, which act by inhibition of adenylate cyclase
and hence decrease the intracellular cAMP levels
and result in a decrease in heart rate, contraction and
conduction velocity [8, 12, 13].
The autonomic centres in the CNS, mainly the vasomotor
centre of medulla and the hypothalamus regulate
the balance between the level of sympathetic and the
parasympathetic output to the cardiovascular system,
depending on the afferent inputs from the periphery
and the CNS [7, 8, 12, 13]. There is normally a tonic
vagal discharge in humans, which overrides the moderate
tonic discharge in the cardiac sympathetic nerves
[7, 8, 12, 13]. Both the sympathetic and the parasympathetic
fibres in the splanchnic thoracic nerves and the
vagi carry afferent input mediated via baroreceptors and
chemoreceptors to the autonomic centres in the CNS,
in addition to the efferent output from the CNS. These
afferents and efferents are involved in mediation of cardiovascular
reflexes as baroreceptor and chemoreceptor
reflexes [7, 8, 12, 13].
The receptors of the autonomic nervous system to
the heart are the target of numerous drugs used in the
treatment of various cardiovascular disorders in both
acute and chronic settings [8, 12, 13].


=== Clinical Relevance  ===
=== Clinical Relevance  ===
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=== Embroyology  ===
=== Embroyology  ===


=== Histoology ===
=== Histology ===
 
=== Arthrokinematics ===
 
== Pathology/Injury  ==
 
== Techniques  ==
 
=== Palpation ===
 
=== Examination ===
 
=== Treatment ===


== Resources  ==
== Resources  ==
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== References  ==
== References  ==
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Revision as of 15:22, 8 March 2018

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Introduction[edit | edit source]

The heart is a muscular pump that serves two functions; to collect oxygen-poor blood from the tissues of the body and pump this blood to the lungs to pick up oxygen and release carbon dioxide and to collect oxygen-rich blood from the lungs and pump this blood to all of the tissues of the body.

It is important to note that, the blood pumped by the heart also circulates many other important substances such as:

1.     Nutrients from digestion are collected from the small intestine and pumped through the circulatory system to be delivered to all cells of the body.

2.      Hormones are produced from one type of tissues and distributed to all cells of the body. The circulatory system carries waste materials (salts, nitrogenous wastes, and excess water) from cells to the kidneys, where they are extracted and passed to the bladder.

3.     The pumping of interstitial fluid from the blood into the extracellular space is an important function of the heart. Excess interstitial fluid is then returned to the circulatory system via the lymphatic system.

Anatomy[edit | edit source]

The general shape and orientation of the heart are that of a pyramid that has fallen over and is resting on one of its sides. Placed in the thoracic cavity, the apex of this pyramid projects forward, downward, and to the left, whereas the base is opposite the apex and faces in a posterior direction.

The average adult’s heart is about 5.5 inches (14 centimeters) long and 3.5 inches (9 centimeters) wide, or approximately the size of one’s fist and also varies with body size. In an infant, the heart is about a thirtieth of total body weight. In an average adult, the heart is about one three-hundredth of total body weight; this equals about 11 ounces (310 grams) in males and 8 ounces (225 grams) in females.

Location of the Heart[edit | edit source]

The heart is roughly in a plane that runs from the right shoulder to the left nipple. It lies in the protective thorax, posterior to the sternum and costal cartilages, and rests on the superior surface of the diaphragm.  The heart is located between the two lungs in the space referred to as the mediastinum("that which stands in the middle"). The human heart assumes an oblique position in the thorax, one-third of the heart is located on the right side, while two thirds is located on the left side of midline. The base is located below the third rib as it approaches the sternum (note that the sternal angle occurs at the level of the second rib). The base is directed superiorly to the right of midline and posterior. The pointed apex projects to the left of midline and anterior. Thus, the heartbeat can be most easily palpated at the left fifth intercostal space, 8-9 cm from the midsternal line (just inferior to the left nipple).

Layers of the Heart Walls[edit | edit source]

Chambers of the Heart[edit | edit source]

Heart Valves[edit | edit source]

Blood Supply[edit | edit source]

Nerve Supply[edit | edit source]

Clinical Relevance[edit | edit source]

Embroyology[edit | edit source]

Histology[edit | edit source]

Resources[edit | edit source]

Recent Related Research (from Pubmed)[edit | edit source]

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References[edit | edit source]

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