The Heart

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Structure

2 Atria, 2 Ventricles - Inside Thoracic cavity

Pericardium - fibroserous sac around heart

Outer fibrous layer coated with vessels, Inner double layer, serous layer

Each layer is a simple squamous Epithelium supported by fibroelastic connective tissue

Anchored to adjacent structure at various points - limits heart movement.

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Atria

Separated by inernatrial septum

right atrium lies in front of left

Right Atrium (RA) recieves blood from superior and inferior venae cavae

Left Atrium (LA) - smaller than right, thicker walls than right

recieves blood from lungs via Pulmonary veins

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Ventricles

Right ventricle (RV) extends from RA - Crescent shape cavity, right atrioventricular orifice

right oval opening between RA and RVsurround by fibrous rings to which 3 cusps of tricuspid valve

Atrial surface - smooth

Ventricular surface - rough

Left Ventricle - thick wall, circular loral cavity

left atrioventricular, guarded by mitral valvue

mitral value is biscuspid, cusps anchored to papillary muscles by chorae tendinae and prevent regurtitation of blood back into LV


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Contractile part

myocardium attached to epicardium, lined by endocardium

 cells branched and striated

cells interconnected, atrial cells separated from ventricular

2 separate functions, connected through Atrioventricular bundle

Cardiac muscle cells - T tubules cross cells at 2 lines

longtudinal tubules of sacroplasmic reticulum parallel to myofibrils

tubules have small dilations

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Conduction system

specialised muscle cell in (SA) node

atrioventricular (AV) node

AV bundle and Purkinje fibres

SAnode (pacemaker) - narrow structure

located beneath and medial to opening of superior vena cava in wall of RA

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AV node

smaller than SA node - interatrial septum above tricuspid valve

lies in atrial septum above triscuspid

AV bundle (bundle of His) bundle of fibres from AV nodes

Purkinke - large diameter muscle cell - transmit APs faster

Innervation of heart

Parasympathetic fibres from cranial nerve

Sympathetic supply arises in upper thoracic region of spinal cord

Only sympathetic fibres

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