Histology - Cardiovascular System

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Wall of the left atrium (has thickest endocardium)

*endocardium: connective tissue, abundant elastic fibers (stained black here)
*myocardium: middle and thickest layer, cardiac muscle
*epicardium: thin layer but thick near AV sulcus

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Right Atrium
*endocardium is thinner than left atrium
*myocardium is more loosely organized in the right than the left atrium
*epicardium has considerable adipose tissue

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left atrium endocardial surface

*dense irregular FECT (w/ fibroblast
*ELASTIC FIBERS - stained black (increase in concent closer to AVsulcus)
*dense myocardium->left atrium

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right atirum

*smooth walled portion is shown (as opposed to the rough portion)
*loose myocardium->right atrium

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rough walled portion of right atrium

*pectinate muscle which includes myocardium and endocardium
*can make out endothelial cells
*myocardium is so thin some areas appear missing->right atrium

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trabecular muscle of right atrium

*pectinate muscle is a simple projection, here the trabecular muscle reestablishes continuity with myocardium

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Outer portion of left atrial wall

*epicardium is more loosely arranged than the endocardium also elastic fibers are less densely concentrated
* nerves and blood vessels are found in the epicardium (are rare in the endocardium)

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image near AV sulcus

*endocardium becomes quite large as you approace the AV sulcus

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left AV sulcus

*wide epicardium
*epicardium because vessels and nerve

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left AV sulcus

*arteries and veins are distinguished by the structure of their walls
*thicker wall in arteries
*nerve has no neurons so not ganglion

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left AV sulcus

*here is ganglion because neurons are found
*nuclei are eccentric nuclei not surrounded by satellite cells which is postganlionic sympathetic or parasympathetic motor
*in the wall of an organ so parasympathetic motor
*autonomic nerve- because cant distinguish if PS motor (pre or post gangi), S motor

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left AV sulcus

*coronary sinus is the only blood vessel that has cardiac and not smooth m in its wall
*large epicardium->left AV sulcus

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endocardial surface of left ventricle

*ventricle because--thinner endocardium, fewer elastic fibers
*left v because--left v is relatively smoother than right v

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left ventricle

*seperate dense regular FECT -->cordae tendinae->must be vventricle
*very thin endocardium->closer to heart apex

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ventricle

*cordae tendinae-> dense regular FECT surrounded by thin endocardium

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junction between right atrium/right ventricle

*spaces-->trabeculae carnae (like trabecular muscles of atria but in ventricle)
*trabeculae carnae are more common in the right ventricle

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wall of right ventricle closer to apex

*crabeculae carnaee->right ventricle

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outer portion of wall of left ventricle

*myocardium densely packed (relative to atrium)
*epicardium similar to that seen in atria->NOT distinguishing feature
*closer to AV sulcus thicker epicardium is

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interventicular septum

*connective tissue stained blue-> membranous IV septum
*cardiac muscle stained red->muscular IV septum
*bundle of his at base of membranous IV
*myocardium of IV is similar to myocardiium of left atrium (thickness, density, lack of trabeculation)

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IV septum

*septal cusp arises frm membranous IV septum->divides right atrium from right ventricle

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membranous IV septum

*root of aorta consists of only connective tissue (stained blue here)
*connective fibers above cusp to become wall of aorta

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right AV valves (tricuspid)

*valve cusps arise from annulus fibrosus (right of connective tissue)
*tissue is difference of myocardiumo of RV or RA

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image of valve cusp of tricuspid

*holding surface: collagen fibers are relatively large
*deforming surface: collagen fibers are less noticeable (small diameter) enriched in elastic fibers

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left AV valve cusp (mitral valve)

*annulus fibrosus connective tissue which intervenes between A and V myocardia
*can distingiush holding and deforming surface by collagen fibers and elastic fibers on deforming side

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Valve cusp of mitral valve

*elastic fibers are black which are concentrated in the deforming surface and less apparent in the holding surface
*deforming surface faces the atrium, holding surface faces the ventricle

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Papillary muscles

*arise out of the floor of ventricles
*dense regular FECT stains red
*cardiac muscle stains blue
*collagen fibers of the chordae tendinae project into cardiac papillary muscle

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Higher mag of papillary muscle

*lined by a layer of endocardium
*layer of purkinje cells just deep to endocardium

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Orgin of Aorta

*arises out of upper portion of IV septum
*valve cusp of aortic seminulnar valve is seen
*holding/deforming surfaces distinguished by differences of collegen content
*aortic sinus is the portion of lumen that lies just above the aortic valve
*wall of aorta has distinct structure

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pulmonary trunk

*arises from tubular extension of roof of right ventricle (the conus arteriosus)
*pulmonary trunk arises from ring-shaped loop
*differences in collagen distinguish the surfaces of the semilunar pulmonary valve

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just proximal to root of pulmonary trunk

*all three hart layers prior to pulmonic root (unlike aortic origin) --- has myocardium and epicardium

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SA node

*mass of connective tissue located at the approximate junction of epicardium and myocardium of right atrium
*nodal artery runs length of this tissue
*conducting cells scattered within (lack staining relative to working cardiac muscle)

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SA node at higher magnification

*conducting cells scattered
*lack of staining because of reduced number of myofibrils
*conducting cells within connective tissue --> node
*junction of epicardium/myocardium ->SA node

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parasympathetic ganglion

*wall of organ + neurons -> postganglionic parasympathetic -> whole structure is ganglion

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AV node

*AV node at junction of myocardium/epdocardium of right atrium w/ connective cells
*NO epicardium in vicinity (unlike SA node)

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AV node (at higher magnification)

*conducting cells visible (lack of staining compared to working cells)
*conducting cells embedded in connective tissue->node
*between endocardium/myocardium -> AV node

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IV septum

*bundle of His located at the base of membranous IV septum
*conducting cells of bundle of His are NOT surrounded by connective tissue
*entire note is surrounded by connective tissue of membranous IV septum
*branch of bundle of his runs down into muscular IV septum will break up into Purkinje

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Bundle branch of bundle of His

*branch runs at the interface between endocardium and myocardium
*stain lighter displaying "hollow centers" as compared to surrounding working cells of muscular IV septum

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Bundle of His where bundle branch has become Purkinje fibers

*stain lightly displaying "hollow centers"
*form superficial layer upon the myocardium just below endocardium
*not specifically encased by connective tissue
*thick layer of Purkinje cells -> IV septum or papillary muscle

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papillary muscle

*Purkinje cells lie deep to endocardium
*Purkinje cells stain lighter than the deeper working myocardial cells

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Elastic artery

*three basic layers
- thinest bordering lumen is tunica intima (endothelium and connective tissue)
-middle layer is tunica media and is the thickest (vascular smooth muscle/elastic fibers)
-outermost layer is tunica adventitia (variable in thickness, corarser collagen (stained green here) )

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Elastic artery at higher magnification

*numerous elastic fibers within tunica media which comprise the elastic lamina

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outer portion of elastic artery (tunica adventitia)

*more collagen than elastic fibers
*blood vessel and nerve embedded within tunica adventitia called vasa vasorum and nervi vasorum

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elastic artery (stained with H&E)

*distinct elastic lamina (hallmark of this type of vessel)
*tunica adventitia lacks elastic lamina same for tunica intima

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large muscular artery

*tunica media does not contain abundance of elastic lamina
*elastic fibers are contentrated at internal elastic lamina and external elastic lamina which serve as boundaries between tunica intima tunica intima/media and tunica media/adventitia resp.

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inner layers of muscular artery

*presence of internal elastic lamina
*few elastic fibers within tunica media instead can see vascular smooth muscle cells without obscured by elastic lamina

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outer layers of muscular artery

*external lamina more substantial collection of elastic fibers compared to internal (so is wider)
*tunica adventitia ends indistinctly

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(smaller) muscular artery

*lack of elastic lamina
*has internal elastic lamina
*external elastic lamina moderate in content
*blood vessel (vasa vasorum) and nerve (nervi vasorum) in tunica adventitia

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inner two layers of muscular artery
* tunica intima is thin -- as muscular arteries become aterioles the tuica intima can become a single layer of endothealial cells (with minor amounts of connective tissue)
*internal elastic lamina visible
*

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ateriole and venule

*lined by endothelium which constitutes tunica intima
*primary layer of the venule is tunica adventitia (fibroblasts)
*primary layer of arteriole is tunica media (vascular smooth muscle cells)
*this difference -> wall thickness/lumen ratio is much higher for the ateriole than venule

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ateriole and venule

*venule has wall which is tunica intima (endothelium only) and olnly a layer or two of fibroblasts within tunica adventitia

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example of microcirculation: arteriole

*smallest ateriole possible with only one smooth muscle cell layer
*capillary is only a single layer of endothelium (lumen only big enough for a single blood cell)
*same structure but bigger-> post capillary venule

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Addipose tissue

*capillary and post capillary venule have same structure but differ in size

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venule and post capillary venule

*post-capillary venule is too large to be a capillary (ie more than one RBC can fit in lumen)
*post-capillary venule also has a second cell outside endothelial cell (the pericyte)

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wall thickness of medium size vein
*unlike venules, has tunica media consisting of a few layers of vascular smooth muscle
*like venules, primary layer is the tunica adventitia
*tunica intima consits of a single layer of endothelial cell w/ little connective tissue.

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wall of medium sized vein (higher magnification)

*tunica intima is only a single layer
*smooth muscle cells present (tunica media) which are loosely arranged compared to arteriole
*relative difference in smooth muscle is more apparent in vein/artery case vis.arteriole/venuole
*like all veins tunica adventitia blends with surrounding tissues

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low magnification of vena cava

*shows three layers, tunica adventitia is biggest

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outer portion of vessel wall of vena cava

*longitudinal smooth muscle within tunica adventitia
*dense connective tissue between these longitudinal pockets
*no other blood vessel has this arrangment of smooth muscle in the tunica adventitia

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lymphatic vessel

*key distinguishing feature: asymmetry of smooth muscle within tunica media--smooth muscle has variable thickness
*smooth muscle is not circular because smooth muscle is arranged in spiral fashion around the long axis
*lined by endothelium (tunica intima), variably thick layer of connective tissue comprising the tunica adventitia, primary layer