HISTOLOGY OF CIRCULATORY SYSTEM II

T- TUBULES & SARCOPLASMIC RETICULUMLess regular arrangementT- Tubules are more numerousAt level of Z- lineDIAD

CONDUCTING SYSTEMMitochondria more numerousLipofuscin pigment granules

CARDIAC FIBROUS SKELETONSeptum membranaceumTrigona fibrosaAnnuli fibrosa

Composed of dense connective tissue

CONDUCTING SYSTEM

CIRCULATORY SYSTEMBLOOD VASCULAR SYSTEMLYMPH VASCULAR SYSTEM

COMPONENTSHEARTARTERIESCAPILLARIES

LYMPHATIC CAPILLARIESLYMPH VESSELSLYMPHOID ORGANS

DIVISIONS

MACROVASCULATURE: > 0.1µm, large arterioles, muscular & elastic arteries, muscular veins

MICROVASCULATURE: < 0.1µm, arterioles, capillaries, post capillary venules

Exchange vessels

TISSUE COMPONENTSEndotheliumMuscular tissueConnective tissue (Elastic elements)

STRUCTURAL PLAN OF BLOOD VESSELS

TUNICA INTIMAEndotheliumBasal laminaSub endothelial connective tissueInternal elastic lamina

TUNICA MEDIASmooth musclesElastic lamellae, reticular fibersGround substance elementsExternal elastic lamina

TUNICA ADVENTITIACollagen & elastic fibers

VASA VASORUMVessels of vesselsArterioles, capillaries, venules in

adventitia

INNERVATIONSympathetic fibers (norepinephrine)VasoconstrictionArteries in Skeletal Muscles- cholinergic

vasodilator fibers

ENDOTHELIUM: Semi permeable barrier

Monitor bidirectional exchangeNonthrombogenic surface;

heparin, tissue plaminogen activator & Von Willibrand factor

Regulate Vascular tone & Blood flow; Contraction: endothelin 1 & ACE Relaxation: NO & Prostacyclin

Inflammation & Local Immune response; Adhesion of WBCs, expression of P-Selectin, Weibel Palade

BodiesGrowth Factors;

VEGF in Vasculogenesis, Angiogenesis, role of Angiopoeitins

LipolysisProduce Vasoactive substances

Thrombosis, emboli (Role of TPA)

VASCULAR SMOOTH MUSCLESPresent in all vessels EXCEPT capillaries

and post capillary venulesEnclosed in basal lamina & connective

tissueArranged helicallyConnected by gap junctions

VASCULAR CONNECTIVE TISSUE

Variable proportionCollagen, IV, III, IElastic fibersGround substance; heterogenous gel

Medical ApplicationArteriosclerosis Thickening of walls of small arteriesMonkeberg’s calcific sclerosisAtherosclerosis

LARGE ELASTIC ARTERIEST. INTIMAIntima is thicker; smooth muscles in sub

endothelial connective tissueInternal elastic lamina, though present not

prominent

T. MEDIAConcentric lamellae of elastic fibers (40-70)Reticular fibers, smooth muscles

T. ADVENTITIALess developed

Arterial Sensory ReceptorsCarotid & Aortic Sinus:

BaroreceptorsTunica Media is thin--- allows distensionAfferent impulses via 9th cranial nerveVasomotor center in brainEfferent adjust lumen to control BP

Carotid & Aortic Bodies:Chemoreceptors Para ganglia with rich capillary networkGlomus type I cells; dense core granules containing

Dopamine, AchSupported by Satellite Type II cellsIon channels in Glomus cells respond to Low Oxygen,

High CO2 or AcidosisAfferents to brain efferents to cvs or respiratory

system

MEDIUM SIZED, MUSCULAR ARTERIEST. INTIMASubendothelial layer thinProminent internal elastic lamina

T. MEDIASmooth muscles- 40 layersElastic fibers

T. ADVENTITIAConnective tissue, vasa vasorum,

lymphatics

SMALL ARTERIES & ARTERIOLES<0.5mm lumenThin subendothelial connective tissueInt. elastic lamina absent in small arteriolesT. Media: smooth muscle layerAdventitia is thin

Hypertension

CAPILLARIESDiameter : 5-7 µmSingle layer of endothelium; permit metabolic

exchangeFunction in groups- Capillary BedsRichness conforms to metabolic activity of

tissueStructure and pulsatile flow of blood through

capillaries and thoroughfare channel.

TYPES

ContinuousFenestratedSinusoidal

CONTINUOUS CAPILLARIESNo fenestrations, complete basal laminaPinocytic vesiclesLocation:Muscles, nervous tissue, exocrine glands

FENESTRATED CAPILLARIESTranscellular openings (80nm)Limited by cell membraneCovered by diaphragm ( thinner than cell

membrane, proteoglycans)In endocrine glandsKidneys etc

SINUSOIDAL CAPILLARIESDiameter 30-40µmEndothelial cells discontinuous layerFenestrations without diaphragmIncomplete basal laminaMacrophagesFound in liver, hematopoietic organs

PERICYTESCells at periphery of continuous capillariesenclosed in own basal laminaMesenchymal originActin, myosin– contractile propertiesRole in repair process

Diabetic Microangiopathy