13J VETERINAR\ PATHOLOGY. 



ISCHEMIA. 



DEFINITION. 

 ETIOLOGY. 



Diiitlnished calibre of supplying arteries. 

 Stiiiiiilatioii of z'aso constrictor nerves. 

 Inhibition of vaso dilator nerz'cs. 

 Tonic spasms of z'cssel musculature. 

 Occnision of supplying arteries. 

 Mechanical. 

 Tumors. 

 Thrombi, etc. 

 Collateral hvpcremia. 

 APPEARANCE. 



Maci-oscopic. pale, flabby, lozcer temperature. 

 Microscopic, cell degeneration, atrophy or necrosis. 

 EFFECTS— Depend upon extent and duration aud may be atrophy or 

 necrosis. 



AxHiiiA. as usually cnnsidei ed, is a condition in which there 

 is eitlier a deticicnc_v in tlie <iualit\- (tt in the quantity of blood. 

 The di.scussion of this theme \\-ill be found in special pathol- 

 ogy- 



LscHK-MiA is a condition in which there is insufficient or total 

 absence of blood in a part of the body. 



Etiology. — Ischemia ma^' be caused bv influences that dimin- 

 ish the calibre or occlude the \-essels supplying blood to a part 

 or by collateral hyperemia. The calibre of arteries may be 

 diminished bv crmtraction of the \-essel musculature induced by 

 low temperature, high temperature, drugs, etc., which stunulate 

 the vaso-constrictor nerves, or inhibit the vaso-dilator nerves 

 or cause tonic spasms of the vascular muscle. The supplying 

 arteries mav be occluded by mechanical pressure produced by 

 Ijandages, ligatures, harness, collar, thronibi. emboli, neoplasms, 

 tissue proliferations and tissue infiltrations. Ischemia in cme 

 part may be caused by hyperemia in a related part, because the 

 blood of the entire bodv is easilv contained in the vessels main- 

 tained at the normal calibre, blood pressure causing an equal 

 distribution of it; and if the \'essels of one area are increased in 

 calibre, followed bv an increased inflow of blood, the quantitv of 

 blood will be diminished in some part, thus a marked hvpere- 

 mia of the spleen is usually accompanied bv ischemia of the 

 stomach. It is possible for sufficient blood to collect in the ves- 

 sels of the liver to drain the system to a sufficient extent that 

 the animal would die of ischemia of the brain. 



Appearance. — Macroscopic. — .\n ischemic tissue appears blood- 

 less and is pale, flabby and of a lower temperature than 

 the same tissue with a normal blood supply. If incised the tis- 

 sue appears drv and there will be limited or no hemorrhage. 



