LECTURE XV 

 PATHOLOGY 



Physiology is the study of the body organs and their func- 

 tions in health. 



Pathology is the study of diseased organs and their disordered 

 functions. Healthy conditions are taken as a basis for studying 

 the diseased conditions. Pathological processes are but healthy 

 ones modified. 



Hyperemia (Congestion) 



Definition. — Hyperemia is an abnormal accumulation of blood 

 in any part, due either to an increased inflow or a decreased 

 outflow. The color of an hyperemic part may be distinctly red 

 in active hyperemia or bluish in passive hyperemia. 



A practical example is congestion of the lungs of a fat hog 

 exercised on a hot day, or the first stage of founder in a horse's 

 foot, or the congestion of a cow's udder after calving. 



There are two kinds of hyperemia, active and passive. Gen- 

 erally speaking, both types are local conditions. 



Active hyperemia is characterized by an excessive quantity of 

 blood in the arteries of some tissue or organ. It is caused by 

 disturbances of the arteriole nerve supply (vasomotors), i.e. any 

 agencies that produce dilation of the arteries, as body tempera- 

 ture disturbances, chemical irritants, etc. It may l)e the result 

 of lack of lilood elsewhere in the body ; e.g. sudden chilling of 

 the skin of a horse frequently produces active hyperemia of the 

 lung or other internal organs. Active hyperemia is usually tem- 

 porary, and permanent injury may be slight or may not occur. 

 As a rule a part so affected is red, warm and dry. An active 

 hyperemia may lead, if long continued, to enlargement of the 

 part or organ. The vessels themselves may enlarge to several 

 times their former size. 



Passive hyperemia, passive congestion (venous or mechani- 

 cal), is a condition in which the current of venous blood is 

 obstructed, outflow is decreased, and blood accumulates in veins 



77 



