Main exogenous causes of pathology: chemical, physical and biological. Homeostatic mechanisms. Laboratory semeiotics. Organic markers of pathology. Structure and setting up of a clinical pathology laboratory: POCT, General Laboratory, specialist laboratory. Analytical cycle. Analytical variability. Blood sample. Collection of urine. Capture of cerebrospinal fluid. Collecting feces. Collection of saliva, sweat and tears. Transport and storage of biological samples. Blood cells. The blood count. Anemia. Normal and pathological serum proteins. Acute phase proteins. Electrolytes. Blood clots.