Placoid scales are found in sharks and rays, and can vary greatly in external appearance. Scales of a White Shark. Photographer: Sue Lindsay Â© Australian Museum. Unlike the scales of bony fishes, placoid scales do not increase in size as the fish grows, instead new scales are added between older scales.Placoid scales are often referred to as denticles.Each placoid scale consists of a flattened rectangular base plate which is embedded in the fish, and variously developed structures, such as spines, which project posteriorly on the surface.The spines give many species a rough texture.here are large differences in the development of these spines between different species. Placoid scales are composed of a vascular (supplied with blood) inner core of pulp, a middle layer of dentine and a hard enamel-like outer layer of vitrodentine.
Approach Considerations. The treatment of gallstones depends upon the stage of disease. Ideally, interventions in the lithogenic state could prevent gallstone formation, although, currently, this option is limited to a few special circumstances. Asymptomatic gallstones may be managed expectantly.
Gallstones can be divided into 2 categories: Cholesterol stones (80%) and pigment stones (20%). Most patients with gallstones are asymptomatic. Stones may temporarily obstruct the cystic duct or pass through into the common bile duct, leading to symptomatic biliary colic, which develops in 1-4% of patients with gallstones annually. Cholecystitis occurs when obstruction at the cystic duct is prolonged (usually several hours) resulting in inflammation of the gallbladder wall.