tailieunhanh - Ebook Harrison's endocrinology (3rd edition): Part 2

(BQ) Part 2 book "Harrison's endocrinology" presents the following contents: Diabetes mellitus, obesity, lipoprotein metabolism; disorders affecting multiple endocrine systems; disorders of bone and calcium metabolism; laboratory values of clinical importance. | SECTION III DIABETES MELLITUS OBESITY LIPOPROTEIN METABOLISM CHAPTER 16 BIOLOGY OF OBESITY Jeffrey S. Flier Eleftheria Maratos-Flier In a world where food supplies are intermittent the ability to store energy in excess of what is required for immediate use is essential for survival. Fat cells residing within widely distributed adipose tissue depots are adapted to store excess energy efficiently as triglyceride and when needed to release stored energy as free fatty acids for use at other sites. This physiologic system orchestrated through endocrine and neural pathways permits humans to survive starvation for as long as several months. However in the presence of nutritional abundance and a sedentary lifestyle and influenced importantly by genetic endowment this system increases adipose energy stores and produces adverse health consequences. DEFINITION AND MEASUREMENT Obesity is a state of excess adipose tissue mass. Although often viewed as equivalent to increased body weight this need not be the case lean but very muscular individuals may be overweight by numerical standards without having increased adiposity. Body weights are distributed continuously in populations so that choice of a medically meaningful distinction between lean and obese is somewhat arbitrary. Obesity is therefore more effectively defined by assessing its linkage to morbidity or mortality. Although not a direct measure of adiposity the most widely used method to gauge obesity is the body mass index BMI which is equal to weight height2 in kg m2 Fig. 16-1 . Other approaches to quantifying obesity include anthropometry skinfold thickness densitometry underwater weighing CT or MRI and electrical impedance. Using data from the Metropolitan Life Tables BMIs for the midpoint of all heights and frames among both men and women range from 19 to 26 kg m2 at a similar BMI women have more body fat than men. Based on data of substantial morbidity a BMI of 30 is most commonly used as a threshold for obesity in