Nursing 105

Essentials of Nursing Study Guide

©2018 Achieve Page 8 of 160 is the body’s conversion of nutrients into energy. Basal metabolism is the amount of energy needed to maintain essential physiologic functions when a person is at complete rest, both physically and mentally. Metabolism is a set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The word metabolism can also refer to all chemical reactions that occur in living organisms, including digestion and the transport of substances into and between different cells, in which case the set of reactions within the cells is called intermediary metabolism or intermediate metabolism . Metabolism is usually divided into two categories: Catabolism breaks down organic matter, for example to harvest energy in cellular respiration, and anabolism uses energy to construct components of cells such as proteins and nucleic acids. Process #3 Absorption is the process by which the end products of digestion pass through the small and large intestines into the blood or lymph systems. Digested food is now able to pass into the blood vessels in the wall of the intestine through the process of iffusion . The small intestine is the site where most of the nutrients from ingested food are absorbed. The inner wall, or mucosa , of the small intestine is lined with simple columnar epithelial tissue. Structurally, the mucosa is covered in wrinkles or folds called plica circulares , which are considered permanent features in the wall of the organ. They are distinct from rugae , which are considered non-permanent or temporary, allowing for distention and contraction. From the plicae circulares project microscopic finger-like pieces of tissue called villi . The individual epithelial cells also have finger-like projections known as microvilli . The function of the plicae circulares, the villi and the microvilli is to increase the amount of surface area available for the absorption of nutrients. Each villus has a network of capillaries and fine lymphatic vessels called laterals close to its surface. The epithelial cells of the villi transport nutrients from the lumen of the intestine into these capillaries (amino acids and carbohydrates) and lacteals (lipids). The absorbed substances are transported via the blood vessels to different organs of the body where they are used to build complex substances such as the proteins required by our body. The food that remains undigested and unabsorbed passes into the large intestine. Absorption of most nutrients takes place in the jejunum , with the following notable exceptions: • Iron is absorbed in the duodenum. • Vitamin B12 and bile salts are absorbed in the terminal ileum. • Water and lipids are absorbed by passive diffusion throughout the small intestine. • Sodium bicarbonate is absorbed by active transport and glucose and amino acid cotransport. • Fructose is absorbed by facilitated diffusion. Process #4 Metabolism