Anatomy & Physiology

Anatomy & Physiology Study Guide broken down further into nucleotides. Next, brush border enzymes digest these nucleotides into sugars, phosphates, and nitrogenous bases that are absorbed by active transport. However, nucleic acids represent only a small fraction of all the nutrients absorbed each day. Once the molecules are broken down into their purest form, the body uses these substances for energy through a series of chemical reactions that form a metabolic process called the Kreb , or TCA , cycle. This process is aerobic, which means it requires oxygen, and when energy is created, it is temporarily held by the electron carriers NAD and FAD. Another procedure, called oxidative phosphorylation, is the final metabolic pathway in cellular respiration and the creation of energy within the cell. 23.14 Nutrition Proper nutrition is an essential component of sustaining body functions. Without the appropriate nutrients in a particular balance, a person cannot maintain homeostasis, and the breakdown or lack of processes would occur representative of specific pathologies. Nutrient intake occurs primarily by the method of ingestion of food. Some nutrients are stored in the body and can be accessed if consumption decreases, whereas other nutrients are saved and need to be replenished regularly. The nutrient classes include carbohydrates, proteins, fats, minerals, vitamins, and water. The primary source of energy, four calories of energy per gram, is carbohydrates which can be divided into two groups: simple (e.g., table sugar) and complex (e.g., vegetables and whole grains) carbohydrates. Proteins are the building blocks of the body as the amino acids arise from their consumption. They produce energy and promote strength and growth. Proteins provide four calories of energy per gram. Fats are another source of energy and are a significant source of calorie intake, essential for development especially in the infant. It provides nine calories of energy per gram consumed. Unfortunately, Americans consume more fat than is necessary on average, and this overabundance can lead to the number one killer of Americans: heart disease. Humans are unable to survive more than a few days without water. Nearly two-thirds of the body is water, and though water has no caloric value, it is essential for life-sustaining processes and normal daily functioning. Vitamins (organic substances) and minerals (inorganic elements) are needed in varying degrees and are usually obtained through a balanced diet; however, supplementation is necessary for some patients. Vitamins and minerals do not supply calories or energy but are needed for physiological processes. The dietary intake of these nutrients are pertinent to avoid disease, but it is equally important to obtain adequate calorie intake. Daily calorie requirements for each vary dependent upon gender, weight, age, and physical activity. The basal metabolic rate (BMR) measures the energy used during rest, and though it is an underutilized test, it can be useful as a component for determining a patient’s calorie requirement. 23.15 Aging Essentially, healthy digestion and absorption occur in elderly individuals. However, many changes in the digestive system parallel age-related changes discussed in connection with other systems: Achieve Page 324 of 368 ©2018