Chapter 26. Nutrition and Metabolism

Arcuate nucleus of the hypothalamus

An important brain center for appetite regulation All five peptides have receptors in the arcuate nucleus, although they act on other target cells in the body as well. The arcuate nucleus has two neural networks involved in hunger. One group secretes neuropeptide Y (NPY), itself a potent appetite stimulant. The other secretes melanocortin, which inhibits eating. Ghrelin stimulates NPY secretion, whereas insulin, PYY, and leptin inhibit it. Leptin also stimulates melanocortin secretion

Vitamins

Coenzymes for many metabolic pathways; antioxidants; component of visual pigment; one hormone (vitamin D)

Carbohydrates

Fuel; a component of nucleic acids, ATP and other nucleotides, glycoproteins, and glycolipids

Lipids

Fuel; plasma membrane structure; myelin sheaths of nerve fibers; hormones; eicosanoids; bile acids; insulation; protective padding around organs; absorption of fat-soluble vitamins; vitamin D synthesis; some blood-clotting factors

Leptin

Long-Term Regulator of Appetite Leptin is secreted by adipocytes throughout the body Its level is proportional to one's fat stores, so this is the brain's primary way of knowing how much body fat we have

Proteins

Muscle contraction; ciliary and flagellar motility; structure of cellular membranes and extracellular material; enzymes; major component of connective tissues; transport of plasma lipids; some hormones; oxygen binding and transport pigments; blood-clotting factors; blood viscosity and osmolarity; antibodies; immune recognition; neuromodulators; buffers; emergency fuel

Peptide YY (PYY)

Short-Term Regulators of Appetite related to neuropeptide Y (NPY) secreted by enteroendocrine cells in the ileum and colon, but they sense that food has arrived even as it enters the stomach. They secrete PYY long before the chyme reaches the ileum, and in quantities proportional to the calories consumed The primary effect of PYY is to signal satiety and terminate eating. PYY remains elevated well after a meal. It acts as an ileal brake that prevents the stomach from emptying too quickly, and therefore prolongs the sense of satiety.

Cholecystokinin (CCK).

Short-Term Regulators of Appetite secreted by enteroendocrine cells in the duodenum and jejunum. It stimulates the secretion of bile and pancreatic enzymes, but also stimulates the brain and sensory fibers of the vagus nerves, producing an appetite-suppressing effect. Thus, it joins PYY as a signal to stop eating.

Ghrelin

Short-Term Regulators of Appetite secreted by parietal cells in the gastric fundus, especially when the stomach is empty. Produces the sensation of hunger and stimulates the hypothalamus to secrete growth hormone-releasing hormone. Within an hour after eating, ghrelin secretion ceases.

Water

Solvent; coolant; reactant or product in many metabolic reactions (especially hydrolysis and condensation); dilutes and eliminates metabolic wastes; supports blood volume and pressure

Minerals

Structure of bones and teeth; component of some structural proteins, hormones, ATP, phospholipids, and other chemicals; cofactors for many enzymes; electrolytes; oxygen transport by hemoglobin and myoglobin; buffers; stomach acid; osmolarity of body fluids

Micro-nutrients

also known as minerals and vitamins because only small quantities are required.

Macro-nutrients

also known as water, carbohydrates, lipids, and proteins because they must be consumed in relatively large quantities

Nutrient

any ingested chemical that is used for growth, repair, or maintenance of the body. Nutrients fall into six major classes: water, carbohydrates, lipids, proteins, minerals, and vitamins

Essential nutrients

eight of the amino acids, and one to three of the fatty acids. it is essential that they be included in the diet.

Insulin

secreted by the pancreatic beta cells It stimulates glucose and amino acid uptake and promotes glycogen and fat synthesis. But it also has receptors in the brain and functions, like leptin, as an index of the body's fat stores.

gastric peristalsis

stimulates hunger

Nutrition

the source of fuel that provides the energy for all biological work and of the raw materials for replacement of worn-out biomolecules and cells