Essentials of Human Physiology for Pharmacy

106 Essentials of Human Physiology for Pharmacyof air in and out of the lungs so that uptake of oxygen from the atmosphereand elimination of carbon dioxide from the body are maximized. Anenhanced rate of glycogenolysis (breakdown of glycogen into its componentglucose molecules) and gluconeogenesis (formation of new glucose fromnoncarbohydrate sources) in the liver increases the concentration of glucosemolecules in the blood. This is necessary for the brain because glucose is theonly nutrient molecule that it can utilize to form metabolic energy. Anenhanced rate of lipolysis in adipose tissue increases the concentration offatty acid molecules in the blood. Skeletal muscles then utilize these fattyacids to form metabolic energy for contraction. Generalized sweating elicitedby the sympathetic system enables the individual to thermoregulate duringconditions of increased physical activity and heat production. Finally, theeye is adjusted so that the pupil dilates, letting more light in toward theretina (mydriasis) and the lens adapts for distance vision.The parasympathetic system decreases heart rate, which helps to conserveenergy under resting conditions. Salivary secretion is enhanced tofacilitate swallowing food. Gastric motility and secretion are stimulated tobegin processing of ingested food. Intestinal motility and secretion are alsostimulated to continue processing and to facilitate absorption of these nutrients.Exocrine and endocrine secretion from the pancreas is promoted.Enzymes released from the exocrine glands of the pancreas contribute to thechemical breakdown of the food in the intestine, and insulin released fromthe pancreatic islets promotes storage of nutrient molecules within the tissuesonce they are absorbed into the body. Another bodily maintenance typeof function caused by the parasympathetic system is contraction of the urinarybladder, which results in urination. Finally, the eye is adjusted so thatthe pupil contracts (miosis) and the lens adapts for near vision.Pharmacy application: cholinomimetic drugsCholinomimetic drugs produce effects in a tissue resemblingthose caused from stimulation by the parasympathetic nervoussystem. These drugs have many important uses including treatmentof gastrointestinal and urinary tract disorders that involvedepressed smooth muscle activity without obstruction. For example,postoperative ileus is characterized by a loss of tone or paralysisof the stomach or bowel following surgical manipulation.Urinary retention may also occur postoperatively or may be secondaryto spinal cord injury or disease (neurogenic bladder).Normally, parasympathetic stimulation of the smooth muscle ineach of these organ systems causes contraction to maintain gastrointestinalmotility as well as urination. The pharmacotherapyof these disorders has two different approaches. One type of agentis a muscarinic receptor agonist that mimics the effect of the