Anatomy & Physiology

Anatomy & Physiology Study Guide • Generally speaking, children and young adults have 20 primary teeth (deciduous teeth) that are replaced by the 32 secondary dentition later on in life. The pharynx is a passageway between the oral cavity and esophagus: • Propulsion of the bolus through the pharynx results from contractions of the pharyngeal constrictor muscles and the palatal muscles, and from the elevation of the larynx. The esophagus, described as a muscular tube, transports solids and liquids from the pharynx to the stomach through the esophageal hiatus, an opening in the diaphragm. • The esophageal mucosa consists of stratified epithelium. Esophageal glands of the submucosa contain mucous secretion to aid in the reduction of friction during the passage of foods. The amount of skeletal and smooth muscle of the muscularis externa change from the passage from the pharynx to the stomach. • Swallowing (deglutition) is divided into three phases: buccal, pharyngeal, and esophageal. Swallowing begins with the bolus being compacted and then moved into the pharynx, next is the elevation of the larynx, then the reflection of the epiglottis, and finally closure of the glottis. Once the upper esophageal sphincter is opened, peristalsis will move the bolus down the esophagus to the lower esophageal sphincter. The stomach is a J-shaped organ that receives the bolus from the esophagus and aids in chemical and mechanical digestion: • The stomach has four major functions: (1) storage of ingested food, (2) mechanical breakdown of food, (3) disruption of chemical bonds by acid and enzymes, and (4) production of intrinsic factor. • The four regions of the stomach are the cardia, fundus, body, and pylorus. The pyloric sphincter guards the exit out of the stomach. In a relaxed state, the stomach lining contains numerous rugae (ridges and folds). • Within the gastric glands, parietal cells secrete intrinsic factor and hydrochloric acid. Chief cells secrete pepsinogen, which is converted by acids in the gastric lumen to the enzyme pepsin. Enteroendocrine cells of the stomach secrete a variety of compounds, but the most notable one is the hormone gastrin. • Gastric control involves the cephalic phase, which prepares the stomach to receive ingested materials; the gastric phase, which begins with the arrival of food in the stomach; and the intestinal phase, which controls the rate of gastric emptying. The small intestine digests and absorbs nutrients, and associated glandular organs assist with the digestive process: • Most of the important digestive and absorptive functions occur in the small intestine. The pancreas, liver, and gallbladder provide digestive secretions and buffers. • The small intestine consists of the duodenum, the jejunum, and the ileum. A sphincter, the ileocecal valve, marks the transition between the small and large intestines. Achieve Page 326 of 368 ©2018