Calcium Antagonism & Gastrointestinal Motility [antikvár]

Anatomy of the gastrointestinal tract The gastrointestinal tract is a muscular canal, lined by mucous membrane, which leads from the mouth to the anal orifice and displays, at successive levels, variations in structure adapted to the ingestion, mastication, transport, digestion and absorption of food and alsó to the elimination of the unabsorbed or unabsorbable residues. Anatomical aspects The esophagus The esophagus connects the pharynx to the stomach. It is approximately 25 cm long and transports food to the stomach by peristaltic activity. Macroscopically, three parts can be distinguished: the cervical, thoracic and abdominal segments. Clinically, three constrictions are important in the passage of instruments along the esophagus: at its commencement (15 cm from the incisor teeth); where it is crossed by the aortic arch and the left principal bronchus (25 cm from the incisor teeth); where it pierces the diaphragm (40 cm from the incisor teeth). Microscopically, the structure of the esophagus follows the same generál pattern as the rest of the alimentary tract, being förmed of four layers: the mucous membrane; the submucous layer; the muscular layer; the serous or fibrous layer (Fig. 1). The muscular layer consists of striated muscle and smooth muscle. Striated muscle is generaily limited to the upper two thirds; the lower third contains smooth muscle only. In the upper quarter, both layers (circular and longitudinal) are striated; in the second quarter, bunFig. 2: Smooth muscle cell: principal features of organisation. dles of smooth muscle appear (Fig. 2). The muscular layers thicken caudally and the external longitudinal layer connects with the inner circular layer at the gastric end of the esophagus. This specific arrangement of muscle fibres leads to sphincteric effects at the gastroesophageal junction. The functional sphincteric mechanism, capable of contraction and relaxation, which is present at the end of the esophagus (the last 3-4 cm), is called the lower esophageal sphincter (LES). The stomach The stomach is the most dilated part of the gastrointestinal tract and is situated between the end of the esophagus and the beginning of the small intestine. The shape and ----1 Dense body merni bodies