digestion and peristalsis.

anatomy and anterograde background biology body bolus choke contraction deglutition design diagram difficulty digestion digestive distally dysphagia esophagus function gastric gastrointestinal graphic healthy illustration inner intestine large longitudinal medical medicine movement muscle oesophagus organ peristalsis peristaltic pharynx problems radially relaxation response science stomach swallow swallowing symmetrical throat tongue tract tube wave wavelike