Human Anatomy and Physiology Transport and mixing of food in the alimentary tract

Food reception Mastication Teeth Incisors, canines (55 lb, cutting and tearing) Premolars and molars (200 lb, grinding) Grind and breakdown food Stimulate saliva production Mix food with saliva

Process of deglutition

Esophagus Upper sphincter Ensures breathing commences Lower sphincter Prevents acid reflux (heartburn) Food passage takes about 9 seconds

Stomach Anatomy Cardiac sphincter

Stomach Motor functions Receptive relaxation Food storage (1.5 L) Gastric peristalsis Slow emptying

Gastric motility Slow waves and spike potentials

Regulation of gastric motility 1. Stomach i. Volume of chyme Smooth muscle excitability ii. Presence of protein Gastrin release from antral mucosa

Regulation of gastric motility 2. Duodenum i. Distention of the duodenum ( ) ii. Acidity of duodenal chyme ( ) iii. Presence of protein, sugars and fats cause hormones to be released from duodenal mucosa (gastric inhibitory peptide GIP, secretin)

Small intestine Mixing and propulsive contractions combined (segmentation)

Control of motility in small intestine Neural: slow waves Hormonal Up-regulatory: gastrin, CCK, secretin, insulin Down-regulatory: glucagon

Ileocecal valve Function Prevent backward flow Operation Opens upon pressure differences

Large Intestine Motility Rhythmical: every 30 minutes Mass movement: coincides with ileum contraction (follows a meal)

Large Intestine anatomy Tenia coli Haustra alter their location

Defecation Contraction of abdominal wall musculature and lowering of diaphragm places pressure on colon wall. External and internal sphincters open (nervous system)