Lecture 48 – Gastrointestinal physiological: control of digestion

Question 1

Name the three phases of control of gastric secretion and motility and identify the stimuli related to each phase.

Answer 1

o Cephalic = anticipation of eating
o Gastric = bolus of food entering stomach
o Intestinal = regulation of release of chyme from stomach to small intestine

Question 1

Explain how gastric secretions and stomach motility are controlled.

Answer 1

o Involves neural signals, hormonal regulation and local feedback mechanisms

Question 2

List the major enzymes, or enzyme groups, involved in the chemical digestion of carbohydrates, lipids (fats) and proteins.

Answer 2

o Carbohydrates
 Salivary amylase (mouth), pancreatic amylase (duodenum), maltase/sucrase/lactase (brush boarder)
o Proteins
 HCl/pepsin (stomach), trypsin/chymotrypsin/carboxypeptidase (pancreas), aminopeptidase/dipeptidase (brush boarder)
o Lipids
 Lingual lipase (mouth), bile/pancreatic lipase (small intestine)

Question 3

Identify and describe structural modifications of the wall of the small intestine that enhance digestion and absorption.

Answer 3

o Large surface area via being lined with villi
o Inward folding villi and the microvilli, improve absorption by increasing the surface are absorption occurs over
o Digestion occurs at cells surfaces on the apical surface of GI epithelial cells sit a set of enzymes embedded into the membrane.
o These enzymes engage in the final chemical digestive process

Question 4

Describe the defecation reflex.

Answer 4

o Stretch of rectum wall
o Spinal cord mediated parasympathetic nervous system reflex
o Walls of sigmoid colon and rectum contract
o Internal anal sphincter relaxes
o Faces pushed into anal canal
o External anal sphincter (skeletal muscle) under voluntary control