lecture 15

Question 1

what is the GI tract and what can it do?

Answer 1

• Vast body surface area exposed to
  external environment
• Sees food as well as potentially toxic
  substances/infectious agents & has
  unique mechanisms to deal with this
• Muscular sphincters & valves partially
  segregate function within the tube

Question 2

How does the GI tract use its mechanisms to deal with potentially toxic substances.

Answer 2

• Sense & expel noxious substances (vomit,
  diarrhea)
• Specialized populations of T cells localized
  to the intestinal mucosa (e.g. Peyer’s
  patches)

Question 3

How long is the GI tract and how is this possible?

Answer 3

28 ft long and it is folded extensively in the abdominal cavity

Question 4

What is the luminal surface area of the GI tract and why?

Answer 4

approx 200-400 m^2 due to many villi/microvilli

Question 5

What is the timing of ingesting meals?

Answer 5

Its highly variable, around 30-80 hours. approx 5-8 hours in stomach and small intestine, and the remainder of the time in the colon

Question 6

What does gut microbiome do in the GI tract?

Answer 6

Gut microbiome (bacteria, etc.) protects against pathogenic microbes that enter/reside in the tract

Question 7

What does the intrinsic nervous system do regarding the GI tract?

Answer 7

controls and coordinates function such as the opening and closing of sphincters.

Question 8

What are the 4 basic processes of the GI tract?

Answer 8

1. Motility
   * Peristalsis
2. Secretion
   * Saliva, mucous
   * Antibodies (IgA)
   * Digestive enzymes
   * Bile
   * Bicarbonate
3. Digestion
4. Absorption
   * Water
   * Nutrients

Question 9

What does the cephalic phase of digestion and absorption refer to?

Answer 9

processes in the mouth

Question 10

Where does chemical and mechanical digestion begin?

Answer 10

Begins in the mouth

Question 11

What is the mechanical thing that the mouth does?

Answer 11

Chewing (mastication)

Question 12

What do secretions in the mouth do and how does this happen?

Answer 12

Secretions are in response to sensory stimuli (sight, smell, taste) and they prepare GI tract for food processing

Question 13

What is salivary secretion under control by

Answer 13

Under autonomic control

Question 14

What is salivary secretion stimulated by?

Answer 14

Stimulated by sympathetic & parasympathetic nervous systems

Question 15

What does salivary secretion do?

Answer 15

• Softens & lubricates food

Question 16

What does salivary secretion provide?

Answer 16

Provides enzymes: amylase & some lipase (no protein digestion)

Question 17

What does the gastric phase of digestion and absorption refer to?

Answer 17

processes that occur in the stomach

Question 18

What happens in the gastric phase of digestion and absorption.

Answer 18

• Secretory cells of the gastric mucosa
• Influence of parasympathetic nervous system (i.e. rest & digest)
• Increases intestinal & gland activity
• Relaxes sphincter muscles in the GI tract
• Digestion of protein & fat, but not carbohydrate in the stomach

Question 19

What does the pancreas do?

Answer 19

Pancreas is the main contributor of digestive enzymes.

Question 20

In what form are enzymes released from the pancreas?

Answer 20

Enzymes are released from the pancreas in inactive form. ex. trypsinogen
* Activated in small intestine by
enterokinase in brush border of
duodenum e.g. trypsin for protein
digestion

Question 21

What does the gallbladder do?

Answer 21

Gallbladder stores bile produced by liver for fat digestion

Question 22

How does small intestinal mucosa promote nutrient absorption?

Answer 22

Small intestinal mucosa has villi which increases surface area to
promote nutrient absorption

Question 23

What happens regarding the small intestine upon opening of pyloric sphincter?

Answer 23

• Secretions into the lumen of the small intestine upon opening of pyloric sphincter & food (chyme) entering the upper duodenum
  1. Bicarbonate – from cells in the intestinal epithelium & in pancreatic secretions
  2. Digestive enzymes – from the pancreas
  3. Bile acids (as bile fluid) – from the liver/gallbladder

Question 24

Where are digestive enzymes anchored?

Answer 24

Digestive enzymes anchored on the luminal surface of small intestine epithelial cells
1. Disaccharidases
2. Amino peptidases