0206 - Functions of the GI Tract

Question 1

What are the functions of the mouth?

Answer 1

Chewing (Mastication)

Voluntary movement, breaking food and mixing with saliva to form a bolus. Salivary amylase works to begin digestion.

Question 2

What are the three phases of swallowing?

Answer 2

Oral phase (voluntary, tongue moves up, pushing bolus back)
Pharyngeal phase (involuntary - food moves to oesophagus and UOS and LOS relax)
Oesophageal phase (involuntary, food moves to stomach, LES closes last)

Question 3

Outline the pharyngeal phase of swallowing

Answer 3

Reflex sequence. Food enters oropharynx, soft palate closes off the nasopharynx, the larynx moves upwards and is closed off by epiglottis, the UOS relaxes, and oesophageal peristalsis begins.

Question 4

Outline the Oesophageal phase of swallowing.

Answer 4

Involuntary sequence controlled by swallowing centre. Two forms of peristalsis - primary peristalsis that starts below UOS and is caused by act of swallowing. If unsuccessful, secondary peristalsis is triggered by distension to keep the food moving.

Question 5

What are the functions of the stomach?

Answer 5

Accommodation of food (largely in fundus)
Physical digestion (mixing, grinding, and peristalsis)
Secretion of gastric juice containing HCl and enzymes
Chemical digestion via Pepsin (protein-> peptides) and Gastric lipase (break down triglycerides)
Endocrine - Gastrin (stimulates acid secretion) Somatostatin (inhibits acid secretion).Stomach accommodation

Question 6

What are the three forms of small intestine digestion?

Answer 6

3 areas - Pancreatic juices, bile, and membrane digestion

Question 7

Briefly outline pancreatic juice digestion

Answer 7

In small intestine
Pancreatic amylases digest polysaccharide carbohydrates into oligosaccharides.
Trypsin and chymotrypsin hydrolize proteins into oligopeptides
Pancreatic lipases break down lipids (TAGs) into fatty acids and monoglycerides.

Question 8

Briefly outline bile digestion

Answer 8

Bile salts assist in emulsification (into micelles) and absorption of lipids, cholesterol and phospholipids.

Question 9

Briefly outline small intestine membrane digestion

Answer 9

Brush border enzymes contain oligosaccharidases to digest oligosaccharides into monosaccharides, and peptidases to digest oligopeptides into amino acids.

Question 10

Briefly outline small intestine absorption

Answer 10

Monosaccharides and AAs are absorbed through specific membrane transporters, whereas FAs, cholesterol and lipids diffuse through the cell.

Question 11

Outline the balance of fluid in the GI tract

Answer 11

2L of liquid ingested, plus 1L saliva, 2L gastric juice, 1L bile, 2L pancreatic juice and 1L intestinal juice secreted per day =9L/day ingested or secreted
SI absorbs 8L and LI absorbs 0.9L, leaving 8.9L absorbed and 0.1L excreted in faeces per day.

Question 12

What are the small intestine endocrine hormones? What do they do?

Answer 12

Secretin stimulates pancreas secretion.

Cholecystokinin contracts the galbladder.

Question 13

What is the small intestine’s immune function?

Answer 13

Lymphocytes are diffused in mucosa and aggregated in Peyer’s patches. They protect against bacteria, viruses and protozoa, and permit tolerance.

Question 14

What are the functions of the large intestine?

Answer 14

Proximal colon - absorb fluids and electrolytes.
Distal colon - store colonic contents
Rectum - Defecation.

Question 15

What is a major complication of a low fibre diet?

Answer 15

Diverticulosis - diverticula form in large intestine, essentially as outpouchings.

Question 16

What are the two forms of motility in the colon?

Answer 16

Segmentation

Mass peristalsis - 1-3/day - push fecal matter long-distance. Haustra disappear with the contractions.

Question 17

What are the three requirements for normal GIT motility?

Answer 17

1. Smooth muscle in gut wall.
2. ENS (control system)
3. Communications - CNS, Sympathetic/parasymp, hormones.

Question 18

What are the seven major functions of the liver?

Answer 18

Over 200 functions in seven major areas:
Carbohydrate metabolism
Lipid Metabolism
Protein Metabolism
Detoxification
Bile secretion
Defence
Storage

Question 19

Briefly outline the liver’s role in carbohydrate metabolism.

Answer 19

Maintain normal blood glucose level through glycogen synthesis, glycogenolysis, and gluconeogenesis.

Question 20

Briefly outline the liver’s role in lipid metabolism

Answer 20

Synthesise cholesterol, fatty acids, and phospholipids. Synthesise VLDL to transport triglycerides and cholesterol.

Question 21

Briefly outline the liver’s role in protein metabolism.

Answer 21

Synthesise over 30 proteins, incl albumin, lipoproteins, and coagulation factors
Uptake and metabolise amino acids
Synthesise glutathione for detoxification and protection against oxidative stress
Detoxify ammonia by forming urea.

Question 22

Briefly outline the liver’s role in detoxifying bilirubin.

Answer 22

Macrophage releases unconjugated bilirubin from Hb into bloodstream where it conjugates with albumin (conjugated = water soluble). It is released from the albumin and enters hepatocytes, which conjugate it with glucuronic acid, and release it in bile where it enters the GIT and feces.

Question 23

Briefly outline the liver’s role in bile production and secretion.
(Including role of bile)

Answer 23

Synthesise bile salts from cholesterol. Bile helps lipid digestion and absorbtion of lipid-soluble vitamins (A, D, E, K). The liver also excretes waste products through bile.

Question 24

Briefly outline the liver’s role in defence of the body.

Answer 24

Kupffer’s cells (macrophages) in the liver filter the blood, removing bacteria, endotoxins, parasites, and aging red blood cells.

Question 25

Briefly outline the liver’s role as a storage organ.

Answer 25

Liver stores lipid-soluble vitamins (A, D, E, K), copper, and iron.

Question 26

What does the liver function test detect?

Answer 26

Detoxification, hepatic cell damage, bile duct cell damage, synthetic function (i.e. protein synthesis), and inflammation.

Question 27

Summarise the functions of the GIT.

Answer 27

Ingestion - Eating/Drinking
Secretion - Produce and release fluids by epithelial cells and accessory organs
Digestion - Mechanical and chemical
Motility - Contractions mix food and juices, move along GIT
Absorption - Uptake small molecules from GIT to blood or lymph
Defecation - Pass faeces - mix of indigestible good, bacteria, and shed cells.
Liver functions.