Introductions to the functions and control of the alimentary tract

Question 1

What are the 3 digestive functions of the stomach?

Answer 1

1. Accommodation & storage
2. Mechanical and enzymatic breakdown
3. Slow delivery of chyme to duodenum

Question 2

What is the purpose of bile salts?

Answer 2

The salts in bile emulsify fat (break fat into small droplets, like a detergent) so that digestive enzymes (e.g. pancreatic lipase) can act on fat more effectively.

Question 3

What is the purpose of the stomach and how long can food remain in the stomach?

Answer 3

Stomach: Food stored here during the first stage of digestion; may remain there for ~1hr unmixed (acts as a reservoir)

Question 4

What is the purpose of the antral region of the stomach Antral region

Answer 4

It mixes/grinds food with gastric secretions → Digestion

Question 5

What is the purpose of the colon/ rectum?

Answer 5

Storage of indigestive residues and faecal matter

Question 6

The stomach stores 2-3 litres of gastric juice/24hr (mucus, pepsinogen, intrinsic factor, lipase) which help in digestion and absorption of food.

What is the purpose of mucus in the stomach?

Answer 6

Mucus (secreted by goblet cells and mucus neck cells) – acts as a lubricant by acting as a barrier that protects the stomach and colon especially from gastric acid (prevents trauma)

Question 7

What does lipase do in the stomach?

Answer 7

Lipase – converts triglycerides to fatty acids and glycerol

Question 8

What does pepsin do in the stomach?

Answer 8

Pepsin (secreted by chief cells or peptic cells as pepsinogen): protein digestion

Question 9

What cells are HCl secreted from?

What does HCl do in the stomach?

Answer 9

HCl (secreted by parietal cells) – important in defence

Question 10

What is the purpose of intrinsic factors in the stomach?

Answer 10

Intrinsic (secreted by parietal cells) – for vitamin B12 absorption

Question 11

What are paracrine secretions?

Where are they secreted from?

How are they different from local hormones?

Give an example

Answer 11

• Often called “local hormones”
• Secreted from cells in the mucosa, but unlike hormones, the chemical acts locally on adjacent cells via the interstitial fluid

Somatostatin inhibits gastrin release in the stomach

Question 12

What do salivary glands secrete? (2)

Answer 12

mucus (lubrication for mastication and speech); lipase

Question 13

What do gastric glands secrete? (3)

Answer 13

Hydrochloric acid, pepsin, mucus

Question 14

What does the pancreas secrete?

Answer 14

bicarbonate ions, enzymes (e.g. amylase, lipase, carboxypeptidase)

Question 15

What does the liver secrete?

Answer 15

Liver: bile salts, bile acids

Secretions from numerous glands with ducts enter the lumen of the gut and are involved in digestion, lubrication and protection

Question 16

What do carboxypeptidase is a protease enzyme do?

Answer 16

hydrolyses (cleaves) a peptide bond at the carboxy-terminal (C-terminal) end of a protein or peptide

Question 17

What does Amylase hydrolase?

Answer 17

Amylase hydrolyses starch into sugars

Question 18

Salivary glands, gastric, pancreas, liver and carboxypeptidase and amylase are all a type of ______ secretion?

Answer 18

Exocrine

Question 19

Where are gastrin cells located?

Answer 19

stomach (G-cells in antrum)

Question 20

Where is Secretin located?

Answer 20

duodenal mucosa

Question 21

Where are pancreozymin-cholecystokinin located?

Answer 21

duodenal mucosa

Question 22

Where is B-cells located?

Answer 22

pancreas (beta-cells)

Question 23

What the difference between exocrine and endocrine secretions?

Answer 23

Endocrine glands release chemical substances directly into the bloodstream or tissues of the body. The chemical substances released by the endocrine glands are known as hormones. Exocrine glands release chemical substances through ducts to outside the body or onto another surface within the body.9

Question 24

In order for the body to use the food where must nutrients be transported to and from?

Answer 24

• For food to be of use to the body, the nutrients resulting from digestion must be transported across the intestinal epithelium into the blood (e.g. glucose, amino acids) or lymph via lacteals (fats/lipids)

Question 25

Where does the absorption of solids and fluids occur?

Answer 25

Absorption occurs mainly in the small intestine

Absorption of fluid occurs in the small intestine and colon

Question 26

How much water does the colon absorb?

Answer 26

Colon absorbs 90% of water, reducing the volume to 200ml of semi-solid faecal matter

Question 27

Where does motility occur?

Answer 27

Storage, e.g. proximal stomach, descending colon

Question 28

What does the movements of the muscular wall (mostly smooth muscle except extreme ends of the upper oesophagus/rectum) allow:

Answer 28

1. Movement from one region to another (law of gut); mass evacuation
2. Mechanical degradation, e.g. gastric antrum
3. Mixing lumen contents, e.g. small intestine
4. Transport of nutrients, water and of urea and electrolytes
5. Digestion and absorption

Question 29

Give some examples of bodily excretion

Answer 29

• Drugs and some products of normal metabolism may leave the body in:
Saliva
Bile
Faeces
(Vomit)
• Indigestible food residues (e.g. tomato skin) leave the body in the faeces

Question 30

The gut is unsterile as it is open to external environment

Give some examples of how the gut helps to protect itself

Answer 30

1. Sight, smell and taste alerts us to harmful food substances
2. Vomit reflex
3. Acid in stomach (HCl) kills most harmful bacteria
4. Mucus secretions
5. Natural bacterial flora prevents colonisation of harmful bacteria
6. Aggregation of lymphoid tissue (e.g. Peyer’s patches) able to mount a response to food-borne antigens - analyse and respond to pathogenic microbes
7. Peyer’s patches: located in the lamina propria layer of the mucosa and extending into the submucosa of the ileum

Question 31

Describe the metabolic functions of the liver

Answer 31

• The liver is a major metabolic organ in the abdominal cavity and weighs about 1.3 Kg in an adult.
• It is involved in carbohydrate, nitrogen and lipoprotein metabolism as well as the production of bile and excretion of bilirubin

Question 32

Give the list of functions and mechanisms of the gut?

Answer 32

1. Storage
2. Paracrine secretions
3. Exocrine secretions
4. Endocrine secretion
5. Absorption
6. Motility/transport
7. Excretion/transport
8. Defence
9. Metabolism

Question 33

What factors and mechanisms are involved with storage and digestion?

Answer 33

Mastification, swallowing, enzymatic digestion absorption

Question 34

What factors and mechanisms are involved with motility?

Answer 34

Peristalsis, mass movement, Ach, motilin, NO and VIP

Question 35

What factors and mechanisms are involved with defence?

Answer 35

Smell, sight, taste, gastric acid, vomit reflex, mucus, immune system, IgA

Question 36

What factors and mechanisms are involved with exocrine secretion?

Answer 36

Saliva secretion, mucus secretion, HCl, pepsin, HCO3, amylase, lipase, bile salts,

Question 37

What factors and mechanisms are involved with endocrine secretion? (3)

Answer 37

Insulin, gastrin and secretin

Question 38

What factors and mechanisms are involved with paracrine secretion?

Answer 38

Somatostatin

Question 39

What factors and mechanisms are involved with excretion

Answer 39

defecation

Question 40

Describe the integrated response to a meal

Answer 40

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