Intro to Functions of Alimentary Tract

Question 1

What is the gastrointestinal tract?

Answer 1

The main organs of the digestive system form the gastrointestinal (GI) tract to create an open tube that runs from the mouth to the anus

Question 2

What passes through the GI tract?

Answer 2

Everything we eat is processed through the GI tract

Question 3

What is the role of the digestive system?

Answer 3

The digestive system:

• prepares ingested nutrients for digestion & absorption
• protects against consumed micro organisms and toxins

Question 4

What processes occur to ensure the functions of the digestive system are carried out?

Answer 4

• ingestion
• digestion
• absorption
• elimination

Question 5

What do the processes of the GI tract depend upon?

Answer 5

The processes occurring in the GI tract depend upon the motility / movement of the GI tract and the digestive juices & enzymes secretions

Question 6

What are the functions of the digestive tract?

Answer 6

Accommodation & Storage
Mechanical & enzymatic breakdown
Slow delivery of chyme to duodenum

Question 7

What does the pancreas secrete?

Answer 7

a bicarbonate rich solution

Question 8

How does the stomach accommodate storage during digestion?

Answer 8

Food stored during the first stage of digestion may remain in the stomach for ~1 hr unmixed - acts as a reservoir

Question 9

Explain how the fundus is adapted to aid storage of food in the stomach?

Answer 9

The fundus and body of the stomach have thinner muscle tone which relax to allow a larger volume (~1.5 L) of food storage

Question 10

What is the role of vagal reflex in storage of food?

Answer 10

Vagal reflex inhibits smooth muscle tone - mechanoceptors cause fundic relaxation via VIP/NO

Question 11

What is the role of the antrum in storing food in the stomach?

Answer 11

The antral region mixes / grinds food with gastric secretions enabling digestion

Question 12

What is the role of the colon / rectum?

Answer 12

Storage of indigestive residues and faecal matter

Question 13

Where are gastric secretions stored?

Answer 13

The stomach stores 2-3 Litres of gastric juices every 24 hrs

Question 14

What does gastric juice consist of?

Answer 14

mucus
pepsinogen
intrinsic factor
lipase

Question 15

What is the role of gastric secretions?

Answer 15

Aid in digestion and food absorption

Question 16

Where is mucus secreted from?

Answer 16

Goblet cells and mucus neck cells

Question 17

What is the role of mucus?

Answer 17

Acts as a lubricant by acting as a barrier to protect the stomach and colon esp. from gastric acid
- prevents trauma

Question 18

What is the role of lipase?

Answer 18

converts TG → FA + glycerol

Question 19

Where is pepsin scereted from?

Answer 19

Secreted by chief cells / peptic cells as the precursor pespinogen

Question 20

What is the role of pepsin?

Answer 20

protein digestion

Question 21

Where is HCl secreted from?

Answer 21

Parietal cells

Question 22

What is the role of HCl?

Answer 22

important in defence and converts pepsinogen →pepsin

Question 23

Which cells secrete Intrinsic factor (IF)?

Answer 23

parietal cells

Question 24

What is the role of Intrinsic Factor?

Answer 24

aids vitamin B12 absorption

Question 25

Describe features of paracrine secretions

Answer 25

local hormones secreted from cells in mucosa Chemicals act locally on adjacent cells via interstitial fluid

Question 26

Give an example of a paracrine secretion

Answer 26

somatostatin - inhibits gastrin release in stomach

Question 27

What is the role of gastrin?

Answer 27

Controls parietal cell acid secretion

Question 28

Where are exocrine secretions from?

Answer 28

Salivary glands Gastric glands Liver Pancreas

Question 29

What exocrine secretions are produced in the salivary glands?

Answer 29

Mucus; lubrication for mastication and speech | Lipase

Question 30

What does the exocrine pancreas secrete?

Answer 30

Bicarbonate ions | Enzymes; amylase, lipase, carboxypeptidase

Question 31

What exocrine secretions are produced by the gastric glands?

Answer 31

HCl, pepsin, mucus

Question 32

What does the exocrine liver secrete?

Answer 32

bile salts and bile acids

Question 33

What is the role of exocrine secretions?

Answer 33

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

Question 34

What is carboxypeptidase?

Answer 34

Protease enzyme that hydrolyses a peptide bond at the carboxy-terminal (C-terminal) end of a peptide/protein

Question 35

What is amylase?

Answer 35

hydrolyses starch -> sugars

Question 36

What are endocrine secretions?

Answer 36

Hormones synthesised by ductless glands

Question 37

How do endocrine secretions achieve their effect?

Answer 37

Enter bloodstream to travel to their target tissue(s) where they bind to specific receptors to elicit their effects

Question 38

Name endocrine secretions and where they're secreted

Answer 38

Gastrin - stomach (G cells in antrum) Secretin - duodenal mucosa pancreozymin-CCK - duodenal mucosa Insulin - pancreatic beta Cell

Question 39

How is food made of use to the body?

Answer 39

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 40

Where does absorption of food occur?

Answer 40

absorption occurs mainly in small intestine

Question 41

Where is fluid mostly absorbed?

Answer 41

Absorption of fluid occurs in the small intestine and colon | - colon absorbs 90% water

Question 42

Where is digested food predominantly stored before excretion?

Answer 42

proximal stomach and descending colon

Question 43

How does motility of food occur in the GI tract?

Answer 43

Movement of muscular wall (mostly smooth muscle except extreme ends of the upper oesophagus / rectum)

Question 44

What is the significance of gut motility?

Answer 44

Allows: - movement from one region to another; mass of evacuation - Mechanical degradation (gastric antrum) - Mixing lumen contents e.g. small intestine - Transport of nutrients, water and of urea and electrolytes - Digestion and absorption

Question 45

How are drugs and metabolism excreted?

Answer 45

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 via the faeces

Question 46

What is the significance of the gut epithelium in defence?

Answer 46

If there is a breach in the barrier 'toxins' will enter the blood it's largest lympho-epithelial organ and mucosal surface Is exposed to the heaviest burden of environmental antigens

Question 47

How is the gut protected from the external environment?

Answer 47

- Sight, smell and taste alerts us to harmful food substances - vomit reflex - HCl in stomach kills bacteria - Mucus secretions - Natural bacteria flora prevents harmful bacteria colonisation - Lymphoid tissue aggregation; react to food borne antigens - Peyer's patches in lamina propria

Question 48

Where are the metabolic functions of the gut carried out?

Answer 48

In the liver - involved in carbohydrate, nitrogen and lipoprotein metabolism - produces bile and excretes bilirubin

Question 49

Outline the functions and mechanisms of the GI tract

Answer 49

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