Tri B - Gastrointestinal System

Question 1

Name the parts of the digestive system

Answer 1

Mouth & pharynx
Oesophagus
Stomach
Small and large intestine
Accessory organs -
Teeth, tongue and salivary glands
Liver, gallbladder pancreas

Question 2

What is the function of the GI tract?

Answer 2

Breakdown and absorption of food
Mechanical digestion = chewing swallowing
Chemical digestion = large molecules –> small molecules

Question 3

Describe the process of absorption

Answer 3

Products of digestion
–> absorbed by epithelial cells in wall of gut
–> nutrients transferred to blood vessels
–> nutrients delivered to tissues

Question 4

Describe the wall of the GI tract

Answer 4

Mucosa - inner layer of epithelium
Submucosa - connective tissue, vessels, glands
Muscularis - Smooth muscle layer

Question 5

Describe the mucosa

Answer 5

Absorptive & secretory function
Lamina propria –> connective tissue, vessels, supportive
Muscularis mucosae - inner muscular layer

Question 6

Describe the muscularis

Answer 6

Inner circular layer –> contraction narrows gut
–> outer longitudinal layer
contraction shortens the gut

Question 7

What is the function of the mouth?

Answer 7

Food ground by teeth –> mastication
Food mixed with saliva
Tasting of food

Question 8

What is the structure and function of the oesophagus?

Answer 8

Collapsible muscular tube
Transports food to stomach
Secretes mucus
Food propelled by peristalsis

Question 9

What is the function of the lower oesophageal sphincter?

Answer 9

Controls entrance to stomach
Ring of smooth muscle
Prevents acid reflux

Question 10

Describe peristalsis

Answer 10

Contraction and relaxation
Waves of contraction propels food

Question 11

What is the function of the stomach?

Answer 11

Stores food
Mechanical and chemical digestion
Peristalsis

Question 12

Describe the anatomy of the stomach

Answer 12

Cardia - mucus glands
Fundus and body - secretes HCl and enzymes
Pylorus - pyloric sphincter controls exit

Question 13

Describe the cells of the stomach

Answer 13

Mucus surface & neck cells - secrete mucus
Parietal cells - secrete HCl - acidic environment
Chief cells - secrete pepsinogen & gastric lipase
Entereo endocrine cells - secrete gastrin

Question 14

What is the function of the liver?

Answer 14

Metabolism of: Carbohydrates, lipids, proteins
Bile synthesis - extraction of bilirubin
Vitamin storage and activation of vitamin D

Question 15

What is the function of the pancreas?

Answer 15

Secretes pancreatic juice –> buffers acidic chyme
Contains digestive enzymes: Pancreatic amylase
- Trypsin chymotrypsin
- Pancreatic lipase
Release of enzymes controlled by hormones; secretin, cholecystokinin

Question 16

Describe the biliary system

Answer 16

Bile produced in liver, stored in gallbladder
Consists of water, bile salts, bile pigments, bilirubin
Control is hormonal - CCK
Stimulus is chyme in duodenum

Question 17

What is the function of the small intestine?

Answer 17

Digestion and absorption of products and water

Question 18

Describe the structure of the small intestine

Answer 18

Duodenum - mixes chyme with pancreatic and liver secretions
Jejunum - most digestion and absorption
Ileum - absorbs vitamin b12
Large surface area
1. long - 4.5-6.5m - circular folds
2. Villi - increase absorption
3. Microvilli - folds increase surface area

Question 19

Describe the large intestine

Answer 19

Consists of: caecum, colon, rectum, anus
Completes food and water absorption
Forms and expels faeces
Presence of bacteria

Question 20

Describe the journey of the products of digestion

Answer 20

Products of digestion
–> epithelial cells
–> blood or lymph
–> tissues

Question 21

Describe the digestion of carbohydrates

Answer 21

Carbohydrates
–> digestion
–> polysaccharides
–> di- and tri- saccharides
–> monosaccharides (glucose, fructose, galactose)

Question 22

Describe absorption of carbohydrates

Answer 22

Glucose and galactose absorbed by secondary active transport
Co-transported with sodium ions
Both have to bind to transport protein
Moves down concentration gradient

Question 23

Describe the digestion of proteins

Answer 23

Proteins
–> peptides (by pepsin)
–>Amino acids (by pancreatic enzymes)

Question 24

Describe absorption of proteins

Answer 24

Amino acids absorbed by secondary active transport with sodium or hydrogen ions
Some will share same transport systems

Question 25

Describe the digestion of lipids

Answer 25

Triglycerides (fats)
–> monoglycerides and 2 fatty acids

Question 26

Describe lipids

Answer 26

Hydrophobic molecules
Form large droplets with small surface area
Bile salts can speed up digestion and absorption

Question 27

Describe the effect of bile salts on lipids

Answer 27

They emulsify fats to form smaller droplets
Products = 1. Short chain fatty acids
2. Long chain fatty acids
3. Monoglycerides
2 and 3 bind with bile salts forming micelles
Bile salts are amphipathic
They surround 2 and 3, keeping them soluble

Question 28

Describe micelles

Answer 28

Move to fill brush border of intestinal epithelium
–> Long chain fatty acids and monoglycerides diffuse out

Question 29

Describe what happens to fatty acids when they are inside the cell

Answer 29

Reform into triglycerides
Combine with cholesterol and proteins to form chylomicrons
Chylomicrons expelled from cell by exocytosis

Question 30

Describe lacteals

Answer 30

Lymphatic vessels associated with villus, drain back into blood
Absorb nutrients from gut
–> used as fuel