Digestion and Intestinal Absorption (part 1)

Question 1

state the 4 primary functions of the digestive system

Answer 1

1. digestion
2. absorption
3. secretion
4. mobility

Question 2

state the main hierarchical structure of the gastrointestinal tract (6 main structures)

Answer 2

mouth –> pharynx –> oesophagus –> stomach –> small intestine –> large intestine

Question 3

state the 4 accessory organs in the gastrointestinal tract

Answer 3

1. salivary glands
2. liver
3. gallbladder
4. exocrine pancreas

Question 4

state the 4 main structures (inside –> out) of the gastrointestinal wall

Answer 4

1. mucosa
2. sub-mucosa
3. muscularis externa
4. serosa

Question 5

state the 2 enteric nervous system structures within the gastrointestinal wall

Answer 5

1. sub-mucosal plexus

2. myenteric plexus

Question 6

state, and define, the 3 structures in the ‘mucosa’ (inner layer of the gastrointestinal wall)

Answer 6

1. epithelium - contains both endocrine + exocrine cells
2. lamina propria - loose connective tissue
3. muscularis mucosa - layer of smooth muscle

Question 7

state, and define, the 2 structures in the ‘sub-mucosa’ (lateral to the mucosa in the gastrointestinal wall)

Answer 7

1. blood + lymphatic vessels - penetrate layers above and below as well
2. sub-mucosal plexus - a network of neurones for control of muscular activity

Question 8

state, and define, the 3 structures in the ‘muscularis externa’ (lateral to the sub-mucosa in the gastrointestinal wall)

Answer 8

1. circular muscle - contraction produces narrowing of lumen
2. myenteric plexus - innervated via autonomic NS, also connected to the sub-mucosal plexus
3. longitudinal muscle - contraction shortens the lumen

Question 9

state, and define, the function of the ‘serosa’ (outer layer of the gastrointestinal wall) - 2 points

Answer 9

1. connective tissue surrounding the outer surface of the tract
2. sheets of connective tissue connect serosa to the abdominal wall to hold the GI tract in place

Question 10

state, and explain, what it is meant by the key term - ‘cephalic phase’ (3 facts)

Answer 10

1. brains anticipation of food (sight, smell, or thought)
2. saliva production increased - parasympathetic NS activity
3. stimulation of gastric juice + insulin secretion

Question 11

state the 4 functions of the mouth in the digestion process

Answer 11

1. mechanical breakdown of food
2. mixing of food with saliva
3. initiate chemical digestion of carbs (salivary amylase)
4. antibacterial action

Question 12

state the 4 functions of saliva in the digestion process

Answer 12

1. bicarbonate (neutralises acid)
2. mucus - lubricates and protects from abrasion
3. salivary amylase - breakdown of carbs
4. lysozymes - destroy certain bacteria (prevents tooth decay)

Question 13

state the 2 functions of salivary amylase in the digestion process

Answer 13

1. begins carb digestion

2. begins starch hydrolysis (limited - <5% starch digestion, unless chewing is prolonged)

Question 14

state the function of the following: 1)Pharynx, and 2) Oesophagus in the digestion process

Answer 14

1. Pharynx - conduction of food into oesophagus

2. Oesophagus - conduction of food into the stomach

Question 15

what does the Epiglottis do during swallowing?

Answer 15

the Epiglottis closes to prevent aspiration of food into the trachea

Question 16

explain the role of sphincters in the process of digestion

Answer 16

sphincters at the bottom of the Pharynx and in the opening into the stomach prevent movement of air and stomach contents re-entering the oesophagus

Question 17

state, and explain, what it is meant by the key term - Peristalsis (2 points)

Answer 17

1. the movement of contents in a tube due to progressive contraction
2. this ‘wave’ compresses the lumen and forces food through

Question 18

state what it is meant by the key term - ‘secondary peristalis’

Answer 18

if a particularly large bolus does not reach the stomach, then reflexes initiate repeated waves of activity in the muscle surrounding the oesophagus

Question 19

state the 5 functions of the stomach in the digestion and absorption process

Answer 19

1. mechanical breakdown of food (and churning - chyme)
2. secretion of acid (HCl) - kills bacteria
3. pepsin secreted as ‘pepsinogen’ - begins protein digestion
4. gastric lipase
5. storage

Question 20

state the 4 functions of the small intestine in the digestion and absorption process

Answer 20

1. chemical digestion of all nutrients (pancreatic and brush border enzymes)
2. absorption of digestive end products, water, ions and vitamins
3. hormone secretion
4. secretion of bicarbonate rich fluid

Question 21

state the 3 functions of the ‘colon’ (large intestine) in the digestion and absorption process

Answer 21

1. absorption of ions and water
2. transformation of ‘chyme’ into faeces
3. storage of faeces

Question 22

state what it is meant by the key term - chyme

Answer 22

the pulpy acidic fluid which passes from the stomach to the small intestine, consisting of gastric juices and partly digested food

Question 23

state the role of the rectum in the digestion and absorption process

Answer 23

storage of faeces

Question 24

what is needed for Vitamin B12 absorption?

Answer 24

gastric intrinsic factor (GIF)

Question 25

what activates pepsinogen

Answer 25

pepsinogen is activated into pepsin by the stomaches acid environment

Question 26

state the two other cell types in the stomach, as well as their functions

Answer 26

1. entero-chromaffin-like cells (ECL) - release histamine | 2. D cells - secrete somatostatin

Question 27

explain the negative feedback loop of HCl secretion into the acid (3 points)

Answer 27

1. ACh (enteric nerve), histamine and Gastrin have a positive effect on production 2. HCl secretion has a positive effect on somatostatin secretion 3. somatostatin inhibits action of HCl secretion, histamine secretion, and gastrin secretion

Question 28

where is gastrin secreted by

Answer 28

G cells release gastrin

Question 29

explain what it is meant by potentiation (in consideration of HCl secretion in the stomach)

Answer 29

activation of 3 substances combined is greater than the sum of the individual effects

Question 30

state the 4 stimuli which initiate the 'Gastric Phase' (in the stomach)

Answer 30

1. stomach distension 2. acidity 3. amino acids 4. peptides

Question 31

state the location in the gastrointestinal wall, and the function, of the - epithelium

Answer 31

mucosa, contains both exocrine and endocrine cells

Question 32

state the location in the gastrointestinal wall, and the function, of the - lamina propria

Answer 32

mucosa, loose connective tissue (between the epithelium and the muscularis mucosa)

Question 33

state the location in the gastrointestinal wall, and the function, of the - muscularis mucosa

Answer 33

mucosa, layer of smooth muscle

Question 34

state the location in the gastrointestinal wall, and the function, of the - blood and lymphatic vessels

Answer 34

sub-mucosa, penetrate layers above and below as well

Question 35

state the location in the gastrointestinal wall, and the function, of the - sub-mucosal plexus

Answer 35

sub-mucosa, a network of neurones for control of muscular activity

Question 36

state the location in the gastrointestinal wall, and the function, of the - circular muscle

Answer 36

muscularis externa, contraction produces narrowing of the lumen

Question 37

state the location in the gastrointestinal wall, and the function, of the - myenteric plexus

Answer 37

muscularis externa, innervated by the autonomic NS, also connected to the sub-mucosal plexus

Question 38

state the location in the gastrointestinal wall, and the function, of the - longitudinal muscle

Answer 38

muscularis externa, contraction produces shortening of the lumen

Question 39

state what it is meant by the key term - churning

Answer 39

The stomach lining contains muscles which physically squeeze and mix the food with strong digestive juices