Digestion and Absorption

Question 1

What are the layers of the gut?

Answer 1

Serosa (connective tissue, longitudinal smooth muscle)
Muscularis externa (myenteric plexus, circular smooth muscle)
Submucosa (submucosa, lamina propria, epthelium)

Question 2

What does the enteric nervous system influence?

Answer 2

All digestive processes

Question 3

Myentric plexus

Answer 3

Exerts control primarily over GI motility

Question 4

Submucous plexus

Answer 4

Sensing the environment within the lumen
Regulating GI blood flow
Controlling epithelial cell function

Question 5

What glands are in the mouth and what do they secrete?

Answer 5

Salivary glands -> saliva

Question 6

What glands are in the stomach and what do they secrete?

Answer 6

Oxyntic or gastric and pyloric glands -> gastric juices

Question 7

What glands are in the pancreas and what do they secrete?

Answer 7

Acini and duct system -> pancreatic juices

Question 8

What glands are in the liver and what do they secrete?

Answer 8

Hepatocytes, bile canaliculi and ducts gallbladder -> bile

Question 9

What is the main function of the mouth, pharynx and salivary glands?

Answer 9

Starts digestion by physically chewing the food and breaking it down with saliva

Question 10

Saliva functions

Answer 10

Maintaining healthy oral tissues. Contains thiocyanate ions (bactericidal), proteolytic enzymes (lysozyme) and antibodies
Starts the digestion of carbohydrates
Contributes to the digestion of fats
Dissolves components contributing to taste
By its absence provides urge to drink
Provides mucus
Keeps mouth oist for speech, oral comfort, chewing and swallowing

Question 11

Salivary amylase

Answer 11

Produced by the acini cells
pH optimum 6.9 (4-11)
Activity may continue for 15-30 min in mouth and stomach
Breaks down alpha 1,4 glucosidic bonds:
starch, glycogen -> maltose, maltotriose

Question 12

Salivary lipase

Answer 12

Able to work without the bile at low pH
Active also in stomach
Converts triglycerides to long chain fatty acids
MAy act as a signal to start digestion
May be important in babies and pancreatic and bile insuffieciency

Question 13

Main functions of the stomach

Answer 13

Storage of food
Churn and mix food with gastric secretions: digestion
Exocrine secretions: gastric juice
Paracrine and endocrine secretions: histamine and gatsrin
Slow emptying of digestive contents into small intestine

Question 14

What are the main functions of the pancreas?

Answer 14

Exocrine: panvreatic juices (enzymes) and alkali secretions
Endocrine: secretion of insulin and glucagon

Question 15

Liver main (digestion) related functions

Answer 15

Production and secretion of bile acid and alkaline fluid
Degradation and conjugation of waste metabolic products
Detoxification
Regulation of nutrient metabolism

Question 16

Bile

Answer 16

Synthesised in the hepatocyte
Stored in the gall bladder
Released into the duodenum after a meal

Question 17

What is the composition of bile?

Answer 17

Bile acids
Phospholipids
Cholesterol
Bilirubin
Electrolytes (Na+, K+, Ca2+)
Detoxified drugs and toxins

Question 18

What are the functions of bile?

Answer 18

Emulsification or detergent actin of fat particles

Help in absorption of fats by forming complexes called micelles

Question 19

Main functions of the small intestine

Answer 19

Duodenum: mixing secretions from pancreas, liver and its own with food, neutralisation of acids, further digestion, absorption
Jejunum: completing breakdown, nutrient absorption
Ileum: nutrient absorption

Question 20

Three main mechanisms for absorption

Answer 20

1. Passive absorption - diffusion
   - slow needs concentration gradient or charge gradient
2. Facilitated transport
   - slightly faster, involves membrane carrier, controllable eg fructose
3. Active transport
   - uses energy - ATP - fast uses Na+/K+ pump
   Controllable

Question 21

Protein digestion

Answer 21

Starts in stomach - pepsin
Continues in small intestine - trypsin, chymotrypsin, carboxypeptidase
Continues at brush border amino peptidase
Amino acids and peptides absorbed by active transport via 7 sodium linked carriers

Question 22

Emulsifying agents

Answer 22

fatty acids
monoglycerides
cholesterol
lecithin
protein
bile acids

Question 23

Characteristics of the large intestine

Answer 23

Mucosa, relatively smooth, no villi, Crypts of Lieberkuhn and goblet cells

Question 24

Main functions of the large intestine

Answer 24

Absorption of water and electrolytes from chime to form solid faeces.
Colonic bacteria activity production of short chain fatty acids and production of vitamins
Storage of faecal matter
Transport (motility)