Digestion and Absorption of Lipids

Question 1

What are the functions of bile?

Answer 1

• digestion and absorption of fats
• excretion of water-insoluble substances

Question 2

What is bile formed by?

Answer 2

hepatocytes from the liver and ductal cells from the bile duct

Question 3

Where is bile stored during the interdigestive period?

Answer 3

in the gallbladder

Question 4

How is bile released?

Answer 4

chyme causes release of CCK which causes the gallbladder to contract

Question 5

What are primary bile acids?

Answer 5

cholic and chenodeoxycholic acids synthesised from cholesterol but are more water soluble than cholesterol

Question 6

Where are primary bile acids actively reabsorbed?

Answer 6

at the ileum

Question 7

What are secondary bile acids?

Answer 7

deoxycholic and lithocholic acids produced by deconjugation and dehydroxylation of 1º bile acids by intestinal bacteria

Question 8

Give examples of bile pigments

Answer 8

bilirubin and biliverdin

Question 9

What are bilirubin and biliverdin?

Answer 9

yellow metabolites of haemoglobin used for excretion

Question 10

What happens to bilirubin?

Answer 10

it is converted to brown urobilin by bacteria

Question 11

What are phospholipids of bile mostly?

Answer 11

lecithins (second most abundant organic bile compounds)

Question 12

What do lecithins do?

Answer 12

increase cholesterol solubilisation in bile micelles

Question 13

What is the major route for cholesterol excretion?

Answer 13

bile micelles

Question 14

How are bile salts produced?

Answer 14

bile acids are conjugated with glycine or taurine

Question 15

What does bile acid conjugation do?

Answer 15

• make them more amphipathic
• make them less susceptible to hydrolysis by pancreatic enzymes

Question 16

How does bile acid conjugation aid fat absorption?

Answer 16

it is easier to form micelles which reabsorb poorly and stay in the gut for longer

Question 17

What does enterohepatic circulation do?

Answer 17

recycle bile from the small intestine to the liver and back

Question 18

Where are bile salts reabsorbed?

Answer 18

only in the terminal ileum

Question 19

How much bile salt does each meal require?

Answer 19

4-8g so the total pool must recirculate twice per meal to facilitate it

Question 20

What is the rate of synthesis of bile determined by?

Answer 20

the rate of return to the liver

Question 21

What are the 3 phases of assimilation of lipids?

Answer 21

1. digestive phase
2. absorptive phase
3. post-absorptive phase

Question 22

What does intragastric lipolysis account for?

Answer 22

20-30% of total lipid digestion

Question 23

What are lingual lipases responsible for?

Answer 23

0.015% of gastric lipase activity

Question 24

How does intra-intestinal digestion of fats work?

Answer 24

• alkaline pH
• adequate Ca2+
• bile salts
• lecithin
• lipolytic enzymes

Question 25

What are the 3 lipid soluble lipases of the pancreas?

Answer 25

- glycerol ester hydrolase (main lipase) - cholesterol esterase - phospholipase A2

Question 26

Why must fats be soluble in water?

Answer 26

for digestion and absorption

Question 27

What does lecithin do to bile?

Answer 27

increase its detergent power

Question 28

Where are micelles formed and what do they do?

Answer 28

in the lumen of the small intestine to help transport lipids into the intestinal cells or enterocytes

Question 29

What do micelles contain?

Answer 29

20-30 molecules of lipids and bile salts

Question 30

Why are micelles extremely hydrophobic?

Answer 30

due to the cholesterol and fat-soluble vitamins within

Question 31

When are lipids absorbed from micelles?

Answer 31

once they come into contact with the microvilli

Question 32

What is the rate limiting step of fat absorption?

Answer 32

migration of the micelle from chyme to the microvilli surface

Question 33

What is fat in the stool from?

Answer 33

colonic bacteria and desquamated intestinal cells

Question 34

What happens in the post-absorptive phase of fat absorption?

Answer 34

- re-esterification - formation of chylomicrons for re-esterified lipids - lymphatic transport

Question 35

Why is there no re-esterification for medium or short-chain fatty acids?

Answer 35

they are bacterial sources and don’t form micelles or chylomicrons

Question 36

What are the 2 types of GIT disorders?

Answer 36

functional and structural

Question 37

What are common signs and symptoms of GIT disorders?

Answer 37

- blood in your stool - very narrow stool - changes in bowel habits - unusual or severe abdominal pain - unintentional/unexplained weight loss - heartburn not relieved by antacids - fatigue

Question 38

What are primary causes of functional GIT disorders? | 10

Answer 38

- low fibre diet - not enough exercise - travelling or other changes in routine - eating large amounts of dairy products - stress - resisting the urge to have a bowel movement - overusing laxatives - taking certain medicines - pregnant - ageing

Question 39

Give examples of functional GIT disorders

Answer 39

- gastroesophageal reflux disease - peptic ulcers - IBS - constipation

Question 40

What happens in gastroesophageal reflux disease?

Answer 40

weakening of lower oesophageal sphincter and reflux of gastric acid irritates the oesophagus, damages the lining and causes inflammation

Question 41

What are causes of gastroesophageal reflux disease?

Answer 41

pregnancy, alcohol, certain foods and medication

Question 42

What are the 2 types of peptic ulcers and what are they caused by?

Answer 42

- gastric ulcer caused by helicobacter pylori infection, alcohol or drugs e.g. NSAIDs - duodenal ulcer cause by stress or overproduction of gastric acid

Question 43

What is IBS caused by?

Answer 43

certain foods, medicines or emotional stress

Question 44

What are potential remedies of IBS?

Answer 44

decreased caffeine/alcohol, minimised stress, increased dietary fibre and medication

Question 45

What is constipation?

Answer 45

difficult or infrequent passage of stools caused by inadequate fibre or disruption of regular routine

Question 46

What are treatments of constipation?

Answer 46

increased dietary fibre, regular exercise and laxatives

Question 47

Give examples of GIT structural disorders

Answer 47

- haemorrhoids - diverticulosis - colon polyps and cancer - liver diseases

Question 48

What are haemorrhoids and what are they caused by?

Answer 48

swollen blood vessels that line anal opening caused by chronic excess pressure from straining during bowel movement, persistent diarrhoea and pregnancy

Question 49

What are treatments of haemorrhoids?

Answer 49

improving bowel habits and surgery

Question 50

What is diverticulosis?

Answer 50

small out-pouching in muscular wall of large intestine common in individuals over 60

Question 51

What is diverticulosis caused by?

Answer 51

high pressure over weakened area

Question 52

What are treatments of diverticulosis?

Answer 52

antibiotics and increased fluids

Question 53

What do almost all colorectal cancers begin as?

Answer 53

polyps

Question 54

Give examples of liver diseases

Answer 54

- fatty liver - hepatitis - fibrosis - cirrhosis - cancer