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Human Physiology - Hormones and Health > Digestion and Absorption of Lipids > Flashcards

Digestion and Absorption of Lipids Flashcards

1
Q

What are the functions of bile?

A
  • digestion and absorption of fats
  • excretion of water-insoluble substances
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2
Q

What is bile formed by?

A

hepatocytes from the liver and ductal cells from the bile duct

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3
Q

Where is bile stored during the interdigestive period?

A

in the gallbladder

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4
Q

How is bile released?

A

chyme causes release of CCK which causes the gallbladder to contract

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5
Q

What are primary bile acids?

A

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

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6
Q

Where are primary bile acids actively reabsorbed?

A

at the ileum

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7
Q

What are secondary bile acids?

A

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

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8
Q

Give examples of bile pigments

A

bilirubin and biliverdin

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9
Q

What are bilirubin and biliverdin?

A

yellow metabolites of haemoglobin used for excretion

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10
Q

What happens to bilirubin?

A

it is converted to brown urobilin by bacteria

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11
Q

What are phospholipids of bile mostly?

A

lecithins (second most abundant organic bile compounds)

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12
Q

What do lecithins do?

A

increase cholesterol solubilisation in bile micelles

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13
Q

What is the major route for cholesterol excretion?

A

bile micelles

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14
Q

How are bile salts produced?

A

bile acids are conjugated with glycine or taurine

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15
Q

What does bile acid conjugation do?

A
  • make them more amphipathic
  • make them less susceptible to hydrolysis by pancreatic enzymes
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16
Q

How does bile acid conjugation aid fat absorption?

A

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

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17
Q

What does enterohepatic circulation do?

A

recycle bile from the small intestine to the liver and back

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18
Q

Where are bile salts reabsorbed?

A

only in the terminal ileum

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19
Q

How much bile salt does each meal require?

A

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

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20
Q

What is the rate of synthesis of bile determined by?

A

the rate of return to the liver

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21
Q

What are the 3 phases of assimilation of lipids?

A
  1. digestive phase
  2. absorptive phase
  3. post-absorptive phase
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22
Q

What does intragastric lipolysis account for?

A

20-30% of total lipid digestion

23
Q

What are lingual lipases responsible for?

A

0.015% of gastric lipase activity

24
Q

How does intra-intestinal digestion of fats work?

A
  • alkaline pH
  • adequate Ca2+
  • bile salts
  • lecithin
  • lipolytic enzymes
25
Q

What are the 3 lipid soluble lipases of the pancreas?

A
  • glycerol ester hydrolase (main lipase)
  • cholesterol esterase
  • phospholipase A2
26
Q

Why must fats be soluble in water?

A

for digestion and absorption

27
Q

What does lecithin do to bile?

A

increase its detergent power

28
Q

Where are micelles formed and what do they do?

A

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

29
Q

What do micelles contain?

A

20-30 molecules of lipids and bile salts

30
Q

Why are micelles extremely hydrophobic?

A

due to the cholesterol and fat-soluble vitamins within

31
Q

When are lipids absorbed from micelles?

A

once they come into contact with the microvilli

32
Q

What is the rate limiting step of fat absorption?

A

migration of the micelle from chyme to the microvilli surface

33
Q

What is fat in the stool from?

A

colonic bacteria and desquamated intestinal cells

34
Q

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

A
  • re-esterification
  • formation of chylomicrons for re-esterified lipids
  • lymphatic transport
35
Q

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

A

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

36
Q

What are the 2 types of GIT disorders?

A

functional and structural

37
Q

What are common signs and symptoms of GIT disorders?

A
  • 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
38
Q

What are primary causes of functional GIT disorders?

10

A
  • 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
39
Q

Give examples of functional GIT disorders

A
  • gastroesophageal reflux disease
  • peptic ulcers
  • IBS
  • constipation
40
Q

What happens in gastroesophageal reflux disease?

A

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

41
Q

What are causes of gastroesophageal reflux disease?

A

pregnancy, alcohol, certain foods and medication

42
Q

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

A
  • gastric ulcer caused by helicobacter pylori infection, alcohol or drugs e.g. NSAIDs
  • duodenal ulcer cause by stress or overproduction of gastric acid
43
Q

What is IBS caused by?

A

certain foods, medicines or emotional stress

44
Q

What are potential remedies of IBS?

A

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

45
Q

What is constipation?

A

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

46
Q

What are treatments of constipation?

A

increased dietary fibre, regular exercise and laxatives

47
Q

Give examples of GIT structural disorders

A
  • haemorrhoids
  • diverticulosis
  • colon polyps and cancer
  • liver diseases
48
Q

What are haemorrhoids and what are they caused by?

A

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

49
Q

What are treatments of haemorrhoids?

A

improving bowel habits and surgery

50
Q

What is diverticulosis?

A

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

51
Q

What is diverticulosis caused by?

A

high pressure over weakened area

52
Q

What are treatments of diverticulosis?

A

antibiotics and increased fluids

53
Q

What do almost all colorectal cancers begin as?

A

polyps

54
Q

Give examples of liver diseases

A
  • fatty liver
  • hepatitis
  • fibrosis
  • cirrhosis
  • cancer

Human Physiology - Hormones and Health (14 decks)

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