Unit 2 - Digestion/ Absorption Flashcards

1
Q

How are carbohydrates digested?

A
  • polysaccharides digested by salivary amylase
  • majority digested by pancreatic amylase - occurs in duodenum (breaks down into oligosachharides by splitting 1,4 glycosidic bond)
  • brush border enzymes - breaks down into monosaccharides
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2
Q

give example of brush border enzymes

A

maltase
sucrase
lactase
dextrinase

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3
Q

if there is a low concentration of glucose, how are carbohydrates absorbed?

A

absorbed into enterocytes across apical surface by SGLT1 then across basolateral surface by GLUT2

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4
Q

if there is a high concentration of glucose, how are carbohydrates absorbed?

A

SGLT1 are saturated so absorbed via GLUT2 through apical and basolateral surface

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5
Q

how are monosaccharides transported to liver?

A

in blood via hepatic portal vein

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6
Q

how are proteins broken down?

A
  • gastric digestion by proteolytic enzymes which are secreted in their inactive form: pepsinogen and then activated in acidic environment (lumen of stomach) to pepsin
  • pancreatic digestion: trypsinogen/ chymotrypsinogens which are activated in response to alkaline environment - converted by enterokinase
  • further digestion by exopeptidases
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7
Q

how are proteins absorbed?

A

by enterocytes at brush border via carrier protein then exported into extracellulr space across basolateral membrane
- M cells package proteins into vesicles

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8
Q

how are lipids digested?

A
  • emulsification by bile salts initially: hydrophilic regions of bile salts repel so droplets are formed
  • lipolytic enzymes from pancreas digest lipids - secreted in their inactive form but activated by trypsin in duodenum
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9
Q

give two examples of lipolytic enzymes

A
  • phospholipase A2- cleaves fatty acids

- colipase - anchors lipase to micelles= maximal SA

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10
Q

how are lipids absorbed?

A

micelles pass across brush border - re-esterified in endoplasmic reticulum and form chylomicrons - released by exocytosis and join lacteal duct

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11
Q

what are the three stages of digestion?

A

cephalic
gastric
intestinal

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12
Q

describe the cephalic phase

A

neurogenic signals from cortex/ appetite centres relayed to stomach via parasympathetic efferent responses - vagal stimulation increases salivary secretion and vasodilation

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13
Q

describe the gastric phase

A

distension of stomach walls activates mechanoreceptors which activates local enteric reflexes and vago-vagal reflexes -which leads to release of gastrin from G cells -
= causing release of HCl acid by parietal cells
= release of pepsinogen by chief cells
= increased motility

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14
Q

in the intestinal phase why is secretin released?

A

HCl acid from stomach passes into small intestine - secretin inhibits acidity and stimulates release of bicarbonate rich solution by acinar cells of duodenum

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15
Q

what causes the release of CCK? and what is the effect of CCK?

A

fat in chyme
= inhibits stomach motility and release of gastrin
= stimulates release of pancreatic enzymes (lipase)
= causes contraction of gall bladder

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16
Q

what is the effect of orexin?

A

increases appetite

17
Q

what is the effect of ghrelin?

A

stimulates food intake, appetite and promotes food storage

18
Q

what is the effect of leptin?

A

made by adipocytes

- controls energy expenditure in the long term - inhibits hunger

19
Q

what is PYY?

A

gut peptide - reduces food intake, decreases appetite