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gi tract > Absorption and digestion > Flashcards

Absorption and digestion Flashcards

1
Q

What types of carbohydrate may be present in the gut?

A
  • Polysaccharides
  • Disaccharides
  • Monosaccharides
  • Only monosaccharides are absorbed
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2
Q

What happens to carbohydrates of plant origin?

A
  • These are non-digestible
  • They pass into the colon where they provide nutrients for the bacteria there
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3
Q

What monosaccharides do we want to break our carbohydrates down into?

A
  • Glucose
  • Galactose
  • Fructose
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4
Q

What is starch made up of?

A
  • Amylose chains
  • Amylopectin chains
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5
Q

Describe the structure of amylose

A
  • Straight chains of glucose monomers
  • Joined together by alpha 1-4 glycosidic bonds
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6
Q

What enzyme breaks down amylose?

A
  • Amylase
  • Breaks amylose down into maltose
  • Maltase breaks maltose down into glucose x2
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7
Q

Describe the structure of amylopectin

A
  • Branched chains of glucose
  • Alpha 1-4 glycosidic bonds join glucose monomers together
  • Alpha 1-6 glycosidic bonds create branches
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8
Q

What enzyme breaks down amylopectin?

A
  • Amylase breaks down 1,4 bonds to give alphadextrins
  • Isomaltase breaks down 1,6 bonds to give amylose
  • Amylase then breaks down 1,4 bonds of amylose
  • Maltase breaks maltose into glucose
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9
Q

What is lactose?

A
  • Common dietary sugar found in milk
  • Disaccharide of glucose and galactose
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10
Q

How is lactose broken down?

A
  • Lactase (a brush-border enzyme)
  • Broken down into glucose and galctose
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11
Q

How is sucrose broken down?

A
  • Sucrase (a brush-border enzyme)
  • Breaks down sucrose into glucose and fructose
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12
Q

How is glucose absorbed into intestinal epithelial cells?

A
  • Co-transported with Na+
  • Through Sodium-glucose transporter 1
  • Glucose cannot bind to transporter unless Na+ has previously been bound
  • Then passes into blood via Glut 2 transporter
  • Galactose absorbed in the same way
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13
Q

How is fructose absorbed into intestinal epithelial cells?

A
  • Through Glut 5 transporter
  • Then leaves cell via Glut 2 transporter
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14
Q

How is an Na+ gradient maintained in intestinal enterocytes?

A
  • Na+/K+ ATPase
  • Creates low cytosolic Na+ within enterocytes
  • Sets up gradient to move Na+ along with glucose/galactose into cell
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15
Q

Where does the glucose/galactose/fructose pass after it leaves the enterocyte via Glut 2?

A
  • Passes into venous system
  • Drains to portal system of liver
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16
Q

Outline how proteins are digested within the stomach?

A
  • Chief cells secrete pepsinogen
  • Pepsinogen converted to pepsin by HCl
  • Protein broken down to oligopeptides and amino acids
17
Q

Outline how proteins are digested within the intestinal lumen

A
  • Pancreas releases an array of zymogens
  • Enteropeptidase activates trypsinogen to trypsin
  • Trypsin activates all other proenzymes
  • Endopeptidases and exopeptidases break proteins down to amino acids and short peptides
  • Brush border enzymes and cytosolic enzymes work on short peptides
18
Q

What are the 5 major proteases of the intestine?

A
  • Trypsinogen/trypsin
  • Chymotrypsinogen/chymotrypsin
  • Proelastase/elastase
  • Procarboxypeptidase A/carboxypeptidase A
  • Procarboxypeptidase B/carboxypeptidase B
19
Q

What is the difference between endopeptidases and exopeptidases?

A
  • Endopeptidases produce shorter polypeptides by breaking bonds in the middle of the chain
  • Trypsin, chymotrypsin and elastase are all endopeptidases
  • Exopeptidases cleave bonds at the end of chains
  • Examples include the carboxypeptidases (A and B)
20
Q

What allows peptides to be absorbed into enterocytes?

A
  • PepT1 transporter
  • Co-transports short chain peptides with Na+
21
Q

How does water move out of the small intestines?

A
  • Can move via paracellular route through tight junctions
  • Can move transcellularly
  • Relies on movement of Na+
22
Q

What allows water to move paracellularly?

A
  • Accumulation of Na+ in intercellular spaces
23
Q

How is water secreted by enterocytes?

A
  • Cl- moves into cell through Na+/K+/Cl- channel
  • Rise in cAMP in cell causes secretion of Cl- through CFTR protein
  • Causes Na+ to be drawn through tight junctions
  • H2O follows into lumen of gut
24
Q

What are the symptoms of vitamin B12 deficiency?

A
  • Neurological problems
  • Megaloblastic anaemia
25
Q

What causes vitamin B12 deficiency?

A
  • Lack of intrinsic factor - vit B12 needs to bind to this so it can be absorbed in the distal ileum
  • Hypochlorhydria - gastric atrophy leads to inadequate HCl - cobalamin not released
  • Not enough B12 in food
  • Inflammation of terminal ileum e.g. due to Crohn’s disease
26
Q

What causes lactose intolerance?

A
  • Deficiency of lactase enzyme
  • Diminishes after age 2
27
Q

What are the symptoms of lactose intolerance?

A
  • Diarrhoea - lactose remains in gut lumen, creating high osmotic pressure; water drawn into lumen
  • Flatus and bloating - lactose fermented in colon
28
Q

What are the symptoms of irritable bowel syndrome?

A
  • Abdominal pain
  • Bloating
  • Flatulence
  • Diarrhoea
  • Constipation
  • Rectal urgency
29
Q

What are the risk factors for IBS?

A
  • Female: male ratio is 2:1
  • 20s-40s more affected
  • Associated with psychological disorders
30
Q

Which part of gluten causes coeliac disease?

A
  • Gliadin fraction
  • Found in wheat, rye, barley
31
Q

What causes coeliac disease?

A
  • Immunological response to gluten
  • Damages mucosa of small intestine
  • Villi flatten
  • Crypts hypertrophy
  • Lymphocytes found in epithelium/lamina propria
  • Genetic factor
31
Q

What causes coeliac disease?

A
  • Immunological response to gluten
  • Damages mucosa of small intestine
  • Villi flatten
  • Crypts hypertrophy
  • Lymphocytes found in epithelium/lamina propria
  • Genetic factor
32
Q

What are the symptoms of coeliac disease?

A
  • Malabsorption and impaired digestion
  • Diarrhoea
  • Weight loss
  • Flatulence
  • Distension
  • Pain
  • Anaemia (decreased iron absorption)
  • Neurological symptoms (decreased calcium)
33
Q

How do we investigate coeliac disease?

A
  • Blood tests looking for IgA to smooth muscle endomysium and tissue transglutaminase
  • Upper GI endoscopy
  • Duodenal biopsy - mucosal pathology (reduced or absent villi)
34
Q

How do we treat coeliac disease?

A
  • Gluten free diet

gi tract (23 decks)

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