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GI System > Intestines, Absorption, Digestion > Flashcards

Intestines, Absorption, Digestion Flashcards

1
Q

Glucose can only be absorbed with what ion?

What happens to carbs of plant origin that can’t be digested?

A

Na+

Utilised and partially digested by bacteria in colon, providing nutrients for colonic mucosa

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2
Q

Name 3 common dietary carbohydrates

A
  • Starch
  • Lactose
  • Sucrose
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3
Q

Describe the structure of starch

A
  • Straight chains of glucose called Amylose, held together by Alpha 1-4 bonds
  • Branched chain of glucose called Amylopctin, held together by Alpha 1-6 bonds
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4
Q

Describe digestion of Starch into glucose

A
  • Salivary and pancreatic amylase break Alpha-1,4 bonds in Amylose, releasing Maltose (Maltese converts to glucose)
  • Amylase breaks Alpha-1,4 bonds in Amylopectin, releasing Alpha Dextrins
  • Isomaltase needed to break Alpha-1,6 bonds of Alpha Dextrins into Amylose. Amylase converts this into glucose
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5
Q

What are the 3 monosaccharides we get from digesting common carbohydrates

A
  • Glucose (from starch, lactose, sucrose)
  • Galatose (from lactose)
  • Fructose (from sucrose)
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6
Q

Describe monosaccharide absorption into an enterocyte

A
  • Na-K ATPase on BM moves Na into blood
  • Na and Glucose/ Galctose diffuse in through SGLT 1 on AM (from gut lumen, requires Na+ binding to monosaccharide)
  • Fructose diffuses in through GLUT5 on AM
  • All 3 monosaccharides leave cell through GLUT2 on BM-> blood to reach liver
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7
Q

What are the 4 stages of protein digestion?

A
  1. Stomach (H+, Pepsin)
  2. Intestinal lumen (Trypsin)
  3. Brush border of enterocytes
  4. Cytosol peptidases
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8
Q

Describe the 1st stage of protein digestion (in stomach)

A
  • Pepsinogen released from Chief cells and gets converted to Pepsin by HCl
  • Pepsin acts on proteins-> Oligopeptides and amino acids then move to SI
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9
Q

Describe the 2nd stage of protein digestion (in intestine)

A
  • Pancreases releases Proteases as zymogens
  • Trypsinogen converted to Trypsin by Enteropeptidase/ Enterokinase (a brush border enzyme)
  • Trypsin activates other Proenzymes/ Zymogens as well as itself
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10
Q

List 5 Proenzymes/ Zymogens converted by Trypsin into Active Enzymes

A
  • Trypsinogen
  • Chymotrypsinogen
  • Proelastase (Becomes elastase)
  • Procarboxypeptidase A (Becomes carboxypeptidase A)
  • Procarboxypeptidase B (Becomes carboxypeptidase B)

(All released by Pancreas)

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11
Q

Compare the 2 groups of Proenzymes released from Pancreas, after they have ben activated by trypsin

A

Endopeptidases;

  • Break bonds in middle of polypeptide
  • Produce shorter polypeptides

Exopeptidases;

  • Break bonds at ends of polypeptide
  • Produce dipeptides/ amino acids
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12
Q

Name 3 Endopeptidases and 2 Exopeptidases

A

Endo;

  • Trypsin
  • Chymotrypsin
  • Elastase

Exo;
- Carboxypeptidase A and B

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13
Q

Describe the 3rd stage of protein digestion (Brush border enzymes)

A
  • Brush border of enterocytes also contain Proteases, but sometimes can’t completely digestion into amino acids
  • Short peptides and amino acids can be absorbed into enterocyte via PepT1
  • Amino acids are taken in with Na+ via a Symport
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14
Q

Describe the 4th stage of protein digestion (Cytosol)

A
  • Small peptides broken down by cytosolic peptidases into amino acids
  • Certain di- and tri-peptides can also be absorbed into blood, as can amino acids
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15
Q

In the SI, water absorption is driven by the Na-K ATPase, Sodium movement into Enterocytes and Osmosis.

(Water follows sodium)

What are 2 pathways it takes?

A
  • Transcellular

- Paracellular

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16
Q

Compare water/ electrolyte uptake in SI and LI

A
  • Both have Na-K ATPase on BM

On AM;

  • In SI, Na is transported with Glucose/ Amino acids
  • In LI, Na channels exist which are induced by Aldosterone
17
Q

Na is the ion that drives water absorption in intestines.

Which ion drives water secretin into intestinal lumen?

A

Cl-

18
Q

Describe Water Secretion into Intestinal Lumen

A
  • Cl enters enterocyte with Na and K, through Symport on BM
  • cAMP levels rise in cell, activating CFTR protein on AM
  • Cl leaves cell via CFTR on AM and Na+ follows it across tight junctions
  • Water follows the sodium via osmosis
19
Q

What are 4 causes of Vit B12/ Cobalamin deficiency?

A
  • Lack of IF
  • Hypochlorydia (inadequate stomach acid, needed to make Vit B12 available for binding to IF)
  • Inadequate intake (strict vegetarians)
  • Inflammatory disorders of Ileum (Crohn’s)
20
Q

Why do Lactose Intolerance patients get the following when they ingest lactose;

  • Diarrhoea
  • Flatulence/ Bloating
A

Diarrhoea;
- Lactose remain in gut creating a high osmotic effect, pulling water into lumen

Flatulence/ Bloating-
- Lactose fermented in colon producing ‘gas’

21
Q

Irritable Bowel Syndrome (IBS) is common, affecting 10-15% of adults

List 5 symptoms

A
  • Ab pain (often cramping, relived by defecation
  • Bloating
  • Flatulence
  • Diarrhoea/ constipation (sometimes alternating)
  • Rectal urgency (urgent need to defecate)
22
Q

The causes of IBS are multi-factorial

Describe the Aetiology of IBS

A
  • More common in females (2:1)
  • Most affected in age range of 20s to 40s
  • Commonly associated with psychological disorders
23
Q

Describe the physiological basis of Coeliac disease

A

Immune response to Gliadin component of Gluten, leading to damage of intestinal mucosa

24
Q

List 3 foodstuffs that contain gluten (the Gliadin component to be exact)

A

Wheat
Rye
Barley

25
Q

What are 3 ways the intestinal mucosa can be damaged in coeliac disease?

What do these lead to overall?

A
  • Flattening, then absence of Intestinal Villi
  • Hypertrophy/ Lengthening of Intestinal Crypts
  • Lymphocytic infiltration of Epithelia and Aamina Propria

All these combine to lead to impaired digestion/ malabsorption

26
Q

Coeliac disease is under diagnosed, in fact 1% of the western population is thought to be affected

Describe the Aetiology
What’s the treatment?

A
  • Cause unknown but thought to be due to genetic factors

- Guten free diet (quick clinical improvement, slower histological improvement)

27
Q

List 3 groups of symptoms of Coeliac Disease

A
  • Most symptoms related to malabsorption (diarrhoea, weight loss, flatulence, ab pain)
  • Anaemia (impaired iron absorption)
  • Neurological symptoms (Hypocalcaemia)
28
Q

What are 2 types of investigations that can be done to look for Coeliac disease

A
  1. Bloods;
    - IgA antibodies
    - Smooth Muscle Endomysium
    - Tissue Transglutaminase
  2. Upper GI endoscopy + biopsies to look for mucosal pathology (absent/ reduced villi)

GI System (26 decks)

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