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S3: Gastrointestinal > 5b.) The Intestines > Flashcards

5b.) The Intestines Flashcards

1
Q

Define absorption

A

Movement of electrolytes, water and nutrients form the gut lumen to blood

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2
Q

Compare the jejunum and ileum in terms of:

  • Where they are
  • The thickness of their intestinal walls
  • Length of vasa recta
  • Number of arcades
A
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3
Q

Describe the blood supply to the intestines

A

SMA gives off following branches:

  • Jejunal and ileal arteries: jejenum & ileum
  • Ileocolic: terminal ileum, caecum
  • Right colic: ascending colon
  • Middle colic: transverse colon

Ileocoli, right colic and middle colic anastomose to form the marginal artery

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4
Q

Describe the venous drainage of the intestines

A
  • Superior rectal vein becomes IMV when it comes out of pelvis
  • Inferior mesenteric vein joins the splenic vein
  • Splenic vein adn superior mesenteric vein join to form the portal vein which forms behind the neck of the pancreas
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5
Q

Describe the properties of chyme once it has left duodenum, include:

  • Tonicity
  • pH
  • Digestion
A
  • Isotonic
  • Neutral
  • Digestion nearly complete
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6
Q

Absorption requires a large surface area; describe 3 structural features of intestines that increase surface area

A
  • Plicae circulares (permanent intestinal folds)
  • Villi
  • Microvilli
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7
Q

State the 3 main epithelial cell types in intestines and what each one does

A
  • Enterocytes (most)= absorptive cells
  • Goblet cells= mucus secreting
  • Enteroendocrine= produce hormones
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8
Q

How often is the mucosa of intestinal glands shed?

A

Constantly shed evey 3-6 days

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9
Q

Describe the structure of intestinal glands (crypts of Lieberkuhn)

A

???

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10
Q

Only monosaccharides can be absorbed; true or false?

A

True

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11
Q

State the three monosaccharides that can be absorbed

A
  • Glucose
  • Fructose
  • Galactose
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12
Q

Glucose can only be absorbed alongside Na+; true or false

A

True

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13
Q

State 3 common dietary carbohydrates

A
  • Starch (polysaccharide)
  • Lactose (disaccharide)
  • Sucrose (disaccharide)
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14
Q

Describe the structure of starch

A

Consists of:

  • Amylose: straight chains of glucose with alpha 1-4 bonds
  • Amylopectin: branched chains of glucose with alpha 1-4 bonds on straight chains and alpha 1-6 bonds on branch points
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15
Q

Which bonds, in starch, can salivary and pancreatic amylase break?

What do you end up with once they have broke these bonds?

A

Salivary and pancreatic amylase can break alpha 1-4 bonds:

  • In amylose: this produces the disaccharide MALTOSE
  • In amylopectin: this produces shorer but still branched chains of glucose called ALPHA DEXTRINS
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16
Q

What enzyme is required to break alpha 1-6 bonds (in branches of amylopectin in starch)?

A

Isomaltase

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17
Q

State the monosaccharide components of maltose

A

2 x glucose

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18
Q

Summarise starch digestion

A
  • Salivary and pancreatic amylase break alpha 1-4 bonds in produce:
    • Maltose from amylose
    • Alpha dextrins from amylopectin
  • Isomaltase required to break alpha 1- bonds in amylopectin
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19
Q

State the monosaccharide components of lactose

A

Glucose and galactose

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20
Q

State the monosaccharide components of sucrose

A

Glucose and fructose

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21
Q

What enzyme breaks lactose into it’s monosacchardie components?

A

Lactase

(Lactose -> glucose + galactose)

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22
Q

What enzyme breaks sucrose into its monosaccharide components?

A

Sucrase

Glucose + fructose

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23
Q

What is starch?

A

Polysaccharide of glucose

24
Q

Describe glucose and galactose absorption in enterocyte

A
  • NA+/K+ ATPase on basolateral membrane creates low intracellular Na+
  • SGLT-1 transports glucose or galactose coupled to Na+ into enterocytes (energy from dissipation of Na+ gradient)
  • Glut2 transports glucose or galactose into plasma down concentration gradient
25
Q

Describe absorption of fructose in enterocyte

A
  • Facilitated diffusion of fructose via GLUT5 transporter into enterocyte
  • Fructose can leave via GLUT2 or it’s own transporter
26
Q

State two brush border enzymes involved in starch digestion

A
  • Maltase (maltose -> glucose + glucose)
  • Isomaltase (breaks alpha 1-6 bonds)
27
Q

Briefly describe/state the 4 stages of protein digestion

A
  1. Stomach (H/pepsin)
  2. Intestinal lumen (Trynpsin…..)
  3. Brush border
  4. Cytosol (cystosolic peptidases
28
Q

Describe stage 1 of protein digestion in the stomach

A
  • Pepsinogen released from chief cell
  • HCL converts pepsinogen -> pepsin
  • Pepsin digests proteins into either oligopeptides or amino acids
  • Oligopeptides or amino acids move to small intestine
29
Q

Describe stage 2 of protein digestion in the small intestine

A
  • Pancreas releases zymogens
  • Zymogens acitvated in intestinal lumen
  • Trypsinogen is activated by enteropeptidase (enterokinase) into trypsin
  • Trypsin activates many other zymogens

Endopeptidases- produce shorter poplypeptides

Exopeptidases- produce dipeptides or amino acids

30
Q

Describe stage 3 of protein digestion

A
  • Enterocytes have proteases/peptidases in their brush border
  • These enyzmes break down proteins further but can’t always break them down into aa
  • HOWEVER, intestine can absorb short peptides (as well as aa) by Peptide transporter 1 (PepT1)
  • AA transported in cell using amino acid transporters
31
Q

Describe stage 4 of protein digestion

A

Cytosolic peptidases, in cytosol of enterocyte, break down small peptides (transported in by PepT1) into amino acids. NOTE: certain di- and tri- peptides can also be absorbed into the blood hence these cytoslic peptidases don’t have to break them down into single aa all the time

32
Q

Explain the difference between exopeptidases and endopeptidases

Provide examples of each

A
  • Endopeptidases: tyrpin, chymotrypsin, elastase
  • Exopeptidases: carboxypeptidase (A&B)
33
Q

Explain what drives the movement of water out of lumen of intestine into enteroctyes

A
  • Na+/K+ ATPase in basolateral membrane
  • Decreases intracellular [Na+]
  • Na+ diffuses into enterocyte down conc gradient taking other stuff with it e.g. electrolytes, glucose….
  • Creates osmotic gradient
  • Water moves from area of high water potential to an area of low water potential
  • Fluid absorbed is isosmotic
34
Q

Compare the transporters on both the basolateral and apcial membrane in small and large intestine

Relate this to their ability to absorb water

A

Small Intestine

  • Apcial membrane: Na+ cotransported wtih e.g. glucose, aa

Large Intestine

  • Apical membrane: Na+ channels which are induced by aldosterone

Aldosterone can increase amount of Na+ body abosrobs- has greater effect on large intestine than small intestine

JUST CHECK THIS FC

35
Q

Explain the principles behind oral rehydration fluid

A

Oral rehydration fluids contain a mix of salt and gluocse to stimulate maximum water uptake. Increased Na+, increases amount of Na+ absorbed and therefore the amount of glucose absorbed (as it is co transported with Na+) this generates greater osmotic gradient to stimulate water uptake

36
Q

Describe water secretion into intestine

A
  • Cl- enters crypt epithelial cell via NKCC1 (transported with Na+ and K+ adn 2Cl-)
  • Cyclic AMP levels increase in cell
  • Incrased cyclic AMP activates CFTR
  • Cl- ions secreted
  • Na+ is drawn into lumen across tight junctions
  • NaCl secretion creates osmotic gradient to move water into lumen

JUST CHECK

37
Q

Describe some causes of vitamin B12 (cobalamin) deficiency

State potential consequences of B12 deficiency

A
  • Lack of intrinsic factor: e.g. if parietal cells damaged
  • Hypochlorhydria: inadequete stomach acid possibly due to gastric atrophy or PPIs; acis is important in initial release of B12
  • Inadequete intake: often vegetarians
  • Inflammatory disorders of ileum: as this is where it is absorbed e.g. in Crohn’s disease

Consequences: megaoblastic anaemia, neurological symptoms (see MEH for more)

38
Q

Describe the symptoms of lactose intolerance and why you get them

A

Lactose cannot be digested due to lack of lactase (different types of lactose intolerance, see BL) hence lactose remains in gut leading to:

  • High osmotic effect- draw water in- diarrhoea
  • Lactose is fermented- gas - bloating
39
Q

After what age is the enzyme lactase less expressed?

A

2 years

40
Q

State some symptoms of IBS

State who’s more affected in terms of gender, age, other morbidities

A
  • Abdo pain (sometimes relieved by defaecation)
  • Bloating
  • Flactulence
  • Diarrhoea/constipation
  • Rectal urgency

More common in females (2:1), 20-40s most affected, more common in those with psychological disorders (maybe due to low serotonin and serotonin has role in enteric nervous system)

41
Q

What is coeliac disease?

A

Immunological response to gliadin fraction of gluten which is found in wheat, rye and barley results in damage to mucosa of intestines e.g.:

  • Absence of intestinal villi
  • Hypertrophy/lengthening of intestinal crypts
  • Lymphocytes infiltrate epithelium and lamina propria
  • Impaired digestion/malabsorption
42
Q

There is a high risk of coeliac disease in what type of twins?

A

Monozygotic

43
Q

State some symptoms of coeliac disease

A
  • Diarrhoea
  • Weight loss
  • Flactulence
  • Abdo pain
  • Anaemia (impaired Fe absorption)
  • Neurological symptoms (hypocalcaemia)

Most related to malabsorption

44
Q

State 2 investigations for coeliac disease and state which is “gold standard”

A

Bloods:

  • IgA antibodies to smooth muscle endomysium and tissue transglutaminase

Upper GI endoscopy:

  • Duodenal biopsy to look for mucosal pathology and absent villi *GOLD STANDARD
45
Q

How do you treat coeliac disease?

A

Gluten free diet. Get clinical improvement quickly (days/weeks) and histological improvement (weeks/months)

46
Q

Describe two benefits of fibre

A
  • Fibre helps lower cholesterol: fibre binds bile salts, which are made of cholesterol, meaning we have to make more bile salts and hence use up more cholesterol
  • Bacteria in large bowel can use fibre. Good diversity of colonic bacteria linked to whole body general health
47
Q

Describe how stem cells in intestinal glands (crypts of Leiberkuhn) help to regenerate intestinal epithelia

Why are paneth cells useful to stem cells?

A
  • Stem cells at base of gland migrate to surface
  • Mature as they migrate into variety of cell types

Paneth cells produce antimicrobial peptides which protect stem cells against infection

48
Q

What do we mean when we talk about segmentation in the intestines?

A

Idea that intestines can contract to push food along but then contract at a more distal part and cause almost a shunting effect; keeps food in intestines for longer to maximise absorption

49
Q

Portal vein supplies what percentage of blood going to the liver

A

70-80%

50
Q

Describe the pathophysiology of coeliac disease

A

Autoimmune response to the gliadin portion of gluten

51
Q

What is gluten found in?

A

Wheate, rye, barley and oats

52
Q

Describe symptoms of coeliac disease

A
  • Diarrhoea
  • Flatulence
  • Weight loss
  • Abdominal pain
  • Steatorrhoea
  • Fatigue
53
Q

Explain why you get weight loss, diarrhoea and flatulence in coeliac disease

A
  • Weight loss: autoimmune reaction to gliadin in gluten destroys villi so leads to malabsorption
  • Diarrhoea: malabsorption increases osmolarity of lumen of gut hence less water leaves gut/more is drawn in leading to diarrhoea
  • Flatulence: bacteria in gut ferment unabsorbed substances in bowel and produce gas
54
Q

How is coeliac disease diagnosed?

A
  • Blood test: serum antibodies to tTG
  • Upper GI endoscopy and duodenal mucsoal biopsy (will often repeat this after gluten has been removed from diet)
55
Q

How do you treat coeliac disease?

A

Gluten free diet

S3: Gastrointestinal (18 decks)

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