The Intestines Flashcards
Compare and contrast the features of the jejunum and ileum
Identify the branches of the superior mesenteric artery that supplies the midgut
Jejunal and ileal - supply the jejunum and ileum
Ileocolic - supplies ileum leading the colon and the appendix area
Right colic - supplies the ascending colon
Middle colic - supplies the transverse colon
Identify the veins that drain the midgut
Which veins make up the Portal Vein?
Superior mesenteric Vein and Splenic vein
When the terminal branches of the middle colic, right colic and ileocolic anastamose they form which artery?
The Marginal Artery
What features of the small intestine allow for increased surface area for absorption?
Villi and microvilli
Plica circularis (permanent folds)
How fast or slow do contents move through the small intestine and why?
Slow movement allows for precise control of what is/ isn’t absorbed
How often is mucosa of the intestinal epithelia shed?
Every 3-6 days
Which cells make up the epithelia of the small intestine and what is the function of each?
- Enterocytes - absorption cells
- Goblet cells - mucus producing
- Enteroendocrine cells - produce hormones
Which cells line the intestinal glands (Cryps of Lieberkuhn) and what is the function of each?
- Stem cells - migrate to surface to replace lost cells
- Paneth cells - produce antimicrobial peptids to defend stem cells
Which size of carbohydrate can be absorbed in the small intestine?
Monosaccharides only
(Glucose, Galactose, Fructose)
How is starch digested?
- Amylase breaks alpha 1-4 glycocydic bonds
- Isomaltase breaks alpha 1-6 glycocydic bonds
What are short unbranched and short but branched chains of glucose called?
- Short and unbranches = maltose
- Short and branched = alpha dextrins
Which 2 monosaccharides make up lactose?
Glucose and Galactose
Which two monosaccharides make up sucrose
Glucose and Fructose
How are monosaccharides absorbed across the enterocyte?
- SGLT1 co-transports Na+ and glucose (or Galactose) across the brush border
- GLUT5 transports fructose across the brush border
- Monosaccharides transported across basolateral membrane by GLUT 2 transporter
- Na+/ K+ ATPase maintains the gradient
How are proteins digested in the stomach?
Pepsinogen released from chief cells in the stomach
Pepsinogen activated to pepsin by HCl which digests proteins to oligopeptides/ amino acids
Which protease released by the pancreas activates other proteases once activated? Which enzyme activates it?
Trypsin
Activated from trypsinogen by enterokinase on epithelial cells
What’s the difference between endopeptidases and exopeptidases?
Endopeptidases→ break bonds in middle of polypeptide
Exopeptidases → break bonds at the end to give individual amino acids
Name some main endopeptidases and exopeptidases?
endopeptidases:
- Trypsin
- Chymotrypsin
- Elastase
exopeptidases:
- Carboxypeptidase (A & B)
Which transporter can asborb short peptides across the brush border into the enterocyte?
PepT1
How are amino acids transported into the enterocyte?
Co-transported with Na+
What is the final step of protein digestion?
cytosolic peptidases in the cytosol of the enterocyte breaks down small peptides so they can be absorbed into blood
How is water absorbed in the small intestine?
Water follows the movemenent of Na+ into the enterocyte
Either moves transcellularly or paracellularly
What is the key difference between Na+ absorption in the small and large intestine?
Small intestine: Na+ transported with glucose/ amino acids
Large intestine: Na+ channels which are induced by aldsoterone when blood pressure gets low (Increased Na+ absorption → water follows)
What components make up oral rehydration solution?
Mixture of glucose and salt (NaCl)
Allows for maximal water uptake as water follows Na+ which is absorbed with glucose
What drives water movement out of enterocytes and into the gut?
Driven by chloride movement
- Chloride co-transported with Na and K into epithelial cell
- Levels of cAMP rise and activates CFTR channel
- Cl- ions are secreted
- Na+ driven into lumen by tight junctions
- Water follows NaCl secretion and moves down the osmotic gradient
What 4 reasons pertaining to the GI system can lead to a vitamin B12 deficiency?
- Lack of intrinsic factor released by parietal cells
- Hypocholorhydria (inadequate stomach acid)
- Inadequate intake seen in strict vegetarians
- Inflammaotry disorders of the ileum where B12 is absorbed e.g. crohn’s
What is the basic defect in lactose intolerance?
A deficiency in the enzyme lactase as the brush border of enterocytes meaning lactose cannot be digested
What is the consequence of not being able to breakdown lactose?
- Lactose cannot be absorbed and remains in the gut lumen
- Lactose is osmotically active drawing water into the lumen
- This leads to diarrhoea
- Lactose in the gut it fermented causing bloating and flatulence
What are some of the symptoms of irritable bowel syndrome?
- Abdominal pain (often cramping, sometimes relieved by defaecation)
- Bloating
- Flatulence
- Diarrhoea/ constipation
- Rectal Urgency
What is the incidence of irritable bowel syndrome?
- Affects 10-15% of adults
- More common in females vs males (2:1)
- 20s-40s the most affected age range
- Associated with psychological disorders
What is the pathology in coeliac disease?
An immunological response to the gliadin component of gluten
found in wheat, rye and barley
What damage to the intestinal mucosa occur in coeliac disease?
- absence of intestinal villi
- hypertrophy/ legnthening of intestinal crypts
- lymphocytes infiltrate epithelium and lamina propria
- Impaired digestion/ malabsorption
What are some of the symptoms of coelic disease?
- Majority related to malabsorption
- diarrhoea
- weight loss
- flatulence
- abdo pain
- Anemia by impaired Fe2+ absorption
- Neurological symptoms (hypocalcaemia)
What investigations would you do if you suspected someone has coeliac disease?
- Bloods - looking for IgA antibodies to smooth muscle endomysium and tissue transgluataminase
-
Upper GI endoscopy + biopsy is the gold standard
- looking for mucosal pathology and reduced/ absent villi
How do you treat coeliac disease?
Strict gluten free diet
Will see clinical improvement very quickly and histological improvement in weeks/ months
