GI Tract Theme 3

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  • Created by: Splodge97
  • Created on: 22-05-17 21:53
What is fibre?
Dietary carbohydrate made mostly of cellulose, has beta-1,4 linked glucose making it indigestible
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What are the features of starch?
Isn't cariogenic unless high residence time, should comprise 35% energy in diet. In form of amylose (linear, A-1,4 linked glucose) or amylopectin (branched, A-1,4 and A-1,6 links).
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Describe starch digestion by A-amylase
In the mouth digests A-1,4 links (except adjacent to a 1,6 branch point or at end of a chain) so digests amylose (and partially amylopectin). Action prevented in stomach by low pH.
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How is starch digested further?
Salivary and pancreatic amylases produce maltose, maltotriose and A-limit dextrins before oligosaccharides in the duodenum and jejunum complete digestion.
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What oligosaccharidases are present in the duodenum and jejunum?
Sucrase (sucrose-->glucose+fructose), associated with isomaltase (hydrolyses 1,6 links so digests A-limit dextrins/amylopectin); also lactase (lactose-->glucose+galactose) and maltase (maltose--> 2 glucose)
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How does SGLT-1 act to absorb carbohydrate?
Actively uptakes glucose and galactose at apical membrane; symporter which has Na+ grad set up by Na+/K+/ATPase
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How does GLUT-5 act to absorb carbohydrates?
Allows passive facilitated diffusion of fructose at the apical membrane
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How does GLUT-5 act to absorb carbohydrates?
Transports monosaccharides into the blood at the basolateral membrane
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What are the syymptoms of lactose intolerance?
Osmotic diarrhoea and (through digestion via colonic bacteria) flatulence, borborygimi (gurgling) and distension. To prevent should have no more than 5-10g lactose a day.
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What is sucrase-isomaltase deficiency?
Inherited, low sucrase-isomaltase activity means intolerance to starch and sucrose
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What is glucose-galactose malabsorption syndrome?
Rare hereditary disorder, mutation of SGLT-1 prevents absorption of glucose and galactose; diet very restrictive
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Why can protein still be comsumed after gastrectomy (stomach removal)?
As pepsin only accounts for 15% of protein digestion
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What is the role of trypsin?
Enterokinase makes from trypsinogen; performs 85% protein digestion. Activates chymotrypsinogen to chymotrypsin and pro-elastase to elastase (these act on the bulk of chains) and procarboxypeptidase to carboxypeptidase (hydrolyses ends).
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What are the actions of the BBM peptidases?
Aminopeptidase = cleaves single AA from end. Dipeptidyl aminopeptidase = cleaves dipeptide from end. Dipeptidase = cleaves dipeptides to 2AA's.
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Where does protein absorption occur?
Duodenum and jejunum - despite this slow as many stages
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How does PEPT1 (peptide transporter 1) act in protein absorption?
Allows small peptides to enter via symport with H+ at apical membrane. Peptides hydrolysed in the cell by cytosolic proteases. Requires H+/Na+ symporter to remove H+ so conc grad maintained; in turn needs Na+/K+/ATPase to work (so indirectly active).
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How do specific amino acid transporters play a role in protein absorption?
Seven at the BBM (5 sodium dependant, 2 facilitated diffusion). Five at the basolateral membrane (2 sodium dependant, 3 facilitated diffusion).
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How are vitamins normally absorbed?
Water soluble = specific transporter in duodenum/jejunum. Lipid soluble (like Vit K) = require presence of dietary fat.
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How is vitamin B12 absorbed in the terminal ileum?
Proteins B12 associated with in meat hydrolysed in stomach. B12 binds to R proteins (glycoproteins from salivary/gastric glands). In SI pancreatic proteases destroy complex so B12 binds to IF; complexes resist digestion. B12-IF receptors accept.
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What occurs once B12-IF complexes have entered the gut epithelia?
Stored for 5-7 hrs (thought mitochondria remove IF), then B12 released to bind to transcobalamine II in the blood
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What constitutes early lipid digestion (before the duodenum)?
Small amount by lingal lipase, then a little more by gastric lipase (not optimal as prefferred pH 6-7). Both convert triglycerides to 2-monoglyceride and 2NEFA's.
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What occurs once lipids enter the duodenum?
Rate of release by pyloric sphicter reduces. In SI lipids esterified by bile salts and lecithin (phospholipid) to increase surface area for lipiolytic enzymes from the pancreas (which fully digest).
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Which pancreatic enzymes act in lipid digestion?
Pancreatic lipase hydrolyses triglycerides, requires colipase to displace bile salts. Cholesterol esterase removes an NEFA from cholesterol esters to form cholesterol. Phospholipase A2 hydrolyses phospholipids to an NEFA and a lysophospholipid.
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What are micelles?
Formed from the products of lipid digestion surrounded by bile salts; when complete 5mm in diameter, contain 20-30 molecules. Once critical micelle conc reached act as a surfactant (mix with chyme so efficient digestion).
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How are lipids absorbed?
Micelles pass from high conc in lumen into unstirred layer at BBM of jejunum and ileum. Creates solution saturated with digestion products; diffuse into the epithelium (cholesterol facilitated). Long chain FA's enter via MVM-FABP (secondary AT).
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How are chylomicrons formed from the produucts of lipid digestion?
In gut epithelia the digestive products are re-constituted at the SER (enter via cytosolic lipid tranport proteins (FABP/sterol carriers)) to form pre-chylomicrons. Golgi adheres/adds apo proteins to form chylomicrons (exocytosed into lacteals).
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Why is entry of fatty acids into the blood so slow?
Due to fatty layer formed by lipids in the stomach and fact chylomicrons must enter lymph (too big for transport via normal means, may block capillaries) and travel to the thoracic duct before reaching the venous system
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How are bile salts (from micelles) processed?
Absorbed at the terminal ileum, may be conjugated with glycine/taurine. If conjugated taken up by Na+/bile co-transporter into blood, bind to albumin and return to liver via hepatic portal system (form more bile). If not pass through BBM into faeces.
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What are widespread malfunctions of the GI tract?
Diarrhoea (acute loss of 1-20g/day, chronic loss of 200-1500g/day - water/electrolyte loss requires oral rehydration therapy), gastroenteritis (infection/food poisoning, causes diarrhoea/vomiting) and gastrointestinal cancer
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What causes oropharyngeal dysphagia (difficulty swallowing)?
Inadequate trachea closure through neuromuscluar disease/stroke (temporary) weakening muscles. Causes coughing/choking, then pneumonia if food enters lungs.
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How is oropharyngeal dysphagia treated?
S+L therapy or PEG (percutaneous endoscopic gastronomy) where food inserted through nose (short term) or into stomach (long term)
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What is oesophageal dysphagia? How is it treated?
Food sticking after swallowing due to aphasia (lack of peristalsis and failure of lower oesophageal sphincter) or strictures (narrowings of oesophagus). Causes regurgitation and weight loss, resolved via S+L therapy/dietary management.
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What is heartburn?
Reflux of gastric acid into the oesophagus (not protected by mucous from low pH). Increased risk in pregnancy/obesity (as pressurise stomach) and via alcohol, smoking, chocolate, coffee, drugs and menstrual hormones.
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What may result if heartburn becomes chronic?
GORD (gastro-oesophageal reflux disease) where oesophagus ulcerated or Barret's oesophagus where abnormal cell growth; both increase cancer risk
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What is hiatus hernia? How is it treated?
Usually no symptoms. Stomach rises through oesophageal aperture of diaphragm in heavy coughing/vomiting/straining/exercse/pregnancy. Fixed surgically. Increased risk after multiple pregnancies.
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What is dyspepsia?
Indegestion - presents as pain (as acid enters peptic ulcer), nausea, distension, discomfort, flatulence and regurgitation. Treated by helicobacter eradication therapy (week course of antibiotics and gastric acid supressant) to heal peptic ulcer.
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What is steatorrhoea?
Insufficient fat absorption so faeces >5g fat/day. Due to pancreatic insufficiency/coeliac disease/Crohn's/gastric surgery/daiabetes/antibiotics/lymphoma. Causes chronic diarrhoea and bulky/smelly/greasy stools. Cause treated alongside supplements.
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What is Coeliac disease?
Intolerance to gluten (protein in bread/wheat/flour) causes damage/bleeding of villi of SI so SA reduced (and iron/folate supplements needed). Must avoid gluten to allow villi to heal (improving absorption).
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What is Crohn's disease?
Imflammatory bowel disease, possibly genetic; present as inflamed/bleeding area. Prolong remission by corticosteroids/immunosupressants; relapse treated by IV fluids, transfusions, IV steroids (to regain remission), parental nutrition or surgery.
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What is ulcerative colitis?
Inflammatory bowel disease, possibly genetic/dietary, more common than Crohn's. Occurs in rectum or caecum, causes itchy red eyes and ulcers on arms/legs. Remission pronged by corticosterioids/immunosupressants, surgery if severe (as colon short).
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How can stomas be used for feeding?
In gastrostomy (stoma to stomach) or jejunostomy (stoma to jejunum)
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How can stomas be used in the treatment of intestinal disease?
After total colectomy (LI removal) due to Crohn's/ulcerative colitis/cancer; means electrolyte/water balance reduced so product liquid. Better after colestomy (colon cancer removed but some LI remains) as some absorption/product more viscous.
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What is diverticular disease?
Experienced by those >65 in MEDC's; high proccessed diet means large amount absorbed so little passes into LI to produce faeces. More pressure used to squeeze colon, creating asymptomatic pockets in bowel wall (through muscular hypertrophy).
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What are the risk factors of constipation?
Colorectal cancer, diabetes, metabolic imbalance, Parkinson's, psycological problems, dementia, polypharmacy, age, immobility and spinal cord injuries. Lifestyle factors also influence (fluid/fibre intake and frequency of eating).
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What occurs in IBS? How is it treated?
High amplitiude pressure waves along the GI tract causing abdomiinal pain and diarrhoea/constipation. Cause unknown - related to stress/diet/anxiety/depression, so these aim to be controlled.
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What will be assessed if a data set has normal distribution?
Mean and standard deviation
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What will be assessed if a data set is non-parametric?
Median and range
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What statistical tests can be used to analyse experiments repeated on the same subjects?
Normal distribution = Paired t-test. Non-parametric = Willcoxon test.
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What statistical tests can be used to analyse experiments involving two different samples?
Normal distribution = Independant t-test. Non-parametric = Mann-Whitney test.
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Card 2

Front

What are the features of starch?

Back

Isn't cariogenic unless high residence time, should comprise 35% energy in diet. In form of amylose (linear, A-1,4 linked glucose) or amylopectin (branched, A-1,4 and A-1,6 links).

Card 3

Front

Describe starch digestion by A-amylase

Back

Preview of the front of card 3

Card 4

Front

How is starch digested further?

Back

Preview of the front of card 4

Card 5

Front

What oligosaccharidases are present in the duodenum and jejunum?

Back

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