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GI & Metabolism (BS)
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Body Systems STRAND 3 - GI & metabolic medicine and abdominal anatomy
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BODY SYSTEMSGI & METABOLISM
,Medic_Summaries (Body Systems)
GI & Metabolism Strand
Burden of GI illness:
- GI diseases affect huge numbers of people worldwide
- Symptoms referable to the GIT are common
Major functions of GIT:
- Motility (peristalsis):
- Smooth muscle contraction
- Co-ordinated to move bolus forwards
- Need relaxation of sphincters
- Digestion
- Secretion
- Absorption
Organs of the GIT:
- Stomach:
- Storage vessel
- Churns food
- Produces acid to start breakdown
- Pancreas:
- Exocrine secretions aid digestion:
- Discharge into intestine via pancreatic duct (amylase, lipase, trypsin)
- Need basic medium for efficiency, so pancreas also produces bicarbonate
- Endocrine secretions regulate carbohydrate metabolism:
- Glucagon, insulin, gastrin, somatostatin
- Liver:
- Synthesises bile (stored in gall bladder), proteins (clotting factors)
- Metabolises carbohydrates, proteins, fats
- Stores carbohydrates, fat-soluble vitamins
- Detoxifies blood from GIT
- Intestine:
- Small: major role in absorption, mostly jejunum (impossible to survive without it)
- Large: major role in water absorption (possible to survive without it)
2 Adapted from Lectures at the University of Leeds Medical School
,Medic_Summaries (Body Systems)
Diseases of the GIT:
- Oral:
- Mucous membrane (Apathy’s ulcers)
- Anywhere (cancer)
- Salivary glands (inflammation, stones, cancer)
- Oesophagus:
- Reflux symptoms (oesophagus, Hiatus hernia)
- Cancer (squamous (middle), Aden (lower))
- Motility problems (achalasia (failure to open lower sphincter when swallowing))
- Stomach:
- Ulcers (Helicobacter pylori (H. Pylori), aspirin/NSAIDs)
- Cancer (H. Pylori)
- Pyloric stenosis due to ulceration
- Duodenum:
- Ulcers (H. pylori, aspirin/NSAIDs)
- Rarely, invasion by cancer from the pancreas
- Liver:
- Viral hepatitis (acute (any), chronic (HBV, HCV))
- Autoimmune hepatitis, primary biliary cirrhosis
- Cirrhosis (caused by chronic liver inflammation of any aetiology, alcoholic liver
disease, fatty liver, viral or autoimmune liver disease)
- Biliary tree:
- Gallstones (often silent)
- Present with biliary colic, cholecystitis, cholangitis, biliary obstruction
- Pancreas:
- Acute pancreatitis (gallstones, alcohol)
- Chronic pancreatitis (usually from repeated attacks of acute pancreatitis)
- Pancreatic cancer
- Small intestine:
- Crohn’s disease or Meckel’s diverticulum
- Small bowel obstruction
- Acute ischaemia (may lead to large resection)
- Large intestine:
- Appendicitis
- Cancer
- Ulcerative colitis or Crohn’s disease
- Diverticular disease (often silent, can inflame (diverticulitis), perforate or bleed)
Symptoms of GI disease:
- Dysphagia/odynophagia (difficulty/pain in swallowing)
- Nausea/vomiting (feeling of/act of being sick)
- Dyspepsia (feeling of early fullness/discomfort after eating normal-sized meal)
- Heartburn (regurgitation of acid causing a burning sensation)
- Bloating (sensation of abdominal swelling or visible distension of abdomen)
- Abdominal pain
- Diarrhoea (three or more liquid stools per day)
- Constipation (fewer than three stools per week; often straining and incomplete evacuation)
- Steatorrhoea (bulky, fatty, pale stools; difficult to flush)
- Haematochezia/malaena (passage of bright red blood, black and sticky stools)
Healthy diet supplies:
- Energy
- Building blocks for metabolism
- Essential nutrients
Guidelines for nutritional requirements:
- Energy balance key to maintenance of healthy weight, ideally: INTAKE = EXPENDITURE
- Energy expenditure depends on metabolic rate
- Metabolic rate depends on age, weight, sex, amount/intensity of physical activity
3 Adapted from Lectures at the University of Leeds Medical School
, Medic_Summaries (Body Systems)
Macronutrients:
- Can be used immediately for energy generation
- Excess carbohydrates and fats can be stored
- Fat stores are the main source of energy (80-90%)
- No storage of protein, but in starvation, muscle tissue can be metabolised for energy or to
provide amino acids for other reactions
Protein:
- Average adult requires ca. 0.75g/kg/day (eg. 75kg man requires ca. 50g protein/day)
- Athletes/body builders often recommended 1.2-1.7g/kg/day
- Proteins are constantly being synthesised and degraded (average 250g/day)
- Individual proteins vary in rate of turnover from minutes to years
Nitrogen balance:
- Healthy adult:
- N2 intake = N2 excretion
- Negative nitrogen balance:
- N2 intake < N2 excretion
- Occurs during fasting or illness
- Body is breaking down proteins for energy
- Positive nitrogen balance:
- N2 intake > N2 excretion
- Occurs during growth or pregnancy
- Body is building new tissue
Essential amino acids:
- Nine AAs cannot be synthesised by humans (must be obtained from diet)
- Other AAs may be required in diet under certain conditions
- Essential AAs: Met, Val, His, Leu, Phe, Trp, Iso, Lys, Thr
Problem for vegetarians?:
- Not all sources of protein contain the complete range of amino acids
- Animal proteins are complete, but plant proteins generally are not
- CYSTEINE, METHIONINE and TRYPTOPHAN most commonly lacking in plant proteins
- A good source of these amino acids include beans, rice, nuts and corn
We need lipids:
- Triacylglycerols for energy (1g fat provides 9kcal (39kJ))
- Carbohydrate and protein only provide 4kcal (17kJ)
- Cholesterol/fatty acids as precursors for important molecules (hormones, prostaglandins)
- The body can store unlimited amounts of triacylglycerol in adipose tissue
- Adipose tissue protects vital organs and gives our body and face shape
Fat in the diet:
- Saturated: no double-bonds; found in meat/dairy products (RDI: 10%)
- Mono-unsaturated: one double-bond; found in olive/peanut oil (RDI: 12%)
- Polyunsaturated: more than one double-bond; found in corn/sunflower oil (RDI: 6%)
- Trans (hydrogenated): trans double-bonds, found in cakes/biscuits/pastry (RDI: <2%)
- Total fat RDI: <35%, though <30% is desirable
Carbohydrates:
- Polysaccharides (mainly starch)
- Disaccharides (mainly sucrose)
- Monosaccharides (mainly glucose/fructose)
- Non-starch polysaccharides (dietary fibre)
4 Adapted from Lectures at the University of Leeds Medical School
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