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Clinical Biochemistry: Introduction to Clinical Biochemistry > Pancreas and GI Tract Physiology > Flashcards

Pancreas and GI Tract Physiology Flashcards

1
Q

Decribe the GI Tract

A
  • Muscle that extends from the mouth to the anus (~10 m)
  • Mainly smooth muscle under involuntary control
  • Striated muscle under voluntary control at upper oesophagus and external anal sphincter
  • Main organs of the GI Tract are Stomach, Small intestine, Large intestine, Pancreas, Gall bladder
  • Accessory organs are Salivary glands, Liver, Gall bladder, Pancreas
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2
Q

What are the functions of the GI Tract?

A
  • Ingestion: Mouth, Oesophagus)
  • Digestion (Mechanical/Chemical): Mouth, Stomach, Small intestine, Large intestine
  • Absorption: Small intestine, Large intestine
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3
Q

How is GI Tract function regulated?

A

Parasympathetic nervous system

  • Stimulation of vagal nerve, release of acetylcholine (neurotransmitter)

Intrinsic nervous system

  • Stretch receptors located in oesophagus, stomach, intestine

Hormones

  • Released as a result of the above act on nearby (paracrine) or far away tissues (endocrine)
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4
Q

What are the phases of digestion and absorption?

A
  • Neurogenic phase
  • Gastric phase
  • Intestinal phase
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5
Q

Describe the Neurogenic Phase of Digestion and Absorption

A
  • Initiated via intake of food into the mouth (sight, smell, taste)
  • Stimulation of cerebral cortex and appetite centres in amygdala and hypothalamus
  • Stimulates the parasympathetic nervous system, the vagal nerve & acetylcholine release to prepare stomach for arrival of food.
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6
Q

Describe the Gastric Phase of Digestion and Absorption?

A
  • Initiated by distension of the stomach which stimulates contraction of stomach
  • Increased Gastrin secretion from G cells via vagal stimulation and stretch receptors stimulates parietal cells to produce gastric acid
  • Gastrin also increases release of pepsinogen from Chief cells which is activated to pepsin in the acidic environment and begins to degrade protein
  • Release of intrinsic factor from parietal cells to bind vitamin B12 preventing degradation and facilitating
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7
Q

Describe the intestinal phase of Digestion and absorption?

A
  • Intestinal phase of digestion and absorption begins when chyme (mixture of partially digested food) enters duodenum
  • Fats, amino acids, and carbohydrates stimulate cholecystokinin (CCK) release from duodenal I cells (chemoreceptors). This stimulates pancreatic acinar cells to secrete digestive enzymes, and the gall bladder to expel stored bile
  • A fall in pH (pH<4.5) stimulates duodenal S cells to secret secretin. This stimulates pancreatic duct cells to secrete HCO3-to neutralise pH, and also inhibits gastrin secretion
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8
Q

How does food travel in the Gastrointestinal system?

A
  • Symmetrical contraction and relaxation of smooth muscles that propagates in a wave down a tube
  • Behind food contract and infornt of the food relaxes
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9
Q

What are the functions of the stomach?

A
  • Mechanical breakdown of food
  • Release of gastric acid (HCl) from parietal cells
  • Release of intrinsic factor from parietal cells (B12 absorption)
  • Release of pepsinogen from chief cells
  • Release of gastrin from G cells
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10
Q

What are stomach cell types?

A
  • Mucous neck cell - Mucus and Bicarbonate secretion
  • Parietal Cells - Gastric acid and Intrinsic factor secretion
  • Enterochromaffin-like cell - Histamine secretion
  • Chief Cells - Pepsinogen and Gastric lipase secretion
  • D-Cells - Somatostatin secretion (inhibits acid)
  • G-Cells - Gastric Secretion (stimulates acid)
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11
Q

How is Gastrin Regulated?

A

Released from G cells in antrum of stomach, duodenum and pancreas

Gastrin release is stimulated by:

  • Neurogenic control
  • Stretch receptors in stomach
  • Presence of partially digested proteins in stomach

Gastrin release is inhibited by:

  • Presence of acid in stomach
  • Somatostatin
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12
Q

What effect that Gastrin have in the Gut?

A

Gastrin stimulates secretion of:

  • Gastric acid
  • Pancreatic juice
  • Pepsinogen
  • Somatostatin
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13
Q

What is the structure of the intestines?

A

Small intestine (95% absorption of small nutrients)

  • Duodenum
  • Jejunum
  • Ileum

Large intestine (absorption of fluid)

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14
Q

What is the function of the pancreas?

A
  • Endocrine – secretes insulin, glucagon, somatostatin
  • Exocrine – secretes pancreatic juice

Responsible for most digestion that takes place

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15
Q

What is the function of the gallbladder?

A

Stores Bile produced by the Liver

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16
Q

What makes up Pancreatic Juice?

A
  • Fluid
  • Bicarbonate – to neutralise gastric acid
  • Electrolytes
  • Enzymes
  • Proteases – trypsin, chymotrypsin, elastase
  • Lipase, cholesterol esterase
  • Amylase
17
Q

What is the digestion and absorption of Carbohydrates?

A

Mostly in the form of starch

  • Amylase in saliva helps to digest starch but inhibited by stomach pH
  • Amylase released from pancreas in duodenum to further digestion
  • Disaccharides are digested by enzymes at brush border membrane

Leads to absorption of monosaccharides: Glucose, Fructose, Galactose

18
Q

How are proteins digested and absorbed?

A
  • Acid in the stomach helps to denature proteins and activate pepsin from pepsinogen
  • Trypsin, chymotrypsin, elastase and other proteases are secreted by the pancreas into duodenum
  • Eventual digestion to di and tripeptides and disingle amino acids which are absorbed
  • Small peptides and amino acids are absorbed by the brush border membrane
19
Q

How are Fats disgested and absorbed?

A
  • Triglycerides, cholesterol, fat-soluble vitamins are non-water soluble fats so need bile acids to emulsify
  • This allows lipase and cholesterol esterase released from the pancreas to digest the fats
  • Fats can then diffuse across the phospholipid membrane of the brush border enterocyte cells
  • These are made into chylomicrons and enter the lymph system and then liver
20
Q

What are some signs and symptoms of malabsorption?

A
  • Diarrhoea
  • Steatorrhoea (fatty stools –foul odour, pale)
  • Malnutrition
  • Abdominal pain
  • Abdominal distension
21
Q

Which tests are used for confirmation of malabsorption?

A
  • U&E - Electrolyte Balance
  • Calcium, Albumin - Vitamin D deficiency
  • Phosphate, Mg2+
  • Vitamins and trace elements
  • CRP, ESR - Inflammation
  • FBC - Anaemia
  • Iron, Ferritin - Iron deficiency
  • Prothrombin time/INR - Vitamin K deficiency
  • Vitamin B12/Folate - Haematinic deficiency
22
Q

Describe presentation and cause of Gastric Ulcers?

A
  • Gastric and duodenal ulcers present with epigastric pain at mealtimes, bloating, nausea and vomiting, haematemesis
  • Helicobactor pylori is the main cause of peptic ulcer disease
  • Rarely (~0.5% cases) ulcers may be due to Zollinger-Ellison syndrome due to a gastrin secreting neuroendocrine tumour. Likely refractory to common treatments
23
Q

What are the investigations used for the causes of Gastric Ulcers?

A
  • H.pylori stool antigen test
  • Fasting gastrin is useful in diagnosis of Zollinger-Ellison
24
Q

What are some investigations for intestinal function?

A
  • Anti-TTG antibodies - Coeliac screen
  • Hydrogen breath test - Disaccharidase deficiency, Lactose intolerance
  • Markers of intestinal inflammation - CRP/ESR (non-specific), Faecal calprotectin specific IBD
  • Endoscopy
  • Biopsy
25
Q

What is Faecal Calprotectin?

A
  • Calcium-binding protein present in high concentration in neutrophils
  • When neutrophils are localised to intestine due to inflammation, faecal calprotectin is secreted into the lumen and excreted in faeces
  • Used to differentiate function disease (IBS) from organic disease (IBD) but also raised in: GI malignancy, infection, gastric ulcers, esophagitis, diverticulitis, use of NSAIDs
  • Good ‘rule out test’ . Used to stratify referrals/ colonoscopies
26
Q

Describe Pancreatic Function tests

A

Invasive (direct) function tests

  • Specific
  • Sensitive
  • BUT unpleasant for patient, time consuming, specialist skills and equipment required
  • Rarely used in routine practice

Non-invasive (indirect) function tests

  • Not as specific for pancreatic function
  • Not as sensitive – may not pick up pancreatic insufficiency until severe
  • BUT quick and easy to carry out, convenient for the patient and cheap
  • Used in routine practice
27
Q

How is Direct Pancreatic Function testing conducted?

A

Stimulate pancreatic secretion of enzymes, bicarbonate, fluid and collect directly from pancreas using an endoscope

Can stimulate with:

  • CCK, Secretin or CCK AND Secretin (Gold Standard)
  • Lundh test meal

Measure volume, [bicarbonate], enzyme activity. This can pick up mild insufficiency

28
Q

How is Indirect Pancreatic Function testing conducted?

A

Measurement of pancreatic enzymes in:

  • Stool - faecal elastase (mostly useful test for chronic pancreatic insufficiency)
  • Blood - amylase, lipase (only used for acute pancreatitis)

Convenient – random faeces sample

Not sensitive at picking up mild pancreatic insufficiency

Measured by immunoassay

29
Q

How is the Hydrogen Breath test conducted?

A

Hydrogen breath test (Disaccharidase deficiency,Intestinal bacterial overgrowth)

  • Sugars that are not digested and absorbed into the enterocyte travel to the large intestine
  • Bacteria ferments with the sugars and produce methane and/or hydrogen which increases in breath
  • Fast overnight

Intestinal Bacterial Overgrowth - Give glucose/ lactulose (not absorbed by intestine)

Dissacharide Deficiency - Give fructose, lactose for disaccharidase deficiency

30
Q

What are non-biochemical tests for Pancreatic Function?

A
  • CT scan - Computed Tomography
  • ERCP - Endoscopic Retrograde Cholangiopancreatography
  • MRCP - Magnetic Resonance Cholangiopancreatography

Clinical Biochemistry: Introduction to Clinical Biochemistry (11 decks)

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