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Clinical Biochem > GI Tract > Flashcards

GI Tract Flashcards

1
Q

What are the major functions of the digestive tract ?

A
  1. motility - propel ingested from mouth downwards
  2. secretion of juices - aid in digestion & absorption
  3. digestion - food broken down into absorbable molecules
  4. absorption - nutrients, electrolytes, water absorbed or transported from lumen of GIT to blood
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2
Q

What does the GI tract consist of ?

A
  • oral cavity/mouth
  • pharynx
  • oesophagus
  • stomach
  • small intestine
  • large intestine
  • rectum
  • anus
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3
Q

Define bolus

A
  • portion of food swallowed at one time
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4
Q

Describe saliva

A
  • water, salts, enzymes, mucus secreted by salivary glands to;
  • moisten food & aid swallowing
  • beginnings carbohydrate digestion
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5
Q

Describe what occurs in the oesophagus during digestion ?

A
  1. epiglottis closes airway
  2. bolus moved along by peristalsis
  3. cardiac sphincter - keeps food from backing up into oesophagus
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6
Q

Describe the anatomy of the oesophagus

A
  • 25cm long
  • 2 muscular rings - 1 at top and 1 at bottom = upper & lower oesophageal sphincter
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7
Q

Describe the upper oesophageal sphincter

A
  • open reflexively upon swallowing
  • remains open for 0.5-1 s
  • this allows bolus to enter oesophagus
  • typically disconnected from pharynx prevents swallowing air
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8
Q

Describe the lower oesophageal sphincter

A
  • relaxes reflexively 2 seconds after being stimulated by swallowing
  • controls how quickly food travel from the throat to the stomach after being swallowed
  • prevents the regurgitation of food, gastric juice & air
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9
Q

Describe what happens in the stomach ?

A
  • gastric glands secrete gastric juice kills most bacteria, protein digestion begins & mucous secreted to protect lining
  • chyme = semi-liquid mass of partially digested food
  • pyloric sphincter - regulates passage of chyme into small intestine
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10
Q

Describe Chyme

A
  • semi-fluid mass of partly digested food that is expelled by stomach via pyloric valve into duodenum
  • results from chemical & mechanical breakdown of bolus
  • slowly passes through pyloric sphincter into duodenum where nutrient extraction begins
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11
Q

Define the pyloric sphincter

A
  • muscular valve that opens to allow food to pass from the stomach to the top of the small intestine (duodenum)
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12
Q

Define mucus

A
  • physical barrier between lumen & epithelium
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13
Q

Define bicarbonate

A
  • buffers gastric acid to prevent damage to epithelium
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14
Q

Define intrinsic factor

A
  • complexes with vitamin B 12 to permit absorption
  • glycoprotein produced by parietal cells of the stomach
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15
Q

What are the 2 types of pancreatic secretions ?

A
  1. Endocrine functions = secretes insulin & glucagon
  2. Exocrine functions = secretion of pancreatic juice, 2 components - aqueous & enzymatic component
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16
Q

Describe the aqueous component

A
  • HCO3
  • Important for neutralising stomach acid, so pancreatic enzymes can function
17
Q

Describe the enzymatic components of exocrine pancreatic secretions

A
  • Essential for digestion & absorption of carbohydrates, fats, proteins
    (trypsin,chemotrypsin,lipase & amylase)
18
Q

What are the 3 sections of the small intestine ?

A
  1. duodenum
  2. Jejunum
  3. Ileum
19
Q

Describe the duodenum

A

opening from common bile duct secretes fluid from;
- liver & gallbladder - bile emulsifies fats
- pancreas - amylase breaks down carbohydrates, sodium bicarbonate neutralises acidic chyme & lipase

20
Q

Describe the small intestine

A
  • 3 sections = duodenum, jejunum, ileum
  • where most of the absorption of nutrients take place
  • receives bile & pancreatic juice
  • folded many times to fit in the abdomen
21
Q

What are the main functions of the large intestine ?

A
  1. absorbing water & electrolytes
  2. producing & absorbing vitamins
  3. forming & propelling faeces towards the rectum for elimination
22
Q

What are the secretions of the large intestine ?

A
  • alkaline secretion - neutralises acids produced by intestinal bacteria
  • mucous for protection, lubrication of faecal matter
  • vitamin B & K absorption made from bacterial flora in colon
23
Q

Describe the absorption of carbohydrates

A
  • enterocytes absorb glucose & galactose through an Na-dependant secondary active transport, while fructose is absorbed by facilitated transport
24
Q

Briefly describe the absorption of proteins

A
  • whole proteins = endocytosis
  • amino acids & di & tripe-tides by Na-dependent 2ry active transport
25
Q

Define peptic ulcer

A

Heliobacter pylori infection major cause, secretes urease enzyme neutralises environment

26
Q

How do you test for H.pylori infection?

A

Urea Breath Test = depends on urease activity of organism to detect activate infection
- 13 C labelled urea given by mouth, CO2 detected in breath

27
Q

Describe Zollinger-Ellison syndrome

A
  • rare endocrine disorder with 3 interrelated pathologies
    1. gastrinoma = gastrin secreting tumour
    2. increased gastric acid secretion
    3. peptic ulcers
28
Q

What are some examples of upper GI tract issues ?

A
  • dysphagia = difficulty swallowing
  • gastritis = inflammation of stomach lining
  • peptic ulcers = erosions of lining of stomach or duodenum
29
Q

Define pancreatitis

A
  • commonly caused by gallstones & alcoholism
  • plasma amylase activity measured - for diagnosing acute pancreatitis
30
Q

Define Plasma amylase

A
  • arises from pancreas & salivary glands
  • activity 10x normal diagnostic of acute pancreatitis
  • activity returns to normal within 3-5 days
31
Q

What are some symptoms of acute pancreatitis ?

A
  • severe belly pain that may spread to back/chest
  • nausea/vomiting
  • rapid heart rate
  • fever
  • fluid build up in belly
  • lowered BP
32
Q

Describe the Xylose Absorption test

A
  • test for carbohydrate absorption
  • D-Xylose given, rapidly absorbed from small intestine, excreted in urine, little metabolised in liver
  • assess intestines ability to absorb monosaccharide
  • bacterial overgrowth & renal disease can give false positives
33
Q

Describe Disaccharidase Deficiency

A

-most common = intolerance to one of the disaccharides (lactose, maltose,sucrose)
- defect may be congenital or acquired
- activity measured in intestinal mucosa biopsy specimens

34
Q

Describe Hartnup Disease

A
  • impaired transport of neutral amino acids & deficiency of some essential amino acids
35
Q

What are some specialist tests that can be carried out on the GI tract ?

A
  • endoscopy
  • abdominal ultrasound
  • barium X-ray
  • MRI

Clinical Biochem (11 decks)

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