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Module 2- Medical Sciences > The Gastrointestinal Tract > Flashcards

The Gastrointestinal Tract Flashcards

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USMLE® Step 1 flashcards
1
Q

What is digestion?

A

the mechanical and enzymatic process whereby ingested food is converted into simpler, soluble molecules that can be absorbed

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2
Q

What are zymogens?

A

inactive precursors which are produced initially before digestive enzymes.
They are activated by the cleavage (proteolysis) of a portion of the enzyme, which inhibits the catalytic core of the protein.

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3
Q

What is the pancreas made up of?

A
  • ducts
  • lobules
  • acini
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4
Q

Where is the Parotid Salivary gland?

A

behind the tongue

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5
Q

Where is the submandibular salivary gland?

A

below mandibles

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6
Q

Where is the sublingual salivary gland?

A

below the tongue

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7
Q

What is the pharynx?

A
  • A complete muscular organ
  • Keeps air and digestive tracts separate
  • directs food into the oesophagus
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8
Q

What is bolus?

A

chewed food mixed with saliva

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9
Q

How does stomach acidification work in parietal/oxyntic cells?

A

-Water and carbon dioxide combine to form carbonic acid, which disassociate to genetarate H+ AND BICARBONATE
-Bicarbonate is exported in exchange for chloride. Chloride and potassium ions are exported in the gastric lumen by conductance channels
H+ are actively pumped out into the gastric lumen in exchange for potassium through the action of the proton pump

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10
Q

What is the inactive version of pepsin?

A

pepsinogen

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11
Q

how many cleavages are needed to remove the pro-segment?

A

2

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12
Q

How do you activate pepsinogen?

A

remove the pro-segment

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13
Q

What keeps the pro-segment in pepsin in place?

A

electrostatic interactions

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14
Q

What causes the electrostatic attraction in pepsinogen to be lost?

A

acidic conditions so a pH less than 5

this causes a conformational change that leads to a proteolytic cleavage of the pro-segment

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15
Q

What is the pancreas?

A

A fundamental digestive gland whose products are poured into the duodenum (small intestine) and are essential for digestion

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16
Q

What counteracts stomach acidity?

A

Pancreatic fluids

17
Q

Where is bile produced, stored and what is it produced by?

A

Liver
gallbladder
hepatocytes

18
Q

What happens to old red blood cells?

A

they are eaten by macrophages in a process called phagocytosis

19
Q

How is bilirubin produced and removed?

A
  • The haem group of haemoglobin is “opened up” and generates: IRON and BILLIVERDIN
  • Biliverdin is reduced to bilirubin and released into circulation
  • The liver removes bilirubin from the blood and releases it into the bile for excretion
  • Bacteria in the gut metabolise bilirubin to urobilinogen
  • Urobilinogen can be partially reabsorbed by the gut into circulation
  • reabsorbed urobilinogen is filtered by the kidney and excreted in the urine
  • it is removed by the liver and released in the bile once again
20
Q

What is jaundice?

A
  • a yellowish colouring of the skin and sclera
  • accumulation of bilirubin in the body
  • a sign if liver damage
  • caused by haemolysis, obstruction of the bile ducts, dysfunctional liver
21
Q

What are the 4 different types of bile salts?

A
  • cholic
  • deoxycholic
  • chenodeoxycholic
  • lithocholic acids
22
Q

How can bile salts be synthesized?

A
  • cholesterol

- extracted from the bloodstream by the liver

23
Q

What is the function of bile salts?

A
  • detergents to emulsify fats once they reach the small intestine
  • prepare fats for the action of pancreatic and intestinal fat-splitting enzymes
24
Q

What is the pyloric sphincter?

A

-the sphincters or valves of the digestive system which are muscular rings that control the unidirectional flow of food and digestive juices through the GI tract

25
Q

What is chyme?

A

acidic mix of partially digested food and digestive enzymes that reach the intestine

26
Q

What are enterocytes?

A

the cells responsible for absorption and digestion

27
Q

What is the difference between the small intestine and large intestine?

A

small- digestion and absorption

large- absorption of water

28
Q

What are the two steps for digestion?

A
  • Luminal digestion (pancreatic enzymes)

- Brush border digestion (intestinal enzyme)

29
Q

What are the steps for the luminal digestion of sugars?

A
  • Polymer us broken down into oligomers in the lumen
  • Oligomers broken into monomers in the lumen by brush border enzymes
  • Monomers move through transporters into the blood
30
Q

How does glucose absorption occur?

A
  • Glucose is taken up at the lumen side by a Na+/glucose transporter
  • This is an active transport against glucose concentration
  • it is powered electrochemical Na+ gradient enabled by a Na+-K+ pump
31
Q

How does the luminal digestion of proteins occur?

A
  • The polymer is broken into oligomers by luminal digestion
  • Brush border enzymes break down the oligomers into monomers
  • oligomers have to pass through the transporters to get into the blood
  • performed by pancreatic proteases- chymotrypsin and trypsin
  • produced as zymogens- chymotrypsinogen and trypsinogen
32
Q

How is lipid digestion carried out?

A
  • Begins in the oral cavity with lingual lipase
  • Most of digestion is however due to pancreatic lipases secreted by the pancreas
  • they are then emulsifies through gastric peristalsis
  • then emulsification progresses in the duodenum
  • bile salt enables stabilisation of emulsified lipid droplets
33
Q

How does triglyceride digestion and absorption?

A
  • they are broken down into glycerol and fatty acid chains
  • they then travel through transporters in to the blood or interstitial fluid
  • they then undergo a condensation reaction to form the triglyceride once again in the blood
34
Q

What is peristalsis?

A

the mechanism that allows the food to move along the GI tract

35
Q

How is tissues treated to form slides for analysis under a microscope?

A
  • surgical specimen collected
  • fixed in paraformaldehyde
  • Dehydrated in alcohol and embedded in paraffin
  • cut in 4/5 micron slices with microtome
  • pleased on negatively charged microscopy slides
  • processed for starving
36
Q

What is hematoxylin used for?

A

nuclear staining

37
Q

What is eosin used for?

A

counterstaining and cytoplasmic staining

Module 2- Medical Sciences (15 decks)

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