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Kofi: Pure Clinical Sem 3 > GI: Pancreas, Gallbladder & Liver > Flashcards

GI: Pancreas, Gallbladder & Liver Flashcards

1
Q

Describe the key properties of chyme leaving the stomach

A
  • Hypertonic
  • Low pH
  • Partially digested
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2
Q

List the secretions of the exocrine pancreas

A

Acini

  • Amylases
  • Lipases
  • Proteases (trypsin, chymotrypsin, Elastase, Carboxypeptidase

Duct cells

  • Aqueous compenent
  • Bicarbonate
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3
Q

What stimulates pancreatic and biliary secretions?

A

Secretin
CCK (enzymes)
Autonomic (PNS stimulates, SNS inhibits)

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4
Q

Describe the mechanism of secretion of alkaline component?

A
  • Stimulated by secretin
  • Release of aqueous bicarbonate component of pancreatic secretions by duct cells to neutralise chyme. Also released as part of bile
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5
Q

Describe how the microscopic structure of the liver relates to its functions

A
  • Hexgonal arrangement
  • Triad of structures at each corner (portal vein, hepatic artery, bile duct)
  • Substance brought liver start at periphery and work towards middle
  • Central vein in the middle
  • Blood enter lobule via hepatic artery and portal vein
  • Blood flows toward central vein via sinusoids (low pressure)
  • Bile flows out alone canaliculi then bile duct into duodenum
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6
Q

Why are pancreatic proteases release in inactive forms?

A
  • Inactive protease enzymes (zymogen) produced within acinar cells and are concentrated and stored in zymogen granules. Prevent autodigestion of pancreas
  • The enzymes are converted to active forms where they need to be used
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7
Q

Describe the digestive functions of the liver and the components of bile

A

Liver secretes bile into duodenum to emulsify fat so they can be readily digested by lipases secreted by pancreas

Bile consists of

  • Bile acids and bile pigments
  • Alkaline solution
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8
Q

The liver acinus is divided in zone 1, 2, 3 starting from the periphery towards the centre. Where is toxic and ischaemic damage likely to have a greater effect?

A

Toxic
-Zone 1. Last region to receive blood supply

Ischaemic
-Zone 3. Last region to receive blood supply

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9
Q

Describe the function of the gall bladder and the relationship to the formation of gallstones

A
  • Bile is stored in the gallbladder

- Concentrates bile which can lead to gallstones

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10
Q

Describe the secretion of bile acids and the entero-hepatic circulation of bile acids

A

-CCK stimulates bile release by causing gallbladder contraction

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11
Q

What are bile salts?

A

Two primary acids

  • Cholic acid
  • Chenodeoxycolic acid

Bile salts are bile acids conjugated with amino acids

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12
Q

Why are bile acids conjugated?

A
  • Not always soluble at duodenal pHs

- Bile salts have amphipathic structure so can fact at oil/water interface

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13
Q

Describe the mechanisms of digestion of fats

A
  • Lipids tend to form large globules by time reached duodenum which results in small surface area for enzymes to act
  • Bile salts emulsify fat into smaller units to increase surface area and allow lipases to act
  • Bile salts then create micelles with product of lipid breakdown
  • Micelle transports digested lipids to luminal membrane of enterocyte
  • Lipids diffuse into intestinal epithelial cells
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14
Q

What is the enter-hepatic circulation of bile acids?

A
  • Bile salts remain in gut
  • Reabsorbed in terminal ileum
  • Returned to liver in portal blood

Liver recycle bile acids

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15
Q

How are digested fat transported to the blood circulation?

A
  • Inside the enterocyte, lipid molecules are built back up again into triglycerides, phospholipids and cholesterol
  • Lipids packed with apoproteins within enterocyte into chylomicrons
  • Chylomicrons exocytosed from basolateral membrane of enterocyte ad enter lymph capillaries into thoracic duct
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16
Q

What is steatorrhoea?

A
  • Certain pathologies may cause bile acids or pancreatic lipases to not be secreted in adequate amounts
  • Undigested fat appears in faeces. It is pale, floating and foul smelling
17
Q

How does chyme becomes isotonic as it leaves the duodenum?

A
  • Stomach is impermeable to water
  • Duodenum is relatively permeable to water
  • Hypertonic chyme draws movement of water from ECF/circulation into duodenum
18
Q

What are the key points of carbohydrate digestion?

A
  • Carbohydrates are chains of sugars (Polysaccharides, Disaccharides, Monosaccharides)
  • Only monosaccharides can be absorbed (Fructose, Galactose, Glucose)
  • Final breakdown occurs in brush border by brush border hydrolases
  • Glucose can only enter with Na+
  • Fructose can enter from lumen through GLUT-5
19
Q

What are the key points of carbohydrate digestion?

A
  • Carbohydrates are chains of sugars (Polysaccharides, Disaccharides, Monosaccharides)
  • Only monosaccharides can be absorbed
  • Final breakdown occurs in brush border by brush border hydrolases
  • Glucose can only enter with Na+
  • Fructose can enter from lumen through GLUT-5
20
Q

How is starch digested?

A
  • Amylase
  • Break in the middle results in maltose. Maltase can digest maltose
  • Break at the end results in glucose
  • Isomaltase can disrupt branching chains to form glucose from alpha dextrin
21
Q

How are monosaccharides absorbed?

A
  • Na+/K+ ATPase on basolateral membrane maintains a low intracellular Na+
  • SGLT1 bind to Na+. Allows glucose to bind which allows Na+ and glucose to move into cell
  • GLUT2 transports glucose out of enterocyte as the basolateral membrane. Diffuses down gradient into capillary blood
22
Q

What are the principles of oral rehydration?

A
  • Uptake of Na+ generate osmotic gradient and water follows
  • Glucose uptake stimulate Na+ uptake
  • Mixture of glucose and salt will stimulate maximum water uptake
23
Q

What are the principles of protein digestion in stomach?

A
  • Only amino acids, dipeptides and tripeptides absorbed
  • Pepsinogen released from chief cells which gets converted to pepsin by HCl
  • Pepsin acts on protein to form oligopeptides /amino acids which move to the small intestine
24
Q

What are the principles of protein digestion in small intestine?

A
  • Pancreas release proteases as zymogens
  • Trypsinogen conver to trypsin by enteropeptidase. Trypsin then activates other proteases
  • Endopeptidases (Trypsin, Chymotrypsin, Elastase) produce shorter polypeptides
  • Exopeptidases (carboxypeptidase A & B) produce dipeptides and amino acids
25
Q

How are protein product absorbed?

A
  • Amino acids are transported into cell by Na+-amino acid co-transporters (neutral, acidic, basic, imino)
  • Dipeptides/tripeptides moved by H+ co-transporter called peptide transporter 1 into the cell where they are converted to amino acids by systolic peptidases
26
Q

Describe the basis of electrolyte and water uptake in the GI tract?

A
  • Na+ moved by active transport of the cell on basolateral membrane
  • Na+ diffuses into epithelial cells
  • Osmotic gradient from all bsoritpn leads to uptake of water. The fluid absorbed is isoo-smotic
27
Q

What are the similarities and differences in electrolyte/water uptake in small intestine vs the large intestine?

A

-Both have Na+-K+ ATPase on basolateral membrane

Apical membrane

  • Na+ is co-transported in the small intestine
  • Na+ channels in the large intestine which is induced by aldosterone (ENaC)
28
Q

Describe uptake of calcium in the intestine?

A

When calcium intake is low

  • Active transcellular absorption so it enters cell via facilitated diffusion
  • Ca+ ATPase removes Ca+ from basolateral membrane
  • Process requires Vitamin D and is stimulated by parathyroid hormone.

When calcium intake is normal/high
-Passive paracellular absorption

29
Q

Describe the uptake of iron in the GI tract?

A
  • Mostly in haem/Fe2+
  • Gastric acid is important in the process
  • Iron absorbed across apical membrane. This is via co-trasnport with H+
  • If iron levels are low, iron binds to transferrin to be transported to stores
  • If iron levels are high, iron contained in ferritin complexes and trapped in cells. Lost when enterocyte is replaced
30
Q

How are water soluble vitamins absorbed?

A

Absorbed by Na+ co-transport (Vitamin C/B)
-Vitamin B12 absorbed in terminal ileum bound to intrinsic factor which is secreted by gastric parietal cells. Removal of terminal ileum and gastritis can cause B12 deficiency

Kofi: Pure Clinical Sem 3 (44 decks)

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