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Semester 3 - Gastrointestinal > 9.Chyme, Pancreas and Liver > Flashcards

9.Chyme, Pancreas and Liver Flashcards

1
Q

What is the pH and tonicity of chyme as it enters duodenum from stomach?

A

Low pH and hypertonic

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2
Q

Why does chyme become more hypertonic as digestion takes place?

A

breakdown of larger molecules into smaller one which are more osmotically active

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3
Q

How is the epithelium in the duodenum protected from the acidic chyme?

A

Brunners glands secrete alkaline mucus

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4
Q

What happens to tonicity of chyme in the duodenum?

A

Water drawn into the duodenum from the ECF/circulation and becomes isotonic by the time its leaving the duodenum

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5
Q

Why isn’t chyme diluted in the stomach?q

A

Stomach wall largely impermeable to water whereas duodenum is permeable

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6
Q

why must chryme release into duodenum be controlled?

A

Too much can overwhelm duodenum (liver/pancreatic secretions)

  • cannot correct hypertonicity and acidity
  • controlled by pyloric sphincter
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7
Q

How is the acidity of chyme fixed in the duodenum?

A 
Secretions from
◦ Pancreas
- Enzymes
- Bicarbonate ions
◦ Liver
- Bicarbonate ions
- Bile
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8
Q

What stimulates release of secretin?

A

In response to low pH of chyme

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9
Q

What stimulates release of CCK?

A

In response to hypertonicity/small peptides/fats within the chyme in the duodenum

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10
Q

What is the effect of secretin on the pancreas?

A

Stimulate release an aqueous bicarbonate (HCO3-) solution from duct cells

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11
Q

What is the effect of CCK on the pancreas?

A

Stimulates release of enzymes for digestion to neutralise acidic chyme

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12
Q

What is the effect of CCK on gall bladder?

A

Causes contraction of gallbladder and relaxation of sphincter of oddi

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13
Q

What is the sphincter of oddi?

A

a muscular valve that controls the flow of digestive juices (bile and pancreatic juice) through the ampulla of Vater

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14
Q

Into which part of the duodenum does the ampulla of vater open into?

A

Second part

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15
Q

What percentage of pancreas function is exocrine?

A

90%

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16
Q

What is the exocrine function of the pancreas innervated by?

A 
•Sympathetic
-inhibits - reduces blood supply
•Parasympathetic
-Vagus (stimulates)
•Hormones
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17
Q

What is the basic strcuture of pancreas

A
  • Acinus (enzymes)
  • Centroacinar (aqueous component)
  • Duct (modifies aqueous secretion)
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18
Q

What stimulates the acinus of the pancreas?

A

vagus & cholecystokinin (CCK)

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19
Q

What does vagus and CCK stimulate pancreas to produce?

A 
Produces enzymes
◦ Amylases/Lipases (active)
◦ Proteases (inactive)
- Trypsin
- Chymotrypsin
- Elastase
- Carboxypeptidase
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20
Q

Describe production and storage of enzymes

A 
◦ Formed on Rough Endoplasmic reticulum
◦ Moved to Golgi complex
◦ Condensing vacuoles
◦ Concentrated in zymogen granules to be stored
◦ Released with appropriate stimulus
- Parasympathetic / CCK
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21
Q

Where are inactive proteases stored and where are they activated?

A

Zymogen granules in acinar cells

Activated in intestinal lumen

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22
Q

Why are Pancreatic Proteases Released in Inactive Forms?

A

Prevent digestion of pancreas by proteases

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23
Q

Describe zymogen granules

A

Membrane bound
Contain zymogen
◦ Inactive pre-cursor of an enzyme

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24
Q

What is indicated if pancreatic enzymes (amylase/Lipase) appear in blood?

A

Signifies pancreatic damage

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25
Q

Where is the aqueous bicarbonate component of pancreatic secretion secreted from?

A

From duct cells

26
Q

Which main ducts do pancreatic secretion travel to reach duodenum?

A

Pancreatic duct which joins with common bile duct to form ampulla of vater

27
Q

summarise two problems of chyme as it enters duodenum and how it is fixed

A
  1. only partially digested
    ◦ Secrete enzymes for digestion (CCK)
  2. Acidic
    ◦ Neutralise acidic chyme by releasing an aqueous bicarbonate (HCO3-) solution (secretin)
28
Q

How does a high flow rate affect pancreas?

A

◦ Increased secretion of HCO3

◦ Increased HCO3 in pancreatic secretion

29
Q

What are the functions of the liver?

A 
Largest single organ 
◦ Energy metabolism 
◦ Detoxification 
◦ Plasma protein production
Secretion of bile
30
Q

What does the liver secrete into the duodenum?

A

Bile (250-1000mL/day)

31
Q

What does bile consist of and what pH is it?

A
  • Bile acids and bile pigments

- alkaline solution

32
Q

What is the role of bile in digestion?

A

Emulsifying fat (lipids) in duodenum so that they can be readily digested by lipases

33
Q

What are the different lobes of the liver?

A

Left, right, quadrate, caudate

34
Q

What are the Chief functional cells of the liver?

A

hepatocytes

35
Q

What function do hepatocytes have and what adaptations do they have to support it?

A

Very active at producing proteins/lipids for export
◦ Contain lots of rough/smooth ER
◦ Stacks of Golgi membranes
Contain lots of Glycogen

36
Q

What is the shape of the lobules in the liver and what is at each corner?

A

Hexagonal arrangement.

Triad of portal vein, hepatic artery and bile duct at each corner

37
Q

What is present at the centre of each lobule in the liver?

A

Central vein

38
Q

What do the central vein drain into?

A

hepatic veins which drain int IVC

39
Q

What is the difference between hepatic veins and portal vein?

A

hepatic veins drain liver

portal vein brings blood to liver

40
Q

what is the hepatic acinus and the different zone?

A

region of adjoining hepatic lobules made up of 3 zones

41
Q

of the hepatic acinus, which zone is more likely to be affected by toxins?

A

1 as it closest to blood coming in

42
Q

of the hepatic acinus, which zone is more likely to be affected by ischaemia?

A

3 as furthest from blood coming in

43
Q

where does all the blood from the gut drain into?

A

into the liver - portal vein

44
Q

What is bile deposited into from hepatocytes?

A

Canaliculi, into bile duct to duodenum

45
Q

describe the blood flowing into the liver

A

◦ Venous portal blood
◦ Arterial blood (hepatic arteries)
◦ Flowing toward central vein
◦ Which then drains into hepatic veins (vena cava)

46
Q

What is bile produced by?

A

Hepatocytes and duct cells in the liver

47
Q

What are the two components of bile and what is the difference in where they are produced and what they contain?

A

◦ Bile acid dependant

  • Secreted into canaliculi by hepatocytes
  • Contains bile acids and pigments

◦ Bile acid independent

  • Secreted by duct cells
  • Similar alkaline solution to pancreatic duct cells
  • Stimulated by secretin
48
Q

What are the 2 primary bile acids?

A

◦ Cholic acid
◦ Chenodeoxycholic acid
◦ Further bile acids formed in gut

49
Q

What are bile salts?

A

Bile salts are bile acids that are conjugated with the amino acids
◦ Glycine
◦ Taurine

50
Q

Why are bile acids converted to bile salts?

A

◦ Bile acids are not always soluble at duodenal pHs
Bile salts generally are

◦ bile salts have an amphipathic structure

51
Q

How does the structure of bile salts allow emulsification of fats?

A

Bile salts have an amphipathic structure
• Hydrophilic end (water soluble)
• Hydrophobic end (lipid solube)
• Act at oil/water interface

52
Q

Why is emulsification of lipids important?

A

Bile acids emulsify fat into smaller units
◦ Help disperse droplets
◦ Increases surface area for lipases to act

53
Q

What do bile salts form after emulsification of fats and what is the importance of them?

A

Micelles

- act as vehicle for transporting hydrophobic molecules (product of lipid digestion) towards of enterocytes

54
Q

What are the products of lipid digestion transported in micelles?

A

◦ Cholesterol
◦ Monoglycerides
◦ Free fatty acids

55
Q

What happens to bile salts that form micelles?

A

Bile salts reabsorbed in the terminal ileum, returned to the liver in the portal blood. Liver recycles the bile salts

56
Q

What happens to products of lips digestion once inside the enterocytes?

A

Lipids diffuse down concentration gradient into intestinal epithelial cell

Inside cell re-esterified back to
◦ Tri-glycerides
◦ Phospholipids
◦ cholesterol
Reformed lipids packaged with apoproteins
◦ Chylomicrons
57
Q

Where do chylomicrons go from enterocytes?

A 
Exocytosis from basolateral membrane
◦ Too large to enter capillaries
◦ Enter lymph capillaries (Lacteals)
◦ Travel through lymphatic system
◦ Re-enter vascular circulation
◦ Thoracic duct
58
Q

where is bile stored?

A

Gallbladder

59
Q

What does the gallbladder do to the concentration of bile and what may be the effect of it??

A

◦ Concentrates bile (removes water/ions)

◦ This can lead to gallstones

60
Q

WHat is the action of CCK on gallbladder?

A

◦ CCK released from duodenum stimulates gallbladder contraction to release bile
◦ Relaxes ‘sphincter of Oddi’

61
Q

What is steatorrhoea and describe its appearance?

A 
If Bile acids (salts) or pancreatic lipases are not secreted in adequate amounts
◦ Fat appears in faeces
◦ Pale
◦ Floating
◦ Foul smelling
62
Q

Describe how bilirubin is associated with bile?

A

Breakdown product of haemoglobin
◦ Conjugated in liver
◦ Secreted into bile
◦ Excreted in faeces
◦ Accumulates in blood if cannot be excreted
◦ jaundice
◦ if water soluble, bilirubin also excreted in urine giving it a dark colour

Semester 3 - Gastrointestinal (17 decks)

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