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Semester 3 - Gastrointestinal > Session 6 - Physiology of the liver, biliary tree and pancreas > Flashcards

Session 6 - Physiology of the liver, biliary tree and pancreas Flashcards

1
Q

What are the key properties of chyme leaving the stomach?

A
  • Acid
    • Hyper tonic
    • Partially digested
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2
Q

Where is chyme secreted into?

A

The duodenum

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3
Q

How is acidity regulated and corrected?

A

Acidity corrected by HCO3- secreted from pancreas, liver and duodenal mucosa

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4
Q

How is hypertonicity regulated and corrected?

A

• Hypertonicity corrected by osmotic movement of water across duodenal wall

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5
Q

How is digestion completed in the small intestine?

A
  • Digestion completed by enzymes from pancreas and small intestinal mucosa
    • Bile acids from liver
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6
Q

What is Bile made up of?

A

• Bile acid dependent and bile acid independent

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7
Q

Where is bile acid dependent portion of bile acid secreted from?

A

• Cells lining canaliculi

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8
Q

Outline the constituent part of bile acid dependent

A

• Bile acids (salts) - Cholic acid/chenodeoxycholic acid
○ Bile salts conjugated to amino acids, travelling as micelles in biles. Play a major role in digestion and absorption of fats
• Cholesterol
• Bile pigments (majority is bilirubin)

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9
Q

Where is the bile acid independent portion of bile acid secreted from?

A

• Intrahepatic bile duct

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10
Q

What is the bile acid independent portion of bile?

A

• Alkaline juice (HCO3-), like that from pancreatic duct cells

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11
Q

What is the basic functional unit of the liver?

A

• A lobule surrounding a central vein, which drains blood from the liver to the systemic veins

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12
Q

Outline course of blood through liver

A

Blood from hepatic portal vein and arteries enter vessels at the periphery of the lobule and flow through sinusoids lined by hepatocytes to the central vein

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13
Q

Where is bile formed in the liver?

A

• Canaliculi, flow towards periphery in bile ducts

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14
Q

What happens after gastric emptying?

A
  • The duodenum secretes cholecystoinin
    • This stimulates contraction of the gall bladder, ejecting concentrated bile acids together with enzymes from the pancreas
    • Alkali from the pancreas and liver is also released in response to secretin
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15
Q

Outline the path of bile through the body

A
  • Bile acids are released through the ampulla of vater and aid with the digestion of fats.
    • They continue to the terminal ileum where actively absorbed by the epithelium

Venous return from the gut enters hepatic portal blood, where hepatocytes actively take up bile acids and re-secrete them into canaliculi

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16
Q

How come not all bile acids are reabsorbed?

A

• Some are unconjugated from amino acids through the action of gut bacteria and are lost

Hepatocytes subsequently replace them

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17
Q

Where do bile acids return to when they are not needed?

A
  • Gall bladder

* Secreted by canaliculi wall cells a long time before they’re needed

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18
Q

How is the volume of bile acids which need to be stored reduced?

A

• Concentrated by transport of salt and water across the gall bladder epithelium

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19
Q

What does the concentration process of bile acids lead to?

A

• Gall stones

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20
Q

What can gall stones cause in the body?

A
  • Move into biliary tree, causing biliary colic

* Obstruction causes inflammation (cholecystitis) and infection of the gall bladder

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21
Q

Why is pain from gall stones worse after eating?

A

Due to the release of CCK, which causes gall bladder to contract

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22
Q

Name 4 things secreted from pancreas?

A
  • Amylases
    • Lipases
    • Proteases
    • Alkaline juice
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23
Q

Give four types of proteases secreted from pancreas

A
  • Trypsinogen
    • Chymotrypsin
    • Elastase
    • Carboxypetidase
24
Q

What is the function of having multiple proteases?

A

• Cleave proteins at different points to break down into amino acids

25
Q

What is the basic structure of exocrine glands?

A

• Made up of acini and ducts

26
Q

What do acini secrete in the pancreas?

A

Enzymes

27
Q

What do ducts secrete in the pancreas?

A

• Alkaline juice (relatively large volumes involved)

28
Q

Outline the process of acinar secretion

A
  • Enzymes synthesised on ribosomes
    • Packaged into condensing vacuoles by golgi complex
    • Form zymogen granules
    • Zymogen granules secreted by exocytosis

Activated in intestine by enzymatic cleavage

29
Q

What enzyme can be assayed in the blood to assess pancreatic damage?

A

Amylase

30
Q

What hormone stimulates pancreas to secrete enzymes?

A

• Cholecytokinin

31
Q

What is CCK?

A

• Hormone closely related to gastrin
• Released from duodenal APUD cells
○ Stimulated by hypertonicity and fats in the intestinal phase

32
Q

How does CCK reduce stomach acid conc?

A

• Competes with gastrin for place on receptors

33
Q

Give three methods of stimulating pancreatic secretion

A
  • Cephalic phase - Vagus nerve releases Ach
    • Intestinal phase - CCK released

Gastrin

34
Q

How do duct cells secrete HCO3-?

A

Draw out cell

35
Q

How is HCO3- secretion stimulated from duct cells

A
  • Hormone secretin
    • Released from jejunal cells in response to low pH
    • Action of secreting amplified by choleocystokinin
36
Q

Why is HCO3- high in blood?

A

Due to gastric acid secretion

37
Q

Outline process of secretion of HCO3- into ducts of exocrine pancreas

A
  • Na-K-ATPase sets up an Na+ concentration gradient
    • Hydrogen ions are exported from the duct cell into ECF using the Na+ concentration gradient
    • H+ ions combine with HCO3- to form H20 and CO2 which are taken up into the cell
    • H20 and CO2 reform H+ and HCO3- inside the cell
    • HCO3- is exported into the duct lumen
    • H+ ion is recycled, ‘going around in a circle’ to carry more HCO3- from the ECF to the lumen
38
Q

What is duct secretion of alkaline juice stimulated by, and where is the substance released from?

A
  • Secretin

* Released from jejunal cells in response to low pH and CCK

39
Q

Describe the control of acinar pancreatic secretions

A
  • Stimulated by CCK
    • Released from duodenal APUD cells
    • Stimulated by hypertonicity and fats
40
Q

Describe the control and release of pancreatic duct secretions

A
  • Stimulated by secretin
    • Released from Jejunal cells
    • Stimulated in response to low pH
41
Q

What stimulates biliary secretion?

A
  • CCK
    • Released from duodenal APUD cells
    • In response to gastric emptying
42
Q

What are the main difficulties surrounding digestion of fats?

A
  • Tend to form large globules as stomach acid breaks down natural emulsions
    • Low surface area for enzymes to act
43
Q

How do bile acids assist in the digestion of fats?

A
  • Emulsify fats into much smaller globules
    • Increase surface area for lipases to cleave fatty acids and glycerol
    • Colipase links bile acids and lipases to spread them over surface
44
Q

How are micelles of fat digested?

A
  • Glycerol cleaved from fatty acid and absorbed through unstirred layer of mucosa on gut wall
    • Absorbed as TAGs and re-expelled as chylomicrons, structured small particles made up of lipids covered in phospholipids
45
Q

What do chylomicrons do?

A

Facilitate the transport of fat in the lymphatic system from the gut to systemic veins

46
Q

What is steatorrhoea?

A

• If bile acids or pancreatic enzymes are not secreted in adequate amounts, fat appears in faeces. Pale, floaty and smelly

47
Q

What is jaundice?

A
  • Bile pigments are excretory products
    • Most common bile pigment in bilirubin, produced as a product of haemoglobin breakdown.
    • If bile can be excreted, it accumulates in blood causing jaundice
48
Q

What are the two main roles of the liver

A

• Blood related

Gut related

49
Q

Give three blood facing functions of the liver

A
  • Energy metabolism
    • Detoxification
    • Plasma proteins
50
Q

What is the main function of the gut liver?

A
  • Secretion of bile
    • Bile acids and alkaline juice for digestion
    • Excretion of bile pigments
51
Q

What are the three parts of the hepatic triad?

A
  • Hepatic portal vein - enters sinusoids lined with hepatocytes
    • Branch of hepatic artery
    • Bile canaliculi
52
Q

What lines the ducts of the hepatic triad?

A

• Hepatocytes

53
Q

What are two components of bile?

A
  • Bile acid dependent

* Bile acid independent

54
Q

Where does the bile acid dependent portion of bile come from, and what is it secreted into?

A
  • Canaliculi by hepatocytes

* Contains bile acids and pigments

55
Q

Where does the bile acid independent portion of bile come from?

A
  • Secreted by duct cells

* Alkaline juice like that from pancreatic duct cells

56
Q

Give two types of bile acid?

A
  • Cholic acid

* Chenodeoxycholic acid

57
Q

What happens to bile acids to make them soluble?

A

• Conjugated to amino acids
• Travel in bile as micelles
○ Bile acids
○ Cholesterol

Phospholipid

Semester 3 - Gastrointestinal (28 decks)

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