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WP 20 Biomed > Physiology > Flashcards

Physiology Flashcards

1
Q

What are the main functions of the liver?

A

Storage (carbs, lipids, vitamins, minerals).
Synthesis (carbs, proteins, angiotensinogen, IGF-1, RBC).
Breakdown of Products (hormones, toxic substances such as alcohol and drugs).

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2
Q

What are the major components of bile?

A

water, bile salts, bilirubin, cholesterol, fatty acids, lecithin, Na, K, Ca, Cl, HCO3

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3
Q

What are the major differences between hepatic bile and gallbladder bile?

A

Hepatic bile contains higher concentrations of water and electrolytes which are reabsorbed by the gallbladder mucosa. This leaves bile salts, cholesterol and lecithin to become more concentrated in the gallbladder bile.

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4
Q

What causes relaxation of the sphincter of Oddi and mediates gallbladder contraction?

A

CCK.

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5
Q

What stimulates the hepatic duct cells to release bicarbonate ions?

A

Secretin

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6
Q

What are some relevant functions of CCK?

A

Causes release of digestive enzymes in the acinar cells of the pancreas.
Causes relaxation of the sphincter of Oddi and contraction of the gallbladder.

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7
Q

What percentage of bile salts are recycled? And where are they absorbed?

A

95%, other 5% is eliminated in faeces.

Terminal ileum.

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8
Q

What are the secretory cells of the pancreas?

A

Acinar cells.

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9
Q

Name some important digestive enzymes secreted by the pancreas and their function.

A

Trypsin and chymotrypsin split proteins into smaller peptides.
Carboxypolypeptidase splits some peptides of various sizes but dont cause release of amino acids.
Pancreatic amylase -> carb digestion.
Pancreatic lipase -> fat digestion.
Cholesterol esterase -> hydrolyses cholesterol ester.
Phospholipase -> splits fatty acids from phospholipids.

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10
Q

How is a pH of 7-8.5 achieved in the duodenum?

A

CCK is released to cause bile (pH 6-7) to flow into the duodenum.
Low pH imitates the release of secretin from S cells which release bicarbonate into the chyme and increase pH.

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11
Q

How are pancreatic zymogens activated in the small intestine?

A

Trypsinogen and pancreatic secretory trypsin inhibitor (PSTI) are packaged into zymogens at the GA of the cell. They are released into the small intestine and trypsinogen is activated to trypsin by enteropeptidase by removing the trypsinogen activation peptide from the molecule. Activation of trypsin initiates a cascade where it initiates other molecules.

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12
Q

What are the processes occurring in zone III of the hepatic lobule?

A

Glycogenesis

Glycolysis

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13
Q

What are the processes occurring in zone I of the hepatic lobule?

A

Gluconeogenesis
Amino acid catabolism
Glycogen degradation.

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14
Q

What is the composition of bile?

A

Water, bile salts, bilirubin, cholesterol, fatty acids, lecithin, Na, K, Ca, Cl, HCO3

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15
Q

What is the most abundant substance secreted in bile?

A

Bile salts.

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16
Q

Approximately how much bile is secreted every day?

A

600mL - 1L

17
Q

What are the two main functions of bile?

A

Lipid digestion and absorption.

Excretion of waste products (bilirubin and excess cholesterol).

18
Q

How does secretin alter the composition of bile as it moves through the bile ducts.

A

In its course through the bile ducts, a second portion of liver secretion (containing water, Na and bicarbonate ions) is added to the initial bile from secretory epithelial cells that line the ductules. This is stimulated by secretin and assists in neutralising the acid which enters the duodenum from the stomach.

19
Q

What is the total volume of the gallbladder?

A

30-60mL.

20
Q

Does bile change in the gallbladder, and if so how?

A

Bile becomes more concentrated in the gallbladder. This occurs through the gallbladder epithelium. Most is caused by active transport of Na out of the epithelium, followed by secondary absorption of Cl, water and most other diffusa le constituents.
This can increase bile concentration up to 20-fold.

21
Q

What stimulates CCK release?

A

Presence of fatty foods in the duodenum.

22
Q

What neural stimulation does the gallbladder recieve?

A

The gallbladder recieves ACh-secreting nerve fibres from both the vagi and the intestinal ENS. These are the same nerves that promote motility and secretion in other parts of the GIT.

23
Q

What % of bile salts are recycled, and what % are excreted in faeces.

A

95% are recycled and taken up in the terminal ileum.

5% are lost in faeces.

24
Q

What is the rate limiting step in bile formation?

A

Canicular bile acid secretion into the bile.

25
Q

How and where are secondary bile acids formed?

A

Secondary bile acids are formed by bacteria in the colon through the removal of hydroxyl group at C-7.

26
Q

What are primary bile acids? How are they reabsorbed?

A

Bile acids which have been conjugated in the liver.

Reabsorbed via intestinal bile acid transporter (IBAT) in the terminal ileum.

27
Q

What is the total amount of bile in the body at any one time?

A

~3-4g.

28
Q

What is the max synthetic capacity of the liver for bile? Why does this affect the necessity to recycle bile salts?

A

3g /day
100g of fat every day must be solubilised by bile. Therefore, the liver can’t make enough bile acids spontaneously to achieve these demands. Therefore, it must be recycled.

29
Q

By which enzyme is trypsinogen converted to trypsin? And where is this enzyme released?

A

Enterokinase; released from the intestinal mucosa in the duodenum.

30
Q

What mechanisms allows protection of the pancreas from its own trypsin?

A

Trypsin inhibitor is secreted by the pancreas. It is formed in the cytoplasm of glandular cells and it prevents activation of trypsin both inside the secretory cells and in the acini and ducts of the pancreas.
If a duct is blocked and pancreatic secretions become pooled. The trypsin inhibitor can become overwhelmed and thus the pancreas begins to digest itself.

31
Q

How are digestive enzymes stored in the acinar cells?

A

They are stored as zymogens granules which are released via exocytosis with neurohormonal stimulated with a meal.

32
Q

What is secretin and where is it secreted?

A

A polypeptide, present in the inactive form of pro-secretin in S cells in the mucosa of the duodenum and jéjunum.

33
Q

At what pH is secretin stimulated?

A

<4-4.5

34
Q

What is the neutralisation reaction of chyme?

A

NaHCO3 + HCl —-> NaCl + H20 + CO2.

35
Q

What is the pH of the duodenum?

A

PH ~7-8.5

36
Q

How is trypsinogen activated to its active form of trypsin?

A

Enteropeptidase cleaves the trypsinogen activation peptide (TAP) from the N-terminal region of trypsinogen —> trypsin.

WP 20 Biomed (5 decks)

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