9.Chyme, Pancreas and Liver

Question 1

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

Answer 1

Low pH and hypertonic

Question 2

Why does chyme become more hypertonic as digestion takes place?

Answer 2

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

Question 3

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

Answer 3

Brunners glands secrete alkaline mucus

Question 4

What happens to tonicity of chyme in the duodenum?

Answer 4

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

Question 5

Why isn’t chyme diluted in the stomach?q

Answer 5

Stomach wall largely impermeable to water whereas duodenum is permeable

Question 6

why must chryme release into duodenum be controlled?

Answer 6

Too much can overwhelm duodenum (liver/pancreatic secretions)

• cannot correct hypertonicity and acidity
• controlled by pyloric sphincter

Question 7

How is the acidity of chyme fixed in the duodenum?

Answer 7

Secretions from
◦ Pancreas
- Enzymes
- Bicarbonate ions
◦ Liver
- Bicarbonate ions
- Bile

Question 8

What stimulates release of secretin?

Answer 8

In response to low pH of chyme

Question 9

What stimulates release of CCK?

Answer 9

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

Question 10

What is the effect of secretin on the pancreas?

Answer 10

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

Question 11

What is the effect of CCK on the pancreas?

Answer 11

Stimulates release of enzymes for digestion to neutralise acidic chyme

Question 12

What is the effect of CCK on gall bladder?

Answer 12

Causes contraction of gallbladder and relaxation of sphincter of oddi

Question 13

What is the sphincter of oddi?

Answer 13

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

Question 14

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

Answer 14

Second part

Question 15

What percentage of pancreas function is exocrine?

Answer 15

90%

Question 16

What is the exocrine function of the pancreas innervated by?

Answer 16

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

Question 17

What is the basic strcuture of pancreas

Answer 17

• Acinus (enzymes)
• Centroacinar (aqueous component)
• Duct (modifies aqueous secretion)

Question 18

What stimulates the acinus of the pancreas?

Answer 18

vagus & cholecystokinin (CCK)

Question 19

What does vagus and CCK stimulate pancreas to produce?

Answer 19

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

Question 20

Describe production and storage of enzymes

Answer 20

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

Question 21

Where are inactive proteases stored and where are they activated?

Answer 21

Zymogen granules in acinar cells

Activated in intestinal lumen

Question 22

Why are Pancreatic Proteases Released in Inactive Forms?

Answer 22

Prevent digestion of pancreas by proteases

Question 23

Describe zymogen granules

Answer 23

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

Question 24

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

Answer 24

Signifies pancreatic damage

Question 25

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

Answer 25

From duct cells

Question 26

Which main ducts do pancreatic secretion travel to reach duodenum?

Answer 26

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

Question 27

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

Answer 27

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

Question 28

How does a high flow rate affect pancreas?

Answer 28

◦ Increased secretion of HCO3 | ◦ Increased HCO3 in pancreatic secretion

Question 29

What are the functions of the liver?

Answer 29

``` Largest single organ ◦ Energy metabolism ◦ Detoxification ◦ Plasma protein production Secretion of bile ```

Question 30

What does the liver secrete into the duodenum?

Answer 30

Bile (250-1000mL/day)

Question 31

What does bile consist of and what pH is it?

Answer 31

- Bile acids and bile pigments | - alkaline solution

Question 32

What is the role of bile in digestion?

Answer 32

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

Question 33

What are the different lobes of the liver?

Answer 33

Left, right, quadrate, caudate

Question 34

What are the Chief functional cells of the liver?

Answer 34

hepatocytes

Question 35

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

Answer 35

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

Question 36

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

Answer 36

Hexagonal arrangement. | Triad of portal vein, hepatic artery and bile duct at each corner

Question 37

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

Answer 37

Central vein

Question 38

What do the central vein drain into?

Answer 38

hepatic veins which drain int IVC

Question 39

What is the difference between hepatic veins and portal vein?

Answer 39

hepatic veins drain liver | portal vein brings blood to liver

Question 40

what is the hepatic acinus and the different zone?

Answer 40

region of adjoining hepatic lobules made up of 3 zones

Question 41

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

Answer 41

1 as it closest to blood coming in

Question 42

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

Answer 42

3 as furthest from blood coming in

Question 43

where does all the blood from the gut drain into?

Answer 43

into the liver - portal vein

Question 44

What is bile deposited into from hepatocytes?

Answer 44

Canaliculi, into bile duct to duodenum

Question 45

describe the blood flowing into the liver

Answer 45

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

Question 46

What is bile produced by?

Answer 46

Hepatocytes and duct cells in the liver

Question 47

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

Answer 47

◦ 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

Question 48

What are the 2 primary bile acids?

Answer 48

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

Question 49

What are bile salts?

Answer 49

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

Question 50

Why are bile acids converted to bile salts?

Answer 50

◦ Bile acids are not always soluble at duodenal pHs Bile salts generally are ◦ bile salts have an amphipathic structure

Question 51

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

Answer 51

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

Question 52

Why is emulsification of lipids important?

Answer 52

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

Question 53

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

Answer 53

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

Question 54

What are the products of lipid digestion transported in micelles?

Answer 54

◦ Cholesterol ◦ Monoglycerides ◦ Free fatty acids

Question 55

What happens to bile salts that form micelles?

Answer 55

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

Question 56

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

Answer 56

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 ```

Question 57

Where do chylomicrons go from enterocytes?

Answer 57

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

Question 58

where is bile stored?

Answer 58

Gallbladder

Question 59

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

Answer 59

◦ Concentrates bile (removes water/ions) | ◦ This can lead to gallstones

Question 60

WHat is the action of CCK on gallbladder?

Answer 60

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

Question 61

What is steatorrhoea and describe its appearance?

Answer 61

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

Question 62

Describe how bilirubin is associated with bile?

Answer 62

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