PHS 202 Biliary System

Question 1

Name 7 GIT Hormones

Answer 1

Gastrin
Secretin
CCK
GIP
VIP
Glucagon
Motilin

Question 2

Function of gastrin

Answer 2

Stimulates gastric secretion and motility
Growth of gastric mucosa.

Question 3

Function of secretin

Answer 3

Stimulates:
● Pepsin secretion.
● Pancreatic HCO -3 secretion.
● Biliary HCO -3 secretion.
● Exocrine pancreas growth.
Inhibits:
Gastric acid secretion

Question 4

Function of Cholecystokinin (CCK)

Answer 4

Stimulates:
● Pancreatic enzyme secretion.
● Pancreatic HCO-3 secretion.
● Gallbladder contraction.
● Exocrine pancreas growth. 1
● Accelerates secretin action
Inhibits:
Gastric emptying

Question 5

Function of Glucose-Dependent Insulinotropic Peptide (GIP)

Answer 5

Stimulates:
Insulin secretion (from pancreatic β cells) Inhibits:
Gastric acid secretion

Question 6

Functions of motilin

Answer 6

Stimulates:
● Gastric motility.
● Intestinal motility.

Question 7

The biliary system consists of

Answer 7

•The liver
•The gall bladder
•Associated ducts:
–Hepatic ducts (right, left and common)
–Cystic duct
–Common bile duct

Question 8

Function of the liver

Answer 8

Synthesis & Secretion of bile.
•Metabolic processes (e.g. gluconeogenesis, glycogenolysis).
•Detoxification and degradation (e.g. drugs and hormones).
•Synthesis of plasma proteins (e.g. albumin and clotting factors).
•Storage (e.g. iron and Vit B12).
•Activation of vitamin D.
•Removal of bacteria and old RBC.
•Excretion of cholesterol and bilirubin.

Question 9

Bile is secreted by

Answer 9

hepatocytes

Question 10

How much bile is secreted per day and what is the pH?

Answer 10

About 500 ml (250-1200ml) is secreted per day.
pH 8

Question 11

What % of water do hepatic and gall bladder bile have?

Answer 11

H: 98%
GB: 89%

Question 12

What amount of bile salts do hepatic and gall bladder bile have? (gm/dl)

Answer 12

H: 1.1
GB: 6

Question 13

What amount of bilirubin do hepatic and gall bladder bile have? (gm/dl)

Answer 13

H: 0.04
GB: 0.3

Question 14

What amount of cholesterol do hepatic and gall bladder bile have? (gm/dl)

Answer 14

H: 0.1
GB: 0.3-0.9

Question 15

What amount of Fatty Acids do hepatic and gall bladder bile have? (gm/dl)

Answer 15

H: 0.12
GB: 0.3 - 1.2

Question 16

What amount of Lecithin do hepatic and gall bladder bile have? (gm/dl)

Answer 16

H: 0.04
GB: 0.3

Question 17

What amount of Na+ do hepatic and gall bladder bile have? (mmol/L)

Answer 17

H: 145
GB: 130

Question 18

What amount of K+ do hepatic and gall bladder bile have? (mmol/L)

Answer 18

H: 5
GB: 12

Question 19

What amount of Ca2+ do hepatic and gall bladder bile have? (mmol/L)

Answer 19

H: 5
GB: 23

Question 20

What amount of Cl- do hepatic and gall bladder bile have? (mmol/L)

Answer 20

H: 100
GB:25

Question 21

What amount of HCO3- do hepatic and gall bladder bile have? (mmol/L)

Answer 21

H: 28
GB: 10

Question 22

What amount of pH do hepatic and gall bladder bile have? (mmol/L)

Answer 22

H: 8.3
GB: 7.3

Question 23

What amount of pH do hepatic and gall bladder bile have? (mmol/L)

Answer 23

H: 8.3
GB: 7.3

Question 24

What amount of pH do hepatic and gall bladder bile have? (mmol/L)

Answer 24

H: 8.3
GB: 7.3

Question 24

What amount of pH do hepatic and gall bladder bile have? (mmol/L)

Answer 24

H: 8.3
GB: 7.3

Question 25

Functions of bile

Answer 25

Bile salts play an important role in fat digestion and absorption.
Excretion of waste products (e.g. bilirubin).
Bicarbonate in bile neutralizes acid in duodenum.

Question 26

Characteristis of Bile salts

Answer 26

Most important component of the bile.
They are Na+ and K + salts of bile acids.
They are derivatives of cholesterol.
Recycled through the enterohepatic circulation.

Question 27

Functions of bile salts

Answer 27

Emulsify large fat particles into smaller ones that can be attacked by lipase (detergent action).

Help in the transport and absorption of fat (micellar formation).
Prevent precipitation of cholesterol by keeping them in solution (prevent gall stones).

Stimulate bile secretion by liver cells.

Question 28

Functions gall bladder

Answer 28

No digestive role.
Stores bile.
Concentrates bile.
Empties during meals.
Secretes mucus.

Question 29

Regulation of bile secretion and gall bladder emptying

Answer 29

Chemical:
Bile salts: most important stimulant of bile secretion by liver cells.

Hormonal:
Secretin: secreted in response to acid chyme, causes secretion of bile rich in water and HCO3-
CCK: secreted in response to fatty acids in duodenum, causes gall bladder to contract and sphincter of Oddi to relax

Neural
Vagal stimulation:
Increases bile secretion
Weak contraction of gall bladder

Question 30

What is jaundice and what causes it?

Answer 30

Jaundice: yellowish discoloration of the skin, sclera & mucous membranes due to a high blood bilirubin level.

Causes:
Pre-hepatic: due to excess production of bilirubin e.g. haemolytic anaemia.
Hepatic: liver disease e.g. hepatitis
Post-hepatic: obstruction to bile flow e.g. gall stones.

Question 31

Movement of bile from the gall bladder

Answer 31

It is poured into the bile canaliculi from where it ultimately goes to the
common hepatic duct which join with cystic duct to form the common bile duct. During interdigestive period when the sphincter of Oddi is closed, the bile is directed via the cystic duct to the gallbladder, where it is stored and concentrated.
* During meals, the sphincter of Oddi is relaxed, and when food reaches the duodenum, there occurs release of CCK which causes contraction of the gallbladder. Then the bile is released into the duodenum along with the pancreatic juice through the common opening ampulla of Vater.

Question 32

What is bile?

Answer 32

Bile is a digestive juice, formed continuously in the liver by the hepatic
cells (hepatocytes), and by epithelial cells lining the bile ducts (ductal
cells).

Question 33

What are bile acids?

Answer 33

Primary bile acids are cholic acid and chenodeoxycholic acid. These
are synthesized by hepatocytes from cholesterol.
* Secondary bile acids are deoxycholic acid and lithocholic acid. These
are formed from the primary bile acids in the colon by the action of
intestinal bacteria and a small quantity of ursodeoxycholic acid is
formed from chenodeoxycholic acid.
* The conjugation of bile acids. In the liver, the bile acids are conjugated
with either glycine (an amino acid) or taurine (an amino acid
derivative) forming the conjugated bile acids.
* The conjugated bile acids namely glycocholic acid and taurocholic acid
form bile salts in combination with sodium or potassium.

Question 34

Relationship between bile acids and bile salts

Answer 34

Bile salts are sodium and potassium salts of bile acids conjugated with
either taurine or glycine.

Question 35

What is Enterohepatic circulation of bile salts? Why is it necessary?

Answer 35

Enterohepatic circulation is the recirculation of bile salts from the liver to small intestine and back again. This circulation is necessary because of
the limited pool of bile salts available to help breakdown and to absorb fat.

Question 36

Clinical implications of enterohepatic circulation

Answer 36

As bile salts are required for proper digestion and absorption of fats, therefore any condition that disrupts enterohepatic circulation (e.g. ileal resection or small intestinal diseases such as sprue or Crohn’s disease) leads to decreased bile salt pool and malabsorption of fat and fat-soluble
vitamins.

The clinical manifestations of such conditions are:
* Steatorrhoea, i.e. increased fat content in the stools,
* Nutritional deficiency due to malabsorption and
* Watery diarrhoea because the bile salts which inhibit water and
sodium absorption from the colon are decreased due to excessive loss in stools.

Question 37

Composition of pancreatic juices

Answer 37

1.5 L/day, alkaline (pH 8)
Composition and function:
Digestive enzymes: peptidases (trypsin and chymotrypsin), lipases, and amylase.
Water
HCO3-: neutralize the gastric acid
Provides optimum medium for action of pancreatic enzymes.

Question 38

What is the pancreas?

Answer 38

The pancreas—an elongated, accessory digestive gland—lies
retroperitoneally and transversely across the posterior abdominal wall,
posterior to the stomach between the duodenum on the right and the spleen on the left

Question 39

Parts of the pancreas

Answer 39

Exocrine part, which produces a secretion called pancreatic juice that contains enzymes capable of hydrolysing proteins, fats and carbohydrates.
* Endocrine part of the pancreas, the islets of Langerhans, produces the hormones insulin and glucagon, which
play a key role in the carbohydrate metabolism

Question 40

Parts of the pancreas

Answer 40

Exocrine part, which produces a secretion called pancreatic juice that contains enzymes capable of hydrolysing proteins, fats and carbohydrates.
* Endocrine part of the pancreas, the islets of Langerhans, produces the hormones insulin and glucagon, which
play a key role in the carbohydrate metabolism

Question 41

Regulation of the cephalic phase of pancreatic secretion

Answer 41

Regulation of this phase is mainly through the reflex vagal stimulation, which occurs:
* By conditioned reflexes, initiated by sight, smell and thought of food and
* Unconditioned reflexes, initiated by stimulation of taste buds by the food in the mouth cavity, the act of chewing and swallowing.
Afferent impulses, from the cerebral cortex (during conditioned reflexes) and from the mouth (during unconditioned reflexes) reach the dorsal nucleus of vagus. Stimulation of efferents in vagus nerve supplying the exocrine part of pancreas enhances secretion from both, acinar as well as ductal cells:
* Enzyme secretion from acinar cells is enhanced due to stimulation of enteric neurons, which release acetylcholine. Acetylcholine exerts its effect on the acinar cells by activating phospholipase.
* Bicarbonate secretion from the ductal cells is enhanced by stimulation of enteric neurons which release noradrenergic transmitters.

Question 42

Regulation of the Gastric phase of pancreatic secretion

Answer 42

occurs when the stomach is distended by the food
regulated by neural control exerted through the vagus and hormonal control executed through the hormone
gastrin:
* Vagus stimulation (vagovagal reflex), which occurs due to distension of the body of the stomach by the food results in secretion of low volumes of pancreatic juice containing HCO3
− and enzymes.
Acetylcholine is the transmitter.
* Gastrin hormone is released from antral G-cells by the food breakdown products (primarily amino acids and peptides). Gastrin released in the blood, while reaching the pancreas, stimulates the acinar cells and produces a low-volume, high-enzyme pancreatic secretion.

Question 43

Regulation of intestinal phase of pancreatic secretion

Answer 43

The intestinal phase of pancreatic secretion begins when the chyme enters the duodenum and jejunum. It is characterized by a marked increase in the secretion of both enzymes and aqueous component of
pancreatic juice. This phase is regulated by the hormones secretin and cholecystokinin (CCK).

Question 44

Hormonal regulation of pancreatic secretion

Answer 44

Mainly hormonal:
Secretin: acid chyme in duodenum stimulates secretions rich in water and HCO3- but poor in enzymes
CCK: digestive products of proteins and fat in duodenum stimulates secretions of pancreatic juice rich in enzymes.

Both hormones are secreted by upper intestinal cells.

Question 45

Function of a trypsin inhibitor

Answer 45

If even a small amount of trypsin is released into the pancreas, the resulting chain reaction would produce active enzymes that could digest the pancreas. It is therefore, not surprising that the pancreas normally
contains a trypsin inhibitor, which is secreted by the same cells and at the same time as the pancreatic proenzymes. The trypsin inhibitor protects the pancreas from autodigestion

Question 46

Function of pancreatic juices

Answer 46

1. Digestive functions.
   The pancreatic juice is the major source of digestive enzymes that digest all components of the food—proteins, carbohydrates, fats and nucleic acid.
2. Neutralizing function.
   Pancreatic juice is highly alkaline due to high concentration of HCO3− and neutralizes the gastric HCl in the chyme that enters the duodenum.

Question 47

Mechanism of pancreatic secretion

Answer 47

The acinar cells of the exocrine part of the pancreas produce the pancreatic enzymes which are synthesized in the ribosomes of the rough endoplasmic reticulum. The raw material for the synthesis of enzymes is amino acids-derived from the blood.

• After synthesis in the rough endoplasmic reticulum, the enzymes pass to the Golgi complex where they are surrounded by membranes and then released into the cytoplasm as secretory (zymogen) granules.
• The zymogen granules move to the luminal surface of the cells. When stimulated, the acinar cells pour the enzymes in the lumen of acini by exocytosis. After passing through the intercalated and interlobar ducts,
  ultimately the pancreatic juice containing these enzymes is poured into the duodenum through the main and accessory pancreatic ducts.
• Within the cells, these enzymes are stored in inactive form (proenzymes). They become active only after mixing with duodenal contents. Activation is initiated by the brush border enzyme enteropeptidase (enterokinase) present in the epithelial cells lining the
  duodenum.

Question 48

Describe the acinar cells of the pancreas

Answer 48

Acinar cells lining the alveoli appear triangular in section.
Numerous secretory (or zymogen) granules can be demonstrated in the cytoplasm, especially in the apical part of cells.
The acinar cells produce thick secretion containing numerous enzymes (listed in composition of pancreatic juice).
Centroacinar cells. The centroacinar cells that are so called because they appear to be located near the centre of the acinus (alveolus). These cells really belong to the intercalated ducts, which are invaginated into the acinus

Question 49

Describe the pancreatic ducts

Answer 49

The intercalated ducts, which receive secretions produced by the acini, pass it on to the interlobular ducts. Ultimately, the pancreatic secretion passes into the duodenum through the main pancreatic duct and accessory pancreatic duct.

Main pancreatic duct, also known as a duct of Wirsung,
begins in the tail and runs the length of the gland, receiving numerous tributaries on the way. It joins the common bile duct to form the ampulla of Vater, which opens into the second part of the duodenum at about its middle on the major duodenal papilla. Ampulla of Vater is guarded by the sphincter of Oddi.

Accessory pancreatic duct, also called a duct of Santorini, when present, drains the upper part of the head and then opens into the duodenum about 2 mm above the main duct on the minor duodenal papilla.

Question 50

Difference between Secretin and CCK mechanism of action

Answer 50

Secretin: responds to a decrese in temperature, acts on ducts to produce more HCO3- to neutralize acid
CCK: Acts on acinar

Question 51

Difference between Secretin and CCK mechanism of action

Answer 51

Secretin: responds to a decrese in temperature, acts on ducts to produce more HCO3- to neutralize acid
CCK: Acts on acinar

Question 52

Characteristics of secretin

Answer 52

Source of secretin is endocrinal S-cells located among the epithelial cells of mucous membrane of the duodenum and jejunum.
Stimulant for the release of secretin is low pH (< 4.5) of
chyme caused by the presence of gastric HCl.
Actions. Secretin enters the blood circulation and after reaching the pancreas it acts on the duct cells and produces a large amount of watery juice with high concentration of HCO3−.
Other actions of secretin are:
Also stimulates bile secretion,
Potentiates the effect of CCK on pancreas and
Along with CCK causes contraction of pyloric sphincter delaying gastric emptying and thus preventing the reflux of the duodenal contents into the stomach
Regulated via positive feedback

Question 53

Characteristics of CCK

Answer 53

ource of secretion of CCK is endocrinal I-cells located
among the epithelial cells of mucosa of the duodenum and
jejunum. Stimulantsfor the release of CCK are amino acids, fatty acids and monoglycerides present in the chyme.
Actions. CCK passes via blood to the pancreas and causes secretion of pancreatic juice rich in enzymes.
Other actions of CCK are:
Contraction of gall bladder to release bile.
Potentiates the effect of secretin to produce more alkaline pancreatic juice.
Increases the secretion of enterokinase (enteropeptidase) from the duodenum.
Inhibits the gastric motility.
Increases the motility of the small and large gut.
Increases the pancreatic growth (trophic effect).
It is also found in the neurons in the brain (especially in the cerebral cortex), where it is involved in the regulation of food intake and is related to the production of anxiety and analgesia.
Regulated via negative feedback