NTA Level 4 • Semester 1 • PST04103

Accessory Organs of Digestive System

Human Anatomy and Physiology • Source Session/Topic 15

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Session 15: Accessory Organs of Digestive System

Total Session Time: 120 minutes

Learning Tasks

By the end of this session, students are expected to be able to:

• Describe the Accessory Organs of Digestive System

• Describe the Structure and Functions of the Liver

• Describe the Structure and Functions of Gallbladder

• Explain Organization of the Biliary System

• Explain Bile Production, Circulation and Functions

• Identify Structure of Pancreas

Prerequisites

• None

Resources Needed:

• Flip charts, marker pens, and masking tape

• Black/white board ,chalk and whiteboard markers

• Overhead Projector and Transparencies or Slide Projector/LCD and

Computer

• Handout 15.1: Macroscopic Structure of the Liver

• Handout 15.2: Microscopic Structure of the Liver

• Handout 15.3: Blood Supply to the Liver and Gallbladder

• Handout 15.4: Structure of Gallbladder

• Handout 15.5: The Biliary System

• Handout 15.6: The pancreas

SESSION OVERVIEW

SESSION CONTENTS

STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)

READ or ASK students to read the learning tasks and clarify

ASK students if they have any questions before continuing

STEP 2: Overview of Accessory Organs of Digestive System (10 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What are the accessory organs of the digestive system? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• Accessory organs of gastrointestinal tract: The organs which are not

directly part of gastrointestinal tract but their products are

essential for the digestive system to accomplish its primary function

• These organs include:

o The liver

o Gallbladder and bile duct

o Pancreas

• These are essential for the digestive system as they either produce or

store secretions essential the digestion to take place

STEP 3: Structure and Functions of the Liver (35 minutes)

• Liver is the largest gland in the body, weighing between 1 and 2.3Kg

• In adults the liver weighs 2% of body mass

• Occupying the greater part the right hypochondriac, part of the

epigastric and frequently extending into the left hypochondriac

regions as far as the left lateral line

• The liver is divided into right and left lobes by fossae for the

gallbladder and the inferior vena cava

• The right lobe of liver is the largest lobe, whereas the left lobe of

liver is smaller

wedge shaped

• The quadrate and caudate lobes are described as arising from the right

lobe of liver, but functionally are distinct these are seen on the

posterior side of the liver making it to have four lobes:

o The quadrate lobe

▪ It is visible on the upper part of the visceral surface of the liver

▪ It is bounded on the left by the fissure for ligamentum teres and

on the right by the fossa for the gallbladder

▪ Functionally it is related to the left lobe of the lever

o The caudate lobe

▪ It is visible on the lower part of the visceral surface of the liver

▪ Itis bounded on the left by the fissure for the ligamentum venosum

and on the right by the groove for the inferior vena cava

▪ Functionally, it is separate from the right and the left lobes of

the live

• Surfaces of the liver include a diaphragmatic surface in the

anterior, superior, posterior directions and a visceral surface in the

inferior direction

o The diaphragmatic surface of the liver, which is smooth and domed, lies

against the inferior surface of the diaphragm

o Associated with it are the sub phrenic and hepatorenal recesses

▪ The sub phrenic recess separates the diaphragmatic surface of the

liver from the diaphragm and is divided into right and left areas by

the falciform ligament, a structure derived from the ventral mesentery

in the embryo

▪ The hepatorenal recess is a part of the peritoneal cavity on the

right side between the liver and the right kidney and right suprarenal

gland

▪ The sub phrenic and hepatorenal recesses are continuous anteriorly

o The visceral surface of the liver is covered with visceral peritoneum

except in the fossa for the gallbladder and at the porta hepatic (gateway

to the liver)

• Structures Related to Liver

o The right anterior part of the stomach

o The superior part of the duodenum

o The lesser omentum

o The gallbladder

o The right colic flexure

o The right transverse colon

o The right kidney

o The right suprarenal gland

[pic]Refer students to Handout 15.1: Macroscopic Structure of the Liver

Structure

• The porta hepatic serves as the point of entry into the liver for the

hepatic arteries and the portal vein, and the exit point for the

hepatic ducts

• The liver is attached to the anterior abdominal wall by the falciform

ligament and, except for a small area of the liver against the

diaphragm (the bare area), the liver is almost completely surrounded

by visceral peritoneum

• Additional folds of peritoneum connect the liver to the stomach

(hepatogastric ligament), the duodenum (hepatoduodenal ligament), and

the diaphragm (right and left triangular ligaments and anterior and

posterior coronary ligaments)

• The connective tissue septa divide the liver into hexagon-shaped

lobules with a portal triad at each corner

• The triad are so named because three vessels – the hepatic portal

vein, hepatic artery and hepatic duct are commonly located in them

• Hepatic nerves and lymphatic vessels often too small to be easily seen

in light micrographs are also located in these areas

• Liver lobules are hexagonal in outline and are formed by cubical-

shaped cells; the hepatocytes arranged in pair, between them are

columns of cells called sinusoids

• Hepatic macrophages (Kupffer cells) are also present which function in

destroy and ingest worn out cells and foreign particles in the liver

• A central vein is in the centre of each lobule

• Central veins unite to form hepatic veins, which exit the liver on its

posterior and superior surface and empty into the inferior vena cava

• Hepatic cord radiate out from the central vein of each lobule like the

spokes of a wheel

• The hepatic cords are composed of hepatocytes, the functional cells of

the liver

• The spaces between the hepatic cords are blood channels called hepatic

sinusoids

• The sinusoids are lined with a very thin, irregular squamous

epithelium consisting of two cell populations; endothelial cells and

Hepatic phagocytic cells (kupffer cells)

• A cleft-like lumen, the bile canaliculus lie between the cells within

each cord

[pic]Refer students to Handout 11.2: Microscopic Structure of the Liver

Functions of hepatocytes

|Activity: Buzzing (5 minutes) |

| |

|ASK students to pair up and buzz on the following question for 2 |

|minutes |

| |

|What are the functions of hepatocytes? |

| |

|ALLOW few pairs to respond and let other pairs to add on points not |

|mentioned |

| |

|WRITE their response on the flip chart/board |

| |

|CLARIFY and SUMMARIZE by using the content below |

• Hepatocytes have six major functions, which are:

o Bile production

o Storage

o Interconversion of nutrients

o Detoxication

o Phagocytosis

o Synthesis of blood components

Main Functions of the Liver

• Nutrient and vitamin metabolism and storage

o Glucose and other sugars

o Amino acids (Deamination of amino acids),the end product is urea which is

then excreted in the urine)

o Lipids

o Fatty acids

o Cholesterol

o Lipoproteins

o Fat-soluble vitamins

o Water-soluble vitamins

• Breakdown of erythrocytes and defence against microbes

• Detoxification of drugs and noxious substances

• Inactivation of hormones such as Steroids

• Production of heat

• Formation and Secretion of biles

• Synthesis of plasma proteins

o Acute-phase proteins

o Albumin

o Clotting factor

o Steroid-binding and other hormone-binding proteins

• Immunity; by Kupffer cells

Vascular Supply and Lymphatic Drainage

• The vessels connected with the liver are the portal vein, hepatic

artery and hepatic veins

• The portal vein and hepatic artery ascend in the lesser omentum to the

porta hepatis, where each bifurcates

• The hepatic bile duct and lymphatic vessels descend from the porta

hepatis in the same omentum

• The hepatic veins leave the liver via the posterior surface and run

directly into the inferior vena cava

[pic]Refer students to Handout 15.3: Blood Supply to the Liver and

Gallbladder

STEP 4: Structure and functions of the Gallbladder (15 minutes)

• The gallbladder is a pear-shaped sac lying on the visceral surface of

the right lobe of the liver in a fossa between the right and quadrate

lobes

• It is about 8 cm long and 4 cm wide

• The gallbladder has the following structures

o A rounded end (fundus of gallbladder), which may project from the

inferior border of the liver

o A major part in the fossa (body of gallbladder), which may be against the

transverse colon and the superior part of the duodenum

o A narrow part (neck of gallbladder) with mucosal folds forming the spiral

fold

• The walls of the gallbladder is formed by three tunics which are

o Inner mucous layer which folded into reggae and this allows it to expand

o The muscular layer which contains smooth muscles that allows the

gallbladder to contract

o The outer covering layer of the serosa

• Function of the gallbladder

o It stores and concentrates the bile which is secreted by the liver

o Concentration of the bile by up to 10 or 15 fold by absorption of water

through the walls of the gall bladder

o Release of stored bile

• Gallbladder receives many small vessels from hepatic bed and cystic

arteries a branch of right hepatic artery

• Venous drainage is through the multiple small veins from the

gallbladder bed

[pic]Refer students to Handout 11.4: The Gallbladder

STEP 5: Organisation of the Biliary System (10 minutes)

Biliary system

• Is the duct system for the passage of bile extends from the liver,

connects with the gallbladder, and empties into the descending part of

the duodenum

• The coalescence of ducts begins in the liver parenchyma and continues

until the right and left hepatic ducts are formed

• These drain the respective lobes of the liver

• The two hepatic ducts combine to form the common hepatic duct, which

runs, near the liver, with the hepatic artery proper and portal vein

in the free margin of the lesser omentum

• As the common hepatic duct continues to descend, it is joined by the

cystic duct from the gallbladder

• This completes the formation of the bile duct

• At this point, the bile duct lies to the right of the hepatic artery

proper and usually to the right of, and anterior to, the portal vein

in the free margin of the lesser omentum

• The omental foramen is posterior to these structures at this point

• The bile duct continues to descend, passing posteriorly to the

superior part of the duodenum before joining with the pancreatic duct

to enter the descending part of the duodenum at the major duodenal

papilla

• Therefore the bile either empties directly into the duodenum or is

diverted for minutes up to several hours through the cystic duct into

the gallbladder

• The clinical importance of this system is if there is a tumour of the

head of pancrease will cause obstruction to the bile duct and cause a

condition known as obstructive jaundice

[pic]Refer students to Handout 15.5: The Biliary System

STEP 6: Bile Production, Circulation and Functions (15 minutes)

• The liver produces and secretes about 600-1000ml of bile each day

• Continuous bile formation is an important function of the liver

• Bile is used as a vehicle for the secretion of bile acids

• Bile salts are quantitatively the major constituents of bile and are

circulated in the enterohepatic circulation between the liver and the

small intestine with high efficiency

• Synthesis of bile acids is a major route of cholesterol metabolism

• Bile is synthesised through a series of chemical reactions in

hepatocytes then secreted into minute bile canaliculi that originate

between the hepatic cells

• The mechanism involved in the transcellular movement of bile salts

across hepatocytes is poorly understood

• The body produces about 800 mg of cholesterol per day and about half

of that is used for bile acid synthesis

• 90% of excreted bile acids are reabsorbed by active transport in the

ileum and recycled in what is referred to as the enterohepatic

circulation which moves the bile salts from the intestinal system back

to the liver and the gallbladder

• Clinical significance is, since bile acids are made from endogenous

cholesterol, the enterohepatic circulation of bile acids may be

disrupted to lower cholesterol

• Bile circulation.

o Bile is produced by hepatocytes in the liver

o Bile draining through the many bile ducts that penetrate the liver

o During this process, the epithelial cells add a watery solution that is

rich in bicarbonates that dilutes and increases alkalinity of the

solution

o Bile then flows into the common hepatic duct, which joins with the cystic

duct from the gallbladder to form the common bile duct

o The common bile duct in turn joins with the pancreatic duct to empty into

the duodenum

o If the sphincter of Oddi is closed, bile is prevented from draining into

the intestine and instead flows into the gallbladder, where it is stored

and concentrated to up to five times its original potency between meals

o This concentration occurs through the absorption of water and small

electrolytes, while retaining all the original organic molecules

o Cholesterol is also released with the bile, dissolved in the acids and

fats found in the concentrated solution.

o When food is released by the stomach into the duodenum in the form of

chyme, the duodenum releases cholecystokinin, which causes the

gallbladder to release the concentrated bile to complete digestion

o Most bile salts are absorbed in ileum and carried in the blood back to

liver

o The concentration of bile salts in bile is 0.8%, however the gall bladder

removes water from the bile, concentrating it between meals

o It concentrates it up to 5 times

• Bile has no enzyme but plays a role in the digestion by neutralize and

diluting stomach acids and emulsifying fat

• Bile constitutes of :

o Water

o Mineral salts

o Mucous

o Bile pigment (bilirubin),

o Bile salts which are derived from the primary bile acids

o cholesterol

• Bile plays an important role in fat digestion and absorption due to

the presence of bile acids by do the following;

o They help to emulsify the large fat particles of the food into many

minute particles, the surface of which can then be attacked by lipase

enzymes secreted in pancreatic juice.

o They aid in absorption of the digested fat end products through the

intestinal mucosal membrane.

• Bile serves as a means for excretion of several important waste

products from the blood.

• These include especially bilirubin, an end product of haemoglobin

destruction, and excesses of cholesterol.

Composition of Bile

• Water constitute 97.0%, in the gall bladder the amount is reduced 5

folds

• Bile pigments 0.2%

• Cholesterol0.06%

• Inorganic salts 0.7% such as Na+, K+& Ca2+ salts Cl- HCO3 & Phosphorus

• Fatty acids 0.15%

• Lecithin 0.1%

• Fat 0.1%

• Alkaline phosphatase

• Proteins

STEP 7: Structure and Functions of Pancreas (20 minutes)

|Activity: Brainstorming (5 minutes) |

| |

|Ask students to brainstorm on the following question: |

| |

|What are the functions of the pancreas? |

| |

|ALLOW few students to respond |

| |

|WRITE their responses on the flip chart/ board |

| |

|CLARIFY and SUMMARISE by using the content below |

• The pancreas lies mostly posterior to the stomach

• It extends across the posterior abdominal wall from the duodenum, on

the right, to the spleen, on the left

• It is 12 to 15 cm long; weighs approximately 60gm

• Composed of endocrine and exocrine glandular tissue

o Exocrine portion makes up majority of pancreas; has a compound acinar

arrangement and tiny ducts which unite to form the main pancreatic duct,

which empties into the duodenum

o It secretes pancreatic juice which consists of pancreatic enzymes

o Endocrine portion – embedded between exocrine units; called pancreatic

islets; constitute only 2% of the total mass of the pancreas; made up of

alpha cells and beta cells which produce glucagon and insulin

respectively and pass its secretions into capillaries

• The pancreas is (secondarily) retroperitoneal except for a small part

of its tail and consists of a head, uncinate process, neck, body, and

tail:

o The head of pancreas lies within the C-shaped concavity of the duodenum

o Projecting from the lower part of the head is the uncinate process, which

passes posterior to the superior mesenteric vessels

o The neck of pancreas is anterior to the superior mesenteric vessels, and,

posterior to the neck of the pancreas, the superior mesenteric and the

splenic veins join to form the portal vein

o The tail of pancreas ends as it passes between layers of the spleno-renal

ligament.

• The pancreatic duct begins in the tail of the pancreas

• It passes to the right through the body of the pancreas and, after

entering the head of the pancreas, turns inferiorly

• In the lower part of the head of pancreas, the pancreatic duct joins

the bile duct

• The joining of these two structures forms the hepatopancreatic ampulla

(Ampulla of Vater), which enters the descending part of the duodenum

at the major duodenal papilla

• Surrounding the ampulla is the sphincter of ampulla (sphincter of

Oddi), which is a collection of smooth muscle

• The accessory pancreatic duct empties into the duodenum just above the

major duodenal papilla at the minor duodenal papilla

• If the accessory duct is followed from the minor papilla into the head

of the pancreas, a branch point is discovered

o One branch continues to the left, through the head of the pancreas, and

may connect with the pancreatic duct at the point where it turns

inferiorly

o A second branch descends into the lower part of the head of pancreas,

anterior to the pancreatic duct, and ends in the uncinate process

• The main and accessory pancreatic ducts usually communicate with each

other

• The presence of these two ducts reflects the embryologic origin of the

pancreas from dorsal and ventral processes

• The blood supply; the arterial supply is through pancreatic arteries

the branches of splenic artery, gastro-duodenal and superior

mesenteric arteries

• Venous drainage follows arterial supply

• Splenic vein drains the body and tail

• Innervation of Pancreas is from sympathetic and parasympathetic nerves

of coelic and superior mesenteric ganglion of thoracic plexus and

vagus nerve

• Note: Digestive enzymes produced by pancreas will be discussed in

Session: 24 of this module

[pic]Refer students to Handout 15.6: The Pancreas

STEP 8: Key Points (5 minutes)

• Accessory organs of the gastrointestinal tract are the liver,

gallbladder, bile duct and pancreas

• The liver is divided into right and left lobes by fossae for the

gallbladder and the inferior vena cava

• Bile contains water, bile pigments, cholesterol ,inorganic salts such

as Na+, K+& Ca2+ salts Cl- HCO3 & Phosphorus ,fatty acids, lecithin,

fat ,Alkaline phosphatase, proteins

• Pancreas composed of endocrine and exocrine glandular tissue

STEP 9: Evaluation (5 minutes)

• What are the accessory organs of digestive system?

• What are the components of bile?

• What are the functions of the pancreas?

• What are the functions of gallbladder?

References

Gastrointestinal tract image. (2015). Retrieved September, 27, 2015 from

http://www.freeed.

net/sweethaven/MedTech/NurseCare/fig91801.

Seeley, R. R., Stephens, T. D.& Tate, P. (2003). Anatomy and Physiology.

New York:

McGraw-Hill

Shier, A., Butler, J., & Lewis, R. (2004). Hole’s Human Anatomy &

Physiology. New York:

McGraw-Hill

Standring, S. (2008). Grays’s Anatomy The anatomical basis of clinical

practice. United

Kingdom: Churchill Livingstone Elservier.

Thibodeau, G. A., & Patton, K. T. (1999). Anatomy & Physiology. Saint

Louis: Mosby,

Von Hoffman Press, Inc.

Tortora, G.J & Derrickson, B (2009). Principles of Anatomy and Physiology

12th Edition,

USA, John Wiley & Sons Inc, USA

Waugh, A. & Grant, A. (2006). Ross and Willson Anatomy and physiology in

Health and

illness. United Kingdom: Churchill Livingstone Elservier

|[pic] |Handout 15.1: Macroscopic Structure of the Liver |

[pic]

Source: Standring, S., 2008.

|[pic] |Handout 15.2: Microscopic Structure of the Liver |

[pic]

Source: Standring, S., 2008

|[pic] |Handout 15.3: Blood Supply to the Liver and Gallbladder |

Source: Moore, K. L., & Agur, A. M. R. (2007)[pic]

[pic]

Source: Moore, K. L., & Agu, A. M. R. (2007

Source: Standring, S., 2008.

[pic]

|[pic] |Handout 15.4: Structure of Gallbladder |

[pic]

Source: Standring, S., 2008.

[pic]

Source: Standring, S., 2008.

|[pic] |Handout 15.5: The Biliary System |

[pic]

Source: Standring, S., 2008.

[pic]

Source: Standring, S., 2008

|[pic] |Handout 15.6: The pancreas |

[pic]

Source: Standring, S., 2008.

[pic]

Source: Standring, S., 2008.

[pic]

Source: Brooks Cole Thomson learning, 2001

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