Download Title: Pancreas, Liver and Gallbladder

Title: Pancreas, Liver and Gallbladder – Accessory Organs of Digestion
1- Introduction: The principle digestive function of the pancreas is to secrete
pancreatic juice, the liver produces and secretes bile and the gallbladder stores
and concentrates the bile.
2- After leaving the stomach the liquid chyme passes through the pyloric sphincter
into the small intestine. However, chemical digestion in the small intestine
depends on the activities of the pancreas, liver and gallbladder. These organs are
considered accessory digestive organs because they do not actually come in
contact with food, however their contributions allow digestion to progress.
3- The Pancreas – The pancreas is about 6 inches long and 1 inch thick that lies
below the stomach along the greater curvature of the stomach. It tapers from a
wide head to a narrow tail (with the body in the middle) It is attached to the
duodenum via two ducts.
a- Pancreatic juice exit the exocrine cells of the pancreas into small ducts that
eventually fuse to form the pancreatic and accessory duct. The secretions
from these ducts then enter the duodenum
1- In most people the pancreatic duct (the larger of the two) merges with
the bile duct coming from the liver and gallbladder prior to entering
the duodenum
2- Diagram
b- The duct enters the duodenum about 4 inches below the stomach, This
allows the pancreatic juice and the bile to mix with the chyme almost upon
entering the intestine
c- The entrance of this fluid into the small intestine is controlled by a mass of
skeletal muscle called the “Sphincter of Oddi”
d- Histology of the Pancreas
1- The pancreas is made up of small clusters of granular cells. About
99% of theses cells are clusters of exocrine cells called ascini. These
ascini cells secrete the pancreatic juices.
2- The remaining 1% are endocrine cells clustered into groups called the
“Islets of Langerhans” These cells secrete insulin and glucagons and
are involved with glucose regulation in the body. Failure of these cells
to work properly or failure of the body to respond to these cells results
in diabetes.
a- Alpha cells in the Islets produce Glucagon, Beta cells in the Islets
produce Insulin – Negative feedback
e- Pancreatic Juice
1- Everyday the pancreas produces about 1.2 – 1.5 quarts of pancreatic
juice. This juice is mostly water, salt, sodium bicarbonate and
enzymes. Because of the sodium bicarbonate the pH is about 7.1 – 8.2,
this buffers the acid in the chyme and inactivates the pepsin. If the
pepsin was not inactivated it would continue to digest the small
intestine.
2- Pancreatic juice contains amylase, which continues to digest
carbohydrates, trypsin to digest proteins and lipases which continue to
digest lipids.
3- The pancreatic juice also contains ribonuclease and deoxyribonucleae
which digests nucleic acids.
4- Just like pepsin in the stomach, trypsin is stored as trypsinogen and
does not become active until in comes in contact with an enzyme
called enterokinase found in the cilia of the small intestine.
4-The Liver and Gallbladder
1- The liver is the heaviest organ in the body. In the average adult it
weighs between 3 and 4 pounds. It is second in overall size to the skin.
2- The liver is found directly below the diaphragm and on the right side
of the body
3- The gallbladder is found in a depression located on the posterior side
of the liver.
4- In addition to the formation and secretion of bile, the liver metabolizes
cholesterol and fat, stores glycogen, synthesizes urea, cleans bacteria
out of the blood, breaks down hemoglobin, detoxifies alcohol and
drugs, serves as a resevoir for vitamin D and steriod hormones
5- The liver converts glucose (and stores it as glycogen) through the
procress of gluconeogenesis. When needed this glycogen can be
broken down back to glucose in the process of glycolysis. In the case
of glycolysis:
a- Glucagon is released from the pancreas in response to low
blood sugar levels. Adrenalin is also released as this is seen as
a threat to the body both enzymes act to cause the breakdown
of glycogen in the liver to relase glucose and prevent the
uptake of glucose from the cells into the blood
6- The functions of the liver can be summed up as:
a- Carbohydrate metabolism
b- Lipid metabolism
c- Protein metabolism
d- Processing drugs and hormones
e- Excretion of bilirubin
f- Synthesis of bile salts
g- Storage
h- Phagocytosis
i- Activation of Viatmin-D
1- Vitamin Deficiencies -
7- Anatomy of the Liver
a- In humans the liver is divided into two principle lobes, a large
right lobe and a smaller left lobe by the falciform ligament. The
quadrate lobe and the caudate lobe are two small lobes that are
continuous with the left lobe.
b- The falciform ligament, which divides the liver also helps to
support the liver in the abdomen by attaching to the diaphragm.
c- The round ligament found within the falciform ligament is a
remnant of the umbilical cord
8- Histology of the liver
a- The lobes of the liver are made up of functional units called
lobules.
b- A lobule is typically a six-sided structure containing
specialized epithelial cells called hepatocytes.
c- Hepatocytes lie along sinusoids (found instead of capillaries)
through which blood passes through. They contain phagocytes
called Kupffer cells that clean up worn out blood cells, bacteria
and other debris.
d- Diaphragm – Lobule
e- Diaphragm of the liver blood flow
9- Bile Duct System
a- Bile is secreted by the hepatocytes and then travels through a
variety of ducts in the liver and gallbladder before entering the
duodenum.
b- Bile is temporarily stored in the gallbladder before entering the
intestines. Each day hepatocytes secrete between 800-1000 ml
of bile into the gall bladder. Bile has pH of between 7.6 and
8.6 making it a base.
c- In the gallbladder the bile is concentrated up to 10X. Bile is a
potassium salt that is used to emulsify fats in the body as they
exit the stomach and enter the small intestine
d- Diaphragm
10- Bile
a- Each day the hepatocytes produces about 1 liter of bile. Bile is
a brow-green liquid with a pH of 7.6 – 8.6.
b- Bile contains water, salt, cholesterol, and several different
pigments.
c- The principal bile pigment is bilirubin. Bilirubin is produced
from the breakdown of old red blood cells and is secreted into
the small intestine. In the small intestine it is further broken
down to stercobilin, which gives feces it brown color.
d- Bile salts play a role in the emulsification of large lipid
globules into small lipid globules. Small lipid globules have a
greater surface area for pancreatic lipase to work on.
e- Bile is reabsorbed in the small intestine.