Download The gallbladder is a thin walled green muscular sac on the inferior

The gallbladder
is a thin walled green muscular sac on the inferior surface of the liver.
The gallbladder stores bile that is not immediately needed for digestion
and concentrates it. When the muscular wall of the gallbladder
contracts bile is expelled into the bile duct.
Bile secretion:
Bile is necessary for digestion and absorption of lipids in the small
intestine. Bile is a mixture of bile acids, bile pigments and cholesterol.
Bile is produced and secreted by liver, stored in gallbladder, and ejected
into the lumen of small intestine. It emulsify lipids to prepare them for
digestion.
When chyme reaches the small intestine CCK is secreted which
stimulates contraction of gallbladder and relaxation of sphincter of Oddi,
to flow bile into the lumen of the duodenum. When lipid absorption is
complete, bile acids are recirculated to liver. figure(11)
Figure (11)bile secreon
The function of the gall bladder is :1-to store bile
2- to concentrate bile ( epithelial cells of gall bladder absorb ions and
water)
3 -to eject bile into the lumen of the small intestine.
l.
Bile is constituents of
*bile acid (50%)
*bile pigments as billirubin (2%).
*cholesterol (4%)
*and phospholipids (40%).
*Bile contains electrolytes and water..
The main stimulus for ejection of bile is CCK which is secreted by I cell in
response to amino acids and fay aci d. 95% of secret ed bi ll acids are
recirculated to the liver, bile acid excreted in feces 5% , must be
replaced by synthesis of new bile acids.
Role of bile secretion
A-detergent action :
Bile secretion decrease the surface tension of the substance so it will
brake them into smaller particle called micelles to increase the surface
area to about 1000 me s original one in which lipase will do it’s effect .
B –hydrotropic effect :
Which means makes lipid water soluble to pass easily via epithelial cell
membrane bile secretion regarded as amphipathic molecule which
means that it has 2 poles one is the hydrophilic pole which is formed
from dissociate carboxyl group or hydroxyl group and the other is the
methyl group which represent the hydrophobic pole of the bile salts
.bile salts arrange themselves around the lipid molecule in such away
that the hydrophilic group in the surface and the hydrophobic toward
the lipid particles so the surface of lipid will be water soluble.
Digestion
I t is chemical breakdown of ingested food into absorbable molecules,
The digestive enzymes are secreted by salivary gland, gastric gland,
pancreatic glands, and apical membrane of intestinal epithelial cells.
Digestion of carbohydrates:
Three major sources of carbohydrates exist in the normal human diet.
These are sucrose (table sugar), lactose (disaccharide) in milk and
starches (polysaccharides) present in all non animal foods, and grains.
Other carbohydrates ingested are glycogen, alcohol and other.
Carbohydrate digestion and absorption:*Carbohydrates start breaking down in the mouth.
*The enzyme salivary amylase starts breaking up the starches reducing it
into smaller glucose molecules where in the stomach it continues to be
broken down further.
*Upon entering the small intestine the pancreas releases the enzyme
pancreatic amylase to help complete the hydrolysis of starch into
smaller chains of glucose molecules – monosaccharide's, which is 1
molecule of sugar.
* The monosaccharide's are absorbed into the small intestine and
delivered to the liver by way of the hepatic portal vein.
*After the liver processes the nutrients, the nutrients enter into the
blood stream circulating throughout the body.
Lipid or fat digestion and absorption :In the stomach fats are broken down into glycerol and fatty acids.
*
The digestion of fats starts in the stomach when mixed with the
*enzyme lipase.
*The major part of the breakdown takes place in the small
intestine.
*In the duodenum the enzyme pancreatic lipase furthers the
process by breaking the fats down from triglycerides to
monoglycerides (which is 1 fay aci d ins tead of 3 fay aci ds
connected to a glycerol molecule).
*Bile is produce in the liver and secreted by the gall bladder which
increases the lipids solubility, breaking it down into droplets,
making it easier for the small intestine to absorb.
*When foods with high lipid content enter the stomach, the
hormone – gastric inhibitory peptide is released, slowing down
movement flow out of the stomach.
*This is why we feel full after eating high fat foods.
Protein Digestion and Absorption:-
*Proteins are split into linked amino acids called peptides and
then into individual amino acids.
*In the stomach the enzyme pepsin starts the breakdown of
proteins into smaller units called polypeptides and peptides.
*In the duodenum of the small intestine the pancreatic enzymes
trypsin and chymotyrpsin also split proteins into polypeptides and
peptides.
*In the jejunum of the small intestine an enzyme created by the small
intestine called peptidase splits the large peptides into smaller peptides
and than into amino acids.
*All of these smaller protein fragments go directly to the liver by the
hepatic portal vein.
Once in the liver one of three things happens to the proteins:
1. It converts to glucose,
2. It converts to fat or
3. It is directly released into the blood as amino acids.
Glossary of Terms
Duodenum –
long.
Jejunum –
long.
Ileum – The third secon of the sma l l int es ne.
-2 meters
It i s 1.5 met ers l ong.
Hepatic Portal Vein – The vein that delivers nutrients rich blood to the
liver.
Esophageal Sphincter – A gateway separating the esophagus and the
stomach, controlling the entry of food.
Pyloric sphincter – A gateway separating the stomach and the small
intestine, controlling the entry of chyme.
Chyme – A slushy acidic mixture of food and digestive juices.
Enzymes – Protein molecules that increase the speed of chemical
reactions in the body. They work by combining with and altering the
molecules of other chemical substances. The digestive enzymes split
large molecules of food into smaller units for absorption.
Villi – Projections along the small intestinal wall increasing area surface
for greater absorption.
Hydrolysis – splitting of substances by adding water
Glycerol – the combination of fats and oils.
Absorption
It is movement of nutrients, water and electrolytes from the
lumen of the intestine into the blood. There are two path for
absorption, a cellular path and paracellular path.
In the cellular path
the substance must cross the apical (luminal) membrane,
then enter the tight junction intestinal epithelial cell,
and be extruded from the basolateral membrane.
In paracellular, through intercellular spaces between intestinal epithelial
cells, and to the blood.
The structure of intestinal mucous is suited for absorption of large
quantities of nutrients though villi and microvilli which increase the
surface of a small intestine.
The villi are largest in the duodenum, where digestion and absorption
occur and shortest in the terminal ileum. The surface of the villi are
covered with epithelial cells,
the apical surface of epithelial cells is further expanded by tiny
enfolding called microvilli, this microvilli surface is called the brush
border because it is brush like appearance, under light microscopy.
The villi and microvilli increase total surface area by 600 fold. The
epithelial cells of small intestine are replaced every 3-6 days.