Download Microstructure Of The Digestive System II

Microstructure Of The Digestive System II
by:
dr. Sutrisno Darmosumarto,Sp.A
Department of Histology & Cell Biology
Faculty of Medicine
Gadjah Mada University
The Salivary glands:
• The main glands are: parotid, submaxillary(submandibular), sublingual and palatin
glands.
• Two kinds of pars secretory cell: serous and mucous cell
Parotid Glands
• Branched acinous gland.
• Its secretory portion  serous cells  have a moderate amount of ribosomal RNA in their
basal regions.
• The secretory granules  positive periodic acid-schiff (PAS) reaction  the presence of
polysaccharides (sialomucin and sulfomucin).
• Rich in proteins and have a high amylase activity.
• The encapsulating connective tissue contains plasma cells and lymphocytes.
• The plasma cells secrete IgA  with a proteinaceous secretory piece synthesized by the
seromucous acinar cells.
• The IgA-secretory piece complex  into the saliva , resistant to enzymatic digestion 
immunologic defense mechanism.
Palatine gland:
• In the palatum molle
• Consist of mucous cell
Submaxillary/submandibulary gland:
• Branched tubuloacinar gland  seromucous cells  amylolytic activity of saliva.
• The demilunes  secrete the enzyme lysozyme  hydrolyze the wall of bacteria.
• Consists of 80% serous cells, 5% mucous cells, and 5% striated ducts; 10% vessels, nerves,
and excretory ducts.
Sublingual Gland:
• The structure similar with submaxillar gland, but consist of 60% mucous cells, 30 % serous
cells, and 10% vessels, nerves, and excretory duct
• Branched tubulo-acinar gland.
Histophysiology of the Salivary Glands
• Moistening and lubricating  performed by the water and glycoproteins of saliva.
Microstructure Of The Digestive System II | BLOG: MISC ’09 | Source : ELS FK UMY
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Digestion of carbohydrates  due to salivary amylase activity  begins in the mouth but
takes place also in the stomach before the gastric juice acidifies the food,
The function of the intercalated ducts  transport of saliva to larger ducts,
Primary saliva has the same ionic composition of blood  isosmotic.
The duct cells actively reabsorb sodium and excrete potassium  hypotonic and has a
higher concentration of potassium and a lower concentration of sodium than blood.
The striated ducts  ion-transporting cells, sensitive to aldosterone.
Human salivary glands (although sensitive to hormones) controlled by the sympathetic and
parasympathetic nervous systems
THE PANCREAS
• A mixed exocrine and endocrine gland.
• The exocrine portion  acinar gland  serous cell  protein-synthesizing cell  richest
RNA content cells.
Enzyme synthesis:
• Basal portion, the proenzymes  RER  golgi apparatus inactive enzymes 
secretory vesicles.
• Mature secretory granules (zymogen), membrane-bound  apical portion.
• The number granules depends on the digestive phase  maximum in fasting.
Structure:
• Covered by capsule of connective tissue  sends septa  pancreatic lobules.
• The acini surrounded by a basal lamina supported by reticular fibers, rich in capillary
network.
• Secretes, water, ions, trypsinogen, chymotrypsinogen, carboxypeptidase, ribonuclease,
deoxyribonuclease, lipase, and amylase.
• Secretion stimulated by secretin and cholecystokinin.
THE LIVER
• The liver is the largest organ situated in the abdominal cavity .
• 70% of its blood comes from the portal vein; the smaller percentage is supplied by the
hepatic artery.
• Through the portal vein, all the material absorbed via the intestines reaches the liver
except the lipids, which are transported mainly by the lymph vessels.
• The position of the liver  for gathering, transforming, and accumulating metabolites and
for neutralizing
• Eliminating toxic substances  occurs in the bile  important in lipid digestion.
The Hepatic Lobule:
• Hepatocytes are grouped in plates  interconnected  liver lobules
• The liver lobule forms a prismatic polygonal mass of liver tissue about 0.7 x 2 mm in size,
in close contact along most of their extent, making it difficult to establish precisely the
exact limits between different lobules.
• The portal spaces  at the corners of the polygons  occupied by the portal canals,
containing:
Microstructure Of The Digestive System II | BLOG: MISC ’09 | Source : ELS FK UMY
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venule (a branch of the portal vein);
arteriole (a branch of the hepatic artery);
duct (part of the bile duct system);
lymphatic vessels.
The hepatocytes  a layer of one cell thick  brick wall  radial pattern
The space  sinusoid, irregularly, dilated, lined discontinously by endothelial cells
and Kupffer cell  easy flow of macromolecule
Kupffer cell: clear vacuoles, lysosomes, and GER scattered throughout the cytoplasm
 fagositosis.
The Hepatocyte
• Polyhedral, diameter of approximately 20-30 µm.
• Stained with HE  the cytoplasm is eosinophilic large numbers of mitochondria and to
some extent smooth endoplasmic reticulum.
• 2 hepatocytes form the bile canaliculus .
• In this cell, the granular endoplasmic reticulum.
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Several proteins (blood albumin and fibrinogen) synthesized in GER.
Smooth endoplasmic reticulum  conjugation in which various substances are bound to
sulfate or glucuronide during the process of inactivation or detoxification before excretion
from the body.
Administration barbiturates  increase in the SER  enzymes activity increase 
treatment of icterus.
Glycogen  the amount depends upon the nutritional state  depot of glucose 
mobilized if the blood glucose level falls below normal  maintain a steady level of
blood glucose, the main metabolite used by the body.
The liver cell has many mitochondria, spherical or ovoid form. And lipid droplets.
The golgi system  near the bile canaliculi.
LIVER HISTOPHYSIOLOGY & FUNCTION
• Endocrine and exocrine functions,
• Synthesizes and accumulates certain substances,
• Detoxifies others,
• Transports still others.
Protein Synthesis
• Synthesizing the proteins for its own maintenance.
• Produces various proteins for export (albumin, prothrombin, and fibrinogen of the blood
plasma)  synthesized on the GER  gradually releases the protein produced into the
bloodstream  as an endocrine gland.
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Radioautographic studies : synthesized in the GER  migrates to the golgi region 
extruded into the blood.
5% by Kupffer cells; 95% by hepatocytes.
Bile Secretion
Microstructure Of The Digestive System II | BLOG: MISC ’09 | Source : ELS FK UMY
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Bile transform and transport into the bile canaliculi.
Consist of: water, bile acids and bilirubin.
About 10% of these compounds are synthesized in the smooth endoplasmic reticulum by
conjugation of cholic acid with the amino acids glycine and taurine  produces
glycocholic and taurocholic acids.
The bile acids  emulsifying the lipids and promoting easier digestion by lipase and
subsequent absorption.
Bilirubin is formed in the macrophage system (this includes the Kupffer cells of the liver
sinusoids) and is transported to the hepatocyte.
In the smooth endoplasmic reticulum of the hepatocyte, hydrophobic (water-insoluble)
bilirubin is conjugated to glucuronic acid, forming a water-soluble bilirubin glucuronide.
In a further step, the bilirubin glucuronide is secreted into the bile canaliculi.
The hepatocyte also has the ability to actively transport several dyes. This ability to
eliminate dyes is used as a test of liver function. One of the dyes classically used for this
purpose is sulfobromophthalein (Bromsulphalein, BSP).
Metabolic Function of hepatocyte:
• Converting lipids and amino acids  glucose by glyconeogenesis.
• The main site of amino acid deamination  urea  transported by the blood to the
kidney and excreted
Detoxification & Inactivation of hepatocyte:
• Various drugs and substances can be inactivated by oxidation, methylation, and
conjugation.
• Glucuronyl transferase (an enzyme that conjugates glucuronic acid to bilirubin) 
conjugation of steroids, barbiturates, antihistamines, and anticonvulsants.
• The enzymes located mainly in the smooth endoplasmic reticulum.
THE GALLBLADDER
• Hollow, pear-shaped, attached to the lower surface of the liver.
The wall :
(1) mucous layer composed of columnar epithelium  secretes mucus, and lamina propria,
(2) layer of smooth muscle, thin and irregular
(3) well- developed perimuscular connective tissue layer, and
(4) serous membrane.
The main function :
• Store bile and concentrate by reabsorbing water  depends upon an active sodiumand chloride-transporting mechanism in its epithelium.
• The water reabsorption  an osmotic consequence of the sodium pump.
Contraction of the smooth muscle of the gallbladder is induced by cholecystokinin, a hormone
produced in the mucosa of the small intestine.
Microstructure Of The Digestive System II | BLOG: MISC ’09 | Source : ELS FK UMY
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