1. IN THE NAME OF GOD THE COMPASSIONATE THE MERCIFUL

2. Histology Lecture 19 Digestive System Part 3

3. Digestive Glands Digestive glands are consist of: Salivary glands
Pancreas
Liver
Gall bladder

4. Salivary Glands
There are many minor salivary glands scattered throughout oral mucosa and three pairs of major salivary glands
Three pairs of major salivary glands are:
Submandibular glands
Sublingual glands
Parotid glands
They have lobular organization composed of branched tubuloalveolar glands with connective tissue capsule and septa that organize the glands into lobes and lobules
Each individual acinus is also invested by a thin layer of CT
Saliva secretion is controlled by autonomic nerves
Sympathetic stimulation = sparse thick saliva
Parasympathetic stimulation = copious, watery saliva

5. Salivary Gland Cells
Serous cells are actually seromucous cells that produce proteins and polysaccharides
They are pyramidal and have basal spherical euchromatic nucleus
Cytoplasm is basophilic due to presence of a developed RER, Golgi apparatus
Apically located granules that are usually eosinophilic and rich in ptyalin (salivary amylase)
Many basal mitochondria
Intercellular canaliculi, plasmalemma processes
Organized as acinus or demilune that secrete proteins, polysaccharides and ptyalin

6. Salivary Gland Cells Mucous cells are cuboidal or pyramidal
Mucous cells have a heterochromatic basal flattened nucleus
Apical cytoplasm is pale or blue/purple
Their structure is acinar or tubular
They have less RER, fewer mitochondria but greater GA
Intercellular cacanaliculi and processes are much less than serous cells

9. Salivary Gland Cells
Myoepithelial cells (Basket cells) have large processes which form desmosomal contact with acini and ducts cells,
Their processes are rich in actin and myosin
Basket cells have a common basal lamina with acinar cells
They attach to basal lamina by hemidesmosome

11. Salivary Gland Ducts
Intercalated duct are smallest branches lined by short, cuboidal or squamous cells and myoepithelial cells
Striated duct have large diameter composed of cuboidal to low columnar cells which are eosinophilic, and secrete fluid and ions, basolateral membrane folded with Na – ATPase pump, elongated mitochondria
Striated ducts join each other and forming intralobular ducts that are invested by more CT elements
These ducts join each other and forming larger caliber ducts known as interlobular ducts (excretory ducts)
Excretory duct have large diameter, large lumen, cuboidal or columnar cells, located outside of lobules

14. Parotid Gland The largest salivary gland but produce 30% of saliva
Connective tissue capsule is well developed forms many septa divided the glands into lobes and lobules
Branched acinar structure
All serous cells, but actually they are seromucous
Secrete amylase(Ptyalin)
Lymphocytes and plasma cells are located in connective tissue elements produce IgA
After 40 year of age adipose tissue invaded the gland

16. Submandibular Gland
Extensive connective tissue capsule and abundant septa
Branched tubuloacinar gland produce 60% of saliva
Mucous and serous acini; mucous acini with limited number of serous demilunes
About 80% of cells are serous (basophilic)
Lysozyme, mucous and amylase
Striated ducts are much longer than the other two glands

18. Sublingual Gland It is very small that produce 5% of total saliva
Glands invested by scant CT capsule
Branched tubuloacinar gland
Mostly mucous cells in acini with some serous demilunes
Produce mix saliva but mostly mucous saliva

20. Saliva Saliva includes water, enzymes, IgA, mucous, ions
Primary saliva manufactured by acinar cells is isotonic with plasma
Secondary saliva is altered by striated duct cells
Moisten and lubricate food for swallowing
Enzymes like amylase and lipase to begin digestion
Saliva has protective effect on oral cavity tissues
Participate in taste sensation
IgA, lactoferrin, lysozyme have different role against antigens and microorganisms

21. Pancreas Pancreas is a mixed exocrine and endocrine gland
Thin capsule with septa between lobules
Exocrine part organized as a compound tubuloacinar glands similar to parotid gland
Endocrine part are islets of Langerhans scattered among the excretory units
Centroacinar cells occupy the lumen of the acini, these cells are beginning of the duct system
Centroacinar cells are pale, low cuboidal with receptors for secretin and acetylcholin
Intercalated ducts, Intralobular ducts, and interlobular ducts

23. Pancreas
Serous cells are truncated pyramidal in shape basophilic,with a round nucleus that is located basally, RER, GA, and secretory granules
Zymogen granules contain: trypsinogen, chymotrypsinogen, carboxypeptidase, ribonuclease, DNAase, lipase, elastase, amylase
Secretion controlled by secretin and CCK from duodenum and vagus nerve
Centroacinar cells and intercalated ducts manufacture a serous, bicarbonate-rich alkaline fluid
Main pancreatic duct goes to duodenum

25. Liver
Liver is the largest gland in the body, weighing about 1500 gr , it has endocrine and exocrine functions
Dense irregular connective tissue capsule of liver is loosely attached to liver except at porta hepatis where blood and lymph vessels and bile ducts enter or exit the gland
Receives portal blood (75%) from small intestine via portal vein and oxygenated blood from hepatic arteries (25%)
CT elements are sparse, bulk of liver is composed of hepatocytes
Liver has a lobular organization
Classical lobule in which hepatocytes arranged as an hexagon
Portal area (triad) is where three classical lobules are in contact with each other, more CT elements present, houses branches of hepatic artery, tributaries of portal vein, interlobular bile ducts, and lymph vessels

27. Liver
Portal areas are isolated from liver parenchyma by modified hepatocytes which form the limiting plate
Space of Möll separates the limiting plate from the CT elements of portal area
Longitudinal axis of each classical lobule is occupied by central vein
Hepatocytes radiate from central vein and separating from each other by vascular spaces known as hepatic sinusoids
Limiting membrane pierced by inlet venules and inlet arterioles to join hepatic sinusoids
Blood from periphery flows slowly through sinusoids into central vein

29. Liver
Central vein terminates in sublobular vein, these veins also join each other forming collecting veins which in turn form hepatic veins
In classical lobule concept blood flow from periphery to center of lobule
Bile manufactured by hepatocytes flow in opposite direction in small intercellular spaces known as bile canaliculi
Portal lobule is a triangular region that portal area is located in its center and central veins form apices of the triangle
Hepatic acinus (acinus of Rappaport) is diamond-shaped, a distributing artery located in center of acinus, three regions of parenchyma surrounding the artery(zone I, II, III)

31. Liver
The space between the anastomosing plates of hepatocytes are occupied by hepatic sinusoids
Sinosuidal lining cells are fenestrated are not in contact with each other
They prevent direct contact between blood and hepatocytes
Resident macrophages known as Kupffer cells associated with lining cells
The space that separates sinusoidal lining cells from hepatocytes is called perisinusoidal space (space of Disse)
Microvilli of hepatocytes occupy much of the space
Type III collagen that is present in space support lining cells(no basal lamina)

33. Liver
Fat storing cells ( known as Ito cells or Stellate cells) may present in Disse space and store vitamin A
Pit cells which are natural killer cells also may be seen in space of Disse
Hepatocytes are polygonal µm diameter, forming anastomosing plates of one to two thickness cells, eosinophilic with 1 or 2 spherical nuclei,
In lateral domain bile canaliculi form between two cells, microvilli, Na-K ATPase and gap junctions are common characteristics of lateral domain
Bile canaliculi between hepatocytes leading to hepatic ducts with simple cuboidal epithelium

36. Liver
Sinunosoidal domains of cell membrane have many microvilli protrude to perisinusoidal space (of Disse), endocrine secretion of hepatocytes release here
Hepatocytes are large cells which are contain RER, free ribosomes, several sets of Golgi apparatuses, SER, mitochondria, lipid droplets, glycogen
Bile secreted from hepatocytes into bile canaliculi contains water, ions, bile salts and acids, phospholipids, cholesterol, & bilirubin

39. Liver Functions Glycogen storage Lipid metabolism
Vitamin storage (A, D, B12 )
Bile production (Bile acids solubilize lipids and aid digestion)
Detoxification of drugs and toxins in SER
Synthesis of plasma proteins (albumin)
Metabolism of lipid, carbohydrate, proteins
Erythrocyte breakdown (Bilirubin formed in breakdown of RBC)
Complex IgA with secretory component

40. Gall Bladder
Mucosa is lined by simple columnar epithelium with two type of cells: more clear cells and infrequent brush cells
Cells have microvilli, Na –K ATPase pump
Epithelial layer is highly folded
lamina propria is composed of loose CT, in the neck region lamina propria houses simple tubuloalveolar mucus glands
Smooth muscle layer is composed of thin obliquely oriented fibers with perimuscular connective tissue
Serosal and adventitial membrane
Stores and concentrates ml bile
Cholecystokinin and acetylcholine stimulates contraction to force bile into small intestine
CCK released from duodenum in response to lipids in duodenum

42. Department of Histology
F.Rajaei