Histology of The Accessory Organs of The Digestive System

Accessory Organs Include: 1- Salivary Glands (3?) 2. Pancrease (exo. & endo.) 3. Liver & Gallbladder

Salivary Glands Made of 2 portions 1. Secretory Portion: composed of serous &/or mucous cells Arranged in acini (Alveoli) Couched by myoepithelial cells 2. Ducts Portion: highly branched ducts Intercalated (smallest)  Striated  Interlobular  Interlobar  Principal (Terminal)

Serous Cells - seromucous cells  both proteins & Polysaccharides - Single, round, basal nucleus - Highly developed RER & Golgi complex - Secretory granules (amylase)

Mucous Cells - single, flat, basal nucleus -  RER &  Golgi - Abundant secretory granules in the apical region

Myoepithelial (Basket) Cells Made of: 1. Cell body: contains the nucleus 2. Several long processes: envelope the acinus & ?? Duct rich in actin & myosin  resemble ?? Muscle cells Fxn.: processes contract  press the acinus  release of secretory products

Parotid Gland - Purely serous  amylase - C.T. capsule  septa  lobes & lobules *  40y:  invaded by adipose tissue into the parenchyma

Submandibular Gland Mixed with serous Predominance (90% serous acini) *Many striated duct profiles -C.T. Septa

Sublingual Gland Mixed with ?? Predominance * Composed of mucus acini capped by serous demilunes

Pancreas On post. Abdominal wall, behind the ??  150 g Covered by flimsy C.T. capsule that Forms septa  lobules 2 components Exocrine: pancreatic juice Endocrine: hormones & G.F.

Exocrine Pancreas Tubuloacinar gland Produces: HCO 3 - rich fluid digestive proenzymes (Trypsinogen, p. lipase, amylase) 2 types of cells: - Acinar cells (40-50 = acinus) - Centroacinar cells (3-5 in each acinus)

Acinar Cells Truncated pyramids Basal round nucleus  proenzyme-containing granules (Zymogen granules)

Centroacinar Cells Spindle-shaped cells Extensions of intercalated ducts into Pancreatic acini  Duct Cells Contain receptors in their basal memb. For the hormone ?? Secrete: alkaline (HCO3-) solution *under stimulation by secretin

Endocrine Pancreas Composed of spherical cell aggregations  Islets of Langerhans  1 million islets in each H. pancreas  1-2% of pancreatic mass (1.5g) * Composed of 5 cell types Undifferentiated histologically

Islets of Langerhans Cells 1.  cells:  70% of total cells in the islets secrete ??   bld. Glucose level 2.  cells:  20% of total cells in the islets secrete glucagon   bld. Glucose level 3.  cells:  5% of total cells secrete somatostatin (GHIH)   release of GH   cell proliferation 4. G cells:  1-2% of total cells secrete gastrin  ??

5. PP cells:  1 % of total cells secrete Pancreatic polypeptide   exocrine secretions of pancreas * PP level is elevated: in anorexia nervosa patients in fasting individuals during exercise But, decreased by more food intake

Diabetes Mellitus Hyperglycemic metabolic disorder results from: 1. Lack of insulin production by ?? Cells (Type I) 2. Defective insulin receptors on target cells (Type II) Type II: non-insulin dependent  common the type I  40 years

Type I Diabetes Insulin-dependent or juvenile diabetes  20 years 3 cardinal signs: 1. polydipsia: constant ?? 2. polyphagia: undiminished hunger 3. polyuria: excessive ?? * Histologically: atrophied & fibrotic islets

Liver & Gallbladder

General Histology of The Liver Classical Hepatic Lobule Functional unit of the liver Hexagon shape 2 mm long & 0.7mm in diameter Surrounded by thin C.T. elements

General Histology of The Liver Each Lobule is composed of the following: 1. Hepatocytes: liver cells arranged in rows of 1-2 cell thick (Hepatic laminae/plates) ~80% liver volume Fxn.: Secretory: ?? Metabolism: breakdown fatty acids, A.A., & glycogen to glucose.

2. Central vein: In the center of the lobule  Hepatic veins  IVC 3. Portal Triad: At periphery of lobule Usually 3 per each lobule Contain branches of ?3? 4. Sinusoids: Spaces between ?? Rows Contains bld. From 2 sources: ? & ?

5. Kupffer cells: Phagocytes (WBCs) Fxn.: Filtration of bld. by destroying bacteria & other foreign materials that may enter from intestine. 6. Bile canaliculi: Small ducts between hepatocytes that collect bile produced by ??

Portal Triad

Distributing Arterioles

Concepts of Liver Lobules 3 concepts 1. Classical lobule: 1 st to be defined for bld. Flow from periphery (triads) to center of the lobule (CV) 2. Portal lobule: for bile flow Definition: The triangular area whose center is portal triad & periphery is imaginary lines connecting the 3 surrounding CV

Concepts of Liver Lobules 3. Portal (Hepatic) acinus: Diamond-shaped Center: distributing arteriole (??) or the line connecting 2 portal triads Periphery: central veins * Describe the order in which hepatocytes Degenerate due to toxic or hypoxic inj. Divided into 3 zones: Zone I: periportal, richest in O 2 Zone III: centrilobular, poorest O 2 supply   sensitive to ischemic inj. Zone II: midlobular zone.

Hepatic Sinusoids & Hepatocytes Hepatocytes arranged in plates of 1-2 cell thick Radiate from CV to periphery of classical lobule Spaces between the plates  Sinusoids * Hepatocytes separated from bld. in sinusoids by: Sinusoidal Lining Cells (SL cells)

Sinusoidal Lining Cells Have: 1. Clusters of fenestrae  sieve plates 2. Gaps in between   0.5  m  only molecules  ?? Can leave the sinusoids into the space ?? * Kupffer cells are associated with SL cells in the sinusoids

Perisinusoidal Space of Disse The space between ?? And SL cells Supported by reticular fibers (Collagen type ??) Contains: 1. Plasma escaping from sinusoids 2. Microvilli of hepatocytes  Facilitate exchange of materials by  surface area 3. Fat storing cells (hepatic stellate, Ito cells)  Vit. A 4. Natural killer cells (pit cells)

Liver Cirrhosis Due to inj. Or inflammation  parenchymal damage   Ito cells  Myofibroblasts  collagen fibers  Obstruct blood circulation of the liver

Domains of Hepatocyte Membrane 2 domains - lateral: face other hepatocytes formation & release of bile - Sinusoidal: face the space of Disse 1. release of endoc. Secretions 2. transport of materials

Lateral Domain Form intercellular space of 1-2  m  bile canaliculi Microvilli project into canaliculi   surface area   bile secretion Sinusoidal Domain Microvilli project into ??   s.a. x6  facilitate exchange of materials release of endoc. secretions

Gallbladder 4 layers 1. Epithelium: simple columnar 2. Lamina Propria: vascularized L.C.T. 3. Smooth Muscle: oblique fibers 4. Serosa and Adventitia *mucosa is highly folded in an empty bladder