Digestive System Glands Zukesti Effendi Zulham Department of Histology Faculty of Medicine USU histologi.usu.ac.id

Glands Salivary Glands Liver Gall Bladder Pancreas

Salivary Glands Salivary glands –Minor –Major Sublingual glands Submandibular glands Parotid glans Regions of salivary glands –Secretory portions –Duct portions

Secretory Portions Serous cells –Truncated pyramids; single, round, basally located nuclei –Well developed RER, Golgi complex, basal mitochondria, → abundant apically situated secretory granules rich in ptyalin (amilase) –Basal aspects o/t lateral cell membranes form tight junctions –Intercellular canaliculi –Interdigitation process Mucous cells –Truncated pyramids; single, flattened, basally located nuclei –Less extensive RER, fewer mitochondria but greater Golgi complex → >> carbohydrate component, abundant apically situated secretory granules Myoepithelial cells (basket cells) –Share the basal laminae o/t acinar cells –Envelop acinus and intercalated ducts –Cytoplasmic process are rich in actin and myosin → resemble smooth muscle → contract → facilitating release o/t secretory product

Mucous Cell Serous Cell

Duct Portions Secretory potions → intercalated ducts → striated ducts → intralobular ducts → interlobular ducts → intralobar ducts → interlobar ducts → terminal (principal) duct Intercalated ducts: simple cuboidal ep + myoepithelial cell Striated duct: –simple cuboidal to low columnar ep –Basolateral membrane are highly folded, subdividing into longitudinal compartment that occupied by elongated mitochondria –Na – ATPase pumps Na out o/t cell into CT → conserving sodium Salivon –functional unit of a salivary gland –Acinus + intercalated duct + striated duct Secretory activity is stimulated via parasympathetic and sympathetic innervation

Sublingual glands The gland is composed of mucous tubular secretory units capped by serous serous demilunes. Produced mixed, but mostly mucous, saliva EM: apical accumulations of secretory vesicles Scant CT, and its duct system doesn’t form terminal duct, Instead, several ducts open into the floor o/t mouth and into the duct of the submandibular gland

A. EM of mucous acini of the Sublingual Gland. C, capillary; I, Intercalated Duct; L, lumen of Acinus; arrows, Myoepithelial Cell. 1,850 X Sublingual Gland Intercalated Duct AcinusMyoepithelial Cell Figure B. Mixed acini of same Sublingual Gland shown in Figure A. C, capillary; M, Mucous Cells; Mi, Mitochondria; S, serous demilune; SD, Secretory Duct. 1,000 X Sublingual Gland Mucous CellsMitochondria Secretory Duct C. EM of serous Acinus Sublingual Gland. C, capillary; G, Golgi Complex; L, lumen; N, nerve; Nu, Nucleus; RER, rough Endoplasmic Reticulum; V, secretory vesicles. 5,200 XAcinus Sublingual GlandGolgi ComplexNucleus Endoplasmic Reticulum

Submandibular Glands Produces mixed, but mostly serous, saliva Electron-dense core product (secretory granules) of unknown composition The number of serous demilunes is limited. The striated ducts of the submandibular gland are much longer than those of parotid or sublingual gland → display many cross sectional profiles of striated duct (characteristic feature) CT capsule o/t submandibular gland is extensive and forms abundant septa, which subdivide the gland into lobe and lobules.

Parotid Glands Produced serous saliva → ptyalin Electron-dense core product (secretory granules) of unknown composition. CT capsule forms numerous septa → subdivide the gland into lobes and lobules

Liver Has both exocrine (bile) and endocrine functions (by hepatocytes) Is enveloped by peritoneum –Simple squamous epithelium –Dense irregular CT capsule (Glisson’s capsule) Hepatocytes are arranged in hexagon-shaped lobules (classical lobules) –In human, boundaries of the classical lobules can only be approximated –Longitudinal axis is occupied by central vein –Portal areas (triads): where 3 classical lobules are in contact each other CT elements are increased; hepatic artery, portal vein; interlobular bile ducts; lymph vessels

Classic Lobules (pigs)

3 Concepts of Liver lobules Classical liver lobules –Concept: Blood flows from the periphery to the center of the lobule (central vein) –Bile enters into bile canaliculi and flows to the periphery of the lobule to the interlobular bile ducts of the portal areas Portal lobules –Concept: exocrine secretion (bile) flows to central lumen of acinus –Triangular region whose center is the portal area and whose periphery is bounded by imaginary straight line connecting the three surrounding central veins that form the three apices of the triangle Hepatic acinus (acinus of Rappaport) –Concept: blood flow from distributing arterioles → on the order in which hepatocytes degenerate subsequent to toxic or hypoxic insults –3 concentric regions of hepatic parenchyma surrounding a distributing artery in the center.

3 Concepts of Liver Lobules

Hepatic Sinusoids and Perisinusoidal Space of Disse Hepatic sinusoids: the space between the plates of hepatocytes –Sinusoidal lining cells (endothel) –Fenestrated 0.5 µm –Macrophage → Kupfer Cells Endothels are separated from hepatocytes by perisinusoidal space (Space of Disse) –Collagen III; No basal lamina –Nonmyelinated nerve fibers –Fat storing cells (Ito Cells/Stellate cells) –Pit cells → NK cells

sinusoid fenestra

Ito Cell

Kupfer Cells Space of Disse

Hepatic Duct Bile canaliculi → labyrinthine tunnels → cholangioles → canals of Hering → interlobular bile ducts → right and left hepatic duct Cholangioles –At the periphery of classic lobules –Short tubules composed of a combination of hepatocytes, low cuboidal cells, and occasional oval cells Canals of Hering –Slender branches of interlobular bile ducts –Composed of low cuboidal cells and some ovoid cells Cuboidal cells secrete a bicarbonate-rich fluid under influenced of hormon secretin of DNES cells

Hepatocytes 2 domains: lateral and sinusoidal Lateral domains –Form bile canaliculi –Fascia occludentes prevent leakage of bile from bile canaliculi –Short, blunt microvili project into bile canaliculi (exocrine secretion) –High levels of Na-K ATPase and adenylate cyclase –Isolated gap junctions Sinusoidal domains –Microvili projects into space of Disse –Endocrine secretion

Bile Canaliculi

Gall Bladder Mucosa –Empty gallbladder is highly folded into tall, parallel ridges; bile distended gallbladder reduces the plications to a few short folds → smooth mucosa –Simple columnar epithelium Clear cells Brush cells –Lamina propria is a vascularized loose CT Simple tubuloalveolar glands Smooth muscles are oriented oblique and longitudinal Adventitia –Glisson’s capsule of Liver –peritoneum

Histophysiology Store, concentrate, and release bile Epithelium –Luminal surface display short microvili coated by a thin layer of glycocalyx –Supranuclear: secretory granules containing mucinogen –Basal region is rich in mitochondria

Pancreas Produced exocrine and endocrine secretions CT capsule forms septa → sudivide the gland into lobules

Exocrine Pancreas Tubuloacinar gland 40 – 50 acinar cells form a round to oval acinus 3 – 4 centroaciner cells occupied acinar lumen → beginning of the duct system Acinar cell –Truncated pyramid; round nucleus; basally located; basophilic cytoplasm –Apex, facing the lumen, is filled with zymogen granules. Number of secretory granules diminished after meal. –Basal cell membranes have receptors for cholecystokinin and acethylcholine The Golgi complex varies in size in inverse relation to the zymogen granule concentration –Smaller when zymogen granules are numerous –Larger after the granules release their content Zymogen granules may release their contents individually or several granules may fuse each other, forming a channel to the lumen

Exocrine Pancreas Duct System Centroacinar cells of terminus intercalated duct → intralobular ducts → interlobular ducts → main pancreatic duct → common bile duct → papilla of Vater Centroacinar cells: pale, simple low cuboidal ep

Endocrine Pancreas Islet of Langerhans –Richly vascularized spherical conglomeration of cells Cells: , , , PP, G –Cannot be differentiated by routine examination → IHC, EM Each islet is surrounded by reticular fibers, which also enter the islet to encircle the capillaries that pervade it.

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