Digestive System Digestive Glands

◇ small digestive glands: found in the wall of digestive tract. ◇ accessory glands (large digestive glands): Components of Digestive Glands salivary glands pancreas liver

◇ Parenchyma: ( functional portion of an organ ) acini / gland cells ducts ◇ Stroma : ( non-functional portion of an organ ) capsule CT inside the organ. General Structure of Digestive Glands

Salivary Glands

serous acinus mucous acinus seromucous / mixed acinus General structure of the large salivary glands Parenchyma acinus duct intercalated duct striated/secretory duct interlobular duct excretory duct types of acinus Salivary Glands

Model ( structure of the large salivary glands) serous acinus seromucous / mixed acinus mucous acinus intercalated duct striated /secretory duct demilume

Model Section (H&E) serous acinus mucous acinusseromucous /mixed acinus

serous acinus: comprised by serous cells. *zymogen granules in apical cytoplasm. mucous acinus: comprised by serous cells. *mucinogen granules in cytoplasm. seromucous acinus: comprised by both cells. / mixed acinus *demilume Structural Characteristic of gland Cell: Salivary Glands

serous acinus: *zymogen granules in apical cytoplasm.

Serous cell: basal lamina (bl); connective tissue (ct); desmosome (d); endothelium (en); Golgi complex (g); intercellular space (is); lumen (l); microvilli (mi); mitochondria (m); nucleus (nu); RER (re); secretion granule (sg) x.

mucous acinus: *mucinogen granules in cytoplasm. n

n Detail of mucous cell: Sero-mucous cell (sc); Golgi complex (gc); intercellular space (is); secretion granule (sg); lumen (l); nucleus (n); RER (re) x. re is sg

seromucous acinus / mixed acinus demilume

acinus duct intercalated duct: simple squamous/cuboidal epith. striated/secretory duct: simple tall columnar epith. interlobular duct: pseudostratified columnar epith. excretory duct: stratified squamous epith. Salivary Glands

intercalated duct: simple squamous or cuboidal epith. Salivary Glands

intercalated duct: simple squamous or cuboidal epith. Salivary Glands

LM EM

basal lamina (bl); desmosome (d); nerve fibers (nf); Golgi complex (g); intercellular space (is); mitochondria (m); nucleus (nu); RER (re) x. EM nu re m g bl Detail of intercalated duct cell

striated/secretory duct: simple tall columnar epith. Salivary Glands

striated/secretory duct Salivary Glands Note: the basal striations

Striated duct: blood vessel (bv); connective tissue (ct); lumen (l); nucleus (nu). × 2750.

Basal portion of striated duct cell: basal lamina (bl); basal membrane pleat (bmp); collagen fiber (cf); mitochondria (m); nucleus (nu). ×

striated/secretory duct Salivary Glands The secretory ducts ， which are continuous with the intercalated ducts ， are wider and lined with a simple columnar epithelium. As the secretion from the acini passes through the secretory ducts ， the epithelium can re-absorb sodium （ Na + ） and water from the lumen to the interstitium （间质） and transport potassium (K + ) into the saliva ， thus changing the consistency of the saliva. The secretory ducts drain into interlobular ducts which run between lobules.

interlobular duct: pseudostratified columnar epith. Salivary Glands excretory duct: stratified squamous epith.

Salivary glands include * Parotid G. * Submandibular G. * Sublingual G. Function: * moistening food. * carbohydrate digestion. * Secrete IgA.

Parotid G. Mucous A Serous A. Mixed A. Inter- calated D Submandibular G.Sublingual G. +++ short + Structural Features of Salivary Glands Striated D + ++ long short long none few none

Pancreas The pancreas is a lobular organ. The pancreas has both exocrine functions (releases digestive enzyme secretions into the intestines) and endocrine functions (releases hormones into the blood).

Pancreas Parenchyma exocrine gland endocrine gland produces pancreatic juice produces hormones

Parenchyma make section

Parenchyma exocrine gland endocrine gland endocrine gland exocrine gland exocrine gland

Parenchyma exocrine gland endocrine gland

Acini Pancreas Exocrine Pancreas Ducts wholly consists of serous acini. small centroacinar cells in the lumen. intercalated ducts interlobular ducts main pancreatic ducts major duodenal papilla

Exocrine Pancreas The yellow arrows are pointing to the characteristic centroacinar cells which are the key to identifying the pancreas. Notice how they stand out against the dark cells of the acini. Here is another look at the Exocrine Pancreas and the Acini (white dotted lines) which make it up. Pancreas Acinus Central Acinar Cells

Exocrine Pancreas Pancreas Acinus Centroacinar Cell Acinar Cell Low power (LM) high power (LM)

Ducts Intercalated ducts ： simple squamous or cuboidal epith. Interlobular ducts ： columnar epith. pancreatic ducts ： tall columanr epth. Exocrine Pancreas major duodenal papilla (similar to salivary glands. REMEMBER: there are no striated ducts in the pancreas. )

* amylase （胰淀粉酶） ： hydrolyses starch & glycogen. * lipase （胰脂肪酶） ： hydrolyzes triglycerides ( 甘油三酯 ). into fatty acids and mono-glycerides ( 甘油单酯 ). * cholesterol esterase （胆固醇酯酶） ： breaks down cholesterol esters （酯） into cholesterol and a fatty acid. * trypsin （ 胰蛋白酶） and chymotrypsin ( 糜蛋白酶 ) ： hydrolyze proteins. * ribonuclease （核糖核酸酶） & deoxyribonuclease （脱氧核 糖核酸酶） ： split nucleic acids. Exocrine Pancreas It releases the pancreatic juice. pancreatic juice contain many kinds of enzyme:

Pancreas Endocrine Pancreas Islets of Langerhans scatter throughout the exocrine pancreas. Three types of cells : A-cells (20%) glucagon B-cells (75%) insulin D-cells ( 5% ) somatostatin Capillaries: each islet is richly supplied with blood vessels.

Pancreas Endocrine Pancreas A-cells B-cells D-cells A-cells B-cells A-cells

capillaries

Liver

General Introduction * The largest gland (~ 2% of body weight in adult). * Respectively receives both venous & arterial blood through the portal V. (~75%) & hepatic A (~25%). * CT of capsule extended into the parenchyma, forming “classical” liver loblules. * Functions as an exocrine gland (secreting bile) and other very important roles.

Liver section liver loblules

Liver Structures of Liver Lobule

Liver Structures of Liver Lobule

Model of Liver Lobule

Liver Structures of Liver Lobule * six-sided prism with a central V. at its center. * sheets of hepatocytes ( or hepatic plates ) extend radially from the central V. * sinusoids between hepatic plates. portal triads ( or portal area): in the corner of lobules.

Liver Structures of Liver Lobule hepatic plates

Liver Portal Triads ( or Portal Area) * Definition: The area of CT found in the angles where adjacent hepatic lobules meet. * Components: CT. + portal triad interlobular A interlobular V interlobular bile duct

Liver Portal Triads ( or Portal Area)

Liver Portal Triads ( or Portal Area) interlobular A interlobular bile duct interlobular V

Liver Sinusoids * Dilated anastomosing ( 吻合 ) venules between the hepatic plates. * Blood pathway: periphery central V. * Kupffer cells line in the wall of sinusoids. * EM ( endothilium of sinusoid ) significant gaps; numerous fenestration; incomplete basal lamina.

Liver Sinusoids Model

Sinusoids SEM Sinusoids

Scanning Electron M.(SEM) Ec: Erythrocyte; BC: Bile Canaliculus DS: Disse’s Space S: Sinusoid H: Hepatocyte Mv: Microvili

Sinusoids TEM SD: Space of Disse fenestration endothilium

Sinusoids Kupffer Cell (LM) (TEM) Kupffer Cell

Liver Hepatocyte * typically large polyhedral cells with large round centrally located nucleus. * abundance of organelles relates to its functions: Mitochondria: provide energy RER: protein synthesis SER: bile formation / metabolism of lipids and hormones / detoxification. Lysosome: defence Microbody: detoxification. Inclusions: glcogen particles, lipid droplets and pigments.

Liver Hepatocyte MODEL

Model of Hepatocyte

Hepatocyte (EM)

* Produce bile. * Degrade glycogen to glucose under regulation of hormones. * Involve the blood lipid metabolism. * Synthesize the blood plasma proteins: Albumin: major plasma protein ； Fibrinogen ； thrombin ( 凝血酶 ) ； Clotting （凝结） factor III. * Detoxification Functions of Hepatocyte Liver

Bile Canaliculus Definition: the tubular space limited by plasma membrane of two adjacent hepatocytes. Structure: LM: network-like structures are seen by silver impregnation. EM: * plasma membrane of adjacent hepatocytes forms the wall of bile canaliculi. * tight junctions form seals.

Bile Canaliculus Blie canaliculi stained by silver impregnation (LM)

Bile Canaliculus BC

Bile Canaliculus

Freeze Fracture SEM

Liver Perisinusoidal space (Disse’s Space) A space between endothelium & hepatocyte. Be visible under EM. Occupy by numerous microvilli of hepatocytes. Fill with blood plasma. have fat-storing cells (storing fat & vitamin a) A site for substance exchange between the blood & the hepatocytes.

Perisinusoidal space (Disse’s Space) Disse’s Space

Scanning Electron M.(SEM) Ec: Erythrocyte; BC: Bile Canaliculus DS: Disse’s Space S: Sinusoid H: Hepatocyte Mv: Microvili

Perisinusoidal space (Disse’s Space)

Sinusoids TEM SD: Space of Disse fenestration endothilium

E: Erythrocyte S: Nucleus of Endothelial Cell D: Disse’s Space BC: Bile Canaliculus TEM

*cell junction surface * Perisinusoidal surface: face to perisinusoidal space * bile canalicular surface: face into the bile canaliculus Liver Three functional surface on the surface of hepatocyte

Blood Supply Portal V→ interlobular V → → Hepatic A→interlobular A → → sublobular V sinusoids central V hepatic V Inferior vena cava (75%) (25%) Liver

Bile canaliculi →periperal bile ductules ( Hering’s ) interlobular bile duct Left & right hepatic ducts Common hepatic duct Common bile duct Duodenum papilla Cystic ductGall bladder Biliary Passages

Liver Classification of Lobules Classic lobule Portal lobuleLiver acinus

Liver Classic lobule A hexagonal structure with the central vein at its center; at the six corners of the lobule are hepatic triads.

Liver A triangular structure with the portal area at its center. Three central veins are found at the peripheral boundary points. Portal lobule

Liver An elongate olive- shaped lobule; a central vein is at the ends of the two elongated points of the olive. Liver acinus

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