Digestive System Digestive Glands

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

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

Salivary Glands

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

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

serous cell: *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. sg

mucous cell: *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

LM EM

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.

striated/secretory duct Salivary Glands The secretory ducts can re-absorb sodium （ Na + ） and water from the lumen to the interstitium and transport potassium (K + ) into the saliva ， thus changing the consistency of the saliva.

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

Salivary glands include three pairs. * Parotid G. * Submandibular G. * Sublingual G. Structural Features of Salivary Glands

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 digest different nutritional substances regulate blood sugar level

Parenchyma make section Section of pancreas (HE, low power)

Parenchyma endocrine glands exocrine glands Section of pancreas (HE, low power)

Parenchyma exocrine gland endocrine gland Section of pancreas (HE, high power)

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

Exocrine Pancreas Acinus

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

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. )

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

sketch map

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 Pig liver

Liver section liver loblules Human liver

Liver Structures of Liver Lobule

Liver Structures of Liver Lobule

Model of Liver Lobule

Liver Structure of Liver (in section) Liver Lobule Portal Triads ( or Portal Area) central V. hepatic plates sinusoids DCT in the corner of liver lobules.

Liver Structures of Liver Lobule * six-sided prism with a central V. at its center. * hepatic plates extend radially from the central V. * sinusoids between hepatic plates.

Liver Structures of Liver Lobule hepatic plates

Liver Structures of Liver Lobule hepatocyte EM sinusoid

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 fenestration

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

Sinusoids TEM SD: Space of Disse fenestrations 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: glycogen 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

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

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