DIGESTIVE GLANDS Department of Histology and Embryology Li jinxin No.1020603

Objectives General structure of salivary glands（唾液腺）. Histological organisation of the exocrine and endocrine pancreas and the three cell-types of pancreatic islets（胰岛） and their hormones. General structure of the liver, the histological organisation of a liver lobule（肝小叶）, and the micro-Structure and functions of hepatocytes（肝细胞） and Kupffer cells.

component Within the wall of various regions of the digestive tract. Digestive glands outside the digestive tract include three pairs of large salivary glands, pancreas and liver. salivary glands liver pancreas

1. Salivary glands around and open into the oral cavity 1.1 General structure The salivary glands are compound tubuloacinar(复管泡状腺）. The acini（腺泡） can be serous（浆液性的）, mucous （粘液性的）or seromucous. The duct system consists of intercalated （闰管）, secretory (striated), interlobular and major excretory ducts.

1.1.1 Serous acini （浆液性腺泡） Composed of serous cells with a small lumen. Serous cells are pyramidal in shape with a round nucleus. Apical cytoplasm contains zymogen granules (酶原颗粒). Produce serous (watery), secretion containing more enzymes(酶).

1.1.2 Mucous acini （粘液性腺泡） Composed of mucous cells with a large lumen. Mucous cells are pyramidal with a flattened nucleus against basal plasma membrane. Pale stained or foamy(泡沫状的) appearance. Cytoplasm is full of mucigen granules(粘原颗粒). produce mucous (viscous), secretion containing more mucus glycoprotein(糖蛋白).

1.1.3 seromucous (mixed acini) composed of both serous and mucous cells, mainly mucous cells with a serous demilune (半月).

1.2 Distinctive features of three pairs of salivary glands（自学内容） 1.2.1 Parotid gland (腮腺) entirely serous. long intercalated duct. large amount of adipose cells.

1.2.2 Submandibular gland (下颌下腺) mixed, mainly serous acini; longer secretory duct (striated duct).

1.2.3 Sublingual gland (舌下腺) Mixed, mainly mucous acini; rare intercalated and secretory ducts.

2. Pancreas Exocrine pancreas Endocrine pancreas

2.1 Exocrine pancreas 2.1.1 Acini Serous acini– basophilia of basal cytoplasm, zymogen granules in apical cytoplasm. Centroacinar cells（泡心细胞） -- small, pale stained cells in the lumen of acini, beginning of the intercalated ducts.

2.1.2 Ducts Long intercalated ducts (squamous epithelium), no striated ducts. Intralobular ducts (cuboidal) → interlobular ducts (columnar) → main pancreatic duct (high columnar with goblet cells). 2.1.3 Function Secrete pancreatic juice containing enzymes, such as trypsinogen （胰蛋白酶）, amylase（淀粉酶）, lipase（脂肪酶 ) .

2.2 Endocrine pancreas (pancreatic islets ) Groups of endocrine cells scattered among exocrine acini; more in the tail of pancreas. Cells arranged in cords, pale stained, invested with fenestrated capillaries.

Three different cell-types can be distinguished by Mallory staining:A-cell, B-cell and D-cell.

A-cells 20%,located at the periphery. red granules can be seen in the cytoplasm. secrete glucagon（胰高血糖素） raising blood glucose level. A-cell

B-cells 70%; located in the central portion. Yellowish secretory granules. secrete insulin（胰岛素） lowering blood glucose level. Damage of B-cells induces diabetes（糖尿病）. B-cell

D-cells 5%; scattered between A-cells or B-cells. secrete somatostatin (生长抑素) which inhibits the release of insulin and glucagon. D-cell

PP cells secrete pancreas polypeptide（胰多肽）.

3. Liver largest internal organ. diverse functions. divided into hepatic lobules（肝小叶） and portal areas（门管区）.

hepatic lobules (a)

hepatic lobules (b) Central vein Hepatic plates

Central vein Hepatic plates hepatic lobules (c)

Central vein Hepatic plates Portal area hepatic lobules (d)

3.1 Hepatic lobule basic structural unit; polygonal prism with a central vein in the center and radially arranged hepatic plates（ 肝板） and sinusoids. Central vein Hepatic plates sinusoid

3.1.1 Central veins terminal hepatic venules with numerous pores in their very thin walls. Central vein

3.1.2 Hepatic plates anastomosing plates of 1 row of hepatic cells (hepatocytes), between which are tiny anastomosing secretory channels called bile canaliculi（胆小管）.

Hepatocytes liver parenchymal cells. large polygonal cells with 1 or 2 large and round nuclei. acidophilic cytoplasm containing basophilic "granules".

EM: a. abundant mitochondria (1000-2000/cell), energy supply. b. Golgi complexes (about 50/cell). c. abundant RER, synthesis of plasma proteins. d. numerous SER, metabolism of glycogen and lipids; production of bile; detoxication（解毒） of toxin（毒素） or drugs; inactivate hormones. e. lysosomes f. Peroxisomes（微体） g. inclusions (glycogen particles, lipid droplets, pigments).

Three functional surfaces sinusoidal surface(35%) have numerous microvilli projecting into the Disse space. canalicular surface (10%) . cellular surfaces possess cell junctions.

3.1.3 Sinusoids Large and irregular sinusoidal capillaries between hepatic plates. Lined with endothelium Have Kupffer cells, part of mononuclear phagocytic system. endothelium Kupffer cell

3.1.4 Perisinusoidal space (space of Disse) The space between endothelial cells and hepatocytes, about 0.4 µm. Contains fluid similar to plasma and microvilli from liver cells. Fat-storing cells are found in the space, which store vitamin A and produce type Ⅲ collagen fibers (reticular fibers). The site of exchange of materials between blood and hepatocytes.

3.1.5 Bile canaliculi Formed by indented plasma membranes of opposing hepatocytes. Microvilli extend into canalicular lumen which contains bile, secretion of liver. Junctional complexes.

3.2 Portal areas Interlobular bile ducts Interlobular artery connective tissue with portal triad (门三联管)at the corners among adjacent hepatic lobules. Interlobular veins -- branches of the portal vein. Interlobular arteries -- branches of the hepatic artery. Interlobular bile ducts -- intrahepatic branches of the hepatic duct. Interlobular vein

3.3 Blood supply sinusoids → central vein → portal vein (75%, nutrients) → interlobular veins ↓ sinusoids → central vein → hepatic artery (25%, oxygen) → interlobular arteries↑ (lobules) (hilus) (portal areas) sublobular veins → hepatic vein → inferior vena cava.

3.4 Passage of bile bile (liver cells) → bile canaliculi → interlobular bile ducts (hepatic lobules) (portal areas) → left and right hepatic ducts (hilus) → common hepatic duct → commom bile duct. cystic duct ↗

Exercise 1.What’s the function and stucture of pancreas islet. 2.What is hepatic lobule？Describe the structure and functions of a liver lobule. 3.Explain the structure and function of hepatocyte.

谢谢！