The Digestive System

Exocrine gland---with duct Constituents of multicellular gland: secretory portion: tubular,acinar or tubuloacinar gland duct: passage of secretions Exocrine gland---without duct

Exocrine gland

Salivary gland Acinus: mucous acinus, serous acinus,mixed acinus Duct: intercalated duct,striated duct,interlobular duct and common duct Serous acinus Mucous acinus Cell type CytoplasmNucleusSecretions Serous cell Deep stained Spherical,near the base Protein Mucous cell Light-blue stained spindle,near the base Mucoprotein (mucus)

Salivary gland

Serous acini

Mucous acini

Mixed acini and semilune Semilune: several serous cells arranged like half-moon in the mixed acinus

Salivary glands 1. components: parotid gland,submandibular gland and sublingual gland,etc. gland and sublingual gland,etc. 2. function: secreting saliva.

The characteristics of 3 pairs of salivary glands Parotid gland Submandibular gland Sublingual gland AciniDuctsSecretion Pure serous gland Long I.D. 25% saliva More salivary amylase, less mucus Mixed gland, More serous acini Short I.D., Long S.D. 70% saliva Less salivary amylase, more mucus Mixed gland,more mixed and mucous acini Without I.D. 5% saliva Most mucus

Parotid gland---pure serous gland

Submandibular gland---mixed gland

Sublingual gland---mixed gland

Pancreas Parenchyma: exocrine portion: pancreatic secretions involved in food-digestion. endocrine portion(pancreas islet): secreting hormones

1. Exocrine portion acini ducts Consists of serous cells surrounded by basal lamina ， Without myoepithelial cells, With several centro-acinar cells in acinus cavity. Long I.D.,no S.D.

Exocrine portion of pancreas

2. Endocrine portion (pancreas islet) A cell B cell D cell PP cell Rate(%)DistributionSecretion20%PeripheryGlucagon-- Increase blood glucose levels blood glucose levels 70%CenterInsulin-- Decrease blood glucose levels 5% 5% Somatostatin— Pancreas Inhibit the secretion polypeptide of other cells of other cells

Diabetes: absence or inadequate amounts of insulin. insulin.

Liver The largest digestive gland. The C.T.sends the septa into the parenchyma, separating the hepatic lobules. The portal area is present at the corner of the lobules.

Classic hepatic lobule It is a structural unit of liver. Components Hepatic plates: a single layer of hepatocytes arranged in radial. Sinusoids: between hepatic plates and anastomose with each other. Central vein: occupies the centre of the liver lobule.

hepatocyte 3 functional surfaces:sinusoidal.., canalicular.., intercellular.. LM: Profile:large,polyhedral in shape. Cytoplasm:rich in Mitochondria, Golgi complex, SER,RER, lipid droplets, glycogen,etc. Nucleus: large,central,lightly stained, with obvious nuceulus. EM: numerous microvilli protruding into sinusoids and bile canaliculi.

Function of hepatocyte 1.Bile secretion 2.Synthesis and storage 3.Detoxification and inactivation 4.Defence :related to Kuffer cell 5.Hemopoiesis

Bile canaliculus It is a small canal formed by opposed grooves In the surface of adjacent hepatocytes.

Bile canaliculi

Sinusoid Kuffer cell : macrophage in sinusoid

Space of Disse Space of Disse Space between hepatocytes and endothelium. Microvilli of hepatocytes protrude into it, which enhance the exchages of materials. Storing fat cells :in space of Disse.responsible for the storage of Vit.A and production of fibers.

Portal area （ portal canals ） portal triad: Interlobular arteries Interlobular veins Interlobular bile ducts Hepatic artery Portal vein Common bile duct

Hepatic circulation Common bile duct Portal vein Hepatic artery Hepatic vein Interlobular bile ducts Interlobular vein Interlobular artery vein Bile canaliculi sinusoids Central vein Hepatic hilum Hepatic lobule Portal area

Key points 1. The structure and function of pancreas.(exocrine portion and endocrine portion),the cellular components of pancreas islet and their function. 2.The definition of hepatic lobule and portal area.sinusoid,space of Disse,Kuffer cell; 3.The formation of bile canaliculi.