Classification of Glands Glands Associated with the Gastrointestinal Tract

Classification of Glands

Salivary Glands There are three pairs of major salivary glands : Parotid Submandibular Sublingual There are many small salivary glands in the oral cavity Major glands are surrounded by dense connective tissue capsule Capsule sends septa separating the parenchyma into lobules Each lobule consists of many secretory acini and excretory ducts

Secretory Part of The Glands Serous cells are characteristically protein synthesizing cells, pyramidal in shape with broad base and narrow apical region. Mucus cells are basically cuboidal to columnar have condensed, basally located flat nuclei. They are characteristically mucus synthesizing cells and they form tubules Acini are surrounded by myoepithelial cells Serous demilunes are serous cells capping the mucus acini

Glandular Duct System Intercalated duct Striated duct Interlobular duct Intralobular duct Main duct

Parotid Gland Branched acinar Capsule sends septa dividing it to lobes Lobules Serous acini Secretes proteins: amylase, proline-rich protein Acinar cells

Submandibular Gland A mixed gland Branched Tubuloalveolar Capsule Lobules Serous Demilunes Secrete amylase, proline-rich protein and lysozyme Ducts

Sublingual Gland A mixed gland Branched tubuoalveolar Capsule Lobules Serous Demilunes Secrete amylase, proline-rich protein and lysozyme

Pancreas It is mixed gland Looks like parotid gland Islands of Langerhans No striated ducts Centroacinar cells

Liver It is divided into lobules: Classical Portal lobule Liver acinus Classical lobule is hexagonal in shape Central vein Portal triads Perisunusoidal space (of Disse)

Portal Triads: A branch of the portal vein, a branch of the hepatic artery and a branch of the bile duct - are called portal triads. Portal triads are a key feature of the organization of the liver. Portal triads are embedded in interlobular connective tissue.

The Liver Lobule The "classical" liver lobule is hexagonal(six-sided). It is delimited by interlobular connective tissue (only little, if any, visible in humans; plentiful in e.g. pigs). In its corners we find the portal triads.

In cross sections, the lobule is filled by cords of hepatic parenchymal cells, hepatocytes, which radiate from the central vein and are separated by vascular sinusoids. Hepatocytes are separated from the bloodstream by a thin fenestrated simple squamous epithelium, which lines the sinusoids.

Between the hepatocytes and the epithelial cells is a narrow perisinusoidal space (of Disse). Contents of the blood plasma can freely enter the perisinusoidal space through the fenestrations of the epithelium lining the sinusoids. Fixed macrophages, Kupffer cells, are attached to the epithelium.

The liver lobule is drained by the central vein, which open into the sublobular veins of the liver. These in turn coalesce to form the hepatic veins. They run alone through the tissue, are usually covered by connective tissue and eventually empty into the inferior vena cava.

Liver Functions Protein synthesis Bile secretion Metabolic storage Metabolic functions Detoxification

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Gallbladder The gallbladder is a hollow, pear-shaped organ attached to the lower surface of the liver. It can store 30 to50 mL of bile. The wall of the gallbladder consists of a mucosa composed of simple columnar epithelium and lamina propria, a layer of smooth muscle, a perimuscular connective tissue layer, and a serous membrane

The mucosa has abundant folds that are particularly evident when the gallbladder is empty. The epithelial cells are rich in mitochondria. All these cells are capable of secreting small amounts of mucus. Tubuloacinar mucous glands near the cystic duct are responsible for the production of most of the mucus present in bile.

The main function of the gallbladder is to store bile, concentrate it by absorbing its water, and release it when necessary into the digestive tract. This process depends on an active sodium-transporting mechanism in the gallbladder's epithelium.