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Salivary glands * The name salivary glands are applied to groups of glands that secrete seromucoid secretion (the saliva) in the oral cavity. * The saliva has the following functions: 1. It lubricates and moistens the buccal mucosa and lips. 2. It washes the mouth against the bacteria. 3. It buffers the acidity of the contents of the mouth cavity. 4. It transformes the food into a semisolid mass in order to be swollowed and to be tasteed easily. 5. It can digest certain food; it contains amylase enzyme which converts starch to maltose. * Types of salivary glands: {A} The main large salivary glands (Major or proper salivary glands): 1. Two parotid glands: present in front of both types. 2. Two submandibular glands: - They are called submaxillary gland in certain animals. - In humans, they lie against the inner aspect of the mandible. 3. Two sublingual salivary glands: - They are present below the mucous membrane of the floor of the mouth. - The major salivary glands are present outside the oral cavity, but they open within it. They are compound tubulo-alveolar glands. They originate from the ectoderm of the oral cavity. {B} The minor or accessory salivary glands: - They are scattered throughout the oral cavity. - They are simple tubulo-alveolar glands. - Examples: 1. Labial glands (lip). 2. Buccal glands (cheeck). 3. Lingual glands (tongue). 4. Palatine glands (soft palate).

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** The general histological structure of salivary glands: Each salivary gland is formed of: 1) Stroma: It is a connective tissue framework, which includes: i. C.T capsule: It which covers the whole gland from outside. It riches in collagenous fibers, blood vessels and nerves. ii. C.T trabeculae: Which covers the C.T septa which divide the gland into lobes and lobules. iii. C.T reticular network: Which are present in the background of the whole gland. A network of collagenous and reticular fibers supports the adenomeres. 2) The parenchyma: - It is different from organ to other organs. - It is formed of epithelial cells. - The parenchyma includes: i. The acini (secretory portion) which are formed of collections of cells, they secrete saliva. They are arranged in tubules and acini, are composed of serous cells, mucous cells and mesothelial (Basket) cells. ii. The ducts (excretory portion) which are lined with epithelial cells, they conduct saliva to the mouth.

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{1) The acini of salivary glands: There are three types of secretory acini which are: a) Serous acini b) Mucous acini They are formed of collections of high They are formed of collection of cuboidal cells. cuboidal cells. They have small diameters. They have large diameters. Structure: Structure: L/M: L/M: - They are pyramidal or triangular cells - They are cuboidal or pyramidal in have broad basal part and narrow apical shape. part. - The cytoplasm is pale and acidophilic - Their cytopalsm has basal basophilic and has a foamy appearance. and apical acidophilic . - The nuclei are flattened in shape and - The nucleus is rounded and central in peripheral in position. position. - Their lumen is wide. - Their lumen is surrounded and very narrow. E/M: E/M: - The cytoplasm is less basophilic, rich - The cells have typical structure of in glycoprotein and appears vaculated protein secreting cells. due to dissolved mucus. - Apical cytoplasm contains secretory - Few cell organoids are found around granules rich in ptyaline. the basal nucleus. - Basal basophilia is due to presence of - They contain few secretory canaliculi well developed RER and rich in RNA. at the cell boundaries. - The basal part of plasma membrane - They have clear boundaries. interdigitate with neighbouring cell. - The basket cells are more numerous. - They have non-clear boundaries. - They have fewer mitochondria, less - The supranuclear cytoplasm is rich in RER, greater Golgi bodies indicating the cytoplasmic granules. greater CHO components of their - Presence of many canaliculi at the cell secretory products.

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boundaries. - The interdigitations are less extensive - The lateral plasma membranes have than those of the serous cells. tight junctions. - The basket cells are less numerous.

Function: Function: They produce watery secretion They produce thick viscid (serous fluid) rich in proteins that also glycoproteins (glycosaminoglycan) containing enzymes. mucous. Examples: - Parotid gland. - Von – Ebner salivary gland. c) Muco-serous acini: - They are mixed secretory units. - They are made of mucous secretory cells, but, in addition, a small cap of serous secretory cells is present on one side of the mucous acini. This cap is termed serous Demilune or crescent of Gianuzzi. ** Myoepithelial cells (Basket cells): These cells lie between the bases of secretory cells of the acini and their basement membrane. * Structure: L/M:- They are special cells which surround the serous and mucous acini. - They have central nuclei. E/M:- They are branched cells with multiple cytoplasmic processes. - The cytoplasmic processes extend to encircle the secretory unit. - The cytoplasmic processes are contractile, because they contain contractile myo-filaments (actin and myosin microfilaments are seen in the cytoplasm). Function: The myoepithelial cells re responsible for promotion of salivary secretion into the salivary duct system.

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I. The parotid gland

* There are two parotid glands (one in front of each ear). * They may enlarge in children in a disease called Mumps. * Each gland is formed of C.T stroma and a parenchyma of acini only. * The stroma is formed of: 1) The capsule: The capsule is well developed and very thick and numerous septa. It is covered by fascia and skin. 2) The trabeculae: The trabeculae descend from capsule dividing the gland into lobes and lobules. They carry the blood and lymph vessels as well as the different ducts of the gland. 3) The reticular C.T network: * The parenchyma is formed of (it is a compound tubulo-alveolar gland): 1) End piece (glandular portion or secretory part): - The secretory unit are purely serous.

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- Mixed in young sheep and dogs.

2) Duct system: i. Intercalated duct: It is lined with simple cuboidal cells with secretory granules. ii. Striated duct (salivary duct): It is lined with simple columnar ion-transport cells. iii. Inter-lobular duct: It is lined with simple columnar cells. iv.Near the opening: It is lined with stratified squamous epithelium and smooth muscle fibers. * The acini of this gland secrete watery saliva rich in amylase enzymes, electrolytes, gamma globulins and parotid hormone which has anti-insulin action.

II. The submandibular salivary gland (submaxillary salivary gland) * They are mixed gland; the serous cells are the main component. * These glands lie against the inner aspect of the body of the mandible and they produce 70 % of total salivary volume. * Their main (Wharton’s ducts) open into the floor of the oral cavity beside each other, posterior to lower incissor teeth. * Each submandibular gland is a compound tubulo-alveolar gland. * Each gland is formed of: 1) C.T stroma: It is formed of a thick covering, C.T capsule, thin trabeculaeand a fine reticular network. 2) Parenchyma: - It is of serous, mucous and mucoserous acini. The serous acini are more numerous than the mucuos, with the ratio of 5/1. - The small ducts of the gland secrete anti-bacterial enzymes called lysozyme and lactoferrin. III. The sublingual salivary glands

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* They are mixed glands, the majority of their acini are of mucous type and they produce about 5 % of total salivary volume. * They are present near the midline, below the mucous membrane of the floor of the mouth cavity. * Each gland is a compound tubulo-alveolar gland. It is formed of: 1) C.T stroma: It is formed of a very thin C.T capsule, thick trabeculae and a reticular network. 2) Parenchyma:- It is formed of acini and ducts. The acini are mainly mucous. There are also some serous and mucoserous acini. Some serous cells are present as demilune (crescent) on mucou acini. - The ducts of salivary glands conduct the secreted saliva, lysozymes and immunoglobulin. They secrete also hormones and they have stem cells for regeneration of acinar cells. The salivary acini secrete about one litre saliva per day. - They probably lyozyme enzyme. The liver * The liver is single organ which is the largest and the heaviest gland in the * It is the largest compound metabolic organ in the body.

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* It is considrered as a mixed gland (exocrine and endocrine) i.e. it forms and secretes bile, so it is considered as an exocrine gland, moreover it secretes useful materials as glucose, plasma proteins and lipoproteins directly into the blood, so it is called an endocrine gland. * Structure of the liver: 1) C.T stroma (framework): I. Fibrous stroma: a. Capsule: (Glisson’s capsule) msothelium - It is a thin connective tissue capsule. - The capsule is covered partially by peritoneum. b. Trabeculae: (C.T septa or interlobular C.T) - They are formed of a very thin layer of C.T cells and fibers which demarcate the hepatic lobules. - They contain branches of hepatic artery, portal vein and bile duct. - They divided the liver into polygonal prisms (the hepatic lobules). - These C.T septa are not apparent in normal human liver, but may be apparent in diseased liver cirrhosis (fibrosis). These septa are thick in the liver of pig and camel. II. The reticular C.T network: - It is fine C.T network which form the framework of the hepatic lobules. - It supports the contents of the hepatic lobule. 2) Parenchyma: There are three concepts of the liver lobulation: i. Hepatic lobule … the structural unit. ii. Portal lobule … the functional unit. iii. Liver acini. I. Hepatic lobule: * Definition: - A typical classic hepatic lobule is hexagonal in outline. It is a mass of liver tissue that surrounds a central vein. - This central vein drains the blood of hepatic lobule.

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- The human classic hepatic lobule is not easy to recognize because it is not well demarcated by C.T septa. * Structure: Each hepatic lobule includes: 1- A central vein arround which are arranged, the hepatic laminae or plate separated by the hepatic sinusoids. 2- Portal area: (portal canal, portal triad, portal radicale) - It is a triangular shaped areas of C.T, between three hepatic lobules and present at approximately three of six angles of the hepatic lobules. - Each portal area contains: ► Branch of hepatic artery. ► Branch of portal vein. ► One or more bile duct. ► Lymph vessels. ** Hepatic laminae (hepatic plates or hepatic cords): - The hepatic cells (hepatocytes) are arranged into laminae ot plates. - These hepatic lobules or cords radiate from the central vein. - These hepatic plates are formed of two or more rows of liver cells. - The rows of liver cells (hepatocytes) enclose between them very narrow canals known as bile canaliculi which carry the secreted bile to the bile ductules. - The liver plates are separated from each other by blood sinusoids and by perisinusoidal spaces. These spaces are called the spaces of Disse. ** Hepatic blood sinusoids: They are wide, irregular tortuous blood spaces and radially arranged. * Site: They are present between the plates of liver cells. * Function: They receive blood from the hepatic artery and portal vein, and conduct it to the central vein. * Structure: They are lined with 2 types of cells: {1} Undifferentiated endothelial cells (simple squamous endothelial cells):

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- They are flat cells with small dark flattened nuclei. - They form non-continuous wall because they are separated from each other by many fine holes through which blood plasma can pass outside the blood sinusoids to reach the perisinusoidal spaces. - They have gaps and fenestrae and deficient or absent basal lamina. {2} The Van Kupffer cells (Fixed macrophages): - They are the most important phagocytic cells in the body. - They are present in the wall of blood sinusoids of the liver. - They are satellate phagocytic cells with processes (many pseudopodia). - Their processes project into the lumen of the blood sinusoids. - The cell membrane of these cells contains many microvilli to increase their surface area. - The cytoplasm of these cells is basophilic and is rich in phagocytic vesicles and contains many haemosidrin granules and secondary lysozymes. It also contains pigments or destructed RBCs. - They can be stained with vital stains as trypan blue. ** The perisinusoidal spaces: * Definition: It is a real narrow space of varying widths, between the wall of the hepatic sinusoid and the cell membrane of the hepatocyte. * It contains the following: 1- Supporting reticular fiber: (type III collagen) 2- Fat cells known as adipocytes or lipocytes: - They contain fat droplets and vitamin A. - They are considered as supporting cells. 3- Blood plasma: It contains no blood cells and no blood platelets. 4- Microvilli: They are projections from the cell membranes of the liver cells. 5- Satellate-shaped phagocytic pit cells. 6- Non-myelinated nerve fibers.

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** The liver cells or hepatic cells or hepatocytes: * Structure: L/M: - They are polyhedral (polygonal) in shpe. - They have rounded nuclei, they have smooth surfaces, they vary in size from one cell to another. multinucleated with one or more nucleoli - The cytoplasm is vacuolated, due to presence of variable amounts of of glycogen and fat droplets. E/M: The hepatocyte is a very active cell. The cytopalsm of liver cells contains all cell organoids and cell inclusions which are as follows:

1- Mitochondria: They are numerous and are various sizes. Their number may reach upto 1000 in each hepatocyte. 2- Golgi apparatus: It is present in the form of saccules scattered around the nucleus. It plays an important function during the secretory activities of liver cells and formation of lysosomes and secretion of plasma proteins. 3- Rough endoplasmic reticulum: It is well-developed. It synthesizes plasma proteins and the protein part of the lipoprotein (extrinsic protein). 4- Smooth endoplasmic reticulum:

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responsible for detoxification of toxic substances and for the regulation of glycogen metabolism. It is well-developed and forms the lipid of lipoproteins. 5- Free ribosomes: They are scattered in the cytoplasm. They are responsible for the synthesis of the intrinsic proteins used by the cell. 6- Lysosomes: They are present close to the bile canaliculi. They digest and eliminate waste products. 7- Cell inclusions glycogen, fat & peroxisomes 8- The nucleus is large and central with prominent nucleolus. Hepatocytes may be binucleated. It contains both euchromatin and heterochromatin.

* Hepatocyte has three surfaces: 1) Surface facing blood sinusoids and facing the space of Disse: - It has numerous microvilli projecting into perisinusoidal space to increase the absorptive surface area. - Between the microvilli, the hepatocyte secretes a useful substance into the blood plasma. 2) Surface facing bile canaliculi: It forms the wall of a bile canaliculus projects into its lumen by few microvilli (short microvilli). 3) Surface facing the adjacent hepatocyte (the line of contact between the two adjacent hepatocytes): The cells membranes of the two adjacent liver cells are slightly bound together by junctional complex (smooth and with desmosomes). II. Liver acinus (vascular hepatic unit) * Definition: It is a diamond-shaped part of liver tissue (in cross section). The liver acinus is a subdivision of the liver structure. * Structure: - It is formed of liver substance that comprises parts from two adjacent classic hepatic lobules.

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- It is formed of a central vascular cord surrounded by liver tissue. The vascular core is formed of branches from the hepatic artery and portal vein which arise at right angles from the vessels in the portal canal. These branches carry nutritive substances and oxygen to the liver tissue. Therefore, the liver cells near these vessels are richly supplied with blood, while the liver cells present at the periphery of the liver acinus receives less amounts of oxygen and of nutritive materials. - The concept of the liver acinus helps us in understanding that the hepatic cells surrounding the central vein have poor blood supply than other parts. - The cells of the hepatic acinus can be subdivided into three zones to their blood supply: ► Zone III: The outermost area extends as far as the central vein and the most oxygen poor of the 3 zones. ► Zone I: Comprises cells closest to the blood vessels, therefore, the richest oxygen. ► Zone II: Comprises intermediate cells in location and in blood supply. ** The duct system for the biliary passage: * To convey the bile to the duodenum. * The bile which is secreted by liver cells passes through the following channels: 1) Bile canaliculi: (intralobular) - They are present between the rows of liver cells. - They anastomose freely as they extend toward the periphery of the classic hepatic lobule. - They have no wall of their own, but they are lined by the liver cells. - Few microvilli project from the surrounding liver cells into their bile canaliculi. - They are minute channels and irregular course. - At the periphery of the classic hepatic lobule and near to the portal tracts, these bile canaliculi empty into short canals known as canals of Hering and preductules or cholangioles.

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2) Canals of Herring: - It is a short connection between the bile canaliculi and the bile ductule (within the portal area). - They are bordered partly by hepatocytes and partly by duct cells which are simple cuboidal cell. 3) Preductules or cholangioles: - They are also present at the periphery of classic hepatic lobules collecting bile from the bile canaliculi. - They are lined with simple cuboidal epithelium. - The bile which is present in the canals of Hering and in the preductules is collected into the bile ductules. 4) Bile ductules: - They are lined with simple cuboidal epithelium. - Bile ductules drain their secretion into bile ducts. 5) Bile ducts: - They are formed by collections of the bile ductules. - They are lined by simple cuboidal epithelium. - They are present in the C.T of the portal tracts. 6) Intra-hepatic ducts: - They are formed as a result of collection of bile ducts. - They are lined by simple columnar epithelium. 7) Extra-hepatic ducts: - They are lined by simple columnar epithelium. - The epithelium is surrounded by connective tissue and smooth muscles. 8) Common bile duct: - It is lined by simple columnar epithelium. - Tubulo-alveolar mucous glands are present in the C.T under their eoithelium. - Smooth muscles are present in the wall of the common bile duct.

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III. Portal lobule - It is the functional unit of the liver. - It is a triangular area of liver tissue in which 3 central veins are present at its 3 corners. - A portal tract (portal canal) is present in the centre of each portal lobule. - It consists of the parenchyma of three adjacent hepatic lobules. - Imaginary lines passing between three central veins delinate the periphery of the portal lobules, centered by bile ductule (portal area). - This triangular area is drained by the bile duct (interlobular) located in the portal area (portal triad). - This portal tract contains a bile duct, through this bile duct is collected from the liver cells. Therefore, the direction of the bile flow is toward the centre of the portal lobule. ** Functions of the liver: {1} Protein synthesis: {2} Production of bile (exocrine function): {3} Protective function: {4} Transferring secretory IgA from the space of Disse into bile. {5} It regulates the metabolism of carbohydrates, fats and proteins. {6} Storage of glycogen, iron, copper, amino acids and vitamin (A, B, D, K). {7} It is involved in the secretion of immunoglobulins (IgA and IgM). ** Gall bladder: * Definition: It is a hollow, pear-shaped organ attached to the lower surface of the liver. * Structure: The wall of the gall bladder consists only of three layers (no submucosa): 1) Mucosa:- It is highly folded with no villi. - Lamina epithelialis is simple columnar cells with microvilli and goblet cells in ruminants - Lamina propria (C.T corium) contains tubulo-alveolar mucous glands near the cystic duct only

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2) Musculosa: It is formed mostly of oblique muscle fibers and some longitudinal smooth muscle fibers with elastic and collagenous fibers (smooth muscle fibers are thin). 3) Adventitia: It is formed of fibrous C.T which is partially covered by peritoneum. * Functions: 1. Storage and concentration of the bile. 2. It adds mucus to the bile. Pancreas - It is a large lobulated important mixed gland. - It has an exocrine (it produces digestive juices) and endocrine (it manufactures hormones) functions. - It is present in U-shaped of the abdomen in the concavity of the duodenum. - It consists of a head, body and tail. - Its endocrine part is known as pancreatic islets of Langerhans (they are scattered among the exocrine secretory acini). The exocrine part is compound tubulo-alveolar gland. - The pancreas communicates with the duodenum by the pancreatic duct.

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* Structure: 1) C.T stroma: a. Capsule: - It is a very thin and soft. - It is covered partially with peritoneum. b. Trabeculae: - They descend from the capsule dividing the gland into lobules. - They carry ducts, blood and lymph vessels. c. Reticular C.T: 2) Parenchyma: The parenchymatous tissue of the pancreas includes exocrine and endocrine portions: I. Exocrine portion: 1) Secretory portion: (pancreatic acini) - Its structure is as the serous acini. - The centro-acinose cells: 1. They are small cells found in the middle of the pancreatic acini (if an acinus is cut in the proper plane). 2. They represent terminal cells of tiny intercalated ducts which are partly invaginated into the lumen. 3. This duct is telescoped inside the pancreatic acinus. - The pancreatic acini secrete some alkaline pancreatic juice rich in enzymes. These enzymes are carried to the intestine along certain pancreatic ducts. 2) Duct portion: (pancreatic ducts) - Centro-acinar cells: i. They are flat cells or low cuboidal cells line the lumen of the acinus. ii. There are no striated ducts. - Intercalated ducts: i. They are telescoped in the pancreatic acini and are lined with simple cuboidal cells (flat or low cuboidal cells). ii. They are the first ducts which arise from the pancreatic acini. iii. They are collected to from the interlobular ducts. - Intralobular ducts:

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i. They are small and few. ii. They are lined by simple cuboidal epithelium. - Interlobular ducts: i. they are lined with simple cuboidal epithelium. ii.These ducts are found in the C.T septa between the lobules. - Interlobar ducts: Interlobular join each other to form interlobar ducts, found in the C.T septa between the lobes. - The main pancreatic ducts (large excretory ducts): i. They are lined with simple columnar epithelium with goblet cells. ii. The main duct joins the common bile duct before opening in the duodenum to drain into it via the ampulla of Vater (its lumen is wide). * Function of exocrine panreas: The acinar cells of the exocrine pancreas produce, store and release a large number of enzymes i.e. pancreatic amylase, pancreatic lipase, ribonuclease, deoxyribonuclease, proenzyme trypsinogen and chymotrypsinogen. II. Endocrine pancreas: (pancreatic islets or Islets of langerhans) - They are spheroid encapsulated bodies, sacttered between the pancreatic acini (intralobular). - They are easily recognized at L/M level as large pale areas among the darker staining secretory acini. ** Cells of islets of Langerhans: Cells Hormones Functions 1. Beta cells (70 %) Insulin Decrease blood glucose level. 2. Alpha cells (20 %) Glucagon Increase blood glucose level. 3. Delta cells (5 %) Somatostatin - Paracrine inhibits hormone release. - Endocrine reduces

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contraction of alimentary tract, gall bladder and smooth muscles. 4. C-cells (1 %) Gastrin Stimulates production of HCl by parietal cells of stomach. 5. P-cells (F-cells)(1 %) Pancreatic polypeptide Inhibits exocrine secretion of pancreas.

** The differences between parotid and pancreas: Item Salivary gland Pancreas Definition They are two exocrine salivary Single and mixed digestive glands present in the front of gland present in the two ears. concavity of the duodenum. Capsule Thick formed of fibrous C.T Thin formed of loose C.T

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and rich in fat cells. with few fat cells. Trabeculae Thick and fibrous. Thin and loose and may detach from the section. Acini - They are purely serous. - The cells have basophilic - The cells have no basal striations. basophilic striations. - They are larger and vary - They have basophilic granular in shape. cytoplasm and central rounded - The pancreatic acini have nulcei. apical acidophilic cytoplasm - No centro-acinar cells. and basal basophilic striations. - The nuclei are near to the base of the cells. - Presence of the centro- acinar cells in the centre of the acini. Ducts - Abundant. - Rare and relatively few. - Acidophilic salivary (secretory) - No salivary ducts are seen ducts are predominent inside inside the lobules. the lobules. - Less number of the ducts - Presence of many ducts which which are: are: 1. Intercalary: They are 1. Intercalary: They are long and telescoped in the multiple and not telescoped in acini. the acini. 2. Intralobular: No 2. Intralobular: Striated secretory ducts appear in secretory ducts. the lobules. 3. Interlobar ducts: Which are 3. Interlobar ducts: Which lined with pseudostratified are lined with simple columnar epithelium. columnar epithelium.

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4. Main ducts: Which lined with 4. Main ducts: Which lined stratified squamous epithelium. with simple columnar epithelium. Islets of - Absent. - Present (if the section is Langerhans - No endocrine cells, however, in the tail of the pancreas ) parotin hormone which is an and may be absent (if the anti-insulin is secreted by section is in the head of parotid. pancreas). - Few ganglion nerve cells. - Presence of Islets of Langerhans with alpha, beta and F-cells which secrete hormones. - Many ganglion nerve cells.

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