Prof.Athraa Histology lecture 7 SALIVARY GLANDS • The major salivary glands consist of 1. Parotid 2. Submandibular 3. Sublingual glands. • The minor salivary glands include 1. Lingual 2. Labial 3. Buccal 4. Molar 5. Palatine glands. • The major salivary glands are surrounded by a capsule. The minor salivary glands do not have a capsule. • The basic secretory unit of salivary glands, the salivon, consists of 1. Acinus 2. Intercalated duct 3. Excretory duct • Three types of acini are described: • Serous acini, which contain only serous cells and are generally spherical • Mucous acini, which contain only mucous cells and are usually more tubular • Mixed acini, which contain both serous and mucous cells. 1 Prof.Athraa Histology lecture 7 Parotid Gland • Completely serous • Largest of the major salivary glands. • Large amounts of adipose tissue often occur in the parotid gland; this is one of its distinguishing features. • The facial nerve (cranial nerve VII) passes through the parotid gland Submandibular Gland The submandibular glands are mixed glands that are mostly serous in humans. Sublingual Gland • The small sublingual glands are mixed glands that are mostly mucous secreting in humans. • The smallest of the paired major salivary glands LIVER Overview • The largest mass of glandular tissue • The largest internal organ weighing approximately 1,500 g • Anatomically divided by deep grooves into two large lobes (the right and left lobes) and two smaller lobes (the quadrate and caudate lobes) • Several vitamins stored or biochemically modified by the liver: 1. Vitamin A 2. Vitamin K 2 Prof.Athraa Histology lecture 7 3. Vitamin D • Bile production is an exocrine function of the liver. It is composed of: 1. Water 2. Bile salts 3. Bile pigment 4. Phospholipids 5. Electrolytes • Many actions of hormones are modified in the liver. These include: 1. Vitamin D 2. Growth hormone 3. Thyroxin 4. Insulin • The structural components of the liver include: 1. Parenchyma, consisting of organized plates of hepatocytes 2. Connective tissue stroma that is continuous with the fibrous capsule. 3. Sinusoidal capillaries (sinusoids), the vascular channels between the plates of hepatocytes. 4. Perisinusoidal spaces (spaces of Disse), which lie between the sinusoidal endothelium and the hepatocytes. • The Hepatic lobule consists of stacks of anastomosing plates of hepatocytes that radiate toward a central vein. Corners of the polygonal lobule are occupied by the portal triad, which contains branches of portal vein, hepatic artery, bile ducts, and small lymphatic vessels. 3 Prof.Athraa Histology lecture 7 • Hepatic sinusoids form irregular vascular channels that run parallel and between the plates of hepatocytes. Hepatic sinusoids are lined with a thin discontinuous endothelium. • The perisinusoidal space (space of Disse) lies between hepatocytes and the endothelium; it is the site of exchange of materials between blood and liver cells. • The sinusoidal endothelium includes specialized stellate sinusoidal macrophages (Kupffer cells), which remove senile red blood cells and recycle iron molecules. • Hepatic stellate cells (Ito cells) reside in perisinusoidal spaces and are loaded with lipid droplets for storage of vitamin A. HEPATOCYTES • Hepatocytes (constitute 80% of liver cells) are large, polygonal cells with spherical nuclei (often binucleated) and acidophilic cytoplasm • The basal surface of hepatocytes has contact with the perisinusoidal space (of Disse), whereas the apical surface is connected to the adjacent hepatocyte to form a bile canaliculus. • Bile canaliculi drain into the short canals of Hering, which are partially lined by hepatocytes and cuboidal cholangiocytes (cells lining the biliary tree). • Canals of Hering harbor specific hepatic stem cells. BILIARY TREE • The biliary tree is the three-dimensional system of channels of increasing diameter that bile flows through from the hepatocytes to the gallbladder and then to the intestine. 4 Prof.Athraa Histology lecture 7 • The biliary tree is lined by simple cuboidal or columnar epithelial cells called cholangiocytes, which monitor bile flow and regulate its content. • Bile (produced by hepatocytes) is collected by the bile canaliculi and drains to the canals of Hering. From there, it continues to flow into the intrahepatic bile ductules and further into the interlobular bile ducts (part of the portal triad). Interlobular ducts eventually merge to form the left and right hepatic ducts that exit the liver in the porta hepatis. • Extrahepatic bile ducts carry the bile to the gallbladder and eventually into the duodenum. GALLBLADDER • The gallbladder is a pear-shaped, distensible sac with a volume of about 50 mL. • The gallbladder concentrates and stores bile. • Mucosa of the gallbladder has numerous deep folds (to increase surface area), a lamina propria rich in blood vessels, and a well- developed muscularis externa (no muscularis mucosae or submucosa). • The tall columnar cholangiocytes are specialized for water uptake from bile. • Deep diverticula of the mucosa, called Rokitansky- Aschoff sinuses, often extend through the muscularis externa. • Contraction of the muscularis externa forces bile out through the cystic duct and common bile duct to the duodenum. PANCREAS • Is an exocrine and endocrine gland. • The exocrine component synthesizes and secretes hydrolytic digestive enzymes into the duodenum that are essential for digestion in the intestine. • It contains serous acini, which comprises most of the mass of the pancreas. 5 Prof.Athraa Histology lecture 7 • Pancreatic acini are unique because their intercalated ducts begin within the acinus; therefore, nuclei of duct cells located inside the acinus are referred to as centroacinar cells (a characteristic feature of the pancreas). • The pancreatic acinar cell is pyramidal in shape • Intercalated ducts secrete large amounts of sodium and bicarbonates to neutralize the acidity from the stomach. • Intercalated ducts drain pancreatic acini into intralobular ducts, larger interlobular ducts, and finally into the pancreatic duct, which empties into the duodenum. • The endocrine component (islets of Langerhans) synthesizes and secretes the hormones into the blood to regulate glucose, lipid, and protein metabolism. • Islets of Langerhans are dispersed in the pancreas and contain three primary types of cells: 1. A cells (produce glucagon) 2. B cells (produce insulin) 3. D cells (produce somatostatin). 6.