Salivary Glands

• They are exocrine glands that produce saliva, which has digestive, lubricant and protective functions. They are made up of lobules separated by septa of connective tissue that originate from a capsule.
• The presence of food in the mouth, as well as smell and sight, stimulate the salivary glands to secrete saliva that contains the enzyme, salivary amylase or ptyalin, besides salts and other substances. The salivary amylase digests amide and other polysaccharides (e.g. glycogen), reducing them into maltose molecules (disaccharides).

Division

Secreting Portion

• Formed by acini with mucous or serous cells, and myoepithelial cells.
• Serous Cells:
-Pyramid-shaped, with a wide base lying on a basal lamina and an apex with small and irregular microvilli towards the lumen
-Possess many granules of acidophilic secretions(apex), has a basophilic basal region(accumulation of R.E.R.)


• Mucous Cells:
-Cubic or Cylindrical Shaped with a flat, oval and peripheral nucleus.
-Cell not stained much, cytoplasm slightly basophilic (few R.E.R.)

• Myoepithelial cells:
-Modified epithelial cells with contractile properties, present in some simple and compound glands.
-Located around the secreting unit
-The contraction of these cells accelerates the secretion of saliva and avoids the excessive distension of the secreting portion.

Duct System(Conducting Portion)

Intercalated Ducts

• The secreting ends continue and empty their products in these ducts: They are short ducts, formed by simple cubic epithelium
• They converge into the interlobular duct inside the glandular lobules

Striated Ducts • Many short intercalated ducts join to form this Duct • They have radial striations that expand the cell’s base all the way up to the nucleus. They are formed by simple columnar epithelium. • Ultrastructure: -Present Characteristics of Ion-transporting cells(active transportation) -Invaginations of the basal plasmatic membrane with numerous elongated mitochondria • Converge into the interlobular duct inside the glandular lobules

Interlobular Ducts

• The Striated Ducts of each lobule converge and empty into the greater ducts located in the septa of connective tissue that separates the lobules
• At first, they are formed by Stratified Cubic Epithelium and then the Distal Portion changes to Stratified Columnar Epithelium

• The Main Duct of each major salivary gland empties into the oral cavity and has a Stratified Keratinized (or not) Squamous Epithelium, it depends on the species.

• There exist three major salivary glands that are covered by a Connective Tissue rich in Collagen Fibers

• Types:

Parotid

• It’s the largest of all three pair salivary glands and produces most of the saliva
• Located in the lateral plane, below and in front of the auricle.
• A Compound Acinar Gland
• Formed exclusively by serous cells


Submandibular

• It’s round and around the size of a nut
• Compound Tubuloacinous Gland
• Formed by 90% of serous cells and 10% of mucous cells with serous demilunes(mixed cells).

Sublingual • Smallest of all three; located below the mucosa of the mouth’s floor. • Compound Tubuloacinous Gland • Mostly mucous cells with a few serous demilunes.

Pancreas

Mixed Exocrine and Endocrine Gland that produces digestive enzymes and hormones.

Endocrine Portion • Pancreatic Islets(of Langerhans) • Secrete Insulin and Glucagon hormones.

Exocrine Portion • Compound Acinar Glands formed exclusively by Serous Cells • A thin capsule of connective tissue covers the pancreas and sends septa inside it, separating it into lobules • The acini are surrounded by a basal lamina that is supported by a delicate and highly vascularized sheet of Reticular Fibers • Secretes water, ions and proteases • Absence of Striated Ducts • Intercalated ducts converge into the interlobular ducts with a simple columnar epithelium • Presence of Centroacinar Cells: -A pale cell with a very stained nucleus which is found inside the serous acinus and between them. -Only exist in the pancreatic acini

Liver

• It is an organ where the nutrients absorbed in the digestive tract are processed and stored to be used by other organs
• Captures, transforms, accumulates metabolites, neutralizes and eliminates toxic substances
• Lined by a thin capsule of Connective Tissue (Glisson’s Capsule)
• Mixed Exocrine and Endocrine Gland
-Exocrine Portion: Secretes the bile which is important in the digestion of lipids
-Endocrine Portion: Albumin and Fibrinogen

Classic Hepatic Lobule (swines)
• Hexagonal shape
• Constituents :

Center • Centrilobular Vein • Has a wall composed of endothelial cells supported by scarce quantities of collagen fibers

Along it • Cords of Hepatocytes with a radial arrangement • Epithelial cells grouped into interconnected plates • Between the cords of hepatocytes we find the sinusoid capillaries • The endothelial cells of the sinusoids are separated from the hepatocytes by a discontinuous basal lamina and a subendothelial space(Space of Disse) that has many collagen and reticular fibers • The sinusoids with spaced endothelial cells allow a greater interaction between the blood and the hepatocytes

Edges • Portal Canal or Portal Triad • Branch of the Portal Vein -Venule -Carries in 70% to 80% of the blood coming from the digestive system filled with nutrients, toxins and CO2 • Branch of the Hepatic Artery -Arteriole -Carries in 20% to 30% of the arterial blood rich in O2, responsible for the oxygenation of the hepatocytes. • Bile Duct -Biliary Ductule -Formed by Columnar or Cubic Simple Epithelium -Has a distinct sheet of connective tissue -Transports the bile produced by the hepatocytes to the hepatic ducts • Connective Tissue lines the portal canal • Limiting Plate -Composed of hepatocytes -Delimitates the portal • Space of Mall: Located between the Limiting Plate and the Portal Space

Cell Types

Hepatocytes
• Cubic cells with a central nucleus
• Dominions Lateral:
-Invaginations of the membrane of each hepatocyte, that when adjoined to one another through occlusive and GAP junctions, delimit the tubular space named Bile Canaliculus
-Bile Canaliculus
-Delimited only by the plasmatic membrane of 2 hepatocytes
-Has a small amount of microvilli inside
-Conduct the gall to the bile ductules
• Basal/ Apical Surfaces facing the Space of Disse, have many microvilli

Ultrastructure
• Can have 1 to 2 nuclei
• R.E.R., S.E.R., A.G., Peroxisomes, Mitochondria, Lipid Droplets and Lysosomes are very evident
• The hepatocyte does not store proteins in secretion granules in the cytoplasm, instead it continuously secretes it in the blood circulation.

Kupffer Cell
• Specifically Liver Macrophages
• Digest hemoglobin
• Metabolize hematids
• Secrete proteins related to the immune processes
• Destroy bacteria

Ito Cells
• Lipid storing cells that contain lipid inclusions rich in vitamin A
• Capture, store and release retinoids, extracellular matrix and proteoglycans

• The hepatic lobules in swine are separated from each other by a layer of connective tissue
• Hepatic Regeneration
-Although at a slow rhythm, it has an extraordinary renewing capacity

Gallbladder

• Hollow organ with a pear-like shape adhered to the liver’s surface
• Stores the bile
• Lined by Simple Columnar Epithelium
-Cells with a high amount of mitochondria and nucleus in the basal third
-All secrete a small amount of mucus
• Typical Lamina Propria
• Muscularis Mucosae without any peculiarities
• The Mucosa Layer has many folds
• Submucosa with mucous glands secreting mucus
• The Muscularis Layer presents connective tissue around its periphery
• Typical Serosa