A. General Structure: The liver is the body's largest gland. It is partly covered by a thin capsule (Glisson's capsule) and has a sparse, delicate, reticular connective tissue stroma accompanying the blood vessels as they penetrate the parenchyma. Its predominant cell type is the hepatocyte. These cells are arranged in one- or 2-cell-thick plates that are separated by the hepatic sinusoids. The liver has a dual blood supply, the portal vein and the hepatic artery; it also has 3 drainage systems, the hepatic veins, lymphatic vessels, and bile ducts.
B. General Functions: The liver has several important functions, most of which are carried out by hepatocytes. Its main role in digestion involves the enzymatic processing (metabolism) of nutrients absorbed by the intestines to provide the body with the chemical building blocks and fuel needed to support life. Some hepatocyte enzymes aid in detoxification by modifying potentially dangerous chemicals and drugs and rendering them harmless. Hepatocytes synthesize many important proteins; albumin, prothrombin, fibrinogen, lipoproteins) and secrete them into the blood, thus acting as an endocrine gland. They also synthesize bile from the wastes of erythrocyte destruction and secrete it into the biliary tract, acting as an exocrine gland. The liver also serves as a storage site for glucose, fats, and vitamin A
nC. Blood Supply:
n1. Hepatic portal vein. 2. Hepatic artery. 3. Hepatic sinusoids. 4. Central veins. 5. Hepatic veins.
nD. Cell Types:
n1. Hepatocytes. 2. Kupffer's cells. Monocyte-derived members of the mononuclear phagocyte system. 3. Fat-storing cells.
LIVER
Cell Types : Pancreatic acinar cells 2. Endocrine cells.
Digestive System
1. Pancreatic acinar cells. Each acinus consists of several pyramid-shaped, enzyme secreting cells whose apices border on a small lumen and whose bases abut a basal lamina. Acinar cells synthesize a wide variety of enzymes that can hydrolyze proteins (proteases, such as trypsin, chymotrypsin, and elastase), lipids (lipases, such as triacylglycerol lipase and phospholipase A,), carbohydrates (amylase), and nucleic acids (ribonuclease and deoxy ribonuclease). Enzymes are packaged and stored in the acidophilic apical region as membrane-bound zymogen granules. Here they await exocytosis in response to stimulation by cholecystokinin, which is produced by enteroendocrine cells in the small intestine, or parasympathetic stimulation via the vagus nerve. The enzymes in the granules are zymogens, which are inactive before the release. One such zymogen, trypsinogen, is enzymatically converted to the active protease trypsin in the small intestine by enterokinase, an enzyme that is secreted by enterocytes.
2. Endocrine cells.
PANCREAS
General Structure and Function of Pancreas : The pancreas is a serous, compound acinar gland that resembles the parotid gland in its microscopic appearance. important member of digestive system.
It differs in that it lacks striated ducts and contains islets of Langerhans.
The lobules of the pancreas contain serous adenomeres that secrete a variety of digestive enzymes into a branched duct system that empties into the duodenum.
SALIVARY GLANDS
A. General Structure and Function: Three major pairs of glands, the parotid, submandibular, and sublingual, surround the oral cavity. The lobules of each gland contain numerous adenomeres that empty their secretions (saliva) through a series of intercalated, striated, and interlobular ducts into the oral cavity. The saliva moistens the food, lubricates the digestive tract, and begins the enzymatic digestion of carbohydrates. The glands also excrete certain salts; they protect against bacterial invasion through the mouth by releasing lysozyme and IgA into the saliva.
B. Cell Types:
1. Serous and mucous cells are the predominant secretory cells of salivary adenomeres of digestive system. The key to identifying the 3 types of salivary glands in tissue sections lies in knowing the differences in the staining properties of the cells, their organization, and the proportion of each type found in each gland. a. Serous cells. These relatively small basophilic cells produce a protein-rich, watery secretion and usually form acinar (spheric) adenomeres. b. Mucous cells. Larger and more acidophilic than the serous cells, these may have a foamy appearance. They produce a thick glycosaminoglycan-rich secretion (mucus) and usually form tubular adenomeres.
C. Parotid Glands: These branched acinar glands contain almost exclusively serous secretory cells. The granules in these cells are PAS-positive (owing to their polysaccharide content) and are rich in protein. Parotid secretions, about 25% of the total salivary volume.
D. Submandibular (Submaxillary) Glands: These branched tubuloacinar glands, which produce about 70% of the salivary volume, contain both serous and mucous adenomeres (mostly serous). The serous acini are composed of small basophilic cells with PAS-positive cytoplasm and basal membrane infoldings.
E. Sublingual Glands: These are also branched tubuloalveolar glands containing both mucous and serous cells (mostly mucous). While only mucous adenomeres are present, many are capped by serous demilunes. These glands produce about 5% of the salivary volume.
ANAL CANAL
APPENDIX (VERMIFORM APPENDIX)
-This is a narrow fingerlike evagination of the inferior end of the cecum. Histologically, it resembles the colon except that it has a smaller lumen, fewer and shorter crypts, many more lymphoid nodules, and no teniae coli.
-ANAL CANAL
-In humans, this canal is about 4 cm long and connects the rectum and the anal opening. The mucosa of the first 2 cm has typical colonic epithelium with very short crypts. This is replaced by stratified squamous epithelium, which continues to the anal opening.
LARGE INTESTINE (COLON)
This includes the cecum; the ascending, transverse, descending, and sigmoid colon; and the rectum. It converts undigested material received from the small intestine into feces by removing water and adding mucus. The colon is shorter than the small intestine and has a wider lumen. The colon's lining has no folds, except in the rectum. No villi are present. The epithelium is simple columnar with a great abundance of goblet cells. The mucosa has many deep crypts of Leiberkuhn, containing abundant goblet cells and few enteroendocrine cells.
Parts of Small Intestine
1. Duodenum. The major distinguishing feature of this C-shaped first part of the small intestine is the presence of duodenal (Brunner's) glands in the submucosa. The mucous cells of these glands produce an alkaline secretion. It protects the duodenal lining from the acidity of the chyme and raises the luminal pH to the optimum level for pancreatic enzyme activity. It is also the point of entry for the bile and pancreatic ducts, which penetrate the full thickness of the duodenal wall. It typically exhibits fingerlike or leaflike villi and relatively few goblet cells.
2. Jejunum. An intraperitoneal organ, the jejunum has long leaflike vilii, many plicae circulares, and an intermediate number of goblet cells. The key to its identification, however, is that although it has villi (and is thus part of the small intestine), it contains neither Brunner's glands nor Peyer's patches.
3. Ileum. This intraperitoneal organ has fewer villi, which are short and broad-tipped (clublike), and relatively abundant goblet cells.