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| COMPONENTS OF THE DIGESTIVE TRACT |
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Definition
| The gastrointestinal tract is a system of organs devoted to nutrition. It includes: the oral cavity (mouth, teeth, tongue, and salivary glands), pharynx, esophagus, stomach, small intestine (duodenum, jejunum, and ileum), large intestine (cecum and appendix, ascending, transverse, descending, and sigmoid colon), rectum and the anal canal. The digestive system also includes gland such as the gallbladder, pancreas, and liver. |
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Term
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Definition
• Epithelium: oral mucosa (generally nonkeratinized stratified squamous epithelium). The epithelium is always a wet mucus membrane due to underlying small accessory salivary glands.
• Connective tissues: a thin superficial layer of loose connective tissue (lamina or tunica propria) with papillae interdigitating with epithelial pegs and a deeper layer with coarse collagen bundles (submucosa) containing numerous small (unnamed) salivary glands.
• Tissue underlying the submucosa may be skeletal muscle (cheeks, soft palate, and lips) or bone (hard palate and gingiva). |
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Definition
• Filiform papillae: are finger-like in shape; they have no taste buds; and their epithelial cells may be partially keratinized. They scrape food off the surface of the tongue.
• Fungiform papillae: are shaped like mushrooms. Their epithelial surface is not keratinized. Taste buds may be scattered on their epithelial surface.
• Circumvallate papillae: are on the posterior boundary of the anterior 2/3 of the tongue and are arranged in a V shaped line anterior to the sulcus terminalis. They are large (numbering only 6-12 total) and submerged into the surface of the tongue. Circumvallate papilla contain scattered taste buds and are surrounded by a moat of saliva. Salivary glands (the glands of von Ebner) underlying the moat secrete saliva, flushing the moat and keeping the taste buds reactive to changing chemical stimuli.
The tongue is a structure of digestion and phonation. It consists mainly of extrinsic and intrinsic skeletal muscle fibers. Instrinsic muscles of the tongue consist of superior and inferior longitudinal fibers, vertical and transverse fibers. The tongue is covered with nonkeratinized stratified squamous epithelium Connective tissue, the lamina propria, is found between the epithelium and intrinsic muscle. The anterior two-thirds of the dorsal (upper) surface of the tongue has many small surface projections called papillae. The posterior 1/3 of the dorsal surface of the tongue contains the lingual tonsil. |
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Term
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Definition
• Enamel: most highly calcified tissue in the human body (95-98%). Enamel matrix is secreted by ameloblasts and subsequently calcified through the formation of enamel rods bound together by interrod enamel. Enamel is formed only over the crown of the tooth and cannot be replaced because the ameloblasts die at tooth eruption.
• Dentin: calcified tissue (approximately 70% mineralized) secreted by odontoblasts. It is initially secreted in an unmineralized state called predentin.
• Cementum: covers the dentin of the root of the tooth. It is similar to bone, but it lacks Haversian systems and blood vessels.
• Tooth pulp: loose connective tissue with odontoblasts, fibroblasts, thin collagen fibers and ground substance.
• Periodontal ligament: dense connective tissue forming the periosteum of the alveolar bone and attaching to the cementum of the tooth. The periodontal ligament allows some movement of the tooth and it absorbs some of the pressure that would be otherwise exerted on the bone during mastication. The periodontal ligament has a relatively high rate of protein turnover. |
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Definition
| The pharynx is derived from the foregut. It is divided into three regions, the nasopharynx, the oropharynx, and the laryngopharynx. The oropharynx begins at the palatoglossal folds and is continuous with the oral cavity. It is lined with stratified squamous epithelium and contains powerful constrictor muscles controlled by CNX. |
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Term
| GENERAL FEATURES OF GI TRACT STRUCTURE |
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Definition
• The mucosa: the innermost layer consisiting of epithelium with underlying connective tissue.
• The submucosa: the layer of connective tissue surrounding the mucosa.
• The muscularis externa: the layer of muscle surrounding the submucosa.
• The serosa: the layer of visceral peritoneum ( a layer of simple squamous epithelium with connective tissue) surrounding the abdominal organs or the adventitia , the layer of connective tissue surrounding organs outside of the abdominopelvic cavity (eg. esophagus, portions of the rectum and anal canal)
From the level of the esophagus to the upper half of the anal canal the wall of the GI tract is composed of four concentric tubes (layers). |
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Term
| GENERAL FEATURES OF GI TRACT STRUCTURE |
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Definition
• The mucosa: the innermost layer consisiting of epithelium with underlying connective tissue.
• The submucosa: the layer of connective tissue surrounding the mucosa.
• The muscularis externa: the layer of muscle surrounding the submucosa.
• The serosa: the layer of visceral peritoneum ( a layer of simple squamous epithelium with connective tissue) surrounding the abdominal organs or the adventitia , the layer of connective tissue surrounding organs outside of the abdominopelvic cavity (eg. esophagus, portions of the rectum and anal canal)
From the level of the esophagus to the upper half of the anal canal the wall of the GI tract is composed of four concentric tubes (layers). |
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Term
| STRUCTURAL AND FUNCTIONAL FEATURES OF THE MUCOSA |
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Definition
• The mucosal epithelium lines the surface of the oral cavity and GI tract and is in contact with the contents of the lumen. It forms a barrier that regulates the movement of substances between the body tissues and the lumen of the GI tract. It contains epithelial cells. The mucosa is generally simple columnar epithelium with an underlying connective tissue layer, the lamina propria. The functions of the epithelium include.
• Promotion of digestion of food substances within the lumen of the GI tract by secretion of enzymes and ions that regulate pH.
• Absorption of the the products of digestion.
• Secretion of protective mucus.
• Secretion of hormones with localized actions (enteroendocrine cells).
• The lamina propria (loose connective tissue) supports the epithelium. It contains
• small blood vessels and lymphatic vessels ( called lacteals in the small intestine) .
• glands, lymphoid tissue and some smooth muscle cells.
• Diffuse lymphoid tissue composed of macrophages, lymphocytes, plasma cells, and granulocytes that participate in local immune mechanisms. |
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Definition
| a layer of smooth muscle, separates the lamina propria from the submucosa. The name means literally the “muscle of the mucosa”. This muscle first appears in the upper part of the esophagus but forms a complete layer only at the level of the stomach. The actions of smooth muscle cells in the muscularis mucosa produce some movement of the mucosa without involving the submucosa and muscularis externa. |
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Term
| STRUCTURAL FEATURES OF THE SUBMUCOSA |
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Definition
• This is a layer of loose connective tissue that contains larger diameter collagen fibers than does the lamina propria.
• It also contains large diameter blood vessels. These vessels supply and drain the smaller vessels in the lamina propria. This layer maintains the vascular supply to and lymphatic drainage of the mucosa.
• It contains a nerve plexus of autonomic neurons, the SUBMUCOSAL NERVE PLEXUS or MEISSNER'S PLEXUS, that innervates the muscularis mucosae and certain sensory and secretory epithelial cells. It provides neural regulation of mucosal movement, of local hormonal secretions, and of secretory activity of epithelial and gland cells through the activities of its neurons .
• Mucus glands are found in the submucosa of the esophagus and duodenum. Secretions of the glandular endpieces protect the mucosal surface.
• Lymphoid nodules are found in the mucosa and submucosa anywhere along the GI tract. Some form stable aggregates of nodules, e.g., Peyer’s patches. Cells in the nodules participate in immunological responses to antigenic substances in the lumen. |
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Term
| STRUCTURAL FEATURES OF THE MUSCULARIS EXTERNA |
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Definition
• Smooth muscle cells adjacent to the submucosa are arranged in a tight helix that appears as a circle in tissue cross sections, hence it is called the circular layer.
• Smooth muscle cells surrounding the circular layer are arranged that is nearly parallel to the long axis of the digestive tract, hence it is called the longitudinal layer. The circular and longitudinal layers of muscle control the unidirectional movement of the intestinal contents from the esophagus to the anal canal.
• Between the circular and longitudinal layers of muscle there is another plexus of autonomic neurons called the myenteric plexus or Auerbach’s plexus. The myenteric plexus is supported by a thin layer of loose connective tissue between the layers of muscle. The activity of neurons in this plexus initiate and coordinate the contractile activity of the circular and longitudinal layers of smooth muscle. Innervation of the plexus by external autonomic neurons further modulates the inherent activity of the plexus.
• Exceptions to the above structural features of the muscularis externa:
• At the level of the upper esophagus the muscularis externa has striated muscle in place of smooth muscle.
• In the cardiac region and body of the stomach, a third, incomplete layer of obliquely arranged smooth muscle may be seen between the submucosa and the circular layer of the muscularis externa.
• The pyloric sphincter between the stomach and the duodenum is formed by a thickening of the circular smooth muscle layer of the muscularis externa.
• In the colon, the smooth muscle cells in the longitudinal layer are condensed into three longitudinal bands of muscle, the taenia coli.
• In the distal part of the anal canal the inner circular layer of smooth muscle forms the internal anal sphincter, the outer longitudinal layer of smooth muscle becomes tendinous, and a third layer of muscle, the external anal sphincter beomes prominent. |
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Term
| STRUCTURAL FEATURES OF THE MUSCULARIS EXTERNA |
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Definition
• Smooth muscle cells adjacent to the submucosa are arranged in a tight helix that appears as a circle in tissue cross sections, hence it is called the circular layer.
• Smooth muscle cells surrounding the circular layer are arranged that is nearly parallel to the long axis of the digestive tract, hence it is called the longitudinal layer. The circular and longitudinal layers of muscle control the unidirectional movement of the intestinal contents from the esophagus to the anal canal.
• Between the circular and longitudinal layers of muscle there is another plexus of autonomic neurons called the myenteric plexus or Auerbach’s plexus. The myenteric plexus is supported by a thin layer of loose connective tissue between the layers of muscle. The activity of neurons in this plexus initiate and coordinate the contractile activity of the circular and longitudinal layers of smooth muscle. Innervation of the plexus by external autonomic neurons further modulates the inherent activity of the plexus.
• Exceptions to the above structural features of the muscularis externa:
• At the level of the upper esophagus the muscularis externa has striated muscle in place of smooth muscle.
• In the cardiac region and body of the stomach, a third, incomplete layer of obliquely arranged smooth muscle may be seen between the submucosa and the circular layer of the muscularis externa.
• The pyloric sphincter between the stomach and the duodenum is formed by a thickening of the circular smooth muscle layer of the muscularis externa.
• In the colon, the smooth muscle cells in the longitudinal layer are condensed into three longitudinal bands of muscle, the taenia coli.
• In the distal part of the anal canal the inner circular layer of smooth muscle forms the internal anal sphincter, the outer longitudinal layer of smooth muscle becomes tendinous, and a third layer of muscle, the external anal sphincter beomes prominent. |
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Term
| STRUCTURAL FEATURES OF THE SEROSA/ADVENTITA |
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Definition
Serosa: In regions of the abdominal cavity the serosa (equivalent to the visceral peritoneum) represents the final layer covering the GI organs. It consists of a membrane formed by a layer of simple squamous epithelium and loose connective tissue containing large blood and lymphatic vessels and nerves. The simple squamous epithelial cells face the peritoneal cavity. Histologists call this type of membrane a mesothelium. The serosa is moistened by transudation of fluid from capillaries in its loose connective tissue and by peritoneal fluid contained between the parietal and visceral layers of the peritoneal cavity. Normal amounts of peritoneal fluid facilitates friction-free sliding of the loops of the intestine over one another during peristalsis. The serosa is continuous with the mesenteries that suspend the organs within the abdominal cavity (eg. mesentery proper, transverse and sigmoid mesocolon, greater and lesser omenta). Those abominal organs that do not have mesentaries (ie. retroperitoneal organs ) are covered by serosa ( in this case, parietal peritoneum) on their anterior and sometimes lateral surfaces but are connected to the posterior body wall by an adventitia. For simplicity and because this is not block 2 of gross anatomy, remember only that the stomach, small and large intestine are covered by a serosa. Question for review? How many organs are located within the peritoneal cavity? ☺
Adventitia: Because the esophagus, rectum, and anal canal are generally outside the abdominal cavity, these regions have an adventitia not a serosa. An adventitaa is merely fascia, containing adipose cells, blood vessels and nerves that forms the outer covering of and organ and binds it to adjacent organs. |
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Term
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Definition
Mucosa :
• The epithelium lining the esophagus is a nonkeratinized stratified squamous epithelium, the type of epithelium used to line body cavities or tubes that are subject to stress.
• Glands are present in the lamina propria of the esophagus only at the superior (proximal) and inferior (distal) ends of the esophagus. Because these glands resemble the mucosal glands present in the cardiac region of the stomach (considered below), they are called esophageal cardiac glands. Cells in these glands secrete mucus high in proteoglycans.
• A muscularis mucosa is present separating the mucosa from the submucosa.
Submucosa:
• Submucosal glands or esophageal glands are present throughout the length of the esophagus. Use these glands and the stratified squamous epithelium to identify the esophagus. Cells in these glands secrete proteoglycan-rich mucus that reaches the epithelial surface through ducts within the mucosa that open onto the epithelial surface.
Muscularis Externa:
• In the esophagus consists of an inner circular layer of muscle fibers and an outer longitudinal layer of muscle fibers. These fibers are skeletal in the upper 1/3 of the esophagus, both smooth and skeletal in the middle 1/3 of the esophagus, and smooth in the lower 1/3 of the esophagus.
Adventitia:
• The esophagus has a thick tunic of connective tissue ( an adventita) that binds it to its buddy the trachea. It is not covered by peritoneum or located mainly in the abdominal cavity and, thus, does not have a serosa. Review question: What is the embryonic relationship between the trachea and the esophagus? |
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Term
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Definition
Mucosa :
• The epithelium lining the esophagus is a nonkeratinized stratified squamous epithelium, the type of epithelium used to line body cavities or tubes that are subject to stress.
• Glands are present in the lamina propria of the esophagus only at the superior (proximal) and inferior (distal) ends of the esophagus. Because these glands resemble the mucosal glands present in the cardiac region of the stomach (considered below), they are called esophageal cardiac glands. Cells in these glands secrete mucus high in proteoglycans.
• A muscularis mucosa is present separating the mucosa from the submucosa.
Submucosa:
• Submucosal glands or esophageal glands are present throughout the length of the esophagus. Use these glands and the stratified squamous epithelium to identify the esophagus. Cells in these glands secrete proteoglycan-rich mucus that reaches the epithelial surface through ducts within the mucosa that open onto the epithelial surface.
Muscularis Externa:
• In the esophagus consists of an inner circular layer of muscle fibers and an outer longitudinal layer of muscle fibers. These fibers are skeletal in the upper 1/3 of the esophagus, both smooth and skeletal in the middle 1/3 of the esophagus, and smooth in the lower 1/3 of the esophagus.
Adventitia:
• The esophagus has a thick tunic of connective tissue ( an adventita) that binds it to its buddy the trachea. It is not covered by peritoneum or located mainly in the abdominal cavity and, thus, does not have a serosa. Review question: What is the embryonic relationship between the trachea and the esophagus? |
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Term
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Definition
| Mucosa: The mucosa of the stomach, when active, is thrown into irregular folds called rugae. It consists of a lining epithelium of simple columnar cells that secrete a protective mucous sheet high in proteoglycans. Gastric glands open into the epithelium at gastric pits and a lamina propria containing many plasma cells and a muscularis mucosae are present. Gastric glands vary according to the region of the stomach in which they are contained. |
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Term
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Definition
| Mucosa: The mucosa of the stomach, when active, is thrown into irregular folds called rugae. It consists of a lining epithelium of simple columnar cells that secrete a protective mucous sheet high in proteoglycans. Gastric glands open into the epithelium at gastric pits and a lamina propria containing many plasma cells and a muscularis mucosae are present. Gastric glands vary according to the region of the stomach in which they are contained. |
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Term
| Glands of cardiac region: |
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Definition
small region, surrounding the esophageal orifice.
• The mucosal glands are simple or branched tubular cardiac glands, containing cells that secrete protective mucus high in neutral glycosaminoglycans. |
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Term
| Glands of cardiac region: |
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Definition
small region, surrounding the esophageal orifice.
• The mucosal glands are simple or branched tubular cardiac glands, containing cells that secrete protective mucus high in neutral glycosaminoglycans. |
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Term
| Glands of fundus and body of the stomach: |
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Definition
• The mucosal glands are branched tubular glands that have functionally distinct zones. Small depressions in the epithelium (gastric pits) mark the entrance to these glands. A characteristic of the fundus and the body of the stomach is that the pits are short and the glands are long.
• The glands extend from the deepest portion of each pit. The part of the gland connected to each pit is called the neck of the gland, generally a short part of the gland The base of each gland extends downward from its neck, through the lamina propria, to the level of the muscularis mucosae.
• Five cells types are found in the glands. |
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Term
| CELLS OF THE GLANDS OF THE FUNDUS AND BODY OF THE STOMACH: |
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Definition
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Definition
| located only in the neck of the gland, secrete mucus, high in acidic proteoglycans. They are somewhat shorter than the surface epithelial cells, and they contain fewer secretory droplets than the surface cells. |
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Term
| 2. Undifferentiated stem cells |
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Definition
| These cells are located in the neck of each gland near the base of the pit where they divide by mitosis to form new surface epithelial cells as well as all types of gland cells, except the enteroendocrine cells. Most newly formed cells migrate toward the surface, forming new cells. Surface cells have a life-span of approximately 3-5 days. Fewer newly formed cells migrate deeper into the glands to replace the parietal and chief cells that have a longer life-span. |
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Definition
| secrete H+ and Cl-, reducing the pH of gastric juice to 1.5-2.0. HCl detoxifies incoming chyme and provides the correct pH for gastic enzymes to function. Parietal cells also secrete intrinsic factor, a glycoprotein that binds avidly to vitamin B12 to form a complex that can be absorbed in the ileum. Located predominantly in the upper part of the body of the gastric glands, parietal cells are large, pale, and round or pyramidal in shape and are characterized by one or two centrally located nuclei, an acidophilic cytoplasm, and large numbers of mitochondria. Parietal cells have deep invaginations of their apical surface that are visible with the electron microscope. This invagination penetrates the cell extensively to produce a complicated intracellular canaliculus. Secretion of H+ and Cl- occurs across the membranes of the canaliculi. When the parietal cell is not actively secreting HCl, a complex tubulovesicular system is visible just beneath the canalicular membranes, but when the parietal cell is actively secreting ions, the tubulovesicular system disappears and microvilli reappear within the canalicular space. |
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Definition
| are zymogenic cells (enzyme-producing cells) located predominantly in the lower portion of the body of the gland. These cells are smaller than parietal cells, and they have basophilic cytoplasm due to a higher content of rough endoplasmic reticulum. Chief cells secrete pepsinogen. Granules in the apical cytoplasm of chief cells contain the inactive proenzyme pepsinogen. Pepsinogen is converted to the active protease pepsin in the acid environment of the stomach lumen. Chief cells also secrete gastric lipase and rennin ( milk digestion). |
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Term
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Definition
| are zymogenic cells (enzyme-producing cells) located predominantly in the lower portion of the body of the gland. These cells are smaller than parietal cells, and they have basophilic cytoplasm due to a higher content of rough endoplasmic reticulum. Chief cells secrete pepsinogen. Granules in the apical cytoplasm of chief cells contain the inactive proenzyme pepsinogen. Pepsinogen is converted to the active protease pepsin in the acid environment of the stomach lumen. Chief cells also secrete gastric lipase and rennin ( milk digestion). |
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Term
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Definition
| These cells are tiny endocrine glands within the stomach that secrete small polypeptide hormones that have regional effects on the stomach. More than 20 hormones have been identified in enteroendocrine cells by immunocytochemical staining. Most enteroendocrine cells contain granules of specific size and density located in the basal portion of the cell, close to capillaries in the lamina propria. Well known polypeptides secreted by these cells include: gastrin, secretin, cholecystokinin, enteroglucagon, vasoactive intestinal peptide, motilin, somatostatin and serotonin. |
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Term
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Definition
| These cells are tiny endocrine glands within the stomach that secrete small polypeptide hormones that have regional effects on the stomach. More than 20 hormones have been identified in enteroendocrine cells by immunocytochemical staining. Most enteroendocrine cells contain granules of specific size and density located in the basal portion of the cell, close to capillaries in the lamina propria. Well known polypeptides secreted by these cells include: gastrin, secretin, cholecystokinin, enteroglucagon, vasoactive intestinal peptide, motilin, somatostatin and serotonin. |
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Term
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Definition
Pyloric glands have long gastric pits and short endpieces. Most pyloric gland
cells are mucus cells and secrete mucus and lysozyme. The predominant enteroendocrine cell in this region produces gastrin (G cells). G
cells are typically found at the base of the glands.
A muscularis mucosae demarcates the mucosa from the submucosa.
Submucosa of the stomach: typical, connective tissue, vessels, submucosal plexus
Muscularis Externa: inner oblique (most developed in body and cardiac region), middle circular, and outer longitudinal. The middle circular layer is thickened to form the pyloric sphincter.
Serosa: layer of visceral peritoneum: continuous with the greater and lesser omenta. |
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Term
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Definition
Pyloric glands have long gastric pits and short endpieces. Most pyloric gland
cells are mucus cells and secrete mucus and lysozyme. The predominant enteroendocrine cell in this region produces gastrin (G cells). G
cells are typically found at the base of the glands.
A muscularis mucosae demarcates the mucosa from the submucosa.
Submucosa of the stomach: typical, connective tissue, vessels, submucosal plexus
Muscularis Externa: inner oblique (most developed in body and cardiac region), middle circular, and outer longitudinal. The middle circular layer is thickened to form the pyloric sphincter.
Serosa: layer of visceral peritoneum: continuous with the greater and lesser omenta. |
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Term
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Definition
| The small intestine is part foregut and part midgut.It consists of three anatomic regions, the duodenum, jejunum, and ileum |
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Term
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Definition
The mucosa of the small intestine is involved in the digestion and absorption of food molecules. The small intestine has a lining of simple columnar epithelium Due to its absorptive function, it is necessary for the small intestine to have a large surface area. Surface area in the small intestine is increased in three ways.Grossly, transvers folds of the mucosa and submucosa, the plicae circulares, increase the surface area. Second, the lamina propria and its overlying epithelium form conical or somewhat flattened projections into the lumen called villi. Finally, the surface of the absorptive cells contains many microvilli for absorption of foodstuffs.
The muscularis mucosae does not project into villi as a layer, but individual smooth muscle cells extend from the muscularis mucosae into each villus where their contractile activity promotes movement of the villus in relation to the contents of the intestine. This movement promotes enzymatic digestion and absorption of food molecules, and it assists in the movement of nutrients in the lymphatic vessels in the lamina propria. Intestinal glands or Crypts of Lieberkühn are located between the villi. |
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Term
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Definition
The mucosa of the small intestine is involved in the digestion and absorption of food molecules. The small intestine has a lining of simple columnar epithelium Due to its absorptive function, it is necessary for the small intestine to have a large surface area. Surface area in the small intestine is increased in three ways.Grossly, transvers folds of the mucosa and submucosa, the plicae circulares, increase the surface area. Second, the lamina propria and its overlying epithelium form conical or somewhat flattened projections into the lumen called villi. Finally, the surface of the absorptive cells contains many microvilli for absorption of foodstuffs.
The muscularis mucosae does not project into villi as a layer, but individual smooth muscle cells extend from the muscularis mucosae into each villus where their contractile activity promotes movement of the villus in relation to the contents of the intestine. This movement promotes enzymatic digestion and absorption of food molecules, and it assists in the movement of nutrients in the lymphatic vessels in the lamina propria. Intestinal glands or Crypts of Lieberkühn are located between the villi. |
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| Cell types in the surface epithelium of the small intestine: |
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Definition
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Term
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Definition
are the predominant cells in the epithelium. They are simple columnar cells with a distinct pattern or polarization. For example, the nucleus is always basal and the apical surface of each cell is covered by approximately 3000 microvilli. These microvilli function in absorption and comprise a striate border or brush border. The absorptive cells are attached laterally to their cell neighbors by junctional complexes that form a barrier between the lumen and the intercellular spaces.
Disaccharidases and dipeptidases, important digestive enzymes, are located in the glycocalyx covering the striate (brush) border. The glycocalyx consists of fine filamentous extensions from the plasma membrane of the microvilli and the protective mucus secretions of the goblet cells. Amino acids and simple sugars pass through the absorptive cells into blood vessels in the lamina propria. Lipid processing occurs within the absorptive cells and the products of lipid catabolism pass into lymphatic capillaries within the lamina propria called lacteals. |
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Definition
| are interspersed between the absorptive cells. They gradually increase in number from the duodenum to the ileum. They secrete protective mucus high in proteoglycans onto the surface epithelium. |
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| Cell types in the intestinal glands: |
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Definition
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Term
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Definition
| They are interspersed between the absorptive cells and the goblet cells. In the small intestine, these cells secrete many products including secretin, cholecystokinin, gastric inhibitory peptide, and motilin into the lamina propria. |
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Term
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Definition
| are found only in the base of each intestinal gland in the small intestine. The secretory products of these cells have not been fully defined, but it is known that they secrete lysozyme, an enzyme that plays a role in controlling intestinal bacteria. |
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Term
| • M cells (membranous epithelial cells) |
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Definition
| are flattened and located only over lymphoid nodules located in the mucosa and lamina propria. Their apical surfaces have small folds rather than a microvillus border. These cells endocytose antigens from the lumen. They then pass the antigens to lymphoid cells in the underlying nodules to initiate and facilitate immune responses to antigenic substances in the intestinal lumen. |
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Term
| • Undifferentiated stem cells |
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Definition
| in the lower 1/3 to 1/2 of the intestinal glands, undergo continual mitosis. The daughter cells differentiate into all of the cell types that occur in the epithelium. New Paneth cells move to the base of the gland, but all other cell types move toward the tips of the villi. As a result, the oldest cells (except for Paneth cells) are found on the tips of the villi. The entire epithelium is renewed every 3-7 days. The high rate of mitosis required to maintain this rapid rate of renewal makes this epithelium exquisitely sensitive to antimitotic agents, such as chemotherapeutic drugs and ionizing radiation. |
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Term
| • Undifferentiated stem cells |
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Definition
| in the lower 1/3 to 1/2 of the intestinal glands, undergo continual mitosis. The daughter cells differentiate into all of the cell types that occur in the epithelium. New Paneth cells move to the base of the gland, but all other cell types move toward the tips of the villi. As a result, the oldest cells (except for Paneth cells) are found on the tips of the villi. The entire epithelium is renewed every 3-7 days. The high rate of mitosis required to maintain this rapid rate of renewal makes this epithelium exquisitely sensitive to antimitotic agents, such as chemotherapeutic drugs and ionizing radiation. |
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Term
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Definition
| lacteals (lymph vessels) are present as well as a prominent muscularis mucuosae. Projecting into the mucosa and lamina propria are many lymphoid nodules. These are prevalent in the small intestine (particularly the ileum) and are called Peyer’s patches. |
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Term
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Definition
| lacteals (lymph vessels) are present as well as a prominent muscularis mucuosae. Projecting into the mucosa and lamina propria are many lymphoid nodules. These are prevalent in the small intestine (particularly the ileum) and are called Peyer’s patches. |
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Term
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Definition
| Projecting into the mucosa and lamina propria are many lymphoid nodules. These are prevalent in the small intestine (particularly the ileum) |
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Term
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Definition
| Projecting into the mucosa and lamina propria are many lymphoid nodules. These are prevalent in the small intestine (particularly the ileum) |
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Term
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Definition
| Submucosal glands or Brunner’s glands are present in the duodenum (but not in the jejunum or ileum). In the duodenum, these gland secrete alkaline mucus to offset the acidity of the food entering from the pylorus. |
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Term
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Definition
| Submucosal glands or Brunner’s glands are present in the duodenum (but not in the jejunum or ileum). In the duodenum, these gland secrete alkaline mucus to offset the acidity of the food entering from the pylorus. |
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Term
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Definition
| present in the duodenum (but not in the jejunum or ileum). In the duodenum, these gland secrete alkaline mucus to offset the acidity of the food entering from the pylorus. |
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Definition
| inner circular and outer longitudinal layer of muscle. |
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Term
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Definition
| visceral peritoneum covering the small intestine; consists of connective tissue with a single layer of simple squamous epithelium. |
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Definition
Crypts of Lieberkühn lead into tubular glands that containing simple columnar cells, many goblet cells, and enteroendocrine cells.
The large intestine is part midgut and part hindgut. (Where is that division?) The major function of the mucosa of the large intestine is to reabsorb water and electrolytes and to add mucus to the undigested material from the small intestine. Water absorption occurs passively across their apical surface of the simple columnar cells due to a gradient There are no villi in the large intestine and a brush border on the surface of the simple columnar absorptive cells is absent as well. Crypts of Lieberkühn lead into tubular glands that containing simple columnar cells, many goblet cells, and enteroendocrine cells. |
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Term
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Definition
Crypts of Lieberkühn lead into tubular glands that containing simple columnar cells, many goblet cells, and enteroendocrine cells.
The large intestine is part midgut and part hindgut. (Where is that division?) The major function of the mucosa of the large intestine is to reabsorb water and electrolytes and to add mucus to the undigested material from the small intestine. Water absorption occurs passively across their apical surface of the simple columnar cells due to a gradient There are no villi in the large intestine and a brush border on the surface of the simple columnar absorptive cells is absent as well. Crypts of Lieberkühn lead into tubular glands that containing simple columnar cells, many goblet cells, and enteroendocrine cells. |
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| two predominant cell types; goblet and simple columnar cells, a lamina propria. Lymphoid nodules are present |
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| two predominant cell types; goblet and simple columnar cells, a lamina propria. Lymphoid nodules are present |
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| Blood vessels, nerves, and lymphatics. |
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| a complete inner layer of smooth muscle (inner circular) and an incomplete outer layer of longitudinal muscle that is confined into three bands (taenia coli) |
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| The large intestine is covered by visceral peritoeneum or a serosa. |
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| The large intestine is covered by visceral peritoeneum or a serosa. |
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| GUT ASSOCIATED LYMPHOID TISSUE (GALT) |
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Definition
• About one-fourth of the mucosa consists of lymphoid tissue. This lymphoid tissue is in the form of lymphoid nodules, as well as loosely organized lymphocytes, macrophages, eosinophils, and plasma cells in the lamina propria.
• The M cells (described above) overlying Peyer’s patches and other large lymphoid nodules also transport antigens from the lumen to the lamina propria surrounding the nodules where they can stimulate lymphocyte and plasma cell activity. |
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