No anatomically distinct sphincter at gastroesophageal junction, but it functions as one by preventing acid reflux from stomach.
At least 17 different types of enteroendocrine cells have been described
Digestiv tube.english histology
State University of Medicine and Pharmacy “Nicolae Testemitanu” DIGESTIVE TRACTDepartment of Histology, Cytology and EmbryologyTatiana Globa
BASIC PLAN OF THE DIGESTIVE TUBEFour functional layers: Tunica mucosa: This layer is composed of epithelium, connective tissue and muscle. These tissues can usually be found in distinct layers as follows: lamina epithelialis mucosae: consists only of epithelium lamina propria mucosae: consists of either loose areolar or reticular connective tissue lamina muscularis mucosae: consists of smooth muscle Tunica submucosa: consists of loose connective tissue, nerves, blood vessels, and glands in some organs Tunica muscularis: consists of at least two layers, an inner circular and an outer longitudinal with parasympathetic ganglia located between the layers Tunica adventitia or tunica serosa: consists of loose connective tissue.
Esophagus: The esophagus connects the oral cavity with the stomach allowing and aiding in the movement of food particles to the stomach. It is a muscular tube having the layers described above for the typical tubular organ. In the esophagus the layers are specialized for the function of further fragmenting food particles.
Layers of the esophagus Tunica mucosa: epithelium: consists of stratified squamous epithelium that can be highly folded in an empty organ; lamina propria: consists of loose connective tissue, contains esophageal cardiac glands that are simple branched tubular glands, they produce mucus, mucin, chlorides and some biologically active substances. lamina muscularis mucosae: consists of longitudinally oriented smooth muscle fibers that form 1 layer (can be 2) Tunica submucosa: consists of loose connective tissue that is very elastic allowing for expansion when food is present; contains esophageal glands proper; they are compound tubuloalveolar glands, which produce mucous.
Layers of the esophagus Tunica muscularis: consists of smooth and/or skeletal muscle;Proximal end – skeletal muscle cellsMiddle region – skeletal plus smooth muscleDistal end – smooth muscle cells inner circular layer outer longitudinal layer Tunica adventitia/serosa: consist of typical loose connective tissue that blends into the connective tissue of surrounding tissues. Serosa: only at distal end that enters peritoneal cavity.
Comparative characteristic of the wall structure of esophagus and stomach Esophagus Stomach Mucosa EpitheliumStratified squamous nonkeratinized Simple columnar glandular Lamina propria of mucosaContains esophageal cardiac glands that Contains gastric glands that are simpleare simple branched tubular glands. branched tubular. Differ 3 groups ofThey produce mucus, mucin, chlorides glands:and some biologically active substances. 1. cardiac glands in the cardiac region 2. pyloric glands in the pyloric region 3. fundic or gastric glands in the fundic region. Muscularis mucosaeConsists of longitudinally oriented Consists of 3 layers of smooth muscle:smooth muscle fibers that form 1 layer Inner – circular(can be 2) Middle – longitudinal Outer – circular
SubmucosaContains esophageal glands proper. Glands are absent.They are compound tubuloalveolarglands, which produce mucous. Muscularis externaIn the upper one-third – is striated Present only smooth muscle thatmuscle. forms 3 layers:In the middle one-third – is striated Inner – obligue;and smooth muscle. Middle – circular;In the distal third – is smooth as in Outer – longitudinal.rest of the digestive tract. Between the muscle layers is presentIt forms 2 layers: inner – circular; Auerbach’s plexusouter – longitudinal Superficial tunicaIn the thoracic cavity is adventitia. Serosa is present.After entering the abdominal cavity isserosa.
STOMACH Structure - 4 Regions Cardia Fundus Body Pylorus Functions: Continue digestion of carbohydrates started in mouth Add acidic fluid Transform food into chyme (mechanical & chemical breakdown) Promote initial digestion of proteins (via pepsin) and triglycerides (via lipase)
STOMACH Cardiac region – surrounds the cardiac orifice Fundus – dome-shaped region beneath the diaphragm Body – midportion of the stomach Pyloric region – made up of the antrum and canal which terminates at the pylorus The pylorus is continuous with the duodenum through the pyloric sphincter
The inner surface of the stomach is irregular. There are:• Rugae – are longitudinally oriented folds• Gastric (mamillated) areas – are bulging irregular areas• Gastric pits – funnel- shaped depressions. Gastric glands empty into the bottom of the gastric pits
Layers of the TUNICA MUCOSA Epithelium: consists of simple columnar epithelium that forms branched, tubular glands; organized into gastric pits that open onto the lumen and gastric glands that empty into the base of the gastric pits Lamina propria: consists of loose areolar connective tissue that in the glandular stomach is minimal between gastric glands and difficult to see in sections; highly vascular containing many blood and lymphatic capillaries Lamina muscularis mucosae: consists of several layers of smooth muscle oriented both longitudinally and circularly; usually not very thick
Epithelium simplecolumnarglandular of the stomach mucosae Gastric glands simple tubular fewbranched
Glands of the Stomach Fundus and Body Mucous neck cells – found dispersed between the parietal cells; secrets a mucus that is thinner than that secreted by the surface mucous cells; mucus protects other glandular cells from action of proteases and HCl. Parietal cells (oxyntic cells) – found throughout the gastric gland; round cells that contain distinct eosinophilic (pink) cytoplasm and round, prominent nucleus; Secrete HCl and intrinsic factor, needed for absorption of vitamin B12 in the ileum. Chief cells (zymogenic cells) – found mostly near the base of the gastric glands; very basophilic (purple) containing basally positioned nucleus and prominent basophilic apical cytoplasm filled with many ribosomes; secrete pepsinogen, which is activated to pepsin by HCl in the stomach. Pepsin is an enzyme which is able to break down proteins. Endocrine cells – difficult to distinguish by conventional light microscopy; Several types are present; some secrete gastrin, glucagon and somatostatin, histamine, endorphins, serotonin, cholecystokinin (CCK) among other hormones. Undifferentiated cells – located primarily in the neck region; difficult to identify in routine H&E sections; undergo mitosis to form more cells then differentiate into the other cell types present in the gland
Parietal cell Intracellularcanalicular system Mitochondria
Endocrine cellsType:G-cells – gastrin – is theprincipal agent for stimulatingthe secretion of HCl andpepsinogenD-cells produce somatostatin.They inhibit G-cellsEC-cells produce serotonin andsubstance Р which increasestomach activity.ECL-cells produce histaminewhich regulate gastric secretion
STOMACH Tunica submucosa: typical loose connective tissue contains submucosal plexuses also known as Meissners plexuses Tunica muscularis: 3 layers of smooth muscle Outer longitudinal Middle circular Inner oblique between the muscle layers is located the myenteric or Auerbachs plexus Tunica serosa: small amount of loose connective tissue with overlying simple squamous epithelium or mesothelium
Cardiac glands Cardiac glands are tubular, occasionallybranched glands (similar to the cardiac glandsof the esophagus), which contain mainlymucus-producing cells. A few of the secretorycells characteristic for the corpus-fundicglands (chief and parietal cells) may bepresent.
Pyloric glands Pyloric glands are more coiled than corpus-fundic glands, and they may be more branched.The lumen is relatively wide. A few parietal cellsmay be present but chief cells are usually absent.
Shallow gastricpits, with simple orbranched tubularglands Deep gastric pits, Shallow gastric with branched pits, with branched tubular glands tubular glands
SMALL INTESTINE Is the longest component of the digestive tract Is divided into three anatomic segments: duodenum, jejunum, and ileum Functionally, it is the principal site for the digestion of food & for absorption of the products of digestion Endocrine Secretion The bile duct and main pancreatic duct: Join the duodenum at the hepatopancreatic ampulla Are controlled by the sphincter of Oddi
SMALL INTESTINE Specializations of intestinal surface Plicae circulares: deep circular folds of the mucosa circulares and submucosa, most abundant in jejunum Villi – finger-like projections of the mucosa that extend into the intestinal lumen (epithelium plus lamina propria) Intestinal crypts (glands of Lieberkühn) – are simple tubular glands between villi Microvilli – numerous projections of apical plasma membranes of absorptive mucosal cells and give the apical region of the cell a striated appearance, called striated border (brush border)
Villi• Finger-like projections of mucosa• Contain:- fenestrated capillary network- a central, blind- ending lymphatic capillary (lacteal)- few smooth muscle cells derived from muscularis mucosae- myofibroblasts• Are covered by intestinal epithelium – simple columnar
SMALL INTESTINE Layers of the Small Intestine Tunica mucosa: Epithelium - simple columnar Lamina propria - loose connective tissue rich in blood and lymphatic vessels present in the core of the villi and between crypts Lamina muscularis mucosae - thin layer of smooth muscle located at the base of the crypts Tunica submucosa: This layer blends with the lamina propria and is typical. In the duodenum it has coiled branched glands known as Brunners glands, the ducts of which open into the base of the crypts. Tunica muscularis: typical consisting of an inner circular layer and an outer longitudinal layer Tunica serosa: typical
The epithelium of the villus Enterocytes (absorptive cells) Goblet cells – unicellular mucin- secreting glands, increase in number from the proximal to the distal small intestine Enteroendocrine cells resemble those described in the stomach
The epithelium of the crypt Enterocytes (absorptive cells) Goblet cells Enteroendocrine cells Paneth cells – are found in the bases of the glands. They have a basophilic basal cytoplasm & large, intensely acidophilic apical secretory granules. These granules contain: the antibacterial enzyme lysozyme (digests the cell walls of certain groups of bacteria), glycoproteins, an arginine-rich protein & zinc. The antibacterial action & the phagocytosis of certain bacteria & protozoa by Paneth cells suggest that they have a role in regulating the normal bacterial flora of the small intestine. Undifferentiated cells
Gut-Associated Lymphatic Tissue Lymphatic nodules Lymphocytes Macrophages Plasma cells Eosinophils GALT serves as an immunologic barrier
Regional variations in the small intestine:DUODENUM presence of Brunners glands in the submucosa - compound tubuloalveolar branched glands, mixed glands presence of chyme in the small intestine induces cells of Brunners glands to secrete alkaline mucus that neutralizes gastric acid and pepsin and further promotes digestion no plicae circulares
Regional variations in the small intestine:JEJUNUM no glands in the submucosa longest villi of all three regions no lymphoid nodules
Regional variations in the small intestine:ILEUM permanent aggregated lymphoid nodules in the submucosa shortest villi highest number of goblet cells
LARGE INTESTINE Regions Cecum – Appendix Colon Ascending Transverse Descending Rectum Anal canal Functions: Functions Reabsorption of electrolytes & water Formation of waste B vitamins & vitamin K synthesized
LARGE INTESTINEUnlike the small intestine, there are no plicae circulares or villi in the large intestine so the surface of the tunica mucosa is more uniform and flatter than that of the small intestine. Tunica mucosa: mucosa epithelium - simple columnar epithelium that forms straight tubular glands (crypts) lamina propria- loose connective tissue that contains numerous blood and lymphatic vessels, collagen, lymphocytes and plasma cells lamina muscualris mucosae- present beneath the base of the crypts and prominent; undergoes rhythmic contractions Tunica submucosa: typical, contains Peyer’s patches which submucosa are aggregations of solitary follicles or groups of lymph nodules. Each patch contains from 10 to 70 nodules.
The epithelium of the crypt Enterocytes (columnar absorptive cells) – few. Goblet cells – are more numerous than in the small intestine. Enteroendocrine cells Undifferentiated cells
LARGE INTESTINE Tunica muscularis: inner circular and outer longitudinal layers; outer longitudinal layer is organized into three separate bands known as taenia coli; movement of more solid waste to the rectum. Between the taenia coli there is an thin sheet of longitudinal smooth muscle. Tunica serosa is typical. Commensal bacteria reside in the large intestine and play a role in thecontinued digestion of food.
Appendix- Includes a complete layer of longitudinal smooth muscle.- Contains a large number of lymph nodules positioned in both the mucosa and the submucosa.- The muscularis mucosa appear as isolated lengths of smooth muscle.
- is the terminal portion of the alimentary canal Analsinuses
Colorectal Zone (simple columnar epithelium, crypts) Anal Transition Zone(stratified columnar/cuboidal epithelium, anal glands extend into the submucosa) Pectinate line Squamous Zone