HISTOLOGY OF GIT I PROF. DR. FAUZIAH OTHMAN DEPT OF HUMAN ANATOMY FPSK CONTENT Histology of the: - oral cavity - pharynx - peritoneum - oesophagus - stomach - small intestine - large intestine Digestive System Digestive System Structures involved in digestive system The digestive system of mammals consists of the following: -(mouth, oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, rectum, anus) -also includes other associated structures/organs/glands (salivary glands, gall bladder, liver, pancreas). Function of Digestive System Digestion is the process of breaking down food into molecules small enough for the body to absorb. Oral Cavity Diagram uvula Oral Cavity Salivary glands produce large amounts of saliva Saliva contains: water for moistening food Mucus for lubricating food and binding it into a bolus (ball of mush) salivary amylase to start the breakdown of starch taste buds ORAL CAVITY Oral or buccal cavity: Is bounded by lips, cheeks, palate, and tongue To withstand abrasions: The mouth is lined with stratified squamous epithelium The gums, hard palate, and dorsum of the tongue are slightly keratinized How is food swallowed? Food moves to the pharynx, (throat) which in humans, leads to both the trachea and the esophagus. While food is being swallowed, the epiglottis blocks the trachea and the uvula blocks off the nose. Then food reaches the esophagus,(tube that connects the pharynx to the stomach) (throat) uvula Oral Cavity of Pig PHARYNX Lined with stratified squamous epithelium and mucus glands Has two skeletal muscle layers Inner longitudinal Outer pharyngeal constrictors PERITONEUM Peritoneum – serous membrane of the abdominal cavity Visceral – covers external surface of most digestive organs Parietal – lines the body wall Simple squamous epithelium OESOPHAGUS Esophageal mucosa – nonkeratinized stratified squamous epithelium The empty esophagus is folded longitudinally and flattens when food is present Glands secrete mucus as a bolus moves through the esophagus Muscularis changes from skeletal (superiorly) to smooth muscle (inferiorly) GENERAL HISTOLOGY OF GIT Consist of 4 layer arrangement of tissue. 1. Mucosa 2. Submucosa 3. Muscularis 4. Serosa Mucosa Submucosa Muscularis Serosa Composed 1. Layer of epithelium 2. Areolar connective tissue 3. Muscularis mucosae Consists areolar connective tissue that bind the mucosa to muscularis Highly vascular & contain submucosal plexus. Skeletal musclemouth, pharyx, superior and midddle of esophagus Serous membrane that composed aerolar connective tissue & simple squamous epithelium Smooth muscle- 2 sheet; inner(circular fiber Outer( longitudinal) Stomach The stomach has several muscle layers surround the stomach, serving to churn food. The stomach can expand to hold about 2 L of food (= 1/2 gal). It contains acid to digest food (ph = 2) and enzymes to breakdown protein. Stomach diagram Sphincters The cardiac sphincter closes off the top end of the stomach and the pyloric sphincter closes off the bottom Lower digestive tract of the pig Lower digestive tract of pig STOMACH The stomach has three layers of muscle: • an outer longitudinal layer, • a middle circular layer, • an inner oblique layer. The inner lining consists of four layers: • the serosa, • the muscularis, • the submucosa, and • the mucosa. The mucosa is densely packed with gastric glands, which contain cells that produce digestive enzymes, hydrochloric acid, and mucus. Small Intestine and accessory organs Small intestine A lot of digestion happens here. S. int. secretes enzymes and pancreas/gall bladder dump enzymes into duodenum to continue digestion. Liver- The largest internal organ of the body. Makes bile, which aids in the digestion of fat. Detoxifies poisons like alcohol. Stores extra glucose in the form of glycogen. Gall Bladder- Sack on the bottom of one of the liver lobes. Stores bile until it is ready to move into the duodenum. Pancreas- Makes digestive enzymes that are dumped into duodenum of the small intestine. Makes the hormone, insulin, which regulates the amount of sugar in the blood. Small Intestine SECTIONS OF THE SMALL INSTESTINE Duodenum- The first part of the small intestine which has ducts (tubes) leading into it from the liver/gall bladder and pancreas. Bile and pancreatic enzymes are mixed with food here. Jejuno-ileum- All the small intestine except for the duodenum. Digestion of food is completed here and nutrients are absorbed through its walls into the blood stream. Caecum-a pouch off the digestive tract between the small intestine and the colon. Produces enzymes that digest cellulose. (is the appendix in humans) SMALL INTESTINE Small intestine, which has three parts: Duodenum Jejunum Ileum The epithelial component of the small intestine is composed of villi (finger like projections) and crypts (crypts of Liberkuhn). Layer Duodenum Jejunum Ileum serosa normal normal normal muscularis externa longitudinal and circular layers, with Auerbach's same as duodenum (myenteric) plexus in between same as duodenum submucosa Brunner's glands and Meissner's no BG (submucosal) plexus no BG mucosa: muscularis mucosae normal normal normal mucosa: lamina propria no PP no PP Peyer's patches mucosa: intestinal epithelium simple columnar. Contains goblet cells, Paneth cells Similar to duodenum. Similar to duodenum. Villi very long. Villi very short. LARGE INTESTINE Large intestine, which has three parts: Cecum (the vermiform appendix is attached to the cecum). Colon (ascending colon, transverse colon, descending colon and sigmoid flexure) Rectum Plicae circularis (valves of Kerckring) – transverse semilunar folds that contain a core of submucosa Large Intestine The large intestine or colon functions to re-absorb water. Bacteria live here like Escherichia coli (E. coli) which produce gases as they ferment their food. Occasionally, some of this gas is released. As these bacteria digest/ferment left-over food, they secrete beneficial chemicals such as vitamin K, Vitamin B, and some amino acids, and are our main source of some of these nutrients. Sections of Large Intestine Spiral colon-spiraled part of the large intestine. Absorbs water, vitamins, and minerals from the food and moves them into the bloodstream. Descending colon- The part of the large intestine leading from the spiral colon down to the rectum. Same function as the spiral colon. STRUCTURE OF LI; simple columnar epith Crypts of Leiberkuhn lymph tissue (GALT) goblet cells NO kerckring folds or villi or paneth cells Layers: Mucosa, Submucosa, Musc. Ext, and either serosa & adventia Large Intestine Diagram Rectum of digestive tract of the pig Rectum The rectum is the end of the large intestine and functions for storage of the feces, the wastes of the digestive tract, until these are eliminated. The external opening at the end of the rectum is called the anus. The anus has two sphincters, one voluntary and one involuntary. The pressure of the feces on the involuntary sphincter causes the urge to defecate and the voluntary sphincter controls whether a person defecates or not. COLON The colon is characterized by mucosal folds that are no longer called villi. These are lined by many GOBLET CELLS and fewer ABSORPTIVE CELLS. The glands are shorter in the colon than in the small intestine. There are no Paneth cells.