بسم هللا الرحمن الرحيم

بسم هللا الرحمن الرحيم Today, we will leave all hormones and start with another topic which is GI system This lecture is talking about general histology of Gastrointestinal system.. The gastrointestinal divides into: 1-GI tract: (tract i.e. tube) it start from mouth and end at the anal canal 2-The associated organs which help the gastrointestinal,and they have ducts that open in the GI tube ((salivary glands, gall bladder, liver and pancreas)) - salivary glands : - (in the oral cavity),1- parotid (in front of the ear), 2-submandibular(under the mandible), 3-sublingual (below the tongue ), and they are the three pairs of large salivary glands. (these are the major salivary glands ) - We have also minor salivary glands in the oral cavity such as: palatal and labial glands. - The glands secretions help in digestion which is one of the GI tract function -there are other associated organs such as :gallbladder, liver and pancreas. *THE OBJECTIVES: 1) - Describe the cells of the GI tract and their function : histology is always linked to physiology (structure and function) Example : the mucosa of the stomach has 4 types of cells, each cell with a different function and secretion

a) mucous cells : its function is to secrete the mucous that lines the stomach and neutralizes and protects from the acidity of the secretion of HCL b) parietal cells : it secretes HCL c) chief: secretes pepsinogen d) G cell *endocrine cell*: it secretes gastrin hormone *each cell had its own function and structure* 2) Describe the histological features of each part of the GI tract.. Generally, the GIT is composed of 4 layers : mucosa, submucosa, muscularis externa (muscular layer for the peristaltic movement of the GIT), and serosa or adventitia. - If we take the esophagus,pharynx,oral cavity, and anal canal- we will observe that the epithelium stratified squamous nonkeratenized. But why?? Because in these places there is friction,and friction will make injury to mucosa. So,there is mitosis (division,replacement of the injured cells). - Mitosis in these cells happens quickly. So,in these places we have stratified squamus epithelium because its faster in division and replacement of injured cells. -but in the stomach the lining epithelium is simple columnar epithelium (and it s the same in small and large intestines) -the lining epithelium is differ from organ to organ in the GI tract.

- The glands in all GI tract are located in the lamina propria in the mucosa, but in duodenum. there is another gland called burrner gland (in the first inch of duodenum ) located in submucosa, why?? Because this gland make neutralization to acidity of stomach.(because the duodenum is the first part of small intestine that follow the stomach). -so, people may have duodenal ulcer because of decreasing the alkaline secretion acidity will increase and make irritation to mucosa ulcer. -and we have to say that the first inch of duodenum is common site for duodenal ulcer - The places in the GI tract that have glands in submucosa are : duodenum and esophagus. - The most important function of gastrointestinal is digestion(changing of complicated material into simple absorptive material) and absorption. So,proteins, carbohydrates, will convert to a,a, and monosaccharide, and after gastrointestinal they will go to the blood through the portal vein and finally to the liver. And the liver will make enzymes, hormones, coagulative materials, etc. - And the residual material of food go to large intestine (colon), There is going to happen absorption of water and the rest will convert to stool which goes to the rectum and anal canal for defecation.

General structures of digestive tract: - The outer layer is serosa or adventitia. remember the 4 layers!! The difference between serosa and adventitia : Serosa is covered by (mesothelium and it s simple sqaumous epithelium). Adventitia is covered by connective tissue (without the mesothelium, and there is no simple squamous epithelium). - With regard the the outermost layer of the GI tract : Anything inside the abdomen is serosa, and anything outside the abdominal cavity is adventitia. - Toward the lumen After serosa, adventatia layer there is muscular layer called muscularis externa, and this layer composed of : inner circular layer and outer longitudinal layer.( in the stomach its 3 layers, the most inner is vertical, but in most GI its 2 layers). - After muscularis externa there is submucosa which compose of C.T and inside it there is some blood vessels and lymphatic vessels, and in some organs it composed of glands such as duodenum burner gland and esophagus. - Now mucosa : it has villi( in small intestine) and these villi are finger-like projections to increase the surface area of GI tract for absorbtion. - mucosa consist of 3 layers - the first layer is epithelial which differs from one place to another

- The second layer of mucosa is lamina propria and it is loose C.T - The third layer is muscularis mucosa(a thin layer of smooth muscles). - Like muscularis externa it has inner cellular layer and outer longitudinal layer. - and its responsible of movement of mucosa. - but peristaltic movement is from muscularis externa not muscularis mucosa - the movement is done by plexus of nerves, we have 2 types of plexus of nerves: o Meissner s (submucosal plexus) : responsible for the motility of the mucosa only. o Myenteric (or Auerbach s) plexus : it s located between the outer longitudinal and the inner circular of muscalris externa of the GIT. These plexuses are autonomic nervous system ganglia (sympathetic and parasympathetic),, Parasympathetic means secretomotor to the gland, it s also responsible for the peristaltic movement and the motility for the GI tract. through the Vagus Nerve 10 th cranial nerve The sympathetic system has a minor role : it s vasomotor, causes vasoconstriction for the blood vessels,, its inhibition causes vasodilatation. - Fnction of mucosa: *Protecting: why esophagus composed of mucosa stratified squamus non-keratinized?

Because in eating the human may be injured.so,it composed of stratified for protecting,and anal canal is similar to esophagus. *absorbtive: like small intestine, mucosa make finger-like projection to increase surface area and important for absorbtion. ----------- ---------- - GI characterized by existing of goblet cells, these cells are very numerous in large intestine because we need lubrication of the stool. so, goblet cells secret mucus and helps in lubrication. - In large intestine we have tubular glands because of water reabsorbtion. *oral cavity: from the inside its stratified squamus non-keratinized but from outside its stratified squamus keratinized skin. So,in the outside there is sebaceous glands, hair follicle, and sweat glands, but inside it there are not. - In the oral cavity there is teeth(wo0ow, a new information :P) originates from gum or gingiva - Tounge floor of oral cavity. - All of these helps in digestion of food. so, the food and secretion of the glands become moistured and make polus. and this polus come to the dorsal of the tongue and the polus is swallowed. - Dorsum of the tongue is responsible of taste (dorsum of tongue is lined by stratified squamus parakeratinized, but under surface of the tongue its non-keratinized. - Dorsum of the tongue we have lingual papillae which contain taste buds, and these papillae: Circumvallate papillae, Filiform papillae, Fungiform papillae,

and Foliate papillae :which is rudimentary in human, but common in animals. - So the tongue is muscular organ have striated muscles - Tongue is divides into : anterior 2 Third, and posterior one Third, they are separated from each other by sulcus terminalis - Tongue has mucus membrane in the lower surface, and its smooth, but in dorsum of tongue it has papillae. So there is some differences between these parts. - Circumvallate papillae :it is the most important papillae, it located in front of sulcus terminalis, their number about 12, its in the anterior two third but embriologically it is from the posterior Third, its nerve supply is the glossopharyngeal nerve 9 th cranial nerve. - It has sustentacular cells, supporting cells, stem cells and taste cells (bipolar cells). - Bipolar cells: responsible for dissolving of material and conversion of taste to electrical impulses which goes to the taste center in the brain (each taste like sour, sweet, bitter or sour has its own impulses). - Taste is transported by corda tempanei nerve which is branch from the facial nerve 7 th cranial nerve - The taste come from lower part of bipolar - There is gland that opens in sulcus terminalis called von Ebners gland. (it s a serous gland). - In front of the oral cavity there is lips.( very important info. :P :P).

- Lips : skin, transitional zone(red zone) vermilion zone,mucosal zone. Salivary glands: - 3 types 1- Parotid serous secretion 2- Submandibular mixed gland (serous and mucus secretion) 3- Sublingual mucus secretion - Any gland has capsule of C.T and this capsule send C.T septa that divide the gland so the gland will be loops and lobules. - Importance of C.T and septa : inside it there is blood vessels,lymphatics and nerves, and contain ducts which go to oral cavity. - Types of ducts: intercalated duct(intralobular): composed of 5-6 small cuboidal cells, its inside the lobules, when they assemble they will make striated ducts when it comes out of the lobules it is called interlobar duct which convert from simple cuboidal and simple columnar to stratified cuboidal and stratified columnar(so interlobar composed of stratified cuboidal and stratified columnar epithelium) then the duct which opens in the oral cavity is stratified squamus epithelium. Some differences between mucus and serous cells: - Mucus: wide lumen, nuclei are flattened and basal - Serous: very narrow lumen, nuclei are spherical (central or toward the base )

- These are myoepithelial cells in the basal membrane (help in contraction and evacuation of secretion). قول االمام الشافع رحمه هللا : شكوت إلى وك ع سوء حفظ ** فأرشدن إلى ترك المعاص وأخب رن بأن العلم نور ** ونور هللا ال هدى لع صا ي *************************************************************************** ***************************************** ********************************* ************************* *************** ********* Sorry for any mistakes, I tried my best DONE BY : DYA` AL- DEEN SWEEDAT Special thanks for lo6fi and 3li al- yaf3i GOOD LUCK ^_^