GIT Digestive Tract PDF

Gastrointestinal System Digestive Tract Assistant Prof. Tarek Abdelkader Surface Anatomy 1.right hypochondrium (RHC) 2.epigastric region 3.left hypochondrium (LHC) 4.right lumbar region 5.umbilical region 6.left lumbar region 7.right Iliac (Inguinal) 8.pubic (hypogastric) region 9.le...

Gastrointestinal System Digestive Tract Assistant Prof. Tarek Abdelkader Surface Anatomy 1.right hypochondrium (RHC) 2.epigastric region 3.left hypochondrium (LHC) 4.right lumbar region 5.umbilical region 6.left lumbar region 7.right Iliac (Inguinal) 8.pubic (hypogastric) region 9.left Iliac (Inguinal) Different parts of digestive system  Oral cavity The roof is formed by the hard and soft palate The floor of the oral cavity is covered by thin and vascular layer of mucosa supported by geniohyoid and mylohyoid muscles while the tongue rests on it The lateral walls of oral cavity are supported by pads of fat and the buccinator muscle. Oral Cavity Functions of Oral cavity (1) Taste sensation. (2) Grinding of food through the actions of the teeth, tongue, and palatal surfaces. (3) lubrication by mixing with mucus and saliva. (4) limited digestion of carbohydrates and lipids. To achieve these functions the major components of the oral cavity must act together Teeth Tongue Salivary Glands Parotid Sublingual Submandibular  Pharynx The Pharynx is a connection between the oral cavity and the esophagus. This connection serves as a common passageway for solid food, liquids, and air. It’s further divided into: ✓ Nasopharynx ✓ Oropharynx ✓ Laryngopharynx Food normally passes through the oropharynx and laryngopharynx on its way to the esophagus. These regions have a stratified squamous epithelium similar to that of the oral cavity.  Digestive tract main histology (1) Mucosa features a. Epithelium b. Lamina propria c. Muscularis mucosae 2) Submucosa 3) Muscularis externa a. Inner circular b. Outer longitudinal 4) Serosa  Serosa VS Adventitia The Serosa Outermost layer of the gut. It is a serous membrane lined by simple squamous epithelium. This layer is nothing but visceral peritoneum that covers most parts of the gastrointestinal tract and extends over the abdominal wall to form parietal peritoneum. Large blood vessels, lymphatics, and nerve trunk run through serosa. In some places where a peritoneal covering is absent (e.g. thoracic part of the esophagus, duodenum, etc.) the outermost layer is called Adventitia. Serosa covers GIT parts in the peritoneal cavity. Adventitia covers GIT parts that are NOT in the peritoneal cavity. Esophagus It’s a muscular tube that starts from the pharynx and descends through the thoracic cavity to end into stomach. It’s always collapsed unless food is passing through. It’s located posterior to trachea and anterior to vertebral column. The opening between esophagus and stomach is controlled by esophageal sphincter (also known as cardiac sphincter).  Stomach Oesophagus Gastro-oesophageal junction Credit: Prof. Gopal. Stomach ✓ Fundus Doom shaped ✓ Body Contains greater curvature and lesser curvature ✓ Pylorus Antrum Pyloric canal The opening between esophagus and cardiac part of stomach is controlled by esophageal sphincter (also known as cardiac sphincter) The opening between pyloric canal and 1st part of duodenum is controlled by pyloric sphincter  The stomach inner surface is thrown into folds known as rugae. The stomach wall has the same 4 layers: Mucosa (contains gastric pits) Submucosa Muscularis externa Serosa The muscularis externa is different in the stomach as it has 3 layers of muscles (instead of 2). The muscles are arranged from inside out as follows: Oblique muscle layer (inner layer) Circular muscle layer (middle layer) Longitudinal muscle layer (outer layer)  Functions of stomach Mechanical digestion Due to the presence of three layers of muscles, stomach is able to turn and mix the food into Chyme Enzymatic digestion Protein digestion by Pepsin which is activated in acidic environment (Chief cells or Zymogenic cells) Neutralization of any bacteria by HCL (Hydrochloric acid) (Parietal cells) Esophageal reflux or Heartburn Absorption Alcohol, sugar, salt, water and drugs Container and reservoir for food Stomach is distensible due to the presence of rugae and can store the food for up to 4 hours  Left gastric A Common hepatic A Right gastric A Left gastro omental A Right gastro omental A Blood supply Directly from the celiac trunk Branch of the common hepatic A. Right and left gastric are found on the lesser curvature of the stomach Right and left gastro-omental are found on the greater curvature of the stomach Branch of the gastroduodenal A. Branch of the splenic A. from celiac trunk from common hepatic A. Innervation Parasympathetic (from vagus nerve) and sympathetic (from celiac plexus) Lymphatics Drains into the gastric and gastro-omental lymph nodes found at the curvatures that drain in the celiac lymph nodes  Small Intestine Small Intestine is the longest part of GIT tract (about 6.7m). The main part of enzymatic digestion occurs at small intestine due to presence of enzymes (mostly secreted from pancreas not small intestine). Majority of nutrients are absorbed within small intestine. The absorption process takes about 3-6 hours. Small Intestine Small Intestine can be divided into three main parts: Duodenum The shortest section of small intestine and can be further subdivided into 4 parts (1st, 2nd, 3rd and 4th part) Pancreatic enzymes reach small intestine through the 2nd part of duodenum and then it’s mixed with the chyme. Duodenum also receives bile from Liver & Gallbladder. Jejunum It’s about 2.5m long Ileum The longest section of small intestine (about 3.5m long) To increase the surface area for absorption, some anatomical modifications are present: Plica Circularis ( Circular folds on the inner surface) Villi (Finger like projections covered with simple columnar epithelium) Microvilli Function of small intestine Complete digestion Selective absorption Secretion of some hormones Delivers the chyme from stomach to large intestine Villi Crypts Paneth cells Duodenum Most distinctive feature is the presence of Brunner’s gland in the submucosa Jejunum Most distinctive feature is absence of Brummer’s gland in the submucosa. More tall and slender villi Ileum Most distinctive feature is the presence of Peyer’s patches in the mucosa Jejunum Ileum ❑ Mesentery has less arcades (the curved blood vessels that ❑ Mesentery has more arcades (the curved blood vessels that look like an arc) look like an arc) ❑ Mesentery has longer vasa recta (the straight blood vessels ❑ Mesentery has shorter vasa recta (the straight blood arising from the arc) vessels arising from the arc) Large Intestine Parts of Large intestine 1. Caecum (identify ileocecal junction & appendix) 2. Ascending Colon 3. Right colic flexure (or hepatic flexure) 4. Transverse Colon 5. Left colic flexure (or splenic flexure) 6. Descending Colon 7. Sigmoid Colon 8. Rectum (ends at the anal canal and anus which has internal involuntary sphincter and external voluntary sphincter) Characteristic features of Large Intestine Haustrations Appendices epiploicae (Omental appendices) Taeniae coli Large Intestine Lined by simple columnar epithelium & numerous goblet cells. Presence of taenia coli  Foregut Midgut Hindgut Blood Celiac Trunk Superior Mesenteric Inferior Mesenteric Supply (Coeliac Trunk) Artery Artery Organs ✓ Esophagus ✓ 3rd and 4th parts of ✓ Distal 1/3 of ✓ Stomach Duodenum Transverse colon ✓ Liver ✓ Jejunum ✓ Descending ✓ Spleen ✓ Ileum colon ✓ Gall Bladder ✓ Appendix ✓ Sigmoid colon ✓ Pancreas ✓ Caecum ✓ Rectum ✓ 1st and 2nd ✓ Ascending colon ✓ Upper Anal Canal parts of ✓ Proximal 2/3 of ✓ Urogenital Sinus Duodenum Transverse colon  Rectum & Anal Canal Generally, rectum is similar to colon except for: A continuous coat of longitudinal muscle is present. There are no taenia coli. Peritoneum covers the front and sides of the upper one-third of the rectum; and only the front of the middle third. The rest of the rectum is devoid of a serous covering. No appendices epiploicae. As we move into the anal canal, we start observing stratified squamous epithelium Credit: Prof. Gopal. Rectoanal junction  Appendix It’s an extension from the cecum and it’s function is unknown. Receives blood supply from appendicular artery and vein. Appendicectomy is the removal of the appendix in case of its inflammation. Appendix Absence of villi Presence of many lymphatic follicles Appendicitis It means acute inflammation of the appendix, and is the most common cause for acute, severe abdominal pain. The abdomen is most tender at McBurney’s point. This corresponds to the location of the base of the appendix. The condition is seen more commonly in older children and young adults, and is uncommon at the extremes of age. The disease is seen more frequently in the West and in affluent societies. If the appendix is not removed, it can rupture resulting in peritonitis.  Thank you Sources: Grays Anatomy for Students 3rd edition Fundamentals of Anatomy & Physiology-Pearson Textbook of Human Histology (9th edition) Visible Body; Human Anatomy Atlas Prof. Gopal Histology notes.