Digestive System PDF

Digestive System 1  General Structure and Functions Composed of two separate categories of organs: 1. Main Digestive organs Gastro Intestinal tract (GIT) or Alimentary canal. 2. Accessory digestiv...

Digestive System 1  General Structure and Functions Composed of two separate categories of organs: 1. Main Digestive organs Gastro Intestinal tract (GIT) or Alimentary canal. 2. Accessory digestive organs. 2  Oral Cavity (mouth) Entrance to the GI tract and Initial site of digestion Mechanical and chemical digestion 3  Tongue An accessory digestive organ Manipulates and mixes ingested materials during chewing Forms the bolus: a globular mass of partially digested material Performs important functions in swallowing. 4  Tongue Inferior surface of the tongue – attaches to the floor of the oral cavity – By the lingual frenulum. Numerous small projections (papillae) cover the superior (dorsal) surface. Posterior surface contains lingual tonsils. Skeletal muscles move the tongue. 5 6  Salivary Glands Collectively produce and secrete saliva. – a fluid that assists in the initial activities of digestion – 1.0 and 1.5 L saliva secreted daily – Most is produced during mealtime – Smaller amounts are produced continuously to ensure that the oral cavity remains moist. 7  Salivary Glands Three pairs of large, multicellular salivary glands: – parotid glands – submandibular glands – sublingual glands 8  The Parotid Glands Largest salivary glands. – located anterior and inferior to the ear – partially overlying the masseter muscle. Produce about 25–30% of saliva – conducted through the parotid duct to the oral cavity. 9  The Submandibular Glands Inferior to the body of the mandible. Produce most of the saliva Ducts opens through a papilla in the floor of the mouth – lateral to the lingual frenulum. 10  The Sublingual Glands Inferior to the tongue – internal to the oral cavity mucosa. Each gland has multiple tiny sublingual ducts – open onto the inferior surface of the oral cavity – posterior to the submandibular duct papilla. Contribute only about tree to five the total saliva. 11  Teeth Collectively known as the dentition. Responsible for mastication – first part of the mechanical digestion. A tooth has: – exposed crown – constricted neck – one or more roots 12  Teeth Teeth are not living tissue. Comprised of four different types of tissue: – enamel: hardest and contain minerals – Dentin: surrounds the pulp – Cementum: covers the root and helps the tooth stay in place. – Pulp: is the innermost which contains blood vessels, nerves, and connective tissue. 13  Types of teeth Incisors – has a cutting edge Canines – holding; has one cusp on its crown Premolars – grinding; has two or three cusps Molars – grinding; has from three to five cusps 14  Pharynx The pharynx is the part of the throat behind the mouth and nasal cavity, It is above the esophagus and trachea Three parts: – Nasopharynx – 15  Esophagus Muscular tube going from the oropharynx to the stomach Travels and pierces the diaphragm (at T10) Joins the stomach at the cardiac orifice The upper third contains skeletal muscle; The middle third, a combination of skeletal and smooth muscle; and The terminal portion, smooth muscle only. About 25 cm in adult Esophageal hiatus: through diaphragm 16 17  Esophagus Histology – Mucosa – Submucosa – Muscularis Both skeletal and smooth muscle – Adventitia 18  Stomach General – J-shaped – Functions Digestion – Chemical – Mechanical Results in chyme Limited absorption 19  Stomach The stomach is divided into 5 regions: 1. The cardia: is the first part of the stomach below the esophagus. 2. The fundus: is the rounded area that lies to the left of the cardia and below the diaphragm. 3. The body: is the largest and main part of the stomach. where food is mixed and break down. 4. The antrum: is the lower part of the stomach. 20 21  Stomach features The stomach has – the greater and lesser curvatures. The gastric folds (gastric rugae) are coiled sections of tissue that exist in the mucosal and submucosal layers of the stomach. They provide elasticity by allowing the stomach to expand when a bolus enters it. 22 Gastric Rugae 23  Stomach Histological layers – Mucosa: simple columnar Gastric pits and Gastric glands – Submucosa- composed of areolar connective tissue – Muscularis – Inner oblique, Middle circular and Outer longitudinal – Serosa 24 25  Stomach Principal glands consist of four cell type: chief cells parietal cells mucous neck cells endocrine cells 26 Chief cells (or zymogenic cells):  The most numerous of the four types.  They produce pepsinogen Parietal cells (or oxyntic cells)  Parietal cells secrete the hydrochloric acid gastric juice. Mucous neck cells (mucus production) Endocrine cells  release gastrin, and stimulate gastric acid secretion. 27 28  OMENTUM Omenta are the fused peritoneal folds that connect the stomach and duodenum with other abdominal organs. The omenta consist of two layers of peritoneum, which pass from the stomach and the first part of the duodenum to other viscera They are of two types: The greater omentum The lesser omentum 29 30  Mesenteries and mesocolon The mesentery is a fold of membrane that attaches the intestine to the abdominal wall and holds it in place They allow some movement and provide a conduit for vessels, nerves, and lymphatics to reach the viscera and include: The mesentery-associated with parts of the small intestine The transverse mesocolon-associated with the transverse colon The sigmoid mesocolon-associated with the sigmoid colon 31 32  Small Intestine Finishes chemical digestion Responsible for absorbing most of the nutrients. – Ingested nutrients spend at least 12 hours in the small intestine. Thin-walled tube – about 6 meters (20 feet) in length. – coiled 33  Small intestine Is the longest part of the gastrointestinal tract Extends from the pyloric orifice to the ileocecal fold Consists of: The duodenum The jejunum and The ileum 34  Duodenum Is the first and the shortest part of the SI Is a C-shaped structure, adjacent to the head of the pancreas Is 20-25 cm long and is above the level of the umbilicus Its lumen is the widest of the small intestine Is retroperitoneal except for its beginning, which is connected to the liver by the hepatoduodenal ligament, a part of the lesser omentum 35 Pancreas 36  Jejunum The jejunum represents the second part of SI It is mostly in the left upper quadrant of the abdomen and is larger in diameter and has a thicker wall than the ileum The less prominent arterial arcades and longer vasa recta (straight arteries) compared to those of the ileum are a unique characteristic of the jejunum 37 38 39  Ileum Makes up the distal three-fifths of the small intestine Is mostly in the right lower quadrant Compared to the jejunum, the ileum has thinner walls, shorter vasa recta, more mesenteric fat, and more arterial arcades 40 41  Ileum Opens into the cecum Has two flaps projecting into the lumen of the cecum-the ileocecal folds surround the opening Musculature from the ileum continues into each flap, forming a sphincter Possible function of the ileocecal fold include preventing reflux from the cecum to the ileum 42  Histology of small intestine There are four main layers: – Mucosa: Contains the epithelium – Submucosa – Connective tissue layer – Muscularis – Consists of two smooth muscle layers: the outer longitudinal layer and inner circular layer. – serosa – Comprised of loosely arranged fibroblasts and collagen, with the vessels and nerves passing 43  SI The small intestine is the major absorptive site in the gastrointestinal tract Therefore has a number of modifications to aid its function. The mucosa and submucosa form large numbers of folds (plicae) arranged in a circular fashion in the lumen (plicae circulares). Additionally, the plicae contain microvilli to further increase the surface area, which increases absorption. 44 45  Cells of small intestine There are a number of components to the epithelium: Enterocytes – Tall columnar cells, which have an absorptive function and contain brush border enzymes on the surface which have an important digestive function. Goblet cells – Exocrine glands which secrete mucin. Crypts of Lieberkuhn: are glands found in epithelial linining Lacteals:is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine 46  Large Intestine approximate length of 1.5 meters (5 feet) Absorbs most of the water and electrolytes Intestinal continents solidifies and becomes feces. Stores fecal material until the body is ready to defecate. Absorbs a very small percentage of nutrients still remaining in the digested material. Composed of four segments: – the cecum, colon, rectum and anal canal 47 48  Cecum and appendix The cecum Is the first part of the large intestine It is inferior to the ileocecal opening It is an intraperitoneal structure The appendix is attached to the posteromedial wall of the cecum, just inferior to the end of the ileum 49 50  Appendix The appendix Is a narrow, hollow tube connected to the cecum Has large aggregations of lymphoid tissue in its walls Is suspended from the terminal ileum by the mesoappendix, which contains the appendicular vessels 51 52 Positions of the appendix 53  Colon The colon extends superiorly from the cecum and consists of the ascending, transverse, descending, and sigmoid colon Its ascending and descending segments are (secondarily) retroperitoneal and its transverse and sigmoid segments are intraperitoneal 54  Colon At the junction of the ascending and transverse colon is the right colic flexure, inferior to the right lobe of the liver The left colic flexure occurs at the junction of the transverse and descending colon just inferior to the spleen Higher and more posterior than the right colic flexure is attached to the diaphragm by the phrenicocolic ligament 55 Right and left colic flexures 56  Sigmoid Colon The final segment of the colon - the sigmoid colon begins above the pelvic inlet and it is continuous with the rectum 57  Rectum and anal canal Extending from the sigmoid colon is the rectum The rectosigmoid junction is at the end of the sigmoid mesocolon because the rectum is a retroperitoneal structure The anal canal is the continuation of the large intestine inferior to the rectum 58  Accessary digestive organs The Liver The liver is one of accessory digestive organ located primarily in the right hypochondriac regions of the abdomen, just beneath the diaphragm. It is the largest gland in the body. Is the largest internal organ in the body It weighs approximately 1500 g and accounts for approximately 2.5% of adult body weight 59  Functions of The Liver Produce bile: breaks down fats into small droplets Detoxify drugs, metabolites, and poisons. Store excess nutrients and vitamins Synthesize blood plasma proteins such as albumins, globulins, and proteins required for blood clotting. Phagocytize debris in the blood. Help break down and recycle components of aged 60 erythrocytes and damaged or worn-out formed elements. 61 62  Histology of the Liver Histologically, the liver is composed of several components 1. Hepatocytes-the major functional cells of the liver and perform a wide array of metabolic, secretory, and endocrine functions Are specialized epithelial cells with 5 to 12 sides that make up about 80 percent of the volume of the liver  Histology of the Liver 2. Bile canaliculi-small ducts b/n hepatocytes that collect bile produced by the hepatocytes From bile canaliculi, bile passes into bile ductules and then bile ducts Together, a bile duct, branch of the hepatic artery, and branch of the hepatic  Histology of the Liver 3. Hepatic sinusoids- highly permeable blood capillaries which receive blood from branches of the hepatic artery and from branches of the hepatic portal vein. In the hepatic sinusoids are a modified macrophage, fixed phagocytes Kupffer  Bile Ducts of the Liver Bile is secreted by the liver cells -hepatocytes When digestion is not taking place, the bile is stored and concentrated in the gallbladder; later, it is delivered to the duodenum The interlobular ducts join one another and form the right and left hepatic ducts The right hepatic duct drains the right lobe of the liver and the left duct drains the left lobe. 67 Bile transport  Gallbladder Is a pear-shaped sac lying on the visceral surface of the right lobe of the liver. It has: Fundus of gallbladder Body of gallbladder, Neck of gallbladder The gallbladder receives, concentrates, and stores bile from the liver 69 70  The Pancreas Is both an exocrine and an endocrine gland Lies mostly posterior to the stomach Is retroperitoneal except for a small part of its tail Consists of: A head, uncinate process Neck Body and Tail 71  The main pancreatic duct Begins in the tail of the pancreas In the lower part of the head of pancreas, joins the bile duct The joining of these two structures forms the hepatopancreatic ampulla (ampulla of vater), which contains – major duodenal papilla – minor duodenal papilla 72 73 Thanks 74