L3 Digestive System PDF

BIOLS312F Digestive System Dr Emily Wong 1 Anatomy of the Digestive System 2 Discussion What happens to your body when you start eating an apple? 3 Digestive System Starts from the mouth down to anus 4 Please note that due to differing operating systems, some animations will not appear until the pre...

BIOLS312F Digestive System Dr Emily Wong 1 Anatomy of the Digestive System 2 Discussion What happens to your body when you start eating an apple? 3 Digestive System Starts from the mouth down to anus 4 Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in presentation mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Slide Show mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. 6 Basic Processes of Digestive System 1. Ingestion Occurs when taking food into the mouth 2. Secretion Release of water, acids, buffers, enzymes and salts into the lumen of the tract 3. Mixing and Propulsion Alternating contraction and relaxation of smooth muscles in the walls of GI tract mix the food and secretions, and propel them along the tract 6 6 Basic Processes of Digestive System 4. Digestion Mechanical Digestion Cutting the food into smaller pieces e.g. teeth cut, smooth muscle of stomach and small intestine churn the food Chemical Digestion breakdown of the large molecules in food e.g. carbohydrate, lipid, protein, and nuclei acid by digestive enzymes 7 6 Basic Processes of Digestive System 5. Absorption Movement of organic substrates, electrolytes, vitamins & water across digestive epithelium 6. Defecation Removal of waste products, indigestible substances from the body 8 9 Layers of GI tract Muscularis 10 Peristalsis 11 Oral Cavity Chewing o Breaks large pieces of food into smaller particles o Easier for swallowing Saliva o Secreted by the three pairs of salivary glands, including parotid gland, sublingual gland and submandibular gland 12 Components and Functions of Saliva Component Function Water Moistens food, and dissolves molecules to facilitate chemoreception Mucus Lubricates food and facilitates formation of a bolus for swallowing HCO Neutralizes acids in foods and bacterial metabolites Lysozyme Kills bacteria to maintain health of gums and teeth Amylase Begins the digestion of polysaccharides Lipase Begins the digestion of triglycerides 13 Overview of the Major Macromolecules Ingested, Enzymes That Digest Them, and the Resulting Products of Digestion Large carbohydrates are broken down to disaccharides by amylase; then sucrose, lactose, and maltose are broken down into monosaccharides by sucrase, lactase, and maltase respectively. Proteins are digested into peptide fragments by pepsin, trypsin, and chymotrypsin; the fragments are broken down into amino acids by carboxypeptidase and aminopeptidase. Triglycerides are broken down by lipase into monoglycerides and 2 fatty acids. 14 Pharynx and Esophagus (a) Tongue pushes the food bolus to the back of pharynx (b) Soft palate elevates to prevent food from entering nasal cavity (c) Epiglottis covers the glottis to prevent food or liquid from entering the trachea (d) Food moves down into the esophagus 15 Stomach A J-shape organ in the digestive system Connects esophagus to duodenum by the two openings o Upper: lower esophageal sphincter o Lower: Pyloric sphincter 16 Stomach 17 Functions of Stomach Storage of ingested food (chyme) Mechanical breakdown and mixing of ingested food Regulates the emptying of dissolved food into small intestine Secretions o Hydrochloric acid (Gastric juice): kills microbes (pH 2); denatures proteins o Pepsin: protein digesting enzyme o Mucus: Lubricates and protects the stomach wall Limited absorption occurs in stomach 18 Gastric Gland 19 Regulation of HCl Production Parietal cells in stomach secretes about 2L of HCl per day The acid secretion was regulated by four chemical messengers: gastrin (a gastric hormone), acetylcholine (Ach, a neurotransmitter), histamine and somatostatin Somatostatin inhibits acid secretion while the other three stimulate the secretion In case of gastric ulcer, anti-histamine may be prescribed to block histamine receptors in the stomach and suppress the release of acid 20 Regulation of HCl Production 21 How are Gastrointestinal Processes Regulated? Control mechanisms of the gastrointestinal system are governed by the volume and composition of the luminal contents, rather than by the nutritional state of the body. This means that the body is designed to absorb all the nutrients that are ingested, whether or not the body really needs them to function. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in presentation mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Slide Show mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer. Stomach 24 25 Stomach Motility 26 Gastric Motility The force of antral smooth muscle contractions ↑ with, o Concentration of gastrin o Distension of the stomach  After large meal, the force of initial stomach contraction is greater. This results in a greater emptying per contraction. Gastric emptying is inhibited by the following conditions in duodenum o o o o Distension Presence of fat High acidity (low pH) Hypertonic solutions 27 Small Intestine Divided into three segments o duodenum First segment 25 cm (10 in.) long (approximately the width of twelve fingers) o jejunum Middle segment ~1-2 meters long o ileum Longest segment ~ 2-4 meters long 28 Small Intestine 90% of absorption occurs in the small intestine Composed of fingerlike villi and microvilli structures which increase the surface area of the inner wall dramatically Thin layer of epithelium  These structures favor absorption and digestion 29 Villi 30 31 Absorption in the Small Intestine The small intestine is anatomically arranged for a large surface area, which enhances the absorption of nutrients. One of the specialized anatomical structures is the villi. Villi increase surface area and contain blood vessels and lacteal (lymphatic capillary), which play a role in the absorption of nutrients. Another specialized structure is the microvilli. Microvilli increase surface area and form the brush border. 32 Fluid: ingested, absorbed and excreted 33 Pancreas The pancreas has both exocrine and endocrine functions. The exocrine portion secretes pancreatic juice into small intestine via pancreatic duct This is rich in bicarbonate as well as digesting enzymes. Pancreatic secretions o Bicarbonate: neutralizes the acidic chyme o Amylase: carbohydrates digestion o Protease: protein digestion o Lipase: lipid digestion 34 35 Pancreatic Secretions 36 Control of Pancreatic Secretion 37 Control of Pancreatic Secretion 38 Liver and gall bladder 39 Liver Consists of specialized cells called hepatocytes. The liver serves as a secretory organ. One of its major functions is to secrete bile. Bile is a yellow brownish liquid, which contains bile salts, bicarbonate, lecithin (phospholipid), cholesterol, bilirubin (bile pigment) and other ions Functions of bile: o Emulsifies large lipid molecules o Neutralizes acidic chyme 40 Liver The liver also processes and stores nutrients. The liver also serves as a filter and functions in the removal of old red blood cells which leads to hemoglobin processing and the generation of bilirubin. The liver is also responsible for the synthesis of plasma proteins (albumin, clotting proteins, angiotensinogen, steroid binding proteins). 41 Hepatic Portal System The Hepatic Portal System is a specialized vasculature that delivers absorbed nutrients to the liver for processing before they enter the general systemic circulation. Nutrients are absorbed from the small intestine into mesenteric veins which then carry them to the liver via the hepatic portal vein. 42 Bile Secretion and Liver Function 43 Gall bladder a pear-shaped sac Located in a depression of the posterior surface of the liver Stores and concentrates bile prior to excretion into small intestine 44 Large Intestine Consists o Cecum o Colon (accsending, transverse, descending and sigmoid) o Rectum 45 Functions of large intestine Absorption of salt and water Mixing and propulsion of contents Storage and concentration of undigested matter (feces) Defecation 46 Motility of the Large Intestine and Defecation  Contractions of the circular smooth muscle in the large intestine produce a segmentation motion with a rhythm considerably slower (one every 30 minutes) than that in the small intestine.  Three to four times a day, generally following a meal, a wave of intense contraction known as a mass movement spreads rapidly over the transverse segment of the large intestine toward the rectum.  The sudden distension of the walls of the rectum initiates the neutrally-mediated defecation reflex. The reflex response consists of a contraction of the rectum and relaxation of the internal anal sphincter but contraction of the external anal sphincter (initially) and increased motility in the sigmoid colon.  Eventually, a pressure is reached in the rectum that triggers reflex relaxation of the external anal sphincter, allowing the feces to be expelled. Summary of Functions of the Digestive System 48 Pathophysiology of the Gastrointestinal Tract Ulcers Vomiting Gallstones Lactose Intolerance Inflammatory Bowel Disease Constipation and Diarrhea 49 Ulcers Ulcers affects approximately 10% of the population in the USA. An ulcer is an erosion of the lining of the GI wall. This is usually due to pepsin and acid. This is called a peptic ulcer. They are most common in the lower part of the stomach and the initial part of the small intestine. Symptoms include a chronic rhythmic and periodic gnawing or burning pain. This can be alleviated by drinking milk or by using antacids. If the ulcer is deep enough it can affect the blood vessels and result in bleeding. In severe cases the hole can go all the way through the wall and allow the contents to leak out into the abdominal cavity. This is called a perforated ulcer. This is very serious and can lead to an infection of the peritoneum (peritonitis) and can be fatal. Ulcers can be caused by stress, chronic use of aspirin and other non-steroidal anti-inflammatory medications (they decrease mucus and bicarbonate production), chronic alcohol use, the bacteria helicobacter pylori. 50 51 Control of Food Intake 52 Overweight and Obesity Overweight is defined as a state in which an increased amount of fat in the body results in a significant impairment of health. Obesity denotes a particularly large accumulation of fat – that is, extreme overweight. 53 Eating Disorders: Anorexia Nervosa and Bulimia Nervosa Anorexia nervosa is characterized by decreased food intake so severely that the person may die of starvation. Bulimia nervosa is characterized by recurrent episodes of binge eating usually associated with self-induced vomiting, use of laxatives, or vigorous exercise. 54