Human Biology: Digestive System PDF

Lecture 08 Chapter 09 DIGESTIVE SYSTEM  Digestive System and Nutrition Points to ponder ▪ What are the digestive system structures and their functions? ▪ Where does carbohydrate, protein, and fat digestion and absorption occur? ▪ What are the accessory organs of dige...

Lecture 08 Chapter 09 DIGESTIVE SYSTEM  Digestive System and Nutrition Points to ponder ▪ What are the digestive system structures and their functions? ▪ Where does carbohydrate, protein, and fat digestion and absorption occur? ▪ What are the accessory organs of digestion? ▪ Pancreas, liver and gallbladder ▪ What is LDL and HDL? ▪ What is obesity, What is BMI? ▪ What are proteins, lipids, carbohydrates, minerals and vitamins needed for? ▪ Name and explain 4 eating disorders 9.1 Overview of Digestion What are the main steps in the digestive process? 1) Ingestion – intake of food via the mouth 2) Digestion – mechanically or chemically breaking down foods into their subunits 3) Movement – food must be moved along the GI tract in order to fulfill all functions 4) Absorption – movement of nutrients across the GI tract wall to be delivered to cells via the blood 5) Elimination – removal of indigestible molecules 9.1 Overview of Digestion What are the four major layers that make up the wall of the GI tract? Mucosa – innermost layer that produces mucus to protect the lining and also produces digestive enzymes Submucosa – 2nd layer of loose connective tissue that contains blood vessels, lymphatic vessels, and nerves Muscularis – 3rd layer made of 2-3 layers of smooth muscle that move food along the GI tract Serosa – outer lining that is part of the peritoneum 9.1 Overview of Digestion Visualizing the layers of the GI tract An overview of the digestive system 9.1 Overview of Digestion 9.1 Overview of Digestion What is the pathway that food follows? 9.2 The Mouth, Pharynx, and Esophagus The mouth ❑ Three pairs of salivary glands secrete saliva that contains: 1- Salivary amylase: enzyme that begins carbohydrate digestion 2- Mucin: protein that hold food particles together 3- Bicarbonate (HCO3-): Maintains the pH of the mouth between 6.5 and 7.5 4- Lysozyme: enzyme that inhibits bacteria growth ❑ Tonsils at the back of the mouth are lymphatic tissues, important in immunity ❑ The tongue is covered in taste buds and also assists in the mechanical breakdown and movement of food toward the pharynx ❑ The mouth contains teeth that begin the mechanical breakdown of food Salivary glands and tonsils  Anatomy of Mouth and Teeth There are 32 teeth in adults (20 deciduous teeth in babies). Teeth are used for mechanical breakdown of food. Dental caries (cavities) occurs when bacteria metabolize sugars and produce acids; limiting sugar intake and brushing teeth reduces tooth decay. Each tooth is made of a crown ‫ التاج‬and a root ‫الجذر‬. A hard covering of enamel ‫المينا‬and dentin ‫العاج‬covers the crown. 9.2 The Mouth, Pharynx, and Esophagus Anatomy of Mouth 4 types of teeth: - 8 Incisors ‫القواطع‬: sharp edges, cut food - 4 Canines ‫األنياب‬: pointed edges, tear food - 8 Premolars ‫ الضواحك‬and 12 Molars ‫ضوس‬: ‫ ر‬flat surfaces, crushing food 9.2 The Mouth, Pharynx, and Esophagus Anatomy of Teeth - Crown: ‫ التاج‬visible region - Root ‫ الجذر‬: below the gum - Enamel ‫ المينا‬: covers the crown - Dentin ‫ العاجية‬: bone-like layer - Pulp cavity ‫ تجويف اللب‬: contains nerve and blood vessels ‫العصب‬. -The tooth sits in the jawbone ‫عظم الفك‬ 9.2 The Mouth, Pharynx, and Esophagus The pharynx and esophagus The pharynx is a cavity between the mouth and esophagus that serves as a passageway for food (and air). The esophagus is a long, muscular tube that carries food to the stomach. 9.2 The Mouth, Pharynx, and Esophagus How do we swallow food? Temporary halt of breathing Comprises 2 phases: Voluntary and Involuntary ❑ Voluntary phase – In the beginning, food is being swallowed from the mouth into the pharynx. Tongue push the bolus of food into the pharynx. It is a voluntary act ❑ Involuntary phase – Once the food is in the pharynx, swallowing becomes a reflex ‫ال‬ ‫ارادي‬. – The epiglottis covers the voice box to make sure food is routed into the esophagus. – Food moves down the esophagus through peristalsis (rhythmic contraction) ‫انقباضات‬. Swallowing of Food  Peristalsis propels food forward ❑ Chunk of food (Bolus) stretches a portion of the GI tract, causing the smooth muscle in the front of the bolus to relax and the muscle behind it to contract, pushing food forward The peristaltic wave ‫موجة انقباضية‬ of contraction propagates through all parts of the GI tract, but is especially prevalent in the esophagus and the stomach https://www.youtube.com/watch?v=kVjeNZA5pi4 The Process of Swallowing 1717 9.2 The Mouth, Pharynx, and Esophagus Heartburn This occurs when acids from the stomach pass into the esophagus (acid reflux). There is a burning sensation in the esophagus. Chronic heartburn is called gastroesophageal reflux disease (GERD). 9.2 The Mouth, Pharynx, and Esophagus Heartburn The following helps decreasing heartburn. – Avoid high fat meals (Foods that are high in fat may cause heartburn by relaxing the lower esophageal sphincter) – Do not overeat. – Eat several small meals rather than the standard three larger meals each day. – Exercise lightly to loose weight. 9.3 The Stomach and Small Intestine The stomach The stomach is a J-shaped organ with a thick wall. It has 3 main functions: 1) stores food 2) starts digestion of proteins 3) controls movement of the chyme into the small intestine (chyme = mixture of gastric juices and partly digested food) There are three layers of muscle in the muscularis layer of the stomach wall to help in mechanical digestion and allow it to stretch The mucosa layer has deep folds called rugae ‫تموجات سطحية‬, and gastric pits ‫ تجويف‬that lead into gastric glands that secrete gastric juice 9.3 The Stomach and Small Intestine Anatomy of the stomach 9.3 The Stomach and Small Intestine The stomach Specific cells of the stomach secrete gastric juice: 1-2 liter/day most of it after meals and consists of: Pepsin, an enzyme that breaks down proteins HCl, gives the stomach a pH of 2 which activates pepsin and helps kill bacteria found in food Mucus, protects stomach lining from acid and prevents absorption of nutrients. Damage to the mucous layer (by Helicobacter) causes peptic ulcer The stomach empties chyme into the small intestine after 2-6 hrs. 9.3 The Stomach and Small Intestine The small intestine The process of digestion continues in the small intestine specifically carbohydrates and lipids The small intestine averages 6m in length The small intestine has two major functions: digestion and absorption  The small intestine The digestion function of the small intestine is facilitated by : enzymes secreted by the pancreas into the small intestine which digest carbohydrates, proteins, and fats Bile secreted by the liver and stored by the gallbladder and released into the small intestine to emulsify ‫ مزج‬fats Large surface area created by numerous villi (finger-like projections) and microvilli (brush-like structure)  Anatomy of the small intestine ❑ The structure of the small intestine makes it suitable for absorption ❑ The wall of the small intestine contains numerous fold that increase its surface area ❑ Each fold is covered with small finger –like projections called villi (singular villus)  The Villus ❑ Each villus consists of a layer of intestinal cells with a brush-like extensions on their plasma membrane: the microvilli Capillaries ❑ Combined, the folds, villi, and microvilli increase the ability of the intestine to absorb nutrients ❑ At the center of each villus are capillaries and a small lymph vessel called lacteal Human intestinal villi  Functions of the small intestine – Digestion Neutralizes acid from stomach Adds digestive enzymes and bile Breaks food to absorbable materials: -proteins into amino acids -carbohydrates into monosaccharides (glucose) -lipids into fatty acids and glycerol – Absorption 90% of digested food (nutrients) is absorbed in small intestine across mucosa cells into the blood Amino acids and sugars enter the capillaries Fatty acids and glycerol enter the lacteals (small lymph vessels) as chylomicrons 9.3 The Stomach and Small Intestine How are nutrients digested and transported out of the small intestine? 9.3 The Stomach and Small Intestine What are the major digestive enzymes? Important!!  The 4 accessory organs Salivary glands. Pancreas. Liver Gallbladder 9.4 The Accessory Organs and Regulation of Secretions The pancreas Fish-shaped spongy organ behind the stomach Functions of the pancreas 1. Secretes enzymes into the small intestine Trypsin digests proteins. Lipase digests fats. Pancreatic amylase digests carbohydrates. 2. Secretes bicarbonate into the small intestine to neutralize stomach acids 3. Secretes insulin into the blood to keep blood sugar levels under control 9.4 The Accessory Organs and Regulation of Secretions The liver and gallbladder The liver is a large metabolic organ that lies under the diaphragm and is made of 100,000 lobules ‫فصيص‬. It filters blood from the GI tract, thus acting to remove poisons and detoxify the blood. The liver removes iron, vitamins A, D, E, K, and B12 from the blood and stores them. It stores glucose as glycogen and breaks it down to help retain blood glucose levels. 9.4 The Accessory Organs and Regulation of Secretions The liver and gallbladder The liver makes plasma proteins and helps regulate cholesterol levels by making bile salts. It makes bile and then stored in the gallbladder to be secreted into the small intestine to emulsify fats. The liver destroys old red blood cells and breaks down hemoglobin (into bilirubin) and recycle iron. 9.4 The Accessory Organs and Regulation of Secretions Liver disorders Hepatitis – Hepatitis is inflammation of the liver. – It is caused by virus causing Hepatitis A, B, and C, and D. Jaundice – This disease can lead to Jaundice (yellow skin) liver damage, cancer, and/or death.  Liver disorders Gallstones – Solid particles that form from bile, cholesterol, and bilirubin in the gallbladder 9.4 The Accessory Organs and Regulation of Secretions Liver disorders Cirrhosis ‫تليف الكبد‬ – The liver becomes fatty and eventually the liver tissue is replaced by fibrous scar tissue. – It is seen in alcoholics and obese people. – Cirrhosis can lead to liver failure in which the liver cannot regenerate as fast as it is being damaged. 9.5 The Large Intestine and Defecation The large intestine The large intestine includes 4 segments 1) Ascending Colon (Cecum, Appendix) ‫القولون‬ ‫الصاعد‬ 2) Transverse Colon ‫القولون المستعرض‬ 3) Descending Colon ‫القولون النازل‬ 4) Rectum ‫( المستقيم‬Anal canal ‫)قناة الشرج‬ It is larger in diameter but shorter than the small intestine. The cecum has a projection known as the appendix ‫ الزائدة الدودية‬that may play a role in fighting infections. 9.5 The Large Intestine and Defecation The large intestine 9.5 The Large Intestine and Defecation The large intestine Functions to – absorb water to prevent dehydration. – absorb vitamins (B complex and K) produced by intestinal flora. – form and rid the body of feces through the anus. https://youtu.be/Og5xAdC8EUI 9.6 Nutrition and Weight Control What is obesity? What is BMI? When an individual is grossly overweight and has a body mass index (BMI) ≥ 30 ‫مؤشر كتلة‬ ‫الجسم‬, he or she is obese. BMI is a general guide to estimate how much of a person’s weight is due to adipose tissue. It does not take into account gender, fitness, or bone structure. 9.6 Nutrition and Weight Control What is your BMI? Body Mass Index (BMI) 19 25 30 200 underweight healthy weight 195 overweight obese 190 182 180 Height (cm) 177 170 164 158 152 125 23 34 45 57 68 79 90 102 113 125 Weight (Kg) Source: U.S. Department of Agriculture: Dietary Guidelines for Americans, 2005 The body mass index chart. 9.6 Nutrition and Weight Control What is obesity? 9.6 Nutrition and Weight Control To understand weight and nutrition, we first have to understand nutrients Nutrients ‫ العناصر الغذائية‬are components of food that are needed to perform physiological body functions. Nutrients include – carbohydrates. – proteins. – lipids. – minerals. – vitamins. 9.6 Nutrition and Weight Control Can lipids be harmful? Cardiovascular disease (CVD) is often a result of arteries blocked by plaque made of cholesterol and saturated fats Low density lipoprotein (LDL) is the “bad” cholesterol because it carries cholesterol from the liver to the cells LDL is increased by saturated fats and decreased by unsaturated fats High density lipoprotein (HDL) is the “good” cholesterol because it carries cholesterol to the liver where it is converted to bile salts 9.6 Nutrition and Weight Control Can lipids be harmful? 9.6 Nutrition and Weight Control Minerals Major minerals make up components of cells, body fluids, and tissues (i.e., calcium, sodium, potassium). Minor minerals are components of larger molecules (i.e., iron in hemoglobin). A varied and complete diet usually provides necessary minerals.  Vitamins Organic compounds (not including proteins, fats, or carbohydrates) are used for metabolism but not produced in high enough quantities by the body They are taken from food The vitamins are common in fruits and vegetables  Essential Vitamins There is a total of 13 vitamins. Most important are: A B1 C B2 D B6 E B12 K  Eating disorders Anorexia nervosa – psychological disorder due to fear of getting fat; it usually results in self-induced starvation, high physical activity, and may include purging Bulimia nervosa – disorder in which people eat large amounts of high-calorie food followed by purging to avoid weight gain, often more than once a day Binge-eating disorder ‫–اضطراب الشراهة عند تناول الطعام‬ overeating is not followed by purging, and this can lead to depression, anger, anxiety, and more binges 9.6 Nutrition and Weight Control Eating disorders are associated with body image Figure 9.16 The characteristics of different eating disorders. Causes of eating disorders