Human Digestive System.pdf

The Human Digestive System (6 Hours, Chapter 22) Biology (Biol-222) Learning Objectives After studying this chapter, you will be able to: 1. List and describe the functional anatomy of the organs and accessory organs of the digestive system. 2. Discuss the processes and control of ingestion, pr...

The Human Digestive System (6 Hours, Chapter 22) Biology (Biol-222) Learning Objectives After studying this chapter, you will be able to: 1. List and describe the functional anatomy of the organs and accessory organs of the digestive system. 2. Discuss the processes and control of ingestion, propulsion, mechanical digestion, chemical digestion, absorption, and defecation. 3. Discuss the roles of the liver, pancreas, and gallbladder in digestion. 4. Compare and contrast the digestion of the three macronutrients. Biology (Biol-222) 100 Human Digestive System Introduction ➢ Human food consists of macromolecules including proteins, fats, and complex carbohydrates. ➢ The digestive system converts macromolecules into nutrients including amino acids, lipid molecules, nucleotides, and simple sugars (monosaccharides like glugose) which are required for survival. ➢ The digested food will be absorbed by the body and undigested food will be eliminated as waste. Biology (Biol-222) 101 Human Digestive System ❑ The main steps in the digestive process 1. Ingestion: Taking food into the chamber where digestion occurs. 2. Digestion: Breaking food down mechanically and chemically into components that can be absorbed. 3. Nutrient absorption: Movement of nutrient molecules into cells that line the digestive tract then into the circulation (blood or lymph). 4. Elimination: Expelling leftover material that was not digested and absorbed (defecation). Biology (Biol-222) 102 Human Digestive System The Human Digestive System ➢ The components of the human digestive system are divided into two main categories: the alimentary canal and accessory organs. ➢ Food passes in the alimentary canal in the following direction: mouth, pharynx, oesophagus, stomach, small intestine, large intestine (colon), rectum, and anus. ➢ Accessory organs include salivary glands, gall bladder, liver and pancreas Biology (Biol-222) 103 Human Digestive System Human Digestive System Biology (Biol-222) Biology (Biol-222) 104 Human Digestive System The Mouth (oral cavity)  The mouth includes the lips, tongue, palate, gums (gingiva), and teeth.  Mechanical and chemical digestion begins in the mouth.  The mouth contains three pairs of salivary glands which secrete saliva. Human Mouth  The food in mouth is under the effect of teeth, tongue and saliva. Biology (Biol-222) 105 Human Digestive System Teeth ➢ Teeth break food into small pieces (Mechanical digestion) by chewing. ➢ There are four types of teeth adapted for varied diet. ➢ Normally, human adults have 32 teeth. Each jaw has 16 teeth from anterior to posterior ➢ They are:  4 incisors: chisel-shaped for cutting  2 canine (cuspid): pointed for tearing  4 premolars (bicuspid): fairly flat for grinding  6 molars: more flattened for crushing Biology (Biol-222) 106 Human Digestive System Teeth ➢ Each tooth consists of the following parts: crown, neck, and root. ➢ Each tooth also consists of three layers: ▪ Enamel, the hardest material in the body, covers the exposed surface of the tooth (crown) and reduces wear. ▪ Dentin, most (bulk) of the tooth bonelike material. ▪ Tooth’s pulp “pulp cavity”, lies deep inside the tooth. The structure of human tooth ➢ Tooth decay occurs due to bacteria which converts food into acidic plaque that dissolves the tooth making holes (cavity). Biology (Biol-222) 107 Human Digestive System ❑ Saliva and Chemical Digestion ➢ Chemical digestion: Enzymatic breakdown of food into smaller particles that can be absorbed. Saliva: Contains: ➢ Amylase (digestive enzyme that breaks starch down to disaccharides). Salivary Polysaccharide (Starch)amylase Maltose(disaccharide) ➢ Proteins that form mucus which makes small food bits stick together for easy swallow. ➢ Lysozymes that kill bacteria. Biology (Biol-222) 108 Human Digestive System ❑ ▪ ❑ ▪ Pharynx (throat) The entrance to the digestive and respiratory systems (common passage for food and air). It is the swallowing region between mouth and oesophagus. Esophagus Muscular tube that connects the pharynx to the stomach. Biology (Biol-222) 109 Human Digestive System ➢ Swallowing down the tube. ▪ The tongue pushes food to the back of the throat (voluntary action), the food triggers a swallowing reflex (involuntary action) which directs food into the esophagus. ▪ During swallowing, the soft palate moves back and closes the nasal cavity, and a flap-like epiglottis is pushed down to block the entry to larynx (glottis) and trachea, so the food is directed to the esophagus. ▪ Food moves down the esophagus through Peristalsis (involuntary wave of smooth muscle contractions). Biology (Biol-222) 110 Human Digestive System 1 The bolus enters the The pharynx and the soft palate closes the nasal cavity. 2 The larynx rises up to meet the epiglottis. The bolus presses on the epiglottis and Bends it downward, Closing the opening to the windpipe. 3 The bolus enters the Swallowing esophagus. Biology (Biol-222) 111 Human Digestive System  The passage of food is controlled by ring of muscles known as Sphincters. ▪ Gastroesophageal sphincter at the entrance of the stomach, opens to allow passage of food into the stomach, then closes to prevent stomach acid from splashing into the esophagus. ▪ If the gastroesophageal sphincter does not close properly it may result in acid reflux that causes heartburn. Biology (Biol-222) 112 Human Digestive System ❑ The Stomach ➢ Muscular stretchable sac which:1. Mixes and stores food. 2. Secretes substances that begin to break down food. 3. Controls the passage of food into the small intestine. Biology (Biol-222) 113 Human Digestive System ➢ Stomach wall has smooth muscles and a glandular epithelium in the lining. ➢ Presence of food in stomach stimulates the secretion of gastric juice (acid “HCl”+ enzymes (pepsin) + mucus). ➢ The acid unfold proteins and pepsin digest them into polypeptides. ➢ Mucus protects the stomach wall from the damaging effects of HCl and gastric enzymes. ➢ By end of digestion in stomach, food becomes in the form of semiliquid mass called chyme. Biology (Biol-222) 114 Human Digestive System ❑ Liver and gall bladder ➢ Liver is a large organ that stores glycogen, detoxifies substances and produces bile. ➢ Bile is stored in the gall bladder and passed to the duodenum (first part of the small intestine) through bile duct. It doesn’t contain digestive enzymes but it contains bile salts, bile pigments, and cholesterol. Role of bile in digestion ➢ Bile salts assist fat digestion by emulsification, breakdown of fat globules into fat droplets (i.e. mechanical). ➢ Emulsification of fats occurs in the small intestine. Biology (Biol-222) 115 Human Digestive System Liver, Gall bladder, and Pancreas Organs that empty into the small intestine Chyme from the stomach joins bile and pancreatic enzymes, which enter through ducts. Biology (Biol-222) 116 Human Digestive System ❑ Pancreas ➢ It secretes pancreatic juice which passes through pancreatic duct to the duodenum (first part of the small intestine). ➢ Pancreatic juice contains digestive enzymes, and sodium bicarbonates which acts as buffer. ➢ The buffer decreases the acidity of chyme, protecting the intestinal lining and adjust the pH medium for intestinal enzymes. Biology (Biol-222) 117 Human Digestive System ❑ ➢ ➢ ➢ ➢ ➢ Digestion in the Small Intestine Chyme is forced through sphincter into the small intestine (the longest, 4-7 meter). Lining of intestine is highly folded, each fold forms multicelled projections called villi. Cells further carry brush border of microvilli (>1700/cell). All these increase the surface area for digestion and absorption. Blood vessels and lymph vessel called lacteal run through each villus Food becomes mixed with 3 juices: 1. Intestinal juice from the intestine. 2. Pancreatic juice from the pancreas. 3. Bile released from the liver. Enzymes of 1 and 2 digest carbohydrates, proteins, fats and nucleic acids. Biology (Biol-222) 118 Human Digestive System Biology (Biol-222) 119 Human Digestive System Nutrient breakdown locations and products Digestion Mouth Carbohydrates Absorbable products Lipids Salivary amylase begins digestion Stomach Small intestine Proteins Acid, pepsin begin digestion Pancreatic and intestinal enzymes complete digestion Pancreatic and Pancreatic enzymes intestinal enzymes carry out digestion complete digestion with assistance of bile Monosaccharides (simple sugars) Amino acids Biology (Biol-222) Fatty acids, glycerol 120 Human Digestive System ➢ ❑ Most of food digestion, and nutrient absorption take place in the small intestine. Absorption in the small intestine ➢ Absorption is the passage of nutrients, water, salts from the gut into the internal environment (blood). ➢ Products of carbohydrate digestion (simple sugars e.g. glucose), and protein digestion (amino acids) diffuse through the intestinal wall into the blood capillaries. ➢ Products of fat digestion (fatty acids and glycerol) cross the intestinal wall into lymphatic capillaries then to the blood. Biology (Biol-222) 121 Human Digestive System Absorption of nutrients interior of small intestine products of products of carbohydrates and fat digestion protein digestion Absorption. Nutrients move across brush border cells into a villus, then enter the blood or lymph. Biology (Biol-222) 122 Human Digestive System Large intestine Biology (Biol-222) 123 Human Digestive System Concentrating & Eliminating Wastes ❑ Large intestine ➢ It includes caecum, colon (ascending, transverse and descending), and rectum. ➢ Cecum: a pouch at the start of the large intestine. ➢ Appendix: a small wormlike projection that extends from the cecum. ➢ The appendix has no digestive function but is full of white blood cells for defense. Biology (Biol-222) 124 Human Digestive System ❑ Colon ➢ The undigestible materials, cells shed from the gut lining and other wastes materials move to the large intestine (colon). ➢ Most of the remaining water is absorbed in the large intestine so wastes are concentrated, and feces is formed. ➢ Ions and vitamins made by bacteria in the large intestine are also absorbed to blood. Biology (Biol-222) 125 Human Digestive System ❑ Rectum ➢ The final part of the large intestine is the rectum. ➢ The rectum stores feces until enough accumulates to stretch rectal walls and trigger a defecation reflex. ➢ The brain controls the timing of defecation. It sends out signals that cause contraction or relaxation of skeletal muscle in the external anal sphincter. Biology (Biol-222) 126 Summary Digestive system:       The digestive system consists of the alimentary canal (mouth, pharynx, oesophagus, stomach, small intestines, large intestine) and accessory organs (salivary glands, liver, gall bladder, and pancreas). The main processes of the digestive system are: ingestion, digestion, absorption, and elimination. In the alimentary canal the food is propelled by type of movement known as peristalsis. The 32 teeth of adults include incisors, canines, premolars, and molars. Teeth cut, tear, grind, and crush food. Saliva moistens food, begins the digestion of starch, and help to protect against bacteria. Swallowing includes voluntary and involuntary phases. The stomach breaks down food into semiliquid chyme. Biology (Biol-222) 127 Digestion and absorption: Summary  The first part of the small intestine (duodenum) receives secretions from the pancreas, liver, and gall bladder. It is the part where digestion is completed with the help of intestinal enzymes.  Absorption of water and nutrients occurs mainly in the small intestine.  The large intestine absorbs most remaining water and it stores wastes.  Defecation removes waste from the body via the anus.  Mechanical digestion is the break down of food into small particles, whereas chemical digestion converts food molecules into nutrients (carbohydrates into simple sugars, proteins into amino acids, and fat into fatty acids and glycerol) that can be absorbed by the body.  The products of carbohydrates and proteins digestion enter blood Biology (Biol-222) vessels, whereas the products of fat digestion enter lymphatic vessels (lacteal). Biology (Biol-222) 128 Activity 1- Which of the following prevents food from entering the larynx? a. The tongue. b. The soft palate. c. The hard palate. d. The epiglottis. 2- Which of the following is an organ of the alimentary tract? a. Pancreas. b. Small intestine. c. Gallbladder. d. Bile duct. 3- Chemical digestion of proteins start in which of the following? a. Mouth. b. Esophagus. c. Stomach. d. Small intestine. Biology (Biol-222) 129