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digestive system

The document provides an overview of the digestive system, including: 1) It describes the main organs that make up the digestive tract and their functions in digesting and absorbing food. 2) It explains the three main stages of digestion - in the mouth, stomach, and small intestine - and the roles of different organs at each stage. 3) It provides a table summarizing the movement, digestive juices, and food particles broken down by each digestive organ.

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Salivary Glands Overview•
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Introduction to the digestive system, its organs, functions, and processes involved in digestion.

Details on ingestion, digestion, absorption, and elimination processes, emphasizing mechanical and chemical digestion.

Explains the structure of the digestive system, including the GI tract and accessory organs.

Describes how food moves through the GI tract, stages of digestion, and the role of muscles.

Detailed anatomy of various components of the digestive system like mouth, esophagus, stomach, and intestines.General structure of the digestive system, including the four layers of the digestive tract.

Breakdown of digestion and absorption processes, including propulsion, secretion, and defecation.

Classification of digestive organs into GI tract and accessory structures.

Describes peristalsis, mixing, and segmentation in the GI tract.

Role of the mouth in mechanical digestion and the function of saliva.

Information on types of teeth, their functions, and development stages.

Functions of salivary glands in digestion and components of saliva.

Overview of stomach functions, including storage, mixing, and chemical digestion.

Types of cells in the stomach and their functions, including secretion of digestive aids.

Role of the pancreas in digestion, emphasizing enzyme secretion and hormonal functions.

Primary roles of the liver in metabolism, toxin detoxification, and nutrient storage.

Anatomy and physiology of the small intestine, including its role in digestion and absorption.

Function and structure of the large intestine, focusing on absorption and feces formation.

Key hormones involved in digestion, their secretion mechanisms and functions.

Major digestive enzymes, their sources, and functions in breaking down food.

Structure and role of the rectum in fecal storage and defecation process.

Anatomy of the anus and its role in the expulsion of feces.

Summary of the digestive system's importance and its roles in metabolism and waste management.

List of sources and references used in the presentation.

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P a g e | 2 Index Sl. No. TOPIC Page No. 01 Introduction 03 - 04 02 What is the Digestive System 05 03 How does the digestive system work 06 – 09 04 General Structure of the Digestive System 10 05 Regions of the Digestive System 11 06 Functions of the Digestive System 12 - 13 07 Organization of the Digestive System 14 08 Muscular Movement of the GI Track 15 09 Mouth & Oral Cavity 16 10 Teeth 17 11 Salivary Glands 18 12 Stomach 19 13 Gastric Secretory Cells 20 14 Pancreas 21 15 Functions of The Liver 22 16 Small Intestine 23 17 Large intestine 24 18 Major Hormones of The Digestive Tract 25 19 Major Digestive Enzyme 26 20 Rectum 27 21 Anus 28 22 Conclusion 29 23 References 30
P a g e | 3 INTRODUCTION The digestive system is a group of organs working together to convert food into energy and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract (GI tract). The alimentary canal is made up of the oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines. In addition to the alimentary canal, there are several important accessory organs that help your body to digest food but do not have food pass through them. Accessory organs of the digestive system include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. To achieve the goal of providing energy and nutrients to the body, six major functions take place in the digestive system: • Ingestion • Secretion • Mixing and movement • Digestion • Absorption • Excretion The digestive system includes the digestive tract and its accessory organs, which process food into molecules that can be absorbed and utilized by the cells of the body. Food is broken down, bit by bit, until the molecules are small enough to be absorbed and the waste products are eliminated. The digestive tract, also called the alimentary canal or gastrointestinal (GI) tract, consists of a long continuous tube that extends from the mouth to the anus. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The tongue and teeth are accessory structures located in the mouth. The salivary glands, liver, gallbladder, and pancreas are major accessory organs that have a role in digestion. These organs secrete fluids into the digestive tract.
P a g e | 4 Food undergoes three types of processes in the body: ➢ Digestion ➢ Absorption ➢ Elimination Digestion and absorption occur in the digestive tract. After the nutrients are absorbed, they are available to all cells in the body and are utilized by the body cells in metabolism. The digestive system prepares nutrients for utilization by body cells through six activities, or functions. Ingestion The first activity of the digestive system is to take in food through the mouth. This process, called ingestion, has to take place before anything else can happen. Mechanical Digestion The large pieces of food that are ingested have to be broken into smaller particles that can be acted upon by various enzymes. This is mechanical digestion, which begins in the mouth with chewing or mastication and continues with churning and mixing actions in the stomach. Chemical Digestion The complex molecules of carbohydrates, proteins, and fats are transformed by chemical digestion into smaller molecules that can be absorbed and utilized by the cells. Chemical digestion, through a process called hydrolysis, uses water and digestive enzymes to break down the complex molecules. Digestive enzymes speed up the hydrolysis process, which is otherwise very slow. Absorption The simple molecules that result from chemical digestion pass through cell membranes of the lining in the small intestine into the blood or lymph capillaries. This process is called absorption.
P a g e | 5 What is the Digestive System? A digestive system is a group of organs consisting of the central gastrointestinal (GI) tract and its associated accessory organs that break down food into smaller components so that nutrients can be absorbed and assimilated. This provides the necessary energy to sustain the body. The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining waste. Most of these organs make up the gastrointestinal (GI) tract. Food actually passes through these organs. The rest of the organs of the digestive system are called accessory organs. These organs secrete enzymes and other substances into the GI tract, but food does not actually pass through them. Digestive system is a demonic & Complex process in human body. The digestive tract starts at the mouth and ends at the anus. It is the breakdown of large insoluble food molecules which we eat. In the system the large insoluble food molecules breakdown into a small water-soluble food molecule. So that they can be absorbed through the small intestine into blood. It is a process of turning food into the nutrients. The system by which ingested food is acted upon by physical and chemical means to provide the body with absorbable nutrients and to excrete waste products; in mammals the system includes the alimentary canal extending from the mouth to the anus, and the hormones and enzymes assisting in digestion. The system of organs responsible for getting food into and out of the body and for making use of food to keep the body healthy. The digestive system includes the salivary glands, mouth, esophagus, stomach, liver, gallbladder, pancreas, small intestine, colon, and rectum. The digestive system's organs are joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. Two solid organs, the liver and the pancreas (both of which are embryologically derived from the digestive tract), produce digestive juices that reach the intestine through small tubes known as ducts. In addition, parts of other organ systems (for instance, nerves and blood) play a major role in the digestive system.
P a g e | 6 How Does the Digestive System Work? The GI tract is a long tube of varying diameter beginning at the mouth and ending in the anus. The glands of the digestive system consist of the tongue, salivary glands, liver, gall bladder, and pancreas. Digestion can be divided into three stages – the oral phase (mouth), the gastric phase (stomach) and the intestinal phase (small intestine)– depending on the position of food within the digestive tract. At each stage, different nutrients are digested, under varying circumstances. The GI tract begins to form early during the development of the human body, in the third week after fertilization. Around the 16th day of development, the primitive gut is formed through invaginations of embryonic cells. The initial structures of the digestive system extend from the buccopharyngeal membrane to the cloacal membrane. The mouth forms when the buccopharyngeal membrane breaks down and opens the digestive tract to amniotic fluid. For the rest of fetal development, amniotic fluid is actively swallowed. Digestion works by moving food through the GI tract. Digestion begins in the mouth with chewing and ends in the small intestine. As food passes through the GI tract, it mixes with digestive juices, causing large molecules of food to break down into smaller molecules. The body then absorbs these smaller molecules through the walls of the small intestine into the bloodstream, which delivers them to the rest of the body. Waste products of digestion pass through the large intestine and out of the body as a solid matter called stool. Each part of your digestive system helps to move food and liquid through your GI tract, break food and liquid into smaller parts, or both. Once foods are broken into small enough parts, your body can absorb and move the nutrients to where they are needed. Your large intestine absorbs water, and the waste products of digestion become stool. Nerves and hormones help control the digestive process. Table below shows the parts of the digestive process performed by each digestive organ, including movement of food, type of digestive juice used, and food particles broken down by that organ.
P a g e | 7 The digestive process Organ Movement Mouth Chewing Esophagus Peristalsis Stomach Upper muscle in stomach relaxes to let food enter, and lower muscle mixes food with digestive juice Small intestine Peristalsis Pancreas None Liver None Large intestine Peristalsis Mouth Digestion starts in the mouth before you have even taken the first bite of a meal. When you smell, see or think about tasty food your mouth will often start salivating. When you take your first bite this saliva mixes with the food to help break it down so that your body can absorb it. Chewing the food also aids this process while your tongue moves the food around to get it to your teeth and mix it with the saliva.
P a g e | 8 Throat After leaving the mouth the food travels through your throat (also known as the pharynx) towards the esophagus. Esophagus The esophagus is a muscular tube which connects the throat and the stomach. It is about 25cms long and pushes food down towards your stomach through a series of contractions. It takes 2-3 seconds for the food to move through the esophagus. Just before the point at which the esophagus meets the stomach there is a valve which is designed to stop food from passing back upwards. Stomach The stomach is an organ which has strong muscular walls. When the food reaches the stomach, it is mixed with acid and powerful enzymes which break down the food. These gastric juices also work to kill bacteria that may be in the food. The stomach has strong wall muscles which help to turn the food into a liquid or paste. Small Intestine (Small Bowel) After leaving the stomach the food reaches the small intestine. The small intestine is a long tube (more than 6m long and 3.5-5cms wide) which is coiled up in the abdomen. It is made up of three segments - the duodenum, the jejunum and the ileum. Enzymes from the pancreas and bile from the liver work to continue the process of breaking down the food. Similar to the esophagus, contractions help to move the food through. The job of the duodenum is mostly to continue the process of breaking down the food while the jejunum and ileum are mostly responsible for the absorption of water and nutrients into the bloodstream. Around 90% of digestion and absorption takes place in your small intestine. This is why people with Crohn's disease in their small intestine often suffer from vitamin and mineral deficiencies. Food can spend around 4 hours here. Once the small intestine has absorbed all the nutrients any leftover food moves through to the large intestine (also known as colon).
P a g e | 9 Large intestine (colon/large bowel) The large intestine is a wide (around 7-10cms) muscular tube that runs between the cecum (the first part of the large intestine) to the rectum (the last part of the large intestine). It is around 1.5m in length. The parts of the large intestine are the cecum (the beginning of the colon) the ascending (right) colon, the transverse (across) colon, the descending (left) colon and the sigmoid colon - which connects to the rectum. Food waste is moved through the large intestine by contractions and as it passes through more water and nutrients are absorbed so that a stool is formed. This stool is then stored in the sigmoid colon until the body empties it into the rectum. It normally takes around 36 hours for a stool to get through the large intestine. A stool is mostly made up of food debris and bacteria. When the descending colon becomes full it empties the contents into the rectum. Rectum The rectum connects the colon to the anus. It is around 20cm long and holds the stool until your body is ready to push it out. When a stool or gas reaches the rectum, sensors send a message to the brain to let it know that there is something in the rectum. Muscles, known as sphincters, act to hold in the stool until a message is sent from the brain to let the rectum know that the stool can be released. When this happens the muscles relax, releasing the contents. Anus The anus is the last part of the digestive tract and the lining of the upper anus works to detect rectal contents and tell your body whether the contents are liquid, gas or solid. The anus is made up of the pelvic floor muscles and two anal sphincters (internal and external muscle rings) work together to stop a stool from coming out. The external sphincter (voluntary) works to keep the stool in until we can get to the toilet while the internal sphincter (involuntary) stops us from going to the bathroom when we are asleep or unaware of the stool. These muscles relax as the stool is expelled.
P a g e | 10 General Structure of the Digestive System The long continuous tube that is the digestive tract is about 9 meters in length. It opens to the outside at both ends, through the mouth at one end and through the anus at the other. Although there are variations in each region, the basic structure of the wall is the same throughout the entire length of the tube. The wall of the digestive tract has four layers or tunics: ❖ Mucosa ❖ Submucosa ❖ Muscular layer ❖ Serous layer or serosa The mucosa, or mucous membrane layer, is the innermost tunic of the wall. It lines the lumen of the digestive tract. The mucosa consists of epithelium, an underlying loose connective tissue layer called lamina propria, and a thin layer of smooth muscle called the muscularis mucosa. In certain regions, the mucosa develops folds that increase the surface area. Certain cells in the mucosa secrete mucus, digestive enzymes, and hormones. Ducts from other glands pass through the mucosa to the lumen. In the mouth and anus, where thickness for protection against abrasion is needed, the epithelium is stratified squamous tissue. The stomach and intestines have a thin simple columnar epithelial layer for secretion and absorption. The submucosa is a thick layer of loose connective tissue that surrounds the mucosa. This layer also contains blood vessels, lymphatic vessels, and nerves. Glands may be embedded in this layer. The smooth muscle responsible for movements of the digestive tract is arranged in two layers, an inner circular layer and an outer longitudinal layer. The myenteric plexus is between the two muscle layers. Above the diaphragm, the outermost layer of the digestive tract is a connective tissue called adventitia. Below the diaphragm, it is called serosa.
P a g e | 11 Regions of the Digestive System At its simplest, the digestive system is a tube running from mouth to anus. Its chief goal is to break down huge macromolecules (proteins, fats and starch), which cannot be absorbed intact, into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed across the wall of the tube, and into the circulatory system for dissemination throughout the body. Regions of the digestive system can be divided into two main parts: the alimentary tract and accessory organs. The alimentary tract of the digestive system is composed of the mouth, pharynx, esophagus, stomach, small and large intestines, rectum and anus. Associated with the alimentary tract are the following accessory organs: salivary glands, liver, gallbladder, and pancreas.
P a g e | 12 Functions of the Digestive System The function of the digestive system is digestion and absorption. Digestion is the breakdown of food into small molecules, which are then absorbed into the body. The digestive system is divided into two major parts: • The digestive tract (alimentary canal) is a continuous tube with two openings: the mouth and the anus. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Food passing through the internal cavity, or lumen, of the digestive tract does not technically enter the body until it is absorbed through the walls of the digestive tract and passes into blood or lymphatic vessels. • Accessory organs include the teeth and tongue, salivary glands, liver, gallbladder, and pancreas. The treatment of food in the digestive system involves the following seven processes: 1. Ingestion is the process of eating. 2. Propulsion is the movement of food along the digestive tract. The major means of propulsion is peristalsis, a series of alternating contractions and relaxations of smooth muscle that lines the walls of the digestive organs and that forces food to move forward. 3. Secretion of digestive enzymes and other substances liquefies, adjusts the pH of, and chemically breaks down the food. 4. Mechanical digestion is the process of physically breaking down food into smaller pieces. This process begins with the chewing of food and continues with the muscular churning of the stomach. Additional churning occurs in the small intestine through muscular constriction of the intestinal wall. This process, called segmentation, is similar to peristalsis, except that the rhythmic timing of the muscle constrictions forces the food backward and forward rather than forward only. 5. Chemical digestion is the process of chemically breaking down food into simpler molecules. The process is carried out by enzymes in the stomach and small intestines. 6. Absorption is the movement of molecules (by passive diffusion or active transport) from the digestive tract to adjacent blood and lymphatic vessels. Absorption is the entrance of the digested food (now called nutrients) into the body. 7. Defecation is the process of eliminating undigested material through the anus.
P a g e | 13 ➢ Ingestion - The oral cavity allows food to enter the digestive tract and have mastication (chewing) occurs, and the resulting food bolus is swallowed. ➢ Digestion:  Mechanical digestion – Muscular movement of the digestive tract (mainly in the oral cavity and stomach) physically break down food into smaller particles.  Chemical digestion – Hydrolysis reactions aided by enzymes (mainly in the stomach and small intestine) chemically break down food particles into nutrient molecules, small enough to be absorbed. ➢ Secretion – Enzymes and digestive fluids secreted by the digestive tract and its accessory organs facilitate chemical digestion. ➢ Absorption – Passage of the end – products (nutrients) of chemical digestion from the digestive tract into blood or lymph for distribution to tissue cells. ➢ Elimination – Undigested material will be released through the rectum and anus by defecation.
P a g e | 14 Organization of The Digestive System ✓ Organs of the digestive system are divided into 2 main group: the gastrointestinal tract (GI tract) and accessory structures. ✓ GI tract is a continuous tube extending through the ventral cavity from the mouth to the anus – it consists of the mouth, oral cavity, oropharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus. ✓ Accessory structures include the teeth, tongue (in oral cavity), salivary glands, liver, gallbladder, and pancreas.
P a g e | 15 Muscular movement of the GI tract ❖ Peristalsis – Wavelike movement that occurs from the oropharynx to the rectum, allowing GI tract to push food particles toward the anus. ❖ Mixing- Mixing motion in the oral cavity and stomach that allows the GI tract to repeatedly break down food into smaller particles, using mechanical digestion. ❖ Segmentation – regions of the small intestine contracting and relaxing independently, allowing the small intestine to digestive and absorb more efficiently.
P a g e | 16 MOUTH & ORAL CAVITY ➢ Food enters the GI tract by ingestion. ➢ Food is broken down by mechanical digestion, using mastication. ➢ One chemical digestive process occurs where amylase enzyme in saliva breaks down polysaccharide into disaccharides. ➢ The tongue, made of skeletal muscle, manipulates the food during mastication. it also contains taste buds to detect taste sensations(intrinsic). ➢ Food particles are mixed with saliva during mastication, resulting in a moist lump called bolus for easier passage into or pharynx.
P a g e | 17 Teeth ❖Adapted for mechanical digestion (mastication) in the oral cavity. ❖20 deciduous or primary teeth before the age of 6. ❖By age 7, 32 permanent or secondary teeth are developed & are divided into 4 types: incisors (for cutting), Canines (for tearing), Premolars (for crushing), and Molars (for grinding). these teeth follow the human dental formula of 2-1-2-3.
P a g e | 18 SALIVARY GLANDS ➢ 3 pairs of salivary glands called parotid, submandibular, and sublingual gland secrete most of the saliva in the oral cavity, using salivary ducts. ➢ Saliva helps moisten the food during mastication, dissolve the food in forming the bolus, and help cleanse the teeth. ➢ Saliva consists of 99.5% water, the remaining 0.5% is dissolved substances including amylase enzyme (for chemically digesting carbohydrate), bicarbonate ion (HCO3 -; maintains pH of saliva at 6.5-7.5), and many electrolytes.
P a g e | 19 Stomach A pouch-like organ primarily designed for food storage (for 2-4 hours), some mechanical and chemical digestion also occur.  Contains two sphincters at both ends to regulate food movement – cardiac sphincter near the esophagus, and pyloric sphincter near the small intestine.  Divided into 4 regions: cardiac stomach (or cardiac), fundic stomach (or funded), body of stomach, and pyloric stomach (or Pylorus).  Contain thick folds called rugae at its layer, for providing larger surface area for expansion, secretion, digestion, and some absorption.
P a g e | 20 Gastric Secretory Cells ➢Chief cells: secrete pepsinogen (an inactive enzyme). ➢ Parietal cells: secrete hydrochloric and (HCl) and "intrinsic factor" (which helps absorption of vitamin B12 in the intestines). ➢ Mucous cells: secrete mucus and alkaline substances to help neutralize HCl in the gastric juice. ➢G cells: secrete a hormone called gastrin, which stimulates the parietal cells and overall gastric secretion.
P a g e | 21 PANCREAS  Pancreas: most pancreatic enzymes are produced as inactivate molecules, or zymogens, so that the risk of self – digestion within the pancreas is minimized.  More than 98% of the pancreas mass is devoted to its exocrine function: the secretion of pancreatic juice by the pancreatic acini and their ductile cells. Ductile cells produce Sodium bicarbonate which helps neutralize the acidic gastric contents.  Acinar cells of the exocrine pancreas produce a variety of digestive enzymes to break down food substances into smaller absorbable molecules.  Only 2% of pancreas mass is devoted to the islets of Langham, which produce insulin and glucagon, hormones that regulate blood sugar and carbohydrate metabolism (they have opposite effects).
P a g e | 22 Functions of The Liver ❖ Important in carbohydrate metabolism where hepatic cells conduct glycogenesis (converting glucose into glycogen), and glycogenolysis (breaking glycogen down to glucose). ❖ Also is critical in lipid metabolism where hepatic cells produce bile (for fat emulsification), oxidize fatty acids, synthesize various forms of lipids, and convert glucose to fatty acids (lipogenesis). ❖ Other functions of the liver include: Storage of glycogen, iron, and vitamins A, D, B12. ❖ Contains phagocytes to destroy damaged erythrocytes and foreign substances, using phagocytosis. ❖ Detoxifies harmful substances in the blood. ❖ Serves as a blood reservoir (contains 7% of blood volume).
P a g e | 23 SMALL INTESTINE ➢ A long tube, with a small diameter (about 1 inch), extending from pyloric sphincter to the ileocecal valve. ➢ Divided into Duodenum, Jejunum, and ileum. Secretions of Small Intestine: 1. Intestinal glands secrete a watery fluid that lack digestive enzymes but provides a vehicle for moving chyme to villi. Intestinal enzymes include: maltase digests maltose into glucose. sucrose digests sucrose into glucose and fructose. lactase digests sucrose into glucose and glucose. peptidases digest peptides into amino acids. lipases digest triglycerides into fatty acids and glycerol. Nucleases digest nucleotides into nitrogenous bases. Enterokinase converts trypsinogen into trypsin. 2. Digestive enzymes embedded in the surfaces of microvilli split molecules of sugars, proteins and fats. 3. Regulation of small intestine secretions: secretion is stimulated by gastric juice, chyme, and reflex stimulated by distension of the small intestinal wall. 4. Each villus contains blood capillaries to absorb water, glucose, amino acids, vitamins, minerals, and short-chain fatty acids, and also contains lymphatic capillaries called lacteals to absorb long – chain fatty acids in the forms of micelles. 5. Water is absorbed by osmosis, fatty acids are absorbed by diffusion (since they are fat-soluble), and most other nutrients (glucose, amino acids, & minerals) are absorbed by active transport.
P a g e | 24 Large intestine ➢ The last segment of the GI tract, with a large diameter (2-3 inches), extending from the ileocecal valve to the anus. ➢ Divided into cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal, and anus. ➢ The large intestine has little or no digestive function, although it secretes mucus. Its mucosa has no villa or microvillus, but contains numerous goblet cells for secreting mucus to aid in the formation of feces and maintain an alkaline condition.  mechanical stimulation and parasympathetic impulses control the rate of mucus secretion. ➢ The large intestine only absorbs water, electrolytes and some vitamins. ➢ Many bacteria inhabit the large intestine, where they break down certain indigestible substances and synthesize certain vitamins. ➢ feces are formed and stored in the large intestine. Defecation involves a reflex mechanism aided by voluntary contraction of the diaphragm, abdominal muscles, and the external anal sphincter.
P a g e | 25 MAJOR HORMONES OF THE DIGESTIVE TRACT 1. Gastrin: (Gastric & intestinal): released by Gastric cells, in response to the presence of food. Causes Gastric glands to increase their secretory activity. 2. Somatostatin: (Gastric inhibitory peptides - GIP): Inhibits secretion of acid by parietal cells. 3. Cholecystokinin: released by intestinal wall cells, in response to the presence of proteins and fats in the small intestine. It causes gastric glands to decrease their secretory activity and inhibits gastric motility; stimulation of pancreas to secrete digestive enzyme; stimulates gall – bladder to contract and release bile. 4. Secretin: released by cells in the duodenal wall, in response to acidic chyme entering the small intestine.
P a g e | 26 Major Digestive Enzyme ✓ Salivary enzyme: Begins carbohydrates digestion by breaking down starch and glycogen to disaccharides ✓ Gastric enzymes: Pepsin, from Gastric glands – Begins protein digestion. Lipase, from Gastric glands – Begins fat digestion. ✓ Pancreatic enzymes: Amylase, from pancreas – breaks down starch and glycogen into disaccharides. Lipase, from pancreas – breaks down fats into fatty acids and glycerol. ✓ Proteolytic enzymes: Trypsin, Chymotrypsin, and Carboxypeptidase from pancreas breaks down peptides into amino acids. Nucleases, from pancreas breaks down nucleic acids into nucleotides. ✓ Intestinal Enzymes: Peptidase, from mucosal cells, breaks down peptides into amino acids. Sucrase, maltase, and lactase, from mucosal cells, breaks down disaccharides into monosaccharides. Lipase, from mucosal cells, breaks down fats into fatty acid and glycerol. Enterokinase, from mucosal cells, (breaks down) converts trypsinogen into trypsin.
P a g e | 27 RECTUM ➢ The rectum is the concluding part of the large intestine that terminates in the anus. ➢ The average length of the human rectum may range between 10 and 15 cm. Its diameter can be compared to that of the sigmoid colon (the part of the large intestine nearest the rectum) at its onset. However, it becomes larger near the anus, where it forms the rectal ampulla. ➢ The key role of the rectal ampulla is to act as a temporary storehouse for feces. The expansion of the rectal walls causes the stretch receptors within the walls to stimulate the urge to defecate. If the defecation process is delayed, it may result in constipation. When the storage site becomes full, the intrarectal pressure causes the anal canal walls to dilate and expand. This results in the feces entering the canal. ➢ A rectal exam may be conducted to diagnose certain diseases. Certain types of cancers may be diagnosed by performing an endoscopy in the rectum. An endoscopy is a procedure where a doctor uses an endoscope — a small, flexible tube with a camera and light — to examine areas inside the body. Body temperature may also be obtained from the rectal area. In case of infants and babies, this is generally the most accurate method for determining actual body temperature.
P a g e | 28 Anus ❖ The anus is the opening where the gastrointestinal tract ends and exits the body. The anus starts at the bottom of the rectum, the last portion of the colon (large intestine). The anorectal line separates the anus from the rectum. ❖ Tough tissue called fascia surrounds the anus and attaches it to nearby structures. ❖ Circular muscles called the external sphincter ani form the wall of the anus and hold it closed. Glands release fluid into the anus to keep its surface moist. ❖ A plate-like band of muscles, called the elevator ani muscles, surround the anus and form the floor of the pelvis. A network of veins lines the skin of the anus.
P a g e | 29 Conclusion The digestive system starts working as soon as the food touches the lips and is ingested. The various organs work together to run this machinery. The nerves and hormones control the actions of the internal organs. There are mechanical and chemical processes that work simultaneously to digest the food and provide energy to the body. All the steps in this process are necessary and important for this machine to run in a healthy manner. While digestion occurs primarily in the oral cavity, stomach, and duodenum, absorption occurs primarily in the jejunum and ileum, where the method of transport into the circulatory system is slightly different depending on the compound. Finally, we discussed the three segments of the large intestine and their roles in water and salt absorption, as well as the temporary storage of waste products. Although the amount of information about the digestive system may seem overwhelming, the underlying concepts are relatively straightforward, and a systematic approach (like charts, tables, or flashcards) will help you manage this content. In the end, the digestive system’s main purpose is to break down energy-containing compounds and get them into the circulation so they can be used by the rest of the body. Equally as important are the systems the body has for getting rid of compounds from the blood. Buildup of waste products like ammonia, urea, potassium, and hydrogen ions can lead to serious pathology. For instance, hyperammonemia (buildup of ammonia in the blood) can lead to severe, permanent neurological damage. Hyperkalemia (buildup of potassium in the blood) can quickly cause a fatal heart attack. Temperature regulation is similarly important; both hyperthermia and hypothermia can lead to organ dysfunction and, ultimately, death. In the next chapter, we turn our attention to these regulatory systems: the renal system and the skin.
P a g e | 30 REFERENCES 1. Vanat.cvm.umn.edu 2. www.researchgate.net 3. www.webmd.com 4. www.cliffsnotes.com 5. www.ibdclinic.ca 6. www.medicinenet.com 7. www.phschool.com 8. www.medicinenet.com 9. https://www.radford.edu/~jkell/Di gestive%20system_Biology%20104. pdf 10. http://classvideos.net/anatomy/pdf /digestive_systempdf.pdf

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digestive system

  • 1.
    P a ge | 2 Index Sl. No. TOPIC Page No. 01 Introduction 03 - 04 02 What is the Digestive System 05 03 How does the digestive system work 06 – 09 04 General Structure of the Digestive System 10 05 Regions of the Digestive System 11 06 Functions of the Digestive System 12 - 13 07 Organization of the Digestive System 14 08 Muscular Movement of the GI Track 15 09 Mouth & Oral Cavity 16 10 Teeth 17 11 Salivary Glands 18 12 Stomach 19 13 Gastric Secretory Cells 20 14 Pancreas 21 15 Functions of The Liver 22 16 Small Intestine 23 17 Large intestine 24 18 Major Hormones of The Digestive Tract 25 19 Major Digestive Enzyme 26 20 Rectum 27 21 Anus 28 22 Conclusion 29 23 References 30
  • 2.
    P a ge | 3 INTRODUCTION The digestive system is a group of organs working together to convert food into energy and basic nutrients to feed the entire body. Food passes through a long tube inside the body known as the alimentary canal or the gastrointestinal tract (GI tract). The alimentary canal is made up of the oral cavity, pharynx, esophagus, stomach, small intestines, and large intestines. In addition to the alimentary canal, there are several important accessory organs that help your body to digest food but do not have food pass through them. Accessory organs of the digestive system include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas. To achieve the goal of providing energy and nutrients to the body, six major functions take place in the digestive system: • Ingestion • Secretion • Mixing and movement • Digestion • Absorption • Excretion The digestive system includes the digestive tract and its accessory organs, which process food into molecules that can be absorbed and utilized by the cells of the body. Food is broken down, bit by bit, until the molecules are small enough to be absorbed and the waste products are eliminated. The digestive tract, also called the alimentary canal or gastrointestinal (GI) tract, consists of a long continuous tube that extends from the mouth to the anus. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. The tongue and teeth are accessory structures located in the mouth. The salivary glands, liver, gallbladder, and pancreas are major accessory organs that have a role in digestion. These organs secrete fluids into the digestive tract.
  • 3.
    P a ge | 4 Food undergoes three types of processes in the body: ➢ Digestion ➢ Absorption ➢ Elimination Digestion and absorption occur in the digestive tract. After the nutrients are absorbed, they are available to all cells in the body and are utilized by the body cells in metabolism. The digestive system prepares nutrients for utilization by body cells through six activities, or functions. Ingestion The first activity of the digestive system is to take in food through the mouth. This process, called ingestion, has to take place before anything else can happen. Mechanical Digestion The large pieces of food that are ingested have to be broken into smaller particles that can be acted upon by various enzymes. This is mechanical digestion, which begins in the mouth with chewing or mastication and continues with churning and mixing actions in the stomach. Chemical Digestion The complex molecules of carbohydrates, proteins, and fats are transformed by chemical digestion into smaller molecules that can be absorbed and utilized by the cells. Chemical digestion, through a process called hydrolysis, uses water and digestive enzymes to break down the complex molecules. Digestive enzymes speed up the hydrolysis process, which is otherwise very slow. Absorption The simple molecules that result from chemical digestion pass through cell membranes of the lining in the small intestine into the blood or lymph capillaries. This process is called absorption.
  • 4.
    P a ge | 5 What is the Digestive System? A digestive system is a group of organs consisting of the central gastrointestinal (GI) tract and its associated accessory organs that break down food into smaller components so that nutrients can be absorbed and assimilated. This provides the necessary energy to sustain the body. The digestive system consists of organs that break down food, absorb its nutrients, and expel any remaining waste. Most of these organs make up the gastrointestinal (GI) tract. Food actually passes through these organs. The rest of the organs of the digestive system are called accessory organs. These organs secrete enzymes and other substances into the GI tract, but food does not actually pass through them. Digestive system is a demonic & Complex process in human body. The digestive tract starts at the mouth and ends at the anus. It is the breakdown of large insoluble food molecules which we eat. In the system the large insoluble food molecules breakdown into a small water-soluble food molecule. So that they can be absorbed through the small intestine into blood. It is a process of turning food into the nutrients. The system by which ingested food is acted upon by physical and chemical means to provide the body with absorbable nutrients and to excrete waste products; in mammals the system includes the alimentary canal extending from the mouth to the anus, and the hormones and enzymes assisting in digestion. The system of organs responsible for getting food into and out of the body and for making use of food to keep the body healthy. The digestive system includes the salivary glands, mouth, esophagus, stomach, liver, gallbladder, pancreas, small intestine, colon, and rectum. The digestive system's organs are joined in a long, twisting tube from the mouth to the anus. Inside this tube is a lining called the mucosa. In the mouth, stomach, and small intestine, the mucosa contains tiny glands that produce juices to help digest food. Two solid organs, the liver and the pancreas (both of which are embryologically derived from the digestive tract), produce digestive juices that reach the intestine through small tubes known as ducts. In addition, parts of other organ systems (for instance, nerves and blood) play a major role in the digestive system.
  • 5.
    P a ge | 6 How Does the Digestive System Work? The GI tract is a long tube of varying diameter beginning at the mouth and ending in the anus. The glands of the digestive system consist of the tongue, salivary glands, liver, gall bladder, and pancreas. Digestion can be divided into three stages – the oral phase (mouth), the gastric phase (stomach) and the intestinal phase (small intestine)– depending on the position of food within the digestive tract. At each stage, different nutrients are digested, under varying circumstances. The GI tract begins to form early during the development of the human body, in the third week after fertilization. Around the 16th day of development, the primitive gut is formed through invaginations of embryonic cells. The initial structures of the digestive system extend from the buccopharyngeal membrane to the cloacal membrane. The mouth forms when the buccopharyngeal membrane breaks down and opens the digestive tract to amniotic fluid. For the rest of fetal development, amniotic fluid is actively swallowed. Digestion works by moving food through the GI tract. Digestion begins in the mouth with chewing and ends in the small intestine. As food passes through the GI tract, it mixes with digestive juices, causing large molecules of food to break down into smaller molecules. The body then absorbs these smaller molecules through the walls of the small intestine into the bloodstream, which delivers them to the rest of the body. Waste products of digestion pass through the large intestine and out of the body as a solid matter called stool. Each part of your digestive system helps to move food and liquid through your GI tract, break food and liquid into smaller parts, or both. Once foods are broken into small enough parts, your body can absorb and move the nutrients to where they are needed. Your large intestine absorbs water, and the waste products of digestion become stool. Nerves and hormones help control the digestive process. Table below shows the parts of the digestive process performed by each digestive organ, including movement of food, type of digestive juice used, and food particles broken down by that organ.
  • 6.
    P a ge | 7 The digestive process Organ Movement Mouth Chewing Esophagus Peristalsis Stomach Upper muscle in stomach relaxes to let food enter, and lower muscle mixes food with digestive juice Small intestine Peristalsis Pancreas None Liver None Large intestine Peristalsis Mouth Digestion starts in the mouth before you have even taken the first bite of a meal. When you smell, see or think about tasty food your mouth will often start salivating. When you take your first bite this saliva mixes with the food to help break it down so that your body can absorb it. Chewing the food also aids this process while your tongue moves the food around to get it to your teeth and mix it with the saliva.
  • 7.
    P a ge | 8 Throat After leaving the mouth the food travels through your throat (also known as the pharynx) towards the esophagus. Esophagus The esophagus is a muscular tube which connects the throat and the stomach. It is about 25cms long and pushes food down towards your stomach through a series of contractions. It takes 2-3 seconds for the food to move through the esophagus. Just before the point at which the esophagus meets the stomach there is a valve which is designed to stop food from passing back upwards. Stomach The stomach is an organ which has strong muscular walls. When the food reaches the stomach, it is mixed with acid and powerful enzymes which break down the food. These gastric juices also work to kill bacteria that may be in the food. The stomach has strong wall muscles which help to turn the food into a liquid or paste. Small Intestine (Small Bowel) After leaving the stomach the food reaches the small intestine. The small intestine is a long tube (more than 6m long and 3.5-5cms wide) which is coiled up in the abdomen. It is made up of three segments - the duodenum, the jejunum and the ileum. Enzymes from the pancreas and bile from the liver work to continue the process of breaking down the food. Similar to the esophagus, contractions help to move the food through. The job of the duodenum is mostly to continue the process of breaking down the food while the jejunum and ileum are mostly responsible for the absorption of water and nutrients into the bloodstream. Around 90% of digestion and absorption takes place in your small intestine. This is why people with Crohn's disease in their small intestine often suffer from vitamin and mineral deficiencies. Food can spend around 4 hours here. Once the small intestine has absorbed all the nutrients any leftover food moves through to the large intestine (also known as colon).
  • 8.
    P a ge | 9 Large intestine (colon/large bowel) The large intestine is a wide (around 7-10cms) muscular tube that runs between the cecum (the first part of the large intestine) to the rectum (the last part of the large intestine). It is around 1.5m in length. The parts of the large intestine are the cecum (the beginning of the colon) the ascending (right) colon, the transverse (across) colon, the descending (left) colon and the sigmoid colon - which connects to the rectum. Food waste is moved through the large intestine by contractions and as it passes through more water and nutrients are absorbed so that a stool is formed. This stool is then stored in the sigmoid colon until the body empties it into the rectum. It normally takes around 36 hours for a stool to get through the large intestine. A stool is mostly made up of food debris and bacteria. When the descending colon becomes full it empties the contents into the rectum. Rectum The rectum connects the colon to the anus. It is around 20cm long and holds the stool until your body is ready to push it out. When a stool or gas reaches the rectum, sensors send a message to the brain to let it know that there is something in the rectum. Muscles, known as sphincters, act to hold in the stool until a message is sent from the brain to let the rectum know that the stool can be released. When this happens the muscles relax, releasing the contents. Anus The anus is the last part of the digestive tract and the lining of the upper anus works to detect rectal contents and tell your body whether the contents are liquid, gas or solid. The anus is made up of the pelvic floor muscles and two anal sphincters (internal and external muscle rings) work together to stop a stool from coming out. The external sphincter (voluntary) works to keep the stool in until we can get to the toilet while the internal sphincter (involuntary) stops us from going to the bathroom when we are asleep or unaware of the stool. These muscles relax as the stool is expelled.
  • 9.
    P a ge | 10 General Structure of the Digestive System The long continuous tube that is the digestive tract is about 9 meters in length. It opens to the outside at both ends, through the mouth at one end and through the anus at the other. Although there are variations in each region, the basic structure of the wall is the same throughout the entire length of the tube. The wall of the digestive tract has four layers or tunics: ❖ Mucosa ❖ Submucosa ❖ Muscular layer ❖ Serous layer or serosa The mucosa, or mucous membrane layer, is the innermost tunic of the wall. It lines the lumen of the digestive tract. The mucosa consists of epithelium, an underlying loose connective tissue layer called lamina propria, and a thin layer of smooth muscle called the muscularis mucosa. In certain regions, the mucosa develops folds that increase the surface area. Certain cells in the mucosa secrete mucus, digestive enzymes, and hormones. Ducts from other glands pass through the mucosa to the lumen. In the mouth and anus, where thickness for protection against abrasion is needed, the epithelium is stratified squamous tissue. The stomach and intestines have a thin simple columnar epithelial layer for secretion and absorption. The submucosa is a thick layer of loose connective tissue that surrounds the mucosa. This layer also contains blood vessels, lymphatic vessels, and nerves. Glands may be embedded in this layer. The smooth muscle responsible for movements of the digestive tract is arranged in two layers, an inner circular layer and an outer longitudinal layer. The myenteric plexus is between the two muscle layers. Above the diaphragm, the outermost layer of the digestive tract is a connective tissue called adventitia. Below the diaphragm, it is called serosa.
  • 10.
    P a ge | 11 Regions of the Digestive System At its simplest, the digestive system is a tube running from mouth to anus. Its chief goal is to break down huge macromolecules (proteins, fats and starch), which cannot be absorbed intact, into smaller molecules (amino acids, fatty acids and glucose) that can be absorbed across the wall of the tube, and into the circulatory system for dissemination throughout the body. Regions of the digestive system can be divided into two main parts: the alimentary tract and accessory organs. The alimentary tract of the digestive system is composed of the mouth, pharynx, esophagus, stomach, small and large intestines, rectum and anus. Associated with the alimentary tract are the following accessory organs: salivary glands, liver, gallbladder, and pancreas.
  • 11.
    P a ge | 12 Functions of the Digestive System The function of the digestive system is digestion and absorption. Digestion is the breakdown of food into small molecules, which are then absorbed into the body. The digestive system is divided into two major parts: • The digestive tract (alimentary canal) is a continuous tube with two openings: the mouth and the anus. It includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Food passing through the internal cavity, or lumen, of the digestive tract does not technically enter the body until it is absorbed through the walls of the digestive tract and passes into blood or lymphatic vessels. • Accessory organs include the teeth and tongue, salivary glands, liver, gallbladder, and pancreas. The treatment of food in the digestive system involves the following seven processes: 1. Ingestion is the process of eating. 2. Propulsion is the movement of food along the digestive tract. The major means of propulsion is peristalsis, a series of alternating contractions and relaxations of smooth muscle that lines the walls of the digestive organs and that forces food to move forward. 3. Secretion of digestive enzymes and other substances liquefies, adjusts the pH of, and chemically breaks down the food. 4. Mechanical digestion is the process of physically breaking down food into smaller pieces. This process begins with the chewing of food and continues with the muscular churning of the stomach. Additional churning occurs in the small intestine through muscular constriction of the intestinal wall. This process, called segmentation, is similar to peristalsis, except that the rhythmic timing of the muscle constrictions forces the food backward and forward rather than forward only. 5. Chemical digestion is the process of chemically breaking down food into simpler molecules. The process is carried out by enzymes in the stomach and small intestines. 6. Absorption is the movement of molecules (by passive diffusion or active transport) from the digestive tract to adjacent blood and lymphatic vessels. Absorption is the entrance of the digested food (now called nutrients) into the body. 7. Defecation is the process of eliminating undigested material through the anus.
  • 12.
    P a ge | 13 ➢ Ingestion - The oral cavity allows food to enter the digestive tract and have mastication (chewing) occurs, and the resulting food bolus is swallowed. ➢ Digestion:  Mechanical digestion – Muscular movement of the digestive tract (mainly in the oral cavity and stomach) physically break down food into smaller particles.  Chemical digestion – Hydrolysis reactions aided by enzymes (mainly in the stomach and small intestine) chemically break down food particles into nutrient molecules, small enough to be absorbed. ➢ Secretion – Enzymes and digestive fluids secreted by the digestive tract and its accessory organs facilitate chemical digestion. ➢ Absorption – Passage of the end – products (nutrients) of chemical digestion from the digestive tract into blood or lymph for distribution to tissue cells. ➢ Elimination – Undigested material will be released through the rectum and anus by defecation.
  • 13.
    P a ge | 14 Organization of The Digestive System ✓ Organs of the digestive system are divided into 2 main group: the gastrointestinal tract (GI tract) and accessory structures. ✓ GI tract is a continuous tube extending through the ventral cavity from the mouth to the anus – it consists of the mouth, oral cavity, oropharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus. ✓ Accessory structures include the teeth, tongue (in oral cavity), salivary glands, liver, gallbladder, and pancreas.
  • 14.
    P a ge | 15 Muscular movement of the GI tract ❖ Peristalsis – Wavelike movement that occurs from the oropharynx to the rectum, allowing GI tract to push food particles toward the anus. ❖ Mixing- Mixing motion in the oral cavity and stomach that allows the GI tract to repeatedly break down food into smaller particles, using mechanical digestion. ❖ Segmentation – regions of the small intestine contracting and relaxing independently, allowing the small intestine to digestive and absorb more efficiently.
  • 15.
    P a ge | 16 MOUTH & ORAL CAVITY ➢ Food enters the GI tract by ingestion. ➢ Food is broken down by mechanical digestion, using mastication. ➢ One chemical digestive process occurs where amylase enzyme in saliva breaks down polysaccharide into disaccharides. ➢ The tongue, made of skeletal muscle, manipulates the food during mastication. it also contains taste buds to detect taste sensations(intrinsic). ➢ Food particles are mixed with saliva during mastication, resulting in a moist lump called bolus for easier passage into or pharynx.
  • 16.
    P a ge | 17 Teeth ❖Adapted for mechanical digestion (mastication) in the oral cavity. ❖20 deciduous or primary teeth before the age of 6. ❖By age 7, 32 permanent or secondary teeth are developed & are divided into 4 types: incisors (for cutting), Canines (for tearing), Premolars (for crushing), and Molars (for grinding). these teeth follow the human dental formula of 2-1-2-3.
  • 17.
    P a ge | 18 SALIVARY GLANDS ➢ 3 pairs of salivary glands called parotid, submandibular, and sublingual gland secrete most of the saliva in the oral cavity, using salivary ducts. ➢ Saliva helps moisten the food during mastication, dissolve the food in forming the bolus, and help cleanse the teeth. ➢ Saliva consists of 99.5% water, the remaining 0.5% is dissolved substances including amylase enzyme (for chemically digesting carbohydrate), bicarbonate ion (HCO3 -; maintains pH of saliva at 6.5-7.5), and many electrolytes.
  • 18.
    P a ge | 19 Stomach A pouch-like organ primarily designed for food storage (for 2-4 hours), some mechanical and chemical digestion also occur.  Contains two sphincters at both ends to regulate food movement – cardiac sphincter near the esophagus, and pyloric sphincter near the small intestine.  Divided into 4 regions: cardiac stomach (or cardiac), fundic stomach (or funded), body of stomach, and pyloric stomach (or Pylorus).  Contain thick folds called rugae at its layer, for providing larger surface area for expansion, secretion, digestion, and some absorption.
  • 19.
    P a ge | 20 Gastric Secretory Cells ➢Chief cells: secrete pepsinogen (an inactive enzyme). ➢ Parietal cells: secrete hydrochloric and (HCl) and "intrinsic factor" (which helps absorption of vitamin B12 in the intestines). ➢ Mucous cells: secrete mucus and alkaline substances to help neutralize HCl in the gastric juice. ➢G cells: secrete a hormone called gastrin, which stimulates the parietal cells and overall gastric secretion.
  • 20.
    P a ge | 21 PANCREAS  Pancreas: most pancreatic enzymes are produced as inactivate molecules, or zymogens, so that the risk of self – digestion within the pancreas is minimized.  More than 98% of the pancreas mass is devoted to its exocrine function: the secretion of pancreatic juice by the pancreatic acini and their ductile cells. Ductile cells produce Sodium bicarbonate which helps neutralize the acidic gastric contents.  Acinar cells of the exocrine pancreas produce a variety of digestive enzymes to break down food substances into smaller absorbable molecules.  Only 2% of pancreas mass is devoted to the islets of Langham, which produce insulin and glucagon, hormones that regulate blood sugar and carbohydrate metabolism (they have opposite effects).
  • 21.
    P a ge | 22 Functions of The Liver ❖ Important in carbohydrate metabolism where hepatic cells conduct glycogenesis (converting glucose into glycogen), and glycogenolysis (breaking glycogen down to glucose). ❖ Also is critical in lipid metabolism where hepatic cells produce bile (for fat emulsification), oxidize fatty acids, synthesize various forms of lipids, and convert glucose to fatty acids (lipogenesis). ❖ Other functions of the liver include: Storage of glycogen, iron, and vitamins A, D, B12. ❖ Contains phagocytes to destroy damaged erythrocytes and foreign substances, using phagocytosis. ❖ Detoxifies harmful substances in the blood. ❖ Serves as a blood reservoir (contains 7% of blood volume).
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    P a ge | 23 SMALL INTESTINE ➢ A long tube, with a small diameter (about 1 inch), extending from pyloric sphincter to the ileocecal valve. ➢ Divided into Duodenum, Jejunum, and ileum. Secretions of Small Intestine: 1. Intestinal glands secrete a watery fluid that lack digestive enzymes but provides a vehicle for moving chyme to villi. Intestinal enzymes include: maltase digests maltose into glucose. sucrose digests sucrose into glucose and fructose. lactase digests sucrose into glucose and glucose. peptidases digest peptides into amino acids. lipases digest triglycerides into fatty acids and glycerol. Nucleases digest nucleotides into nitrogenous bases. Enterokinase converts trypsinogen into trypsin. 2. Digestive enzymes embedded in the surfaces of microvilli split molecules of sugars, proteins and fats. 3. Regulation of small intestine secretions: secretion is stimulated by gastric juice, chyme, and reflex stimulated by distension of the small intestinal wall. 4. Each villus contains blood capillaries to absorb water, glucose, amino acids, vitamins, minerals, and short-chain fatty acids, and also contains lymphatic capillaries called lacteals to absorb long – chain fatty acids in the forms of micelles. 5. Water is absorbed by osmosis, fatty acids are absorbed by diffusion (since they are fat-soluble), and most other nutrients (glucose, amino acids, & minerals) are absorbed by active transport.
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    P a ge | 24 Large intestine ➢ The last segment of the GI tract, with a large diameter (2-3 inches), extending from the ileocecal valve to the anus. ➢ Divided into cecum, ascending colon, transverse colon, descending colon, sigmoid colon, rectum, anal canal, and anus. ➢ The large intestine has little or no digestive function, although it secretes mucus. Its mucosa has no villa or microvillus, but contains numerous goblet cells for secreting mucus to aid in the formation of feces and maintain an alkaline condition.  mechanical stimulation and parasympathetic impulses control the rate of mucus secretion. ➢ The large intestine only absorbs water, electrolytes and some vitamins. ➢ Many bacteria inhabit the large intestine, where they break down certain indigestible substances and synthesize certain vitamins. ➢ feces are formed and stored in the large intestine. Defecation involves a reflex mechanism aided by voluntary contraction of the diaphragm, abdominal muscles, and the external anal sphincter.
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    P a ge | 25 MAJOR HORMONES OF THE DIGESTIVE TRACT 1. Gastrin: (Gastric & intestinal): released by Gastric cells, in response to the presence of food. Causes Gastric glands to increase their secretory activity. 2. Somatostatin: (Gastric inhibitory peptides - GIP): Inhibits secretion of acid by parietal cells. 3. Cholecystokinin: released by intestinal wall cells, in response to the presence of proteins and fats in the small intestine. It causes gastric glands to decrease their secretory activity and inhibits gastric motility; stimulation of pancreas to secrete digestive enzyme; stimulates gall – bladder to contract and release bile. 4. Secretin: released by cells in the duodenal wall, in response to acidic chyme entering the small intestine.
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    P a ge | 26 Major Digestive Enzyme ✓ Salivary enzyme: Begins carbohydrates digestion by breaking down starch and glycogen to disaccharides ✓ Gastric enzymes: Pepsin, from Gastric glands – Begins protein digestion. Lipase, from Gastric glands – Begins fat digestion. ✓ Pancreatic enzymes: Amylase, from pancreas – breaks down starch and glycogen into disaccharides. Lipase, from pancreas – breaks down fats into fatty acids and glycerol. ✓ Proteolytic enzymes: Trypsin, Chymotrypsin, and Carboxypeptidase from pancreas breaks down peptides into amino acids. Nucleases, from pancreas breaks down nucleic acids into nucleotides. ✓ Intestinal Enzymes: Peptidase, from mucosal cells, breaks down peptides into amino acids. Sucrase, maltase, and lactase, from mucosal cells, breaks down disaccharides into monosaccharides. Lipase, from mucosal cells, breaks down fats into fatty acid and glycerol. Enterokinase, from mucosal cells, (breaks down) converts trypsinogen into trypsin.
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    P a ge | 27 RECTUM ➢ The rectum is the concluding part of the large intestine that terminates in the anus. ➢ The average length of the human rectum may range between 10 and 15 cm. Its diameter can be compared to that of the sigmoid colon (the part of the large intestine nearest the rectum) at its onset. However, it becomes larger near the anus, where it forms the rectal ampulla. ➢ The key role of the rectal ampulla is to act as a temporary storehouse for feces. The expansion of the rectal walls causes the stretch receptors within the walls to stimulate the urge to defecate. If the defecation process is delayed, it may result in constipation. When the storage site becomes full, the intrarectal pressure causes the anal canal walls to dilate and expand. This results in the feces entering the canal. ➢ A rectal exam may be conducted to diagnose certain diseases. Certain types of cancers may be diagnosed by performing an endoscopy in the rectum. An endoscopy is a procedure where a doctor uses an endoscope — a small, flexible tube with a camera and light — to examine areas inside the body. Body temperature may also be obtained from the rectal area. In case of infants and babies, this is generally the most accurate method for determining actual body temperature.
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    P a ge | 28 Anus ❖ The anus is the opening where the gastrointestinal tract ends and exits the body. The anus starts at the bottom of the rectum, the last portion of the colon (large intestine). The anorectal line separates the anus from the rectum. ❖ Tough tissue called fascia surrounds the anus and attaches it to nearby structures. ❖ Circular muscles called the external sphincter ani form the wall of the anus and hold it closed. Glands release fluid into the anus to keep its surface moist. ❖ A plate-like band of muscles, called the elevator ani muscles, surround the anus and form the floor of the pelvis. A network of veins lines the skin of the anus.
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    P a ge | 29 Conclusion The digestive system starts working as soon as the food touches the lips and is ingested. The various organs work together to run this machinery. The nerves and hormones control the actions of the internal organs. There are mechanical and chemical processes that work simultaneously to digest the food and provide energy to the body. All the steps in this process are necessary and important for this machine to run in a healthy manner. While digestion occurs primarily in the oral cavity, stomach, and duodenum, absorption occurs primarily in the jejunum and ileum, where the method of transport into the circulatory system is slightly different depending on the compound. Finally, we discussed the three segments of the large intestine and their roles in water and salt absorption, as well as the temporary storage of waste products. Although the amount of information about the digestive system may seem overwhelming, the underlying concepts are relatively straightforward, and a systematic approach (like charts, tables, or flashcards) will help you manage this content. In the end, the digestive system’s main purpose is to break down energy-containing compounds and get them into the circulation so they can be used by the rest of the body. Equally as important are the systems the body has for getting rid of compounds from the blood. Buildup of waste products like ammonia, urea, potassium, and hydrogen ions can lead to serious pathology. For instance, hyperammonemia (buildup of ammonia in the blood) can lead to severe, permanent neurological damage. Hyperkalemia (buildup of potassium in the blood) can quickly cause a fatal heart attack. Temperature regulation is similarly important; both hyperthermia and hypothermia can lead to organ dysfunction and, ultimately, death. In the next chapter, we turn our attention to these regulatory systems: the renal system and the skin.
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    P a ge | 30 REFERENCES 1. Vanat.cvm.umn.edu 2. www.researchgate.net 3. www.webmd.com 4. www.cliffsnotes.com 5. www.ibdclinic.ca 6. www.medicinenet.com 7. www.phschool.com 8. www.medicinenet.com 9. https://www.radford.edu/~jkell/Di gestive%20system_Biology%20104. pdf 10. http://classvideos.net/anatomy/pdf /digestive_systempdf.pdf