Chapter 17-The Digestive System

1.  esophagus 2.  liver 3.  stomach 4. pyloric sphincter 5.  duodenum 6.  pancreas 7.  jejunum 8.  ileum 9.  cecum 10. appendix 11.  ascending colon 12.  descending colon 13.  sigmoid colong 14.  anus

Functions: mechanical and chemical breakdown of food        *absorption of nutrients Consists of alimentary canal and accessory organs

The Digestive System The digestive system is arranged as a series of organs along a tube called the gastrointestinal (GI) tract AKA alimentary canal

TABLE 15.1 REVIEW OF STRUCTURES OF THE GASTROINTESTINAL TRACT

FIGURE 15.1 The digestive system consists of a long tube, called the gastrointestinal tract, into which accessory glands release their secretions.

The Digestive System Along most of its length, the wall of the digestive system has four basic layers: the mucosa, the submucosa, the muscularis, and the serosa

FIGURE 15.2 Along most of its length, the wall of the digestive system has four basic layers: the mucosa, the submucosa, the muscularis, and the serosa.

Characteristics of the Canal 1.  Mucosa - protects tissues and carries absorption 2.  Submucosa - glands, blood vessels, nerves 3.  Muscular Layer - smooth muscle tissue, circular & longitudinal fibers, pushes food  (PERISTALSIS) 4.  Serosa (serous layer) - visceral perioneum, outer covering of the tube, lubricates surfaces (serous fluid)

Wall of the Alimentary Canal

The Digestive System Each organ helps to breakdown food into molecules small enough to be absorbed into the bloodstream and utilized by the body The digestive organs (mouth, esophagus, stomach, small intestine, and large intestine) are aided by several accessory organs (salivary glands, pancreas, and liver)

FIGURE 15.3a Adult human teeth. (a) The teeth slice, tear, and grind food until it can be swallowed.

Teeth   Incisors Cuspid (canine) Bicuspids Molars

FIGURE 15.3b Adult human teeth. (b) The structure of the human tooth is suited for its function of breaking food into smaller pieces.

The Digestive System Has Specialized Compartments Digestion begins in the mouth where food enters the digestive process The teeth bite, tear, and crush the food into smaller pieces, increasing the amount of surface area available for the action of digestive enzymes Teeth are alive and are surrounded by living tissue that physically supports the teeth and help maintains their health

FIGURE 15.4 part 1 The development of a dental cavity.

FIGURE 15.4 part 2 The development of a dental cavity.

The Digestive System Has Specialized Compartments Three pairs of salivary glands release secretions, called saliva, into the mouth The saliva moistens food, dissolves the chemicals in the food, and contains the enzyme, salivary amylase, which begins digestion of carbohydrates The tongue helps form food into a bolus, a soft mass of food, suitable for swallowing

Submandibular - below jaw Sublingual - under tongue Parotid - ear, cheek Submandibular - below jaw Sublingual - under tongue FIGURE 15.5 Three pairs of salivary glands release their secretions into the mouth. These secretions, collectively called saliva, make food easier to swallow, dissolve substances so they can be tasted, and begin the chemical digestion of starch.

TABLE 15.2 MAJOR DIGESTIVE ENZYMES

FIGURE 15.6 Swallowing consists of (a) voluntary and (b) involuntary phases.

The Digestive System Has Specialized Compartments The pharynx is where the nasal and oral cavities join During swallowing the epiglottis covers the trachea, or windpipe, preventing choking The esophagus is merely a tube that transports food from the mouth to the stomach; no digestive processes occur here Food is pushed through our digestive system by a series of muscular contractions called peristalsis Peristalsis

FIGURE 15.7 Peristalsis is a wave of muscle contraction that pushes food along the esophagus and the entire remaining GI tract. When circular muscles contract, the tube is narrowed and food is pushed forward. The longitudinal muscles in front of the bolus contract, shortening that region.

The Digestive System Has Specialized Compartments The stomach is responsible for the storage of food, turning food into a soupy mixture called chyme, and the addition of digestive enzymes and acids that begin chemical digestion of proteins

FIGURE 15.8a The structure of the stomach is well suited to its functions of churning food and digestive secretions, storing food, and beginning protein digestion. (a) The stomach wall has three layers of smooth muscle, each oriented in a different direction, that allow the stomach to churn and mix food with digestive secretions.

FIGURE 15.8b The structure of the stomach is well suited to its functions of churning food and digestive secretions, storing food, and beginning protein digestion. (b) Gastric glands in the wall of the stomach produce gastric juice, a mixture of hydrochloric acid and pepsin.

FIGURE 15.8c The structure of the stomach is well suited to its functions of churning food and digestive secretions, storing food, and beginning protein digestion. (c) The holes seen in this electron micrograph are the gastric pits, openings in the stomach wall through which gastric glands release their secretions.

The Digestive System Has Specialized Compartments Sphincter muscles allow food to enter the stomach from the esophagus and release it into the small intestine While in the stomach, hydrochloric acid (HCl) kills bacteria, begins the breakdown of protein, and activates the digestive enzyme pepsin The stomach itself is protected from being digested by this caustic combination of chemicals

The Digestive System Has Specialized Compartments The small intestine is where food is both digested into its smallest chemical components and where it is absorbed into the blood The complex chemicals of carbohydrates, proteins, fats and nucleic acids are broken down into their simplest forms in the small intestine by enzymes of the pancreas and the small intestine aided by bile from the gall bladder

The Digestive System Has Specialized Compartments Bile, produced in the liver and concentrated in the gallbladder, aids in the digestion and absorption of fats Occasionally, gallstones form from cholesterol and other substances

TABLE 15.3 REVIEW OF ACCESSORY STRUCTURES OF THE DIGESTIVE SYSTEM

FIGURE 15.13 Gallstones consist primarily of cholesterol that has precipitated from bile during storage in the gallbladder. A gallstone can intermittently or continuously block the ducts that drain bile into the small intestine. The photograph shows a gallbladder and several gallstones.

The Digestive System Has Specialized Compartments The lining of the small intestine is pleated and has numerous finger-like projections called villi to increase surface area In addition, each villus is covered with microvilli, giving the small intestine a velvety appearance called the brush border

FIGURE 15.9a The small intestine is specialized for the absorption of nutrients by structural modifications that increase its surface area. (a) Its wall contains accordion-like pleats called circular folds.

FIGURE 15.9b,c The small intestine is specialized for the absorption of nutrients by structural modifications that increase its surface area. (b) This electron micrograph shows the intestinal villi, the numerous fingerlike projections on the intestinal lining (the mucosa in part c).

FIGURE 15.9d,e The small intestine is specialized for the absorption of nutrients by structural modifications that increase its surface area. (d) The surface of each villus bristles with thousands of microscopic projections (of cell membranes) called microvilli. In the center of each villus, a network of blood capillaries, which carries away absorbed products of protein and carbohydrate digestion as well as ions and water, surrounds a lacteal (a small vessel of the lymphatic system) that carries away the absorbed products of fat digestion. (e) An electron micrograph of the microvilli that cover each villus.

The Digestive System Has Specialized Compartments Each villus contains a network of capillaries and a lacteal, a type of lymph vessel, that carry away the products of digestion; a process called absorption

FIGURE 15.10 The small intestine is the primary site for chemical digestion and absorption. The digestive products, such as monosaccharides, amino acids, fatty acids, and glycerol, enter absorptive epithelial cells of villi by active transport, facilitated diffusion, or diffusion. Monosaccharides and amino acids, along with water, ions, and vitamins, then enter the capillaries within the villus and are carried to body cells by the bloodstream.

The main function of the small intestine is to secrete chemicals that break down food and carry the nutrients away in the blood stream.  In one word: ABSORPTION

The Digestive System Has Specialized Compartments Digestive products are taken directly to the liver The liver monitors blood glucose levels, packages fat molecules with proteins to aid transport in the blood, and removes poisonous substances

FIGURE 15.11 The pancreas, liver, and gallbladder are accessory organs of the digestive system.

FIGURE 15.12 A portal system transports blood from one capillary bed to another. In the hepatic portal system the hepatic portal vein carries blood from the capillaries' network of the villi of the small intestine to the capillary beds of the liver. The liver monitors blood content and processes nutrients before they are delivered to the bloodstream.

The Digestive System Has Specialized Compartments Hepatitis is an inflammation of the liver caused by a virus

Hepatitis A is caused by eating food and drinking water infected with a virus called HAV.  While it can cause swelling and inflammation in the liver, it doesn't lead to chronic disease. Almost everyone who gets hepatitis A has a full recovery, some may need hospitalization Many people are recommended to receive hepatitis A vaccine, including people at increased risk for exposure to hepatitis A virus infection and people who are more likely to get seriously ill if infected with the virus

Hepatitis B is caused by the virus HBV Hepatitis B is caused by the virus HBV. It is spread by contact with an infected person's blood, semen, or other body fluid. And, it is a sexually transmitted disease (STD).     Some people never develop symptoms, others develop chronic symptoms that stay with them their whole life.  

Hepatitis C is caused by the virus HCV Hepatitis C is caused by the virus HCV. It is spread the same way as hepatitis B, through contact with an infected person's blood, semen, or body fluid (see above).    Like hepatitis B, hepatitis C causes swelling of the liver and can cause liver damage that can lead to cancer. Most people who have hepatitis C develop a chronic infection. This may lead to a scarring of the liver, called cirrhosis.  Blood banks test all donated blood for hepatitis C, greatly reducing the risk for getting the virus from blood transfusions or blood products.

TABLE 15.4 FORMS OF VIRAL HEPATITIS

The Digestive System Has Specialized Compartments Undigested and indigestible materials that have not been absorbed by the small intestine move to the large intestine The large intestine absorbs the water, ions, and vitamins found in these materials

FIGURE 15.14 The large intestine consists of the cecum, colon, rectum, and anal canal. It absorbs water from undigested material, forming the feces, and houses bacteria.

Function of Large Intestine Secretes mucus,  reabsorbs water, contains bacteria to aid in digestion  (intestinal flora) Mass Movements (defecation) - removes undigested food The main job is    WATER REABSORPTION...

The Digestive System Has Specialized Compartments Eventually the feces, now in a consistency suitable for elimination, pass from the colon into the rectum and leave the body through the anal canal

How to Make Fake Poop...

TABLE 15.5 EXAMPLES OF NEURAL CONTROLS ON DIGESTIVE ACTIVITY

TABLE 15.6 EXAMPLES OF HORMONAL CONTROL ON DIGESTIVE ACTIVITY

Nerves and Hormones Control Digestive Activities Gastrin, released by the stomach lining, and vasoactive intestinal peptide (VIP), secretin, and cholecystokinin, released by the lining of the small intestine, all cause the release of digestive enzymes The digestive process is partially controlled by physical sensations such as the stretching of the stomach or the detection of food particles in the organs