Digestive System Digestion includes six basic processes 1

Digestive System Digestion includes six basic processes: 1 ingestion 5. absorption 2. secretion 6. defecation 3. mixing and propulsion, 4. mechanical and chemical digestion, Mechanical digestion consists of movements of the gastrointestinal tract that aid chemical digestion. _ Chemical digestion is a series of catabolic (hydrolysis) reactions that break down larger carbohydrate, lipid, and protein food molecules into smaller molecules that are usable by the body cells.

Digestive System Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Digestive System i _ The breaking down of larger food molecules into smaller molecules is called digestion. _ The passage of these smaller molecules into blood and lymph is termed absorption. _ The organs that collectively perform digestion and absorption compose the digestive system and are usually divided into two main groups: those composing the gastrointestinal (GI) tract and accessory structures. _ The accessory structures include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.

Structure of the Wall The GI tract is composed of four layers or tunics: 1. Mucosa - The mucosa, forming the inner lining of the tract, is supplied with a rich network of blood vessels, nerve fibers and endocrine cells. 2. Submucosa Connective tissue that lies just below the mucosa. It contains blood vessels and nerves 3. Muscularis Contains two layers of muscle tissue. Important for peristalsis, mixing of food with digestive juices, and the mechanical breakdown of food 4. Serosa - Outermost covering, composed of visceral peritoneum. It is a continuous tube extending from the mouth to the anus. The loops of the digestive tract are anchored to the posterior wall of the abdominal cavity by a large double fold of peritoneal tissue called the mesentary.

Digestive Organs Mouth/Oral Cavity Pharynx Esophagus Stomach Small intestine Duodenum Jejunum Ileum Large intestine Rectum Anus

The Oral Cavity Roof of the mouth Hard Palate- anterior roof of the mouth Soft Palate- posterior roof of the mouth Sides of the mouth Cheeks- lateral walls of the oral cavity Floor of the mouth Tongue/ functions Swallowing Chewing Speech Taste Bitter, sour, sweet and salt i

Buccal Cavity Palatine Tonsils Tongue gullet – throat Hard Palate lips Uvula Soft Palate

The Oral Cavity _ Teeth l Functions • Divide the food into smaller pieces – Mastication- chewing • Two sets of teeth – Deciduous teeth- baby or milk teeth » Total = 20 » Start to erupt 6 months of age and are complete by 2 years » They loosen and fall out between ages 6 and 12.

The Oral Cavity _ Teeth - continued l Permanent teeth • Total = 32 • All permanent teeth but the third molars have erupted by the end of adolescence • Third molars emerge between 17 and 25 • They often fail to erupt and are said to be impacted

The Oral Cavity _ Types of teeth l l Incisors- biting Canine- tearing Premolars (bicuspids)- grinding Molars- grinding

The Mouth: Teeth Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman,

Wisdom Teeth

Molars _ Crown- upper portion of the tooth that is visible. It is made up of calcium phosphate, the biologically manufactured substance _ Neck- boundary between the root and crown _ Root- portion of the tooth that is embedded in the jawbone

Tooth Terms _ Enamel- covers the crown, very hard _ Dentin- bulk of the tooth, very similar to bone but does not have cells _ Gingiva- gums _ Pulp cavity- contains connective tissue, blood vessels and nerve fibers. Supplies nutrients to tooth tissues and provides tooth sensations _ Root canal- where pulp cavity extends into the root. Provides route for blood vessels and nerves

Pharynx

Pharynx- 3 Divisions _ Nasopharynx- behind the nose and palate _ Oropharynx- behind the mouth to the soft palate, above the hyoid bone _ Laryngopharynx- hyoid bone to the esophagus

Pharynx _ Uvula- a small muscular flap of tissue that hangs from the soft palate and prevents food from entering the nasal cavity during swallowing by closing off the posterior nares _ Tonsils- part of the lymphatic system l l Palatine tonsils- at the posterior end of the oral cavity are masses of lymphoid tissue Lingual tonsils- covers the base of the tongue

Pharynx and Tonsils

Salivary Glands i Saliva- secreted in response to sight, smell or thought of food, or the presence of food in the mouth There are three pairs of salivary glands: 1. parotid Largest gland, lies anterior to each ear 2. submandibular empty their secretions into the floor of the mouth 3. sublingual glands Smallest gland, located on the floor of the mouth inferior to the tongue. Empty their secretions into the floor of the mouth

Salivary Glands

Salivary Glands i

Saliva contents Water Salivary amylase- alkaline secretion, digests starch Amount per day- 1000 to 2000 m. L Ø Function of saliva Ø Prepares food for swallowing- mucus Ø Prevents mouth from drying out Ø Starts the breakdown of starch

animation 1 Swallowing i Deglutition the act of swallowing Bolus the ball of food Involuntary nervous response Starts as a voluntary action but shortly becomes an involuntary action Epiglottis the covering of the opening to the windpipe

Esophagus _ Location: pharynx to the stomach _ Length: 10 inches _ Histology: stratified squamous epithelium l Mucous glands- secrete mucous _ Muscles: Upper 1/3 = skeletal muscle _ Lower 1/3 = smooth muscle _ Middle 1/3 = mixture of both _ Function: carries food from the mouth to the stomach _ Peristalsis: involuntary muscular contractions that move food along the esophagus

Motility: Peristalsis Copyright © 2001 Benjamin Cummings, an imprint of Addison Wesley Longman, Inc.

Stomach

Stomach Man Eating Location: left side and high up in the abdomen. It is “J” shaped Functions: Temporary storage of ingested food Mechanical breakdown of ingested food Breakdown of chemical bonds in food items by acids and enzymes Production of intrinsic factor needed for vitamin B 12 absorption Can store 4 liters of material Food remains in stomach for 2 -6 hours Four divisions of the stomach Cardia- connects the esophagus to the stomach Fundus- bulge of the stomach superior to the cardia Body- large area between the fundus and the curve of the “J” Pylorus- connects the stomach to the small intestine

Stomach

Stomach Sphincter Muscles _ Cardiac sphincter- from the esophagus _ Pyloric sphincter- connects to the small intestine

Rugae Stomach Rugae _ Rugae l Folds of the stomach, they smooth out and disappear as the stomach becomes distended from food

Muscles of the Stomach _ _ Longitudinal muscles Circular muscles Inner oblique muscles These muscles add strength and assist in the mixing and churning of food

Stomach Muscles

Physiology of the Digestive System _ Stomach l Mechanical digestion - churning or turning the food and mixes it until it becomes chyme (semi-fluid mixture of food) l Histology- simple columnar epithelium with mucous cells

Gastric Secretions Three types of gastric glands 1. Mucus cells Secretion - mucus- watery substance Function - Protects stomach lining i Mc. Graw-Hill i 2. Chief cells Secretion - Pepsinogen (inactive form of pepsin); made active in the presence of HCl Function - begins digestion of proteins into polypeptides

Gastric Secretions - cont. 3. Parietal cells Secretion - HCl & intrinsic factor (p. H. 9 -1. 5) Function - Kills bacteria, absorption of vitamin B 12, softens meat & bones, activates pepsinogen, HCl, pepsin, proteins and shorter chain amino acids 4. Intrinsic factor Vitamin B 12 Function- essential for the normal development of red blood cells Malfunction of intrinsic factor = pernicious anemia

Hormones that control Gastric Secretions _ Hormone: Gastrin _ Location of hormone: pyloric region of stomach _ When released: when solid food enters the stomach _ Where does it go? To the blood stream back to the stomach _ What does it do? Stimulates the glands to produce gastric juice

Regulation of Gastric Secretions Three Phases 1. Cephalic phase- parasympathetic reflex (30 -50%) Anticipate food, medulla oblongata, taste, smell, sight And thought of food 2. Gastric phase (40 -50%) Food in the stomach, stimulates more gastrin which in turn stimulates more gastric juices 3. Intestinal phase (5%) Chyme entering the small intestine triggers this phase. This inhibits gastric juices and more gastrin is secreted Stomach Absorption- absorbs only water, certain salts and lipid soluble drugs and also alcohol.

Small Intestine _ Diameter: 4 cm (1. 6 in) to 2. 5 cm (1 in. ) _ Length: 20 feet _ Functions: l l Complete the digestion of food Absorb the end products of digestion into the blood and lymph Secrete hormones that help control the production of pancreatic juice, bile and intestinal juice Control the amount of fluid and electrolytes lost from the body

Small Intestine

3 Division of the Small Intestine _ Duodenum: (latin for 12) l l Length: 10 inches Function: receives chyme from the stomach and digestive secretions from the pancreas and liver _ Jejunum: l l Length: 8 feet Function: bulk of chemical digestion and nutrient absorption

Duodenum valve i Gallstones Duodenum Bile i

Jejunum

3 Division of the Small Intestine _ Ileum l l Length: 12 feet Function: longest section, ends at the ileocecal valve (a sphincter valve) which controls the flow of material from the ileum into the cecum, the first part of the large intestine.

Ileum

Villi and the Small Intestine _ Three parts of the villi: l l l Arteriole Venule Lymph vessel (lacteal)- absorbs fatty acids _ Villi area covered l Larger than the size of a tennis court _ Function l Increase surface area for absorption (600 times)

Villi and the Small Intestine _ Goblet cells l Mucous secreting cells _ Digestive enzymes in the microvilli l l l Peptidase- proteins Maltase, sucrase, lactase- disaccharides Lipase- lipids

The Wall of the Small Intestine Copyright © 2001 Benjamin Cummings, an imprint of

Villi Microvilli

Hormones secreted by Intestinal Cells _ 1. Secretin l Stimulates the pancreas to secrete a fluid high in bicarbonate ions that help neutralize chyme _ CCK (cholecystokinin) l Stimulates the release of bile from the gallbladder and the secretion of digestive enzymes from the pancreas

3 solutions in the small intestine _ The following solution mix with chyme from the stomach in the small intestine: l l l Bile from the liver Pancreatic juice from the pancreas Intestinal juice from glands in the wall of the intestines

Digestion in the Small Intestine _ Bile l l l Produced in the liver Stored in the gallbladder Contains: water, ions, cholesterol, sodium bicarbonate ions (NO ENZYMES) • These act as emulsifying agents- which lower the surface tension of fats, forming small droplets l l Green color comes from broken down hemoglobin Bilirubin- main end product produced by the decomposition of hemoglobin

Digestion in the Small Intestine _ Bile- cont. l l Travels to the small intestine by the bile duct Large amounts of bile are released from the gallbladder in the presence of fatty acids The hormone that causes the gallbladder to contract and eject bile is CCK (cholecystokinin) The stimulus for the release of CCK is fatty acids and amino acids in the duodenum

Digestion in the Small Intestine _ Bile- cont. l l If the gallbladder is removed, there is no storage of bile so it is constantly secreted into the small intestine by the liver Gallstones are hard deposits of cholesterol and or calcium

Gallbladder i The gallbladder is a sac located on the posterior surface of the liver. i The gallbladder stores and concentrates bile. Cholecystokinin (CCK) stimulates the release of bile into the common bile duct.

Gallstones

Pancreas

Pancreas Location: left side behind the stomach Two types of glands: Exocrine gland- secretes materials onto the surface or into a cavity Digestive enzymes (do most of the work in the SI) Amylase- starch to maltose Trypsin- proteins Lipase- fat Nucleases- nucleic acids Sodium bicarbonate ions Neutralizes the chyme p. H of the contents of the small intestine are slightly alkaline- 7. 5 -8

Pancreas _ Endocrine gland- secretes materials into the blood l Regulates blood sugar levels • Insulin • Glucagon l Hormone secreting cells of the pancreas • Beta cells- insulin • Alpha cells- glucagon • Delta cells- somastatin- inhibits the release of both insulin and glucagon

Pancreas _ Pancreatic secretion control l Sight l Sound l Food in the mouth l Hormones • Secretin • Secreted from the intestinal mucosa • When the intestinal content is acidic, secretin aacts as a chemical messenger causing the pancreas to secrete enzymes in response. As a result, the alkalinity of the pancreatic juices neutralizes the acid content in the SI

Liver _ Location: right hypochondriac and epigastric abdominopelvic regions _ Materials carried to the liver from the SI for storage l Vitamins l Minerals l Nutrients _ Functions l Secretes bile l Synthesizes bile salts l Sythesizes plasma proteins l Storage of glucose, iron, vitamins l Detoxification of toxic compounds l Carbohydrate, lipid and proteins metabolism l Filters damaged RBC’s, bacteria and other materials from the blood

Liver i

Liver _ Liver secretions for digestion l Bile- stored in the gallbladder • Water, bicarbonate ions, bilirubin, cholesterol, lipids • Collectively known as bile salts l Emulsification • Creates tiny droplets of fat (which coats the lipid to increase surface area for the lipid enzyme to attack

Large Intestine _ AKA: Colon _ Length: 5 feet _ 3 divisions: l Cecum- vermiform appendix- vestigal organ l Colon • Ascending colon • Transverse colon • Descending colon – Sigmoid colon- S-shaped curve l Rectum- thick muscular layer l Anal canal • Internal sphincter valve- smooth muscle • External sphincter valve- skeletal muscle (voluntary)

Large Intestine Figure 14. 12 Slide 14. 13 A

Large Intestine _ Functions: l l l Large quantities of water are reabsorbed Storage of waste NO digestion of food material _ Solid waste of the large intestine: feces _ Most of the material that enters the large intestine is undigested fiber _ Millions of bacteria inhabit the large intestine and are carried out of the body with the feces

Large Intestine _ Bacteria feed on undigested material in the large intestine and release gas as a waste product _ They also synthesize vitamin K and certain B vitamins which are absorbed into the bloodstream _ The reddish brown color of feces comes from bilirubin from a breakdown of hemoglobin