The DIGESTIVE System

Digestion The breaking down of food by both mechanical and chemical means Mechanical Digestion - various movements of the alimentary canal that aid in chemical digestion Grinding of teeth to soften food Churning of food by smooth muscles to mix with digestive enzymes Chemical Digestion - series of catabolic reactions that break down large molecules into smaller molecules

Absorption The passage of digested food from the alimentary canal into the cardiovascular and lymphatic systems for distribution to body cells

Defecation (Excretion) The elimination of indigestible substances from the alimentary canal

Ingestion Taking food into the body (EATING)

Movement (Propulsion) Passage of food along the alimentary canal

Types of Digestion Chemical digestion is the chemical breakdown of larger nutrient molecules to smaller ones which can be absorbed and used by the body. Mechanical digestion is the physical breakdown of food into smaller pieces.

Gastrointestinal Tract (Alimentary Canal) A continuous tube running through the ventral body cavity extending from the mouth to the anus Organs of the Alimentary Canal mouth - pharynx - esophagus stomach - small intestine - large intestine Accessory Organs teeth salivary glands gallbladder - tongue - liver - pancreas

Structures of the Digestive System

Mouth (Oral or Buccal Cavity) Cheeks Lips (Labia) Vestibule Hard Palate Soft Palate Uvula Tongue Papillae Lingual Frenulum

Oral Cavity

Pharynx Also called the throat Serves as a passageway for food and air Also helps in the formation of words

Esophagus Muscular tube located posterior to the trachea About 10 inches long Does not participate in digestive processes - simply a transport corridor Food is pushed through the esophagus by peristaltic action Forces food down into the stomach Esophageal hiatus - opening in the diaphragm for the esophagus

Lining of the Esophagus

Stomach J-shaped enlargement of the digestive tract located just below the diaphragm Superior portion - continuation of the esophagus Inferior portion empties into the duodenum Position and size of the stomach varies from individual to individual

Histology of the Stomach Composed of the same four tissue types as the other structures of the alimentary canal Mucosa: inner layer lined with epithelium attached to connective tissue protects tissues of the canal and carries on secretion and absorption. Submucosa: loose connective tissue housing blood and lymph vessels and nerves nourishes the surrounding layers of the canal. Muscularis: muscular layer (made up of skeletal and smooth muscle) propels food through the canal. Serosa: composed of visceral peritoneum protects underlying tissues and secretes serous fluid to keep the canal from sticking to other tissues in the abdominal cavity. When the stomach is empty the mucosa lie in large folds called rugae Mucosa contains millions of tiny openings called gastric pits that open into gastric glands Secretes digestive enzymes and a fluid called gastric juice (2-3 liter per day)

Histology of the Stomach

Small Intestine The next part of the alimentary canal Divided into three sections the duodenum, jejunum, and ileum. In the duodenum, chemical digestion is completed. The majority of nutrients are absorbed in the jejunum and ileum.

Large Intestine The last part of the alimentary canal Responsible for the absorption of water, compaction of feces, and the production of Vitamin K

Accessory Organs The accessory organs include the liver, gallbladder, pancreas, and salivary glands which will be discussed in more detail later on in this unit.

Salivary Glands Paired accessory structures that lie outside the oral cavity Secrete their contents (saliva) into ducts that empty into the mouth Parotid Glands - underneath the ears Submandibular Glands - under the mandible Sublingual Glands - under the tongue https://youtu.be/bv4zenvxfhk

Salivary Glands

Saliva Fluid secreted by the salivary glands 99.5% water.5% solutes chlorides -bicarbonates - sodium potassium - phosphates - urea uric acid - globulin -mucin serum albumin Salivary amylase - digestive enzyme begins carbohydrate digestion in the mouth Lysozyme - destroys bacteria in the mouth

Digestion in the Mouth Mechanical Digestion Chewing (Mastication) Tongue manipulates the food Teeth grind up the food and mix it with saliva The result of mechanical digestion is a soft flexible mass of food called a bolus Chemical Digestion Salivary amylase initiates the breakdown of carbohydrates Only chemical digestion in the mouth

Teeth Accessory structures of the digestive system Deciduous teeth (baby teeth) - 20 Permanent teeth - 32 Incisors (8) - 4 on top, 4 on bottom chisel shaped - front of mouth Canines (4) - 2 on top, 2 on bottom sharp pointed tearing teeth Premolars (8) - 4 on top, 4 on bottom Molars (12) - 6 on top, 6 on bottom broad, flat, crushing teeth

Teeth

Portions of the Tooth Crown - exposed portion of the tooth above the gum line Neck - constricted junction line in the tooth between the crown and the root Root - one to three projections of the tooth that are embedded in the sockets of the alveolar processes of the mandible and maxillae

Portions of the Tooth

Composition of Teeth Enamel - outermost portion of the tooth, protects the tooth from wear and tear the hardest substance in the body Dentin - calcified connective tissue that gives the tooth its basic shape and rigidity Pulp Cavity - large cavity enclosed by the dentin that is filled with pulp Cementum - a bone-like substance that covers the dentin of the root

Tooth Structures

Root Canal

Periodontal Ligament An area of dense fibrous connective tissue attached to the socket walls and the cemental surface of the roots of the teeth Anchors teeth in position Serves as a shock absorber when chewing

Swallowing (Deglutition) Moving food from the mouth to the stomach Voluntary Stage - bolus is moved through the mouth into the oropharynx Pharyngeal Stage - involuntary passage of the bolus through the pharynx and into the esophagus Esophageal Stage - involuntary passage of the bolus through the esophagus and into the stomach

Swallowing

Deglutition

Digestive Processes Mastication chewing Maceration muscular waves in the stomach which mix food with gastric juice to form a liquid paste called chyme. Segmentation Short, small mixing movements of the alimentary canal.

Digestive Processes Peristalsis wave-like smooth muscle contractions which help to propel food and wastes along the alimentary canal. Haustral Churning movement of wastes along the large intestine by the contraction of the pouches or the haustra.

Features of the Stomach Cardiac Region where the stomach is connected to the esophagus. Fundus the rounded, superior area of the stomach that acts as a temporary storage for food. Body the large, central portion of the stomach below the fundus.

Features of the Stomach Pylorus the narrow, inferior region of the stomach. Rugae the folds in the stomach that allow for stretching of the stomach with the intake of food. Pyloric Sphincter the one-way valve located between the stomach and the duodenum.

Structures of the Stomach

Stomach Structures

Secretory Cells of the Gastric Glands Chief Cells Digestive enzymes Pepsinogen activated by HCl and converted to Pepsin Parietal Cells HCl Intrinsic Factor (absorption of Vitamin B12) Goblet Cells Secrete mucus to protect the stomach mucosa from the acidic environment

Gastric Gland

Mechanical Digestion in the Stomach Several minutes after food enters, the stomach generates mixing waves that churns the food inside - maceration Food mixes with gastric juices and is converted into a thin liquid called chyme

Chemical Digestion in the Stomach Cephalic Phase - reflexes initiated by sensory receptors in the head sight smell taste thought of food Gastric Phase - sensory receptors in the alimentary canal and stomach initiate nervous and hormonal chemical digestive processes Intestinal Phase - secretion of stomach enzymes that removes nutrients from food

Absorption in the Stomach The stomach does not participate in the absorption of food molecules into the blood However, some substances can be absorbed through the stomach wall Water Weak glucose concentrations Electrolytes Certain drugs (aspirin) Alcohol

Pancreas Oblong gland that lies posterior to the greater curvature of the stomach Connected by ducts to the duodenum Composed of clusters of glandular epithelial cells Two main types of Pancreatic Cells: Pancreatic Islets-Islets of Langerhans (1%) Hormones: insulin, glucagon, somatostatin Acini Cells (99%) Digestive pancreatic enzymes

Pancreas

Pancreatic Juice Alkaline mixture of fluid and digestive enzymes from the acini cells Pancreatic digestive enzymes: Pancreatic amylase carbohydrate digestion Pancreatic lipase fat digestion Chymotrypsin-Trypsin-Carboxypeptidase protein digestion Nucleases nucleic acid digestion Regulated by the intestinal hormones secretin and cholecystokinin

Liver Located just under the diaphragm on the right side of the body Largest organ of the abdominal-pelvic cavity Weighs about 1.4 kgs (3 lbs) Called the chemical factory of the body Completely covered by the peritoneum and a dense layer of connective tissue beneath the peritoneum

Liver Wedged beneath the lower right rib cage and occupying much of the upper right quadrant of the abdomen Largest organ in the human body Weighs between 2.6 and 3.5 pounds and measures about 8 inches across (smaller in women and larger in men) Most complex organ in the body in terms of function

Liver Functions of the liver can be divided into three primary categories: Metabolism Filtration of blood Secretion

Liver Functions of the liver can be divided into three primary categories: Metabolism breakdown of nutrients and drugs brought to the liver in blood coming from the intestinal tract transported by the blood from the liver to other tissues OR stored in the liver for future use Example: glycogen (remains in the liver until it is summoned and released to supply energy needs) Filtration of blood Secretion

Liver Functions of the liver can be divided into three primary categories: Metabolism Filtration of blood 1,450 milliliters of blood circulate through the liver every minute Liver not only extracts wastes and toxic matter from the blood but also regulates overall blood volume. The extensive network of blood vessels within the lobes of the liver can hold about 10 percent of the body s blood volume The volume of blood it stores is determined primarily by the pressure of blood entering and leaving the organ, with low pressures triggering the release of stored blood and vice versa Secretion

Liver Functions of the liver can be divided into three primary categories: Metabolism Filtration of blood Secretion Each day the liver secretes roughly one quart of bile Contains bile salts that facilitate the digestion of fats Bile also plays a central role in waste removal, picking up waste products from the blood and transporting them through a series of ducts for excretion through the intestine. Jaundice a yellowing of the eyes and skin, often occurring in newborns arises as a result of overproduction of bile, blockage of bile movement through the liver s duct system, or leakage of bilirubin (the pigment of bile) into the bloodstream

Anatomy of the Liver Right Lobe - largest lobe of the liver Located on the lateral-right side of the body Caudate Lobe - posterior portion of right lobe Quadrate Lobe - inferior portion of right lobe Left Lobe - smaller, medial lobe of the liver Falciform Ligament - separates the right and left lobes of the liver and anchors it to the diaphragm and anterior abdominal wall

Liver and Pancreas

Lobules of the Liver Smaller functional units of the liver Hepatocytes in the lobules produce and secrete a yellowish, brownish, or olive green liquid called bile (1 quart daily) Composed of bile salts and pigments, lecithin, and several ions ph of 7.6-8.6 Excretory product and digestive secretion Assists in the breakdown of fat molecules (emulsification) Principle bile pigment is bilirubin

Functions of the Liver Metabolism of carbohydrates, fats, and proteins Removal of drugs and hormones Excretion of bile Synthesis of bile salts Storage of vitamins, minerals, and food molecules Phagocytosis of old worn out red and white blood cells Activation of Vitamin D

The Gallbladder A pear shaped sac about 7-10 cm long Located on the inferior surface of the liver Stores and concentrates bile until it is needed by the small intestine for the emulsification of fat

Gallbladder

Bile Pathway

The Small Intestine Duodenum - the beginning of the small intestine where it attaches to the stomach First 6 inches Jejunum - the portion of the small intestine right after the duodenum Normally about 8 ft. long Ileum - the final portion of the small intestine About 12 ft. long Ileocecal valve

The Small Intestine

Wall of Duodenum

Villi in Duodenum

Chemical Digestion of the Small Intestine Complex series of chemical events that results in the breakdown of carbohydrates, fats, and proteins Result of the collective effort of pancreatic juice, bile, and intestinal juice which contain digestive enzymes Results in absorption - passage of digested nutrients into the blood or lymph

Mechanisms to Increase Absorption by the Small Intestines Folds in the intestinal walls of the mucosa layer of tissue (Plicae Circulares) Villi arrangement of tissue of mucosa layer Lacteals - blood capillaries and lymphatic vessels associated with each villi Microvilli arrangement of epithelial cells of the mucosa

Plicae Circulares

Villi of Small Intestine

Villi with Lacteal

Lining of Ileum

Absorption in the Small Intestine 90% of absorption takes place within the small intestine Remaining 10% occurs in the stomach and large intestine Absorption of nutrients occurs through the villi by means of: diffusion facilitated diffusion osmosis active transport

Small Intestine Absorption

Nutrient Absorption

Additional Components of the Small Intestine Intestinal Juice - slightly alkaline secretion (ph 7.6) secreted by intestinal glands rapidly absorbed by the villi and provides a mechanism for absorption of substances in chyme Peyer s Patches - lymphatic glands of the small intestine Brunner s Glands - mucus secreting glands of the small intestine

Mechanical Digestion of the Small Intestine Segmentation - localized contraction of muscles of the small intestine in areas containing food Rate of about 12-16 contractions/minute Sloshing of chyme back and forth within the intestinal lumen Peristalsis - rhythmical contraction of muscles of the small intestines that propels chyme through the intestinal tract

The Large Intestine About 1.5 m (5 ft) in length Cecum - beginning of the large intestine Vermiform appendix Colon - large tube-like portion of large intestine Ascending colon Descending colon Rectum Anal Canal Anus - Transverse colon - Sigmoid colon

Large Intestine Structures

Functions of the Large Intestine Completion of absorption Reabsorption of water Manufacture of certain vitamins Formation of feces Expulsion of feces from the body

Histology of the Large Intestine Walls of the large intestine contain no villi or permanent circular folds in the mucosa layer Epithelial tissue layer contain numerous goblet cells (secretes mucus) Lubricates the colonic contents as it passes through the large intestine

Haustra - series of characteristic pouch like structures that run the entire length of the colon Taenia Coli - bands of smooth muscle that are arranged longitudinally along the length of the colon Anal Columns - parallel ridges of mucosa in the anal canal which reduces friction with feces during defecation

Large Intestine Histology

Mechanical Digestion in the Large Intestine Haustral Churning - the relaxation and contraction of the individual segments of the colon Peristalsis - rhythmical contraction of the colon that moves the contents along through the length of the colon Mass Peristalsis - a strong peristaltic wave that begins about the middle of the transverse colon and drives the colonic contents into the rectum

Chemical Digestion in the Large Intestine Last stage of digestion Due to bacterial action in the large intestine Bacteria ferment any remaining carbohydrates and release hydrogen, carbon dioxide, and methane gas Also converts any remaining proteins into amino acids Absorbs any remaining water and electrolytes

Feces Formation in the Large Intestine By the time chyme has remained in the large intestine for 3-10 hours it has become a solid or semi-solid and is known as feces Consists of water, inorganic salts, sloughed off epithelial cells, products from bacterial decomposition, and indigestible parts of food

Defecation The emptying of the rectum Diarrhea frequent defecation of liquid feces Constipation infrequent or difficult defecation Flatus Expulsion of methane gas from the colon Hemorrhoids Enlarged veins in the lining of the anal canal

Digestive System Diseases and Homeostatic Imbalances

Appendicitis Inflammation of the vermiform appendix Can be caused by an obstruction of the lumen of the appendix by fecal material, a foreign body, stenosis, kinking of the organ, or carcinoma

Appendicitis Symptoms Abdominal pain that: occurs suddenly, often waking a person at night gets worse in a matter of hours begins near the belly button and then moves lower and to the right McBurney s Point Rebound tenderness gets worse when moving around, taking deep breaths, coughing, or sneezing

Cirrhosis of the Liver Distorted or scarred liver tissue due to chronic inflammation Commonly caused by hepatitis, chemical exposure, parasites, and alcoholism Symptoms include: jaundice, bleeding, edema, and increased sensitivity to drugs and chemicals

Cirrhosis of the Liver

Tumors of the Digestive System Can occur in all areas of the digestive system Can be malignant or benign Colorectal Cancer 3rd most common cause of cancer for both males and females Overall mortality rate is over 60% Factors contributing to colorectal cancer include genetic predisposition, diet high in fat, protein, insufficient dietary fiber, and low calcium and selenium in the diet

Gall Stones Crystallization of bile in the gallbladder Can block the bile duct causing intense pain Usually treated with gall stone dissolving drugs, lithotripsy, or surgery

Gall Stones

Hepatitis Inflammation of the liver Can be caused by viruses, drugs, and certain chemicals including steroids and alcohol Many different types of Hepatitis including: Hepatitis A (Infectious Hepatitis) Hepatitis B (Serum Hepatitis) Hepatitis C

Hepatitis A Infectious hepatitis Caused by Hepatitis A virus Usually spread when a person ingests fecal matter even in microscopic amounts from contact with objects, food, or drinks contaminated by the feces, or stool, of an infected person Can range in severity from a mild illness lasting a few weeks to a severe illness lasting several months Generally a mild disease of children and young adults Usually improves without treatment Does not become chronic Characterized by anorexia, malaise, jaundice, nausea, diarrhea, fever, and chills

Hepatitis B Can be acute or chronic (see Hepatitis C for explanation) Caused by the Hepatitis B virus Spread when blood, semen, or other infected body fluid enters the body of a person who is not infected (50-100 more infectious than HIV) Birth (spread from an infected mother to her baby during birth) Sex with an infected partner (primary cause of Hep B in the U.S) Sharing needles, syringes, or other drug-injection equipment Sharing items such as razors or toothbrushes with an infected person Direct contact with the blood or open sores of an infected person Exposure to blood from needlesticks or other sharp instruments NOT spread by sharing eating utensils, breastfeeding, hugging, kissing, holding hands, coughing, or sneezing But CAN be spread in rare cases to babies when they have received food prechewed by an infected person Many people with chronic Hepatitis B virus infection do not know they are infected since they do not feel or look sick they still can spread the virus to others and are at risk of serious health problems themselves

Hepatitis C Can be acute or chronic Caused by the Hepatitis C virus Spread primarily through contact with the blood of an infected person Sharing needles, syringes, or other equipment to inject drugs Needlestick injuries in health care settings Being born to a mother who has Hepatitis C Sharing personal care items that may have come in contact with another person s blood, such as razors or toothbrushes (uncommon) Having sexual contact with a person infected with the Hepatitis C virus (uncommon) NOT spread by sharing eating utensils, breastfeeding, hugging, kissing, holding hands, coughing, or sneezing or through food or water Acute short-term illness that occurs within the first 6 months after someone is exposed to the Hepatitis C virus For most people, acute infection leads to chronic infection Chronic long-term illness that occurs when the Hepatitis C virus remains in a person s body can last a lifetime and lead to serious liver problems, including cirrhosis (scarring of the liver) or liver cancer

Obesity Clinically classified as obese if: > 30% of projected body weight as determined height and frame size doesn t factor in Body Composition Currently over 50% of U.S. population is clinically classified as obese 14% of all male cancers linked to obesity 20% of all female cancers linked to obesity

U.S. surgeon general has said Obesity is the second most serious threat to the health of Americans A serious risk factor for: Heart Disease - Diabetes Hypertension - Cancers Respiratory Disorders Endocrine Disorders Gastrointestinal Disorders Urinary and Reproductive System Disorders

Hemorrhoids Enlarged veins in the lining of the anal canal Common problem, can be painful, but usually not serious Too much pressure on the veins in the pelvic and rectal area causes hemorrhoids Pregnancy Straining Constipation Being overweight Symptoms of both internal and external hemorrhoids include: Bleeding during bowel movements Itching Rectal pain

Dysentery Severe infection of the intestinal wall Leads to severe diarrhea with mucus or blood in the feces Untreated dysentery can be life-threatening, especially if the infected person cannot replace lost fluids fast enough Two main causes: Shigella (bacterium) shilgellosis Entamoeba histolytica (amoeba) Tends to be associated with the Tropics

Peptic Ulcers Crater like lesions that develop in the gastrointestinal tract Gastric Ulcers ---> Stomach Duodenal Ulcers ---> Duodenum Commonly caused by hypersecretion of gastric juices and acids Contributing factors include: stress, cigarette smoking, certain foods, some medications, and bacterial infections

Peptic Ulcers

Celiac Disease Autoimmune disorder that results in damage to the lining of the small intestine when foods with gluten are eaten Damage to the intestine makes it hard for the body to absorb nutrients, especially fat, calcium, iron, and folate Classic symptom: diarrhea other symptoms include bloating, gas, fatigue, low blood count (anemia), and osteoporosis. Many people have no symptoms. Celiac disease affects 1% of healthy, average Americans

Celiac Disease

Crohn's Disease A chronic inflammatory bowel disease that affects the lining of the digestive tract A type of IBD (Inflammatory Bowel Disease) Symptoms: abdominal pain, diarrhea, weight loss, anemia, and fatigue Some people may be symptom free most of their lives, while others can have severe chronic symptoms that never go away Internal tissues may develop shallow, crater-like areas or deeper sores and a cobblestone pattern Caused by a trigger of the body's immune system to produce an unhealthy inflammatory reaction in the digestive tract Ongoing research has uncovered specific genes linked to ulcerative colitis and Crohn's disease

Crohn s Disease

Irritable Bowel Syndrome IBS isn t classified as a true disease functional disorder the digestive system looks normal but doesn't work as it should symptoms don t have an identifiable cause Symptoms: crampy pain bloating, gas mucus in the stool Diarrhea constipation Almost always exacerbated by stress Depending upon the main symptom, IBS patients are classified as constipation-predominant, diarrhea-predominant, or painpredominant

IBS vs IBD IBD (Inflammatory bowel disease) is a broad term that refers to chronic swelling (inflammation) of the intestines. IBD comes in the form of: Crohn s disease ulcerative colitis indeterminate colitis IBS does not cause inflammation, ulcers or other damage to the bowel