Four General Functions Ingestion Digestion Absorption Excretion Ingestion

Four General Functions • • Ingestion Digestion Absorption Excretion

Ingestion Taking food into the body (EATING)

Digestion • The breaking down of food by chemical and mechanical means into usable forms.

Types of Digestion • • Mechanical Digestion – Physically breaking down of food into smaller pieces: - 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 transportation to body cells

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

Gastrointestinal Tract (Alimentary Canal) • • A continuous tube extending from the mouth to the anus Organs of the Alimentary Canal – mouth - pharynx - esophagus – stomach - small intestine - large intestine

Diagram of the Alimentary Canal

Accessory Organs that help with digestion by secreting chemicals such as enzymes and bile. – salivary glands (3 pairs. Parotid glands near the ears. – liver – gallbladder - pancreas

Accessory Organs

Diagram of Accessory Organs

Saliva and Salivary Amylase • • Salivary glands produce saliva which includes water, mucin, bicarbonate ions, and the enzyme, salivary amylase. Salivary amylase helps to chemically break down starch into the disaccharide maltose.

Digestion of Starch by Salivary Amylase

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

Oral Cavity – 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

Tooth Structures

Anatomy of a 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

Anatomy of a Tooth • • Gingiva – the gums or epithelial tissue that help to protect the root of the tooth. Periodontal Ligament - dense fibrous connective tissue attached to the socket walls and the cemental surface of the roots of the teeth to anchor the teeth. Serves as a shock absorber when chewing

Anatomy of a Tooth • 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 – fleshy part of the tooth that contains the blood vessels and nerves. Cementum - a bone-like substance that covers the dentin of the root

Anatomy of a Tooth • Root Canal – the openings in the root that allows for the passage of blood vessels and nerves.

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

Processes of the Digstive System • Deglutition – swallowing

Processes of the Digestive System • • Mastication – chewing Movement of skeletal muscles to close the mandible or jaw to help move the teeth break down food.

Maceration • The breaking down of food into a liquid paste called chyme. Occurs in the stomach.

Segmentation • Short muscle contractions to mix the chyme with enzymes and other secretions. Some propulsion of the chyme also occurs.

�Peristalsis • Involuntary smooth muscle contractions to propel food/chyme/wastes through the alimentary canal.

Haustral Churning • Slow, segmental churning within the large intestinal pouches (haustra) which helps to facilitate water reabsorption.

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

Esophagus • • • About 10 inches long Does not participate in digestive processes – transportation of the bolus to the stomach by peristalsis. Moves food down into the stomach – Esophageal hiatus - opening in the diaphragm for the esophagus – Joins the stomach at the cardiac opening.

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 - pylorus 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 When the stomach is empty the mucosa lie in large folds called rugae. Mucosa contains gastric glands to make gastric juice. – – – Chief Cells Parietal Cells Goblet Cells

Histology of the Stomach

Gastric Glands • Parietal Cells – Secrete hydrochloric acid to activate pepsinogen. • Goblet Cells – Produce mucous for protection • Chief Cells – Secrete Pepsinogen – Enzyme to digests proteins to dipeptides

Gastric Gland

Anatomy of the Stomach • Fundus – The upper, rounded part of the stomach that will expand to hold more food. • Body – The major portion of the stomach. • Pylorus – The distal, narrow end of the stomach that connects to the small intestine

Anatomy of the Stomach

• Anatomy of the Stomach, p. 2 Rugae – Fold of the stomach that allow for stretching. • Cardiac Opening – The opening into the stomach. Is not a true sphinter as food can flow into and out of the stomach. • Pyloric Sphincter – The muscle in the pylorus that controls the movement of chyme into the duodenum (first part of the small intestine)

Stomach Structures

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

Absorption in the Stomach • • Does not participate in the absorption of food molecules into the blood However, can absorb some substances through the stomach wall – – – Water Weak glucose concentrations Electrolytes Certain drugs (aspirin) Alcohol

Chemical Digestion in the Stomach • Cephalic Phase - reflexes initiated by sensory receptors in the head – sight - smell – thought of food • • - taste 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

Pancreas • • Oblong gland that lies posterior to the greater curvature of the stomach Connected by the pancreatic duct to the duodenum Composed of clusters of glandular epithelial cells. Pancreas is the only organ classified as both an endocrine AND an exocrine gland.

Pancreas • 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 and Pancreas

Liver • • • Located inferior to the diaphragm on the right side of the body Largest organ of the abdominopelvic cavity Weighs about 1. 4 kgs (3 lbs) Completely covered by the peritoneum and a dense layer of connective tissue beneath the peritoneum Responsible for MANY regulatory functions for the body.

The Liver and Bile • Hepatocytes 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 – 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 Synthesis of bile Storage of vitamins, minerals, and food molecules Phagocytosis of old worn out red and white blood cells Activation of Vitamin D Storage of glucose and glycogen

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

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.

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

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

The Small Intestine

Modifictions of the Small Intestine • • Villi – Finger-like extensions of the mucosa to increase surface area for absorption of nutrients. Lacteal – lymphatic vessel for lipid absorption.

Villi in Duodenum

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 – osmosis - facilitated diffusion - active transport

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

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

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 • Reabsorption of water • Manufacture of certain vitamins (K) • 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

Summary of Digestion • Mouth – Ingestion – Mastication – form a bolus as food mixes with saliva. – Digestion of carbohydrates with amylase (starch to maltose) – Deglutition

Summary of Digestion • Pharynx – Peristalsis • Esophagus – Peristalsis

Summary of Digestion • Stomach – Maceration and formation of chyme as the bolus mixes with gastric juices. – Digestion of proteins to dipeptides by the enzyme, pepsin. – Peristalsis continues

Summary of Digestion • Small Intestine – Segmentation – Digestion of carbohydrates, lipids, and proteins is completed (mostly in the duodenum) – Nutrient absorption (mostly in the ileum and jejunum) – Peristalsis

Summary of Digestion • Large Intestine – Peristalsis – Haustral churning – Absorption of some vitamins – Absorption of water – Formation and compaction of feces. – Excretion

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

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

Effects of Cirrhosis

Colorectal Cancer • Colorectal Cancer – 3 rd 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

Colorectal Cancer

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

Gallstones

Gallstones

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 A • • • Infectious hepatitis Caused by Hepatitis A virus Spread by fecal contamination of food, clothing, toys, eating utensils, etc. Generally a mild disease of children and young adults Characterized by anorexia, malaise, jaundice, nausea, diarrhea, fever, and chills

Hepatitis B • • Serum hepatitis Caused by the Hepatitis B virus Transmitted by sexual contact, contaminated syringes, transfusion equipment, saliva, tears, and puncture wounds in the skin Can produce cirrhosis and possibly cancer of the liver

Hepatitis

Obesity • Clinically classified as obese if: – Body Mass Index >30 – Females greater than 30% of normal body weight – Males greater than 20% of normal body weight

• • U. S. surgeon general has said obesity is a 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

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

Ulcers

Ulcers

Celiac Disease • A digestive and autoimmune disorder that results in damage to the lining of the small intestine when foods with gluten are eaten. Gluten is a protein found in some grains. The damage to the intestine makes it hard for the body to absorb nutrients, especially fat, calcium, iron, and folate.

Celiac Disease

Celiac Disease

Crohn’s Disase • • Crohn's disease is a chronic disease that causes inflammation—irritation or swelling—in the gastrointestinal (GI) tract. Most commonly, Crohn's affects the ileum of the small intestine and the beginning of the large intestine.

Crohn’s Disease

Crohn’s Disease

Irritable Bowel Syndrome • • • Irritable bowel syndrome commonly causes cramping, abdominal pain, bloating, gas, diarrhea and constipation. IBS is a chronic condition. IBS does not cause changes in the tissues of the intestine.

Irritable Bowel Syndrome