Human Physiology Digestive System 1

Break up, mix, and move food material Secrete enzymes into tube where digestion occurs Digest (breaks down) food particles into smaller molecules Absorb nutrients and fluids Eliminate wastes and residues Function of Digestive system

Alimentary canal – Mouth, Pharynx, Esophagus, Stomach, Small intestine, and Large intestine Accessory digestive organs – Teeth, Tongue, Gallbladder, Salivary glands, Liver, and Pancreas The Digestive system The alimentary canal or gastrointestinal (GI) tract digests and absorbs food

– Ingestion – taking food into the digestive tract – Mechanical digestion – chewing, churning food, segmentation – Propulsion – swallowing and peristalsis – Chemical digestion – catabolic breakdown of food – Absorption – movement of nutrients from the GI tract to the blood or lymph – Excretion – elimination of indigestible solid wastes Processes of the Digestive System: Overview

A complete system with many specialized organs About 6.5 to 8 meters long if extended Lined with mucus-secreting epithelium Movement is one way, from mouth to anus Human Digestive System

1.Mucosa lines digestive tract – Moistened by glandular secretions – Lamina propria and epithelium form mucosa 2.Submucosa 3.Muscularis externa 4.Serosa - serous membrane covering most of the muscularis externa Organization of the Digestive tract

Mechanical processing by the teeth, tongue, and palatal surfaces Lubrication Assistance in swallowing Limited digestion The Oral Cavity

Twenty deciduous (baby) teeth are replaced by 32 adult teeth. Each tooth has a crown and a root. The tongue mixes the chewed food with saliva and then forms the mixture into a mass called a bolus in preparation for swallowing. The Teeth

Parotid, sublingual, and submandibular glands produce saliva – Stimulated by thought of food or ingested food – Watery solution includes electrolytes, buffers, glycoproteins, antibodies, enzymes Functions include: – Lubrication, moistening, and dissolving – Initiation of digestion of complex carbohydrates Salivary glands (3 pairs)

Food is ingested Mechanical digestion begins (chewing) Propulsion is initiated by swallowing Salivary amylase begins chemical breakdown of starch The pharynx and esophagus serve as conduits to pass food from the mouth to the stomach Uvula guards opening to pharynx Ingestion and Mechanical Digestion

Pharynx The air passage and food passage cross in the pharynx because the trachea is ventral to the esophagus. Swallowing occurs in the pharynx and is a reflex action. During swallowing, the air passage is usually blocked off by the soft palate and uvula, and the trachea moves under the epiglottis to cover the glottis opening to the windpipe.

The esophagus is a muscular tube that conducts food through the thoracic cavity and diaphragm into the stomach. Peristalsis begins in the esophagus; this collapsed tube moves the bolus of food downward after swallowing occurs. No chemical digestion occurs in the esophagus. The entrance of the esophagus to the stomach is marked by a constriction, called a sphincter; the sphincter must relax in order for food to enter the stomach. The sphincter prevents food from backing up into the esophagus. Esophagus

The stomach expands to store food. Food in the stomach is churned, mixing the food with gastric juices containing hydrochloric acid and pepsin for the digestion of protein to peptides. Proteins are digested or broken down by the pepsin in the stomach Alcohol, but not food, is absorbed here. In 2–6 hours, the soupy chyme leaves the stomach. Ulcers are usually caused by a bacterial infection. The Stomach

Gastric glands have a variety of secretory cells – Mucous Neck cells– produce mucus – Parietal cells – produce HCl and intrinsic factor – Chief cells – produce pepsinogen Pepsinogen is activated to pepsin by HCl in the stomach – Enteroendocrine cells – gastrin, histamine, cholecystokinin (CCK Stomach secretions

Gastrin – Release is stimulated by presence of protein in stomach – Acts in several ways to increase secretion of HCl and pepsinogen – Enhances gastric motility Gastric Hormones

Preliminary digestion of proteins - pepsin Permits digestion of carbohydrates Very little absorption of nutrients – Some drugs, however, are absorbed Digestion And Absorption In The Stomach

Important digestive and absorptive functions – Secretions and buffers provided by pancreas, liver, gall bladder Three subdivisions: – Duodenum – Jejunum – Ileum Ileocecal sphincter - transition between small and large intestine Small intestine

Structural modifications of the small intestine wall increase surface area – deep circular folds of the mucosa and submucosa – Villi – fingerlike extensions of the mucosa – Microvilli – tiny projections of absorptive mucosal cells’ plasma membranes Small intestine

Glands of the duodenum – Moisten chyme – Help buffer acids – Maintain digestive material in solution Hormones – Secretin - produces alkaline buffers, increase bile by liver and pancreas – Cholecystokinin – increase pancreatic enzymes, stimulates contraction of gall bladder, reduces hunger sensation – GIP – stimulates release of insulin, inhibits gastric secretion and motility Small intestine

The largest gland in the body Performs metabolic and hematological regulation and produces bile Hexagonal-shaped liver lobules are the structural and functional units of the liver Composed of hepatocytes The liver

Hepatocytes’ functions include: – Production of bile – Detoxification The liver Secreted bile flows between hepatocytes toward the bile ducts in the portal triads

A yellow-green Bile salts are cholesterol derivatives that: – Emulsify fat – Facilitate fat and cholesterol absorption The chief bile pigment is bilirubin, a waste product of heme Composition of Bile

Thin-walled, green muscular sac on the ventral surface of the liver Stores and concentrates bile by absorbing its water and ions Releases bile via the cystic duct, which flows into the bile duct The Gallbladder

Pancreatic duct penetrates duodenal wall The Pancreas

Composition of Pancreatic Juice Anatomy – Endocrine Pancreatic islets produce insulin and glucagon – Exocrine Acini (clusters of secretory cells) contain zymogen granules with digestive enzymes – Regions: Head, body, tail Secretions – Pancreatic juice (exocrine) Trypsin Chymotrypsin Carboxypeptidase Pancreatic amylase Pancreatic lipases Enzymes that reduce DNA and ribonucleic acid

As chyme enters the duodenum: – Carbohydrates and proteins are only partially digested – No fat digestion has taken place Digestion continues in the small intestine – Chyme is released slowly into the duodenum – Virtually all nutrient absorption takes place in the small intestine Digestion in the Small Intestine

Junction of the small intestine and the large intestine

The large intestine consists of the cecum, colon, rectum and anal canal. The large intestine does not produce digestive enzymes but does absorb water, salts, and some vitamins. The colon includes the ascending colon, the transverse colon, the descending colon, and the sigmoid colon. Large Intestine

The appendix is an extension of the cecum. Indigestible material is stored in the rectum until the anus allows defecation. Anaerobic bacteria in the feces break down indigestible material and produce some vitamins. Large Intestine

Other than digestion of enteric bacteria, no further digestion takes place Vitamins, water, and electrolytes are reclaimed Its major function is propulsion of fecal material toward the anus Functions of the Large Intestine

Last portion of the digestive tract Terminates at the anal canal Internal and external anal sphincters Defecation reflex triggered by distention of rectal walls The Rectum

Disassembling organic food into smaller fragments Hydrolyzing carbohydrates, proteins, lipids and nucleic acids for absorption Digestion and Absorption of Nutrients

Nervous regulation – Involves enteric nervous system – Coordinates peristalsis and regulates local reflexes Digestive system: Nervous regulation

1.Write the function of Digestive system? 2.Name the organs of alimentary canal or gastrointestinal tract? Alimentary canal – Mouth, Pharynx, Esophagus, Stomach, Small intestine, and Large intestine Accessory digestive organs – Teeth, Tongue, Gallbladder, Salivary glands, Liver, and Pancreas 3.Name the 3 pairs of salivary glands? Parotid, sublingual, and submandibular glands Produce saliva which lubricates and moistens food 4.Name the enzyme present in mouth? Salivary amylase begins chemical breakdown of starch 5.What guards the opening of pharynx? Uvula 6.What is the function of sphincter? Sphincter is present at the entrance of the esophagus to the stomach. It prevents food from backing up into the esophagus. 7.What is the role of stomach in digestion? The food is mixed with gastric juices containing hydrochloric acid and pepsin that helps in digestion of protein to peptides. 8.Which cells in gastric glands produce HCl? Parietal cells 9.Where do you find ileocecal sphincter? between small and large intestine 10.What is villi? Villi is finger like extensions of mucosa in intestine 11.What is the function of villi? Increases the surface area of small intestine and helps in absorption

12.Name the largest gland of the body? Liver 13.Name the structural and functional units of the liver? Hexagonal-shaped liver lobules 14.Write the function of bile? Bile emulsify fat and facilitate fat and cholesterol absorption 15. What is bilirubin? Bilirubin is the chief bile pigment 16. Where is bile produced from? Releases bile via the cystic duct, which flows into the bile duct