The Digestive System Chapter 16 Introduction Structure of the digestive system A tube that extends from mouth to anus Accessory organs are attached Functions include Ingestion Movement Digestion Absorption Defecation Overview of Digestive System Histological Organization Same basic arrangement of tissues from the esophagus to the anal canal Four layers (from innermost to outermost) Mucosa Submucosa Muscularis Serosa Peristalsis Movement and Mixing of Digestive Materials Coordinated motion of the two muscular layers Circular muscles contract, then longitudinal muscles contract Functions Take in food Prepare food for digestion Structure Lined with stratified squamous epithelium Lips surround the opening Roof is formed from the hard & soft palate Tongue dominates the floor The Oral Cavity 1
Found outside the mouth Ducts carry saliva to the mouth Keeps mucous membranes moist Lubricates food and dissolves food Begins carbohydrate digestion 3 pairs Parotid glands Submandibular glands Sublingual glands Salivary Glands 2 sets Deciduous (20) Permanent (32) Held in sockets Gingiva surrounds the base of the teeth Structure Crown Root Neck Teeth Composition Dentin primary substance in tooth Enamel covers crown Cementum covers root Dental caries Wisdom teeth 3 rd molars Teeth formation of erythrocytes The Pharynx and Esophagus Food enters the esophagus from the pharynx The esophagus is a muscular tube behind the trachea Food is moved by peristalsis from the pharynx to the stomach External Anatomy of the Stomach The Stomach Has the same 4 basic layers When the stomach is empty, the mucosa lies in large folds Pyloric sphincter separates stomach from small intestine 2
Histology of the Stomach Gastric Gland Mucosa is simple columnar epithelium with goblet cells Mucosa is folded to form gastric pits Gastric glands secrete gastric juice Chyme Substances that form gastric juice Mucus Hydrochloric acid Pepsinogen Digestion of proteins only Functions of the Stomach Mechanical digestion Food reaches pyloric valve Chemical digestion Digestion of proteins Absorption No food Water, electrolytes Some drugs Alcohol About 18 feet long Functions Most digestion and absorption occurs here The Small Intestine Histology of the Small Intestine A Villus The mucosal surface is folded into villi Intestinal glands are found at the base of villi Secrete intestinal juice - digests all nutrient groups except nucleotides 3
AKA colon About 4.5 feet long Begins with the cecum Appendix is attached Colon connects to the rectum Rectum connects to the anal canal which empties to the exterior through the anus The Large Intestine Histology and Functions of the Large Intestine Mucosa - simple columnar epithelium with lots of mucus glands Functions Completion of absorption Formation of feces Expulsion of feces from the body Digestion in the Large Intestine Mechanical Mixing and peristalsis Mass peristalsis Chemical Mucus secreted No enzymes Bacteria prepare chyme for elimination Feces Formation & Defecation Chyme is now solid or semi-solid - feces Large intestine absorbs any more water and electrolytes from feces Defecation Mass peristalsis pushes fecal material into rectum Rectum stretches - defecation reflex Liver Pancreas Gall bladder Accessory Organs The Liver Performs many life-sustaining functions Location under the diaphragm on the left 4
Outside is a capsule Composed of tiny lobules Each lobule is surrounded by liver cells and sinusoids Bile ducts run between liver cells Histology of the Liver Digestive Function of the Liver Produces bile Composition Water Bile salts Cholesterol Pigments» Bilirubin Digestive function of bile Emulsification of fats Other Functions of the Liver Absorbs and stores iron, several vitamins Detoxifies toxins and hormones Metabolizes proteins, carbohydrates, and lipids Removes bacteria from the blood Produces plasma proteins Removes worn-out and damaged red blood cells Location underside of the left lobe of the liver Function concentrate and store bile Collected from liver Hepatic ducts Adds bile to small intestine Common bile duct Gallstones Cholesterol in bile crystalizes, crystals fuse. The Gallbladder Location in the curvature between stomach and small intestine Connected to the small intestine by the pancreatic duct Produces pancreatic juice Digestion of all the nutrient groups The Pancreas 5