Download Anatomy and Physiology of Digestive system and more Lecture notes Anatomy in PDF only on Docsity!
DIGESTIVE SYSTEM ANATOMY & PHYSIOLOGY
Functions of the Digestive System Ingestion: Active , voluntary process Food must be placed into the mouth before it can be acted on Propulsion: ^ If foods are to be processed by^ more than 1^ digestive organ^ they must be propelled from one organ to the next Peristalsis – involuntary , alternating waves of contraction and relaxation of the muscles in the organ wall Food breakdown: Mechanical digestion – prepares food for further degradation by enzymes Examples : o Mixing of food in the mouth by the tongue o Churning of food in the stomach o Segmentation in the small intestine Food breakdown: Chemical digestion – sequence of steps in which large food molecules are broken down into their building blocks by enzymes Absorption: Transport of digested end products from the lumen of the GI tract to the blood or lymph Digested foods must 1st^ enter the mucosal cells by active or passive transport process (for absorption to happen ) Defacation: Elimination of indigestible residues from the GI tract via the anus (form of feces ) Anatomy of the Digestive System o Organs of the digestive system can be separated into 2 main groups : Alimentary canal , and Accessory digestive organs
Organs of the Alimentary Canal o Also called the gastrointestinal tract o Continuous, hollow muscular tube that winds through the ventral body cavity o Open at both ends Mouth o Food enters the digestive tract through the mouth or oral cavity A mucous membrane-lined cavity Lips: ( Labia ) Protects its anterior opening Cheeks: ^ Form its lateral walls Palate: Divides into 2 : o Hard palate – forms its anterior roof o Soft palate – forms its posterior roof Uvula: Fleshy finger-like projection of the soft palate Extends inferiorly from the posterior edge of the soft palate Vestibule: Space between the lips and the cheeks externally Space between teeth and gums internally Oral cavity proper: Area contained by the teeth Tongue: Muscular tongue Occupies the floor of the mouth Has several bony attachments , 2 of these are: o Hyoid bone , and o Styloid processes of the skull Lingual frenulum: Fold mucous membrane Secures the tongue to the floor of the mouth Limits its posterior movements Palatine tonsils: Paired masses of lymphatic tissue Found at the posterior end of the oral cavity Lingual tonsil: Cover the base of the tongue just beyond Pharynx o From the mouth , food passes posteriorly into the: Oropharynx: Posterior to the oral cavity Laryngopharynx: ^ Continuous with the^ esophagus^ below Common passageways for food , fluids , and air Esophagus o Also called gullet o Runs from the pharynx through the diaphragm to the stomach Size & function: 25 cm ( 10 inches ) long Passageway that conducts food by peristalsis to the stomach Structure: Made up of the same four basic tissue layers or tunics Mucosa: Innermost layer Moist membrane that lines the cavity or lumen Consist primarily of surface epithelium Plus a small amount of connective tissue ( lamina propria ) o A scanty smooth muscle layer Submucosa: ^ Found just beneath the mucosa Soft connective tissue layer containing blood vessels , nerve endings , lymph nodes , and lymphatic vessels Muscularis externa: A muscle layer typically made up of an inner circular layer Outer longitudinal layer of smooth muscle cells
Lesser curvature: Concave medial surface Lesser omentum: Double layer of peritoneum Extends from the liver to the greater curvature Greater omentum: ^ Another extension of the peritoneum Drapes downward and covers the abdominal organs Stomach mucosa: Simple columnar epithelium composed entirely of mucous cells Produce a protective layer of bicarbonate-rich alkaline mucus Clings to the stomach mucosa Protects the stomach wall from being damaged by acid and digested by enzymes Gastric glands: Smooth lining dotted with millions of deep gastric pits Secrete the solution called “ gastric juice ” Intrinsic factor: Substance needed for the absorption of vitamin B12 from the small intestine Chief cells: Produce protein-digesting enzymes Mostly pepsinogens Parietal cells: ^ Produce corrosive^ hydrochloric acid o Makes the stomach contents acidic and activates the enzymes Enteriendocrine cells: Produce local hormones such as gastrin o Important to the digestive activities of the stomach Chyme: Heavy cream that resembles after the food has been processed Small Intestine o Body’s major digestive organ Location: Muscular tube extending from the pyloric sphincter to the large intestine Size: Longest section of the alimentary tube Average length of 2.5 to 7 m ( 8 to 20 feet ) in a living person
Subdivisions: 3 subdivisions : o Duodenum – contribute 5% o Jejunum – contribute 40% o Ileum – contribute 60% Ileocecal valve: Joins the large and small intestine Hepatopancreatic ampulla: Flask-like Literally the “ liver-pancreatic-enlargement ” Microvilli: ^ Tiny projections of the plasma membrane Give cell surface a fuzzy appearance “ brush border ” o Complete the digestion of proteins and carbohydrates Villi: Finger-like projections of the mucosa Give it a velvety appearance and feel o ( like the soft nap of a towel ) Lacteal: Rich capillary bed and a modified lymphatic capillary Circular folds: Also called “ Plicae circulares ” Deep folds of both mucosa and Submucosa layer Do not disappear when food fills the small intestine Peyer’s patches: Resemble the look of the tonsils Capture and destroy bacteria Large Intestine o Much larger in diameter than the small intestine o But shorter in length Size: ^ 1.5 m^ ( 5 feet )^ long Extends from the Ileocecal valve to the anus Functions: Dry out indigestible food residue by absorbing water Eliminate residues from the body as feces Subdivisions: ^ Frames the small intestines on^ 3 sides Subdivisions : Cecum , Appendix , Colon , Rectum , and Anal canal Cecum: Saclike cecum 1 st^ part of the large intestine Appendix: Wormlike appendix Potential trouble spot Ideal location for bacteria to accumulate and multiply Ascending colon: Travels up the right side of the abdominal cavity Makes a turn, the right colic (or hepatic ) flexure ,
Crown: Enamel - covered crown Exposed art of the tooth above the gingival or gum Enamel: Hardest substance in the body Fairly brittle (heavily mineralized with calcium salts ) Root: Outer surface of the root is covered by a substance ( cementum ) o Attaches the tooth to the periodontal membrane ( ligament ) Dentin: Bonelike material Underlies the enamel and forms the bulk of the tooth Pulp cavity: Surrounds a central pulp cavity Contains a number of structures ( connective tissue , blood vessels , and nerve fibers ) collectively called the pulp Root canal: Pulp cavity extends into the root Becomes the root canal Provides a route for blood vessels , nerves and other pulp structures Salivary Glands o 3 pairs of salivary glands o Empty their secretions into the mouth Parotid glands: Lie anterior to the ears Empty their secretions into the mouth Submandibular and sublingual glands: Empty their secretion into the floor of the mouth through tiny ducts Saliva: Product of salivary glands Mixture of mucus and serous fluids Salivary amylase: Clear serous portion contains an enzyme Bicarbonate-rich juice Begins the process of starch digestion in the mouth Pancreas o Produces enzymes o Break down all categories of digestible foods Location: Pancreas is a soft , pink triangular gland Extends across the abdomen from the spleen to the duodenum Lies posterior to the parietal peritoneum Location referred to as retroperitoneal Pancreatic enzymes: Secreted into the duodenum in an alkaline fluid Neutralizes the acidic chyme coming in from the stomach Endocrine function: Produces hormones insulin and glucagon
Liver o Largest gland in the body Location: Located under the diaphragm (more to the right side of the body) Overlies and almost completely covers the stomach Falciform ligament: Delicate mesentery cord Liver has 4 lobes Suspended from the diaphragm and abdominal wall Function: ^ Liver’s digestive function is to produce^ bile Bile: Yellow-to-green Watery solution containing bile salts , bile pigments , cholesterol , phospholipids , and a variety of electrolytes Bile salts: Emulsify fats by physically breaking large fat globules into smaller ones Providing more surface area for the fat - digesting enzymes to work on Gallbladder o Bile is concentrated by the removal of water Location: Small , thin-walled green sac Snuggles in a shallow fossa in the inferior surface of the liver Cystic duct: Bile backs up the cystic duct Enters the gallbladder to be stored Physiology of the Digestive System o Digestive system takes in food ( ingest it ), breaks it down physically and chemically into nutrient molecules ( digests it ), and absorbs the nutrients into the bloodstream, then, it rids the body of indigestible remains ( defecates ) Activities Occurring in the Mouth, Pharynx, and Esophagus o Activities that occur in the mouth , pharynx , and esophagus are food ingestion , food breakdown , and food propulsion Food Ingestion and Breakdown o Once food is placed in the mouth , both mechanical and chemical digestion begin Physical breakdown: 1 st^ step Food is physically broken down into smaller particles by chewing Chemical breakdown: 2 nd^ step Food is mixed with saliva , salivary amylase begins the chemical digestion of starch, breaking it down into maltose Stimulation of saliva: Simple pressure of anything put into the mouth and chewed will also stimulate the release of saliva Passageways: Pharynx and the esophagus have no digestive function Simply provide passageways to carry food to the next processing site, the stomach Food Propulsion – Swallowing and Peristalsis o Food to be sent on its way to the mouth , it must first be swallowed Deglutition: Or swallowing Complex process that involves the coordinated activity of several structures: o Tongue , soft palate , pharynx , and esophagus Buccal phase of deglutition: 1 st^ phase Voluntary buccal phase – occurs in the mouth o Once the food has been chewed and well mixed saliva Bolus ( food mass ) o Forced into the pharynx by the tongue
