Eating, pooping, and peeing THE DIGESTIVE SYSTEM

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1 THE DIGESTIVE SYSTEM Ingested food is not technically in the body until it is absorbed so it needs to be: Mechanically and chemically reduced Transported by the blood to the cells Large portions are not used and pass through I. The Digestive system includes: A muscular tube: the digestive tract or gastrointestinal tract (GT) oral cavity to large intestine Various accessory organs Teeth, tongue, salivary glands, liver, pancreas II. Functions of the digestive system Ingestion materials enter the digestive tract via the mouth Mechanical processing Crushing and shearing, swirling and mixing Digestion Chemical breakdown of food into organic fragments Secretion Release of water, acids, enzymes, buffer, and salts Absorption Movement of molecules Excretion Removal of waste products from body fluids Defecation of feces Movement of digestive materials Visceral smooth muscle shows rhythmic cycles of activity Pacemaker cells Peristalsis Waves that move a bolus The Oral Cavity The mouth opens into the oral or buccal cavity The Pharynx Funnel shaped structure that is the common passageway for food, liquids, and air Walls are composed of skeletal muscle with an inner lining mucous membrane Pharyngeal muscles assist in swallowing Pharyngeal constrictor muscles During breathing, the lower portion of the pharynx is constricted, preventing air from entering the esophogus The Esophagus Page 1 of 5

2 Carries solids and liquids from the pharynx to the stomach Posterior to the trachea and originates at the level of the larynx where the pharynx terminates The wall of the esophagus contains either skeletal or smooth muscle, depending on the location The esophagus has two muscular sphincters Upper esophageal sphincter at the beginning of the esophagus Lower esophageal sphincter at the end of the esophagus just before it enters the stomach This prevents regurgitation of food from the stomach into the esophagus heartburn Swallowing (deglutition) Initiation is voluntary, but proceeds automatically once it begins The Swallowing Process Voluntary Swallowing reflex Once in the esophagus, the bolus is pushed towards the stomach by the peristaltic wave The Stomach The most stretchable part of the GI tract J-shaped pouch continuous with the esophagus and the small intestine Functions of the stomach Bulk storage of undigested food Mechanical breakdown of food (churning) Disruption of chemical bonds via acids and enzymes (gastric secretions) Limited absorption To move food into the small intestine The Small Intestine and Associated Glandular Organs Small intestine Important digestive and absorptive functions Receives secretions and buffers provided by pancreas, liver, gall bladder The Intestinal Wall The pancreas Endocrine functions Insulin and glucagons Exocrine functions Carbohydrases Lipases Nucleases Proteolytic enzymes The liver: largest internal organ Performs metabolic and hematological regulation and produces bile Page 2 of 5

3 Metabolic regulation All blood leaving the absorptive surfaces of the digestive tract enters the hepatic portal system and flows into the liver Metabolizes carbohydrates on demand Metabolizes lipids Amino Acid metabolism Removal of waste products Neutralizes ammonia to urea Circulating toxins, drugs Mineral and vitamin storage The Large Intestine It s called large because its diameter is larger than that of the small intestine About 5 feet long, ends at the anus Functions of the large intestine Little or no digestive function Reabsorb water and compact material into feces Absorb vitamins produced by bacteria Store fecal matter prior to defecation The rectum Last 7.5 inches of the digestive tract The external opening is called the anus Internal and external anal sphincters Physiology of the large intestine Reabsorption in the large intestine includes: Water Vitamins K, biotin, and B5 Organic wastes bacteria convert bilirubin to urobilinogens and sterobilinogens (these give feces their brown or yellow color) Bile salts Toxins Mass movements of material through colon and rectum Defecation reflex triggered by distention of rectal walls Conscious effort to open the external sphincter Tensing the abdominal muscles Elevate intraabdominal pressures by closing glottis THE URINARY SYSTEM An Overview of the Urinary System I. Functions of the urinary system Excretion The removal of organic waste products from body fluids Elimination The discharge of waste products into the environment Homeostatic regulation of blood plasma Page 3 of 5

4 Regulating blood volume and pressure Regulating plasma ion concentrations Stabilizing blood ph Conserving nutrients II. Urinary system includes: The kidneys Produce urine The ureters The urinary bladder Stores urine The urethra III. Nephron functions include: Production of filtrate Reabsorption of organic nutrients Reabsorption of water and ions Secretion of waste products into tubular fluid IV. Principles of Renal Physiology Urine production maintains homeostasis Regulating blood volume and composition Excreting waste products Urea: most abundant organic waste (breakdown of amino acids) Creatinine: generated from skeletal muscle tissue Uric acid: recycling of nitrogenous bases from RNA molecules V. Urine Transport, Storage, and Elimination Urine production ends with fluid entering the renal pelvis Rest of urinary system transports, stores and eliminates Ureters Bladder Urethra The ureters Pair of muscular tubes Extend from renal pelvis to the bladder Peristaltic contractions force urine toward the urinary bladder The urinary bladder Hollow, muscular organ Reservoir for the storage of urine Contraction of detrusor muscle voids bladder Internal features include Trigone Neck Internal urethral sphincter Ruggae The urethra Extends from the urinary bladder to the exterior of the body Page 4 of 5

5 Passes through urogenital diaphragm (external urinary sphincter) Differs in length and function in males and females Micturition reflex and urination Urination coordinated by micturition reflex Initiated by stretch receptors in wall of bladder Urination requires coupling micturition reflex with relaxation of external urethral sphincter Page 5 of 5