Transcript Digestion
Why is digestion important? Foods such as bread, meat and vegetables are not in a form the body can use. Must be broken down and changed into smaller molecules that can be absorbed. The body can then use these molecules to build and nourish cells and provide energy. Digestion Digestion involves a series of interconnected steps. 1. Ingestion- food enters through mouth 2. Mechanical Processing- movement and chewing of foods by tongue, teeth and mixing. 3. Digestion- chemical breakdown of food for absorption 4. secretion- aids digestion by releasing water, acids, and enzymes. 5. Absorption- movement of sm. Molecules, electrolytes, vitamins and water. 6. Excretion- Elimination of wastes from body. Functions of the Oral Cavity (Buccal) 1. Analysis of potential foods 2. Mechanical processing using teeth, tongue and palatal surfaces. 3. Lubrication by mixing with mucous and salivary secretions. tear, gnaw and grind food- mastication tongue compresses and distorts the foods shape, does a sensory analysis of temp., touch and taste hard and soft palates sublingual, submaxillary and parotid glands 4. Digestion by salivary enzymes. salivary amylase- breaks down starch in foods The Pharynx common passageway for solid food, liquids and air Pharyngeal muscle contractions during swallowing propel food along the esophagus and into the stomach The Esophagus muscular tube ~1 ft. long and 2 cm in diameter posterior/dorsal to trachea carries solids and liquids from pharynx to stomach (through an opening in the diaphragm esophageal hiatus) peristalsis- waves of muscular contractions The Esophagus SWALLOWING complex reflex that transports food proper texture and consistency begins with the compaction of food, by the tongue, to form the bolus or small mass the tongue pushes the food down and elevates the soft palate the epiglottis directs the bolus passed the closed glottis and into the entrance of the esophagus (guarded by the upper esophageal sphincter) the opening of the lower esophageal sphincter is triggered by the approach of the bolus food enters the stomach Esophagus Circular muscles contract, constricting passageway and pushing bolus ahead Food bolus Longitudinal muscles contract, shortening passageway ahead of the bolus Sphincter closed Stomach Relaxed muscle layer Sphincter open Stomach The Stomach 4 MAJOR FUNCTIONS: 1. temporary storage of ingested food 2. mechanical breakdown of resistant materials 3. breaking of chemical bonds using acids and enzymes 4. production of the intrinsic factor compound necessary for absorption of Vitamin B12 Vit. B12 – found in the food from animals, bound to protein Hydrochloric acid produced by the stomach releases Vit B12 from proteins in foods Upon release, binds with intrinsic factor for absorption The Stomach produces a soupy mixture chyme rugae- ridges and folds in stomach, when full or stretched, it disappears Lesser Omentum- connects the lesser curvature of the stomach and deuodenum to the liver Greater Omentum- hangs from stomach, connects the stomach with the diaphragm, spleen and colon The Stomach THE GASTRIC WALL secretes parietal and chief cells Parietal cells- secrete intrinsic factor (absorbs vit. B12) and hydrochloric acid Chief cells- secrete pepsinogen, which is converted to pepsin, by the hydrochloric acid released in parietal cells Heartburn We’ve learned that in order for food to enter the stomach it must pass through an opening between the esophagus and stomach (a gate) Usually, this opening closes as soon as food passes through. But if it doesn't close, acid from your stomach can get through the opening and into your esophagus. This is called reflux. Stomach acid can irritate the esophagus and cause heartburn. The Small Intestine ~ 6m or 20 ft. long and 4cm in diameter runs from stomach to lg. intestine most important digestion processes are completed here intestinal wall is lined with villi- finger-like projections that increase surface area for absorption LATIN- Villus “Shaggy Hair” The Small Intestine 3 SUBDIVISIONS: Duodenum- closest to stomach ~1 ft. length Jejunum- an abrupt bend begins the Jejunum bulk of chemical digestion and nutrient absorption ~ 8 ft. in length Drastic Wt. Loss Ileum- third segment ends at a sphincter called ileocecal valve. this valve controls the flow of chyme from ileum to the cecum of the Large Intestine. Digestion Disorder - Ulcers Ulcers are sores on the lining of your digestive tract. Peptic ulcers are ulcers that form in the stomach or the upper part of the small intestine in the duodenum. We used to think these were caused by stress, spicy foods, and alcohol. Now we know that most peptic ulcers are caused by a particular bacterial infection in the stomach and upper intestine, by certain medications, or by smoking. Small Intestine Final Products of Sm. Intestine 80% of all absorption takes place here simple sugars fatty acids amino acids (which get absorbed with water) The Pancreas lies behind/dorsal to stomach toward spleen elongated organ, pinkish grey in color ~ 6 in. in length knobbly texture, soft, easily torn produces pancreatic juice to keep chyme pH levels under control Secretes hormones including insulin and glucagon Pancreatitis – inflammation of pancreas The Liver Largest visceral organ in the body reddish brown in color ~3.3lbs 4 LOBES: Right Left Quadrate Caudate Inferior vena cava Stomach Right lobe of liver Right hepatic duct Common bile duct Pancreas Hepatic portal vein Gallbladder Pancreatic duct Duodenum Functions of the Liver Metabolic Regulation: extract absorbed nutrients or toxins from blood monitor/adjust blood glucose levels Ex.) If blood glucose levels rise- liver removes glucose and synthesizes glycogen. If glucose levels fall- liver breaks down glycogen and releases glucose. remove circulating toxins and metabolic wastes absorb and store fat-soluble vitamins A,D,K and E. Functions of the Liver cont. Hematological Regulation: largest blood reservoir in the body removes aged and damaged RBC debris and pathogens are removed from circulation Functions of the Liver cont. Bile: synthesized in liver, excreted to the duodenum bile ducts from each of the 4 lobes unite to form the common hepatic duct, which meets the cystic duct to form the common bile duct which empties into the duodenum Bile consists of water, ions, bilirubin (pigment from hemoglobin) cholesterol and lipids Bile salts- help breakdown insoluble lipids Gallbladder located under the right lobe of the liver stores bile and concentrates bile for release into the duodenum Emulsification- bile salts break apart large drops of lipids and make them accessible for pancreatic lipases pancreatic lipase is a pancreatic enzyme that breaks down triglycerides stores digestive juices that are made by the liver. Sometimes these juices become solid and form stones, called gallstones. The Large Intestine horseshoe shape ~5 ft. long, 3” in width begins at the end of the ileum and end at the anus lies below stomach and liver and almost completely frames the sm. intestine Functions of the Large Intestine 1. reabsorb water and compact the feces 2. absorb vitamins liberated (separated) by bacteria 3. store fecal material prior to defecation 3 Major Regions of the Lg. Intestine Cecumcollects and stores material from the ileum and begins the process of compaction appendix attaches to cecum (~3.5”) inflammation of appendix appendicitis 3 Major Regions of the Lg. Intestine cont. Colon- has a larger diameter and thinner wall compared to the small intestine Bears haustrae (pouches) and the taenia coli (longitudinal bands of muscle) Ascending, Transverse and Descending Colon which curves and re-curves forming the Sigmoid Colon Transverse colon Ascending colon Cancer Descending colon 3 Major Regions of the Lg. Intestine cont. Rectumend of the digestive tract last portion is called the anorectal canal very close to the anus has an internal anal sphincter circular muscle inside and an external anal sphincter that guards the exit of the canal defecation Digestion Disorder - Hemorrhoids Hemorrhoids are swollen veins in your rectum or anus The type of hemorrhoid you have depends on where it occurs Internal hemorrhoids involve the veins inside your rectum. Internal hemorrhoids usually don't hurt but they may bleed painlessly. Prolapsed hemorrhoids may stretch down until they bulge outside your anus. A prolapsed hemorrhoid may go back inside your rectum on its own, or you can gently push it back inside. External hemorrhoids involve the veins outside the anus. They can be itchy or painful and can sometimes crack and bleed. Digestion Disorder of Intestines Irritable bowel syndrome (IBS) common problem with the intestines with IBS, the intestines squeeze too hard or not hard enough and cause food to move too quickly or too slowly through the intestines IBS usually begins around age 20 and is more common in women. Constipation Constipation is when you have trouble having bowel movements. Your stools may be very hard, making them so difficult to pass that you have to strain. Or you may feel like you still need to have a bowel movement even after you've had one. Digestion and Absorption Typical meal- mixture of carbohydrates, proteins, lipids, water, electrolytes and vitamins each of these components is handled differently Lg. organic molecules are broken down through hydrolysis in order for absorption to occur amylase breaks down carbohydrates into simple sugars. proteinases break bonds between amino acids lipases separate fatty acids from glycerides Digestion and Absorption cont. Water, electrolytes and vitamins can be absorbed without a preliminary process fat-soluble vitamins – enclosed within fat droplets, absorbed with the products of lipid digestion water soluble vitamins – (9 of them) important cofactors in enzyme reactions