Presentation on theme: "Digestive System. Function Takes in food Propulsion of food Breaks food down Mechanically and Chemically-Digestion Absorbs nutrients into bloodstream."— Presentation transcript:
Function Takes in food Propulsion of food Breaks food down Mechanically and Chemically-Digestion Absorbs nutrients into bloodstream Reclaims water Excretes waste
Two Major Parts Gastrointestinal Tract Also called The Alimentary Canal Includes: mouth, pharynx, esophagus, stomach, small intestine and large intestine Accessory Organs Include: teeth, tongue, salivary glands, liver, gall bladder and pancreas
Mouth (Oral Cavity) Begins the digestive process by breaking down food Protected by lips Cheeks form the walls Hard Palate is the roof Soft Palate is the posterior roof Tongue is the floor
Tongue The tongue attaches to the hyoid bone and to the styloid process of the skull The inguinal frenulum holds the tongue to the floor of the mouth and keeps it from sliding posteriorly
Frenulum Medical Problem When a child has a short frenulum or an attachment that is farther forward, surgery is sometimes required to improve speech
Tonsils Part of the body’s defense system Palatine Tonsils Lingual Tonsils at the base of the tongue
Salivary Glands Food enters the mouth & teeth break the food down mechanically Salivary Enzymes Ptyalin and Amylase work on chemically digesting starches Salivary enzymes also attack bacteria in the food.
Pharynx Passageway that connects nasal cavity and oral cavity to the esophagus Respiratory and digestive function Food triggers involuntary reflexes
Esophagus Muscular Tube connecting pharynx to stomach 10 inches long Between esophagus and stomach is a ring- like valve that is closed until food pushes on it
Stomach Preparation of food for digestion Mechanically mixes food Chemically liquefies food Kills Bacteria and Parasites
Gastric Pits Gastric pits cover the lining of the stomach Secrete gastric juice Intrinsic factor- absorption of Vitamin B 12 Parietal cells produce Hydrochloric Acid (HCl) Which provide the protein digesting enzyme, pepsin
Pyloric Sphincter (Valve) A full stomach can hold 4 liters or 1 gallon of food Empty, it folds up The Pyloric Sphincter keeps food from being forced into the intestine too early
Small Intestine Stomach empties into small intestine, (resembles coiled hose) Juices from pancreas and gall bladder mix in here
Absorption This is the site of nutrient absorption Large surface area covered with projections (villi) Vitamins, minerals, carbs, protein, fat and bile salts go to the bloodstream
Large Intestine 5 feet long Water is absorbed with any remaining nutrients and feces are formed Bacteria plays an essential role here and we have about 4 pounds of it
Pancreas Produces digestive enzymes Also part of endocrine system producing hormones: insulin and glucagon
Gall Bladder Reservoir for bile Secretes bile to break down fats Green and snuggles in near the liver
Liver Largest gland in the body Has 4 lobes Metabolic and Regulatory Produces Bile Secretes through hepatic duct
Function Ingestion Propulsion Mechanical and Chemical Digestion Absorption of nutrients Absorption of water Defecation
Ingestion Food is placed in the mouth Physical / Mechanical breakdown = chewing Chemical = Saliva contributes amylase (Ptyalin is one type) to break down starch into maltose or to predigest fruit and grain (carbohydrates) No Absorption except sublingual drugs/ vitamins through oral mucosa
Propulsion Deglutination = Swallowing Propelled to next digestive organ by peristalsis –Contraction and relaxation of muscles that is involuntary
Mechanical Mixing in mouth by tongue and teeth Churning in stomach Prepares food for further chemical breakdown
Chemical Large molecules are broken down into building blocks Hydrolysis = Water molecules are added to split larger molecules Water is also softening agent
Absorption Nutrients move from the lumen of the gastrointestinal tract to the blood or lymph
Defecation Elimination of indigestible portions of food Only happens in the large intestine Water removal is important
Microorganisms The gastrointestinal tract contains an immensely complex ecology of microorganisms. A typical person harbors more than 500 distinct species of bacteria. The number and type vary dramatically by region. In healthy individuals the stomach and proximal small intestine contain few microorganisms, largely a result of the bacteriocidal activity of gastric acid.
Microorganisms Most are located in the illeum (pH 7.5) and colon (pH 6.8) bacterial populations in the large intestine digest carbohydrates, proteins and lipids that escape digestion and absorption in small intestine. This fermentation, particularly of cellulose, is of critical importance to herbivores. Assists in absorption of Vitamin K
Enzymes Salivary amylase (also called Ptyalin) breaks starch (a polysaccharide) down to maltose (a disaccharide) Bicarbonate ions in saliva act as buffers, maintaining a pH between 6.5 and 7.5. Mucins (mucous) lubricate and help hold chewed food together in a clump called a bolus
Gastric Juice Pepsinogen is converted to pepsin, which digests proteins. Pepsinogen production is stimulated by the presence of gastrin in the blood (discussed below). Hydrochloric acid (HCl) converts pepsinogen to pepsin which breaks down proteins to peptides. HCl maintains a pH in the stomach of approximately 2.0. It also dissolves food and kills microorganisms. Mucous protects the stomach from HCl and pepsin.
More Enzymes Pancreatic Juice Pancreatic juice contains sodium bicarbonate which neutralizes the acidic material from the stomach. Pancreatic amylase digests starch to maltose. Trypsin and Chymotrypsin digest proteins to peptides. Like pepsin (produced in the stomach), they are specific for certain amino acids, not all of them. They therefore produce peptides. Lipase digests fats to glycerol and fatty acids.
Even More Enzymes Liver The liver produces bile which is stored in gallbladder and sent to the duodenum through a duct. Bile emulsifies fats (separates it into small droplets) so they can mix with water and be acted upon by enzymes.
Yes! More Enzymes Small Intestine: Peptidases complete the digestion of peptides to amino acids. Maltase completes the digestion of disaccharides.
Hormones Hormones, reach their target cells by the circulatory system. Examples are Gastrin and Secretin
Gastrin The presence of food in the stomach stimulates stretch receptors which relay this information to the medulla oblongata. The medulla stimulates endocrine cells in the stomach to secrete the hormone gastrin, into the circulatory system. Gastrin stimulates the stomach to secrete gastric juice.
Secretin Secretin is produced by cells of the duodenum. It’s production is stimulated by acid chyme from stomach. It stimulates the pancreas to produce sodium bicarbonate, which neutralizes the acidic chyme. It also stimulates the liver to secrete bile.
Polyps Polyps are small growths in the epithelial lining of the colon. They can be benign or cancerous and can be removed individually. A low-fat, high-fiber diet promotes regularity and is recommended as a protection against colon cancer.
Ulcers An ulcer is an irritation due to hydrochloric acid and pepsin found in gastric juice, penetrating the mucous lining of the stomach or duodenum. It is believed that ulcers are caused by the bacterium Helicobacter pylori, which, can thrive in the acid environment of the stomach. The presence of the bacteria on portions of the stomach lining prevents it from secreting mucous, making it susceptible to the digestive action of pepsin.