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Digestive System Digestion • Processing of food • Types – Mechanical (physical) • • • • • Chew Tear Grind Mash Mix – Chemical • Catabolic reactions • Enzymatic hydrolysis – Carbohydrate – Protein – Lipid 2 Digestion • Phases – – – – Ingestion Movement Digestion Absorption 3 Digestive System Organization • Gastrointestinal (Gl) tract (Alimentary canal) – Tube within a tube – Direct link/path between organs – Structures • • • • • • • • • • • Mouth Oral Cavity Pharynx Esophagus Stomach Duedenum Jejenum kIleum Cecum Ascending colon Transverse colon 4 Digestive System Organization • • • • Descending colon Sigmoid colon Rectum Anus • Accessory structures – Not in tube path – Organs • • • • • • Teeth Tongue Salivary glands Liver Gall bladder Pancreas 5 Anatomy of the Mouth and Throat 6 The Major Salivary Glands 7 Major Salivary Glands Parotid gland(25%) • is the largest of the three glands and is located below and in front of the ears, • secretes a fluid rich in amylase • Becomes infected and swollen with the mumps Submandibular Glands(70%) • located in the floor of the mouth on the inside surface of the lower jaw • Secretes mostly a serous fluid Sublingual glands(5%) • Are the smallest of the salivary glands and is located on the floor of the mouth under the tongue. 8 Saliva-Functions and composition Saliva Functions • Moistens the mouth • Digest a little starch and fat • Cleanses the teeth • Inhibits bacterial growth • Dissolves molecules so they can stimulate taste buds • Dilute and buffer foods • Moistens food and binds particles together to aid in swallowing(Bolus formation) Saliva –Composition • Is a hypotonic solution of 99% water and other solutes • pH of 6.8 to 7.0 • Solutes in saliva • Salivary amylase- an enzyme that begins starch digestion • Lingual lipase- activated by stomach acid and digest fat after the food is swallowed • Mucus- binds and lubricates the food mass and aids in swallowing • Lysozyme- kills bacteria 9 Mastication(Chewing) • Mastication is a repetitive sequence of jaw opening and closing with a profile in the vertical plane called the chewing cycle. • Mastication consists of a number of chewing cycles. • The human chewing cycle consists of three phases: 1. Opening phase: the mouth is opened and the mandible is depressed 2. Closing phase: the mandible is raised towards the maxilla 3. Occlusal or intercuspal phase: the mandible is stationary and the teeth from both upper and lower arches approximate 10 Deglutition (swallowing) • Sequence – Voluntary stage • Push food to back of mouth – Pharyngeal stage • Raise – Soft palate – Larynx – Tongue to soft palate – Esophageal stage • Contract pharyngeal muscles • Open esophagus • Start peristalsis 11 Phases of Deglutition • Coordinated by swallowing center in the medulla oblongata and pons Buccal phase • The voluntary stage in which the tongue collects food, presses it against the plate to form a bolus, and pushes it back into the oropharynx Pharyngeal-esophageal phase • Three actions block food and drink from reentering the mouth or entering the nasal cavity or larynx • The root of the tongue blocks the oral cavity • The soft palate rises and blocks the nasopharynx • The muscles pull the larynx up against the epiglottis to close the airway that leads to the trachea Esophageal Stage- Food is moved through the esophagus by peristalsis (the wave like muscle contractions of the inner circular and outer longitudinal muscles). • At the end of the pharyngeal stage of the swallow, it must relax to allow the bolus to enter the esophagus. 12 Structure of GI tract Structure of GI tract Mucosa • The inner layer of the tract that is a mucous membrane that is composed of a layer of epithelium- simple columnar in most of the GI tract • a thin layer of smooth muscle ( is responsible for the mucosal folds, or rugae, that serves to increase the surface area for digestion.) • Is the most highly differentiated layer of the GI tract. Submucosa • binds the mucosa to the underlying muscle layer. • blood vessels, lymphatics, a nerves plexus, glands that secrete lubricating mucus into the lumen • A thick layer of muscle that under lies the submucosa • begins at the mouth where it is composed of a mixture of smooth and striated muscle (for voluntary swallowing) and the external sphincter where it is skeletal. • At the distal pharynx it turns into all smooth muscle that courses throughout the rest of the tract. • The involuntary smooth muscle consist of an inner circular and an outer longitudinal layer. 14 Structure of GI tract..ctd Serosa The outermost layer of the GI tract. • Composed of a thin layer of r tissue topped by a serous membrane (mesothelium) • Begins in the lower 3 to 4 cm of the esophagus and ends with the sigmoid colon • When the outer fibrous layer is attached to surrounding tissue it is called adventitia • See this at the oral cavity, pharynx, most of the esophagus, and the rectum It secretes fluid that allows the tract structures to glide over each other without friction. It is also referred to as visceral peritoneum. 15 Peristalsis and Segmentation 16 Law of Gut • Peristaltic Movement + • Movement towards gravity(Mouth to anus) 17 Esophagus • Usually collapsed (closed) • Functions – Secrete mucous – Transport food • Sphincters – Upper – Lower 18 Esophagus..ctd Esophagus • A straight muscular tube about 25-30 cm long • It begins at the level of the cricoid cartilage, inferior to the larnyx behind the trache a and extends through the chest cavity, pierces the diaphragm at the esophageal hiatus , and meets with the stomach at an opening called the cardiac orifice. • It transports food to the stomach and secretes mucus, which aids transport. • • The inferior segment is constricted forming the lower esophageal sphincter which, along with the diaphragm, closes to prevent back flow of stomach contents Heartburn- when HCl from the stomach regurgitates back into the lower esophagus resulting in a burning sensation. 19 Stomach • Usually “J” shaped • Left side, anterior to the spleen • Mucous membrane – – – – G cells – make gastrin Goblet cells – make mucous Gastric pit – Oxyntic gland – Parietal cells – Make HCl Chief cells – Zymogenic cells • Pepsin • Gastric lipase 20 Anatomy of the Stomach 21 Stomach • 3 muscle layers – Oblique – Circular – Longitudinal • Regions – – – – Cardiac sphincter Fundus Antrum (pylorus) Pyloric sphincter • Vascular • Inner surface thrown into folds – Rugae • Contains enzymes that work best at pH 1-2 22 Stomach • Functions – Mix food – Reservoir – Start digestion of • Protein • Nucleic acids • Fats – Absorbs • • • • Alcohol Water Lipophilic acid B 12 – Activates some enzymes – Destroy some bacteria – Makes intrinsic factor – B 12 absorption – Destroys some bacteria 23 Stomach-Phases HCl Generation Small Intestine • Extends from pyloric sphincter Æ ileocecal valve • Regions – Duodenum – Jejenum – Ileum • Movements – Segmentation – Peristalsis 26 Small Intestine • Absorbs – – – – – 80% ingested water Electrolytes Vitamins Minerals Carbonates – Lipids • • • • Monoglycerides Fatty acids Micelles Chylomicrons • Active/facilitated transport • Monosaccharides – Proteins • Di-/tripeptides • Amino acids 27 Small Intestine-structure Structure of the Villi in the Small Intestine 29 Small Intestine • Secretes digestive enzymes – Peptidases • Amino• Di• Tri- – – – – Sucrases Maltase Lactase Saccharidases • Di• Tri- – Lipase – Nucleases 30 Small Intestine • Control • Requires pancreatic enzymes & bile to complete digestion 31 Absorption at intestine Large Intestine • Extends from ileocecal valve to anus • Regions – Cecum – Appendix – Colon • Ascending • Transverse • Descending – Rectum – Anal canal 33 Anatomy of the Large Intestine 34 Large Intestine • Histology – No villi – No permanent circular folds – Smooth muscle • Taeniae coli • Haustra – Epiploic appendages – Otherwise like rest of Gl tract 35 Large Intestine • Functions – Mechanical digestion • Haustral churning • Peristalsis • Reflexes – Gastroileal – Gastrocolic – Chemical digestion – Bacterial digestion – Absorbs •More water •Vitamins –B –K – Concentrate/eliminate wastes • Ferment carbohydrates • Protein/amino acid breakdown 36 Feces Formation and Defecation • Chyme dehydrated to form feces • Feces composition – – – – – Water Inorganic salts Epithelial cells Bacteria Byproducts of digestion • Control – Parasympathetic – Voluntary • Defecation – Peristalsis pushes feces into rectum – Rectal walls stretch 37 Defecation Summary-Digestion and absorption 39 Excretory System The Kidney Nephron Countercurrent Multiplication and Concentration of Urine Figure 26.13b Glomerulus Glomerular Filtrate Ureters and Urinary Bladder Urinary Bladder Composition of Urine Urinary bladder structure Innervations of urinary bladder Micturition Skin and sweat glands Functions • • • • • • • • Skin performs the following functions: Protection Sensation Heat regulation Control of evaporation Storage and synthesis Absorption Water resistance Perspiration • Perspiration (sweating, transpiration or diaphoresis) is the production of a fluid consisting primarily of water as well as various dissolved solids (chiefly chlorides), that is excreted by the sweat glans in the skin of mammals Liver Internal structure-liver Functions-Liver Liver cells Intestinal juices daily secretions Bile secretion Composition of Bile Enterohepatic circulation Gall bladder-function
