The Digestive System

Digestive System is approximately 8 meters long

Human digestive system After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested. Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours. In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

Digestion Processing of food Types Mechanical (physical) Chemical Chew Tear Grind Mash Mix Chemical Catabolic reactions Enzymatic hydrolysis Carbohydrate Protein Lipid

Digestion Phases Ingestion Movement Digestion Absorption Further digestion After chewing and swallowing, it takes 5 to 10 seconds for food to pass down the esophagus to the stomach, where it spends 2 to 6 hours being partially digested. Final digestion and nutrient absorption occur in the small intestine over a period of 5 to 6 hours. In 12 to 24 hours, any undigested material passes through the large intestine, and feces are expelled through the anus.

Digestive System Organization Gastrointestinal (Gl) tract or 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

Digestive System Organization Descending colon Sigmoid colon Rectum Anus Accessory structures Not in tube path Organs Teeth Tongue Salivary glands Liver Gall bladder Pancreas

Anatomy of the Mouth and Throat

Human Deciduous and Permanent Teeth

Dorsal Surface of the Tongue

The Major Salivary Glands

Alimentary canal Mouth- physical and chemical breakdown. Mastication-the act of chewing Saliva contains enzyme amylase to break down carbohydrates

Pharynx- contains opening to trachea as well Pharynx- contains opening to trachea as well. Epiglottis covers opening of trachea. Esophagus-muscular tube dorsal to trachea Relies on a rhythmic wave-like motion called peristalsis

Peristalsis and Segmentation series of involuntary wave-like muscle contractions which move food along the digestive tract

Anatomy of the Stomach

Stomach 3 muscle layers Regions Vascular 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

Stomach Functions Absorbs Mix food Alcohol Reservoir Water Start digestion of Protein Nucleic acids Fats Activates some enzymes Destroy some bacteria Makes intrinsic factor – B 12 absorption Destroys some bacteria Absorbs Alcohol Water Lipophilic acid B 12

Small Intestine Extends from pyloric sphincter  ileocecal valve Regions Duodenum Jejenum Ileum Movements Segmentation Peristalsis

Small intestine The walls of the small intestine are lined with millions of microvilli. This is the site of nutrient absorption. Small intestines also produce many digestive enzymes to break large polymers completely down into monomers. Chyme- the thin liquid mush that is your food being passed through the intestines

Small Intestine Intestinal glands – Intestinal enzymes Duodenal glands – Alkaline mucous Paneth cells – Lysozyme Microvilli Lacteals Plica circularis Smooth muscle Lymphatic tissue – GALT Vascular

Small Intestine Absorbs 80% ingested water Electrolytes Lipids Vitamins Minerals Carbonates Active/facilitated transport Monosaccharides Proteins Di-/tripeptides Amino acids Lipids Monoglycerides Fatty acids Micelles Chylomicrons

Structure of the Villi in the Small Intestine

Villi and microvilli

Small Intestine Secretes digestive enzymes Peptidases Sucrases Maltase Amino- Di- Tri- Sucrases Maltase Lactase Saccharidases Lipase Nucleases

Small Intestine Requires pancreatic enzymes & bile to complete digestion

Liver Location R. Hypochondrium Epigastric region 4 Lobes Left Quadrate Caudate Right Each lobe has lobules – Contains hepatocytes – Surround sinusoids – Feed into central vein

Liver Functions Makes bile Detergent – emulsifies fats Release promoted by: Vagus n. CCK Secretin Contains Water Bile salts Bile pigments Electrolytes Cholesterol Lecithin

Liver Detoxifies/removes Stores Activates vitamin D Drugs Alcohol Stores Gycolgen Vitamins (A, D, E, K) Fe and other minerals Cholesterol Activates vitamin D Fetal RBC production Phagocytosis Metabolizes absorbed food molecules Carbohydrates Proteins Lipids

Liver Dual blood supply Hepatic portal vein Hepatic artery/vein Direct input from small intestine Hepatic artery/vein Direct links to heart

Gall bladder- stores and concentrates bile Bile is a bitter, greenish-yellow alkaline fluid, stored in the gallbladder between meals and upon eating is discharged into the duodenum where it aids the process of digestion. Pancreas- produces insulin, pancreatic juices amylase and lipase. Pancreatic juice digests all major nutrient types.

The Duodenum and Related Organs

The Organs and Positions in the Abdominal Cavity

Large Intestine Extends from ileocecal valve to anus Regions Cecum – Appendix Colon Ascending Transverse Descending Rectum Anal canal

Anatomy of the Large Intestine

Large Intestine Histology No villi No permanent circular folds Smooth muscle Taeniae coli Haustra Epiploic appendages Otherwise like rest of Gl tract

Large Intestine Functions Mechanical digestion Haustral churning Peristalsis Reflexes Gastroileal Gastrocolic Chemical digestion – Bacterial digestion Ferment carbohydrates Protein/amino acid breakdown Absorbs More water Vitamins B K Concentrate/eliminate wastes

You’ve got company! Living in the large intestine is a community of helpful bacteria Escherichia coli (E. coli) produce vitamins vitamin K; B vitamins generate gases by-product of bacterial metabolism methane, hydrogen sulfide

Feces Formation and Defecation Chyme dehydrated to form feces Feces composition Water Inorganic salts Epithelial cells Bacteria Byproducts of digestion Defecation Peristalsis pushes feces into rectum Rectal walls stretch Control Parasympathetic Voluntary

Structures of the Alimentary Canal

Digestion and pH Location pH Enzymes Molecules digested Mouth neutral Amylase Starch Stomach acidic Pepsin (a peptidase) Initial protein digestion Small intestine Basic to neutral Mixture of amylase, peptidases, lipases Digestion of starches, final breakdown of proteins, digestion of lipids.

Hormones and digestion Many hormones produced by the digestive system itself are responsible for appetite and digestion. Gastrin in the stomach, produced when food is present, signals release of acid. Secretin signals the release of sodium bicarbonate by the pancreas. Ghrelin and Leptin, recently discovered, control appetite. Changes in these hormones cause overeating, because people with too little of these hormones don’t realize they’re full.

Does a colon need cleaned? Products like these raise worry in people who believe their colon is “dirty.” These are laxatives that are unnecessary, or even harmful. “Cleansing” products can disrupt bowel function and do not cure any real illnesses. A diet high in fiber is a healthier option.