Digestive System: Path of food Page 3 : Notes Digestive System: Path of food

Alimentary canal: Open at both ends Irregular tube about 29 ft. (9m) long Also called gastrointestinal tract or GI tract Food travels: mouth -> pharynx -> esophagus -> stomach -> small intestine -> large intestine -> rectum Food does not travel through: liver or pancreas

Two forms of digestion: Mechanical – teeth tear food into smaller pieces and stomach churns Chemical – enzymes break large molecules into smaller molecules (molecular level) Foods undergo digestion, absorption and metabolism.

Digestive System: Functions in altering food in to a form that can be absorbed by cells Serves as a system that also eliminates wastes (feces) Composed of main organs and accessary organs: Main organs – food passes through Accessary organs – can secrete into the GI tract (teeth, tongue, salivary glands, liver, gallbladder, pancreas & appendix)

Walls of the digestive tract: Mucosa - lines inside of GI tract Submucosa - connective tissue with blood vessels + nerves Muscularis – circular and longitudinal muscle layers; perform peristalsis Serosa – outermost covering connects to mesentery Google; digestive tract + layers

Path of food: Mouth Where digestion begins! Roof has hard and soft palates with the uvula (prevents food from entering nasal cavity) Floor has tongue and muscles, attached by the frenulum Tongue surface has papillae (bumps on tongue), largest is vallate

Accessory glands: Salivary glands: Produce saliva Three pairs: Contains mucus and digestive enzymes Salivary amylase – Carb. Digestion Three pairs: Parotid – largest, back of throat Submandibular – under jaw Sublingual – under tongue

Teeth: Incisors – sharp, cutting Canines (cuspids) – tear or pierce Premolars (bicuspids) And Molars (tricuspids) – tricuspids Both have large, flat surfaces for grinding or crushing

How many teeth? Deciduous teeth (baby teeth) 20 teeth 6 months: average age for first eruption Complete set at about 2 years of age Permanent teeth (adult teeth) 32 teeth 6 years: average age for first eruption Complete set between 17-24 years of age

Sections of a typical tooth Crown Neck Root

Pharynx: Tubelike structure made of muscle and lined with mucous membrane Food is small rounded mass, called bolus Three regions: Nasopharynx Oropharynx Laryngopharynx

Esophagus: Muscular, mucus-lined tube Connects the pharynx to stomach About 10 inches long Cardiac sphincter: Ring of muscle tissue at end that leads to stomach

Stomach: Pouch that stores food Muscular walls mix food with gastric juice that contains hydrochloric acid and enzymes (produced by gastric glands) Empty – folds line inside called rugae Chyme – food is a semi-solid mixture when it exits Pyloric sphincter – ring of muscle tissue

Muscularis of stomach:

Small intestine: 20 feet long 3 sections: Duodenum – first section – 12 in. Jejunum – middle section Ileum – last section

Small intestine: Internal – mucus lining has intestinal glands and circular folds called plicae Covered by small projections called villi Microvilli are small projections on villi Increase surface area for absorption of nutrients

Villi and microvilli:

Liver: Largest gland in the body Secretes bile, yellowish-brown liquid Emulsifies fats and eliminates cholesterol from body

Pancreas: Lies behind stomach Secretes pancreatic juice that contains enzymes Breaks down proteins, lipids, + carbs Secretes sodium bicarbonate (alkaline substance that neutralizes HCl

The Ducts

Large intestine: 5 feet long with regions (cecum, ascending, transverse, descending, sigmoid and rectum)

Large intestine: Undigested and unabsorbed food is acted on by bacteria Absorbs vitamins (K + B-complex) No villi here Absorption of salts and water Ileocecal valve is doorway in to the large intestine

Appendix: Wormlike tubular structure Contains lymphatic tissue May be involved in immunity

Peritoneum: Large, moist slippery sheet of serous membrane Lines abdominal cavity + covers organs Has two extensions: 1. mesentery - giant, pleated fan that encloses the small intestine and attaches it to the posterior abdominal wall 2. greater omentum – pouchlike extension, shaped like an apron, hangs over the intestines (lace apron)