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DIGESTIONDIGESTION
Digestion• Mechanical and chemical breakdown of foods...
• Absorption of resulting nutrients by cells
• ALIMENTARY CANAL: tube extending 9 meters from the mouth to the anus
• Mucosa—Submucosa—Muscular layer--Serosa
• LUMEN: space within the intestines
OrgansALIMENTARY CANAL
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small Intestine
• Large Intestine
• Anal Canal (rectum & anus)
ACCESSORY ORGANS
• Salivary
Glands
• Liver
• Gallbladder
• Pancreas
Mouth• Digestion begins
here
• Mechanical & chemical (starches: amylase)
• Lips, teeth, cheek, tongue, salivary glands, papillae, palate, frenulum, tonsils, vestibule, tongue
DIAGRAM OF MOUTH
Tongue
• Function: Mix food particles with saliva during chewing and move food toward the pharynx during swallowing
• PAPILLAE: bumps on tongue; taste buds
• FRENULUM: flap that anchors tongue to bottom of oral cavity
Salivary Glands
• Moisten food; secret amylase to begin starch digestion
• 3 pairs of major salivary glands• PAROTID glands - largest of the major
glands - secretes a clear, watery fluid rich in amylase
• SUBMANDIBULAR glands - predominantly serous secretion w/ few mucous cells
• SUBLINGUAL glands - smallest of the major glands - secretion primarily mucous type
DIAGRAM OF SALIVARY GLANDS
Teeth• Function: Break pieces of food into
smaller pieces
• BOLUS: moist ball of food
• INCISORS: (8) chisel-shaped with sharp edges to bite off larges pieces of food
• CUSPIDS: (4) “canine” teeth; sharp
• BICUSPIDS: (8) tear & grind
• MOLARS: (12) flattened surface to grind food particles
• <Wisdom Teeth> 3rd set of molars; late teens; early 20’s
Parts of Teeth• CROWN: projects beyond the gum
• ROOT: anchored to the alveolar process of the jaw
• ENAMEL: covers the crown
• DENTIN: bulk of the tooth below enamel
• PULP: combination of blood vessels, nerves, and connective tissue (blood vessels and nerves reach pulp cavity through ROOT CANAL)
• GINGIVA: gum
TEETH
TOOTH
Pharynx• Connects the nasal & oral cavities with the
larynx & esophagus
• “back of throat”
• 3 parts
• nasopharynx: communicates with the nasal cavity & provides a passageway for air during breathing
• oropharynx: passageway for food moving downward from the mouth and for air
• laryngopharynx: passageway to the esophagus
TONSILS
• Produce antibodies to fight infection
TYPES
LINGUAL
• PALATINE
• PHARYNGEAL
Uvula
• Cone-shaped projection
• Function: drawn upward during swallowing to close the opening between the nasal cavity & the pharynx
Esophagus• passageway from the pharynx to the
stomach
• “food tube”
• 25 cm long
• PERISTALSIS: muscular contractions that move food
• No digestion occurs here
• EPIGLOTTIS: flap that closes trachea when we swallow to prevent food/liquid from entering the trachea
• LOWER ESOPHAGEAL SPHINCTER: prevents food from backing up into esophagus
Stomach• J-shaped pouch
• Just below diaphragm
• 1 L capacity or more!
• RUGAE: folds
• 4 regions: cardiac, fundic, body, and pyloric
• CHYME: semifluid paste of food
• Chemical digestion of proteins
• Gastric juice: HCl & pepsin…highly acidic (pH 2)
• PYLORIC SPHINCTER - valve that controls food backing up in the stomach
FUNCTIONS OF THE STOMACH
• Begins mixing process with gastric juice
• Begins protein digestion
• Moves food to small intestine
• Limited absorption
THE STOMACH
Gastric Secretions• Gastric glands contain 3 types of secretory cells:
mucous cells, chief cells, & parietal cells = gastric juices
• Mucous cells secrete mucus to prevent stomach from digesting itself!
• Chief cells secrete digestive enzymes
• Parietal cells releases hydrochloric acid
• Pepsin: digestive enzyme in gastric juice
• Pepsin w/ HCl begins the digestion of nearly all proteins into polypeptide strands
• Gastrin: hormone that regulates gastric secretions
Small Intestine• Most important organ of digestion
• 6 m if stretched out!
• Most absorption takes place here
• Many folds (intestinal villi)– increase the surface area for easier absorption
• 3 regions: DUODENUM;
JEJUNUM;
ILEUM
Portions of Small Intestine
• Duodenum
• C shaped
• Receives chyme from stomach
• Receives pancreatic juice & bile
• Several enzymes released to complete digestion of proteins, dipeptides, disaccharides, fats
• Jejunum
• Absorption of digested nutrients
• Ileum
• Absorption of digested nutrients
More about the Small Intestine
• MESENTARY: tissue that suspends the jejunum & ileum from the abdominal wall
• Lacteal: lymphatic capillary found in the intestinal villi
• FUNCTIONS:
• Receive secretions from pancreas & liver
• Completes digestion
• Absorbs products of digestion
Large Intestine• Shaped like an upside down U
• 1.5 m long
• No villi
• Absorbs water & electrolytes
• Forms FECES (75% water; undigested material; bacteria; electrolytes
• ILEOCECAL SPHINCTER: b/w ileum of small intestine & cecum of large intestine
Regions of Large Intestine
• CECUM
• ASCENDING COLON
• TRANSVERSE COLON
• DESCENDING COLON
• SIGMOID COLON
Other Info to Know about the Large Intestine
• APPENDIX: lymphatic tissue between small & large intestine
• HEMORRHOIDS: “pain in the rear”…enlarged/inflammed rectal veins…itching, burning, bleeding
• MUCUS produced in colon serves 2 functions:
• Binds fecal matter
• Protects intestinal wall against abrasive action of undigested waste
LARGE INTESTINE VS. SMALL INTESTINE: larger diameter
NO VILLI
Rectum & Anus
• Feces stored in the rectum
• ANAL CANAL: passageway through which feces passes as it passes out the body through the anus
• DEFECATION: removal of feces
• INTERNAL & EXTERNAL ANAL SPHINCTERS control the release of feces
ACCESSORY ORGANS
Liver• Heaviest organ is body (3
pounds)
• Well-supplied with blood vessels
• Right & left lobes
• *blood sugar maintenance
• *lipid metabolism (bile secretion)
• Produce BILE
• *emulsification of fats
• *protein metabolism (most important function)
• *stores glycogen, iron, vitamins A, B12, D
• *removes toxic substances such as alcohol (detoxification)
Gallbladder
• Stores bile & releases bile to duodenum
• Released through COMMON BILE DUCT
• Cholesterol in bile can form crystals (GALLSTONES)
Pancreas
• Secretes pancreatic juice
• Enzymes that digest carbohydrates
• (amylase), fats (lipases), proteins (trypsin…), & nucleic acids (nucleases)
• Neutralizes stomach acid
• Produces insulin
• Pancreatic duct: connects with duodenum