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