DIGESTION

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

TYPESLINGUAL

• 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