DIGESTIVE SYSTEMMechanical and chemical breakdown of foods and the absorption of the resulting nutrients by cells.

Chapter 15

SENSE OF SMELL AND TASTE

• Smell and taste receptors are chemoreceptors (receptors stimulated by binding of certain chemicals).

• Aid in food selection

Sense of smell

• 12 million olfactory receptors• Yellowish-brown masses of epithelium• Upper portion of nasal cavity• Bipolar neurons • Stimulated by odorant molecules• Send impulses to olfactory bulbs, are analyzed

and travel along olfactory tracts to the temporal lobe

• Anosmia is the complete or partial loss of smell.

Sense of taste• 10,000 taste buds located on the surface of the tongue; 1,000

on roof of mouth and throat (found within papillae: tiny elevations on tongue)

• Taste buds contain 50-150 taste cells that are replaced every 3 days

• Tongue has taste pores and taste hairs• 5 primary taste sensations:• Sweet (tip of tongue)• Sour (sides of tongue) • Salty• Bitter (back of tongue)• Umami (delicious)• (6.) Alkaline• (7.) Metallic

• Pathway to brain: • taste cells facial, glossopharygeal, vagus nerves medulla

thalamus

Digestion

• Mechanical digestion: breaks large pieces into smaller ones without altering their chemical composition.

• Chemical digestion: breaks food into simpler chemicals.

• 2 parts of digestive system (pg. 403)

• Alimentary canal: tube that extends mouth to anus• Muscular tube about 8 meters long• Wall has 4 layers• Mucosa: contains tiny projections (lumen) that increase

absorption area; has glands to secrete mucus to protect other layers• Submucosa: contains blood vessels that nourish• Muscular: produces movements• Serosa: serous fluid lubricates tube outer surface

• Peristalsis: wavelike motion that propels food down the tube

• Accessory organs: secrete substances in canal to digest

MAIN DIGESTIVE ORGANS AND FUNCTIONS

• MOUTH: mastication (pg. 406)

SPECIAL STRUCTURES

FUNCTION DESCRIPTION

LIPS Sense texture and temp of food Skeletal muscle sensory receptors

CHEEKS Expression, chewing Skin & fat

TONGUE Mix (bolus), taste, friction (papillae)

PALATE Hard- bony anterior roof Soft- muscular posterior roof (covers nasal cavity)

UVULA Gag reflex Cone shaped projection in back

FRENULUM Connects tongue to floor of mouth Membranous fold

TONSILS Protect against infection Lymphatic tissue/tonsillitis

TEETH : break down food to increase surface area for enzymes to be effective (pg. 407)

• Primary teeth (deciduous)• Acquired from 6 months-2 years• 20 teeth total • Roots are reabsorbed before next set come in

• Secondary teeth (permanent) • 32 teeth total• Incisors: bite off pieces of food• Canine: grasp or tear food• Premolars/Molars: grind food particles

• 2 portions (pg. 408)• Crown: part that projects beyond gum • Is covered by enamel-contains Ca salts; strongest substance in body; if

damaged it does not come back• Root: anchored to jaw

• Dental caries (cavities): caused by bacteria that release acid that decay enamel

SALIVARY GLANDS• Secrete saliva that moistens food particles, binds them, and

begins chemical digestion of carbohydrates. It is also a solvent that aids in tasting food and cleanse mouth and teeth. (pg. 410)• 2 types of secretory cells• Serous cells: produce a watery fluid that includes amylase (enzyme

that splits starch and glycogen molecules into disaccharides)• Mucous cells: secretes mucus that binds food particles and lubricates

food during swallowing.

• Parasympathetic nerve impulse elicit saliva secretion or inhibits it if food smells good or bad.

• Major Glands• Parotid - largest; anterior to ear; secretes amylase• Submandibular – floor of mouth; serous and mucus• Sublingual – smallest; inferior floor of mouth; mucous

PHARYNX• Passageway posterior to mouth whose muscular walls aid in

swallowing. It connects the nasal and oral cavities with the larynx and esophagus.

• Structure• Nasopharynx- airway• Oropharynx- food down and air up• Laryngopharynx- food down

• Peristalsis starts here

ESOPHAGUS• Food passageway that aids in swallowing.• Straight, collapsible tube about 25 cm long• Leads from pharynx to stomach• Posterior to trachea• Penetrates diaphragm at the esophageal hiatus• Esophageal sphincter: area where stomach and

esophagus meet; contains circular smooth muscle that stays closed to prevent contents from regurgitating into the esophagus. When peristaltic waves reach the stomach, the muscle fibers temporarily relax and allow the food to enter.

SWALLOWING MECHANISM1. Soft palate raises preventing food from

entering nasal cavity.2. Hyoid bone and larynx are elevated. Epiglottis

(flap like structure) closes off the top of the larynx so that food is less likely to enter the trachea.

3. Tongue is pressed against the soft palate, sealing off the oral cavity from the pharynx.

4. Longitudinal muscle in the pharyngeal wall contract, pulling the pharynx upward toward the food.

STOMACH • Structure• J-shaped, pouchlike organ that hangs inferior to diaphragm• Upper left portion of abdomen• 1 liter capacity• 40 million cells line the stomach and can secrete 2 to 3 liters of

gastric juice per day• Contains rugae (thick folds)

• Functions• Receives food from esophagus• Mixes food with gastric juice• Initiates protein digestion• Limited absorption (water, salts, alcohol)• Moves food to small intestine

• Regions of stomach• Cardiac: small area near esophageal opening• Fundic: temporary storage area• Body: main portion• Pyloric: narrow canal to small intestine• Pyloric sphincter: muscle valve that controls gastric emptying

• Problems• Ulcers: an open sore in mucous membrane from

tissue breakdown• Hiatal Hernia: portion of the stomach protrudes

through a weakened area of the diaphragm.

Gastric secretions (pg. 413 )

• Gastric glands line the inner stomach which is thick with mucus• 3 types of secretory cells• Mucous: mucus; to prevent products of these stomach from digesting

itself ;produce gastric juice• Parietal: secrete HCL acid • Chief: digestive enzymes

• Gastric juice• Pepsin: most important digestive enzyme; begins the digestion of

protein• Intrinsic factor: helps small intestine absorb vitamin B12

• Gastrin: increase secretory activity of gastric glands and stimulates cell growth

• Chyme: paste of food particles and gastric juice

LIVER• Structure• upper right quadrant of abdominal cavity• reddish-brown with many blood vessels• heaviest organ in body; 3 lbs.• 2 lobes (large right/smaller left) separated by hepatic

lobules• Functions (pg. 418)• Carbohydrate metabolism• Lipid metabolism• Protein metabolism • Storage• Blood filtering• Detoxification• Secretion of bile (yellow-green liquid secreted from

hepatic cells)

• Problems• Jaundice: yellow eyes and skin due to a buildup of

bile, blocked bile duct, diseased liver• Hepatitis: inflammation of the liver; Types A-G (pg

419)

PANCREAS• Structure• Near posterior abdominal wall in the C-shaped curve of

duodenum• Contains pancreatic acinar cells that produce pancreatic juice• Pancreatic duct: connects with duodenum at same place the

bile duct of liver and gallbladder joins• Hepatopancreatic sphincter: controls the movement of

pancreatic juices into duodenum

• Function• Secretes pancreatic juice that contains enzymes that

digest carbohydrates, fats, nucleic acids and proteins

• Problems• Pancreatitis: results from blockage in release of

pancreatic juice• Cystic Fibrosis: excessive production of mucus

blocking the release of digestive enzymes.

GALL BLADDER• Structure• Pear shaped sac on inferior surface of liver• Connects to cystic duct which joins hepatic duct to

form common bile duct

• Function• Stores bile between meals • Reabsorbs water to concentrate bile• Releases bile into small intestine

• Problems• Gall stones: cholesterol in bile forms crystals and

blocks flow in cbd; painful

SMALL INTESTINE• Structure• 3 parts (5-6 meters long)• Duodenum: about 25 cm long/5cm in diameter; most fixed portion• Jejunum• Ileum

• Mesentery• double-layered fold of peritoneal membrane• suspends jejunum and ileum from posterior wall• supports the blood vessels, nerves, and lymphatic vessels that supply

intestinal wall• Greater Omentum• Drapes from stomach over intestines and within folds• Fat accumulation occurs here

• Intestinal villi• Greatly increase surface area to absorb

• Ileocecal sphincter• Joins the ileum to the large intestine

• Function• Receives secretions from pancreas and liver• Completes digestion of the nutrients in chyme• Absorbs the products of digestion (*most important

absorbing organ)• Transports the residues to the large intestine• Chyme takes 3-10 hours to pass through

• Problems• Diarrhea: organ becomes irritated and a strong

peristaltic rush passes contents through without any absorption

• Celiac disease: reaction to gluten that causes malabsorption

• Lactose intolerance: not producing sufficient lactase to adequately digest lactose causing diarrhea, cramping and bloating

LARGE INTESTINE• Structure• Greater diameter than small intestine• 1.5 meters long• Parts• Cecum • Appendix (consists of lymphatic tissue but has no known

digestive function) hangs from this area• Colon

• Ascending – goes upward• Transverse – longest, most movable, goes across• Descending – goes down• Sigmoid – S curve

• Rectum – lies by sacrum• Anal canal• Anus – 2 sphincters

• Internal – involuntary control• External – voluntary control

• Function• Little or no digestive function • Absorbs water and electrolytes from chyme remaining• Forms and stores feces• Includes materials not digested or absorbed• About 75% water• Color derives from bile pigments• Odor is produced by bacteria• Secretes mucus to protect wall, bind feces and control pH• Slower peristaltic waves only 2 to 3 times a day

• Problems• Hemorrhoids – enlarged and inflamed branches of the rectal

vein that cause itching, pain, and bleeding. Caused by pressure.• Crohn’s disease – inflammation in digestive tract