Chapter 29: Nutrition and Chapter 29: Nutrition and Digestion (pg 634 – 651)Digestion (pg 634 – 651)

Section 1: Nutrition depends on digestion and Section 1: Nutrition depends on digestion and absorptionabsorptionSection 2: Each region of the digestive tube is Section 2: Each region of the digestive tube is specializedspecializedSection 3: A healthful diet provides both fuel Section 3: A healthful diet provides both fuel and building materialsand building materialsSection 4: Nutritional disorders damage healthSection 4: Nutritional disorders damage health

Section 1: Nutrition depends Section 1: Nutrition depends on digestion and absorptionon digestion and absorption

• Food is a source of energy derived Food is a source of energy derived from complex polymersfrom complex polymers

• Polymers can not be used directly Polymers can not be used directly by the body but must be simplified by the body but must be simplified into universal monomers into universal monomers

• Cells take up these monomers and Cells take up these monomers and convert them into useful productsconvert them into useful products• Amino acids Amino acids protein protein

Stages of Food ProcessingStages of Food Processing

• Nutrition – how your body gets raw Nutrition – how your body gets raw material from foodmaterial from food

• 4 Stages4 Stages• IngestionIngestion• DigestionDigestion• AbsorptionAbsorption• EliminationElimination

Ingestion and DigestionIngestion and Digestion

• IngestionIngestion• Eating or drinkingEating or drinking• Mouth acts as an organ for ingestion and Mouth acts as an organ for ingestion and

digestiondigestion• DigestionDigestion

• Breaking down food into small particles for Breaking down food into small particles for the body to absorbthe body to absorb• Polysaccharides Polysaccharides monosaccharides monosaccharides

• Two StepsTwo Steps• MechanicalMechanical

• Chewing to decrease the size of food and increase Chewing to decrease the size of food and increase surface area of food for the next stepsurface area of food for the next step

• ChemicalChemical• Breaking chemical bonds in the food to produce Breaking chemical bonds in the food to produce

monomersmonomers

Absorption and EliminationAbsorption and Elimination

• AbsorptionAbsorption• Cells take up the monomers produced Cells take up the monomers produced

from chemical digestionfrom chemical digestion• Blood can transport some of the Blood can transport some of the

monomers to other parts of the bodymonomers to other parts of the body

• EliminationElimination• Removal of undigested foodRemoval of undigested food

Section 2: Each region of the Section 2: Each region of the digestive tube is specializeddigestive tube is specialized

• Digestion occurs in a specialized tube, Digestion occurs in a specialized tube, the alimentary canalthe alimentary canal• Food moves only in one directionFood moves only in one direction• The alimentary canal (complete digestive The alimentary canal (complete digestive

tract) has many loops to increase tract) has many loops to increase absorption time of monomersabsorption time of monomers

• Lined by epithelial tissue which secretes a Lined by epithelial tissue which secretes a protective mucusprotective mucus• Stomach acid has a pH of 2Stomach acid has a pH of 2• Your stomach lining is replaced every 3 daysYour stomach lining is replaced every 3 days

Organs of the Digestive Organs of the Digestive SystemSystem

• Six main organsSix main organs• MouthMouth• PharynxPharynx• EsophagusEsophagus• StomachStomach• Small IntestineSmall Intestine• Large IntestineLarge Intestine

• Accessory glandsAccessory glands• Salivary glands, pancreas, liver, and Salivary glands, pancreas, liver, and

gallbladdergallbladder

Mouth (Oral Cavity)Mouth (Oral Cavity)

• Food triggers Food triggers nervous reflex that nervous reflex that causes salivary causes salivary glands to deliver glands to deliver saliva to mouth.saliva to mouth.

• Saliva contains Saliva contains • Mucin:Mucin:

• Protects and lubricates Protects and lubricates mouthmouth

• Amylase: Amylase: • Enzyme that hydrolyzes Enzyme that hydrolyzes

starch and glycogenstarch and glycogen

Tongue: tastes foods, manipulates it during chewing, and shapes food into bolus

Throat (pharynx)Throat (pharynx)

• Pharynx – junction Pharynx – junction between esophogus between esophogus and airwayand airway• Epiglottis temporarily Epiglottis temporarily

seals off the airway to seals off the airway to direct food down into direct food down into the stomachthe stomach

• Esophagus – connect Esophagus – connect pharynx to the pharynx to the stomachstomach• Food pushed viaFood pushed via

peristalsis (rhythmic (rhythmic contraction of smooth contraction of smooth muscle in one direction)muscle in one direction)

• Contraction is a wave - Contraction is a wave - like motionlike motion

Stomach (upper abdominal Stomach (upper abdominal cavity)cavity)

• Elastic muscular sac (stretch 2 L)Elastic muscular sac (stretch 2 L)• Gastric juice is secreted to break down Gastric juice is secreted to break down

food into chymefood into chyme• Mixture of mucus, HCl, and enzymesMixture of mucus, HCl, and enzymes

• Pepsin: hydrolysis of proteins*Pepsin: hydrolysis of proteins*

• Stomach muscles contract pushing the Stomach muscles contract pushing the chyme to the small intestinechyme to the small intestine

• Both ends of the stomach are generally Both ends of the stomach are generally sealed offsealed off• Heartburn and vomitHeartburn and vomit

*Secretion of gastric juice

• Pepsin: secreted in an inactive form: pepsinogen • Comes from chief cells located in gastric

pits• HCl is also in pits

• Secreted by parietal cells• Acid coverts pepsinogen into active

pepsin• Positive feedback: once some is activated

the rate increases.

*Secretion of gastric juice

Small Intestine, Liver, and Small Intestine, Liver, and PancreasPancreas

• Small intestine completes digestion (1Small intestine completes digestion (1stst portion) portion) and begins absorption of nutrients (rest of and begins absorption of nutrients (rest of intestine)intestine)• 11stst portion = duodenum (first 25 cm) portion = duodenum (first 25 cm)

• Chyme mixes with bile produced by the liverChyme mixes with bile produced by the liver• Bile is stored in the gallbladder & contains no digestive Bile is stored in the gallbladder & contains no digestive

enzymesenzymes• Bile contains salts that act as detergents that aid in the Bile contains salts that act as detergents that aid in the

digestion and absorbtion of fats.digestion and absorbtion of fats.

• PancreasPancreas• Produces several hydrolytic enzymes and an alkaline Produces several hydrolytic enzymes and an alkaline

solution rich in bicarbonate solution rich in bicarbonate • Acts as a buffer and to neutralize acidic chymeActs as a buffer and to neutralize acidic chyme

• Digestion results in individual amino acidsDigestion results in individual amino acids

Enzymatic Action

• Large circular folds Large circular folds in the liningin the lining• Lined with finger like Lined with finger like

projections called projections called villi.villi.

• Villi have Villi have microscopic microscopic appendages call appendages call microvillimicrovilli

• Projections increase Projections increase surface area and surface area and increase rate of increase rate of absorption.absorption.

Small intestineSmall intestine

Small intestineSmall intestine

• Each villus is a net of microscopic blood vessels and a vessel of the lymphatic system (lacteal).

• Nutrients are absorbed across the intestinal epithelium of the blood vessels and lacteals.• Sometimes passive (fructose)• Sometimes pumped across concentration

gradient (amino acids, peptides, vitamins, glucose)

• Lacteals converge into larger vessels of the lymphatic system.

• Blood vessels converge into the hepatic portal vessel.

Hepatic Portal Vessel

• Leads directly to the liver.• Why the liver?

• Metabolic versatility to interconvert various organic molecules

• Ensues first access to amino acids and sugars.

• Important to control sugar levels in the body.

• From the liver blood travels to the heart, which pumps nutrients all over the body.

Small intestineSmall intestine

Large Intestine (colon)Large Intestine (colon)

• Food moves from the small intestine Food moves from the small intestine past the colon into the large intestinepast the colon into the large intestine

• Connected to small intestine in T shape• Sphincter controls movement of material

• Pouch called the cecum

• Main branch is upside-down U shape (1.5 m long).

• Appendix: contributes to body defenses

Large Intestine (colon)Large Intestine (colon)

• Focus is absorption of waterFocus is absorption of water• 7 L of fluid used daily 7 L of fluid used daily • Most is reclaimed in small intestineMost is reclaimed in small intestine• Together small & large reabsorb 90% of waterTogether small & large reabsorb 90% of water

• Undigested food is passed as fecesUndigested food is passed as feces• Absorbed water makes feces more compact Absorbed water makes feces more compact

and solidand solid• 12-24 hours before material travels the length 12-24 hours before material travels the length

of the digestive system.of the digestive system.• Terminal part of colon is called rectum.Terminal part of colon is called rectum.

• Between the rectum and anus are two sphicters.Between the rectum and anus are two sphicters.