Chapter 21

Obtaining FoodAll animals eat other organisms

Herbivores: eat autotrophsCarnivores: eat other animals.

- meat eating plantsOmnivores: eat plants and animals

Animals differ in how food is ingestedSuspension feeders: filter food from waterSubstrate feeders: eat through a substrateFluid feeders: sucking fluidsBulk feeders: ingest large pieces of food, using

various ‘utensils’

Processing FoodIngestion: act of eatingDigestion: breaking down food into small, absorbable

moleculesMechanically broken into piecesChemical breakdown catalyzed by enzymes that add H2OOccurs in compartments so only food, not self, is digested

Absorption: cells in GI tract take up digestion productsTransported in blood to wherever neededExcess intake converted to fat for storage

Elimination: undigested material passes out GI tract

Understanding Food Processing4 main stages Chemical Breakdown

Comparative CompartmentalizationGastrovascular cavity Alimentary canal

Digestive CycleFood ingested into a mouth openingPushed into a pharynx or throatPasses through an esophagus to a secondary

structureCrop: pouch like organ to soften and store foodStomach and gizzard: churn and grind food;

some storageFood chemically digested and nutrients

absorbed in the intestinesUndigested materials exit via the anus

Human Digestive SystemAccessory glands in the alimentary canal secrete digestive juices through ducts

Moved through the canal by peristalsis, alternating waves of contraction and relaxation of smooth muscles

Passage regulated by sphincters

The Mouth Mechanical breakdown and mixing of food w/ saliva

Teeth chew, cut, smash, and grind the foodEasier to swallow and expose to enzymesIncisors bite chunks, canines tear, and molars grind

Chemical digestion starts w/ saliva, a glycoprotein that protects the mouth and lubricates foodSight and smell can stimulate before food continues itSalivary amylase for carb digestion, bicarbonate to

neutralize, and mucins to lubricateTongue is a muscle that manipulates food, allows

taste, and forms a food bolusPushed back into the pharynx

The EsophagusPharynx has esophagus and trachea, or windpipeEsophagus closed so air can enter larynx, voice

box, then into lungsTongue pushes bolus which relaxes sphincter and

closes epiglottis over larynxBolus passes and pharynx returns for breathingEsophagus is a muscular tube that is voluntarily

controlled at the top, peristalsis continues the length ofLined with stratified squamousLength varies with species

The StomachPrevents need for constant feeding

Stores and mixes foodSecretes gastric juices (pH=2) of mucus,

enzymes, and acidBreaks food, kills bacteria and microbes3 cell types produce

Peristaltic contractions transforms bolus into acidic, nutrient-rich chyme

Sphincter controls release to small intestineSmall amounts at regular intervals

Gastric JuicesCells in gastric glands produce

Mucous cells: lubricate and protect liningParietal cells: produce H+ and Cl- ions to form HCl

Coverts pepsinogen to pepsinChief cells: secrete pepsinogen

Pepsin increases pepsinogen production = positive feedbackPepsin starts digesting proteins by splitting

polypeptide chainsSecretion as pepsinogen and mucus prevents

digestion of stomach liningEpithelium regularly replaced

Controlling DigestionSight, smell, and/or taste of food signals brainBrain signals stomach to start producing gastric

juicesStomach produces hormone gastrin in presence

of foodEnters circulatory system and reenters stomach

wall Stimulates more gastric juice production

Increase in acidity inhibits gastrin so less juices produced

Protects stomach lining

Digestive AilmentsAcid reflux

Backflow of chyme into esphogeal openingPepcid AC, Zantec, and Prilosec slow or limit acid

productionGastric Ulcers

Corrosive effect of gastric juices due to lack of mucus

Helicobacter pylori results in localized loss of protection Mild inflammation from WBC’s attack H. pylori

Can reach a point where a hole develops

Small Intestine (SI) EnzymesPancreas produces

enzymes and bicarbonate solutionProtein degradationBuffer to neutralize

chymeLiver produces bile to

emulsify fatsGall bladder stores

bileAll mix in the

duodenum

Small Intestine Digestion

Carbs started in the oral cavityProteins started in the stomachFats undigested until duodenumAll finished by duodenum, rest of SI for absorption

Small Intestine Absorption

SI has huge surface area as a result of foldingLarge circular folds

Small finger-like villi Each villi covered with epithelial cells containing microvilli

Absorption via diffusion or against [gradients]

Liver’s Role Key in regulating metabolism

Direct transport of nutrients from SI and LIRemoves excess glucose from blood and converts to

glycogen to store in liver cellsCoverts substances into new, essential proteins

E.g plasma proteins for blood clottingModifies and detoxifies substances in blood before

they reach the heartConverts toxins to inactive products to be released

in urineExcess can cause damage

Large Intestine (LI)also called the colon, joins SI at a T-shaped junction

Blind pouch on one end = cecum with attached appendixAbsorbs water from alimentary canal leaving solids behind

Solidifies as moves along colon via peristalsis to produce feces containing indigestible plant fibers and prokaryotes

Rectum stores feces until eliminationTwo sphincters, a voluntary and an involuntary one, controlWater reclamation inhibited = diarrheaPeristalsis too slow, excess water reabsorbed = constipation

Comparative GI tractsLength of GI tract often

related to dietHerbivores and

omnivores longer Herbivores lose many

nutrients to fecesRecycle feces to regain

Ruminants have 4 chambered stomachsRegurgitate food from 1

to another = chew cud

Nutritional NeedsAll animals, regardless of diet, have the sameFuel to power all activitiesOrganic molecules to build own moleculesEssential nutrients or substances that can’t

be self madeMust obtain from food

Combinations of 4 major biological molecules

Essential Nutrients4 classes

Essential fatty acids: most diets provide ampleEssential amino acids: 8 of 20 AA’s needed for

proteins Can’t be stored, deficiencies effect others Meat, eggs, milk, and cheese provide all in correct amounts

Vitamins and mineralsUndernourishment: diet chronically deficient in

caloriesCommon during drought, war, anorexia nervosa

Malnourishment: long term diet absence of 1+ essential nutrientMore common, can be obese

Vitamins and MineralsVitamin: an organic nutrient that must be obtained from

diet, but required in minute amountsTiny amounts, but serious complications when deficientExcess can be problematic tooWater-soluble excess excreted in urine (Vitamin C and B’s)Fat-soluble excess build up in fat (Vitamins A, D, E, and K)

Minerals: simple inorganic nutrients needed in small amounts

Many are components of various enzymes and vertebrate processesBone growth, ATP, and hemoglobin

Grocery ShoppingVegetarians need to make sure a variety of foods

eaten to ensure adequate nutritional requirementsMexican diet of corn tortillas and beans

Vitamin and mineral supplements aim to guarantee RDA’sLevels are debated, at least can be wasteful, worst

harmfulFood label ingredients listed most to least amounts

Look for high fructose corn syrupFood serving size and energy content (calories)% of nutrients related to disease

Health and ObesityOvernourishment: consuming more food energy

than needed for normal metabolismNow recognized as a major global health problem

In the US 30% obese, 35% overweight, can start at 15Inheritance is 1 known factor in addition to lifestyleLeptin findings not applicable to humans

Leptin is produced by adipose tissues; high levels should inhibit loss of body fat stimulate

Defective leptin gene in mice = severe obesity, injection of leptin reverses Gene not in obese humans

Comparative FeedingHydra (Phylum Cnidaria) uses tentacles to

catch prey and bring it close to the entrance of the gastrovascular cavity.

Annelids take food into a mouth down a short esophagus into the crop and then the gizzard.

- crop: pouch-like organ where food is stored and softened.

- gizzard: muscular pouch (stomach) where food is churned.

Arthropods (chelicerates and mandibulata) use a crop to store food. The midgut contains gastric pouches whereby nutrients are absorbed. The hindgut functions as a “large intestine” whereby water is absorbed and waste products are compacted.

Aves have three separate chambers for food processing.- crop, stomach and a gravel filled gizzard (grinding seed)