Nutrition and Digestion

Chapter 21

Obtaining Food

• Animals differ in dietary types– Herbivores: eat autotrophs (plants)– Carnivores: eat other animals– Omnivores: eat plants and animals

• Animals differ in how food is ingested– Suspension feeders: filter food from water– Substrate feeders: eat through a substrate– Fluid feeders: sucking fluids– Bulk feeders: ingest large pieces of food, using

various ‘utensils’

Processing FoodIngestion: act of eatingDigestion: breaking down food into absorbable molecules

2 stagesMechanicallyChemically (Polymers to monomers)

Compartmentalized so only food, not self, is digestedAbsorption: cells in digestive tract take up digested

productsBlood transportsExcess intake converted to fat

Elimination: undigested material is excreted

Variability of Animal Digestive TractsPhago-/Pinocytosis• Entirely intracellular

digestion– Form food vacuoles– Lysosomes break down

• Sponges only examples

Gastrovascular Cavity• Extracellular digestion starts

– Single opening– Enzymes into cavity

• Ends intracellularly– Phago-/pinocytosis for by

products

• Also circulatory system

Complete Digestive Tract

• Entirely extracellular digestion– Two openings– Nutrients absorbed for use

• Specialized organs for each stage

• Most animals

Comparative Digestive Tracts• Length and adaptations of GI

selected for by lifestyle– Herbivores & omnivores longer

than carnivores– Herbivores lose many nutrients to

feces• Recycle feces to regain• Specialized mircobes in cecum

• Ruminants (cattle, goats, deer, etc.)– 4 chambered stomachs– Regurgitate food from 1st 2 to 2nd 2

= chew cud

Mammalian Digestive System

• Alimentary canal structures

• Accessory glands (green) secrete digestive juices

• Peristalsis moves food

• Regulated by sphincters

• Time varies at each stage

Digestive Cycle• Food ingested into a mouth opening• Pushed into a pharynx or throat– Passes through an esophagus to a secondary

structure• Crop: pouch like organ to soften and store food• Stomach and gizzard: mechanical processing; churns

and grinds food; some storage

• Chemically digested and nutrients absorbed in the intestines

• Undigested materials exit via the anus

Mouth

• Sight, smell & thought initiate– Saliva protects and lubricates

• Salivary amylase, mucins, bicarbonate, and antimicrobials• Chemical digestion: starch to maltose

– Food presence maintains

• Specialized teeth to mechanically breaks down• Tongue mixes/manipulates– Taste– Bolus formation

Pharynx• Esophagus and trachea

– Mouth and nasal cavity cross– Regulation interruption and the Heimlich maneuver

• Eating– Epiglottis covers trachea– Esophageal sphincter relaxes– Peristalsis moves food (voluntary muscles)– Lined with stratified squamous cells

• Breathing– Trachea open– Esophagus closed– Heimlich maneuver

Stomach

• Prevent needs for constant feeding– Stores and mixes food

• Gastric juices for chemical digestion– Sight, smell, and/or taste stimulates production– Pepsin breaks down protein– Stomach protection

• Pepsinogen converted to pepsin (HCl trigger)• Epithelial replacement (3 days)• Positive and negative feedback mechanisms

• Bolus into chyme• Sphincter controls small, regular release to small

intestine (SI)

Small Intestine

• 3 sections, only duodenum (1st) digests, rest absorbs– Fat digestion started

• Liver produces bile, stored in gall bladder

– Other molecules finished• Pancreas secretions to neutralize chyme and assist breakdown

• Villi with microvilli to increase surface area– Absorption into blood (diffusion)

• Peristalsis moves

Large Intestine (Colon)• Joins to small intestine– Cecum with attached appendix

• Absorbs water, salts, and minerals– Moves via peristalsis – Solids left are feces

• Indigestible plant fibers, bacteria (E. coli), and dead cells• Stores in rectum until elimination– Two sphincters (voluntary and involuntary) control– Water reclamation inhibited by irritation diarrhea– Peristalsis too slow constipation

Digestive Ailments• Acid reflux

– Backflow of chyme into esophageal opening = heartburn– Lifestyle changes– Pepcid AC, Zantec, and Prilosec slow or limit acid production

• Gastric Ulcers– Corrosive effect of gastric juices (old)– Helicobacter pylori to blame (new)

• Loss of mucus and destroy cells• WBC’s attack H. pylori = mild inflammation

– Can reach a point where a hole develops• Lining destroyed faster than replaced

• Lactose intolerance– Lactase absence in SI– Bacteria in LI ferment sugar

Liver’s Role • Key in regulating metabolism– Direct transport of nutrients from SI and LI– Removes excess glucose = converts to glycogen for

storage• Coverts substances into new, essential proteins• Modifies and detoxifies– Inactive products released in urine• Urine tests

– Excess can cause damage

Nutritional Needs

• Same for all animals, regardless of diet• Fuel for all activities• Organic molecules to build own molecules– Carbohydrates– Fats – Lipids

• Water• Essential nutrients are substances that can’t

be self made

Essential Nutrients

• Essential fatty acids: most diets provide ample• Essential amino acids: 8 of 20 AA’s needed for proteins– Can’t be stored, deficiencies affect others– Meat, eggs, milk, and cheese are ‘complete’ while plants

aren’t• Vitamins and minerals• Disorders– Undernourishment from low caloric diet– Malnourishment from absence of 1+ essential nutrient– Overnourishment from consuming more calories than need

Vitamins and Minerals

• Tiny amounts needed, but deficiency can cause serious complications– Excess can be problematic too

• Vitamins are organic (13 )– Water-soluble excess excreted in urine (Vitamin C and

B’s)– Fat-soluble excess build up in fat (Vitamins A, D, E, and

K)• Minerals are inorganic (many)• (Table 21.18A and B)

Truth in Labeling

• Vitamin and mineral supplements aim to guarantee recommended dietary allowances (RDA’s)– Levels are debated– Varies with age and sex

• Ingredients listed most to least amounts– High fructose corn syrup– Whole wheat vs enriched wheat flour– Food serving size and energy content (calories)– Emphasize nutrients related to disease and healthy diets

Weight Loss Plans

• Increased spending to market weight loss plans– Hasn’t resulted in thinner or healthier individuals

• Trends in dieting often repeated– New ‘fad’ diets introduced intermittently– Can trade one problem for another

• Initial results from water loss– Problems in maintenance– Healthy lifestyle and eating only 100% effective way

• Gastric by-pass