Download Nutrition and Digestion

Chapter 21
Obtaining Food
 All animals eat other organisms
 Herbivores: eat autotrophs
 Carnivores: eat other animals.
- meat eating plants
 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 Food
 Ingestion: act of eating
 Digestion: breaking down food into small, absorbable
molecules
 Mechanically broken into pieces
 Chemical breakdown catalyzed by enzymes that add H2O
 Occurs in compartments so only food, not self, is digested
 Absorption: cells in GI tract take up digestion products
 Transported in blood to wherever needed
 Excess intake converted to fat for storage
 Elimination: undigested material passes out GI tract
Understanding Food Processing
4 main stages
Chemical Breakdown
Comparative Compartmentalization
Gastrovascular cavity
Alimentary canal
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: churn and grind food; some
storage
 Food chemically digested and nutrients absorbed in the
intestines
 Undigested materials exit via the anus
Human Digestive System
Accessory 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 food
 Easier to swallow and expose to enzymes
 Incisors bite chunks, canines tear, and molars grind
 Chemical digestion starts w/ saliva, a glycoprotein that
protects the mouth and lubricates food
 Sight and smell can stimulate before food continues it
 Salivary amylase for carb digestion, bicarbonate to neutralize,
and mucins to lubricate
 Tongue is a muscle that manipulates food, allows taste, and
forms a food bolus
 Pushed back into the pharynx
The Esophagus
 Pharynx has esophagus and trachea, or windpipe
 Esophagus closed so air can enter larynx, voice box,
then into lungs
 Tongue pushes bolus which relaxes sphincter and
closes epiglottis over larynx
 Bolus passes and pharynx returns for breathing
 Esophagus is a muscular tube that is voluntarily
controlled at the top, peristalsis continues the length of
 Lined with stratified squamous
 Length varies with species
The Stomach
 Prevents need for constant feeding
 Stores and mixes food
 Secretes gastric juices (pH=2) of mucus, enzymes,
and acid
 Breaks food, kills bacteria and microbes
 3 cell types produce
 Peristaltic contractions transforms bolus into acidic,
nutrient-rich chyme
 Sphincter controls release to small intestine
 Small amounts at regular intervals
Gastric Juices
 Cells in gastric glands produce
 Mucous cells: lubricate and protect lining
 Parietal cells: produce H+ and Cl- ions to form HCl

Coverts pepsinogen to pepsin
 Chief cells: secrete pepsinogen

Pepsin increases pepsinogen production = positive feedback
 Pepsin starts digesting proteins by splitting
polypeptide chains
 Secretion as pepsinogen and mucus prevents digestion
of stomach lining
 Epithelium regularly replaced
Controlling Digestion
 Sight, smell, and/or taste of food signals brain
 Brain signals stomach to start producing gastric juices
 Stomach produces hormone gastrin in presence of
food
 Enters circulatory system and reenters stomach wall

Stimulates more gastric juice production
 Increase in acidity inhibits gastrin so less juices
produced
 Protects stomach lining
Digestive Ailments
 Acid reflux
 Backflow of chyme into esphogeal opening
 Pepcid AC, Zantec, and Prilosec slow or limit acid
production
 Gastric 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) Enzymes
 Pancreas produces
enzymes and
bicarbonate solution
 Protein degradation
 Buffer to neutralize
chyme
 Liver produces bile to
emulsify fats
 Gall bladder stores bile
 All mix in the
duodenum
Small Intestine Digestion




Carbs started in the oral cavity
Proteins started in the stomach
Fats undigested until duodenum
All finished by duodenum, rest of SI for absorption
Small Intestine Absorption
 SI has huge surface area as a result of folding
 Large 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 LI
 Removes excess glucose from blood and converts to
glycogen to store in liver cells
 Coverts substances into new, essential proteins
 E.g plasma proteins for blood clotting
 Modifies and detoxifies substances in blood before
they reach the heart
 Converts toxins to inactive products to be released in
urine
 Excess 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 appendix
 Absorbs 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 elimination
 Two sphincters, a voluntary and an involuntary one, control
 Water reclamation inhibited = diarrhea
 Peristalsis too slow, excess water reabsorbed = constipation
Comparative GI tracts
 Length of GI tract often
related to diet
 Herbivores and
omnivores longer
 Herbivores lose many
nutrients to feces
 Recycle feces to regain
 Ruminants have 4
chambered stomachs
 Regurgitate food from 1
to another = chew cud
Nutritional Needs
 All animals, regardless of diet, have the same
 Fuel to power all activities
 Organic molecules to build own molecules
 Essential nutrients or substances that can’t be self
made
 Must obtain from food
 Combinations of 4 major biological molecules
Essential Nutrients
 4 classes
 Essential fatty acids: most diets provide ample
 Essential 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 minerals
 Undernourishment: diet chronically deficient in
calories
 Common during drought, war, anorexia nervosa
 Malnourishment: long term diet absence of 1+
essential nutrient
 More common, can be obese
Vitamins and Minerals
 Vitamin: an organic nutrient that must be obtained from
diet, but required in minute amounts
 Tiny amounts, but serious complications when deficient
 Excess can be problematic too
 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: simple inorganic nutrients needed in small
amounts
 Many are components of various enzymes and vertebrate
processes
 Bone growth, ATP, and hemoglobin
Grocery Shopping
 Vegetarians need to make sure a variety of foods eaten to
ensure adequate nutritional requirements
 Mexican diet of corn tortillas and beans
 Vitamin and mineral supplements aim to guarantee
RDA’s
 Levels are debated, at least can be wasteful, worst harmful
 Food label ingredients listed most to least amounts
 Look for high fructose corn syrup
 Food serving size and energy content (calories)
 % of nutrients related to disease
Health and Obesity
 Overnourishment: consuming more food energy
than needed for normal metabolism
 Now recognized as a major global health problem
 In the US 30% obese, 35% overweight, can start at 15
 Inheritance is 1 known factor in addition to lifestyle
 Leptin 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 Feeding
 Hydra (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)