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Ch 21 Digestion and
Nutrition
Ingestion methods…..
• All animals consume energy
– Herbivores
– Carnivores
– Omnivores
– Suspension feeders – particles suspended in water
(clams, oysters, humpback whale)
– Substrate feeders – live in or eat their way through
(earthworm, maggot)
Fluid Feeders: obtain food by sucking nutrient-rich fluids
from a living host
Ex: mosquitoes, ticks, butterflies
Bulk Feeders: ingest large pieces of food
Ex: snake, human
4 stages of Food Processing:
• Ingestion  Digestion  Absorbtion 
Elimination
• Breaking down of Organic Molecules:
– Lipids (Fat)  glycerol + fatty acid
– Polysaccharide  Monosaccarides
– Proteins  Amino acids
– Nucleic acids  nucleotides
• Some organisms only have one opening, a
gastrovascular cavity, they eat and
eliminate out of the same opening.
• Most have 2 openings, Alimentary canal,
made up of a mouth and an anus.
• The Human Digestive system consists of
an alimentary canal and accessory
glands
Alimentary canal: mouth, oral cavity,
tongue, pharynx, esophagus, stomach, sm
intestine, large intestine, rectum, anus
Digestive glands: salivary, pancreas, liver
(Liver secretions stored in Gall bladder)
• Digestion begins in the oral cavity
• Salivary glands secrete saliva
– glycoprotein: slippery; protection of oral
cavity and lubrication of food
– Buffers: neutralize food acids
– Antibacterial agents to kill bacteria
– Amylase: digestive enzyme most active
against carbohydrates
• Both mechanical and chemical digestion
start in the oral cavity
• Tongue: used to taste food and to form a
bolus for swallowing; pushes food into
pharynx.
• After swallowing, peristalsis moves
food through the esophagus to the
stomach
• Swallowing process:
– Tongue pushes the food into the pharynx
– Esophageal sphincter
relaxes
– Epiglottis covers larynx
– Peristalsis pushes the
food toward the
stomach
• Stomach stores and breaks down food with
acids and enzymes
• Chemical digestion - gastric juice which
contains mucus, enzymes (pepsin), and HCl
(pH~2)
• Human stomach lining is fully replaced every
three days **cancer treatments**
• Gastrin: hormone stimulating the secretion of
gastric juice
• Chyme: nutrient rich “broth” formed after
digestion of foods in the stomach
– Leaves the stomach only a little at a time
• The small intestine is the major organ of chemical
digestion and nutrient absorption
• 3 Parts
– Pyloric sphincter 1. Duodenum 2. Jejunum3. illium
• Nutrients that result from digestion are absorbed into the
blood from the small intestine
• Pancreas: secretes digestive enzymes and buffer
solution
• Liver produces bile to break down fats
– Bile is stored in the gallbladder
• Most digestion occurs in the duodenum
• Nutrient absorption occurs in the jejunum and ileum
Villi and microvilli: fingerlike projections that increase the
surface area of the small intestine lining
The large intestine (colon) reclaims water and
compacts the feces
3 parts: cecum, rectum, anus
The small intestine empties into the cecum of the
large intestine
-The appendix – suggested role in immunity;
attaches to the end of the cecum
Large intestine functions:
1. Absorb water resulting in solidification of feces
Inflammation of the lining cells may impair this
function and result in diarrhea
2. Absorb vitamins produced by bacteria
Adaptations of vertebrate digestive
systems reflect diet
• Carnivores often have large, expandable
stomachs to accommodate large and
infrequent meals
• Herbivores &
omnivores have longer
canals to allow for digestion
and absorption
• Most herbivores have extra chambers to
house digestive microbes
– May involved an enlarged cecum
How could this be a draw back?
• Ruminants: four-chambered stomach
found in herbivorous mammals
– Produces “cud” which is further breakdown of
the cellulose in plants.
– Chambers contain symbiotic microbes
– Digest the microbes along with the nutrients
produced
Urinary System:
Eliminates waste products from the
body and maintains fluid/salt
balance.
- The blood, which carries waste enters the
kidneys through the Renal Artery
- 1,100-2,000 L of blood pass each day
- blood moves through the kidneys, and is
fitered by nephrons.
- Filtrate is refined to urine
Nephron: miniature filter
1. Bowman’s capsule envelops a ball of
capillaries called the glomerulus. (This is
the blood filtering portion of the kidney)
2. Blood pressure forces water and solutes
into the nephron tubule creating the 180 L
of filtrate.
3. Rest of the nephron filters the filtrate
solution down to urine (takes any
nutrients out) Excess salts, water, urea,
glucose, and amino acids make urine.
4. Many nephrons drop their urine into a
collecting duct.
5. Collecting duct directs urine into the renal
pelvis and then the ureter and on to the
bladder to wait for elimination through the
urethra.
• Urine in kidneys  Ureters (tubes) 
bladder  Urethra  toilet
Overview: A healthy diet
satisfies 3 needs
• All animals must obtain:
1. Fuel to power all body activities
2. Organic molecules to build the animal’s
molecules
3. Obtain essential nutrients the animal cannot
make for itself
Chemical energy powers the
body
• Cellular metabolism produces the body’s
energy currency, ATP, by oxidizing
organic molecules digested from food
– The richest energy source is fat
The energy content of foods is measured in
kilocalories
• Rate of energy consumed by the body is
called metabolic rate
– Basal metabolic rate: the number of
kilocalories a resting animal requires for basic
living
– Breathing, beating heart, maintain body
temperature
• Any excess energy is stored as glycogen
or fat
• Diet must supply essential nutrients
• Essential nutrients: must be obtained in
preassembled form b/c cannot make
– minerals
– Malnourishment: results of long-term
absence of one or more essential nutrients
– 8 of the 20 amino acids are essential and
must be obtained in the diet
• A healthy diet includes 13 vitamins and
many essential minerals
• Vitamin: organic nutrient
– Helps activate enzymes during Chem Rxns
– Ex: Vit. K – helps with blood clotting
• Minerals: inorganic nutrients usually
required in small amounts
– Ex: calcium, phosphorus
– You can have to much!!
Too Much….
• Minerals:
– calcification of organs,
– prevents absorption of other vitamins and
minerals
– Black fingernails
– Garlic breath and skin
– Diarrhea
– Liver damage
– Seizures
Too Much…
Vitamins:
• rapid heartbeat
• Nausea
• Muscular incoordination
• Vertigo
• Joint pain
• Fainting
• Hair loss
Food Labels