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Flashcards in lecture 16 Deck (20):

three dietary categories

1. herbivores: eat autotrophs such as plants and algae
2. carnivores: eat other animals
3. omnivores: eat both plants and animals


four mechanisms that animals use to obtain and ingest food

1. suspension feeders: extract particles suspended in the surrounding water
2. substrate feeders: these organisms live within or atop their food source
-they eat their way through the food source
-ex) earthworms
3. fluid feeders: suck nutrient rich fluids from their host
-host can be plant or animal
-ex) mosquitoes
4. bulk feeders: ingest large pieces of food
-utilizes utensils pieces of food
-kill prey
-tear off pieces


four stages of food processing

1. ingestion
2. digestion
3. absorbtion
4. elimination



-this is the actual act of eating



-this is the breakdown of food into molecules small enough to be absorbed by the body
-this stage occurs in two stages:
1. mechanical breakdown:
-occurs in the mouth of humans and many other animals
-teeth break food into smaller pieces, increasing surface area
2. enzymatic breakdown:
-enzymes breakdown the chemical structure of the molecules
-occurs via the addition of water



-the products of enzymatic digestion are absorbed into the cells lining the digestive tract
-these products then enter the blood stream and are delivered to the cells of the body



-undigested material passes through the digestive tract


compartmentalized digestion

-digestion must occur in specialized compartments
-in order to avoid digestion of self tissues
-food vacuole is the smallest digestive compartment
-fuses with lysosome which contains digestive enzymes
-most animals contain a internal compartment
-permits extracellular digestion
-gastrovascular cavity: digestive cavity with only one opening the mouth)


steps in compartmentalized digestion

1. gland cells lining the cavity secrete digestive enzymes
2. enzymes break down soft prey tissues
3. other cells present engulf small food particles
4. food particles are broken down in food vacuoles
5. undigested material is expelled through the mouth


alimentary canal

-has two openings a mouth and an anus
-most mammals
-may lead into a crop, a gizzard or a stomach
-stomach and gizzard may temporarily store food
-churn and grind food
small intestine:
-bulk of enzymatic digestion and all nutrient absorption occurs here
-undigested materials are expelled through the anus


1/3 example of alimentary canals

1. earthworm
-food enters pharynx from mouth
-passes through esophagus and is stored in the crop
-gizzard contains sand and gravel and digests the food
-digestion and subsequent absorption occurs in the intestine
-dorsal fold increases the surface area for absorption


2/3 example of alimentary canals

2. grasshopper
-uses a crop to store food also
-digestion occurs in the mid-gut region
-gastric pouches here increases the surface area for absorption
-hind gut is to absorb water and compact waste


3/3 example of alimentary canals

3. birds
-three separate chambers
-a crop
-a stomach
-a gizzard: filled with gravel to pulverize food
-chemical digestion and absorption occur in the small intestine


human digestion

-peristalsis propels food through the GI tract
-alternating waves of smooth muscle contraction and relaxation
-sphincters regulate the passage of food into and out of the stomach
-cardiac sphincter
-pyloric sphinter



-has accordion-like folds to increase absorptive surface area
-can stretch to accommodate up to 2L of food and liquids
-stomach secretes gastric juice:
-composed of mucus, strong acid and enzymes
-hydrochloric acid begins breakdown of chemicals bonds in food
-kills most bacteria that have entered with food pH=2
-mucus protects stomach lining from harsh acidity
-HCI also converts certain enzymes into their active form
-hormonal control of digestion
-gastrin is released from stomach cells into the blood in response to food
-circulation in the blood returning to the stomach to stimulate secretion of more gastric juice


small intestine

-remainder of digestion occurs here
-absorption of nutrients occurs here
-digestive enzymes used during digestion are synthesized by:
-the pancreas: pancreatic juice which is a mixture of digestive enzymes and bicarbonate
-the liver: produced bile which contains salts that emulsify fats
-bile is stored by the gall bladder until it is required in the small intestine
-small intestine also produce digestive enzymes which aid in digestion
-absorptive surface is increased by villi which are finger-like projections lined with microvilli
-extended into lumen of small intestine greatly increasingly surface area
-absorptive surface of the small intestine is approx 300m2
-roughly the size of a tennis court



-liver is located between the intestine and the heart
-hepatic portal vein receives blood from capillaries of small and large intestine
-transport nutrients absorbed by the intestines directly to the liver
-main liver function is to remove excess glucose from the blood
-convert excess glucose to glycogen
-glycogen is stored in the liver
-liver also produces lipoprotiens that transport fats and cholesterol to the cells of the body
-liver is involved in detoxification and modification of substrate absorbed by the GI tract ex) alcohol and drugs
-then secreted by the kidney into urine
-produces bile
-processes nitrogen wastes from protein breakdown, forming main urine component, urea


large intestine

-1.5m long
-outpocketings include a blind pouch called the caecum and the appendix
-main functions is to absorb any remaining water
-waste products are referred to as feces
-mainly undigestible plant fibers and normal flora from the colon
-especially E.coli
-feces are stored in the anus until elimination


evolutionary adaptations

-non-human animals exhibit different variations on this digestive system plan
-natural selection has favored adaptations that fit an animals digestive system to be structured to digesting the kind of food that the animal eats
-large, expandable stomachs: carnivores
-length of digestive tract: herbivores and omnivores
have longer digestive tracts
-vegetation is more difficult to digest
-longer canal provides more time for digestion
-herbivores also usually have special chambers to house lots of bacteria
-help the animal by digesting cellulose into simple sugars


nutrients supplied from diet

-essential nutrients must be supplied by animal diet
-animals cannot make these from any raw materials
-four classes:
1. essential fatty acids: linoleic acid used to synthesize the plasma membrane
2. essential amino acids: 8/20 cannot be synthesized- most common
3. vitamins
4. minerals
-undernourishment: diet chronically deficient in calories
-malnourished: long term absence of one or more essential nutrients