lecture 16 Flashcards
three dietary categories
- herbivores: eat autotrophs such as plants and algae
- carnivores: eat other animals
- omnivores: eat both plants and animals
four mechanisms that animals use to obtain and ingest food
- suspension feeders: extract particles suspended in the surrounding water
- substrate feeders: these organisms live within or atop their food source
- they eat their way through the food source
- ex) earthworms - fluid feeders: suck nutrient rich fluids from their host
- host can be plant or animal
- ex) mosquitoes - bulk feeders: ingest large pieces of food
- utilizes utensils pieces of food
- kill prey
- tear off pieces
four stages of food processing
- ingestion
- digestion
- absorbtion
- elimination
ingestion
-this is the actual act of eating
digestion
- 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
absorption
- 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
elimination
-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
- gland cells lining the cavity secrete digestive enzymes
- enzymes break down soft prey tissues
- other cells present engulf small food particles
- food particles are broken down in food vacuoles
- undigested material is expelled through the mouth
alimentary canal
-has two openings a mouth and an anus
-most mammals
pharynx:
esophagus:
-may lead into a crop, a gizzard or a stomach
-stomach and gizzard may temporarily store food
-muscular
-churn and grind food
small intestine:
-bulk of enzymatic digestion and all nutrient absorption occurs here
anus:
-undigested materials are expelled through the anus
1/3 example of alimentary canals
- 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
- 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
- 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
stomach
- 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