chapter 34 (digestive system) Flashcards
Digestive system functions
Ingests food
Breaks food down into small molecules that can cross plasma membranes
Absorbs nutrient molecules
Eliminates indigestible remains
Digestive System
Includes all the organs, tissues, and cells involved in ingesting food and breaking it down into smaller components
Contributes to homeostasis by providing body with nutrients needed to sustain life of cells
incomplete digestive tract
has a single opening used as an entrance for food and exit for wastes
complete digestive tract
has two openings
Continuous filter feeders
Always have water moving into the mantle cavity via the incurrent siphon
Particles are deposited on gills.
Size of incurrent siphon permits entry of only small particles.
Do not need food storage area
Discontinuous feeders
Moves rapidly through water using jet propulsion
Uses tentacles to seize prey
Beaklike jaws pull pieces into the mouth with the radula
Food storage area needed
Stomach, with cecum, retains food until digestion is finished
Dentition
differs with mode of nutrition
type, number, arrangement, set of teeth.
Herbivores
Eat only plants
Incisors for clipping
Premolars and molars for grinding
Land snails and some insects are herbivores.
Koalas, which are mammals, eat only eucalyptus leaves.
Grazers, like horses, feed on grasses.
Ruminants, like cattle, goats, and sheep, have a four-chambered stomach which allows them to regurgitate solid material for complete digestion.
Carnivores
Eat only other animals
Pointed incisors and enlarged canines
Shear off pieces small enough to swallow
Spiders and sea stars are carnivores.
Dogs, lions, and dolphins are carnivores.
The lion’s pointed canine teeth are used for
killing, sharp incisors for scraping bones,
and pointed molars for slicing flesh.
Omnivores
Variety of specializations to accommodate both vegetation and meat
Clams and tube worms are invertebrate omnivores.
Humans, pigs, raccoons, and most bears are omnivores.
Dentition of the above is specialized to accommodate vegetable and meat diet.
Better ability to adapt to different food sources
Human Digestive System
Human digestive tract is complete. Part of a tube-within-a-tube body plan Begins with a mouth and ends in an anus Digestion is entirely extracellular. Is mechanical as well as chemical Digestive enzymes are secreted by The wall of the digestive tract Nearby accessory glands
Mouth
Where digestion begins
Tongue
Composed of striated muscle and an outer layer of mucous membrane
Mixes chewed food with saliva
Forms mixture into a bolus
Pharynx
Digestive and respiratory passages come together in the pharynx, then separate.
Soft palate closes off nasopharynx during swallowing
Epiglottis
Epiglottis
Covers the glottis (opening into the trachea)
Keeps food from air passages (most of the time)
Esophagus
Moves food to stomach by peristalsis
Peristalsis – Rhythmical contraction to move contents in tubular organs
Stomach
Stomach wall has deep folds (rugae)
Folds disappear as the stomach fills to an approximate volume of one liter.
Epithelial lining of the stomach has millions of gastric pits, which lead to gastric glands.
Stomach pH
about 2.0, which can kill bacteria in food
pepsin
is a hydrolytic enzyme that acts on protein to produce peptides.
Gastric glands
secrete hydrochloric acid (HCl) and pepsin
what protects the stomach wall from enzymatic action.
A layer of mucus
in the stomach When gastric acid leaks upward
the mucosal lining can be irritated.
GERD
Gastrointestinal reflux disease can cause heartburn
chyme
happens when Food mixes with gastric juices