BIOL 365 Digestive System

Functions of the Digestive system

aquire food, transport food, physical treatment, chemical treatment, absorb nutrients and fluids, rid bidy of wastes

Digestive system of pre-vertebrates

filter feeders, cilia & gill slits, no true stomach, no separate liver or pancreas, no gut muscles

Important in feeding in aquatic systems

suction feeding; creating negative pressure in the mouth

Important traits in terrestrial feeding

muscular tongues, salivary glands, large intestine to reabsorb water

Transportation

“dis-assembly line”, transport along the gut after collection

Physical treatment

mouth begins particle size reduction; size of food must be further reduced to facilitate chemical attack

Chemical treatment

breakdown of petentially useful materials to molecules cells can use

absorbtion

after breakdown, molecules are taken up and circulated to cells and storage areas

Basic parts of the digestive system

mouth parts, esophagus, stomach, small intestine, large intestine (birds have crop and gizzard)

Gripping prey

Teeth in fish, amphibiansm and reptiles are used for ______. (teeth are unspecialized)

True mastication (chewing)

________ only occurs in mammals. (heterodont dentition)

Beaks

Used by birds; they lack teeth, but serrated bills are used for siezing prey and tearing

Highly kinetic jaws

used by snakes, madibles are connected by stretchy ligament

Pharyngeal Region (throat)

some movement by cilia but most is by voluntary swallowing

paristalsis

involuntary contractions by smooth musles to push food along

esophagus

anterior-most part of digestive tract, poorly defined in fishes but well defined in tetrapods (forms a crop in birds)

stomach

storage, physical, and chemical treatment; contains mucous and secretory cells (filter feeders lack a stomach)

chyme

broken down food stuff in the stomach, mostly by mechanical action

Mucus

provided by glands, moisturizes to improve passage and pulverization

bird and crocodilian varient stomachs

anterior end is proventriculus (produces juices) and posterior is gizzard (grinds up food)

ruminant varient stomachs

4 chambers, rumen, reticulum, omasum, abomasum

types of stomach epitheial tissues

esophageal, cardiac, fundic, pyloric

esophageal epithelium

anterior part of stomach, non-glandular

cardic

only found in mammals, columnar cells that secrete mucus

Fundic

epitheium that contains secretory cells for mucus and stomach enzymes (pepsin, lipase, HCl)

Pyloric

“downstream” end of stomach that contains tubular glands like cardiac region

Horse vs. cow

nonruminant not efficient as breaking down food

small intestine

begins posterior to pylorus of stomach, chemical digestion and absorbtion of nutrients, surface area increased by villi and spiraling and coiling

large intestine

major site of water resportion, compacts waste, most developed in terrestrial vertebrates (terminates in rectum and anus in fish and mammals, terminates in cloaca in sharks, reptilians, birds, and amphibians)

Cecum/appendix

pouch in the wall of the digestive tract, contains bacteria that aids digestion (telost fishes have pyloric cecae, few reptiles have cacae, in birds and mammals it is located between small and large intestine)

vestigial cecum/appendix

organ that is no longer used in humans, and function of organ is still debated

Liver, pancreas, gall bladder

digestive accessory organs, products are essential for digestion

liver

largest gland in vertebrate body, detoxifies, filters, regulates glucose, synthesis of molecules, produces bile

Bile

produced in liver and stored in gallbladder, essential for breaking down fat in the small intestine, is alkaline to neutralize stomach acid

70-90% efficiency

digestion of carnivorous fish

40-50% efficiency

digestion of herbivorous fish

gallbladder

stores bile from liver, bile is alakaline to reduce acidity from stomach, needed to break down fat

pancreas

produces enzymes to break down glycerol, fatty acids, and carbohydrates; juice is rich in bicarbonate to neutralize acid

Factors that influence the digestive system

Body size, primary feeding mode (herbivory vs carnivory), amount of indigestable materials in diet

rectum and anus

structures where the digestive system terminates in mammals and fish

cloaca

where divestive and excretory system terminates in svc v gbhyujharks, amphibians, reptiles, and birds

lack of a stomach

trait of lamprey fish

spiral valve

trait of primitive fish to increase surface area for absorbtion

pyloric cecae

trait of teleost fishes

bladder is connected to tract at cloaca

trait of amphibians, reptiles, and birds