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function of digestive system

breaks down, absorbs, and metabolizes nutrients from food

Organs of the digestive system

mouth (buccal cavity)
salivary glands
esophagus
stomach
liver
gallbladder
pancreas
large intestine
small intestine
rectum
anus

Monogastric Stomach

simple stomach

herbivores, carnivores (cats), and omnivores (dogs, pigs, chickens)

Pseudoruminant Stomach

a digastric stomach with 3 chambers

herbivores (horses and rabbits)

Ruminant stomach

Specialized four-compartment stomach consisting of the rumen, reticulum, omasum, and abomasum

herbivores (cattle, sheep, goats)

rumen

storage area for feed, bacteria help break down roughage

Reticulum (honeycomb)

filter/forces roughage back to the mouth for rumination & further breaks down the feed, 2nd compartment

omasum

the muscular third stomach of a ruminant animal, between the reticulum and the abomasum, water absorption happens here

Abomasum (true stomach)

fourth compartment of the ruminant stomach, the glandular portion that secretes digestive enzymes

microbial fermentation

microbes aid in breakdown of roughage and produce volatile fatty acids (VFAs)

allows for ruminants to obtain essential nutrients and prepare them for further digestion

pathway of food through ruminant digestive tract

mouth -> esophagus -> rumen -> reticulum -> omasum -> abomasum -> intestine -> rectum -> anus

nutrition

The process by which your body takes in and uses food

nutrient

Any chemical element or compound in the diet that supports normal maintenance of life processes, reproduction, growth, or lactation

essential nutrient

nutrient that must be supplied by food

digestion

preparation of food/feed for absorption (physical, chemical, or microbial action)

Absorption

Passage of food or nutrients from the gastrointestinal (GI) tract into the blood stream and its distribution

metabolism

Sum of all biochemical processes that nutrients undergo to furnish energy and build new tissues

anabolism

the building up of body cells and substances from nutrients

catabolism

breaking down

process of digestion

prehension -> mastication -> deglutition ->regurgitation -> digestion -> absorption -> assimilation ->egestion

prehension

grasping of food using prehensile tools (lips, tongue, teeth)

mastication

the process of chewing

deglutition

the act of swallowing

regurgitation

the return of swallowed food into the mouth

digestion types

fermentation - microbes

chemical - pH, HCL

mechanical - avian

enzymatic - amylase, pepsin

absorption

The process by which nutrient molecules pass through the wall of the digestive system into the blood (endocrine)

assimilation

the absorption and digestion of food or nutrients by the body or any biological system.

egestion

defecation

mucous neck cells

produce mucus to lubricate the food entering the stomach

parietal cells

secrete hydrochloric acid

chief cells of the stomach

secrete pepsinogen

enteroendocrine cells

secrete hormones and paracrine messengers that regulate digestion

Amylase

Enzyme in saliva that breaks the chemical bonds in starches, secreted by pancreas

lipase

pancreatic enzyme necessary to digest fats

protease

enzyme that breaks down proteins

pepsin

Converted from pepsinogen by the acidic environment of the stomach (HCl), and aids in the digestion of proteins

gastrin

produced by the lining of the stomach (G Cells) in the presence of a meal in order to prompt the release of HCl and digestive enzymes

ghrelin

A hunger-arousing hormone secreted by an empty stomach

Cholecystokinin

a hormone that is secreted by cells in the duodenum and stimulates the release of bile into the intestine and the secretion of enzymes by the pancreas.

insulin and glucagon

hormones that regulate blood sugar

insulin

secreted by pancreas; released after a meal in response to high blood glucose

stimulates storage of glucose in form of glycogen

Glugacon

secreted by the pancreas in response to low blood glucose

stimulates breakdown of glycogen to produce energy

muscle type of digestive tract

smooth

peristaltic contractions

responsible for forward movement of bolus thru digestive tract

negative feedback by norepinephrine

fight or flight vs rest and digest

vagus nerve

link between nervous system and digestive system

brush border

Surface of a cell covered with microvilli. increases surface area of a cell for absorption

enzymes embedded in border to aid in digestion and absorption

classes of nutrients

carbohydrates, fats, proteins, vitamins, minerals, water

water

Transport of nutrients
• Solvent for chemical reactions
• Temperature control (sweat)
• Lubrication

proteins

amino acids
muscle
enzymes
structural components

Carbohydrates

Sugars, starches, and cellulose
• Formed by photosynthesis in plants
• Fundamental unit is glucose

minerals

Act as coenzymes and cofactors for reactions
• Macrominerals
• Ca, P, Mg, K, salt, S
• Microminerals
• Fe, Zn, Cu, Se, I, Mn, Cr

vitamins

Fat soluble
• A, D, E, K
Water soluble
• B vitamins and Vitamin C

lipids (fats)

insulation
protection
energy