gastrointestinal system
a continuous series of hollow muscular tubes that extends from mouth -> anus
- movement of muscles and release of secretions allows for digestion and absorption of food
structures/organs of gastrointestinal system
- nasal passages
- mouth
- salivary glands
- esophagus
- liver
- stomach
- gallbladder
- pancreas
- small intestine
- colon
- rectum
- anus
main role of digestive system
take food and drinks consumed and transfer nutrients, water and electrolytes into body
5 stages of nutrient breakdown
1) ingestion
- physical act of eating
2) digestion
- breakdown of food into small molecules that can be absorbed
3) absorption
- movement of nutrients from digestive tract into circulatory system
4) distribution
- movement thru circulatory system for delivery to tissues/cells
5) usage
- movement of nutrients into cells fro metabolism or anabolic processes
what are the 4 basic digestive processes?
1) motility
2) secretion
3) digestion
4) absorption
digestive processes: motility
- muscular contractions that mix/propel contents of digestive syst.
- SM cells in dig. syst. have constant level of contraction/tone to prevent too much stretching of walls and keep pressure on contents
- propulisive movements push contents forward
what does rate of movement in dig. syst determined by?
what segment of the digestive system it’s in
what do mixing movements help with
mixing the food w/ digestive enzymes and promote absorption by making sure all of it makes contact with walls of dig. syst
what digestive organs use skeletal muscle
- top of esophagus
- mouth
- external anal sphincter
digestive processes: secretion
- excocrine galnds that secrete dig juices into digestive tract lumen
- contents of juices changes in diff parts
- each part also secretes a unique mixture of enzymes, bile salts and mucus
- secretions are reabsorbed after done their job
- endocrine cells are present to secrete gastrointestinal hormones into blood
what determines contents of dig juices
- regional function
- but all contain electrolytes and water
what do gastrointestinal hormones do
control motility and exocrine gland secretion
where do secretory cells get their water and raw materials from?
plasma
digestive processes: digestion
- the biochemical process of enzymatic breakdown of foods that are structurally complex into small absorbable units
- each of the 3 biochemical families of food undergo diff processes
what are majority of carbs ingested as?
polysaccharides
polysaccharides
complex carbs consisting of many glucose molecules
- plant based ones are mainly starches (meats have polysaccharide glycogen)
what are some carbs ingested as?
- disaccharides
– eg, sucrose and lactose
during digestion, what happens to starch, glycogen and disaccharides?
broken down into monosaccharides (only they can be absorbed)
– mainly glucose w/ some fructose and galactose
monosaccharide
simple sugar
- eg, glucose
what are dietary fats normally consumed as?
triglycerides
triglycerides
free fatty acids attached to a glycerol molec
what happens to triglycerides during digestion?
they are broken down by releasing 2 fatty acids
- leaves a monoglyceride ( a glycerol molec with 1 fatty acid attached)
- both free fatty acid and monoglyceride can be absorbed
where does most absorption occur?
small intestine
where is digestion completed?
small intestine
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