Digestion, Absorption, and Transport
process by which food is broken down into absorbable units
passage of nutrients from GI tract into blood or lymp
order of events in digestion
ingestion -> digestion -> absorption -> transport -> metabolism -> excretion
Gastrointestinal tract (GI tract)
flexible muscular tube from mouth, through the esophagus, stomach, small intestine, large intestine, and rectum to the anus
principle organs of the GI tract
stomach, small intestine (about 10ft in length), large intestine
inner space w/in the GI tract
begins digestive process; chews and mixes food w/ saliva
secrete saliva; contribute little to digestion
contains starch digestive enzymes
made of protein; facilitate catalyze chemical reactions; end in -ase
examples of enzymes
carbohydrase, protease, lipases
protects airway from closing during swallowing (closes when swallowing)
passageway for food from mouth to stomach
name for food unit after swallowing
upper esophageal sphincter
prevents backflow of food from esophagus back into mouth
cardiac/lower esophageal sphincter
prevents backflow of food from stomach back into esophagus
circular muscle surrounding and able to close a body opening; help regulate flow of food particles
portion of digestive tract that grinds and churns swallowed food, mixing it with acid and enzymes to form chyme; adds HCL, enzymes, and fluid to bolus; major site of protein digestion
keeps pH of stomach acidic (pH <2)
secreted by goblet cells in stomach to protect stomach from HCL's acidic pH
term for bolus after it is churned, mixed, and ground into semi-liquid mass
how is chyme released?
released into small intestine in small amounts by pyloric sphincter
separates stomach from small intestine and regulates the flow of partially digested food into the small intestine; prevents backflow from small intestine back into stomach; opens about 3x per minute
measure of acidity/alkalinity of a substance
10 ft length; major site of carb and lipid digestion and of nutrient absorption into blood stream and lymphatic system
3 sections of small intestine
duodenum, jejunum, ileum
contains enzymes and bicarbonate
strong base that keeps pH of small intestine basic/alkaline
conducts pancreatic juice from pancreas to duodenum of small intestine
conducts bile from gallbladder to small intestine
gland that secretes digestive enzymes and juices into the duodenum
reabsorbs water & minerals from chyme and leaves semi-solid waste composed of fiber, bacteria, and unabsorbed nutrients; passes waste & unabsorbed nutrients like fiber on to rectum for elimination
3 sections of large intestine
ascending colon, transverse colon, descending colon
separates small and large intestine; lower right side of abdomen
final sphincter muscle
movement of food through GI tract
wavelike muscle contractions that push contents through GI tract
periodic squeezing/contracting or partitioning of intestine at intervals along its length
what is the purpose of segmentation?
to mix chyme and promote close contact with digestive juices & absorptive cells of intestinal wall before contents move along
how do digestive enzymes catalyze hydrolysis reactions?
by splitting reactant into 2 products (with addition of water) then molecule is broken into smaller pieces
usually made of protein; act as chemical messengers; regulate enzyme action
examples of hormones
gastrin, secretin, gastric inhibitory peptide
organs with glands that provide digestive secretions
salivary glands, stomach, pancreas, liver (via gallbladder), small intestine
cell/group of cells that secretes materials
secrete materials out of the body (into digestive tract or onto skin)
secrete materials inside body (into blood)
where is bile produced?
in the liver
where is bile stored?
in the gallbladder
emulsifier that prepares fats/oils for digestion by bringing fats into suspension with water so that enzymes can break them down into their component parts
fingerlike projections from the folds of the small intestine that increase surface area
tiny, hairlike projections on each villus; trap nutrients and transport them into cells
tubular glands that lie between the intestinal villi and secrete intestinal juices into the small intestine
nutrients can cross into intestinal cells freely
when nutrients need specific carrier to transport them from one side of cell membrane to other
when some nutrients must be absorbed actively-these nutrients move against a concentration gradient, which requires energy
what nutrients enter vascular system directly?
amino acids, monosaccharides, & small lipid particles
what nutrients have to enter vascular system via lymphatic system?
larger lipids (monoglycerides, long chain FAs, and fat sol. vit.)
blood circulatory system through which blood lows continuously, picking up and delivering materials as needed
loosely organized system of vessels/ducts that move fluids toward thorasic duct then to vena cave of the heart
clear yellowish fluid almost identical to blood BUT does not contain RBCs or platelets; transports fat and fat soluble vit. to bloodstream
how do long chain FAs and fat-sol vit. absorb into vascular system?
small intestine -> lymp -> vascular system
maintenance of constand internal conditions by body's control systems; constantly react to external forces to maintain limits set by body needs
any hormone that slows motility and inhibits gastric sections
hormone secreted by cells in stomach wall; turned on by presence of protein in stomach; turned off when stomach reaches pH of 1.5
what is the target organ of gastrin?
glands of stomach
where is secretin produced?
produced in cells in duodenum wall
what causes secretin production?
presence of chyme in small intestine triggers release-pyloric sphincter opens, releasing chyme into duodenum
what is the target organ of secretin?
target organ is pancreas
how does secretin get to pancreas?
travels from small intestine to pancreas via vascular system
what does secretin produce?
bicarbonate-rich pancreatic juice
what causes cholecystokinin (CCK) production?
produced when fat is present in small intestine
where is cholecystokinin (CCK) produced?
produced by intestinal wall cells
what is the target organ of cholecystokinin (CCK)?
target organ is gallbladder
what happens when CCK reaches the gallbladder?
causes the release of bile into the small intestine
what happens when CCK reaches pancreas?
it stimulates it to secrete its juices, releasing bicarbonate and enzymes into small intestine which slows gastric motility
how does CCK travel?
travels via vascular system to gall bladder
gastric inhibitory peptide
slows digestion to allow time for fat digestion; slows GI motility; slows gastric secretions
where is gastric inhibitory peptide produced?
produced by intestinal wall cells (like CCK)
how does gastric inhibitory peptide travel?
travels from small intestine (via vascular system) to the stomach
what does bicarbonate do?
where is bicarbonate released?
released by pancreas
what causes secretion of bicarbonate?
secretion turned on by presence of chyme in duodenum
what stops bicarbonate secretion?
secretion turned off by neutral to basic pH in duodenum
how does bicarbonate travel?
travels from pancreas (via vascular system) to small intestine (near pyloric sphincter)
what organs release proteases, lipases, carbohydrases?
secreted by both small intestine (duodenum) and pancreas
what is the target organ of proteases, lipases, and carbohydrases?
target organ is duodenum of small intestine