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Digestion, Absorption, and Transportation - Coggle Diagram
Digestion, Absorption, and Transportation
Organs
Major
Mouth
beginning of digestion process
teeth breakdown food
fluids blend w/ goof to ease swallowing and assist w/ taste
tongue provides taste sensations
once food is swallowed, it passes through pharynx (food is now 'bolus')
epiglottis closes off airway so choking doesn't occur
salivary glands
squirt just enough saliva to moisten each mouthful of food
saliva contains water, salts, mucus, and enzymes that intimate, CHO digestion
saliva also protects the teeth/linings of the mouth, esophagus, and stomach
salivary enzymes break down some CHO
saliva contains
water
salivary amylase
R-factor (protein necessary for vitamin B-12 absorption
Stomach
retains bolus for a while in upper portion
slowly transfers bolus to lower portion
adds juices
grinds to chyme
slowly releases chyme through pyloric sphincter into small intestine
gastric glands
in the stomach, gastric glands secrete gastric juice (water + enzymes + HCl)
strong acidity of stomach prevents bacterial growth and kills most food-bourne bacteria
cells of stomach secrete mucus, protecting them from acid/enzymes/disease-causing bacteria
stomach enzymes work efficiently in acidic environment (digest proteins), salivary enzymes do not (become other proteins to be digested)
gastric juice contains
water
hydrochloric acids (HCl) and intrinsic factor
acid-stable digestive enzymes (eg. pepsin)
Small Intestine
chyme bypasses common bile duct into small intestine - dripping fluids from gallbladder and pancreas)
chyme travels through 3 segments - duodenum, jejunum, ileum
Large Intestine
upon entering the colon, contents bypass opening to the appendix
contents travel through colon to rectum
colon withdraws water, leaving semisolid waste
Accessory
Liver
produces bile - bile salts, pigments, lecithin, cholesterol, water
bile is stored until needed
Gall bladder
stores bile; secretes bile into small intestine
Pancreas
secretes pancreatic juice into small intestine
bicarbonate neutralizes acidic gastric juices
pancreatic enzymes digest CHOs, FATs, and PROs
Muscle Action
Peristalsis
entire inside wall of GI tract is ringed w/ circular muscles
longitudinal muscles surround the rings
rings tighten, long muscles relax - tube is constricted
rings relax, long muscles tighten - tube buldges
wavelike muscular contractions of GI tract that propel contents along
waves normally vary in rates/intensities depending on the part of the GI tract /whether or not food is present
after a meal is eaten, waves are slow and continuous
when GI tract is empty, intestine is quiet except for periodic bursts
stress, medicines, medical conditions may interfere w/ normal GI tract contradictions
Stomach Churning
the stomach has the thickest walls/strongest muscles of all the GI tract organs
possesses a third layer of diagonal muscles that also alternately contracts/relaxes (has three muscle layers)
muscles work to break apart bolus and force chyme downward
pyloric sphincter remains closed
stomach wall releases gastric juices
when chyme is completely liquified (gastric juices) pyloric sphincter briefly opens
allows a small portion of chyme to pass through
Segmentation
periodic squeezing/partitioning of intestine at intervals along its length by its circular muscles
intestinal contractions further break apart food molecules in chyme
promotes close contact w/ digestive juices and intestinal absorbing cells
Sphincter Control
sphincter muscles periodically open and close, allowing contents of GI tract to move along at a controlled pace
upper esophageal sphincter opens in response to swallowing
lower esophageal sphincter (cardic sphincter) prevents reflux of stomach contents
pyloric sphincter holds chyme in stomach long enough for it to thoroughly mix w/ gastric juice and liquify
prevents intestinal contents from backing up into stomach
ileocecal sphincter allows contents of small intestine to empty into large intestine
rectal muscle and two sphincters of anus prevent continuous elimination
Chemical Actions
Hormones
Gastrin
Stimulus
in response to literal/imagined food, the vagus nerve is stimulate, causing gastrin secretion
Site of Secretion/Origin
stomach - cells in stomach wall
Target/Effects
stomach; gastrin stimulates the release of gastric juices from different cells in the stomach
Enzymes
pepsin
Action
Digestion of PRO
Secretin
Stimulus
release caused by presence of acidic chyme in small intestine
Site of Secretion/Origin
small intestinal cells
Target/Effects
Pancreas; acts on pancreas causing it to release alkaline-rich/zinc-rich pancreatic juices
releases digestive enzymes (pancreatic amylase, pancreatic lipase, trypsin)
Enzymes
p. amylase
p. lipase
trypsin
Action
Digestion of CHO/PRO/lipids
Cholecystokinin (CCK)
Stimulus
release caused by presence of fat in the intestine
Site of Secretion/Origin
small intestine
Target/Effects
gall bladder; secretion of bile
no enzymes involved
emulsification of dietary fats
pancreas; stimulates secretion of pancreatic juices into lumen
enzymes: p. amylase, p. lipase, trypsin
digestion of CHO/PRO/lipids
Gastric Inhibitory Peptide (GIP)
Site of Secretion/Origin
small intestine
Target/Effects
Stomach; inhibits secretion of gastric juices, slows release of stomach content into small intestine (prevents acid damage to intestine)
Enzymes
salivary amylase
enzyme for CHO digestion to DS (maltose) level
pancreatic amylase
continues CHO digestion - disaccharides (DS)
pancreatic lipase
primarily causes digestion of TG - MG + 2 free FA
trypsin
continues PRO digestion that was started in the stomach to peptides
di/tri-peptidases
which digest small proteins (peptides, 2-3 amino acids linked together)
maltase
digests maltose to GLU + GLU (eg. found in beer)
lactase
digests lactose to GLU + GAL
sucrase
digests sucrose to GLU + FRU (eg. table sugar)
Basic Reactions
hydrolysis
requires water for reaction to occur
CHO, FAT, PRO degraded into simpler forms
catabolic or breakdown reactions
condensation
release of water in reactions
structural components of nutrients are bound together to form more complex molecules and water is released in the process
anabolic, or building reactions
reduction/oxidation
involves a gain or loss of electrons in a reaction
Digestion
Mouth
a) chewing - muscles in mouth break down food
big pieces go to small pieces of food, greater surface area exposed, increased efficiency for digestion by enzymes
b) fat melts as it warms up to body temperature (eg. chocolate)
c) mixing with saliva (water and mucuous mixture) produced by various glands in the mouth
functions of saliva
moistens & lubricates food through secretion of mucus; softens food
stimulates taste buds by dissolving foods
initial dilution of food to ultimately make it isotonic with plasma
start of CHO digestion; PS to DS (maltose) by action of salivary amylase
slows development of dental caries by protecting tooth surfaces with saliva
contains lysozymes which kill bacteria that enter mouth
esophagus
bolus slides down esophagus and across epiglottis which closes off air passage to lungs; prevents choking on food
conduit to stomach: gravity, lubrication, and peristalsis move food along
bolus enters stomach through cardiac sphincter (aka lower esophageal sphincter)
Stomach Digestion
cardiac sphincter prevents acid backflow from the stomach into the esophagus
stomach has the thickest walls and strongest muscles of all segments of the GI tract
food is held in the upper part of the stomach and slowly passes to the lower section for digestion as stomach expands in volume
in response to food in the stomach or even thinking about food, the vagus nerve in stimulated causing release of the hormone, gastric from cells in the stomach wall
neural system detects distention of stomach wall causing the muscles to contract
gastrin stimulates release of gastric juices from different cells in the stomach
functions of gastric juices
acid denaturing of PRO - change of 3D shape (unravelling)
beginning of proteins digestion via HCL activation of PRO-digesting enzyme pepsin
destruction of foreign organisms (bacteria)
increased solubility of iron and calcium - increased absorption
contains intrinsic factor (protein needed for vitamin B12 absorption
stimulates mucous-secreting goblet cells - thick mucus coating protects stomach wall against possible acid erosion
inactivates many plant and animal hormones that might otherwise act in the body
the pH of the stomach drops to around 1.5 (pH range 1.5-1.7)
once pH drops to 1.5, the acid turns off gastrin-producing cells in the stomach
once gastrin is no longer produced, the glands virtually sotp (or slow) production of gastric juices
pepsinogen - (HCL) - pepsin - 10% of PRO digested in stomach
stomach mechanically mixes and churns up food with gastric juices to produce "chyme" - tiny particles suspended in solution
chyme lo longer resembles food (puree consistency)
chyme empties into small intestine through pyloric sphincter in small quantities (around 5mL, 3x/min
Small Intestine Digestion
pyloric sphincter separates the stomach from the small intestine
a near neutral environment is necessary for digestive enzymes to function in small intestine
5ml (1 teaspoon) of chyme is released into small intestine at one time (around 3x/min
the pyloric sphincter on the intestinal side sense the acidic chyme and closes tighly
acidic chyme in the small intestine causes release of the hormone secretin from the intestinal cells which acts on the pancreas causing it to release alkaline-rich (and zinc-rich) pancreatic juices
pancreatic juices contain
water
bicarbonate (HCO3) - alkaline
pancreatic digestive enzymes
alkaline pancreatic juices neutralize the small volume of acidic mixture present
once the area on the intestinal side of the pyloric sphincter becomes slightly alkaline, this sphincter relaxes and again a small amount of chyme from the stomach enters the small intestine and the process is repeated until the contents of the stomach has been emptied
the small intestine has less of mucous coating than the stomach and is not so well protected from the acid, therefore can only handle small amounts of acid
intestinal cells have a relatively short lifespan (2-3 days) to ensure efficient absorption
chyme travels down the small intestine, through its 3 segments
duodenum (30cm/12inch)
jejunum (120cm/4ft)
ileum (150cm/5ft)
Duodenum/Jejunum
90% of all nutrients are digested and absorbed here
bile is released into small intestine from storage in the gall bladder
goblet cells in small intestine from storage in the gall bladder
goblet cells in small intestine secrete mucus to protect small intestinal cells
crypt glands found between villi secrete intestinal juices into small intestine
intestinal juices contain
water
intestinal digestive enzymes
secretin, CCK, and GIP all help to establish emptying small amounts of chyme from the stomach into the small intestine, causing a slowing down of the passage of "food" through the GI tract
promotes contact w/ digestive juices and optimize absorption, and prevents acid damage to the intestine
all 3 hormones reduce motility
in response to PRO in chyme, crypt glands in the intestine produce DI/TRI-peptidases (enzymes) which digest small proteins (peptides, 2-3 amino acids linked together)
most fibres are not digestible by human enzymes and enter the large intestine undigested
FAT in chyme is emulsified by bile and digested by pancreatic lipase
Ileum
"reserve capacity" for digestion and absportion
terminal ileum only site for vitamin B12 absorption and resorption
a meal can take about 3-10 hours to be digested and absorbed
once chyme enters the small intestine, most of the CHO, PRO, and FAT is absorbed within 30 minutes
gastric emptying is controlled
many factors (other than hormonal control) affect the time needed for digestion and absorption (eg. health of GI tract, fibre content, and binders found in food)
Large Intestine
pH is around 7 (near neutral)
sphicter between small and large intestines is called the ileocecal sphincter
very little amount of chyme (mostly undigested fibres) remains, travels through large intestine to rectum for holding until excretion
bacterial fermentation of fibres, resistant starches, and/or undigested lactose produces short chain fatty acids (2-4C) and gases (methane, carbon dioxide, hydrogen)
bacterial synthesis of vitamins K and biotin
rectum/anus
2 sphincters at end of GI tract: rectal sphincter under involuntary control, anal sphincter under voluntary control
water has been withdrawn in large intestine to produce a semi-solid waste product
digestion summary
digestion transforms food into nutrients for absorption
the 3 energy-yielding nutrients have been disassembled into their basic building blocks
most vitamins and minerals are absorbed intact, but freed from PRO or binders found in foods
undigested residues (eg. fibres, connective tissues) continue travel along Gi tract to maintain muscle tone and efficient peristalsis
fibre contains water and captures other constituents like bile, minerals, additives and contaminants to carry these out of the body
digested nutrients are absorbed from the GI tract as soon as they are ready
most nutrients are absorbed before they reach the large intestine
Absorption
taking up of nutrients into intestinal (enterocytes, absorptive, mucosal)
situation facing the small intestine
for 3-4 hours after eating a meal of rice and beans, vegetables, salad, beverage, and dessert, your body must find a way to absorb trillions of molecules derived from CHO, FAT, and PRO digestion and many vitamins and minerals
Anatomy
small intestine