DI Terms Flashcards
Carbohydrates
-Polysaccharides: starch and glycogen
-disaccharides: glucose and lactose
proteins
polypeptides (pepsin, trypsin, chymotrypsin)
triglycerides
glycerol bound to 3 fatty acids
Ingestion
entry to GI tract
motility
movement for mixing/propulsion
secretion
contributions of water, enzymes, and environmental factors
digestion
breakdown using mechanical and chemical
absorption
entry to body
defecation
exit to gi tract
anatomical components of digestion
GI tract and accessory organs/structures
Mechanoreceptors
detect distention from food entering
osmoreceptors
detect osmotic pressure changing from different food particles entering (these can be called solutes)
chemoreceptors
detect specific nutrient concentrations and acidity
smooth muscle contraction
circular and longitudinal muscle layers
epithelial cells
inner lyaer of gi tract facing lumen
enteroendocrine cells
hormonal secretions
exocrine cells
enzyme and environmental factor secretions
muscous cells
mucus secretions
enteric
autonomic motor, gi tract local neural control, more neurons than spinal cord
enteric nerve plexuses
myenteric and submucosal
connections for communication (enteric nerve plexuses)
-within plexus and between plexuses
-receptors to plexuses/CNS to plexuses
myenteric response
especially to circular/longitudinal muscles
submucosal
especially to epithelial cells
enteroendocrine cells (more)
-one cell surface faces gi tract lumen, encounters stimuli
-stimulation leads to opposite cell surface from gi tract lumen releasing hormone into bloodstream
key hormones released by enteroendocrine cells
- gastrin
- secretin
- cholecystokinin
- somatostatin
salivary centre location
medulla oblongata
cephalic stimuli
sight, smell, taste, hunger, stress, dehydration
saliva composition
-99% water
-mucus
-bicarbonate
-lysozymes
-enzymes (salivary amylase and lingual lipase)
water (saliva)
moisten food and tissues, taste, rinse mouth to prevent bacteria growth
mucus (saliva)
lubricate food, mouth, pharynx to facilitate swallowing
bicarbonate (saliva)
help neutralize food acids (environmental, mouth slightly acidic)
lysozymes (saliva)
kill bacteria to prevent bacterial growth
enzymes (saliva)
start of chemical digestion
salivary amylase
polysaccharides to disaccharide maltose, operate best in slightly acidic environment (mouth to fundus of stomach)
lingual lipase
triglycerides to monoglycerides and fatty acids, operate best in highly acidic environment (body and antrum of stomach)
mastication
chewing, mechanical digestion
rhythmic jaw movements in mastication
voluntary and involuntary mastication patterns and reflexes
mastication involves these
skeletal muscles and tongue, lip, and cheeks activity
goals of mastication
- physical digestion
- motility
- forming bolus
physical digestion = ?
more surface area exposed
motility
mix with enzymes added in mouth (start chemical digestion)
bolus
semisolid mass for swallowing
limited absorption in mouth
some vitamins and minerals, electrolytes, alcohol, drugs
degulitition
swallowing
deglutition 1st stage
voluntary or buccal stage, tongue against palate action pushes bolus into oral pharynx
deglutition 2nd stage
pharyngeal stage in pharynx, involuntary
deglutition 3rd stage
esophageal stage in esophagus, involuntary, motility from peristalsis and circular/longitudinal muscles, lower esophageal sphincter relaxes and bolus enters stomach
regurgitation
backflow into esophagus, insufficient lower esophageal sphincter contraction when stomach motility starts = contents from stomach regurgitating back up esophagus = heart burn
increase relaxing of lower esophageal sphincter
alcohol and smoking
gastric motility
mixing waves (15-25 secs), composed of propulsion (down stomach) and retropulsion (up stomach length)
pacemaker cells in ___
smooth muscle set basic wave rate (can be altered by neural and hormonal)
stronger motility in
body and antrum of stomach
weaker motility in
fundus of stomach
gastric motility leads to
bolus break down to chyme (soupy liquid)
gastric emptying
small amount of gastric juice per mixing wave moves into duodenum
gastric juice
collective name for stomach chyme and secretions
gastric phase
food arrives in stomach - receptors detect increased distension - increased amino acids and peptides - decreased acidity
neural gastric phase
parasympathetic and enteric stimulation to increase HCI (hydrochloric acid, stomach acid) secretion and increase gastric motility for greater gastric emptying
hormonal gastric phase
gastrin secretion, increase HCl secretion, increase gastric motility by relaxing pyloric sphincter - greater gastric emptying
increase contraction of lower esophageal sphincter to prevent regurgitation
key stomach cell types in gastric gland
- exocrine cells
- enterochromaffin-like cells
- mucous cells
- enteroendocrine cells
exocrine cells
-parietal cells: secrete HCl
-chief cells: secret pepsinogen (enzyme) - into stomach free floating
enterochromaffin-like cells
secrete histamine (paracrine substance) into local cell area
mucous cells (gastric gland)
secrete mucous and bicarbonate into stomach lumen to form protective layer lining surface epithelial cells against HCl
enteroendocrine cells
-G cells: secrete gastrin
-D cells: secrete somatostatin into bloodstream
pepsinogen
inactive so doesn’t digest stomach wall cells
converted to active pepsin by HCl
pepsin
break polypeptides (or proteins) into smaller peptide fragments, most active in highly acidic environment
HCl additional functions
- effect mouth added enzymes - increase activity of lingual lipase and reduce activity of salivary amylase
- partially denatures proteins - opens up structure to expose more surface area to chemical digestion
- kills some pathogens
parietal cells form…
hydrogen from water and carbon dioxide
if gastrin (hormone), histamine (paracrine), and/or Acetylcholine (neurotransmitter) released
more acid in stomach lumen (more steps before)
if somatostatin hormone released
less acid in stomach lumen (more steps before)
basolateral membrane
closer to capillaries
apical membrane
closer to stomach lumen
intestinal phase
food arrives in duodenum - receptors detect increased acidity, fats, amino acids, distension
enterogastric reflex
-short reflexes - enteric changes - direct effect stomach
-long reflexes - CNS (sympathetic and parasympathetic) changes - indirectly effect stomach
hormonal (intestinal phase)
CCK and secretin secretion and release into bloodstream/bind target cells in stomach
emotions on gastric emptying
-sad, fear, body pain: inhibit
-anger, aggression: stimulate (fight or flight)
exercise on gastric emptying
depends on intensity
high intensity exercise on gastric emptying
inhibit, nutrients and water remain in stomach longer
moderate intensity exercise on gastric emptying
stimulate
gastric emptying and sports that require hydration and nutrition during performance
inhibit if intensity too high - slower for nutrients and water to get out into small intestine (90% of absorption occurs here) - slows absorption which means limited availability of these nutrients to working tissues
bile produced where?
liver
bile composed of?
- bicarbonate
- bile salts
- bile pigments
- phospholipids
- organic wastes
- cholestrol
bile flows to ___ for storage
gallbladder
bile flows to __ when ___
gallbladder, when not actively needed for digestion
when bile needed for digestion
fatty acids in duodenum release CCK into bloodstream to find target cells in gallbladder and sphincter of oddi
what neutralizes highly acidic chyme that comes into duodenum from gastric emptying and why?
key acid neutralizer is bicarbonate, to create alkaline environment preferred by pancreatic enzymes released into small intestine
bicarbonate comes from (small,large)
-small amount: liver/gallbladder
-large amount: pancreas as component of pancreatic juice
pancreatic juice
pancreatic secretions
process of pancreatic secretions
- pancreatic duct cells forms bicarbonate from water and carbon dioxide
- bicarbonate released into pancreatic duct lumen
- pancreatic duct carries bicarbonate to duodenum
trypsin & chymotrypsin actions
split polypeptides to smaller peptide fragments
carboxypeptidase actions
split final amino acid from end of polypeptide
pancreatic lipase
split triglycerides to fatty acids and monoglycerides
pancreatic amylase
split polysaccharides to disaccharide maltose
trypsinogen
activated to trypsin by enterokinase
enterokinase
brush border enzyme
chymotrypsinogen
chymotrypsin activated by trypsin
procarboxypeptidase
carboxypeptidase activated by trypsin
intestinal juice
collective name for:
1. pancreas, liver, gallbladder contributions
2. stomach chyme
3. intestinal secretions: water and mucus
segmentation
alternating areas of contraction and relaxation create back and forth motion (massaging chyme)
segmental is __ digestion
mechanical (physical)
segmentation also
-motility to mix with chemical digestive enzymes
-weakly propulsive
-helps bring in contact with absorptive surfaces
rate of segmentation
-parasympathetic and gastrin - increase
-sympathetic - decrease
(remember parasympathetic increases digestion)
stages of absorption
- lumen of small intestine through apical surface into absorptive cell
- inside of absorptive cell through basolateral surface to IF
- IF into either blood capillary (CV) or lacteal (immune)
fats for absorption
not very soluble in water intestinal juices so react by forming large fat molecules (fat globules) to minimize surface area
1st digestive step
emulsification, fat absorption without (50%) with (97%)
emulsification
small amounts of triglycerides from fat globule coated in bile salts/phospholipids to form smaller emulsification droplets
bile salts/phospholipids arrangement
polar side (water liking) facing out, non polar side (fat liking) facing in
purpose of bile salts/phospholipids arrangement
repels other emulsification droplets to decrease chances of reforming large fat globule (one way process)
purpose of fat globule to emulsification droplets conversion
exposes more surface area to pancreatic lipase digestive action (triglycerides to monoglycerides and fatty acids)
monoglycerides and free fatty acids crossing
-can cross apical membrane from lumen to inside epithelial cell by simple diffusion
-too many released could reform triglycerides which cannot cross apical membranes
monoglycerides and free fatty acids once inside epithelial cell
reforms triglycerides- further combine with phospholipids and cholesterol to form chylomicron
chylomicron
lipoprotein for transport, inside a vesicle (sac)
chylomicron vesicle
-moves and fuses with basolateral membrane
-membrane opens up and releases chylomicrons by exocytosis into IF
-chylomicrons will enter lacteal as too big to enter blood capillary
lacteal
lymphatic capillary with large pores
2 ions that move based on nutrient needs
- calcium
- iron
calcium movement
-based on blood levels
-transcellular active transport involving release of parathyroid hormone to increase calcium absorption
-paracellular passive transport based on concentration gradient
iron movement
-based on stored levels in epithelial cells
-transcellular active transport with specific iron transporters
-women have many more iron transporters than men due to menstrual cycle losses of epithelial cells
fat soluble vitamins absorption
follow into micelles and cross into epithelial cell with fats by simple diffusion, need fat to absorb fat soluble vitamins
water soluble vitamins
some simple diffusion and active and passive transporters, some will cross in large intestine (vitamin K and some vitamin B)
-vitamin B12 needs to bind intrinsic factor from stomach
-intrinsic factor B12 complex absorbed in ileum by endocytosis
95% of water absorbed by?
osmosis
absorbed carbohydrates and proteins
move from IF into blood capillaries eventually smaller blood vessels join to form portal vein circulating liver
absorbed fats (chylomicrons)
-move from IF into lacteal
-once in lacteal, move into other lymphatic vessels eventually enters bloodstream near subclavian veins circulating liver
