DI Flashcards
pancreatic secretion - enzymes
trypsin, chymotrypsin
splits peptide bonds in proteins to peptide fragments
carboxypeptidase
splits terminal amino acid from carboxyl end of protein
pancreatic lipase
splits 2 fatty acids from triglycerides to free fatty acids and monoglycerides
pancreatic amylase
splits polysaccharides to maltose
protein enzymes (secreted inactive)
with activation in duodenum
trypsinogen
coverted to trypsin activated by enterokinase
chymotrypsinogen
converted to chymotrypsin activated by trypsin
procarboxypeptidase
converted to carboxypeptidase activated by trypsin
bacterial flora
“micriobiome”
- convert some undigested cellulose/fiber to short chain fatty acids
- produce small amounts of vitamin K and B complex
- ferment some undigested carbs to gases
haustral churning
segmentation like process in the large intestion
- mechanical digestion
- contraction of smooth muscles causes segmentation
- local control based on distension of haustra
defacation
- rectum usually empty
- mechanoreceptors detect rectal wall distension
- send signal to medulla oblongata and spinal centres
- rectum contracts, internal anal sphincter relaxes (smooth muscle)
- external anal sphincter contracts intially (skeletal muscle)
- once pressure reached in rectum, external anal sphincter relaxes and feces expelled
neural
short reflexes
Intrinsic control
Stimuli to receptors -> nerve plexuses-> effector cells all within GI tract (enteric ns)
Long reflexes
extrinsic control
neural paths extend outside GI tract up to and back from CNS via afferent neurons and efferent nerves
-back to nerve plexuses via ANS ( sympathetic and parasympathetic )
secretin, gastrin, CCK
main enteroendocrine cells scattered throughout epithelium of stomach
- hormonal gastrointestinal regulation
- Can be excitatory or inhibitory depending on target
enteroendocrine cells
one surface exposed to lumen of GI tract for stimuli of cell encountered
- when stimulated, opposite surface from GI tract lumen releases hormone into blood
- travel in blood to generate response
cephalic phase
- initial phase beginning digestive processes
- sensory signals sent to salivary centre in medulla oblongata -> increase salivation
Both sympathetic and parasympathetic produce salivation
Not antagonistic
sympathetic triggered by stress and dehydration (smaller volume, thick saliva, rich in mucus (dry mouth))
parasympathetic provides basic amount to keep mouth and throat moist, abundant watery saliva rich in enzymes when stimulated
mouth chemical digestion
salivation-saliva production
-salivary glands release into mouth via ducts
99% water : rinses away bacteria dissloves molecules for taste
mucus
lurbicates food, mouth, pharynx to facilitate bolus swallowing
bicarbonate
neutralizes acids in foods (mouth slightly acidic)
lyzsozyme
kills bacteria and prevents bacterial growth in mouth
enzymes salivary amylase lingual lipase
salivary amylase breaks down polysacharides to monosacharides
-wants slightly acidic environement
lingual lipase breaks down tryglicerides to maltose
-wants highly acidic environment
limited absorption in mouth
some vitamins, minerals, electrolytes and drugs
mechanical digestion
chewing : skeletal muscles plus activity of tongue, lips, cheeks
voluntary and involuntary aspects
(rhythmic jaw movements involuntary)
- triggered by pressure food against mouth
- goals :
- more surface area exposed (breakdown)
- mixing with chemical digestion added in mouth
- forming bolus to swallow
deglutition (swallowing)
3 stages
highly complex
coordinated activity involving 22 muscle groups
8 sec food 1 -2 sec for liquids
1st stage of deglutition
buccal stage or voluntary stage
- in mouth
- bolus pushed into oral pharynx by tongue
2nd stage
pharyngeal stage
- in pharynx
- involuntary
- oral pharynx mechanoreceptors send signals to swallowing centre in medulla oblongata when bolus present
- swallowing centre sends signals :
- structure move to blocking positions (uvula, tongue, epiglottis)
- stop breathing briefly
- upper esophageal spincter relaxes : bolus enter esophagus
once in esophagus
everything goes back to normal (blocking positions, breathing resumes)
-upper esophageal sphincter contracts; blocking backflow
3rd stage
esophageal stage
- involuntary
- peristalsis (muscle contraction)
circular muscles contract above bolus
longitudinal muscles contract along esophagus to push bolus down to stomach
-lower esophageal sphincter relaxes; bolus enters stomach
when bolus in stomach
lower esophageal sphincter contracts (prevent regurgitation)
GERD : gatrointestinal reflux disease
when acid comes back up into esophagus
antacids
neutralize acid already secreted
acid blockers
before to prevent acid secretion
alcohol, smoking
relax lower esophageal sphincter
mixing waves / peristalsis
in stomach
- series of muscle contractions
- stronger contractions in antrum minimal in fundus (fundus continuation mouth chemical digestion)
- propulsion : mix with food
- retropulsion : intense contractions backward motion of food in stomach
- pacemaker cells set basic wave
- BOLUS BROKEN DOWN TO CHYME
gastric emptying
- 2-4 hours to get out of stomach
- small amount per wave into deodenum
limited absorption in stomach
some alcohol, aspirin, drugs
stomach -gastric gland
cell types
mucous cells : secrete mucous and bicarbonate
exocrine cells
-cheif cells : secrete pepsinogen
-parietal cells : secrete HCL hydrochloric acid
-enterochromaffin-like cells (ECL) : secrete histamine
Enteroendocrine cells : release into bloodstream
G cells : secrete gastrin
D cells : secrete somatostatin
HCL
activates pepsinogen to pepsin
- increase activity of lingual lipase and inactivates salivary amylase
- denatures proteins
- kills some pathogens
pepsinogen
secreted inactive to doesnt digest cells forming it (activated in stomach lumen)
- once activated to pepsin by HCL, breaks proteins into peptide fragments,
- most active in highly acidic environment
mucus and bicarbonate
secreted by mucous cells
-help form protective barrier for epithelium against HCL
small intestine
many thing still not at an absorbable size when they arrive
90% nutrient absorbtion
- large surface area because of circular folds, villi, microvilli to maximize absorption
- 3-6 hours for digestion and absorption
secretes intestinal juice :
water, mucous, few enzymes
many needed substances needed to continue digestion coming from accessory structure like liver, gallbladder and pancreas (released into duodenum via ducts)
intenstinal phase of gastrointestinal regulation
receptors in duodenum monitor stimuli (acids, fats)
- trigger short and long reflexes
- neural paths (enterogastric reflex)
- hormonal path releases enterogastrones (secretin and cck)
- ultimate event is decreased gastric emptying
- neural path (sympathetic) can constrict pyloric sphincter (decrease gastric emptying)
- trying to match gastric emptying to small intestine digestion
- overload duodenum leads to “dumpring syndrome”
other influences on gastric emptying
inhibiting gastric emptying : sadness,fear, body pain, high exercise
stimulating gastric emptying : anger, aggresion, moderate exercise intesity
liver
metabolic and regulatory roles
- bile production and release
- bile salts (little bicarbonate)
gallbladder
bile storage and release
pancreas
pancreatic juice secretion :
exocrine cells : acinar cells (digestive enzymes)
epithelial cells: duct cells (bicarbonate)
enteroendocrine cells : hormones (insulin, glucagon)
bile
contains bicarbonate, cholesterol, bile pigments, phospholipids, organic wastes, bile salts
bicarbonate sources
pancreas : pancreatic juice
liver : bile (small amount)
enterokinase
attached to wall of intestine, is a brush border enzyme
-activates trypsinogen to trypsin
duct cells
release bicarbonate
acinar cells
release enzymes
small intestine - mechanical digestion
contributiuons from liver, gallbladder, pancreas with stomach chyme propelling to large intestine
-segmentation
segmentation
areas of contraction (where food is present)
areas of relaxation along length of small intestine
contraction breaks food down in a backward and forward motion and brings in contact with absorptive surfaces
more active in prox small intest than distal
- parasympathetic (neural path) and gastrin (hormonal path) can increase
- sympathetic (neural path) can decrease
migrating myoelectric complex (MMC)
after a meal mostly absorbed segmentation stops and this replaces
begins in antrum of stomach
- in steps
- peristaltic wave short dist
- 2 hours to reach large intestine
- returns to start and restarts as long as food present
ileocecal valce
valce from ileum to large intestine
-mostly closed, relaxation needed to enter large intest
gastroileal reflex (neural path)
triggered by food and mixing waves in stomach
- signals ileum to increase peristalsis in ileum and relaxes ileocecal valve
- gastrin (hormonal path) also relaxes ileocecal valve
haustral churning
contractions of smooth muscles producing segmentation like motion
in large intestine
