D2 digestion Flashcards
is digestive juice secreted continuously?
no – its coordinated w presence of food in part of the gut (vol and when)
3 mechanisms that control the secretion of digestive juices
mechanical
hormonal
nervous
describe the process of nervous control of secretion of digestive juices
sight/smell/taste food = medulla sends nerve impulses via VAGUS nerves = stimulate secretion of saliva and stomach wall cells
parasympathetic vs sympathetic control of digestive juices (nervous)
parasym = speed up digestion when food is ingested
sym = slows down digestion when no foods available
2 mechanical functions for control of digestive juice secretion
- stomach contraction
- peristalsis
name the 4 hormones that make up hormornal control of secretion of digestive juices
- secretin
- cholecystokinin
- gastrin
- somatostatin
how does secretin control secretion of digesive juices
- produced by special cells in SI in response to acid fluid
- release of alkali
where are secretin, cholecystokinin, gastrin, and somatostatin secreted from
special cells in SI
SI
G cells in stomach, duodenum and pancreas
special cells in stomach, duodenum, pancreas
how does cholecystokinin control secretion of digestive juices
- presence of food in SI
- release of bile
- secretion of pancreatic enzymes
how does gastrin control the secretion of digestive juices
physical stimulation – presence of food
chemical stimulation – protein
release of gastric acids and enzymes
how does somatostatin control the secretion of digestive juices
prevents release of acid
prevents release of gastrin, CCK, secretin (basicall cancels out the other 3 hormones)
outline the mechanism of secretion control 6
- sight/smell = secretion of gastric juices
- food in stomach = wall stretched = further secretion
- protein = gastrin secreted = further secretion
- gastrin secretion slows at 3.5 pH, stops at 1.5 pH (protein in food acts as buffer to stomach acid)
- partially digested chyme enters duodenum = proteins = secrete gastrin = more juice
- chyme (low protein but w fatty acids and glu) = secretin + cholecytokinin = decr gastric juice secretion
define exocrine gland
have DUCTS that carry their secretory product to surface of body / lumen of gut
what do saliva glands secrete and what is the effect
saliva – mouth
amylase + mucus
starch –> maltose
what do gastric glands secrete and whats the effect
gastric juice – stomach
pepsin + HCl
proteins –> polypeptides
acidic enviro –> kills bacteria
what does the pancreas secrete and whats the effect (exocrine gland)
pancreatic juice – SI
amylase + proteases + peptidases + lipases + nucleases
starch –> maltose
proteins/polypeptides –> polypeptides + peptides + AAs
triglycerides –> fatty acids + glycerol
nucleotides –> pentose sugars + Pi + bases
whats the pH of the stomach
2.0
function of saliva
lubricating the mouth, throat, food bolus
amylase = digestion of starch
outline the path of pancreatic juices 2`
transported by pancreatic duct
enters intestine in duodenum
what cells secrete mucus
goblet cells
what is the function of mucus
forms an effective barrier to HCl and proteases = prevents self digestion (autolysis)
what is chyme
food mixed with gastric juice and churned by muscle action = semi-liquid
what did william beaumont discover and establish
the role of gastric secretions
how was gastric activity first observed and studied
through a opening from stomach interior to outside the body (bc gunshot)
gastric juice collected and tested w diff foods
how is stomach acid produced
by combination of H+ ions and Cl- ions produced by epithelial cells (parietal cells) of stomach lining
release of H+ ions thru protein carriers = intake of K+ ions from stomach lumen (needs ATP)
what does stomach acid do to protease ensymes
activation
pepsinogen (inactive) – HCl removes 44 AA –> pepsin (Active)
proteins –> peptides
purpose of acid conditions in stomach?
favour hydrolysis reactions, helps to control pathogens ingested with food
what happens in stomach pH falls to low
- stomach wall endangered
- secretin and somatostatin = inhibit gastrin secretion = decr acid
- inhibitory drugs presecribed (eg PPI)
when do stomach ulcers form
when stomach lining is disrupted
symptoms of gastric ulcers
tummy owie + hearburn + nausea + shit blood sometimes
causes of gastric ulcers
excess secretion of gastric acid
+ presence of Helicobacter pylori
what prevents H.pylori from being reached by immune response
the mucus layer
what does H. pylori attach to
cells of stomach mucosa (underneath mucus lining)
why cant H+ ions reach H.pylori
its neutralised by HCO ions and ammonium ions (from bacterias secretion of urease = action on urea)
what is gastritis
inflammation at site of h.pylori infection
what could be a further outcome of h.pylori infection
goblet cells fail = decr secretion of mucus = stomach lining exposed to HCl and protease
3 ways h.pylori ulcers are treated
- amoxicillin
- clarithromycin
- proton pump inhibitor
how does amoxicillin treat in gastric ulcers
is an antibiotic
directly inhibits synthesis of bacterial cell walls
how does clarithromycin treat stomach ulcers
is also an antibiotic
prevents growth of bacteria – inhibits translation = no protein synthesis
how do proton pump inhibitors treat stomach ulcers (short)
inhibits acidification
impact of proton pump inhibitors
blocks proton pump (the hydrogen-potassium one)
in parietal cells of gastric gland = decr H+ secretion into lumn = decr hcl prod
may encourage growth of gut microflora
wall of SI contains _______ muscle tissue
involuntary
what does the innermost surface of the SI consist of
epithelium layer (mucosa)
- contains many goblet cells
what does mucus from goblet cells do
adheres to cells lining the gut
protects gut from mechanical damage, resists self-digestion
what cells does the epithelium of the villi contain many of!
goblet cells
name the 4 components of cross section of small intestine wall (Starting from innermost)
- mucosa: enterocytes
- submucosa
- circular muscle layer + longditudinal muscle layer
- serosa
what are enterocytes
cells that have microvilli – digest and absorb substances
name the 5 adaptations of the villi
- microvilli
- large number of mitochondria
- pinocytotic vesicles
- basal channels betw epithelial cells
- tight junctions
how does microvilli improve food absorption
foldings on cell surface (Facing lumen) = incr surface area
how do pinocytotic vesicles impvoe food absorption
in villus – fluid taken up/released in tiny vesicles across plasma membrane
(basically cell drinking)
what do tight junctions do in the villus
bind the individual epithelial cells tgt = only way into tissues is thru epithelium
basal channels below tight junctions
why is insoluble fibre important
incr faecal mass = stinulates peristaltic movements
(non digestible carbs – cellulose, lignin)
materials not absorbed are _______ as __________
egested
faeces
main constituents of insoluble fibre
cellulose and lignin
what are the benefits of a high fibre diet
- improved bowel movement (Stimulates movement of chyme thru gut)
- slows absorption of glucose = decr risk of diabetes
- decr disease of large intestine
why cant humans digest celluose
we dont have cellulase :(
what bacteria is cholera caused by
Vibrio cholerae
how is cholera aquired
drinking water contaminated with shit from infected ppl
- large no. req. – more than 108-109
what toxin does cholera release
enterotoxin
what is the effect of enterotoxin (simple)
loss of irons = loss of water
symptoms of cholera
massive loss of body fluid = dehydration
vomiting, diarrhea
weakness, incr thirst, seizures, drop in blood pressure, decr urine, kidney failure
how does cholera enterotoxin work in DETAIL 4
- enterotoxin consists of two-protein complex
- B part – binds to binding site (glycolipid on plasma membranes of epithelial cells)
- A part – activates enzyme systems of plasma membrane = secretion of Cl ions into gut lumen = sodium ion uptake inhibited
- hypersecretion of CL ions = water loss
treatment of cholera
immediate administration of dilute solution of electrolytes (oral rehydration salts)
= rebalance fluid and ions lost
challenges in treating cholera
ppl weakened by food shortage
drinking water may need to be carreid some distance (inaccessible)
boiling water to make it safe requires scarce fuel
__________ water makes it safe from cholera
boiling
