digestion - lecture 8 Flashcards
describe pancreatic lipases
Pancreatic procolipase – trypsin –> colipase
triglycerides – pancreatic lipase ph 8 –> fatty acids, di and monoglycerides
NEEDS colipase = cofactor, only happens when have it
describe liver
largest gland of body
right and left lobes
for storage, synthesis, detox, metabolism
what does liver secrete
bile from hepatic ducts
bile travels in common bile duct
bile released into si at same place as pancreatic juices
describe liver bile composition -comp stuff
0.5-1l/day
isotonic fluid - sodium, potassium, chloride, BICARB
ph 7.8-8.2 = helps neutralize acidic chyme
describe liver bile composition -solids stuff
~3% solids - NO digestive enzymes tho
bile acts - bile salts
bile pigments - hemoglobin breakdown products
cholesterol
phospholipids
describe bile secretion by liver
continuous
~0.5-1.0 l/day
describe entrance of bile into duo
intermittent = only when meal
volume of bile entering si is <500-700ml/day
moves into gallbladder
what is function of gallbladder
concentrates solids =
hepatic bile 3%
gall bladder bile 10-20% of bile
viscocity increases
reduces ph =
Hepatic bile 7.8-8.2
gall bladder bile 7.0-7.5 - less bicarb
what does gallbladder not do
DOES NOT synthesize bile salts = stores and concentrates THEMMM
What are the results of CHOLECYSTECTOMY
gall bladder removal
Usually bc gallstones
bile salts made from phospholipids precipitates and cholesterol = if not enough bile salts = gallstones and if block cystic duct = bad
but now if removed = still have liver bile only
what are bile salts
synthesized in liver from cholesterol
what do bile salts do
facilitates digestion, transport and absorption of FAT (including cholesterol) by forming water soluble complexes with fats = micelles
facilitates transport and absorption of fat soluble vitamins = a,d,e,k
reduces surface tension and stabilize emulsions = now can be acted upon by lipases
describe bile salts and micelle formation
ampthatic
micelle = inside non polar and outside polar
mixed micelle = a,d,e,k travel in micelle
Surrounded by bile acids
smaller if more bile salts
Circular smaller droplets = more lipases can act
help form stable emulsions = small emulsions = more sa for lipases to act
Describe bile salts - amounts in body
bile salt pool = 3.5g
daily synthesis= 0.5g
daily release into intestine = 15-20g
more bile salts reabs into portal blood and returned to liver via enterohepatic circ
entire bile salt pool recirculated several times a day between liver–>git–>liver
describe hepatic circulation
heart = via aorta to liver and via aorta to intestinal tract
liver secretions go to si
si to liver via hepatic portal vein
liver to heart = via hepatic vein to inferior vena cava
describe enterohepactic circulation
bile salts have diff roles in diff parts of body
absorb recycled and used
back to liver = portal venous return
name intraporal functions of bile salts - 2
regulate hepatic bile flow
regulate synthesis of new bile salts
Describe intraportal functions of bile salts - regulate hepatic flow
the more bile salt returned via portal blood = larger the vol of bile secreted
pos feedback
What will happen to bile secretion if we remove ileum
decrease since less reabs
Describe intraportal functions of bile salts - regulate synthesis of new bile salts
the more bile salt returned in portal blood = smaller the amount of new bile salt being synthesized = more comes back so make less
neg feedback
What will happen to bile salt synthesis if we remove ileum
liver produces more bile salts
name and describe intrahepatic functions of bile salts
keep cholesterol in solution = cholesterol is insoluble in water
if cholesterol precipitates = gives rise to gallstones
in bile solubility of cholesterol increases by 2x10^6
Describe intra intestinal functions of bile salts - 2
intestinal lumen contains v watery medium
act as detergents and help form stable emulsions
assist in transport of fat and fat soluble vitamins (a,d,e,k) from si lumen into intestinal cell
Describe intracolonic functions of bile salts - regulate hepatic flow
inhibit sodium transport and h20 absorp = do not want to absorb too much = constipation
excess bile salt in colon = diarrhea
summarize bile salt function
intraportal = regulate volume of bile secreted by liver and synthesis of new bile salts
intrahepatic = keep cholesterol in soln
intraintestinal = si - emulsify and transport fats
intracolonic = prevents too much water absorp
describe purpose of phases of secretion
cephalic = psychic and gustatory, increase secretion from lover and pancrease to prepare for meal
gastric = not increase secretion at level of si
Intestinal = also increase secretion at si
describe regulation of pancreas secretion
contains cells that release =
larg vol of juice rich in bicarb
small vole of juice rich in - if have lots of acid in duo, decrease acidity of chyme enzymes - fatty meal and need lots of lipases
describe regulation of bile flow
choleretics = agents which cause liver to secrete larger amount of bile
cholagogues = agents which cause increase in gall bladder emptying
describe law of reciprocal activity
if gallbladder contarcted the spincter of oddi will be realxesd and vise versa
if have cck in system
describe summary of Summary of Regulation of Bile and Pancreatic Juice - vagus
cephalic - thinking of food
liver = +
gb contracts and sphincter relaxes = +++
pancreas (low vol/high enzyme/low ph )= +++
pancreas (high vol/low enzyme/high ph) = –
describe summary of Summary of Regulation of Bile and Pancreatic Juice - gastrin
gastric - food in stomach
liver = +
gb contracts and sphincter relaxes = +
pancreas (low vol/high enzyme/low ph) = +
pancreas (high vol/low enzyme/high ph) = +
describe summary of Summary of Regulation of Bile and Pancreatic Juice - cck
released from duo, when fat and protein rich meal
liver = –
gb contracts and sphincter relaxes = +++
pancreas (low vol/high enzyme/low ph) = +++
pancreas (high vol/low enzyme/high ph) = –
describe summary of Summary of Regulation of Bile and Pancreatic Juice - secretin
lots of acidic conetnts in si
liver = + vol/hco3
gb contracts and sphincter relaxes = –
pancreas (low vol/high enzyme/low ph) = –
pancreas (high vol/low enzyme/high ph) = +++
describe summary of Summary of Regulation of Bile and Pancreatic Juice - bile salts
liver = +++
gb contracts and sphincter relaxes = –
pancreas (low vol/high enzyme/low ph) = –
pancreas (high vol/low enzyme/high ph) = –
what happens to polysaccharides as a result of salivary, gastric, pancreatic, and hepatic secretions
salivary and pancreatic amylase make polysacc to dissach must still go to monosacc tho
what happens to proteins as a result of salivary, gastric, pancreatic, and hepatic secretions
pepsin, trypsin and chymotrypsin = convert proteins to small peptides
must still go to aas, di and tri peptides
what happens to fats as a result of salivary, gastric, pancreatic, and hepatic secretions
fats —> mono, diglycerides and FAs
by lipase, colipase and bile salts
describe final steps in digestion
Mediated by intestinal enzymes
produced by mucosa at site where absorption happens
what does si secrete
intestinal juice = water mucus ions
what does si receive
pancreatic juice enzymes to aid digestions
what does si contain
brush border enzymes
attached to microvilli of si epi cells
describe si mechanical digestion
involves segmentation at si = contact absorptive cells
describe si chemical digestion
occurs as chyme mixes with pancreatic juice, intestinal juice and bile
describe si absorption
of digested nutrients at level of si
describe Increased Surface Area in the Stomach for Secretion
tubular glands - secretion
enterocytes = have microvilli, in villus region and also has crypt region = invaginations where fluid secretion happens, completes digestion and absorption - secretion, digestion and absorption
describe crypt cells
lack digestive enzymes
Secrete a large vol - 3l/day of alkaline fluid known as succus entericus
describe secretions in si
crypts –> succus entericus
vol = 3l.day
isotonic = na, k, cl, hco3-
ph ~7.5-9
VILLI do not secrete fluid
what are villi cells
dont secrete fluid but complete digestion and absorb nutrients and fluids
enterocytes in villi make digestive enzymes which remain in brush border
describe small intestine enzymes - vili
enterokinase - lumen epi cells
amylase, lipase, aminopeptidases, dipeptidases
describe disaccharases - vili
brush border
sucrase, maltase, isomaltose, lactase
what do villi cells do
RAPId turnover
cells mature as they migrate up to villus regions - divides and differentiates upwards
cells at tip apoptose and slough into lumen - die by enzymes
describe absorption of digested nutrients in villus
fats absorbed via lacteals = chylomicrons - absorbed at lacteal
carbs and sugars absorbed via capillaru and go to liver via hepatic portal vein
name added enzymes by si = for digestion
disaccharases = disacc to monosacc
peptidases = small peptides to aas di and tripeptides
where is digestion and absorption of nutrients completed
in small INTESTINEEE
describe colonic secretions
small vol
alkaline [bicarb] = 100-150meq/l and [potassium] = 100-150meq/l
lots of mucin for lube
no digestive enzymes or absorption
Bacterial activity = health of body and git, keep bacteria at level of colon
describe regulation of intestinal secretions
Local enteric reflexes
Vago-vagal reflexes
Hormonal factors
describe input vs output - daily (feces)
in = 2000ml h2o, solids 500g
out = 100ml h2o, solids 50g =
(30% bacteria, 30% undigested fiber, 10-20% lipids, 10-20% inorganic matter)
describe daily ml of secretion
Salivary glands = 1500ml
stomach = 2500ml
bile = 500ml
pancreas = 1500ml
intestine = 1000ml
2l ingested + 7l secreted = ~9l must be reasb
what else is reabs into git - besides water
Very large quantities of ions are also reabsorbed from lumen of the GIT
describe Proteins Released into the GIT via Secretions
50g enzymes
30g as cells
80g protein - broken down into aas = aa pool need to return aas for homeostasis
WHAT is being absorbed?
Most of absorption is REABSORPTION
WHERE is it being absorbed?
sites of exchange characterized by = v large sa of si and intimate contact with bvs
describe structure of si
circular folds, villi, microvilli, relative sa = 600
area in excess of need
only gi organ essential to life = colon cannot take over nutrient absorption
describe villus
postprandial flow to intestine = 1-2l/min
efficient absorption = each villus has capillary loop and lacteal, large sa close to blood and lymph flow
Lymph flow = 1-2l/min
name and describe major areas of absorption
duo = most of iron, calcium, cho and protein lipids sodium and water, least bile salts
jejunum = less than duo but still cho and proteins lipids na and h2o, little bile salts
Ileum = less than both above but still cho, proteins lipids na and h20, also only place to have vit b12 and most of bile salts
HOW does absorption take place?
Simple Diffusion
Facilitated Diffusion Active Transport
Pinocytosis
osmosis - water always follows osmotic gradient generated by movement of ions and nutrients
What Limits Absorption?
requirements for absorption =
Adequate Digestion – Enzymes (activated), optimal pH and ionic composition
Adequate Sites for Absorption
Adequate Transit Time for Absorption
Adequate Co-factors, Transporters
describe absorption - by which parts
si = 7l and colon = 2l
describe absorption of water
can absorb more than we usually take in
mac capacity of si = 15l/day
max capacity of li = 4-5l/day
describe carb digestion and absorption
lactose - if no lactase = lactose intolerance – broken down to galactose and glucose
starch = need salivary amylase, and pancreatic amylase and many si enzymes in brush border - critical for them to move into cells – broken down to glucose
sucrose – broken down to fructose and glucose
describe protein digestion and absorption
need pepsin, pancreatic proteases - broken down to aas
either peptidases break in to small peptides or free aas go through carrier mediated transport to aas into cel
describe fat digestion and absorption
triglycerides converted. by lipase, colipase, bile salts to monoglycerides and free fatty acids
monoglycerides either become free fatty acids or glycerol and go directly to capillary
if free fatty acids = makes micelle, help of conjugated bile salts, liver and ileum
micelle into enterocyte = triglycerides resynthesized and mixes with protein, cholesterol and phospholipids to make chylomicrons and go to lacteals
describe efficiency of git
carbs = 99%
fats = 95%
Proteins = 92%
why is git highly efficient
effective coordination of activities - neural, hormonal, motor, secretory, enzymatic - within an organ and between organs
in response to a meal…
wave of secretory activity preceding, accompanying and trailing behind meal
wave of motor activity which receives, accommodates and conveys the meal
describe git transit times
related to functional activities of each organs = times tailored to what needs to be done in terms of processing
mouth = <1sec
eso = seconds
stomach = mins-hours
si = several hours
li = hours -days
name all protective mechanisms
Mucin
Inactive Proteases, Trypsin Inhibitor
Gastric Mucosal Barrier
Sphincters prevent reflux
Negative Feedback Inhibition of Gastrin
Neutralization of duodenal contents
MyogenicMotorComplex= “HOUSEKEEPiING”
* Etc.,Etc.
what does liver produce
bile salts
