GI 3 (physiology)

accessory organs of GI tract

salivary glands

liver

gallbladder

pancreas

liver most general function

produce bile to emulsify fat

gallbladder most general function

store bile

pancreas general GI function

secrete digestive enzymes

4 functions of the liver

bile production and secretion

detoxification of blood

secretion of glucose , TGs, ketone bodies

production of plasma proteins

what does the liver produce in a fasted state

glucose (via gluconeogenesis)

ketone bodies

triglycerides

liver hepatocytes form _

hepatic plates

hepatic plates are arranged into _

liver lobules

what separates hepatic plates

capillary space (sinusoids)

specialized cells found in liver sinusoids

Kupffer cells

function of Kupffer cells

act as phagocytes to engulf and absorb waste material, microorganisms, foreign bodies

flow of portal system in the liver

capillaries (small intestine) - portal vein - liver capillaries (sinusoids) - central hepatic vein

_ drains the liver into the general circulation

central hepatic vein

what liver cells produce bile

hepatocytes

hepatocytes secrete bile into _

bile canaliculi

components of bile

bile salts

bilirubin

cholesterol

phospholipids

inorganic ions

path of bile from the liver

bile canaliculi -> bile ducts -> hepatic ducts

the liver clears blood of compounds and secretes them _

with bile into the intestine

what happens to compounds secreted with bile into the intestines

some excreted in feces AND/OR

some reabsorbed by intestine -> enter hepatic portal v

_ closes the cystic duct to intestine

sphincter of Oddi

what ejects bile from gallbladder into duodenum

contraction of muscularis layer of gallbladder

what hormones regulate the gallbladder

CCK

secretin

CCK impact on gallbladder

stimulates contraction

when is CCK released

when fat and protein are detected in the duodenum

secretin effect on gallbladder

stimulates contraction

secretin effect on liver

stimulates secretion of HCO3, Na, H2O

bile release from gallbladder may be recoved by _

enterohepatic circulation

pancreatic exocrine cells

acinar cells

acinar cells secrete _

pancreatic enzymes

pancreatic ductile cells secrete _

large volumes of fluid containing H2O and HCO3

function of pancreatic secretions

neutralize gastric acid

provide hydrolytic enzymes for digestion

regulation of H20 and bicarb release from pancreas is dependent on

concentration of acid in the duodenum

regulation of pancreatic enzyme release is dependent on _

the amount of protein and fat in the duodenum

enzymes contained in pancreatic juice

trypsin

lipase

amylase

most pancreatic enzymes are produced as _

inactive molecules (zymogens)

pancreas during the cephalic phase

G cells release gastrin

gastrin stimulates water, bicarb, pancreatic enzyme secretion

vagal output also stimulates pancreatic secretions

the intestinal phase of digestion has what effect on pancreas

release of CCK and secretin -> pancreatic enzymes and H2O/bicarb

products of small intestine digestion are absorbed _

across the epithelial lining of intestinal mucosa

what is absorbed in the duodenum and jejunum

carbohydrates

lipids

amino acids

calcium

iron

what is absorbed in the ileum

bile salts

vitamins

water

electrolyes

the mucosa of the small intestine takes on what structure

folded into villi

what is the brush border

additional folds (microvilli) on the membrane of epithelial cells of intestinal villi

the brush border is made up of _

microvilli

microvilli contain _

digestive enzymes

each villi of the intestine contains numerous _

capillaries and lymphatic vessels (lacteals)

what enters villi capillaries

sugars and amino acids

what enters villi lacteals

fat

2 types of digestive enzymes of the small intestine

luminal

membrane-bound

where do luminal digestive enzymes act/secreted from?

act in lumen of intestine

secreted by pancreas

where are membrane-bound digestive enzymes produced

epithelial cells of villi

membrane bound digestive enzymes are bound to _

microvilli

most carbs are ingested as _

starch

amylase cleaves _ to produce _

straight chains -> maltose and maltriose

amylase CANNOT hydrolyze _

branch points of starch

_ are produced as a result of amylase inability to digest branch points

oligosaccharides

examples of polysaccharides

starch

glycogen

cellulose

structure of starch

polysaccharide with straight chains and a few branches

examples of polysaccharides ingested in the diet

amylose

amylopectin

glyocgen

what type of sugar are absorbed by the small intestine

simple sugars (monosaccharides)

membrane bound enzymes break down _ to _

more complex sugars -> monosaccharides

what type of sugars are moved across the epithelial cell membrane of the villi

monosaccharides (glucose and galactose)

how are sugars transported into the villi

via the Na+ dependent active transport mechanism

epithelial cells of the villi secrete monosaccharides into _

capillaries of intestinal villi

_ is uptaken by a Na+ independent carrier

fructose

protein digestion begins where

in the stomach

triggering event for activation of proteases

conversion of trypsinogen to trypsin

what converts luminal trypsinogen to active trypsin

enterokinase

where is enterokinase found

brush border

what happens once trypsin is activated

activates other luminal proteases

phases of protein digestion in the small intestine

luminal

membrane

enterocyte

luminal phase of protein digestion

degraded to individual amino acids and small peptides via pancreatic proteases

what occurs in the membrane phase of protein digestion

microvilli peptidases split peptides of 4+ amino acids

enzymes involved in membrane phase of protein digestion

enterokinase

amino peptidase

enterocyte phase of protein digestion

peptidases in epithelial cells break down smaller peptides

enzymes involved in luminal phase of protein digestion

trypsin

chymotrypsin

carboxypeptidase

components of fat aggregate into _ in the stomach

oil droplets

components of fat

TGs

phospholipids

cholesterol

where are fats emulsified

duodenum

what allows oil droplets to be emulsified

bile salts

lecithin

what effect does emulsification of oil droplets have

makes them susceptible to the actions of pancreatic lipase and other enzymes

enzymes digesting fat in the small intestine

pancreatic lipase

cholesterol ester hydrolase

phospholipase A

what digests triglycerides

pancreatic lipase and colipase

steps in digestion of fats

emulsification of fat droplets

hydrolysis of TGs -> fatty acid and monoglycerides

dissolve FAs and monoglycerides -> micelles

fatty acids and monoglycerides are dissolved into _

micelles

what are mixed micelles

products of fat digestion associated with micelles of bile salts/lecithin

which liver cell is responsible for detoxification

Kupffer cells

mixed micelles are carried to _

brush border of villi -> diffuse into intestinal mucosal epithelial cell

what is enterohepatic circulation

process where bile salts are reabsorbed in the lower intestine and returned to the liver

what happens to fats once inside epithelial cell

they are re-synthesized into TGs and phospholipids

what occurs after re-synthesis of fats

fats are packaged into chylomicrons

chylomicrons are secreted into _

central lacteals of the intestinal villi

chylomicrons are transported by _

lymphatic vessels associated with lacteals

lymphatic vessels transport chylomicrons to _

thoracic duct

enterohepatic circulation allows for _

recycling of bile to the liver

which component of bile is excreted in feces and not involved in enterohepatic circulation

bilirubin

vitamins function as

cofactors or coenzymes

2 classes of vitamins

water soluble

fat soluble

fat soluble vitamins

vit A

vit D

vit E

vit K

fat soluble vitamins are absorbed into

lymphatic circulation

what are zymogens

inactive form of pancreatic enzymes