Lecture 4 Flashcards
what are the parts of the small intestine called?
What is their function?
duodenum - chemical digestion at proximal end
jejunum
ileum
all are responsible for absorption
duodenum receives secretions from pancreas and liver
located right after the stomach and is responsible for the second phase of the digestive process
proximal duodenum
proximal duodenum in very efficient due to surface are…
- folds in the mucosa increase surface area by ____
- crypts and villi _____
- microvilli ____
3 fold
10 fold
20 fold
what is an enterocyte?
lines the gut and is responsible for digestion and absorbtion
enterocyte type of surfaces
apical (luminal)
Basal (lateral)
what occurs in the apical surface of enterocyte?
digestion and absorbtion
what happens in the basal or lateral surface?
products of digestion pass through into bloodstream
intestinal veins then drain into the portal vein and transport absorbed nutrients to the liver
what two functions does the pancreas have?
exocrine function produces secretionswith digestive enzymes that enter thru duodenum
endocrine function releases insulin into blood
pancrease is regulated by ?
acetylcholine, CCK, secretin
types of exocrine pancreatic cells?
acinar cells
duct cells
what percent of exocrine pancreatic cells are acing cells? what do they do?
more than 80%
synthesize stroe and secrete digestive enzymes
what do pancreatic duct cells do?
line the ducts and supply the bicarbonate to nuetralize gastric acid
pancreatic enzymes with the role of protein digestion?
trypsin (most abundant)
chymotrypsin
carboxypolypeptidase
pancreatic enzyme for carbohydrate digestion
amylase
pancreatic enzyme for fat digestion?
lipase
cholesterol esterase
phospholipase
what is the turn off mechanism in the pancreas
trypsin inhibitor produced by acinar cells
where is the gallbladder located
undere the liver
what does the gallbladder do?
stores 50 ml of bile
how does bile release from gallbladder?
fats in duodenum stimulate CCK, which caused gallbladder to contract and release some bile
what are the layers of the gallbladder?
innermost
musculature
innermost layer of gallbladder consists of what kind of cells? what do they do?
highly absorptive epitheleal cells linked by tight junction
- absorbs water and lytes (not Ca++) concentrating the bile
- goblet cells protect the epithelean from injury
what cells are in musculature layer of gallbladder? also, what does the layer do?
muscle cells
contract and relax gallbladder
what causes the gallbladder to contract?
-surface receptors that respond to Ach and CCK cause gallbladder to contract (some food causes contraction too like apple skin)
what causes the gallbladder to relax?
vsoactive intestinal polypeptide (VIP) and nitric oxide (NO)
allows it to fill with bile
bile is synthesised by the _______.
hepatocyte
we make ____ bile a day and it has a pH of about ____?
1 L
7
what are the components of bile?
water, bile salts, bilirubin, cholesterol, fatty acids, lecithin, Na+, K+, Ca++, Cl-, HCO3-
what does bile do?
emilsify fat particles facilitating intestinal absorbtion
transports waste products
bile salts form a sphere called _____, which collect where in the body?
micelles
around fat
what do bile salts do?
help absorb fatty acid in the small bowel
what is postpeandial
postt eating
after eating, the gallbladder will _____
contract
what causes the gallbladder to contract after eating?
WHEN MEAL EMPTIES STOMACH (INTO DUODENUM)
fats trigger the release of cholecystokinin
bind directly to CCK-A receptors on gallbladder
acetylcholine release increases contractions
Where is the sphincter of oddi?
where gallbladder releases into the bile duct to duodenum
when does sphincter of oddi relax?
gallbladder contraction
CCK, VIP, and nitric oxide reduce tone of sphincter to release
what are the parts of the large intestine
cecum
colon
- ascending
- transverse
- descending
- sigmoid
rectum
mucous production that protects the lining of large intestine from bacterial activity
crypts of Lieberkuhn
does the large intestine have any villi or enzymes ?
no
what are the primary functions of the large intestine?
extract and reclain water from the intestine
process feces for elimination
modify bile acids and bilirubin by bacteria
colonic reflexes of the large intestine
defication reflex
gastrocolic reflex
during mixing, the colon shuttles contents back and forth between …
haustral shuttling
periodically contractions sweep through the colon
peristalsis
simultaneous contraction of smooth muscle that happens 10 times per day
mass action contraction
transit time from cecum to the rectum (large intestine)
1-2 days average
following a meal it takes…
___ hrs to reach cecum
___ hrs to reach hepatic flexure
___ hrs to reach splenic flexure
____ hrs to reach sigmoid colon
and rectum at ___.
4
6
9
12
1-3 days
what is the role of the cecum?
absorbs fluid and salts that remain after completion of intestinal digestion and absorption
removes 90% of the fluid it receives from small intestine
what is the role of the ascending and transverse colon?
recover fluid from the digestive process that is left
(5L total per day)
can absorb short chain fatty acids
what is the role of descending and sigmoid colon?
serve as reservoirs
stores waste
what is feces made out of?
3/4 water
1/4 solid matter
what contributes to the solid matter in feces?
30% dead bacteria
10-20% fat
10-20% inorganic matter
2-3% protein
30% undigested roughage
what is responsible for the color of feces?
stercobilin
urobilin
what are the sphincters that assist in defication
innervation internal sphincter
innervation external sphincter (pudendal nerve)
what is the function of the innervation internal sphincter?
sympathetic nerve supply to the internal (involuntary) excites it
parasympathetic inhibits it
relaxes when rectum is distended (full of shit)
what is the function of the innervation external sphincter: pudendal nerve
maintained in tonic contraction until moderate distension increases the force of contraction
urge to defecate first occurs when rectal pressure increases to about ____mmHg
18
both sphincters relax when pressure reaches ______mm Hg to eliminate the contents
55
voluntary defecation can be initiated by ______.
what does straining do?
straining
- forces the abdonimal muscles to contract, lowers pelvic floor 1-3 cm, and relaxes the puborectalis muscle.
- reduces anorectal angle
- external anal sphincter relaxes
what is the puborectalis muscle
muscle strap that goes around rectum
the contracting shortens the muscle and makes angle sharper and prevents defication
why do carbs and proteins have a hard time reaching cells?
they are too large to cross lipid bilayer
how do proteins and carbs get thru membrane if they are too big?
enzymes hydrolases break down proteins and carbs so they can move thru epithelial membranes
where does fat breakdown happen?
stomach
small intestine
proteins are made up of _____ from amino acids, held together by ____.
polypeptides
peptide bonds
amino acids in a…
peptide?
Polypeptide?
protein?
les than 2
less than 10
less than 50
where does protein digestion occur?
stomach
small intestines
pancreas
protein digestion in the stomach
gastrin stimulates parietal cells to secrete HCL and chief cells to produce pepsinogen which denatures protein
protein digestion in the small intestines
polypeptides broken down at intestinal brush border by peptidases
carbohydrates are composed of sugar molecules, such as ?
simple (mono/disaccharide)
complex (starches, polysaccharides)
fiber (dont digest this tho)
examples of polysaccharides that cannot be directly absorbed?
Starches
Amylose
Amylopectin
Dextrin
Glycogen
examples of disaccharides (some are absorbed)
sucrose
lactose
maltose
examples of monosaccharides, that can be transported across membrane and absorbed)
glucose (80% of calories)
galactose (10% of calories)
fructose (10% of calories)
absorbtion in the duodenum includes the capacity to absorb _______.
sugars, dipeptides, tripeptides, fats, Ca++, phosphate, sodium, nonheme iron.
absorbtion in jejunum include ______
majoritey of nutrients
absorption in the ileum include _____
nutrients absorption if jejunal absorption is impaired
small intestion has surface area of _____. with what to help absorption ?
320 ft
folds of kerckring
villi
microvilli of the brush border
where do lipids get sent to after absorption at digestive tract?
what stimulates this?
adipose tissue for storage (insulin)
skeletal muscle for ATP production (insulin)
where does amino acids get sent after being absorbed in the digestive tract?
what stimulates this ?
all tissues for protein synthesis
(insulin)
where does glucose go after being absorbed in digestive tract?
what stimulates this?
all tissues for ATP production
liver and skeletal muscle for storage
insulin
what does the absorptive process require?
luminal processing
absorption into the intestional mucosa
transport into the circulation
what is required for luminal processing to occur and what is it?
process things thru the cytosol
Adequate enzymes
sufficient bile salts and juices
necessary bacteria
alkaline environment
absorption into the intestinal mucosa
absorption into the interstitial brush border of jejunum and ileum
transport into the circulation inlcudes what transport
Nutrients
Water
Ions
pinocytosis - nutrients
osmosis - water
active transport with ion change (Na, Cl)
what do pumps do for transport
moves ions against an electrochemical concentration gradient
what do channels do in transport
high capacity pores in the plasma membrane to transport
what do carriers do to transport?
exchanger carriers transport in opposite directions
co transporters move species in same direction
How does water transport?
passive process across intestinal epithelial cells
how does sodium transport?
facilitates transport of glucose, amino acids
co transports and exchanges
how does potassium transport?
passive and active
how do Cl- ions get transported?
dragged along by Na+ and exchanged for bicarbonate ions
how are bicarbonate ions (HCO3-) transported?
chemical reaction of hydrogen coupling with HCO3- and followed by carbonic acid breakdown
carbohydrates are _____ soluble.
Membrane bound ______ at the brush border of epithelial cells break down ______ before absoption.
water soluble
hydrolases
disaccharides
glucose and galactose are absorbed by __________. it uses energy stored in _____ gradient to move glucose into the cell. _____ has no role
facilitated diffusion
Na+
insulin
protein absorbtion occurs more in _____ than _________.
jejunum
ileum
at least _____ diferrent transport systems transport amino acids into enterocytes
7
smaller protein molecule are transported through _______ dependent amino acids cotransporter
Hows it work ?
sodium/Cl-
low intracellular sodium concentratin provides a strong inward gradient for sodium entry, which drives amino acids in
what is ammonia?
a metabolite of amino acid deamination
(ammonia/keto acids)
why is ammonia bad?
How do we get rid of it?
it crosses epithelial barriers and is highly toxic to the nervous system
cleared by liver and excreted by kidneys in the form of urea
-some excreted from stool in form of ammonium ions
FA diffuse immediately out of micelles into the epithelial cells by ______ diffusion. FA that are less than ____ carbons pass through the entercytes and can be absorbed into the blood.
facilitated
10-12 (short chain)
what happens to fatty acids that have more than 12 carbons?
- reesterfied to form triglyceride in smooth ER
- TG and cholesterol esters are then coated with proteins to form chylomicrons
- these CMs are then secreted from basolateral wall of enterocytes by exocytosis and enter the lymphatic system
where are vitamins and minerals brought into our system?
proximal half of the small intestine
examples of water soluble vitamins
B (1,2,3,5,6), C
these water soluble vitamins are absorbed in the ________ through ______ transport
jejunum
Na cotransport
how is B12 and folic acid get absorbed?
terminal ileum through intrinsic factor
(low can cause annemia)
what are the fat soluble vitamins?
A,D,E,K
how are fat soluble vitamins absorbed into the system?
- must be digested by cholesterol esterase before absorption
- insoluble in gut, so use micelles
how is the mineral calcium absorbed?
active transport in the duodenum
facilitated by vitamin D by stimulating synthesis of calcium binding protein (helps calcium get absorbed)
when is calcium absorption inhibited?
excess fatty acids
phosphates and oxalate anions
- form insoluble salts with Ca++ in intestine
