Human Physiology Unit 4--PART 2 (GI SYSTEM)
Terms in this set (111)
basic definition of GI system
one long tube that extends from mouth to anus
functions of the GI system
1. move nutrients, water, and electrolytes from external to internal
2. remove wastes
3. large immune component because it provides easy access to external
What is GALT?
gut associated lymphoid tissues (use lymphatic filters)
Processes of GI system
What is motility?
movement of materials through GI tract
What is secretion?
1. secretion from interstitial cells to lumen of gut (digestive enzymes)
2. secretion from intestinal cells to blood stream (GI hormones)
3. water and ions from ECF into lumen
What is digestion?
breakdown of complex molecules into simpler molecules
What is absorption?
movement of water, nutrients, and electrolytes from the gut into the blood stream
Three main components of GI system
1. oral cavity
2. GI tract
3. accessory organs
Initial digestion occurs in...
-the oral cavity
-more specifically, in the mouth, pharynx, and salivary glands
five parts of the GI tract
3. small intestine
4. large intestine
5. external opening
Describe the muscle of the esophagus
top third= skeletal muscle (swallow)
bottom 2/3= smooth muscle
What is a stomach?
bag that stores food that can hold 2 to 3 liters
What is chyme?
mixture that leaves the stomach and enters the intestines
What is the pyloric sphinctor?
smooth muscle that regulates chyme from stomach to small intestine
What are the 3 parts of the stomach?
Where does most digestion occur? This is also where most nutrients and secreted fluids are absorbed.
the small intestine
What are the 3 parts of the small intestine?
What 2 things are absorbed in the large intestine?
water and electrolytes
What are the 2 parts of the large intestine?
colon (proximal) and rectum (distal)-where feces is stored
What 2 sphinctors make up the external opening?
external (skeletal muscle) and internal
-two make up the anus
What are the accessory organs?
pancreas and liver
Chyme enters the intestines at the duodenum
via the sphinctor of Oddi
General structure of the wall of the gut
1. mu cosa layer (innermost)
2.sub mu cosa
3. muscularis externis (outermost)
3 parts of mu cosa layer include:
-single layer of epithelial cells
What is the mu cosal layer of epithelial cells made of?
-much variation in cell functions in epithelial cells here
-transporting epithelial cells (enterocytes in small intestine)
-secretory epithelial cells (enzymes, mucus, paracrines into lumen AND hormones into blood stream/paracrines into interstitial fluid)
Where are stem cells kept in gut?
mu cosa layer (epithelial cell layer)
What is the lamina propria?
second part of mu cosa layer
-connective tissue layer that sits under the epithelial cells
-contains blood vessels, lymphatic vessels, and immune cells
What are Peyer's patches?
in the lamina propria of mu cosa layer--clusters of lymphatic tissue (part of GALT)
What is the muscularis mucosa?
third part of mu cosa layer--smooth muscle layer (thin)
mu cosa layer is arranged into villi which are...
finger like projections into the lumen complete with hair like projections (microvilli)
-increase surface area for absorption and form brush border
What is the middle layer of the gut?
Define the submucosa layer
-connective tissue, blood vessels, nerve tissue, lymphatic tissue
-submucosal plexus of enteric plexus is in this layer
What is the enteric plexus?
mini nervous system in the gut
-made of submucosal plexus and myenteric plexus
What three layers make up the muscularis externus?
2 smooth muscle layers
-inner circular layer
-outer longitudinal layer
-change dimensions within the tube
Myenteric plexus is in between these layers
What are the peritoneum and the serosa?
peritoneum--lines abdominal cavity
serosa--thin connective tissue layer continuous with the peritoneum
Smooth muscle in the GI tract operates how?
single unit AKA gap junctions and are electrically connected
What 2 types of smooth muscle contractions are present in the GI tract?
-tonic (contracted for long periods of time until stim to relax)
-phasic (periods of contraction-relaxation cycles)
What kind of wave potentials do smooth muscle cells have?
slow wave potentials
-unstable membrane potential that sometimes reaches threshold and initiates AP's
-regulated by hormones in the gut
What are the 3 types/patterns of smooth muscle contractions?
migrating motor complex, peristaltic contraction, and segmental contractions
What is the migrating motor complex?
-takes about 90 mins to clean up the area
-goes from stomach to large intestine
What is a peristaltic contraction?
progressive contraction that propel bolus forward
-contract, inc. pressure, move food
-during and shortly after a meal
What is a segmental contraction?
mixing and churning of food contractions
-no net movement of bolus
What is the bolus?
clump of food
Acid is secreted by what and where?
by parietal cells in the stomach within the gastric glands
What is secreted during acid secretion?
HCl (1 to 3 L/day)
What is the alkaline tide?
when blood leaving the stomach is relatively high in pH (H+ secreted into the lumen from the stomach when pH is as low as 1 in the stomach)
Bicarbonate is secreted by what and where?
by the pancreas and duodenal epithelial cells into the small intestine
Describe bicarbonate secretion on basal surface.
-CO2 diffuses in
-H+ enters the caps
H+ neutralizes acidic blood (which has excess bicarbonate) and ...
bicarbonate neutralizes acidic lumen (which has excess H+)
Information about the CTFR channel
1. allows chlorine to enter the lumen of the gut
2. found in bicarbonate secretion mechanism
3. ultimately causes water and sodium to travel between epithelial cells towards the lumen
What happens if you have a defective CTFR channel?
-decrease in electric gradient for Na
-decrease in osmotic gradient for H2O
Why is there mucus in the lungs of cystic fibrosis patients?
because they do not have effective CTFR channels, so they have less water in the lumen, making it thicker...mucus
Isotonic NaCl is secreted by what and where?
by crypt cells and in the intestine
What is on the apical surface in isotonic NaCl secretion? basal surface?
apical surface--chlorine leak channels
basal surface--NKCC,Na/K pump (propel water and Na to lumen)
What are digestive enzymes secreted by?
salivary glands, pancreas, epithelial cells of small intestine, and stomach
Where are digestive enzymes stored? And how are they produced?
-stored in an inactive pro-enzyme
-zymogen is any digestive pro-enzyme
-when "pro" sequence is removed = active enzyme
-made like normal proteins (ribsomes to secretory vessels)
Where is mucus made and what secretes it?
-made in mucus cells of the stomach
-secreted by goblet cells in the intestine and salivary glands in the mouth
mucus secretion is mostly under what regulation?
parasympathetic (aka nervous=dry mouth)
Where is bile secreted and what does it aid in?
secreted in liver and aids in fat digestion
What are the main components of bile?
-bile salts (detergent-help dissolve fat mol.s)
-bile pigments (bilirubin-gives color)
-cholesterol (excreted in feces)
-drugs detoxified in the liver (aid in fat digestion)
How is the GI system regulated?
3. paracrines (sometimes)
Neural regulation is controlled by...
long and short reflexes
Long reflex pathway generally includes...
stimulus, CNS, response, inhibit stimulus
What are cephalic reflexes?
long reflexes that initiate outside of the GI tract (specifically, the brain)
What are the 2 types of cephalic reflexes?
-feed forward reflexes--see food, smell food etc
-emotional reflexes--butterflies, vomit at sight of blood
What are short reflexes?
occur via enteric nervous system (the little brain)
Endocrine regulation of the GI system is done by
GI peptides and regulation of motility and secretion
What are the 3 GI peptide groups that regulate GI system?
-all other GI peptides
what is a GI peptide?
hormone, paracine, neuropeptide, or cytokine
How does regulating motility and secretion help to regulate the GI system in general?
-change peristaltic activity
What is digestion?
break down of complex into simple molecules (use mechanical and chemical means)
What is absorption?
movement from GI lumen to the blood stream
Describe the digestion of carbs
-broken down into monosaccharides first
-polysaccharides are broken down by amylases, into disaccharides, which are broken down via disaccharidases into monosaccharides
Name some monosaccharides
glucose, glactose, and fructose
Describe absorption of Carbs (monosaccharides)
-glucose and galactose--via Na dependent mechanisms
-fructose--via Na independent mechanisms
Describe protein digestion
done in 2 ways
Endopeptidases-cleave polypeptide chain in the middle
Exopeptidases-break off single amino acid from the ends of the polypeptide chain
(aminopeptidases break from amino end, carboxopeptidases break from carboxyl end)
Describe absorption of proteins (amino acids)
-Na/amino acid symporter out of lumen
-H+/amino acid antiporter (AA into cell)
-facilitated diffusion/active transport of amino acids out of the cell and into the capillaries
Describe fat digestion
-ingested as triglycerides, cholesterol, phospholipids
-in stomach cant be digested (hydrophobic) so bile salts coat fat molecules and make more soluble
(study diagram in study guide page 19)
Phases of GI function
When does the cephalic phase begin?
when we see, smell, or think about eating food the salivary glands are stimulated and secrete saliva--starts at the mouth
What is saliva's function in the cephalic phase?
works to soften food, salivary amylase begins carb digestion, protection also--lysosomes kill some pathogens
What is chewing's function in the cephalic phase?
breaks up food into many pieces which increases surface area and allows digestive enzymes to attack easier
What is swallowing;s function in the cephalic phase?
from mouth to esophagus, to moving via peristalsis to the stomach
What is the epiglottis?
covers the entrance to larynx when swallowing (prevent food from going down the trachea instead)
What is the lower esophageal sphincter?
ring of muscle that separates bottom of esophagus from the stomach
-removes backlash from the stomach
-acids can squish up into esophagus (heart burn)
-gastric reflux disease is when the sphincter doesnt close efficiently
Once food enters the stomach from the esophagus...
we enter the gastric phase.
In the gastric phase, what are the 3 functions of the stomach?
storage, digestion, and protection
Vagus nerve initiaties what in the stomach?
relaxation of the upper stomach before food arrives (via long reflex)
-short reflexes regulate how much chyme is released into the small intestine
What are the stomach's protective mechanisms?
destroys bacteria and other pathogens because of high acidity (also must protect itself by secreting mucus and bicarbonate)
Secretions in the gastric phase are done by which cells?
What do parietal cells secrete in the gastric phase?
gastric acid (HCl-denature protein; protection)
intrinsic factor (complexes with B12 which is imp. in RBC prod)
What do chief cells secrete in the gastric phase?
inactive enzyme pepsinogen (protein digestion) and gastric lipase (fat digestion)
How do we get pepsin? and what is it?
-combination of pepsinogen and hydrogen ions
-pepsin is an endopeptidase (protein digestion)
What do D cells secrete?
-somatostatin--negative feedback system for gastric phase
What do ECL cells secrete?
-histamine--stimulates parietal cells to secrete gastric acid
What do G cells secrete?
-gastrin which stim. gastric acid secretion
-gastrin secretion is stim by...
------presence of peptides/AA
------gastrin releasing peptide
------coffee even decaff
What do mucous cells secrete?
-mucus and bicarbonate
-forms protective barrier over epithelial cells to protect from high acidosis concentration
What are the 2 major causes of stomach ulcers?
overuse of NSAIDS (ibuprofin)
bacterial infections (cause inflammation)
Some antacids can do what in the stomach?
block/decrease acid secretion
When chyme is produced and sent to small intestine....
the intestinal phase begins.
The intestinal phase is regulated by
motility and secretion
When chyme enters the small intestine,
the enteric NS is activated and stimulates secretion of secretin
Fatty meal stimulates what in the intestinal phase?
stimulates release of CCK (cholecystokinin)
-slows gastric motility and slows gastric secretion
Carbs in the duodenum cause...
GIP(glucose-dependent insulinotropic peptide) to be activated--stimulates insulin secretion from pancreas
Digestive enzymes in the intestinal phase...
secreted in response to presence of chyme in intestine
Where are digestive enzymes located in intestinal phase?
brush border of microvilli
Nutrients are reabsorbed into the small intestine and go to the liver via...
Hepatic Portal System
All absorbed materials of small intestine and all caps form...
Hepatic Portal Vein which travels to the liver
Large intestine is where what is absorbed?
water and electrolytes
Last step of intestinal phase?