GI System Flashcards
What is the GI system
Alimentary tract and associated glands
What happens int he GI system
- digestion and absoprtion of nutrients
- excretion of waste and metabolic by products
Where does digestion being
In the mouth
-secretion of saliva and mechanical breakdown
What happens in the stomach
Storage and digestions
What happens in the small intestine
Digestion and absorption
What happens in the large intestine
Storage, reabsorption and elimination
Where must the venous blood from the GI tract go to
Portal circulation before returning to heart
Why does the venous blood flow go to the portal circulation before returning to the heart
- protection of ingested toxins
- reason for first pass metabolism of drugs
When is GI blood flow reduced
During SNS stimulation
When is GI blood flow increased
During PNS stimulation or after a meal
Lymphatic drainage of the GI
Heavy lymphatic drainage
-required for absorption of large lipids
Where does most action of the gut occur
In the tubular secretions
-small intestine
How does the structure of the tubular sections change along the tract
Changes as function changes along the tract
4 layers of the tubular sections (small intestine)
- mucosa
- submucosa
- 2 mucosal layers
- serosa
What is the mucosal layer and what does it consist of
Innermost layer that Consists of epithelium, lamina propria and muscularis mucosae
What part of the small intestine is closest to the food
The epithelium of the mucosal layer
What all is involved with the epithelial layer of the intestinal mucosa
- absorptive cells
- secretory cells
What type of cells are the epithelial cells of the mucosa
Primarily columnar cells linked via tight junctions
How are the epithelial cells of the mucosa arranged
Into villi (increased surface tension) and crypts (site of stem cells)
What do the absorptive cells of the epithelial layer of the mucosa do
Digest and absorb ingested molecules
What do the secretory cells of the epithelium of the mucosa do
Enteroendocrine-secrete regulatory substances
What are all of the marts of the intestinal mucosa
- epithelial layer
- lamina propria
- muscularis mucosae
Lamina propria of the mucosal layer of the GI
- directly beneath epithelium
- conneactive tissue
- glands, nerve endings, caps and lymph vessels
Muscularis mucosae of the mucosal layer
- thin layer of smooth muscle
- increases epithelial surface area by folding mucosal layer
What are the submucosal, muscular, and serosal layers of the GI
CT
- more glands, blood supply, and lymphatics
- larger nerves forming the submucosal plexus
What is the muscular layer of the GI
- muscularis externus is outer portion of circular layer of smooth muscle
- longitudinal layer of smooth muscle on the inner side
- contains the myenteric plexus
What is inbetween the two layers in the muscular layer of the GI
Myenteric plexus
What is the myenteric plexus
Integration and coordination center for nervous system
Serosa of GI
Holds GI tract in place with connections to abdominal wall
Which of the following layers would you expect to find a high rate of cellular transport
Epithelium
-increased metabolic demand here, also the first place to die from lack of blood supply
Which of the following layers would you expect to find the most ANS control
Muscularis externus
What are the 3 layers of control in the GI system
- endocrine
- paracrine
- neural
CCK in the GI
An endocrine modulator signaled in a paracrine fashion
Where does gastric come from
Gastric antrum (G cells)
What stimulates the release of gastric
Oligopeptides
What is the pathway of action of gastric
Endocrine
What is the target of gastric
ECL cells and parietal cells of the gastric corpus
What is the effect of gastric
Stimulation of parietal cells to secrete H+ and ECL to secrete histamine
What is the source for CCK
Duodenum (I cells)
Stimulus for release of CCK
FA, hydroluzed protein
Pathway of action of CCK
Paracrine, endocrine
Targets of CCK
Vagaries afferent terminals, pancreatic acinar cells
Effect of CCK
Inhibition of gastric emptying and H+ secretion; stimulation of pancreatic enzyme secretion, gallbladder contraction, inhibition of food intake
Source of secretin
Duodenum (S cells)
Stimulus for release of secretin
Protons
Pathway of action of secretin
Paracrine, endocrine
Targets of secretin
A gal afferent terminals, pancreatic duct cells
Effect of secretin
Stimulation of pancreatic duct secretion (H20 and HCO3)
Source of GIP
Intestine (K cells)
Stimulus for release of GIP
FA and glucose
Pathway of action of GIP
Endocrine
Targets of GIP
Beta cells of the pancreas
Effect of GIP
Stimulation of insulin secretion
What are the two neural control centers for the GI system
- extrinsic-normal ANS
- intrinsic-entereic nervous system (ENS)
Extrinsic-PNS division of GI
Increases GI function (enteric systems)
Extrinsic-SNS division of GI
Reduces GI functions (enteric system)
Besides input to the GI system, what do both branches of the ANS do to the GI system
Carry afferent back to CNS
What kind of afferent information does the ANS carry back to the brain from the gut
- meal contents and wall stretch
- reflex arcs on vagus called vagovagal reflexes
Intrinsic neural control
- enteric neurons
- in the two plexuses described before
- receive input from sensory cells in gut
- integrate and send info to muscle and enteroendecrine cells
- ANS can modulate their activity
What can the intrinsic nervous system do for GI
Can direct all GI functions
- don’t need ANS
- release NE/Ach and the GI hormones listed previously
- gut has its own little brain
GI reflex arcs
- stay within the gut (control secretions, motility, etc)
- arcs from gut to prevertebral ganglia then back to gut (one are of gut to another, gastronomic reflex)
- arcs from gut to brain and back (pain, control of motor functions, defecation reflex)
Severing the favus would lead to
Reduced gut sensations
What sites GI lined with
Smooth muscles
What is the muscle that is lining the GI
Muscularis externus
How are the smooth muscles of the GI connected
Via gap junctions into a syncytium
Resting membrane potential of GI smooth muscle
Unstable and generates slow waves
How is the RPM of the gut smooth muscle altered
ANS innervation
Generated by pacemaker cells in the gut walls and carried via gap junctions to rest of smooth muscle
Slow waves
What is it called when a slow wave initiates AP
Spike potentials
When is there more spikes in a slow wave?
The higher the slow wave, the more spikes
What is the threshold of spike potentials
40mv
What channels are sued to generate spike potentials
Slow Ca channels, not fast sodium
How are the contents of the GI tact moved
- peristalsis
- segmentation
Propulsive movement due to gut dissension
Peristalsis
Where does the contaction occur in peristalsis
Behind the dissension
Where is there relaxation in peristalsis
Ahead of dissension
What is required for peristalsis
Myenteric plexus
Mixing only, no forward movement
Segmentation
Increasing SNS activity to the gut would
Increase the negativity of the RMP
What does the SNS do to RMP
Hyperpolarization
What does the PNS do to gut RMP
Hypopolarizes
What is the GI blood supply
Splanchnic circulation
What does the GI tract receive its blood from
Intestinal artery
Where does venous blood from the GI system pass
Through the liver via portal vein then on to vena cava
Lymph flow from splanchnic
Does not go through liver
What does the intestinal artery split into
Caps and found in the villus of the gut
Make up of villi
Large cap beds in each villi
Larger lymphatic lacteals to aid in fat absorption
Local control of blood flow
-dependent upon metabolic demand (O2 levels) of tissue whihc would increase following a meal
Neural and hormonal control of blood flow to gut
Many paracrine substances (CCK, VIP) released by the gut increase blood flow
-SNS reduces flow, PNS increases flow
You are running a marathon and decide to carb load an hour before the race. Predict the effect of exercise on gut function
Reduced absorption of molecules
Prepares tract for food, initiatives by smell, sight, or thought of food
Cephalopod
Basically the same as cephalic, food in mouth increases response
Oral
Propelling food from mouth to stomach
Esophageal
Storage, mixing, and protein digestions
Gastric
Small intestine, digestion and absorption
Duodenal
Large intestine or colonic
Involved in the digestion and absorption of food, absorption of water, production of vitamins by gut flora, and storage and excretion
Intestinal
Responses of GI before/after meal
- inhibit areas behind the meal
- activate the areas ahead of the meal
What does the cephalic and oral phase do
-prepares the GI tract for a meal with sight, smell, or sound of food
. Thinking about the food starts the process as well
What is the difference between the cephalic and oral phases
Only differ in stimuli
-taste of food is prominent in oral phase
What does the cephalic and oral phase ultimately stimulate
PNS stimulation to the GI system
- increases salivary secretions
- gastric acids secretions
- exocrine pancreas secretions
- release of bile from gallbladder
Lubrication and moistening of food for swallowing and aids in mastication and allows taste molecules to dissolve and activate taste receptors
Saliva
What begins digestions
Saliva
What is saliva
Mixture of serous (watery) and mucous secretions from the 3 paired glands
What do the parotid glands make
Mostly serous
What do the sublingual glands make
Secrete mostly mucous
What do the submandibular glands make
Both serous and mucous
How is saliva generated
Filtering plasma, modified as it proceeds into excretory ducts
How does saliva being as
Isotonic fluid
Saliva begins as an isotonic fluid, what happens to after this
- modified to hypotonic and alkaline
- higher levels of K+ and HCO3- than that of plasma
What happens to saliva as flow rate increases
Hypotonicity and alkalinity reduce, although they still remain hypotonic and alkaline
What are the proteins and enzymes added by acinar cells to saliva
- amylase
- lipase
- mucin
- lysozyme
What does amylase added to saliva do
Breaks down carbs
What does lipase in saliva do
Helps digest lipids
What does mucin in saliva do
Lubication, along with water makes it mucous
What does lysozyme in saliva do
Antibacterial, keeps teeth clean
Does SNS or PNS increase secretion of saliva
Both!
SNS and secretion of saliva
- acinar secretion
- SNS (B1 and B2) increases a little-protein rich, sticky
PNS and salivary secretion
- acinar secretion
- M3
- increases a lot- watery
Blood flow secretion with SNS and saliva
- a1
- reduces flow a lot-less saliva made
PNS and blood flow for saliva
- M3
- increases flow a little
- more saliva made
What does SNS stimulation make for saliva
Makes small amounts of proteinaceous saliva
What does PNS stimulation do for saliva
Makes a lot of watery, basic saliva
Which of the following is true regarding the salivary gland secretion
It is alkalosis at high flow rates -LESS alkalotic than at low levels, but still alkalotic none the less
Is swallowing voluntary or involuntary
Initiated voluntarily, proceeds involuntarily
What does swallowing do
Moves food from mouth to esophagus and inhibits respiration during reflex
When does swallowing being
When tongue pushes a bonus of food to back of mouth, into pharynx
What starts the reflex of swallowing
Touch receptors when the food is pushed into the pharynx
What covers the naspharynx
Soft palate
Epiglottis during swallowing
Larynx is lifted and epiglottis covers opening
Which sphincter opens during swallowing
Upper esophageal
What does pharynx do during swallowing
Contracts, bonus is moved into esophagus
What does swallowing end
Oral phase
What does swalllowing being
Esophageal phase
What is the esophageal phase primarily
A transport phase that moves food bonus from mouth to stomach
Long, muscular tube with sphincters at both ends
Esophagus
What are the two sphincters of the esophagus
- upper sphincter (UES)
- lower sphincter (LES)
Striated muscle, protects trachea from swallowed food and gastric reflux
Upper esophageal sphincter
Smooth muscle, protects esophagus from gastric reflux
Lower sphincter (LES)
What kind of muscle is the first 3rd of the esophagus
Striated
What kind of muscle is the last 2/3 of the esophagus
Smooth muscle
Which part of the swallowing reflex prevents aspiration of food
Closure of the epiglottis
When does the upper esophageal sphincter (UES) open
Opens due to swallowing reflex
- pharynx contracts, initiates a peristaltic wave
- food enters esophagus
How is food propelled
Peristaltic wave
- moves bonus to stomach in <6s
- if not sufficient, distention begins another wave
In the esophageal phase, what is released that allows the lower esophageal sphincter (LES) to open
VIP (vasoactive inhibitory peptide)
What does the stomach do during the esophageal phase to get ready to receive bonus of food
Reflex relaxation of stomach
-receptive relaxation
Changes initiated due to food in stomach
Gastric phase
What type of functions does the stomach have
Both mechanical and chemical. Mainly mechanical
What is the mechanical function of the stomach
Mixing, storage, and propulsion of food
What is the chemical action of the stomach
- secretes acid
- secretes and activates pepsinogen and intrinsic factor
- secretion of mucus, water, and HCO3-
What is the stomach lined with
Columnar epithelium in gastric pits
- gastric pits contain secretory cells
- three areas based on type of secretion
What are the 3 areas of the stomach based on type of secretion
- cardia: behind LES, makes mucus
- parietal: proximal stomach, oxyntic glands contain parietal and chief cells
- pyloric:distal stomach, pyloric glands contain G cells and mucous cells
What part of the stomach makes mucous and sits behind the LES
Cardia
What part of the stomach contains oxyntic glands that contain parietal and chief cells
Parietal
What part of the stomach contains pyloric glands that contain G cells and mucous cells
Pyloric
Where does gastric juice come from
Glands
What are the two cell types of the oxyntic glands and what do they secrete?
- chief cells: pepsinogen
- parietal cells: acid
What are the cells of the pyloric glands and what do they secrete
- G cells secrete gastric
- mucous cells secrete mucous
Stomach acid pH
0.8
What kind of transport in the stomach acid
Lots of active transport
What makes acid and bicarbonate in the stomach
Carbonic anhydrase
- H+ pumped into stomach
- bicarbonate exchanged for Cl- with the blood
How do Cl- and K+ enter the stomach
Through channels
What has more K+, gastric juice or plasma?
Gastric juice
What the stomach lined with
Highly alkaline mucous coat
- secreted by mucous glands of the epithelium
- high bicarbonate in the mucous protects stomach cells from secreted acid
When does pepsinogen get activated
Gets activated to pepsin by low pH
What begins protein digestion
Pepsinogen getting activated to pepsin at low pH
What increases the release of pepsinogen
Ach from ANS and ENS
What is intrinsic factor secreted by parietal cells important for
B12 absorption
What does histamine do to acid production
Increases it
-can take an anti-histamine for a stomach ache
How does histamine increase acid production
- ECL cells release histamine directly onto parietal cells
- increases acid production
- ECL cells are activated by gastric
What are ECL cells activated by
Gastric
Where is gastric secreted from
G cells in the antrum in response to proteins in the food
What things are controlled by neural control for gastric secretions
Parietal, ECL, G cells
Neural control of parietal cells
- mediated by PNS
- M3 receptors on parietal cells
- increases secretion
Neural control of ECL
PNS
Produces more histamine
Neural control of G cells
PNS
Produce more gastric
What is also an important stimulus for control of gastric secretions besides neural control
Distention of stomach
Reducing acid production in the stomach
Increasing acid levels in antrum reduces acid production
- signals the meal is over
- D cells make somatostatin, inhibit gastric release
Ingestion of an H2 receptor blocker would cause
Reduced H+ secretion
Higher gastric pH
Vagotomy would have what effect on the stomach
Increase stomach pH
How much digestion doesthe stomach actually do
Very little
- bulk job is to mix and break down food into chyme
- increase surface area for other digestive enzymes to work
- storage to allow small intestine time to digest and absorb
Vagovagal reflex where the stretch of the stomach wall causes relaxation and more stretch
Receptive relaxation
Where does receptive relaxation take place
Primarily in the cardia, fundus, and upper body
Where does mixing and propulsion take place in the stomach
Lower body and antrum
Mixing and propulsion in the stomach
Mixing waves being in body become thronged as they approach antrum
-force chyme against pyloric sphincter to mix, churn and crush
Gastric emptying
Small amounts of chyme are pushed into duodenum through pyloric
- occurs via peristalsis of the antrum
- pyloric pump
Peristaltic wave for gastric emptying
20% of mixing waves generate a peristaltic wave
-move chyme through pyloric sphincter into duodenum of small intestine
What ANS will give you more peristalsis
PNS
What ANS will give you less peristalsis
SNS
What increases gastric emptying
- Stretch of stomach, due to increased motor function
- gastrin, increases activity
What is the rate of gastric emptying tied to
Duodenal digestive time
- stomach must slowly empty to allow small intestine time to work
- enterogastric reflex
What are the two things that are directly from the stomach that affect gastric emptying
Stretch of stomach
Gastrin
This reduces action of pyloric pump and increases pyloric sphincter tone
Enterogastric reflex
What is the enterogastric reflex mediated by
Both the ENS and ANS
- distention of duodenum
- irritation of duodenal mucosa
- low pH
- proteins and fats in duodenal chyme
- non-isotonic chyme
What do duodenal hormones do to emptying
Inhibit it
- CCK released in response to fat in chyme
- secretin released due to acidic chyme
- gastric inhibitory peptide (GIP) released in response to fat and carbs in chyme
What is CCK released in response to
Fats in chyme
What is secretin released in response to
Acidic chyme
What is GIP released in response to
Fat and carbs in chyme
Which of the following would increase gastric emptying
Increased duodenal pH
Damage to the lining of the GI tract, either in stomach ot duodenum
Peptic ulcer disease
Pernicious anemia
- loss of intrinsic factor
- no B12 absoprtion
- no new RBCs
Which of the following would be a treatment for peptic ulcer
Omeprazole (proton pump inhibitor)
What is the most critical portion of the GI system
Small intestinal phase
Where does most digestion occur
Duodenum
Where does most absoprtion occur
Jejunum
What does the ileum do
Absorbs leftovers, bile, B12
What is the intestinal phase highlighted by
- increases pancreatic secretions
- increases gallbladder contraction
- relaxation of the sphincter of Oddi
- interrupting the migrating motor complex
What does the duodenum do
Receives chyme from the stomach and secretions from accessory glands
- liver
- gallbladder
- exocrine pancreas
What do the secretions from the accessory glands that go to the duodenum contain
Digestive enzymes and bicarbonate
-digestive enzymes also held in brush border along epithelium
What is most of the pancreas
Exocrine
- makes pancreatic juice
- digestive enzymes and bicarbonate
- separated from small intestine by the sphincter of oddi
What is the pancreas separated from the small intestine by
Sphincter of oddi
Secrete digestive enzymes in response to PNS and CCK
Acinar cells
What do the acinar cells secrete
- amylase (carbs) and most lipases (fats) secreted as active enzymes
- protease and phospholipases are inactive when secreted
- juice is added by the ductal cells
What cells make the pancreatic juice
Ductal cells
What is pancreatic juice
Isotonic fluid with plasma
- Na+, Cl-, K+ and bicarbonate secreted into duct then modified
- increases flow increases bicarbonate and reduced Cl-
- driven by carbonic anhydrase
- slightly acidification of pancreatic venous blood
- flow increases in response to secretin (released due to acid in duodenum)
What does increased flow do to pancreatic juice
Increases bicarbonate and reduces Cl-
What is pancreatic secretions driven by
Carbonic anhydrase
What does the pancreatic juice do to the pancreatic venous blood
Slightly acidified it
What does pancreatic secretion flow increase in response to
Secretin (released due to acid in duodenum)
What does secretin do for bicarbonate
Increases it
What does CCK increase
Digestive stuff
What is pH sensed by in pancreatic secretion
S cells
What do S cells do in pancreatic secretions
Release secretin
What does secretin do for pancreatic secretion
Increases bicarbonate secretion which is coupled to Cl-, water also follows bicarbonate
What pathology is associated with a disruption in pancreatic secretion regulation
CFTR is mutated in cystic fibrosis and cause of associated pathology
What does enzyme secretion in pacreatic secretion increase to match
Chyme composition
What do fatty acids and amino acids in chyme stimulate
Release of two paracrine factors
- CCK-releasing factor
- monitor peptide
- also release to neural input
What does paracrine factors in pancreatic secretion do
Stimulate I cells
- increase CCK release
- CCK increases enzymatic secretion
What does CCK do
Increases enzyme secretion
What does secretin increase
Bicarbonate
Which of the following is true regarding rate of pancreatic secretion
Increases as chyme pH decreases
This is produced in the liver and stored and concentrated in the gallbladder
Bile
What does bile aid in
Digestions and absoprtion of lipids
-form micelles to allow lipids to escape water environment of intestine
What does bile consist of
Bile salts, cholesterol, phospholipids, water and ions
What is the most important constituent of bile
Bile salts
What happens to bile salts after meal
Recycled
What is bile derived from
Cholesterol
What role does liver have in bile production
Produces primary bile
What role does guys bacteria have in bile production
Makes secondary bile acids
What happens to the primary and secondary bile acids once they are formed
Liver conjugated them into bile salts
- makes them more water soluble
- due to cholesterol backbone, they’re also amphipathic
What are some other things that bile is composed of
-phospholipids, cholesterol, bilirubin, water and ions
What is the water and ion comp in bile similar to
Pancreatic juice
What is the phospholipids, cholesterol, bilirubin, water and ions under the control of
Secretin
Is bile constantly produced in the liver or just sometimes
Constantly
Where is bile stored and concentrated
In the gall bladder
Ejection of bile from gall bladder is under control of ______
CCK
What does the terminal ileum do to bile
Transports bile salts back to liver
-salts are put into gallbladder
How much bile salts are lost in stool
25%
Of the bile salts that do not get excreted, what happens to them
Recirculation of salts back to liver increases bile release (choleretic effect)
Predict the effect of removal (resection) of the ileum
Steatorrhea (fatty stool)
Small intestine mucous
- brunners glands
- protects wall from acid
- increased by stimulation of duodenum, secretin, and vagus tone
- reduced by SNS tone (stress ulcer)
Intestinal juice of the small intestine
- crypts of lieberkuhn-enterocytes
- watery mucous
- 2L a day
- carries peptidases, sucrose, Maltese, isomaltase, lactase, and lipases
What are the different peptidases, sucrose, Maltese, isomaltase, lactas and lipases in intestinal juices important for
Smaller sugar breakdown
Motility of small intestine when chyme is present
Segmentation predominates
- mixes chyme with enzymes
- allows for absorption along intestine
Motilityof small intestine once digestion and absoprtion are complete
Peristalsis occurs to clear intestine of remnants
- moves food bonus to large intestine for further processing
- Ach and NO work in conjunction to constrict and dilate smooth muscle
When does MMC occur
Between meals, cycles every 90 mins until inhibited by a meal
What does the MMC do
Sweeps intestines clean to prepare for next meal
What control is the MMC under
Hormone motilin
What are the 3 phases of MMC
- I (quiet)
- II (small, disorganized contractions)
- III (large peristaltic waves move along length of intestine, moves everything into large intestine)
What are carbs broken down into
Monosaccharides
What proteins broken down into
Amino acids
What are lipids broken down into
Fatty acid and glycerol
What happens to macromolecules before being absorbed
Have to be broken down
What are all enzymatic digestions
Hydrolysis reactions
-adds water to break bonds between subunits
What do dietary carbs consist of
Starch (grains
Sucrose (most sugar )
Lactose (milk sugar)
Where does carbohydrate digestion being
Mouth
Where does most of carbohydrate digestion happen
In the small intestine
What breaks starch down into maltose
Amylase
Oral amylase
Not necessary for digestions
What in the small intestine helps with carbohydrate digestions
- pancreatic amylase
- generates maltose and other short polysaccharides
Enterocytes in the small intestine and carbohydrate digestion
- contain enzymes in their brush border to further digest carbohydrates
- digestion down to a single saccharaide
- some combination of glucose, fructose, and galactose
How are glucose and galactose transported into the cell
SGLT1 transporter
-co transported with Na
How is glucose and galactose transported in the blood
GLUT2 facilitated transport
How is fructose brought into the cell
GLUT5
Where does protein digestion being
Stomach
- pepsinogen is activated by low pH into pepsin
- not necessary for full digestion
Where does most digestion of protein occur
Small intestine
What in the small intestine digests protein
- trypsin, chymotrypsin, elastase produce oligopeptides
- oligopeptidases in the brush border produce individual amino acids
What are single aminoacids tranpsported into the cell with
Na
-each amino acid has its own specific transporter
What are di- and tripeptides cotrasnported with
H+
- pepT1-peptide transporter 1
- can be broken down into single amino acids by cytosolic enzymes
- pepT1 is a transporter for various peptidomimetic drugs
What do dietary lipids consist of
Triglycerides, cholesterol, and phospholipids
Why are lipids difficult to digest
Insolutbility in water
-broken down to fatty acids and other functional groups
Where does lipid digestion occur
Stomach
What do lingual and gastric lipase generate
Glycerol and free fatty acids
Stomach mixing and lipid digestion
Mixes lipids into small droplets
What do lipids in the stomach increase
CCH production which slows gastric emptying
What does intestinal digestion of lipids being with
Emulsification
- addition of bile salts and lecithin surrounds lipid drops
- when mixed, forms progressively smaller drops
- increases surface area for digestion
As intestinal digestion of lipids progresses what happens
Products are taken up into micelles
-increase solubility of fatty acids, not necessary for full digestion
What does the micelle in the small intestine for lipid digestion do
Moves to the brush border and allows fats to enter cells
How does free fatty acid get absorbed
Can cross the cell membranes without aid
How is diffusion of fatty acids aided for absoprtion
By fatty acids binding proteins in epithelium
Once inside, what happens to the free fatty acids
Are reesterified back into original forms and form chylomicrons (resemble single layer cell membrane sacs full of lipids)
What happens once the fatty acids form chylomicrons
Exocytosed from cell, enter lymphatics, then venous blood
-too large to enter caps
All digestive processes occur in what kind of environment
Water
All secretions are dissolved in
Water
GI system secreted about _______ of fluid a day
7L
GI system ingests about ______ of fluid a day
2L
How much fluid does the GI system reabsorb
All but 100mls
Water and solutes
Water follows solutes, water is reabsorbed due to osmotic differences caused by solute transport
How are fat soluble vitamins absorbed
With micelles, packed into chylomicrons and transported out
-ADEK
How are water soluble vitamins absorbed
Co transported with Na
What is the exception of water soluble vitamins
B12
- binds intrinsic factor which protects it from digestion
- has a specific transporter in the ileum
What happens if you get rid of stomach or ileum?
You can absorb B12
How does free iron get absorbed
Binds apoferrin which transports it into the blood
Colonic phase
Large intestine
- reabsorption of water
- absorption of bacterial produced products
- storage
- defecation
How does chyme enter the large intestine
Though the ileocecal valve
-pushed in by the MMC of the small intestine
What is the large intestine lined with
Columnar epithelium cells
-no villi, but crypts present
What does the proximal half of the large intestine do
Mostly handles reabsorption
What does the distal Half of the large intestine do
Storage
Haustra
- muscular arrangements
- little pockets thats turn feces back and forth to allow for reabsorption
- movements less efficient than in small intestine
Where does the colon end
In the rectum
Muscles of the rectum
- only longitudinal
- internal smooth muscle sphincter (involuntary)
- external, skeletal muscle sphincter (voluntary)
What has to occur for defamation to occur
Coordinated reflex of the internal and external sphincter
What are the two types of large intestine motility
Haustration
Mass movement
What is haustration in the large intestine similar to
Segmentation in small intestine, but produces forward movment
- allows forming feces to be fully exposed to absorptive walls numerous times
- can take 15 hours
What is mass movment in large intestine
- modified peristalsis, usually in transverse colon to sigmoid colon
- forces feces towards the rectum about twice a day
Removal of waste from body
Defecation
What initiates the rectosphincteric reflex for defecation
Feces filling the rectum
What sphincter must you consciously release for defecation
External
How are contractions of defecation begun
By local distention and myenteric plexus enhanced by PNS
Increasing abdominal pressure for defecation
Valsalva maneuver
What doesthe large intestine require
Several reflex arc that require the ANS to some degree
Duodenalcolic and gastrocolic reflexes of large intestine
Presence of food in the duodenum or stomach, respectively enhance mass movement in the colon
Gastroileal relfex in the large intestine
Food in stomach opens ileocecal valve and allow remnants to enter colon
Large intestine secretions and transport
- epithelium secretes mucus to lubricate feces as it moves
- absorbs water from feces (lost 100-200mls per day in feces, can reabsorb up to 3x more than normal if diarrhea occurs, primarily passive)
