Unit 4 Physiology: Digestive System
what is the primary function of the small intestine? what are the 3 divisions?
-Coiled, hollow tube •Between stomach and large intestine called the small intestine because its diameter is smaller then the large -Primary site of digestion and absorption (of nutrients and vitamins) - mainly in the duodenum and jejunum -Three divisions 1.Duodenum - also of secretion also happens here (CCK, Secretin, GIP, bicarbonate) - where alot of the digestion occurs. 2.Jejunum - has larger plica then the duodenum because this is where a lot of the absorption takes place so we increase surface area 3.Ileum - has a lymphoid nodule which prevents microbes from spreading into the SI Chyme enters the Duodenum via the Pyloric Valve and exits the Ileum to enter the Cecum via the Ileocecal Valve
what are the three basic principles of control?
1. luminal stimuli: so whats in the lumin of the gut 2. neural regulation 3. hormonal regulation
What are the three layers of the small GI tract wall?
1. mucosa 2. submucosa 3. muscularis externa 4. serosa
what cells are located inside the gastric pit? what hormones goes each cell secrete?
1. mucous cells - mucus and bicarbonate secretion 2. parietal cells - acid (HCI) and intrinsic factor secretion 3. ECL cells - histamine secretion 4. chief cells - pepsinogen secretion
what are the functions of the liver?
1. synthesize bile salts from cholesterol 2. conjugates bilirubin and secretes it into bile 3. synthesizes plasma proteins 4. metabolizes drugs, chemicals and endogenous 5. urea cycle 6. processes nutrients
what are the two regions of the digestive system
1.Alimentary Canal - Mouth to Anus 2.Accessory Organs - Produce substances secreted into the digestive tract - About 2 L of food and drink is ingested each day while 7 L is Secreted into the lumen. - Nearly all of the fluid is Absorbed, mostly from the small intestine, which means that only 0.1 L/day is excreted in feces.
What are the regions of the large intestine? what is the main function of the LI
1.Cecum 2.Ascending Colon 3.Transverse Colon 4.Descending Colon 5.Sigmoid Colon 6.Rectum 7.Anus main function: fluid absorption, storage, and elimination of fecal waste fluid enters the cecum and then becomes semi-fluid, mush, semi-mush, semisolid, and then solid as we absorb fluid Nutrient absorption should be completed before the large intestine. The main functions of the LI are completion of fluid absorption and the storage and elimination of fecal waste. Bacteria breakdown significant amounts of undigested complex carbohydrates and proteins through fermentation (producing lactate and butyric acid).These short-chain fatty acids create a more acidic colonic fluid, which prevents bacterial overgrowth
remember that the digestive system is designed for maximum absorption. what are three things (or structures) that help increase surface area and hence enhance absorption?
1.Circular Folds (Plicae): Folds of mucosa and submucosa extending into the lumen of the SI. 2.Villi: Folds of the mucosa only. Contain blood vessels and lacteal where absorbed substances enter. 3.Microvilli: Microscopic folding of the apical membrane of enterocytes (absorptive ECs). Form the Brush Border. all increase the surface area exposed to the lumen. plicae are the largest, microvilli are the smallest
what are the functions of the digestive system?
1.Ingestion by mouth 2.Secretion by pancreas, small intestine, gallbladder and stomach (secrete into the lumin of the gut) 3.Digestion Mechanical processing via tongue, teeth and digestive tract. Chemical and enzymatic breakdown due do digestive enzymes. 4.Absorption of organic molecules, electrolytes, vitamins and water by digestive epithelium (majority of the absorption happens in the small intestine) 5.Compaction - compressive dehydration of indigestible materials and organic wastes prior to elimination 6.Excretion by liver and gastrointestinal tube 7.Defense against pathogens
what are the different sections of the GI tract?
1.Oral Cavity 2.Esophagus 3.Stomach 4.Small Intestine: Duodenum, Jejunum, Ileum 5.Large Intestine: Cecum, Colon, Rectum, Anus Exocrine secretions from the Liver (and Gallbladder) and Pancreas enter the first part of the SI (Duodenum).
what are the functions of the esophagus ?
1.Transport of solids and liquids from Pharynx to stomach by Peristalsis 2.Prevents air intake - UES 3.Prevents reflux (stomach to esophagus) -LES
what is segmentation?
A series of oscillating contractions of smooth muscle. Between the contracted segments are relaxed areas. Contractile rings occur every few centimeters, dividing the small intestine into segments. - you do move food but you more it forward and backwards. - the goal here is mechanical breakdown and mixing. you want to mix the food with your secretions
how does an amino acid get absorbed? what about dipeptides and tripeptides?
Amino Acids •Cross the apical membrane by sodium-linked secondary active transport or facilitated diffusion •Cross the basolateral membrane by facilitated diffusion Dipeptides and Tripeptides Cross the apical membrane by active transport Broken down inside cells to amino acids Amino acids cross the basolateral membrane by facilitated diffusion
how do we regulate pancreatic secretions?
By what is present in the small intestine When FA and AA are in the lumen of the SI it releases CCK which can travel to the pancreas and tell it to release its enzymes into the duodenum which would allow for digestion of the FA and AA When the acidic chyme increases from the stomach, the SI endocrine cells will secrete secretin which activates the duct cells telling them to release bicarbonate to neutralize the acidity CCK also causes contraction of the gallbladder (so that it can release bile to help break down FA), relaxation of the sphincter of Oddi (which is how the exocrine secretions enter the duodenum), and decreases gastric emptying and HCl secretion. ACH also stimulates secretion by acinar and duct cells
where is CCK made? what are the stimuli for its release? what does it cause in the stomach, pancreas, and liver? what does it do to the sphincter of oddi?
CCK is made in the small intestine stimuli for its release: amino acids (from the breakdown of protein for example) and fatty acids in the small intestine - this is an example of luminal contents casing a hormonal release - these differences in substances in the stomach can be sensed by chemoreceptors that then can release CCK 1. CCK inhibits the stomach (this prevents the stomach from dumping more content into the small intestine, allowing for the SI to work of what is currently present) from acid secretion and motility 2. CCK stimulates acid secretion in the pancreas (to help breakdown the amino acids etc. in the SI), stimulates contraction of the gallbladder (causing it to release bile which can also help break up the fatty acids in the SI) 3. relaxes the sphincter of oddi (which how pancreatic and gallbladder secretions get into the SI) - if its contracted then these secretions cannot get into the SI it also potentiates the action of secretin (it enhances its actions)
what are enterogasterones?
Enterogastrones = hormones secreted by duodenum in response to nutrients and acid in chyme. 1.CCK (Fat, Protein) 2.Secretin (Acid) 3.GIP (Carbohydrate)
what are the different cell types in the epithelium layer of the mucosa?
Epithelial cell types in the Mucosa: A.Absorptive cells (Enterocytes) - absorb nutrients B.Exocrine cells - part of an exocrine gland which is making a product and secreting it into the lumin of the gut C.Enteroendocrine cells - (entero) because they are in the mucosa of the gut (endocrine) because they are what they make goes into the blood. usually what they make comes back and effects actions in the gut. so pretty much they talk to other portions of the gut by traveling in the blood (ex. CCK)
what are the four accessory organs of the GI track and what do they secrete?
Exocrine Secretions that pass through ducts to enter the lumen of the GI. 1.Salivary Glands: Saliva 2.Pancreas: Pancreatic Juice (HCO3- and Enzymes) - remember that CCK stimulates the pancreas to release its enzymes and secretin stimulates the release of bicarbonate which is a buffer 3.Liver: Bile Salts, HCO3- , Organic Waste Products 4.Gallbladder: Stores Bile
how do we regulate gut function?
GI function is regulated to maximize absorption, regardless of whether nutrients are needed. - so its all about maximizing absorption and this occurs through three basic principles Control mechanisms of the gastrointestinal system are governed by the volume and composition of the luminal contents, rather than by the nutritional state of the body. This means that the body is designed to absorb all the nutrients that are ingested, whether or not the body really needs them to function. - which is why excessive consumption can lead to obesity
what are the functions of the hormones secreted from the parietal cells?
HCI: activation of pepsinogen (pepsinogen in secreted in its inactive form from chief cells in the stomach and facilitates protein digestion) - so you begin to break down protein in the stomach Intrinsic factor: needed for vitamin B12 absorption - you need vitamin B12 for RBC maturation and production - lack of B12 would cause anemia
what makes the parietal cells secrete gastric acid (HCI)?
Humoral and Paracrine Regulation of Gastric Acid Secretion 1. gastrin secretion increases HCI secretion 2. histamine secretion increases HCI secretion 3. somatostatin secretion inhibits or decreases HCI secretion gastrin increases HCI secretion and also histamine secretion which also increases HCI secretion (this is a good example of synergy) - these two also put more pumps (proton/K+ pumps) in the membrane the parasympathetic NS would also increase HCI secretion via the release of acetylcholine Gastrin is a Hormone and Histamine and Somatostatin are Paracrine signals. A combination of factors creates a greater level of acid secretion than just additive (i.e. synergistic).
what role does your liver play with regards to bilirubin
IT CONJUGATES IT - You need you liver to conjugate bilirubin so that you can get rid of it in your feces bilirubin comes from the breakdown (or metabolism) of RBC. It is made in the spleen but if we do not conjugate it, it becomes toxic, therefore the liver conjugates it making it easier to eliminate through feces bilirubin is the reason our feces are brown and urine is yellow
What is the mucosa? What are its three layers?
Inner most layer of the GI wall Mucosa: Mucous Membrane Separates GI lumen from internal environment Three layers: 1.Epithelium 2.Lamina propria: Connective Tissue, Blood Vessels, Lymphatic Vessels, Lymph Nodules 3.Muscularis mucosae: thin smooth muscle (moves villi) - can contract and move the villi - villi are the folds of the mucosa
what happens to the monoglycerides and fatty acids once inside the cell?
Inside epithelial cell - Enter smooth ER and re-form triglycerides and other lipids - Lipids enter Golgi apparatus to be packaged into chylomicrons - Chylomicrons are secreted by exocytosis into interstitial fluid - Chylomicrons enter lymphatic system via lacteals - Dietary lipids are absorbed and packaged into chylomicrons by enterocytes - Adipose and muscle cells take up lipids from chylomicrons so all of the other things we have talked about are absorbed into the blood by the chylomicrons are absorbed into the lacteal
lipid digestion
Lipids are not water soluble and do not mix with the stomach or intestinal contents. Lipids form fat droplets Digestion -Bile salts increase the surface area of droplets by breaking each large droplet into several small droplets via emulsification -Enzyme: Lipases are secreted by the pancreas -Lipases can only act on molecules near the edge of the fat droplet BILE SALTS •Synthesized in the liver from cholesterol •Secreted into bile to the duodenum •Amphipathic molecules that can emulisfy fat (break it down into littler pieces)
what are the two kinda of motility in the gut?
Motility is due primarily to contractions of the muscularis externa (circular and longitudinal smooth muscle layers). two types of motility 1. Peristalsis 2. Segmentation
what do the two neural pathways of the enteric NC control? the myenteric plexus and submucosal plexus
Myenteric Plexus •Extends entire length of GI Tract •Controls Muscularis Externa (smooth muscle) - when you activate the myenteric plexus you are going to have more contractions and motor activity but it also inhibits specter activity Submucosal Plexus •Controls function (Secretion, Absorption) of small segments of the GI tract PNS would activate these two and SNS would inhibit
how is absorption controlled by neural regulation?
Neural Regulation comes through the CNS and ENS: 1. Enteric nervous system •Submucosal plexus (regulates secretions in the gut) •Myenteric plexus (regulates moter control) - two networks of nerves that control the motivity and motility 2.CNS contributions to neural control of the GI system through regulation of the SNS (-) and PNS (+).
carbohydrate digestion
Only monosaccharides are absorbed so disaccharides and polysaccharides must be digested first. Digestive enzymes -Salivary Amylase -Pancreatic Amylase -Disaccharidases (lactase, maltase) on the brush border monosaccharides that are absorbed are glucose, fructose, and galactose high fiber diet includes monosaccharides which you cant digest such as cellulose - Cellulose is a plant carbohydrate that cannot be digested. The main undigested material in feces is nonstarch polysaccharides, including cellulose, pectin, etc. (collectively called dietary fiber). A high-fiber diet improves colonic motility and reduces the incidence of constipation.
protein digestion: where does it begin? how does it occur?
Protein digestion starts in the stomach. - Chief cells secrete Pepsinogen (inactive form) - Pepsinogen is converted to Pepsin by Acid (HCl) which is secreted by chief cells in the lumen of the stomach - Pepsin breaks down proteins into smaller peptides.
how do we activate inactive enzymes secreted from acinar cells (also known as proteolytic enzymes)? where do we activate them and what enzymes do we use?
Proteolytic enzymes synthesized, stored and secreted as inactive precursors. Activated in intestinal lumen by two enzymes 1. Enterokinase - an enzyme that lives of the Brush Border - it converts trypsinogen into trypsin 2. Trypsin - once trypsin is active it activates everyone else (all of the other enzymes)
what are the two kinds of movement in the large intestine (colon)? what is required for defecation?
Segmentation "Haustral Shuttling" •Facilitates fluid absorption •goal is to let things hang around longer to slow movement of feces to rectum allowing more time for fluid absorption. - more time haustral shuttling = more fluid absorption Peristalsis "Mass Movements" •Giant contractions that occur 1-3 times/day to propel feces towards rectum for defecation. Relaxation of two sphincters necessary to open sphincter and excrete feces (defecation) •Internal anal sphincter: smooth muscle - involuntary . •External anal sphincter: skeletal muscle - voluntary
what regions of the GI tract have smooth muscle? what regions of skeletal muscle?
Skeletal Muscle 1.Mouth 2.Oropharynx 3.Upper Esophageal Sphincter 4.Esophagus (upper 1/3 only) 5.External Anal Sphincter Smooth Muscle 1.Esophagus (lower 2/3) 2.Stomach 3.Small Intestine 4.Large Intestine 5.Gallbladder 6.Ducts through while bile and pancreatic secretions travel. only region that has both is the esophagus. every thing after the esophagus is smooth muscle until we get to the external anal sphincter remember that skeletal muscle is voluntarily controlled and is under the control of the somatic NS smooth muscle is under control of the autonomic NS Both the Somatic and Autonomic NS innervate the Esophagus to produce motility.
what are the role of lipoproteins?
The liver synthesizes VLDL, which delivers triglycerides to adipose and muscle tissue. so lipoproteins are a shuttle bus for cholesterol and triglycerides and it carries them in the blood to regions that need it VLDL becomes IDL and LDL. LDL delivers fat to the liver and other tissues; LDL receptors are necessary for LDL uptake. Some LDL is also taken up by scavenger receptors. LDL is thought to be bad cholesterol bc it no longer has triglycerides going along with it? Chylomicrons deliver triglycerides to muscle and adipose tissue. The chylomicron remnants then go to the liver. so the intestinal cells make chylomicrons and the liver cells make VLDV HDL is good cholesterol (it brings cholesterol back to the liver for processing - high levels of HDL is good high levels of LDL is bad
What are the four basic digestive processes?
There are four basic digestive processes: 1.Digestion: Mechanical and Chemical 2.Absorption (into the blood) 3.Secretion: (we secrete things into the lumin) Digestive Enzymes, Bile, HCl, HCO3- 4.Motility: Mixing, Mechanical Digestion, Propulsion motility is apart of the mechanical digestion
what is the role of bile salts that are synthesized by the liver?
To synthesizes Bile Salts from Cholesterol -Secreted into Bile, which enters the Duodenum via the Common Bile Duct -Amphipathic (has a polar and a nonpolar region) molecules that emulsify fat a molecule that breaks down large fat droplets into smaller pieces allowing for more surface area to be exposed. this allows the lipases to break them down into fatty acids which can then diffuse through the absorptive cells we also recycle bile salts
What is the teniae coli of the large intestine? what are the haustra?
a band of smooth muscle that contracts haustra: pouches of the large intestine
What is a brush border enzyme?
a collection of enzymes that are peripheral membrane proteins that are attached to the apical surface in this picture the brush boarder enzyme is taking maltose (a disaccharide) and is breaking it into monosaccharides which can then be absorbed into the cell so the brush boarder enzymes live on the surface of the microvillli lactose intolerence is an example of not having the lactase brush boarder enzyme
what is peristalsis?
a form of gut motility is about proportion. moving something from point A to point B Bolus: what we call stuff after you chew it how it works 1.Circular muscles contract behind the bolus while circular muscles ahead relax. 2.Longitudinal muscles ahead of bolus contract shortening adjacent segments. 3.Wave of contraction in circular muscles forces bolus forward. an example of Single unit smooth muscle - cells connected with gap junctions (they work as a team)
what kind of pH do digestive enzymes require?
a neutral pH Digestive enzymes in small intestine require a neutral pH to function. Pancreatic HCO3- is the primary way that acidic chyme from the stomach is neutralized (bile contains HCO3-, too).
What are acinar cells in the pancreas?
acinar cells: synthesize and secrete enzymes for digestion into a duct that will go into the duodenum secretes 1. amylase: breaks down carbohydrates 2. lipases: breaks down lipids 3. proteases: break down proteins 4. nucleases: break down nucleic acids these proteolytic enzymes are stored as inactive precursors so that you only activate them when you need them AND where you need them to work so all of the enzymes made by the pancreas are made in inactive forms and once they enter the small intestine, there is a cascade of events that activates them
How are carbohydrates absorbed into the cell?
active transport and facilitated diffusion in small intestine epithelium as monosaccharides that then diffuses into capillaries as glucose, fructose, and galactose Glucose and Galactose are absorbed in two ways: 1.Secondary active transport across apical membrane 2.Facilitated diffusion across basolateral membrane Fructose is absorbed in one way: - Facilitated diffusion across both membranes
what are the four luminal stimuli produced in the gut?
all of these things can cause hormonal release to control absorption of its contents a. Distension of the wall by the volume of luminal contents b. Chyme osmolarity c. Chyme acidity d. Chyme concentration of specific digestion products (is there glucose in the chyme? amino acids? etc)
what type of organ is the pancreas?
an accessory organ - An organ with both exocrine and endocrine functions. endocrine secretions: insulin and glucagon to regulate blood glucose levels for exocrine secretion (which is the majority - 90% - of what the pancreas does) the pancreas contains two different types of exocrine cells 1. acinar cells: secrete inactive enzymes 2. duct cells: secrete bicarbonate and water that neutralizes gastric H+. - bicarbonate neutralizes the acidic contents that come from the stomach called chyme - these cells can be activated by secretin from the SI
How do parietal cells secrete HCl?
apical membrane: 1. a primary active transporter transports K+ into the epithelial cell from the lumen and H+ from the cell into the lumen 2. there is a Cl- ion channel and a K+ channel (things moving down their gradient) basolateral membrane: 1. secondary active transporter: transports Cl- up its concentration gradient and bicarbonate down its concentration gradient (the Cl- that is now inside the cell and can be transported into the lumen down its concentration gradient though its ion channel) this is how we secrete HCI (gastric acid) into the lumen
What does motility in the gut involve ?
both skeletal and smooth muscle
where do you start carb digestion? where do you start protein digestion?
carb digestion: oral cavity (bc it contains amylase) protein digestion: stomach (bc it contains pepsin)
what are the submucosa?
connective tissue pretty much! Contains: 1.Thick layer of connective tissue that provides Distensibility and Elasticity 2.Large Blood and Lymphatic Vessels 3.Submucosal plexus (Meissner's plexus) - Part of enteric nervous system (the brain of the gut. these neurons can regulate secretions. submucosa starts with S and it regulates secretions which starts with S) The Enteric NS ("Brain of the Gut") is a network of neurons (sensory, motor and interneurons) in the wall of the GI tract. It can regulate GI functions (secretion and mobility) independently but will also regulated by the parasympathetic and sympathetic NS.
what is the function of gastrin? what type of hormone is this? what cell secrete it?
endocrine so it goes into the blood it is secreted by G cells (another cell in the gastric pit) they regulate gastric secretion so gastrin is secreted and comes back to regulate your parietal cells
lipid absorption
fatty acids are what gets absorbed by simple diffusion - so we need lipase to break down the triglyceride into a monoglyceride and free fatty acids - Absorption of monoglycerides and fatty acids by simple diffusion across epithelium.
Where do you make gastrin? what is are the stimuli for its release? what factors inhibit its release? what does it do to stomach acid secretion and motility?
gastrin is made in the stomach stimuli for its release: contents in the stomach like proteins, amino acids and peptides as well as the parasympathetic NS stimuli that inhibit its release: acid in the stomach; somatostatin it causes acid secretion into the lumen of the stomach and stimulates motility in in the stomach
what is special about the salivary glands? what do they initiate?
initiates very small amounts of digestion of polysaccharides by amylase so it begins the process of starch digestion amylase is secreted by the pancreas
what does the liver have to do with urea? what about with nutrients?
it converts ammonia to urea so you can get rid of it you have to get rid of the nitrogen in ammonia, so todo that you liver converts it into urea which can be eliminated - Ammonia (NH3) produced through protein metabolism is converted to Urea in the Urea Cycle , which can be excreted by the kidneys. - how you get rid of ammonia from protein metabolism remember in the kidneys we reabsorb urea to help concentrate urine. Urea makes the osmolarity of the interstitium high. so that when you secrete ADH you have a gradient for water movement the liver also does a lot of carbohydrate and lipid metabolism - the liver secretes a lot of ketone bodies in the presence of glucagon and is inhibited by insulin - the hepatocytes in the liver can also make cholesterol and lipoproteins which are a shuttle bus for protein in the blood. it can also make glycogen and break it down
what is the function of histamine? what type of hormone is it? what cells secrete it?
it increases gastric secretion it is a paracrine hormone - so it doesn't have to go to the blood, it just effects its neighboring cell secreted by ECL cells in the gastric pit
what is the function of the gallbladder?
it stores bile with contains the bile salts responsible for breaking down large fat droplets When the duodenum of the SI has FA in the lumen, it will secrete CCK which will travel through the blood to the gallbladder causing it to contract and CCK also relaxes the spinchter of oddi allowing the bile to flow into the common bile duct and into the SI •Bile is secreted continually by liver •Most stored in Gallbladder (max. volume = 30-60 ml) •Electrolytes and water reabsorbed from bile while in Gall Bladder (5-20x more concentrated) •Cholecystokinin (CCK) stimulates GB contraction and relaxation of Sphincter of Oddi.
where is secretin made? what are the stimuli for its release? what does it cause in the stomach, pancreases, and liver?
made in the small intestine stimuli for its release: acid in the small intestine .(acids that come from the stomach such as chyme are acidic) secretin also inhibits the stomach from acid secretion and motility causing it to chill out, it stimulates bicarbonate secretion by the pancreas (neutralizing the acid content in the SI), it also stimulates the liver to release bicarbonate. it also potentates CCKs actions CCK and secretin are buddies. they enhance each others functions and work together
where is GIP secreted? what are the stimuli for its release? what does it cause in the pancreas?
make in the small intestines stimuli for secretion: glucose and fat in the small intestine it stimulate insulin secretion from the pancreas - this is a feedforward mechanism (so pretty much it is telling the pancreas that there is glucose in the lumin so to start secreting insulin)
what is special about the microvilli? what about the villi? what are enteroendocrine cells?
microvilli are foldings of the apical surface and they form the brush border Each villus contains a capillary bed and a lacteal (lymphatic capillary) where absorbed substances enter. - things that are absorbed are either going to go into the blood capillary or into the lacteal (we will talk later about things that go into the blood cap and things that go into the lacteal) enteroendocrine cells secrete hormones and also lines the mucosa of the small intestine (for ex. they secrete CCK, secretin, GIP) - they will release these hormones whenever they detect the stimulus
what are the functions of the hormones secreted from mucous cells?
mucus and bicarbonate: function is protection (a barrier of protection what is secreted into the lumen of the stomach to protect it
What is the muscularis externa?
muscle Contains: 1.Two layers of smooth muscle A.Inner circular layer: Changes diameter (can contract and relax to control the size of the lumin) B.Outer longitudinal layer: Changes length (can shorten or lengthen the tube) these two play important roles in motility but also help propel things through the GI tract. These is regulated by the myenteric plexus 2.Myenteric Plexus (Auerbach's plexus) - regulates the muscles above. Myenteric starts with M and Muscle starts with M. It is part of the enteric NS -Between Circular & Longitudinal Muscle -Network of neurons that receives input from the Autonomic NS. -Has projections to the Submucosal Plexus, Circular & Longitudinal Muscle
does the gallbladder make bile?
nooooooo! it just stores it
what is the serosa?
outermost layer of the GI tract Serosa Inner layer: Connective Tissue Outer layer: Epithelial Tissue (mesothelium)
What is the hepatic portal vein?
picks up all of the blood from the digestive organs and carries it to the liver this give the liver first dips on whatever you absorb in the digestive organs - this includes -Nutrients, hormones, drugs, toxins are processed by the liver before entering general circulation. •Collects all venous blood from most GI organs. •The HPV sends blood to the liver.
what does poor motility in the large intestine cause? what does excess motility in the large intestine cause?
poor: constipation - things hang around to long and to much water is absorbed excess: diarrhea - things do not hang around long enough so water is not reabsorbed as much
Neural Regulation of Gastric Acid Secretion
showing just the ACH effect ACH binds to a musclerinic (M) receptor which causes more pumps to be added into the membrane Stretch of gastric wall activates both short (Enteric NS) and long (PNS) reflex loops. For the PNS mediated reflex, the Vagus nerve releases......... •ACH that binds to M receptors on Parietal Cells causing Acid secretion •Gastrin Releasing Peptide (GRP) on G cells causing Gastrin secretion - so PNS also causes more gastrin secretion by releasing GRP possible question: which of the following stimulate acid secretion by the parietal cell?
What type of muscles are found in the esophagus? what are the two sphincters found in the esophagus? are they open or closed when you swallow?
smooth and skeletal (Upper 1/3 Skeletal Muscle; Lower 2/3 Smooth Muscle) -Controlled by both the Somatic and Autonomic NS two sphincters Upper and Lower Esophageal Sphincters remain closed between swallows. -Both have tonic contractile properties -UES (which is a skeletal muscle) relaxes during swallow -LES relaxes as peristaltic wave approaches.
so what occurs in the stomach with regards to protein digestion? what occurs in the SI?
stomach: pepsinogen is converted to pepsin which breaks down proteins into smaller peptides these peptides then enter the SI where they are further broken down by trypsin (which is converted from trypsinogen to trypsin by the brush boarder enzyme enterokinase) into dipeptides, tripeptides, and amino acids WHICH CAN ALL BE ABSORBED
what happens in the stomach? what is its function?
stores food after its swallowed - secretes gastric juice - releases food into intestines (duodenum) slowly via relaxation of the pyloric sphincter but the rate that it releases things varies depending on what you have in the stomach Glucose solution is cleared faster then protein solutions which is cleared faster then solid meals (a solid meal takes longer) pylorus region of the stomach controls the emptying of the contents the stomach secretes mucus, pepsinogen, HCI, gastrin
what role does your liver play in protein synthesis? what about with regards to metabolizing drugs, chemicals, and endogenous substances
synthesis of plasma proteins: the liver makes a lot of proteins (such as albumin and fibrinogen) that have a lot of functions in the blood metabolizes drugs, chemicals and endogenous substances by making things more polar so that you can eliminate them
what is the Basic Electric Rhythm (BER)
the Frequency of the slow waves so different regions of your gut have different numbers of waves BER varies in different areas of the GI tract (3 waves/min in stomach, 12 waves/min duodenum). if a wave does not reach threshold you do not get an AP. More APs = more force
what role does the brush border play in carbohydrate digestion
the brush boarder of the digestive tract must have sucrase, lactase, multase if you want to break down those disaccharides you can take it starch, salivary amylase and pancreatic amylase will start to break it down a little into disaccharides and then the brush boarder breaks them down into monocarrides which can then be absorbed
where do things go after the stomach?
the duodenum of the small intestine
Exocrine secretions from the Liver (and Gallbladder) and Pancreas ALL ENTER WHERE?
the first part of the SI (Duodenum) through the sphincter of Oddi
what is the gastric pit? what is located inside?
the gastric pit is located in the stomach and if you were to go inside to of the pit you would find the gastric gland which contains a whole bunch of different cells which secrete different hormones
Why is the stomach acidic?
the pH is 2 this denatures proteins and kills bacteria it is also necessary for activating pepsinogen (is inactive and has to be converted to pepsin) your stomach has protective barriers to protect it form the acidic environment and prevent it from being digested by the pepsin or damaged due to the acidic contents - this barrier is made up of mucosa and bicarbonate
what are the interstitial cells of Cajal?
the pacemaker of the gut Associated Cells that initiate the slow waves. - slow waves are spontaneous depolarizations that are sent to the smooth muscle (similar to what happens in the heart). They so not always reach threshold different regions of your gut will have different amounts of slow waves if the slow wave reaches action potential in the smooth muscle is causes Ca+2 entry which binds to calmodulin which activates myosin light chain kinase which then phosphorylates myosin allow for the smooth muscle to contract - furthermore since these cells are connected by gap junctions the signal can be sent quickly and cause the other smooth muscles to respond producing tension giving you more APs and stronger contractions
how does neural regulation of GI functions work?
there is a stimulus in the GI lumen (such as a change in osmolarity, chemorespters sensing there is glucose there or amino acids) which is sensed by receptors in the wall of the GI tract - these can have short or long reflexes 1. short: they activate the nerve plexus or myenteric submucosal to regulate gland or smooth muscle activity 2. long: they activate the CNS through the afferent neuron to active the PNS for example. - emotional states or hunger can activate the PNS - sight, smell, taste or food can also activate the PNS so the short loop is just the enteric NS within the wall of the gut
which of the hormones secreted by cells in the gastric pit are exocrine hormones? what does it mean that those hormones to be exocrine?
they are secreted into the lumen of the gastric gland and preform their action on the stomach HCI, intrinsic factor, pepsinogen, mucus and bicarbonate
what is peristalsis in the stomach? what is it initiated by? what is its function?
this is motility in the stomach Initiated by pacemaker cells (Interstitial Cells of Cajal) located in GI smooth muscle Smooth muscle cells undergo spontaneous phases of depolarizations and repolarizations = slow waves or Basic Electrical Rhythm (BER) Frequency = 3/minute step of peristalsis (look at picture) Functions: 1.Mix and break down gastric contents 2.Regulate gastric emptying 3.Force chyme through the Pyloric Sphincter but also causes contraction of PS to reduce the volume delivered to SI
how do hormones regulate GI function? what are the five hormones that regulate gut function?
through the endocrine system Endocrine cells distributed throughout the mucosa that secrete hormones (into blood) that regulate gut function. 1.Gastrin - only one that comes from the stomach (but can be secreted for other areas as well) all of the other hormones are secreted from regions of the small intestine 2.Cholecystokinin (CCK) 3.Secretin 4.Gastric Inhibitory Peptide/ Glucose-Dependent Insulinotropic Peptide (GIP) 5.Motilin - activates the MMC between meals There is also paracrine communication in the GI tract. - a neighboring form of communication 1. Histamine secreted by ECL cells in stomach 2. Somatostatin secreted by D cells in stomach and pancreas
where do these smaller peptides travel?
to the small intestine where protein digestion continues Pancreatic proteases released by the pancreas (in inactive forms) and activated in the lumen of the small intestine by the enzyme Enterokinase. - Trypsinogen --> Trypsin trypsin can then activate a number of other enzymes with can travel to the SI to have finish the breakdown of the proteins 2. Brush border proteases - Enterokinase: which converts trypsinogen into the active trypsin
where do things go after the esophagus?
to the stomach where things are now called chyme things pass though the lower esophageal sphincter into the stomach
what is important for B12 vitamin absorption?
vitamin B12 is a water soluble vitamin - it requires a special transport protein called intrinsic factor Vitamin B12 is only absorbed if bound to Intrinsic Factor - there are receptors in the ileum of the SI (which is the last section of the SI) that allow the intrinsic factor to bind along with B12. so then vitamin B12 can then enter the mucosa cells where the blood has B12 binding proteins - a deficiency in intrinsic factor would be anemia - B12 is important for making RBC remember that the intrinsic factor is secreted from the parietal cells (which also secrete HCI aka gastric acid)
what factors dictate the magnitude of the contractions in the stomach?
wether we want to increase or decrease gastric emptying 1.factors increasing the force of antral contractions (and hence) gastric emptying - gastrin (gastric hormone) - detention of the stomach (stretching the smooth muscle and increasing the contraction) 2. factors decreasing the force of antral contractions (and hence gastric emptying) - contents of duodenum - we would want to do this when we want the stomach to chill out so we can process what is currently in the duodenum - so messages from the duodenum (enterogastrones) would decrease contractions and gastric emptying
what is the Migrating Motility Complex (MMC)? what hormone regulates it?
what occurs in between meals (fasting state) approximately every 90 minutes - Intervals of strong propulsive contractions to sweep stomach and small intestine of indigestible material after a meal a 90 minute window between these waves but when a meal is occurring these stop regulated by the hormone motilin which is made by cells in your small intestine and travels to its target cell by blood - Motilin is secreted by M cells located in the duodenum and jejunum. - Intrinsic to ENS and involves the hormone Motilin Continue until meal ingested and effects every area of the gut as it propergates down to each region
what does the intestinal phase ? what hormones does it involve?
when we are telling the stomach to chill out so we can deal with what is in the small intestines The Intestinal Phase involves hormones like CCK, Secretin and GIP that inhibit the activity of the Parietal Cells (and the G and ECL cells).
