Physiology Final- GI tract

Where is gastrin made?

-G cells in the stomach, during the gastric stage- increases with distension, increased peptides ,and decreased H concentration

Functions of the GI tract in Homeostasis

-Intake of nutrients, ions, and water -digestion (macro to micro nutrients) -absorption into the body- in the small intestine mostly -Detox foreign substances- via hepatic portal vein in the liver -Bilirubin excretion-from RBC breakdown by liver- makes your poop brown -immune function- lymph nodes

Can be absorbed if they are small enough into the cell by...

carboxypeptidades(pancreas) and aminopeptidaes(apical membrane of the SI) -split off the AA from the carboyl and amino ends of pepide fragments

Mouth motility

chewing(mastication)- grind to increase the SA -mix with saliva, activate the chemoreceptors -voluntary but there is also brain activity to not grind up your tongue -activated in feedforward and feedback pathways during cephalic phase of FI

Epithelial cells of the GI tract are what?

constantly replaced- new cells arise from the base of the villi, they differentiate as they rise to the top of the villus while the dead cells release their contents into the lumen of the GI tract -17billion epithelial cells are replaced everyday -5 days to replace everything

Pharynx and esophagus

don't contribute to digestion but has a pathway for food

accessory organs

help with the tract by secreting enzymes to break food down

Brush border

it is multiple microvilli and what they cover

Liver

large, upper right of the abdomen -exocrine- bile

Enteric Nervous System

local control of the GI system -form two network of nervous- myenteric plexus and submucosal plexus -neurons synapse with other neurons in a plexus or near the smooth muscle/ glands

Parts of the SI tract

longest region of the gut 1)pyloric sphincter 2)duodenum 3)jejunum 4)ileum 5)ileocecal sphincter

Microvilli

mall projections of cell membranes that increase the surface area of cells. The main functions of microvilli are absorption, secretion, cellular adhesion, and mechanotransduction. These microvilli are organized to form a structure called brush border. Microvilli are found in some epithelial cells of the small intestine, on the plasma surface of eggs, and on white blood cell surface. The function of them depends on the place where they are found in the body. For example, microvilli found in the small intestine increase the absorption surface -cellular structures

Lacteal

most of fat absorbed goes here -it reaches general circulation by the lacteal dumping into the lympathic system into large veins into the thoracic duct

Trace the path through the body to outside

-Mouth, pharynx (not the trachea!! that's where the air goes), esophagus, stomach, small intestine(dudoneum, jejunum, ileum), large intestine(cecum-1st part of the colon, ascending colon,transverse colon, descending colon, sigmoid colon), rectum, anus

What is the secretion in the esophagus?

mucus- makes things slippery, and buffers the PH to protect the wall -no digestion or absorption here

What type of absorption mechanism is like the SI?

renal reabsorption -the intestinal capillaries collect into the hepatic portal vein which goes to the liver and breaks back into the capillaries -triglycerides and the fat soluble vitamins goes into the lacteals of the lymph system

Goblet cells

secrete mucus that lubricates and protects the inner surface of the wall of the small intestine

What are the two transmitters from the enteric NS?

serotonin and nitric oxide

What happens in the epithelial cell?

small peptides combined with peptidaes are made into AA - and then are transported out with the amino acid transporters- facilitated diffusion

What is a key function in the stomach?

storing; contractions are weak in the fundus/ body

What type of cells line the mouth and the esophagus?

stratified squamous (flat) epithelium so they can survive the wear and tear of passing food.

What has more neurons that the spinal cord?

the enteric NS -parasympathetic activate and the sympathetic inhibit(opposite of the exercise state)

What keeps the bacteria out of the LI?

the ileocecal valve/sphincter

Further breakdown of peptides in the SI is....

trypsin and chymotrypsin -major secreted by the pancreas

Sphincter of Oddi

where the point of entry is for the liver and the pancreas secretions

Xerostomia

-people with this have problem chewing, speaking, swallowing, halitosis and tooth decay -no problems digesting though

What influences acid secretion?

-peptides release in the lumen- protein ingestion -proteins on the lumen acidity

SI secretions

-1500ml of water,mucus and high NACL -pancreas secretions:acinar cells- secrete enzymes,duct cells secrete bicarbonate,mucuous -liver-bile salts (cholesterol) to emulsify fats- reabsorbed in distal ileum

How does food get into the esophagus? Anatomy

-Swallowing- Deglutition -oropharyngeal phase -voluntary closing of the lips and elevation of the tongue-irreversible reflex when bolus hits back to the oral cavity -soft palate(uvula) elevates to block the nasal passage -larynx elevates -bolus flattens epiglottis over the glottis(opening)to trachea -upper esophageal sphincter closes rapidly, limits air take and amount of eventual eructation(belching), borborygmi(sounds in GI tract), and flatulation(fart)

Liver path to regulate bile salts

1)through SI- there is a hepatic portal vein that leads up to the liver- synthesizes 5% of the bile 2)bile salts are made 3)goes to gallbladder cause contraction 4)goes down common bile duct- increase the bile flow into the duodenum

Hepatic portal vein

-absorbed nutrients enter the blood capillaries -veneous drainage goes here first before going to the vena cava through the liver- goes into a second capillary system next -liver contains enzymes that detoxify the bad materials in the blood

What happens if you have a weak LES?

-acid reflux, leads to heartburn

What inhibits acid secretion in the SI?

-acid, distention, hypertonic solutions, solutions with AA and fatty acids in SI -mediated by short and long reflex -influence all four of the hormones that directly control acid secretion

What happens in the stomach with peristaltic waves?

-brings as a ripple in the body going to the atrium- too weak to produce mixing of the luminal contents with acid and pepsin -when the wave reaches the muscle surrounding the antrum, it produces a more powerful contraction- mixes luminal contents and close the pyloric sphincter -closing the sphincter, most head back up while only some goes into the duodenum

Chyme

-digestive actions of the stomach reduce food particles to this- molecular fragments of proteins and polysaccharides, fat, salt ,water, and other things ingested in the food -only water can cross the epithelium so no absorption in the stomach

Pancreas

-elongated gland located behind the stomach, endocrine and exocrine functions -exocrine- secretes digestive enzymes and fluid rich in bicarbonate- neutralizes the acidity

Receptive Relaxation

-empty stomach has about 50ml of volume -b4 a meal is swallowed, the smooth muscles in the fungus and body relax before the arrival of food allowing the stomach's volume to increase as much as 1.5 L with little increase in pressure

Pharynx into the Esophagus- anatomy

-esophageal phase- peristaltic wave by the brainstem(5-9 sec) -local stretch activates secondary peristaltic waves if needed to clear -first 1/3 is skeletal muscle and the rest is smooth muscle until the anus 0the LES sphincter relaxes and the bolus enters the stomach

Enterogastrones

-hormones by the IT that inhibit gastric activity -Secretin and CCK

How is the GI process regulated?

-hunger- CNS -Afferent neurons(chemoreceptors, osmoreceptors, and mechanoreceptors from the GI lumen)- afferent neurons target the CNS(long relaxes) and also short is enteric by nerve plexus(stimulated both by the receptors in the FI and the CNS) -the nerve plexus stimulates the smooth muscle or gland- makes a response(short relaxes)

Secretin flow chart

-increase acid in stomach -increase secretin secretion in SI -plasma secretion -bicarbonate secretion in pancreas -flow of bicarbonate into small intestine -neutralization of intestinal acid

CCK secretion flow chart

-increase fatty acids and amino acids -increase CCK secretion -increase plasma CCK -increase enzyme secretion -increase flow of enzymes into small intestine -increase digestion of fats and proteins

What does the inside of the mucosa look like?

-it has circular folds -villi- specialised for absorption in the small intestine as they have a thin wall, one cell thick, which enables a shorter diffusion path. They have a large surface area so there will be more efficient absorption of fatty acids and glycerol into the blood stream. -microvilli- tiny hair-like projections that increase nutrient absorption. These projections increase the surface area of the small intestine allowing more area for nutrients to be absorbed

Bile

-made in the liver- contains HCO3-,cholesterol, phospholipids , bile pigrments, a number of organic wastes, and bile salts -neurtalie the acid in the stomach -bile salts soluble the dietary fats -secreted by the liver into small ducts that join to form the hepatic duct

Motility of the Small Intestines does what

-mixes the luminal contents with various secretions -brings the contents into contract with epithelial surface where the absorption takes place -slowly advances the luminal material toward the large intestine

How are proteins first broken down?

-need 40-50g of protein per day -Proteins are broken down to peptide fragments by pepsin that is produced from an inactive precursor pepsionogen

Where is ACH from?

-neurotransmitter, plexus neurons

What determines the strength of the muscle contraction?

-number of spikes fired determines the strength of it -waves are depolarized due to neurons, hormones, and presence of food in the stomach -contractions more negative when food in SI

Somatostatin comes from

-paracrine substance, inhibits acid secretion -D cells in the stomach wall

Defectation

-rectal stretch stimulates smooth muscle contraction in the walls -inhibites the internal naal sphincter and contracts the external anal sphincter(skeletal muscle) -voluntary relaxation of external sphincter and feces release -sometimes with valsalva maneuver(close mouth, forced, increase thoracic pressure and helps push material out)

Large Intestine Motility

-slow,bacterial growth is friendly when aerobic 1)segmentation- every 30 mins there is shuffling back and forth, drys the material 2)mass movement-Gastrin stimulated-gastrocolic reflex after a meal) -wave of intense peristaltic contraction -starts in transverse colon and travels to the rectum -pack the rectum and stimulate the defecation reflex 3)Defectation

How are the products of protein digestion imported into the cell?

-small pepitides coupled with H+ gradient -AA- coupled with Na gradient

Gallbladder

-small sac under the liver, secreted bile is stored here -concentrates the organic molecules in the bile by absorbing some ions and water

Common bile duct

-smooth muscles in the gallbladder contract and cause the concentrated bile solution to be injected into the duodenum- extension of the hepatic duct

Stomach

-store,dissolve ,and digest macromolecules in food and regulate rate their dump into the SI -acidity environment alters the ionization of the polar molecules that leads to denaturation of proteins - allows more sites for enzymes to break down the proteins -polysacchraides and fat are not dissolved by the acid -low PH kills pathogens

Zymogens

-synthesis and secretion of pepsinogen followed by the intraluminal activation to peps -what occurs with many secreted proteolytic enzymes in the GI tract -enzymes are synthesized and stored intracellular in inactive forms -don't act on proteins outside of the cells that produce them, protect the cells from damage

Saliva functions

-three glands -contains mucus and HCO3-, moistens and lubricates the food particles- facilitating swallowing -contains the enzyme amylase- digests the polysaccharides -reaches the chemoreceptors in the mouth that gives the sensation of taste -kills bacteria and pathogens

What is responsible for the gastric peristaltic waves?

-three per minute is generated by pacemaker cells in the longitudinal smooth muscle layer -undergo spontaneous depolarization and depolarization cycles(slow waves)- basic electrical rhythm of the stomach -through gap junctions in the stomach's muscle layer

How are carbs and sugars ingested ?

1) starches(poly) and ingested small sugars(disaccharides) and metabolized to simple sugars(monosaccharides) by enzymes from the pancrease and by the brush border 2)Fructose is absorbed via facilitated diffusion (GLUT) 3)Glucose and galactose are absorbed with cotransported with Na via SFLT -sugars are then absorbed across the basolateral membrane into the ISF into the blood -Need energy via the NA/K pumps

What are the phases of the GI control?

1)Cephalic- stimuli in your head, afferent sensory and thoughts -feedforward in the feed -stimulated by taste, smell, chewing, emotion -stimulated with Parasympathetic 2)Gastric (food in the stomach) -stretch, acidity, AA, peptides -mediated by short and long reflexes and gastrin(stomach it is made) 3)Intestinal- food present in the small intestine -stretch, acidity, osmolarity and digestive products -mediated by short and long reflexes- secretin, CCK and GIP

Pepsin secretion

1)Chief cells release pepsinogen 2)parietal cells release HCL -pepsinogen is activated to pepsin by acid PH and pepsin itself(autocatalytic) 3)Pepsin is inactivated by alkaline ph in the small intestine 4)converts proteins to peptides

What are the three regions of the stomach?

1)Fundus-storage space 2)Body-secretes mucus, pepsinogen, and HCL, thicker smooth muscle and stronger contractions 3)Antrum- mixing and grading, secretes mucus, pepsinogen, and gastrin -Pyloric sphincter is at the bottom- controls the emptying

What hormones are redundant in the control of the GI?

1)Gastrin 2)CCK-cholecystokinin 3)Secretin 4)GIP- glucose dependent insulinotropic peptide -this stimulated by the receptors in the GI tract and then those hormones stimulate the smooth muscle or gland directly via travel in the blood

What are the three factors that increase the amount of HCL that is secreted from the parietal cells?

1)Gastrin 2)Histamine 3)ACH

Stomach- Exocrine secretions and Functions

1)HCL, Pepsin, Mucus 2)store, mix, dissolve and continue digestion of food and regulates the emptying of dissolved food into the SI -solubilzation of food particles, kills microbes, activates pepsinogen to pepsin -being the process of protein digestion in the stomach -lubricate and protect epithelial surface

Structure of the Gastrointestinal Wall

1)Mucosa- has endothelium, highly convoluted to increase SA for nutrient absorption lamina propria is the inner most part, blood vessels, nerves, lymphoid tissue and glands that support the mucosa -the inner lining is constantly replaced- depends on what is being absorbed, Simple columnar (tall) or glandular epithelium lines the stomach and intestines to aid secretion and absorption -Muscularis mucosa 2)Submucosa - fat, fibrous connective tissue and larger vessels and nerves -specialized nerve plexus called the submucosal plexus- supplies the mucosa and the submucosa 3)Muscularis externa-smooth muscle layer has inner circular and outer longitudinal layers of muscle fibres separated by the myenteric plexus -circular muscle -NS myenteric plexus 4)Serosa- outer layer of the GIT is formed by fat and another layer of epithelial cells called mesothelium- connects to the abdominal wall and supports it

What are the layers of the cells in the stomach?

1)Mucous cells-mucous, bicarbonate secretion 2)parietal cells- acid intrinsic factor secretion- for vitamin B12 absorption in the ileum- need for RBC maturation 3)ECL cell- histamine secretion, paracrine secretion 4)Chief cells- pepsinogen secretion

What are different types of drugs for heartburn, GERD, and excessive acid production?

1)OTC antacid tablets- TUMS,Roladis, peptobismol 2)Histamine bfockers-zantac,tagmet 3)Proton pump inhibitors-priolsec

What are the pancreatic enzymes?

1)Trypsin, chymotrypsin, elastase- substrate protein- break peptide bonds in proteins to form peptide fragments 2)Carbozypeptidase- protein- splits off terminal AA from carboxyl end of the protein 3)liapse- triglyceride- spits off two fatty acids from triglycerides forming FA and monoglycerides 4)amylase- polyasccharide- breaks into maltose 5)rgbonculase,deoxyribonuclease- nucleic acid- split nucleic acids into free nucleotides

Liver-Exocrine secretions and Functions

1)bile salts, bicarbonate, organic waste products 2)secretion of bile, soluble water insoluble fats, neutralize HCL entering SI, elimination in feces

Large Intestine Anatomy

1)cecum with appendix(keeps colony of healthy bacteria to repopulate your gut in case of disaster) 2)ascending 3)transverse 4)descending 5)sigmoid 6)rectum

Regulation of Bile Flow

1)duodenum fatty acids increase CCK secretion 2)increase CCk a- gallbladder contratcts, increase bile flow into common bile duct-increase bile flow into the duodenum b-sphincter of odds relaxes

Pancreas -Exocrine secretions and Functions

1)enzymes, bicarbonate 2)secretion of enzymes and bicarbonate, some non digestive endocrine functions -digest carbs, proteins, fats and AA -neutralize the HCL entering the SI from the stomach

SI-Exocrine secretions and Functions

1)enzymes, salt and water, mucus 2)digestion and absorption of most substances, mixing and propulsion of contents, digestion of macromolecules, maintain fluidity of luminal contents, lubrication and protection

What happens in the enterogastric reflex?

1)increase in acidity, fat, amino acids, hypertonicity, and distention in the duodenum 2)increase secretion of enterogastrones- increases the plasma enterogastrones 3)CCK and Secretin -decrease gastric emptying 4)stimulate neural receptors- decrease gastric emptying , increase sympathetic and decrease the parasympathetic efferents

What does the myenteric plexus and the submucosal plexus do?

1)influences the smooth muscle activity 2)submucosal plexus- influences secretory activity

Fat Digestion and Absorption

1)ingest triglycerides -bile salts and phospholipids break it into emulsion droplets(emulsification) -bile salts and the lipase make micelles -then into the two products below 2)Pancreatic lipase- breaks to monogylceride and fatty acids -diffusion into the cell 3)Synthesize triglyceride-combine with amphipathic proteins 4)Chylomicrons exocytosis into lymphatic into the lacteal - go to the liver

Large Intestine

1)mucus 2)storage and concentration of undigested matter; absorption of salt and water, mixing and propulsion of contents, defecation and lubrication

Esophagus-Exocrine secretions and Functions

1)mucus 2)move food to the stomach by peristaltic waves, lubrication

Overall: Digestion and Absorption in the Stomach

1)physical grinding, mixing, dispersing, reducing size- proteins to peptides 2)not much :weak acids like aspirin- alcohol is much slower than in the SI

LI- secretions, digestion, and absorption

1)protective alkaline mucus with HCO3- and K+, diarrhea can cause acidosis and or K depletion 2)Digestion- bacterial digestion of complex polysaccharide 3)Absorption- products of bacterial metabolism-FA, vitamin K, NaCl, 1.5L of water

Summary of Stomach Motility

1)receptive relaxation 2)begins as a ripple in the body, antrum chews, retropulsion shears and disperses 3)Gastric emptying- stimulated by stomach stretch, chyme fluidity, and is inhibited by enterogastric reflex

Pancreas secretion and role

1)release inactive enzymes that go to active enzymes 2)trypsinnogen to trypsin by membrane bound enterokinase -do all of the body's digestion of macroscopic fuel molecules into absorbable units

Mouth and Pharynx and Salivary Glands- Exocrine secretions and Functions

1)salt and water, mucus, amylase 2)chewing begins, initiation of swallowing relax, moistens the food, lubrication, polysaccharide digesting enzyme

Exocrine and Endocrine

1)secretes its products for example enzymes, into ducts that lead to the target tissue 2)secretes its products, for example hormones, directly into the blood

What are the two steps with motility in the SI?

1)segmentation- processing a meal(short and long reflex regulation)-mixing motility, shuffle back and forth, little net forward movement of chyme 2)migrating myoelectric complex(MMC) after most meal is absorbed -sweeping action of peristaltic waves- intestinal home keeper -homorne motion though to initiate MMC

Gallbladder-Exocrine secretions and Functions

1)stores the bile 2)store and concentrate bile between meals

How many GI cells are reabsorbed every day?

17 million

How much water and food is ingested in a person per day?

500-800 grams of food and 1200 ml of water

How much fluid is from the salivary glands ,gastric glands, pancreas, liver and intestinal glands?

7000ml absorbed into the blood(small intestines) -1400ml absorbed in the blood in the large intestine

Only how much fluid enters the tract?

8L- 99% absorbed- only 100-200 ml is lost in the faces

What is the HCL production and secretion process?

CO2 and H20 is combined with carbonic anhydrase H2CO3 -bicarbonate is counter transported with Cl into the ISF fluid -H is counter transporter into the stomach lumen -look at diagram

Villi

Finger-like projections found in the inner surface of the small intestine are referred to as villi. They are formed by folding the mucosa of the small intestine in order to increase the surface area of nutrition absorption. also help to absorb minerals and electrolytes, as well. Each villus contains brush border cell layer. Small blood vessels and a lymph vessel are connected to each villus helping the movement of substances to and from the bloodstream. The outer layer of the villi has gland cells that release digestive enzymes to the lumen. Villi have low permeability to passive diffusion. -they are found on the layer of tissue

What inhibits HCL excretion in the parietal cells?

Somatostatin

Saliva is secreted from what glands

Sublingeal gland, Submanguilar gland, parotid gland

Small intestine

Three parts: 1)duodenum- short- most of the chyme is digested here 2)Jejunum 3)ileum-long

What are the 7 sphincters?

Upper Esophageal Sphincter(esophagus and pharynx), lower esophageal sphincter(low end of esophagus and stomach), pyloric sphincter(stomach and duodenum), sphincter of Oddi(duodenum and ducts of liver/pancreas),Illeocecal sphincter(small and large intestine- ileum and cecum),internal sphincter(in rectum, involuntary), external sphincter(anal opening, voluntary, skeletal muscle)

Retropulsion

backward motion of chyme that generate strong shear forces that helps to disperse the food particles and improve mixing of the chyme

Where is histamine made?

paracrine agent -ECL cells - released at the mucosal surfaces as a result of exposure to foreign particles. This histamine release causes the capillaries to become more permeable to white blood cells, which move into the capillaries and proceed to target and attack foreign bodies in the affected tissue

Lympathetic Nodules

regions in the small intestine that contain immune cells -kill microorganisms, secrete factors that alter intestinal motility