GI Flashcards
What are the layers of the wall of the GI tract, starting with innermost:
- Mucosa
- Submucosa
- Muscularis
- Serosa
A networks of nerve is between each of the layers
What does the mucosal layer of the esophagus specialized function?
Stratified squamous epithelium that enables gliding of masticated food
What specialized function does the stomach mucosal layer have:
Thick glandular mucosa that provides mucus, acid, and proteolytic enzymes for digestion
What specialized function does the small intestine mucosal layer have:
Villious structure to provide large surface area for absorption
What specialized function does the large intestine mucosal layer have:
Lined with abundant mucus secreting cells that facilitate storage and evacuation of residue
What is the gut nervous system called and what does it innervate?
Enteric nervous system
Stomach muscle, secretory cells, endocrine cells, blood vessels
What is absorbed in the mouth?
Certain drugs that come in contact with the mucosa of the mouth are absorbed into the blood stream
What is absorbed in the stomach?
Water, simple sugars, alcohol
Water, alcohol, copper, iodide fluoride, molybdenum
What is absorbed in the small intestine?
The final steps of digestion; glucose, fructose, fatty acids, glycerol, amino acids are absorbed into the blood stream
Duodenum- Ca, Phos, Mag, Fe, vit A, D, E, K, etc
Jejunum- Lipids, monosaccharides, AA, small peptides, vit A, D, E, K, zinc, etc
Ileum- Bile salts/acids, vit C, vit B12, folate, vit D and K, Mag, etc
What is absorbed in the large intestine?
No chemical digestion, only by bacteria
Absorption of water, some minerals, and drugs
Water, vit K, biotin, Na, Cl, K, short chain fatty acid
What are the parts of the small intestine?
Duodenum to jejunum to ileum
A person unable to absorb bile salts may have had their __________ removed?
Ileum
What hormones stimulate gastric emptying?
Gastrin and motilin
What hormones delay gastric emptying?
Secretin and CCK
What are the 4 main general functions of the GI tract?
- Movement of nutrients-propulsion/mixing
- Secretion of digestive juices
- Digestion of nutrients
- Absorption of nutrients
What does salivary amylase in the mouth do?
Initiates carbohydrate digestion by breaking down polysaccharides into dextrin and maltose
What facilitates muscular movement through the esophagus?
Mucus
Muscle contractions
Gravity (not necessary)
Why is it important for the lower esophageal sphincter to remain tonically constricted?
To prevent the acidic gastric contents from moving into the esophagus. (GERD)
What is the muscular sphincter between the stomach and the duodenum and what does it do?
Pylorus/pyloric sphincter
Controls gastric emptying and limits reflux of bile from small intestine
Where are Chief cells located and what do they do?
Located in the stomach
They produce pepsinogen (the inactive form of pepsin)
Where are Parietal cells located and what do they do?
Located in the stomach
Produce HCl and intrinsic factor which is needed for vit B12 absorption
What do the mucous cells of the stomach do?
Produce an alkaline mucus that shields the stomach wall and neutralize acids close to wall
What is the longest portion of the GI tract?
Small intestine
Describe the lining of the small intestine:
The intestinal wall is marked by circular folds lines with intestinal villi to increase surface area for absorption and digestion. Each villi has microvilli which are covered by a brush border containing digestive enzymes
Where is the ileocecal valve and when does it open?
Located between the small and large intestine
Opened via peristaltic contractions
What are the 2 layers of the enteric nervous system and where are they located?
- Myenteric plexus; lies between the longitudinal and circular muscular layers (GI movement)
- Submucosal plexus; like in the submucosa (secretions and sensory functions)
What does gastrin do and where is it secreted?
Secreted in the stomach by G cells in response to food entry. It mediates gastric acid secretion and increases stomach motility. Promotes constriction of LES.
Also
What does CCK do and where is it secreted?
Secreted by I cells in the duodenum in response to fat. Stimulate release of pancreatic enzyme (lipase) and causes contraction of gallbladder and relaxation of sphincter of Oddi=bile released to duodenum.
What does secretin do and where is it secreted?
Secreted by the mucosa of the duodenum in response to acid from stomach. Stimulates pancreatic fluid and bicarb rich solution release = neutralize acidity in intestine
What do slow waves refer to?
Ongoing basic oscillation in membrane potential that occurs in the smooth muscle of the GI tract by myenteric nerve plexus (especially longitudinal muscle by)
The usual stimulus for peristalsis is ________
Distention of the intestinal walls
stimulates myenteric nerve plexus and circular constriction occurs to propel food forward
_________ contractions serve to keep the intestinal contents thoroughly mixed on a constant basis.
Segmental
What organs do the superior and inferior mesenteric plexus feed?
Superior- Pancreas, Small Intestine
Inferior- Large Intestine
All GI organs send deoxygenated blood to:
The liver via the portal vein
What organs does the splenic artery feed?
Stomach, Spleen, Pancreas
What is the major nerve of the parasympathetic nervous system that provides extensive innervation to the GI tract?
Vagus Nerve
What do the sympathetic nerve endings of the GI tract secrete and why is this important?
They secrete norepinephrine.
Promotes the inhibitory effect of the SNS on the GI tract and has ability to stop/block the movement of nutrients->Vomiting.
What provides chemical control in the Liver?
Insulin-like growth factor(somatomedin)
Angiotensinogen
Angiotensin
Thrombopoeitin
What provides chemical control in the Stomach?
Gastrin Ghrelin Neuropeptide Y Somatostatin Histamine Endothelin
What provides chemical control in the Duodenum?
Secretin
CCK
What provides chemical control in the Pancreas?
Insulin
Glucagon
Somatostatin
Pancreatic polypeptide
What provides chemical control in the Kidney?
Renin
EPO
Calcitriol
Thrombopoietin
How are starches digested?
(Mouth)
-Salivary amylase begins to break down the starch.
(Small Intestine)
-Pancreatic lipase
-Brush border enzymes (lactose, maltose, sucrose)
=simple sugars to be absorbed by capillaries and transported to the portal vein
How are proteins digested?
(Stomach)
-Pepsin in presence of HCl begins break down
(Small Intestine)
-Pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase)
-Brush border enzymes (aminopepsidases and dipepsidases)
=Amino acids to be absorbed by the capillaries and transported to the portal vein
How are unemulsified fats digested?
(Small Intestine)
- Emulsifying agents (bile acids, fatty acids, monoglycerides, lecithin, cholesterol and protein) act on fats
- Pancreatic lipases breakdown to
=monoglcerides/fatty acids and glycerol/fatty acids transported via the portal vein or thoracic duct
What are the functions of the exocrine pancreas?
Secretion of digestive juices into the GI tract via ducts
- Neutralizes acidic chyme entering the duodenum from the stomach
- Produces enzymes: proteases, amylases, and lipases
How does the pancreas protect itself from auto digestion by its own enzymes?
All proteases are secreted in their INACTIVE (aka pro-enzyme) form. Trypsin inhibitor is also produced
What are the functions of the endocrine pancreas?
Produces and secretes hormones into the vascular system
Insulin, Glucagon, Somatostatin
The Islets of Langerhans of the endocrine pancreas are made up of three types of cells. What are they are what do they produce?
- Alpha- Glucagon (converted to glucose)
- Beta- Insulin (glucose uptake)
- Delta- Somatostatin (inhibits alpha/beta)
What is dysphagia and what type of obstructions could it be related to?
Difficulty swallowing d/t mechanical or functional obstructions
What is GERD?
Reflux of acidic chyme from the stomach into the esophagus. Should be inhibited by LES
What is a blocking or narrowing of the opening between the stomach and the duodenum?
Pyloric obstruction
What does an ileus describe?
Failure of normal intestinal motility in the absence of an obstructing lesion
What state could cause natural decrease in the resting pressure of the LES?
Pregnancy (d/t high progesterone)
How can pregnancy predispose an individual to the development of gallstones?
- High progesterone causes an increase in residual volume in the gallbladder causing bile stasis.
- Estrogen
- Down-reg of contractile G proteins in the gallbladder muscle impairs emptying
What is alchalasia?
Denervation of the smooth muscle in the esophagus and LES (causes dysphagia)
What could the constant irritation of the esophagus like in GERD predispose an individual to?
Cancer
What is Barrett Esophagus?
Complication of chronic GERD.
Columnar tissue replaces the normal squamous epithelial cells of the distal esophagus
(Significant cancer risk)
What is a hiatal hernia and what is the most common type?
A defect in the diaphragm that allows a portion of the stomach to pass through the diaphragmatic opening into the thorax
95% sliding hiatal hernia
What is a sliding hiatal hernia?
Portion of the stomach and gastroesophageal junction slip into the thorax (gastroesophageal junction is above diaphragmatic opening)
What is a paraesophageal hernia?
A part of the greater curvature of the stomach rolls through the diaphragmatic defect
What are herniations of the mucsosa of the colon through muscle layers of the colon wall (esp. sigmoid colon)?
Diverticula
What are the two stages of disease involving diverticula?
Diverticulosis- asymptomatic
Diverticulosis- inflammatory state
(pain, diarrhea, constipation, fever, leukocytosis)
What is a volvulus?
Twisting of the bowel on itself causing intestinal obstruction and blood vessel compression
What is the telescoping or invagination of a portion of the bowel into an adjacent portion called?
Intussusception
What is seen with high vs. low intestinal obstructions?
(d/t loss of water and lytes)
Alkalosis with high obstruction
Acidosis with low or late obstruction
What are inflammatory markers present in IBS?
- CRP
- Calprotectin (WBC)
- ESR