Organ Systems II MT4 Dr. Siebeker Flashcards
IBS affects up to ___% of the population and accounts for ___& of visits to Gastroenterologists.
up to 20% of the population
50% of visits to GI drs
What are the symptoms of IBS?
Bloating, pain, constipation/diarrhea, flatulence, belching, nausea, acid reflux
What is the cause of the symptoms of IBS in most cases?
GI infection ==> sm. int. bacterial overgrowth (SIBO) ==> carbohydrate malabsorption.
What are brush border enzymes?
Apical plasma membrane of enterocytes is composed of numerous projections from the cell (microvilli) which make up the “brush border.” The enzymes embedded in those microvilli are referred to as brush border enzymes.
What substances contribute to chemical digestion?
Stomach: HCL, pepsin
Small Int.: Pancreatic enzymes, bile, brush border enzymes
What are the two types of ileocecal valves? .
Papillary = sphincter
Labial = fold
Each person has one valve (one or the other)
Describe the difference between exocrine and endocrine portions of the pancreas.
Exocrine = duct cells and acinar cells Endocrine = Islets of Langerhans -->secrete insulin and glucagon into the blood.
What features of the small intestine serve to improve digestion/absorption?
Folds, villi, microvilli increase surface area. Single enterocyte layer allows quick absorption. Blood and lymph vessels are right underneath enterocytes.
How do enzymes, water and bicarb get into SI?
Main pancreatic duct
How are the cephalic and gastric phases of digestion different?
Cephalic phase triggered by sight, smell, taste, chewing, swallowing.
Gastric phase triggered by gastric distention.
How are the cephalic and gastric phases of digestion similar?
Both result in pancreatic secretions stimulated by Vagus n.
What are the hormones that control pancreatic secretions? What cells secrete them?
CCK, secreted by I cells in sm int
Secretin, secreted by S cells in sm int
What triggers the release of CCK? Secretin?
CCK - Fat and protein
Secretin - H+ (acid) and fat
What does CCK do?
Stimulates acinar cells in pancreas to secrete enzymes and bile for digestion in small intestine
Humans do not make enzymes to digest ________ and _________. Who can digest these?
Fiber and Oligosaccharides.
Bacteria can digest these.
What does Secretin do?
Stimulates duct cells in pancreas to secrete water and bicarb to neutralize acid in small intestine.
What enzyme(s) for carbohydrate digestion are secreted by the pancreas? Where do these act?
Amylase is secreted by the pancreas and acts in the duodenal lumen.
Name the types of carbohydrates that humans can digest.
Amylose/Amylopectin Sucrose Lactose Trehalose Glucose Fructose
What are the three types of fiber?
Soluble fiber (inulin, psyllium, flax, chia, hemp) Insoluble fiber (cellulose, hemicellulose, lectin) Oligosaccharides (MOS, FOS, GOS)
What is the advantage of using Glut2 for fructose transport?
Fructose has better uptake when it is transported 1:1 with glucose.
Where are the carbohydrate transporters located in the enterocyte?
SGLT1, Glut 5 = apical membrane of enterocyte Glut 2 = basolateral membrane of enterocyte
What are the 3 types of carbohydrate transporters and what do they transport?
SGLT1 - glucose and galactose Glut5 - fructoseGlut2 - glucose, galactose, and fructose
When carbs cannot be digested efficiently, what substances are created in or moved into the gut?
1) Carbs are fermented by bacteria –> gas (methane and hydrogen)
2) Carbs have osmotic effect and draw H2O into SI
3) Gas and H2O –> luminal distention –> IBS Symptoms
What is the relationship between brush border enzymes and carbohydrate malabsorption?
BB enzymes required to break down carbs into monosaccharides. Disaccharides and larger cannot absorb across the apical membrane without further digestion. These carbs will sit unabsorbed in SI and become food for bacteria.==> Carbohydrate Malabsorption
Trace the path of a starch from mouth to gut to bloodstream.
Mouth = mechanical, salivary amylase
Stomach = mechanical (churning)
SI = Pancreatic amylase break it into maltose
BB = Maltase breaks it into glucose
SGLT1 transports glucose into enterocyte
Glut2 transports glucose into bloodstream
What is the difference between the congenital and acquired types of primary lactose malabsorption? Which is more common?
Primary Congenital - Born without lactase (rare) Primary Acquired - Loss of lactase after weaning, Autosomal recessive. (most of world’s population)(Both genetic)
What is a common cause of lactose intolerance? Can it be reversed?
Secondary lactose malabsorption - damage to SI (ex. SIBO, Celiac, Gastroenteritis, Radiation Enteritis)
Lactase function can normalize when situation heals if primary acquired deficiency isn’t present.
How does gas production by bacteria in SI contribute to the symptoms of constipation and diarrhea?
Constipation from Methane gas
Diarrhea from Hydrogen gas (also osmotic effect drawing water in)
What enzyme breaks down short peptides (2-3 AA long) into amino acids in the brush border? How is this enzyme activated?
Aminopeptidase
By amino acids, di- and tripeptides (its substrates)
Which pancreatic enzyme(s) does trypsin NOT activate and why?
Trypsin does not activate pancreatic amylase. It is not secreted as proenzyme (no inactive form).
What some factors in the development of carbohydrate malabsorption?
1) No enzymes for some foods (ie fiber)
2) Decreased enzyme function from genetics or SI damage
3) Inefficient transporters
4) Substance is too large
5) Fast transit time
6) Bacterial overgrowth
How does fat help protein digestion?
Detergent action of bile releases enteropeptidase (a BB enzyme).
Enteropeptidase activates trypsin. Trypsin activates chymotrypsin, elastase, carboxypeptidase A&B
What do Carboxypeptidase A and B do? Where do these enzymes act?
Digest polypeptides into amino acids – SI lumen
What are the transporters that get amino acids and peptides into enterocytes?
Numerous BB transporters (Na+) for amino acids. PEPT1 is the transporter for peptides
How is the absorption of amino acids/peptides unlike the absorption of saccharides?
Sugars - only mono- can be absorbed
Proteins - both AA and di and tri peptides can be absorbed because there are intracellular peptidases within the enterocyte to break down peptides.
What are the symptoms of severe protein malabsorption? Why doesn’t it cause the symptoms that carbohydrate malabsorption does?
Muscle wasting, immunodeficiency and edema.
Diff. from carb malab. b/c intestinal bacteria don’t ferment protein, so no gas is created.
What is the significance of tight junctions?
When tight junctions do not function properly –> increased intestinal permeability = leaky gut
What is the junctional adhesion complex?
Composed of zonula occludens, zonula adherens, and macula adherens (desmosomes). Helps to regulate the intercellular passage of substances.
How can zonula occludens be distinguished from zonula adherens and mucula adherens?
The zonula occludens appears as a dark area of the paracellular space between enterocytes near their apical borders.
What are zonula adherens? How do they affect the tight junction?
Adherens junctions.
Actin filaments can contract to pull on the claudin and occludin proteins in zonula adherens to widen junction.
What enzyme(s) for carbohydrate digestion are secreted by the brush border? Where do these act?
Sucrase, Lactase, Trehalase, Maltase, and Isomaltase are secreted by brush border and act in brush border.
How much fructose is absorbed in healthy people? What are some reasons for fructose malabsorption?
15 g (range 5-50g)
Glut5 is easily saturated
Increased consumption of high fructose foods and increasing fructose content in foods (ie fruit)
