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GI Exam 2 > Digestion and Absorption in the GI Tract > Flashcards

Digestion and Absorption in the GI Tract Flashcards

1
Q
  • Digestion begins in _ and is completed in the SI
  • Absorption takes place primarily in _
A
  • Stomach (and mouth )
  • Small Intestine
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2
Q
  • Two main pathways for absorption
A
  • Cellular
    • ​Lumen-apical membrane-intestinal epithelial cell-basolateral membrane-blood
    • Transportes in membrane
  • Paracellular
    • ​Intestinal epithelial cell-lateral intercellular space-intestinal epithelial cell
    • Tight Junctions
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3
Q
  • What carbohydrate digestive enzymes are located in:
    • ​Saliva
    • Pancreas
    • Intestinal Mucosa
A
  • Saliva
    • ​Amlyases
  • Pancreas
    • ​Amylases
  • Intestinal Mucosa
    • ​Sucrase
    • Maltase
    • Lactase
    • Trehalase
    • Alpha Dextrinase
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4
Q
  • What protein digestive enzymes are secreted by the:
    • ​Stomach
    • Pancreas
    • Intestinal Mucosa
A
  • Stomach
    • Pepsin
  • Pancreas
    • Trypsin
    • Chymotrypsin
    • Carboxypeptidase
    • Elastase
  • Intestinal Mucosa
    • Amino-oligopeptidase
    • Dipeptidase
    • Enterokinase
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5
Q
  • What lipid digestive enzymes are secreted by the :
    • ​Saliva
    • Stomach
    • Pancreas
A
  • Saliva
    • ​Lingual Lipase
  • Stomach
    • ​Gastric Lipase
  • Pancreas
    • ​Lipase-colipase
    • Phospholipase A2
    • Cholesterol ester hydrolase
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6
Q
  • What are the two types of digestive activity?
A
  • Cavital (luminal)
  • Membrane (contact)
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7
Q
  • Cavital (luminal) digestion
A
  • Digestion from action of enzymes secreted by salivary glands, stomach and pancreas
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8
Q
  • Membrane (contact) digestion
A

Hydrolysis by enzymes synthesized by epithelial cells/enterocytes

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9
Q
  • Villi are longest in the _ and shortest in the _ of the SI
A
  • Duodenum
  • Terminal Ileum
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10
Q
  • What cell types are pesent in the intestinal epithelium and what are their functions?
A
  • Enterocytes-digestion, absorption, and secretion (replaced 3-6 days); susceptible to chemo
  • Goblet Cells-mucus secreting cells
  • Paneth Cells-mucosal defenses against infection
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11
Q
  • Where does pinocytosis occur?
  • What macromolecule is taken up via pinocytosis?
A
  • Base of microvilli
  • Proteins
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12
Q
  • Besides pinocytosis, what other methods are used by enterocytes to absorb nutrients into the blood?
A
  • Passive diffusion
  • Facilitated diffusion
  • Active transport
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13
Q
  • What barriers/layers must the solute moving from lumen to blood cross?
A
  • Unstirred layer of fluid
  • Glycocalyx
  • Apical Membrane
  • Cytoplasm of Cell
  • Basolateral Membrane
  • Basement Membrane
  • Wall of Blood Capillary or Wall of Capillary of Lymphatic Vessel
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14
Q
  • In what clinical scenarios can the intestine adapt to maintain homeostasis in digestion and absorption?
  • In what clinical scenarios is it limited?
  • In what GENETIC ABNORMALITY is it lost?
A
  • Small bowel resection and bypass
  • Terminal ileum recetion-absorption of B12 and bile salts is abolished
  • Lactase deficiency
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15
Q
  • What are the three end products of carbohydrate digestion?
A
  • Glucose
  • Fructose
  • Galactose
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16
Q
  • What enzyme converts trehalose to glucose?
  • What enzyme converts lactose to glucose and galactose?
  • What enzyme converts sucrose to glucose and fructose?
  • What enzyme converts alpha dextrin to glucose?
  • What enzyme converts maltose to glucose?
  • What enzyme converts maltotriose to glucose?
A
  • Trehalase
  • Lactase
  • Sucrase
  • Alpha dextrinase
  • Maltase
  • Sucrase
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17
Q

_ and _ diffusion are key transport mechanisms in the absorption of carbohydrates

What transporters are present in the small intestine that aid in absorption of carbohydrates?

A
  • Co-transport and facilitated diffusion
  • APICAL
    • ​SGLT1 (Transports Na+/Glucose or Galactose)
    • GLUT5 (Transports Fructose)
  • Basolateral
    • Na+/K+ ATPase
    • GLUT 2 (Transports Glucose, Galactose and Fructose)
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18
Q
  • Lactose intolerance can cause _ because of undigested lactose remaining in lumen and holding H20
  • This also leads to unabsorbed lactose being fermented into methane and H+ gas
A
  • Osmotic diarrhea
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19
Q
  • _ is a brush border enzyme that helps convert trypsinogen to trypsin in the small intestine
  • Trypsin is an _ that helps convert various proteases in the SI into their active form
A
  • Enterokinase
  • Endopeptidase
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20
Q
  • What are the pancreatic endopeptidases?
A
  • Trypsin
  • Chymotrypsin
  • Elastase
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21
Q
  • What are the pancreatic exopeptidases?
A
  • Carboxypeptidase A
  • Carboxypeptidase B
22
Q
  • Pepsin in the stomach breaks down proteins into _ and _
  • Luminal enzymes in the small intestine (Carboxypeptidase A and B, Trypsin, Chymotrypsin and Elastase) convert proteins into _, _, _and _
  • _ in small intestine are further broken down by _ (BRUSH BORDER) to _, _, and _
A
  • Amino acids
  • Oligopeptides

Small Intestine:

  • Amino acids
  • Dipeptides
  • Tripeptides
  • Oligopeptides
  • Oligopeptidases further broken down by peptidase brush border into amino acids and dipeptides, tripeptides
23
Q
  • _ and _ diffiusion are key in absorption of proteins
  • What transporters are present on enterocytes that aid in protein digestion?
A
  • Co-transport and facilitated diffusion (just like carbohydrates)
  • Apical
    • ​Na+/H+ ATPase
    • Na+/Amino Acid cotransporter (4 different types: neutral, acidic, basic, imino)
    • H+/Dipeptide or Tripeptide cotransporter
  • Basolateral
    • ​Na+/K+ ATPase
    • Amino acid transporters (neutral, basic, imino, acidic)
24
Q
  • Chronic pancreatitis and cystic fibrosis-how do these affect protein reabsorption?
A
  • Deficiency of pancreatic enzymes/defect in transporters of enterocytes
25
Q
  • How does congenital trypsin absence affect protein metabolism?
A
  • All pancreatic enzymes are non-functional (need trypsin to become activated)
26
Q
  • Cystinuria
A
  • Defect/Absence in Na+/AA cotransporter on apical membrane of enterocytes and Kidney (specifically di-basic aa transporter (cystine, lysine, argignine, ornithine)
  • Cystine crystals in urine
27
Q
  • HARTNUP
A
  • Cannot absorb neutral AAs
  • AR-SLC6A19 gene
  • Symptoms similar to NIACIN DEF (PALLEGRA)
    • ​Diarrhea
    • Mood swings (serotonin not being synthesized)
    • Neurological problems
    • Red, scaly skin rash
    • Photosensitivity
    • Short Stature
    • Uncoordinated Movements
    • Urine (high levels of neutral aas (ex: tryptophan) and by-products (serotonin)
28
Q
  • _% of protein digestion occurs in stomach
  • Since bile acids are not present _ perform the emulsifying action
A
  • 10%
  • Dietary proteins
29
Q
  • In order to allow sufficient time for the digestion of lipids, _ is secreted immediately when dietary lipids first appear in the small intestine
  • This functions to _
A
  • CCK
  • Decrease rate of gastric emptying
30
Q
  • _% of protein digestion occurs in the SI
  • _ emulsify fats
  • _ are secreted to aid in digestion (Name these)
A
  • 90%
  • Bile salts
  • Pancreatic Enzymes
    • Pancreatic lipase
    • Colipase
    • Cholesterol ester hydrolase
    • Phospholipase A2
31
Q

Pancreatic lipase

Secreted as active or inactive?

Inactivated by _ and resolved with _

A
  • Active
  • Bile salts
  • Colipase
32
Q
  • Colipase
    • ​Secreted in active or inactive?
    • Function?
A
  • Secreted as procolipase (inactive)
  • Activated by trypsin
  • Binds to pancreatic lipase and displaces bile salts (to activate it)
33
Q
  • Cholesterol ester hydrolase
A
  • Catalyzes production of cholesterol
  • Hydrolyzes triglycerides to produce glycerol
34
Q
  • Phospholipase A2
A
  • Breaks down phospholipids into lysolecithin and fatty acids
35
Q
  • What are the steps for digestion and absorption of lipids?
A
  1. Solubilization by micelles (lumen)
  2. Diffusion of micellar content across apical membrane
  3. Reesterification
  4. Chylomicron formation (ApoB important here)
  5. Exocytosis of chylomicron into lymph
36
Q
  • Abetalipoproteinemia is no absorption of lipids caused by lack of _ in chylomicrons
A
  • ApoB
37
Q
  • Errors in lipid metabolism can lead to _
  • Possible mechanisms?
A
  • Steatorrhea
  • Any abnormalities:
    • Pancreatic enzyme secretion
    • Bile acid secretion
    • Emulsification
    • Micelle formation
    • Diffusion into intestinal cells
    • Chylomicron formation
    • Transfer of chylomicrons into lymph
38
Q
  • Factors that can cause a deficit in bile salt (and thus affect absorption of lipids)
A
  • Ileal resection
  • Small intestinal bacterial overgrowth
39
Q
  • Ileal resection
A
  • Interrupts enterohepatic circulation of bile salts
  • Total pool of bile salts is reduced
40
Q
  • SIBO (small intestinal bacterial overgrowth)
    • ​What is it?
    • What are the two main causes?
A
  • Bacteria deconjugate bile salts-impairs micelle formation and leads to fat malabsorption
  • Bacterial overgrowth also damages intestinal mucosa
  • Causes:
    • Decreased acid secretion (remember acid helps destroy bacteria)
    • Small intestine dysmotility
41
Q
  • Tropical Sprue
A

Decreased number of intestinal epithelial cells reduces surface area

Fat malabsorption and steatorrhea

Def of Folate and B12

Diarrhea

Cramps, nausea, weight loss, gas, indigestion

Tx: Tetracycline and folate (6 mo)

42
Q

Celiac Sprue

A
  • Autoimmune disorder
  • Abs against gluten-destruction against small intestinal villi and hyperplasia of intestinal crypts
  • Malabsorption of folate, iron, B12, Ca2+, Vitamins A, B12, and D
  • Sx: Abdominal pain, constipation, diarrhea, unexplained weight loss, vomiting and nausea, steatorrhea, tingling, numbness in hands/feet, itchy skin w/rash, fatigue, seizures, easy bruising, bone fractures
  • Tx: Gluten free diet
43
Q
  • How are fat soluble vitamins (A,D,E,K) absorbed?
A
  • Same mechanism as lipids
    • Solubilization by micelles
    • Diffusion of micellar content across apical membrane
    • Reesterification
    • Chylomicron formation
    • Exocytosis of chlyomicron into lymph
44
Q
  • What are the water soluble vitamins and how are they absorbed?
A
  • Water soluble (B1, B2, B3, B12, C, Biotin, Folic Acid, Nicotinic Acid, Pantothenic Acid)
  • Na+ Dependent cotransport mechanism in small bowel
45
Q
  • Vitamin B12 forms complexes with what proteins to aid in its absorption?
  • What is the function of B12? (What she was specific about?)
A
  • IF,R proteins, and transcobalamin II
  • Important in DNA synthesis in red blood cells
46
Q
  • What can lead to a disruption in the absorption of Vitamin B12?
A
  • Gastrectomy: Loss of parietal cells
  • Gastric bypass
47
Q
  • Pernicious anemia
A
  • Causes:
    • Atrophic gatritis: chronic inflammation, loss of parietal cells
    • Autoimmune metaplastic atrophic gastritis-immune system attacks IF protein or gastral parietal cells
  • remember that B12 is important for DNA synthesis of RBCs (if yopu don’t have IF from parietal cells, can’t properly absorb B12)
48
Q
  • Inadequate Ca2+ absorption can lead to _ in children and _ in adults
  • How is Ca2+ absorbed in the SI?
A
  • Ricket’s
  • Osteomalacia
  • Vitamin D dependent Ca2+ binding protein
49
Q
  • How is iron absorbed in the SI?
A
  • Binds to apoferritin in intestinal cells
  • Binds to transferrin in blood
50
Q
  • Summary of where things are absorbed in the GI tract
A
51
Q
  • Summary of how things are absorbed in the GI tract
A

GI Exam 2 (14 decks)

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