practice questions

• What hormones are involved in maintain calcium homeostasis?

  PTH, calcitonin, calcitriol
• In order for fructose to enter the bloodstream, it must be absorbed by intestinal epithelial cells in the small intestine and cross 2 borders, it does this via?

  GLUT5 on the apical border, GLUT2 on the basolateral border
• How does primary lactase deficiency differ from secondary lactase deficiency?

  Primary: irreversible, inherited

  Secondary: reversible
• What is fructose malabsorption?

  A condition caused by low expression of GLUT5 in the small intestine
• What SNP associated with lactase persistence is common in Caucasian populations and occurs at the intron 13 of the MCM6 gene?


  c -> T
• What enzyme at the brush border breaks down lactose into galactose and glucose?

  lactase
• What gene contains the SNP that causes lactase persistence?

  MCM6
• What is the function of PDX-1?

  Inhibits the function of CDX2 and HNF-1a (they activate LCT transcription)
• What is the optimal scenario for lactose digestion of a lactose intolerance patient?

  slow gastric emptying, slow transit time in the small intestine, fast transit time in the colon
• What is true regarding normal physiological monosaccharide absorption?

  GLUT5 is a sodium-independent transporter, does not require sodium to transport fructose
• Patients with lactose maldigestion could attribute increased symptoms to what?

  SNPs for low expression of CDX-2 and HNF-1a, low levels means less lactase production and less breakdown of lactose
• What is an osteocyte?

  old osteoblasts embedded into the bone matrix
• What does not stimulate expression of bone by inducing osteoclast maturation?

  Estrogen, it stimulates osteoprotegin which is a RANK-L antagonist which inhibits osteoclast maturation
• Why would lactose intolerant patients also get symptoms such as vertigo, cardiac arrhythmia, etc?

  the production of toxic metabolites generated by various colonic bacteria is absorbed into the blood
• What is the active form of vitamin D and where is it found?

  1,25-dihydroxycholecalciferol, found in the kidney
• What SNPs are associated with lactase persistence (mutant)?

  Cdx2, HNF-1a, C>G, C>T
• how does calcitriol decrease the adaptive immune system?

  decreased B and T cell proliferation, decrease antigen presenting cell maturation, inhibits Th17 cell activation and IL-17 secretion, stimulates antimicrobial protein secretion, decreases inflammatory cytokine production
• what occurs in response to low blood calcium levels?

  increased levels of 1a-hydroxylase
• True or false: people with celiac disease will have normal protein digestion and amino acid absorption?

  true
• What are stimulators of bone resorption?

  IL-6, Prostaglandin E2, epidermal growth factor, PTH
• Why do HLA-DQ2 and HLA-DQ8 lead to an increased risk of celiac disease?

  the MHC class 2 receptor binds tightly with gluten which results in a stronger T cell immune response
• Calcitonin 


  inhibits bone resorption and serves to decrease blood calcium levels
• What gene is responsible for lactase persistence?

  MCM6
• What is the transcription factor for osteoblast maturation?

  RunX2
• How do long chain n-3 PUFA contribute to bone health?

  by increasing growth factor stimulation to stimulate osteoblast activity
• What factors contribute to improved tolerance of dairy by those with lactose intolerance?

  the dairy product contains active bacteria cultures, the dairy contains higher fat content
• What is the ideal transit time for a patient with lactose intolerance?

  slow in the stomach, slow in the small intestine, fast in the colon
• which cytokine stimulates MMP-1 and MMP-3 leading to tissue damage?

  TNFa
• What does a DEXA T-score of -2 mean for bone health?

  osteopenia, score of -1 to -2.5
• What stimulates RANK-L and what does not?

  stimulates: calcitriol, PTH, TNFa, IL-6

  does not: IL-4, stimulates osteoprogerin, RANK-L antagonist
• What molecules causes the greatest magnitude of T-cell response in celiac disease?

  deaminated gliadin peptide, possesses a negative charge fitting into the DQ2 MHC class II molecule
• What plays a significant role in the development of osteoporosis?

  low estrogen
• What cytokine and transcription factor helps promote the development of naive T cells into T helper cells?

  IL-12 and Tbet
• What is cortical bone?

  dense tissue that makes up the outer layer of bone and forms the bulk of the interior of long bones