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NBME 21 Answers

nbme21/Block 3/Question#45

A 28-year-old man comes to the physician for ...

Fructose

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 +8  upvote downvote
submitted by yo(21),

I just knew that sperm need fructose, not sure what disease process this is though. He was pretty normal so 5a reducatase doesn't present like that. I wasn't sure if there was any odd use of the other answers. here is a link. Feel free to expand.

https://www.labce.com/spg27422_question.aspx

Fructose makes up 99% of the reducing sugar present in semen. This sugar is produced in the seminal vesicles. Diminished levels of fructose have been shown to parallel androgen deficiency and the testosterone level. Following testosterone therapy, the level of fructose increases. Although the fructose test is not part of a routine semen analysis, it is useful in cases of azoospermia (absence of sperm in semen). In azoospermia secondary to the absence of vesicles or if there is an obstruction, no fructose is present. In testicular azoospermia, fructose is present. When azoospermia and low semen volume exists, the fructose test should also be done, on a postejaculate urine sample to check for retrograde ejaculation. This occurs when the ejaculate goes into the bladder instead of out the urethra. The procedure for determining the amount of fructose in semen involves heating semen in a strong acid in the presence of resorcinol. Fructose gives a red color (Selivonoff reaction) and may be read in a photometer. The normal average is 315mg/dL fructose.

sam.l  Thank you for the explanation. I'm still confused about this answer. I was in between Zinc and fructose. Zinc deficiency also presents with anosmia (pg 71 First Aid 2019). Fructose is used for the movement. His hormones are normal. +1  
d_holles  Apparently diabetes, occlusion, and inflammation can result in ↓ fructose in sperm. Mauss et al, Fert Stert 25, 1974 https://www.fertstert.org/article/S0015-0282(16)40391-2/pdf +1  
cienfuegos  Thanks all for the info, quick note on the Zinc reply above @Sam.I: anosmia = lost sense of smell. +  
sam1  Great find yo! I believe this question was alluding to cystic fibrosis and the congenital absence of the vas deferens. Here is a link to a NEJM article about it below: https://www.nejm.org/doi/full/10.1056/NEJM196807112790203 +  
burak  zinc deficiency cause hypogonadism. there is no hypogonadism, sperms are damaged? +  




 +3  upvote downvote
submitted by nwinkelmann(57),

So I looked into this further too because I pretty much know nothing about the make up of semen. From the research I found, as as stated below by yo, fructose is the most important constituent of semen in terms or sperm function. Below is information I found to address the other answer choices.

Zinc deficiency (in serum), per FA, has been implicated in delayed wound healing, suppressed immunity, male hypogonadism, decreased adult hiar (axillary, facial, pubic), dysgeusia, anosmia, acromdermatitis enteropathica (defect in intestinal zinc absorption), and may predispose to alcoholic cirrhosis. FA didn't specify the levels in the semen, but per the below article, seminal zinc content was found to have nor correlation to sperm/semen activity/level/etc. I don't know if we're supposed to know that, but now I do, lol. https://www.ncbi.nlm.nih.gov/pubmed/3570537.

As hungrybox mentioned, selenlium is only mentioned once in FA as a treatment for tinea, so I looked into it further. Selenium is a content of semen, but levels vary so much that it serves no prognostic clincal relevance to infertility, per this article: https://www.ncbi.nlm.nih.gov/pubmed/3235210.

To rule out all of the answers (because I didn't really know anything about the quality fo semen), I found this "By t-statistics, there was no significant difference in the semen Na concentration among the different groups (7 groups total based on sperm count), indicating the insignificant role of Na in sperm motility.". https://www.ncbi.nlm.nih.gov/pubmed/721152.

Finally, I don't think the 5-alpha reductase enzyme is actually in semen, but I could be wrong. Either way, it wouldn't be abnormally elevated or low if the testosterone levels are normal.





 +0  upvote downvote
submitted by nwinkelmann(57),

So I looked into this further too because I pretty much know nothing about the make up of semen. From the research I found, as as stated below by yo, fructose is the most important constituent of semen in terms or sperm function. Below is information I found to address the other answer choices.

Zinc deficiency (in serum), per FA, has been implicated in delayed wound healing, suppressed immunity, male hypogonadism, decreased adult hiar (axillary, facial, pubic), dysgeusia, anosmia, acromdermatitis enteropathica (defect in intestinal zinc absorption), and may predispose to alcoholic cirrhosis. FA didn't specify the levels in the semen, but per the below article, seminal zinc content was found to have nor correlation to sperm/semen activity/level/etc. I don't know if we're supposed to know that, but now I do, lol. https://www.ncbi.nlm.nih.gov/pubmed/3570537.

As hungrybox mentioned, selenlium is only mentioned once in FA as a treatment for tinea, so I looked into it further. Selenium is a content of semen, but levels vary so much that it serves no prognostic clincal relevance to infertility, per this article: https://www.ncbi.nlm.nih.gov/pubmed/3235210.

To rule out all of the answers (because I didn't really know anything about the quality fo semen), I found this "By t-statistics, there was no significant difference in the semen Na concentration among the different groups (7 groups total based on sperm count), indicating the insignificant role of Na in sperm motility.". https://www.ncbi.nlm.nih.gov/pubmed/721152.

Finally, I don't think the 5-alpha reductase enzyme is actually in semen, but I could be wrong. Either way, it wouldn't be abnormally elevated or low if the testosterone levels are normal.





 -2  upvote downvote
submitted by hungrybox(176),

According to the USMLE, selenium's only use is in selenium sulfide as a treatment for a fungus called Malassezia spp (Tinea versicolor).