Question: TBR Bio, Book I, Section IV, Passage XIII, Question 85

[as8906]

I know there was already a post on this, but the discussion was inconclusive and I thought making a new thread would be a better way of getting attention/responses.

85. During early labor, plasma oxytocin levels are not
higher than prepregnancy levels of 25 pg/mL. What
mechanism(s) could explain an increase in uterine
contractions without an increased plasma level of
oxytocin?

I. An increase in the number of uterine receptors
for oxytocin during late pregnancy.
Il. Paracrine release of oxytocin that does not
communicate with the bloodstream.
III. Increased conjugation ofoxytocin in the liver.

A. I only
B. I and II only
C. II and III only
D. I, II, and III

In their explanation, they stated that statement II was valid. I don't understand how it's possible though, unless my understanding of the word "paracrine" is flawed. Doesn't that refer to communication between cells that are near each other? If so, how could paracrine communication be possible between the hypothalamus and the uterus? Are there other cells that can produce oxytocin?

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[MedPR]

I know there was already a post on this, but the discussion was inconclusive and I thought making a new thread would be a better way of getting attention/responses.

85. During early labor, plasma oxytocin levels are not
higher than prepregnancy levels of 25 pg/mL. What
mechanism(s) could explain an increase in uterine
contractions without an increased plasma level of
oxytocin?

I. An increase in the number of uterine receptors
for oxytocin during late pregnancy.
Il. Paracrine release of oxytocin that does not
communicate with the bloodstream.
III. Increased conjugation ofoxytocin in the liver.

A. I only
B. I and II only
C. II and III only
D. I, II, and III

In their explanation, they stated that statement II was valid. I don't understand how it's possible though, unless my understanding of the word "paracrine" is flawed. Doesn't that refer to communication between cells that are near each other? If so, how could paracrine communication be possible between the hypothalamus and the uterus? Are there other cells that can produce oxytocin?

Yes, oxytocin is produced in tissues like the uterus, placenta, and corpus luteum. If I remember correctly, the passage tells you that or leads you to it.

 

[as8906]

Hey, thanks for the response. I looked through the passage again and I couldn't find were it would lead me to it. Which part of the passage specifically allows me to make that conclusion?

 

[MedPR]

Hey, thanks for the response. I looked through the passage again and I couldn't find were it would lead me to it. Which part of the passage specifically allows me to make that conclusion?

If it's not in the passage then TBR expects that you know it as background knowledge.

 

[Medical Muse]

Here are two explanations I found:

Circulating levels of oxytocin do not change significantly during pregnancy or prior to the onset of labor [55,56]. However, myometrial oxytocin receptor concentrations increase approximately 100 to 200-fold during pregnancy, reaching a maximum during early labor [55,56,58,59]. This rise in receptor concentration accounts for the increased sensitivity of the myometrium to circulating levels of oxytocin during the second half of pregnancy.

Although maternal serum oxytocin levels are not increased prior to the onset of labor or during the first stage of labor, oxytocin derived from the fetus and possibly from local decidual and other uterine sources could act on myometrial oxytocin receptors in a paracrine/autocrine fashion to initiate and maintaine effective uterine contractions.