Calcium and PTH Berkeley Review passage

[deleted647690]

---

Members don't see this ad.

There is a question in Berkeley that says there is an inverse linear relationship between PTH and plasma calcium levels. Doesn't increased PTH cause increased Calcium? If you have BR, I'm referencing question 54 in passage 7 in the chapter on endocrinology

 

[ZPakEffect]

This is a complex issue. In physiological states, there is indeed an inverse relationship between serum PTH level and serum Ca level. This is because PTH release increases whenever the serum Ca level is low and decreases when serum Ca is high. It's a very basic negative feedback homeostatic mechanism. However, if you a pathological state where PTH is constantly being released at a high rate due to something like a parathyroid adenoma, then you will see both hyperparathyroidism and hypercalcemia at the same time.

For MCAT purposes, always assume a physiological state unless otherwise specified. The vast majority of homeostatic mechanisms are negative feedback loops, so you will very often see inverse relationships between serum levels of A and B, even though A stimulates the release of B.

 

[deleted647690]

This is a complex issue. In physiological states, there is indeed an inverse relationship between serum PTH level and serum Ca level. This is because PTH release increases whenever the serum Ca level is low and decreases when serum Ca is high. It's a very basic negative feedback homeostatic mechanism. However, if you a pathological state where PTH is constantly being released at a high rate due to something like a parathyroid adenoma, then you will see both hyperparathyroidism and hypercalcemia at the same time.

For MCAT purposes, always assume a physiological state unless otherwise specified. The vast majority of homeostatic mechanisms are negative feedback loops, so you will very often see inverse relationships between serum levels of A and B, even though A stimulates the release of B.

Oh, I was thinking of it just as PTH causes high levels of Ca, but I didn't see that it said the relationship between Ca level and PTH "secretion", suggesting that it refers to the PTH levels acting in response to Ca levels

 

[deleted647690]

This is a complex issue. In physiological states, there is indeed an inverse relationship between serum PTH level and serum Ca level. This is because PTH release increases whenever the serum Ca level is low and decreases when serum Ca is high. It's a very basic negative feedback homeostatic mechanism. However, if you a pathological state where PTH is constantly being released at a high rate due to something like a parathyroid adenoma, then you will see both hyperparathyroidism and hypercalcemia at the same time.

For MCAT purposes, always assume a physiological state unless otherwise specified. The vast majority of homeostatic mechanisms are negative feedback loops, so you will very often see inverse relationships between serum levels of A and B, even though A stimulates the release of B.

Thank you