PTH has one and only one job: That is to control the serum calcium level and keep it within the right range. If serum calcium is low, the parathyroid glands (four of them) secrete PTH. These glands make and store PTH to release it when needed. When released, PTH works with and through vitamin D to restore calcium to a normal level. PTH acts to control the serum calcium just like TSH acts on the thyroid to control the levels of thyroid hormones (T4 and T3).
See a similar graphic on the AAFP site.
“Hyperparathyroidism is present in more than half of patients who have a glomerular filtration rate <60 mL/min, and is independently associated with increased mortality and an increased prevalence of cardiovascular disease. In patients with stage 4 chronic kidney disease, current guidelines recommend monitoring of serum calcium and phosphate levels every 3–6 months and bone-specific alkaline phosphatase activity every 6–12 months with the goal of normalizing these values.”
The question is, why is hyperparathyroidism associated with chronic kidney disease?
Look to the effect of the parathyroid hormone in the kidneys for the answer.
Further Reading
https://www.aafp.org/afp/2013/0815/p249.html