Chapter 7.4, Problem 8AYLO

Summary Introduction

To discuss:

Two forms of phosphate ions in the blood; the bodily functions of phosphate; and how calcitriol and parathyroid hormone affect blood phosphate levels.

Introduction:

Mineralization is a process (crystallization) that deposits phosphate, calcium, and other ions (from blood plasma) in the tissues of the bone as hydroxyapatite. This process is initiated by the osteoblast by laying collagen fibers on the external surface of the osteon. These fibers are coated with minerals that make the matrix hard. Only if the level of the products (of above minerals) in the plasma reaches the critical value (solubility product), the hydroxyapatite is formed. Sometimes, calcification is repressed by some inhibitors found in the tissue. This inhibitor is deactivated by osteoblast, and it enables the precipitation of the salt in the matrix of the bone. The initially formed crystals perform like a “seed of crystals” that attract more phosphate and calcium from the plasma.