Pth

Bone releases Ca+2

Kidneys conserve Ca+2

Intestine absorbs Ca+2

Kidneys conserve Ca+2

Intestine absorbs Ca+2

Figure 13.25

Parathyroid hormone stimulates bone to release calcium and the kidneys to conserve calcium. It indirectly stimulates the intestine to absorb calcium. The resulting increase in blood calcium concentration inhibits secretion of parathyroid hormone.

of receptors, although norepinephrine has a greater effect on alpha receptors. Table 13.9 compares some of the differences in the effects of these hormones.

Impulses arriving on sympathetic nerve fibers stimulate the adrenal medulla to release its hormones at the same time sympathetic impulses stimulate other effectors. As a rule, these impulses originate in the hypothalamus in response to stress. Thus, the medullary secretions function together with the sympathetic division of the autonomic nervous system in preparing the body for energy-expending action—"fight or flight."

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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