Hormones of Calcium Metabolism and Stress Response Pathways

Describe the sources, targets, and primary effects of the hormones of calcium metabolism

The parathyroid gland is the hormone that affects Ca2+ concentration. When Ca2+ concentration is too low in the plasma, the parathyroid hormone secretion is stimulated, and vice versa. This parathyroid hormone can have several effects. It can send a signal to the bones and the osteoblasts will break down and more Ca2+ enters the blood. It can also stimulate the formation of 1,25 (OH)₂D to reabsorb Ca2+ in the intestines and kidneys so less Ca2+ is excreted, it also increases the excretion of phosphate ions. It also stimulates the reabsorption of Ca2+ in the GI tract. Calcitonin is a peptide hormone secreted by parafollicular cells in the thyroid gland. Calcitonin decreases plasma Ca2+ concentration, mainly by inhibiting osteoclasts, thereby reducing bone resorption. Its secretion is stimulated by an increased Ca2+ plasma concentration, which is the opposite for PTH.

Describe the hypothalamic-pituitary-endocrine organ pathways for the adrenal cortex and thyroid gland

When T3 and T4 levels are low, TRH is activated which activates TSH until T4 and T3 levels are restored (negative feedback). The trophic hormones in these pathways only work in their specific pathways. However, the produced hormones, T3, can have permissive or trophic effects on other hormones, such as growth hormone and epinephrine. The trophic hormones for the adrenal cortex and thyroid only work in these pathways since they operate under negative feedback.

How would you distinguish between primary and secondary hypersecretion?

In primary hypersecretion the gland is secreting too much of the hormone on its own. For example, if there was too much cortisol and it was a primary hypersecretion, we know that the issue must be in the adrenal cortex, perhaps a tumor. Secondary hypersecretion is excessive stimulation of the gland by its tropic hormone. So if for example, ACTH and cortisol levels would be high while the CRH remained low. If the problem was with CRH instead you would see only high levels in each pair of the pathway. It would be increased CRH, ACTH, and cortisol levels. Hyposecretion is too little hormone. Primary hyposecretion can be due to partial damage of gland or enzyme deficiency or lack of nutrients in diet or infection, etc. Secondary hyposecretion is caused due to deficiency of the tropic hormones even though the gland is in good condition. Hyporesponsiveness is reduced responsiveness of target cells to hormone. Most common type of Diabetes Mellitus, type 2 is caused due to hyporesponsiveness of target cells (muscle cells and adipose tissues).

List all hormones involved in a stress response

• Cortisol- gluconeogenesis, uptake of beta-adrenergic receptors to break down adipose+fat tissue, vasocompression, increased heart rate, shuts down non-essential functions such as reproductive and growth functions.
• Epinephrine-vasodilation, higher heart rate.
• GH- inhibited by cortisol at tissues, flight or fight or flight response. These are hormones involved in a stress response.