Growth hormone calcium metabolism

There seems to be no metabolic control exerted on hepatic 25-hydroxylase and so all of the available cholecalciferol is converted. Hydroxylation in the kidney however is an important control point being regulated by PTH, and indirectly therefore by calcium and phosphate concentrations. Stimulation of la-hydroxylase by PTH is via a cyclic AMP (cAMP) -dependent mechanism and longer-term regulation of the activity of this enzyme is via induction mediated by other hormones such as oestrogens, cortisol and growth hormone. Typically, the plasma concentration of 1,25 dihydroxy vitamin D is in the range 20-60 ng/1, that is approximately 1000-times lower than that of its precursor. 

The normal thyroid gland secretes sufficient amounts of the thyroid hormones—triiodothyronine (T3) and tetraiodothyronine (T4, thyroxine)—to normalize growth and development, body temperature, and energy levels. These hormones contain 59% and 65% (respectively) of iodine as an essential part of the molecule. Calcitonin, the second type of thyroid hormone, is important in the regulation of calcium metabolism and is discussed in Chapter 42. 

Further, fish protein hydrolysates contain hormone-like peptides and growth factors that accelerate calcium absorption (Fouchereau-Peron et ah, 1999). These peptides are capable of binding to the cell surface receptors on osteoclasts and have a role in calcium metabolism by decreasing the number of osteoclasts. Therefore, these peptides could be used in the treatment of osteoporosis and Paget s disease. Further,... 

The pharmacokinetics of morphine have been studied,201-203 as has its receptor binding,204-206 and its effects on hypothermia,207 on calcium uptake by synaptosomes208 and lysed synaptosomes,209 on metabolism of catecholamine in brain,210 on levels of corticosteroids and growth hormone in plasma,211 on leuteinising hormone,212 follicle-stimulating hormone,212 and prolactin,212-215 on neuroendocrine function,216 on brain function and biochemistry,217-226 on behaviour,227-240 on the gastrointestinal tract241 and on the cardiovascular... 

Endocrine and metabolic Blood tests Serum concentrations of pituitary horrmones (TSH, LH, FSH, ACTH, growth hormone, prolactin, vasopressin) serum concentrations of other hormones (insulin parathyroid hormone, glucagon, calcitonin, vitamin D) and serum electrolyte concentrations (sodium, potassium, calcium, magnesium)... 

Growth hormone/insulin-like growth factors Absence during bone growth causes slow growth and short stature (dwarfism). Unknown may not be directly related to calcium and vitamin D metabolism. 

This active vitamin D metabolite (1,25 dihydroxycholecalciferol) is an important cofactor for intestinal calcium absorption, which involves calbindins (calcium binding proteins) in the intestine and kidney. Calcitriol is produced in the kidneys by the conversion of 25-hydroxycholecalciferol (calcidiol) and its formation is stimulated by a reduction of plasma calcium and/or phosphate and increased production of parathyroid hormone and prolactin (Figure 6.3). Calcitriol also inhibits the release of calcitonin and, together with PTH, increases the absorption of calcium and phosphate from the gastrointestinal tract and the kidneys. Growth hormone, glucocorticoids, estrogens, testosterone, and the thyroid hormones also influence calcium metabolism. 

The thyroid secretes two types of hormones iodine-containing amino acids (thyroxine and triiodothyronine) and a peptide (calcitonin). Thyroxine and triiodothyronine have very general effects on growth, development, and metabolism. Calcitonin is important in calcium metabolism and is discussed in Chapter 41. This chapter describes the drugs used in the treatment of hypothyroidism and hyperthyroidism (Figure 38-1). 

A condition which clinically resembles osteomalacia. It differs from osteomalacia, however, in that it is due to a primary loss of the proteinaceous bone matrix with a resultant secondary loss of bone calcium. It can occur as part of the general process of ageing, or in conditions such as hyperthyroidism, acromegaly, Cushing s syndrome (because of the effects of thyroxine, growth hormone and cortisol on protein metabolism) and malabsorption (due to deficient amino acid absorption). Serum calcium, phosphate and alkaline phosphatase levels are normal, unlike osteomalacia. 

Three hormones serve as the principal regulators of calcium and phosphate homeostasis parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and the steroid vitamin D (Figure 42-2). Vitamin D is a prohormone rather than a true hormone, because it must be further metabolized to gain biologic activity. PTH stimulates the production of the active metabolite of vitamin D, l,25(OH)2D. l,25(OH)2D, on the other hand, suppresses the production of PTH. l,25(OH)2D stimulates the intestinal absorption of calcium and phosphate. l,25(OH)2D and PTH promote both bone formation and resorption in part by stimulating the proliferation and differentiation of osteoblasts and osteoclasts. Both... 

Conversion of 7-dehydrocholesterol to vitamin D3 and metabolism of D3 to l,25(OH)2D3 and 24,25(OH)2D3. Control of the latter step is exerted primarily at the level of the kidney, where low serum phosphorus, low serum calcium, and high parathyroid hormone favor the production of l,25(OH)2D3, whereas fibroblast growth factor 23 inhibits its production. The inset shows the... 

The thyroid and parathyroid glands serve a number of vital endocrine functions. The thyroid gland synthesizes and secretes the thyroid hormones T3 and T4. These hormones are important regulators of cellular metabolism and metabolic rate. Thyroid hormones also interact with other hormones to facilitate normal growth and development. The parathyroid glands control calcium homeostasis through the release of PTH. This hormone is crucial... 

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