Calcium, phosphate and magnesium
Martin Andrew Crook in Clinical Biochemistry & Metabolic Medicine, 2013
There are a number of mechanisms by which plasma calcium concentrations are controlled. Calcium homeostasis follows the general rule that extracellular concentrations are controlled rather than the total body content. The effectiveness of this control depends upon: an adequate supply of: – calcium,– vitamin D,normal functioning of the: – intestine,– parathyroid glands,– kidneys.
Pathogenesis: Molecular mechanisms of osteoporosis
Peter V. Giannoudis, Thomas A. Einhorn in Surgical and Medical Treatment of Osteoporosis, 2020
PTH, vitamin D, and calcitonin are essential calciotropic hormones that regulate calcium homeostasis (72). PTH acts directly on bone and the kidneys and indirectly (through vitamin D) on the intestine. In bone tissue, PTH increases bone resorption and leads to the release of calcium and phosphate in the extracellular fluid (73–75). PTH acts on the kidneys in three ways: (a) increases calcium tubular reabsorption, (b) diminishes phosphate tubular reabsorption, and (c) increases the activity of the enzyme 1-hydroxylase and therefore stimulates the conversion of 25-hydroxycholecalciferol (25[OH]D3) in the active form of vitamin D (1,25[OH]2D3) (74–77). In the intestine, PTH promotes the absorption of calcium obtained from food through vitamin D.
The locomotor system
C. Simon Herrington in Muir's Textbook of Pathology, 2020
Parathyroid hormone is important in the regulation of calcium metabolism and bone turnover. It has effects on both osteoblastic and osteoclastic activity. Overactivity of the parathyroid glands is classified as primary, secondary, or tertiary (see Chapter 18). Primary hyperparathyroidism is usually due to the presence of a parathyroid adenoma but in <5% of cases there is diffuse hyperplasia of all four glands, or a parathyroid carcinoma. Primary hyperparathyroidism affects 1 in 1,000 people and is the most common cause of hypercalcaemia in asymptomatic individuals. Early diagnosis due to routine measurement of serum calcium means that bone disease is now found in <5% of cases. In secondary hyperparathyroidism there is parathyroid gland hyperplasia and increased PTH secretion which occurs as a physiological response to hypocalcaemia. The most common cause of hypocalcaemia is chronic renal failure. Tertiary hyperparathyroidism may occur in longstanding secondary hyperparathyroidism when an autonomous nodule develops in a hyperplastic gland, resulting in hypercalcaemia.
An unusual case of severe hypercalcemia: as dehydrated as a bone
Published in Journal of Community Hospital Internal Medicine Perspectives, 2021
Roshan Acharya, Dylan M Winters, Cameron Rowe, Nathan Buckley, Smita Kafle, Bhaskar Chhetri
The calcium homeostasis is tightly regulated by various mechanisms. Normal lab ranges are typically around 9.4 mg/dL or 2.4 mmol/L with small percentage leeway in either direction [1]. The dietary gastrointestinal (GI) ingestion of calcium is around 1000 mg daily. However, only 350 mg of calcium is absorbed from the gastrointestinal tract daily which is facilitated by Vitamin D, and the remainder is excreted in feces. The human skeletal system is made of over 1,000,000 mg of calcium and serves as the largest store of total body calcium [1]. PTH increases the serum calcium by bone resorption, increasing gastrointestinal absorption, and decreasing renal excretion [1]. These mechanisms serve to increase and decrease calcium levels depending on the body’s total calcium stores which are primarily measured via calcium-sensing receptors in the parathyroid and renal tubules [1].
Emerging therapeutic targets for retinoblastoma
Published in Expert Opinion on Therapeutic Targets, 2022
Radhika Manukonda, Revu VL Narayana, Swathi Kaliki, Dilip K Mishra, Geeta K Vemuganti
Ca2+ is an abundant intracellular molecule that acts as a second messenger that regulates cell proliferation, gene transcription, and apoptosis. Intracellular calcium homeostasis is critical for cell survival. Any alteration in its equilibrium affects molecular factors and signaling pathways such as Ca2+ channels, transporters, calcium-binding proteins, and Ca2+- adenosine triphosphate (ATP)ases. Altered intracellular calcium levels and signaling pathways cause invasion, tumor metastasis, and favor cell survival [23]. Different research groups have studied the involvement of Ca2+-dependent molecular pathways in Rb tumor progression. Kim et al. elucidated the molecular mechanism of calcium mobilization in human Rb. Intracellular calcium molecules from the internally stored deposits are carried out through the inositol triphosphate (IP3)-dependent pathway via activating M3/M5 muscarinic receptors in the undifferentiated Rb cells [24]. Mergler et al. reported that neoplastic properties in Rb are attributed to Ca2+-dependent signaling pathways. The sensitivity of clinical drug etoposide can be enhanced via upregulation of transient receptor potential cation channel gene expression in etoposide-resistant Wills Eye Research Institute-Retinoblastoma-1 (WERI-Rb1) cells [25]. The above reports suggest that Ca2+ channels/transporters and pumps can serve as potential therapeutic targets of Rb.
Vitamin D: sources, physiological role, biokinetics, deficiency, therapeutic use, toxicity, and overview of analytical methods for detection of vitamin D and its metabolites
Published in Critical Reviews in Clinical Laboratory Sciences, 2022
Jiří Janoušek, Veronika Pilařová, Kateřina Macáková, Anderson Nomura, Jéssica Veiga-Matos, Diana Dias da Silva, Fernando Remião, Luciano Saso, Kateřina Malá-Ládová, Josef Malý, Lucie Nováková, Přemysl Mladěnka
Vitamin D is one of the oldest vitamins made in living organisms, as the earliest life forms were capable of its synthesis. Since humans are able to produce vitamin D in the skin, it is often referred to as a hormone. Vitamin D is crucial for the growth and development of healthy bones from birth until death. Its major function has always been considered the control of calcium homeostasis. However, its non-calcemic functions are of crucial importance too. The ability to synthesize vitamin D in the skin should have been an evolutionary advantage for maintaining adequate plasma levels of vitamin D. However, the modern lifestyle might not be associated with sufficient endogenous synthesis of vitamin D by sun exposure. Surprisingly, even in the twenty-first century with all the knowledge and advances in medicine, we still do not know the precise quantity of vitamin D that is needed for normal homeostasis and its associated calcium-dependent and calcium-independent effects. Regardless, chronic vitamin D deficiency does not only cause rickets in children and osteomalacia/osteoporosis in adults but may have severe long-lasting adverse consequences such as the increased risk of hypertension, type 1 diabetes, multiple sclerosis, and several cancer types.
Related Knowledge Centers
- Bone
- Bone REModeling
- Calcium
- Extracellular Fluid
- Gastrointestinal Tract
- Metabolism
- Blood Plasma
- Kidney
- Fluid Compartments
- Calcium In Biology