Regulation of Phosphate, Calcium, and Magnesium Balance

These flashcards focus on the key terms and concepts related to the regulation of phosphate, calcium, and magnesium balance, covering their roles, mechanisms, and regulatory hormones as presented in the lecture notes.

Phosphate Homeostasis

A physiological regulation mechanism maintaining serum phosphate levels through various pathways involving intestines, bone, and kidneys.

Parathyroid Hormone (PTH)

A hormone that regulates phosphate reabsorption in the proximal tubule by inhibiting Na+/phosphate co-transport, causing phosphaturia.

FGF-23

Fibroblast growth factor 23, a hormone secreted by osteocytes that decreases Na+/phosphate co-transporter in the proximal tubule and suppresses vitamin D synthesis.

Calcium Homeostasis

The regulation of calcium levels in the body involving bone, kidney, intestine, parathyroid hormone, calcitonin, and vitamin D.

Renal Handling of Magnesium

The process through which kidneys filter and reabsorb magnesium, with over 95% reabsorbed and only 5% excreted.

Na+/Phosphate Co-transporter

A transporter located in the proximal tubule that facilitates the reabsorption of phosphate in conjunction with sodium.

Osteomalacia

A condition resulting from phosphate deficiency that leads to impaired bone mineralization.

Calcium Reabsorption in DCT

Calcium reabsorption in the distal convoluted tubule regulated by PTH and not coupled to sodium reabsorption.

Loop Diuretics

Medications that inhibit sodium reabsorption in the thick ascending limb of the loop of Henle, affecting calcium reabsorption.

Thiazide Diuretics

Drugs that increase calcium absorption in the distal convoluted tubule by inhibiting Na+/Cl- symporter activity.

Phosphate Homeostasis

A physiological regulation mechanism maintaining serum phosphate levels through various pathways involving intestines, bone, and kidneys.

Parathyroid Hormone (PTH)

A hormone that regulates phosphate reabsorption in the proximal tubule by inhibiting Na+/phosphate co-transport, causing phosphaturia.

FGF-23

Fibroblast growth factor 23, a hormone secreted by osteocytes that decreases Na+/phosphate co-transporter in the proximal tubule and suppresses vitamin D synthesis.

Calcium Homeostasis

The regulation of calcium levels in the body involving bone, kidney, intestine, parathyroid hormone, calcitonin, and vitamin D.

Renal Handling of Magnesium

The process through which kidneys filter and reabsorb magnesium, with over 95% reabsorbed and only 5% excreted.

Na+/Phosphate Co-transporter

A transporter located in the proximal tubule that facilitates the reabsorption of phosphate in conjunction with sodium.

Osteomalacia

A condition resulting from phosphate deficiency that leads to impaired bone mineralization.

Calcium Reabsorption in DCT

Calcium reabsorption in the distal convoluted tubule regulated by PTH and not coupled to sodium reabsorption.

Loop Diuretics

Medications that inhibit sodium reabsorption in the thick ascending limb of the loop of Henle, affecting calcium reabsorption.

Thiazide Diuretics

Drugs that increase calcium absorption in the distal convoluted tubule by inhibiting Na+/Cl- symporter activity.

Calcitonin

A hormone produced by the parafollicular cells of the thyroid gland that lowers blood calcium levels by inhibiting osteoclast activity and decreasing renal tubular reabsorption of calcium.

Vitamin D

A fat-soluble vitamin that plays a crucial role in calcium and phosphate homeostasis by promoting their absorption from the intestine, and influencing bone mineralization and renal reabsorption.

Phosphaturia

The excretion of abnormally large amounts of phosphate in the urine, often caused by the inhibition of renal phosphate reabsorption.

Hypophosphatemia

A condition characterized by abnormally low levels of phosphate in the blood, which can lead to impaired bone mineralization and muscle weakness.

Hyperphosphatemia

A condition characterized by abnormally high levels of phosphate in the blood, often due to renal failure or excessive intake.

Hypocalcemia

A condition characterized by abnormally low levels of calcium in the blood, which can lead to increased neuromuscular excitability.

Hypercalcemia

A condition characterized by abnormally high levels of calcium in the blood, which can lead to symptoms like kidney stones, bone pain, and fatigue.

Hypomagnesemia

A condition characterized by abnormally low levels of magnesium in the blood, often associated with impaired PTH secretion and action, and cardiac arrhythmias.

Hypermagnesemia

A condition characterized by abnormally high levels of magnesium in the blood, usually due to renal insufficiency or excessive magnesium intake, leading to muscle weakness and cardiovascular effects.

Proximal Tubule

The initial segment of the renal tubule primarily responsible for reabsorbing a large proportion of filtered electrolytes, glucose, amino acids, and phosphate via Na+/phosphate co-transporters.

Distal Convoluted Tubule (DCT)

A segment of the renal tubule where fine-tuning of electrolyte reabsorption, particularly calcium and sodium, occurs, influenced by hormones like PTH and diuretics like thiazides.

Thick Ascending Limb of the Loop of Henle (TAL)

A segment of the renal tubule where a significant amount of sodium, chloride, and potassium is reabsorbed, and which is also a major site for magnesium reabsorption; inhibited by loop diuretics.

Parathyroid Gland

Endocrine glands located in the neck that produce parathyroid hormone (PTH), critical for regulating calcium and phosphate levels in the blood.

Osteocytes

Mature bone cells that reside within the bone matrix and are responsible for regulating bone remodeling and secreting factors like FGF-23.

Intestinal Absorption of Calcium/Phosphate

The process by which calcium and phosphate are absorbed from the diet in the gastrointestinal tract, primarily regulated by active vitamin D (calcitriol).

Calcitriol

The active form of vitamin D, 1,25-dihydroxyvitamin D3, which is crucial for increasing calcium and phosphate absorption from the intestine and regulating bone mineralization.

Renal Phosphate Reabsorption

The process by which phosphate is recovered from the glomerular filtrate in the renal tubules, primarily in the proximal tubule, preventing its excessive loss in urine.

Renal Calcium Reabsorption

The process by which calcium is recovered from the glomerular filtrate in the renal tubules, occurring in multiple segments including the proximal tubule, loop of Henle, and DCT, regulated by PTH.

Magnesium Reabsorption in TAL

A significant portion of magnesium reabsorption occurs in the thick ascending limb of the loop of Henle, influenced by the lumen-positive potential difference and paracellular pathways.

PTH-related protein (PTHrP)

A protein with structural similarity to PTH, often involved in calcium homeostasis, particularly in conditions like humoral hypercalcemia of malignancy, by binding to the same PTH receptor.

Phosphate Binders

Medications used to reduce phosphate absorption from the gut in patients with hyperphosphatemia, often in chronic kidney disease.

Sodium/Calcium Exchanger (NCX)

A transporter located on the basolateral membrane of renal tubular cells (especially in the DCT) that extrudes calcium from the cell into the interstitial fluid, facilitating calcium reabsorption.

Transient Receptor Potential Vanilloid 5 (TRPV5)

A calcium channel located on the apical membrane of the distal convoluted tubule cells, responsible for the entry of calcium from the tubular lumen into the cell, a key step in calcium reabsorption.

Renal Tubules

The functional units of the kidney responsible for reabsorbing essential substances and excreting waste products, playing a critical role in electrolyte balance.