Activity is also decreased by high levels of serum phosphate and by an increase in the production of the hormone FGF23 by osteocyte cells in bone.Calcitriol is also produced outside the kidney in small amounts by many other tissues including placenta and activated macrophages.When the drug alfacalcidol is used, 25-hydroxylation in the liver produces calcitriol as the active metabolite. This will produce greater effects than other vitamin D precursors in patients with kidney disease who have loss of the renal 1-alpha-hydroxylase. Interactive pathway map
Metabolism
The halflife of calcitriol in the body is measured in hours, unlike its precursor calcifediol, whose halflife is measured in weeks. Calcitriol is inactivated by further hydroxylation to form 1,24,25-trihydroxyvitamin D, calcitroic acid. This occurs through the action of the CYP24A1 24-hydroxylase. Calcitroic acid is more soluble in water and is excreted in bile and urine. History
It was first identified in 1971 by Michael F. Holick working in the laboratory of Hector DeLuca, and also by Tony Norman and colleagues. Names
Calcitriol refers specifically to 1,25-dihydroxycholecalciferol. Because cholecalciferol already has one hydroxyl group, only two (1,25) are further specified in this nomenclature, but in fact there are three (1,3,25-triol), as indicated by the name calcitriol. The 1-hydroxy group is in the alpha position, and this may be specified in the name, for instance in the abbreviation 1α,25-(OH)2D3.Calcitriol is, strictly, the 1-hydroxylation product of calcifediol (25-OH vitamin D3), derived from cholecalciferol (vitamin D3), rather than the product of hydroxylations of ergocalciferol (vitamin D2). 1α,25-Dihydroxyergocalciferol (ercalcitriol) should be used for the vitamin D2 product.
A congenital lip pit or lip sinus is a congenital disorder characterized by the presence of pits and possibly associated fistulas in the lips. They are often hereditary, and may occur alone or in association with cleft lip and palate, termed Van der Woude syndrome. Diagnosis
Classification
They are divided into three types based on their location:
commissural pits, which are small pits near the labial commissure of the mouth,
a pit in the upper lip, in which case it may be called a midline sinus of the upper lip, and
pits in the lower lip, in which case it may be called a congenital sinus of the lower lip.In some cases commissural pits have been reported in combination with preauricaluar pits, which are near the ear. Treatment
Lip pits do not usually require any treatment, although in some reported cases surgical excision has been used or if associated with a draining sinus tract. See also
Skin dimple

References


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