Help please

[EJ]

This is another one of those topics that keeps coming up because I really don't think anyone has a true answer but you do have to let common sense play a part.

How did all those 50+ year old tortoises that pop up on a regular basis in the UK survive? I'm sure no UV bulbs or even D3 or it's precursors were provided.

I do hope some of you give my point some thought. Also here is a wonderful explaination of how the calcium process works. I actually got it off the TT list when they had an excellent membership base.

I also just realized ... look at the date... the debate goes on... but this is one of the best explainations I've ever seen... enjoy.

From: "Juan F. Sanz-Cervera"
Date: Sat Aug 18, 2001 1:14 am
Subject: Calcium forms and metabolism

This is from Voet & Voet's 2nd. edition of Biochemistry, John Wiley & Sons, 1995, pp.
1265-1267.

Calcium Metabolism Is Regulated by Parathyroid Hormone, Vitamin D, and Calcitonin.

Ca2+ [Calcium cation] forms hydroxyapatite, Ca5(PO4)3OH, the major mineral constituent of bone, and it is an essential element in many biological processes including the mediation of hormonal signals as a second messenger, the triggering of muscle contraction, the transmission of nerve pulses, and blood clotting. The extracellular concentration of Ca2+ must therefore be closely regulated to keep it at its normal level of ca. 1.2 mM [millimolar; a common concentration unit]. The hormones have been implicated in homeostasis:

1. Parathyroid hormone (PTH), an 84-residue polypeptide secreted by the parathyroid gland, increases serum concentration of Ca2+ by stimulating the resorption from bone and kidney and by increasing the dietary absorption of Ca2+ from the intestine.

2. Vitamin D, a group of steroid-like substances that act in a synergistic manner with PTH to increase serum concentration of Ca2+.

3. Calcitonin, a 33-residue polypeptide synthesized by specialized thyroid gland cells, decreases serum Ca2+ concentration by inhibiting the resorption of Ca2+ by bone and kidney.

The bones, the body's main Ca2+ reservoir, are by no means metabolically inert. The are continually "remodeled" through the action of two types of bone cells: osteoblasts, which synthesize the collagen fibrils that form the bone's organic matrix, the scaffolding upon which its hydroxyapatite mineral phase is laid down; and osteoclasts, which participate in bone resorption. PTH inhibits collagen synthesis by osteoblasts and stimulates bone resorption by osteoclasts. The main effect of PTH, however, is to increase the rate that the kidneys excrete phosphate, the counterion of Ca2+ in bone. The consequent decreased serum phosphate concentration causes hydroxyapatite to leach out of bone through mass action and thus increase serum Ca2+ concentration. Finally, PTH stimulates teh production of the active form of vitamin D by kidney which, in turn, enhances the transfer of intestinal Ca2+ to the blood.
Vitamin D is a group of dietary substances that prevent rickets, a disease of children characterized by stunted growth and deformed bones stemming from insufficient bone mineralization (vitamin D deficiency in adults is known as osteomalacia, a condition characterized by weakened, demineralized bones). Although rickets was first described in 1645, it was not until the early 20th. century that it was discovered that animal fats, particularly fish liver oils, are effective in preventing this deficiency disease. Moreover, rickets can also be prevented by exposing children to sunlight or just UV light in the wavelength range 230 to 313 nm, regardless of their diets. [I think that here they mean "regardless of their vitamin D intake"; obviously, if there is not enough Ca2+ ingested in the diet, serious consequences derive!]
The D vitamins, which we shall see are really hormones, are sterol derivatives in which the stearol B ring is disrupted at its 9,10 position. The natural form of the vitamin, vitamin D3 (cholecalciferol), is nonenzimatically formed in the skin of animals through the photolitic action of UV light on 7-dehydrocholesterol. Vitamin D2 (ergocalciferol), which differes from vitamin D3 only by a side chain double bond and a methyl group, is formed by the UV irradiation of the plant sterol ergosterol. Since vitamins D2 and D3 have essentially identical biological activities, vitamin D2 is commonly used as a vitamin supplement, particularly in milk.
Vitamins D2 and D3 are hormonally inactive as such; they gain biological activity through further metabolic processing, first in the liver and then in the kidney:

1. In the liver, vitamin D3 is hydroxylated to form 25-hydroxycholecalciferol in an oxygen-requiring reaction catalyzed by cholecalciferol-25-hydroxylase.

2. The 25-hydroxycholecalciferol is transported to the kidney, where it is further hydroxylated bya mitochondrial oxygenase, 25-hydroxycholecalciferol-1alpha -hydroxylase, to yield the active hormone 1alpha,25-hydroxycholecalciferol [1,25(OH)2D]. The activity of this hormone is regulated by PTH, so this reaction is an important control point in Ca2+ homeostasis.
1,25(OH)2D acts to increase serum Ca2+ concentration by promoting the intestinal absorption of dietary Ca2+ and stimulating Ca2+ release from bone. Intestinal Ca2+ absorption is stimulated through increased synthesis of Ca2+-binding protein, which functions to transport Ca2+ across the intestinal mucosa. [...]
Vitamin D, unlike the water-soluble vitamins, is retained by the body so that an excessive intake of vitamin D over long periods causes vitamin D intoxication. The consequent high Ca2+ serum concentrations results in aberrant calcification of a wide variety of soft tissues [!!!]. The kidneys are particularly prone to calcification, a process that can lead to the formation of kidney stones and ultimately kidney failure. in addition, vitamin D intoxication promotes bone demineralization to the extent that bones are easily fractured. The observation that the level of skin pigmentation in indigenous human populations tends to increase with their proximity to the equator is explained by the hypothesis that skin pigmentation functions to prevent vitamin D intoxication by filtering out excessive solar radiation.
Calcitonin has essentially the opposite effect of PTH; it lowers serum Ca2+ concentration. It does so primarily by inhibiting osteoclastic resorption of bone. Calcitonin also inhibits kidney from resorbing Ca2+ but in this case the kidney cells that calcitonin influences differ from those that PTH stimulates to resorb Ca2+.
________________________________________
The comments in brackets [] are mine. Fascinating, isn't it? As usual, all the biochemical processes are delicately balanced, and usually much more complicated than one tends to think!

Originally Posted by nina

Mmm. I really wasn't going to get involved in this discussion (have been there before). I am not a scientist, and I might be interpreting information incorrectly, but I do think it's important to recognise that the UVB reaching our torts in the UK for most of the year is far less than the UVB reaching the ground in much of the rest of the world. The farther north you are, the lower the angle of the sun, and also the cloud cover that we have for much of the year (just take a peak through your curtains) also diminishes the UV. Here is an interesting account of UV in nature, and if you look at the graph of the UVB levels around the world in December, you will see that only Scandinavia comes lower than the UK:
http://www.uvguide.co.uk/uvinnature.htm
Also, here is a whole lot of information about sunlight and vitamin D3 production
http://www.uvguide.co.uk/vitdpathway.htm
The point of all this is that I think that while supplements can help greatly with D3 production, it is possible to overdose vitamin D supplements (hypervitaminosis-D). The sun is the best source of UVB (and reptiles can't overdose on UVB from sunlight, as is explained in the link). In the UK the angle of the sun and the weakness of the sun shining through the atmosphere and cloud cover means that to have another light source of UVB is beneficial to tortoises.

[nina]

I knew you could blind me with science, Ed! <vbg> (I can just about manage the UV guide stuff, but was totally flummoxed by that very learned account - never had chemistry at school (they kept sticking me in honours humanities subjects and ignored most of the sciences) and so I always find these things difficult). Shall I just assume that it proved your point?

[EJ]

Actually my point was different but that account explained the process.

In this case (and many others) there is no 'proving' the point one way or the other... it's all opinion.

Originally Posted by nina

I knew you could blind me with science, Ed! <vbg> (I can just about manage the UV guide stuff, but was totally flummoxed by that very learned account - never had chemistry at school (they kept sticking me in honours humanities subjects and ignored most of the sciences) and so I always find these things difficult). Shall I just assume that it proved your point?

[Beverley]

Thank you Ed, for going to the trouble of posting that account, I may have to read over it a few times to fully understand it as I passed chemistry a few years ago now but thank you
Beverley

[nina]

Originally Posted by EJ

Actually my point was different but that account explained the process.

In this case (and many others) there is no 'proving' the point one way or the other... it's all opinion.

I do agree with that to a certain extent - and it's evidenced by the fact that 'best practice' changes radically over time (if you look at some really old care sheets from the TT the diet advice is shocking by today's standards). I hope you didn't think I was being snide in my remarks, though, Ed - I really never took chemistry and genuinely didn't understand most of that article (I looked up homeostasis, and had sort of heard of polypeptides, but soon realized that it was way beyond me)!

[EJ]

I suspect you severely underestemate yourself.

I didn't see any snide remarks at all.

Originally Posted by nina

I do agree with that to a certain extent - and it's evidenced by the fact that 'best practice' changes radically over time (if you look at some really old care sheets from the TT the diet advice is shocking by today's standards). I hope you didn't think I was being snide in my remarks, though, Ed - I really never took chemistry and genuinely didn't understand most of that article (I looked up homeostasis, and had sort of heard of polypeptides, but soon realized that it was way beyond me)!

[sandy]

I never use scare tactics Ed!!!
Tortoises cannot survive without UV which is what I stated.
I give advice I have learnt from experiece in the last 28yrs, and try to pass on what I have
learnt. I have never said my infromation is the only information just my experieces. And I
certainly dont put people down like you do.
I might not be as techincal as you, but pass on my humble learnings. Which just happen to be
totally different from yours. But then I am just a simpleton from the UK.

[Pussygalore]

my thinking is fairly simple in that if they are inside then a UVB kight is good but if you can get them outside then its not essential, I think they get UV rays even on cloudy days as I thought its daylight which we all have whevere we live obviously more on sunny days but still there even if its raining my are outside all summer they have a normal red heat t bulb in their kennels but nothing else even if they don,t come out they sit in the doorway and I,m sure can go a couple of days without uv they would bury themselves/hide away in the wild for several days if it was cold so wouldn,t get uv then, but if and when mine come inside in the autumn then they will have a uv strip light in fact we have uv light in the conservatory as my birds come in there as well over the winter and I think all animals including ourselves feel better for it.

[alby28]

The UV light that it has at the minute says Repti-Glo 8.0 UVB on it.Is this strong enough?Also having problems trying to find a lamp that will hand a 60 watt spot bulb.Do i need a special one or is it just a case of going to the nearest B&Q superstore.Also Mr T seems to be spending a long part of the day in his bedding.Is this normal?The ppl that had him before me have straw/hay bedding in there and wood chips on the floor.








Mark

[Pussygalore]

my heat bulbs are in an ordinary ceramic bulb holder screwed onto the side of the house with the cable comming out via a hole,