How long does calcium...

[moswen]

How long will calcium and vitamins stay in your tort's system while it waits to be absorbed? Like, say I feed my torts in the morning, but it doesn't get warm enough to take them outside right now until between 1-5 pm. If I want to take them out during this time for "optimum uv absorption" does it really do any good?

 

[Maggie Cummings]

We are taught that a tortoise needs to be 80 degrees internally in order to process it's food. So that would make me think that unless he has a basking light to get his internal temp up to 80 degrees or more that his food is just sitting there. But I am not sure about that I am sort of just going on the 80 degree thing.

I don't feed Bob until noon and that's after he's been sleeping on a pig blanket and then basking under a hot light. I feed him and then he becomes active. He was just napping and sleeping all the time under the lights until I feed him...

Don't you have lights for them to bask under?

 

[moswen]

Yes they all have mvbs, but everyone says natural sunlight is better, I just wanted to know if they still have some calcium in their system waiting to be absorbed 5-7 hours after they ingest it, or if I'm just wasting my time taking them out there in the afternoons when it's nice enough.

In the morning I turn on their lights and wait till they come out (usually an hour or less) to bask, then I soak and feed them, so I know they absorb some calcium and vits at that time, but I'm curious if there is still some inside them waiting to be absorbed by the natural sunlight, since that's better than the mvb's. Just curious. I'm positive that there's nothing left in my stomach ~4hrs after I eat, bc that's about when it starts grumbling again lol! Just wondering if it's the same with my torts.

 

[Maggie Cummings]

Yes, natural sunlight is better. But I would say you are using the MVB simply for heat to warm them up. There's probably not much left inside by the time you are taking them outside. BUT that is the important time for them, so I would continue to do it and stop worrying about calcium absorption...

 

[HLogic]

[/size]There are threee (3) different activities occurring here. None of which are so tightly coupled that timing of hours would make a difference - sorta.

1. Digestion and subsequent absorption of nutrients.
2. Conversion of nutrients (pre-cursors) to usable constituents.
3. Storage and metabolism (use, conversion or destruction) of nutrients and usable constituents.

As this discussion would be a full year (or more) of a college or post-grad course. I'll try to 'digest' it into a few key points. Keep in mind this is a severely simplified description...

The digestion of food stuffs occurs initially in the stomach. This is where a physical breakdown of large food items occurs and chemical reactions involving hydrochloric acid and other substances reduce the solid food components to a thick liquid slurry known as chyme. Very little nutrient absorption occurs during this phase. From the stomach, the chyme (nutrient-laden 'soup') is passed to the small intestine. In most cases, the time between ingestion and passage to the small intestines is several (4 - 12) hours. The majority of nutrient absorption occurs in the small intestines. Some additional breakdown of larger compounds occurs in the small intestines allowing the resulting nutrients to be absorbed before the remaining material is passed to the large intestine. Within the large intestine, fermentation processes occur producing/releasing some additional nutrients which are absorbed and finally the resultant feces are excreted from the body into the freshly changed water bowl!

The entire digestion process averages around 24 - 72 hours. The process is accelerated by elevated temperatures. Digestion, apart from the 'chewing' process, is essentially a series of chemical reactions. Most of these chemical reactions require energy to occur and that energy is provided by heat. In general, a chemical reaction will double its reaction rate for every 10° C increase in temperature (Arrhenius equation). The optimum temperature for these reactions within most higher organisms ranges from 70° - 110° F. This is why the '80° rule' is stated - although the optimal temperature is more likely 85° - 95° depending upon the species.

Vitamin D3 synthesis, as most are aware, occurs in the skin with exposure to UVB and, as most are probably unaware, is a two-step process that also requires IR (infrared or heat). The first step converts a starting compound, 7-dehydrocholesterol, to preVitamin D3 utilizing the energy input of UVB in a rather fast reaction. The second step, the conversion of preVitamin D3 to Vitamin D3 is a slower reaction which relies on IR to provide the energy. This is much of the reason that reptiles bask.

Vit D3 synthesis: 7DHC → preVit D3 → Vit D3

Once the intake of the nutrients has occurred, the next step is the conversion of these nutrients into compounds which are usable by the organism. In the case of calcium, it is absorbed in the small intestine and transported by the circulatory system under the control of calcitriol. Calcitriol is the active Vitamin D in calcium regulation/utilization and is the product of a two-step Vitamin D3 metabolism process.

Vit D3 metabolism: Vit D3 → calcidiol → calcitriol

Vitamin D3 probably does not remain in high concentrations in the circulatory system but an intermediate metabolite (the step-one result), calcidiol, is likely used as a storage mechanism. Alternate metabolic conversions occur to prevent the overabundance of preVitamin D3 and Vitamin D3, some of which are reversible thereby extending the potential availability of the functional components. In most healthy organisms, this Vitamin D3 supply pool provides several days to several weeks of available source components.

As you will note, there are many "probably" and "likely" qualifiers in the above. These pathways are reasonably well known in humans and some other organisms. As is almost always the case, the specific details are only partially known, if at all, in reptiles and in particular tortoises. However, it is reasonable to expect that similar processes and pathways exist in these animals as they are common requirements for most higher organisms.

Any questions? Registration for Physiology 285, Organic Chemistry 336 and Biochemistry 467 commences in the Sciences Building rotunda in 30 minutes!!

 

[Tom]

Well done Art. This is one of your best.

I was just gonna say that in tortoises the "digestive" process takes days or weeks, and they don't need to have a fresh meal in their stomach WHILE they are exposed to UV for all the "magic" to happen.

Art, I think your explanation was much more thorough AND eloquently written.

 

[HLogic]

Ya wouldn't expect less from a full-service station, would ya? ‡-)

Thanks for the kudos, Tom.

I was relieved it was an 'easy' question! Heaven help me when the question is, "How does the Kreb's cycle interplay with interim peroxide production affect the oxidase utilization in hepatic metabolic pathways?"

 

[moswen]

Wow art, that was great! Thank you so much, that was easy for me to understand! And, very educational! So, in an extremely, EXTREMELY overly-simplified statement: yes, it is reasonably believed that calcium does stay in my tort's system longer than that, so the mid-late afternoon sunshine does do them good!

Thanks everyone!