文波PTE真题视频系列-RL-15-Vitamin D

PTE讲座最难的就是各种学术话题,比如真核细胞原核细胞,维他命D之类。今天墨尔本悉尼文波PTE培训学校就给墨尔本PTE和悉尼PTE的考生们找到了本题的真题视频。下面开始:

 

 

更难更长的相关视频:

 

墨尔本悉尼文波PTE培训学校提供的文波资料:

 

Vitamin D is not dietary without sunshine.

Vitamin D is not a real vitamin it’s a hormone. And need sunlight to absorb.

Some regions people less expose in sunlight have not enough of Vitamin D and the same 
in winter when people wear more clothes.

食物中也有,但是量不足,人类以前是生活在赤道附近,后来因为迁徙的关系VD的摄取就不足了

 

Vitamin D refers to a group of fat-soluble secosteroids responsible for enhancing intestinal absorption of calcium, iron, magnesium, phosphate and zinc. In humans, the most important compounds in this group are vitamin D3 and vitamin D2 Cholecalciferol and ergocalciferol can be ingested from the diet and from supplements.Very few foods contain vitamin D; synthesis of vitamin D (specifically cholecalciferol) in the skin is the major natural source of the vitamin. Dermal synthesis of vitamin D from cholesterol is dependent on sun exposure Vitamin D from the diet or dermal synthesis from sunlight is biologically inactive; activation requires enzymatic conversion (hydroxylation) in the liver and kidney.

 

Evidence indicates the synthesis of vitamin D from sun exposure is regulated by a negative feedback loop that prevents toxicity, but because of uncertainty about the cancer risk from sunlight, no recommendations are issued by the Institute of Medicine (US), for the amount of sun exposure required to meet vitamin D requirements.

Accordingly, the Dietary Reference Intake for vitamin D assumes no synthesis occurs and all of a person’s vitamin D is from food intake, although that will rarely occur in practice. As vitamin D is synthesized in adequate amounts by most mammals exposed to sunlight[citation needed], it is not strictly a vitamin, and may be considered a hormone as its synthesis and activity occur in different locations. Vitamin D has a significant role in calcium homeostasis and metabolism. Its discovery was due to effort to find the dietary substance lacking in rickets.

 

 

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