SST

Summarize Spoken Text

You will hear a short report. Write a summary for a fellow student who was not present. You should write 50-70 words. You have 10 minutes to finish this task. Your response will be judged on the quality of your writing and on how well your response presents the key points presented in the lecture.

Vitamin D(维生素D)

Updated at: 2018-11-30 新题 预测 机经题

录音原文
Vitamin D refers to a group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, iron, magnesium, phosphate, and zinc. In humans, the most important compounds in this group are vitamin D3 (also known as cholecalciferol) and vitamin D2 (ergocalciferol). Cholecalciferol and ergocalciferol can be ingested from the diet and other supplements.
Very few foods contain vitamin D synthesis of vitamin D in the skin is the major natural source of the vitamin. Demmel synthesis of vitamin D from cholesterol is dependent on sun exposure (specifically UVB radiation). 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, 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 the effort to find the dietary substance lacking in rickets.

讨论区

A
Tony

听了 几个 3.0的 都克顿的不行了 竟然给65 我快疯了

2021-01-09
A
Tony

听了 几个 3.0的 都克顿的不行了 竟然给65 我快疯了

2021-01-09