Question

Mechanism How vitamin d is synthesized from our skin

Answer 1

[AI-generated answer — Bot GPT 3.5]

Vitamin D synthesis in our skin occurs through a series of chemical reactions. Here is a step-by-step mechanism of how it is synthesized:

1. Ultraviolet B (UVB) radiation from sunlight penetrates the epidermal layer of our skin.

2. When UVB radiation reaches a molecule called 7-dehydrocholesterol (a precursor of cholesterol) present in the skin cells, it absorbs the radiation and undergoes a process called photoconversion.

3. Photoconversion causes 7-dehydrocholesterol to rearrange its structure and transform into previtamin D3 (also known as cholecalciferol).

4. Previtamin D3 is an unstable compound and undergoes a thermal isomerization reaction. It turns into vitamin D3 (cholecalciferol) spontaneously or with the help of body heat.

5. From the skin cells, vitamin D3 enters the bloodstream.

6. In the liver, vitamin D3 undergoes hydroxylation (addition of a hydroxyl group) by an enzyme called 25-hydroxylase. This results in the formation of 25-hydroxyvitamin D3 (calcidiol or calcifediol).

7. 25-hydroxyvitamin D3 then enters the kidneys, where it undergoes another hydroxylation step by an enzyme called 1-alpha-hydroxylase. This final step leads to the formation of 1,25-dihydroxyvitamin D3 (calcitriol), which is the biologically active form of vitamin D.

Once calcitriol is formed, it acts as a hormone, exerting various physiological effects throughout the body to regulate calcium and phosphate metabolism, bone health, and immune function.

It's important to note that this mechanism primarily refers to the synthesis of vitamin D3 from sunlight exposure. However, vitamin D can also be obtained from dietary sources, such as fortified foods or supplements, which bypass this synthesis process.

Answer 2

[AI-generated answer — Explain Bot]

Vitamin D can be synthesized by the human body through a process called photolysis, which occurs in the skin. Here is the mechanism explaining how this synthesis occurs:

1. The process begins when the skin is exposed to ultraviolet B (UVB) radiation from the sun. UVB rays have a wavelength between 270-315 nm and are responsible for initiating the synthesis of vitamin D.

2. When UVB rays penetrate the skin, they interact with a substance called 7-dehydrocholesterol, which is present in the epidermis (outermost layer) of the skin. 7-dehydrocholesterol serves as a precursor molecule for vitamin D synthesis.

3. Upon exposure to UVB rays, 7-dehydrocholesterol undergoes a photochemical reaction, resulting in the conversion of this precursor molecule into previtamin D3. This process is called photolysis.

4. Previtamin D3 is thermally unstable and therefore undergoes a rearrangement into its more stable form, which is called vitamin D3 (also known as cholecalciferol). This rearrangement is facilitated by the heat from the skin.

5. Vitamin D3 is then absorbed into the bloodstream, where it binds to a vitamin D-binding protein for transportation to the liver.

6. In the liver, vitamin D3 undergoes hydroxylation, a process in which a hydroxyl group (OH) is added to the molecule, forming 25-hydroxyvitamin D3 (calcidiol). This step is catalyzed by an enzyme called 25-hydroxylase.

7. Calcidiol is further modified in the kidneys, where it undergoes a second hydroxylation reaction catalyzed by another enzyme called 1α-hydroxylase. This reaction produces the biologically active form of vitamin D, known as 1,25-dihydroxyvitamin D3 (calcitriol).

Overall, the synthesis of vitamin D from our skin involves the conversion of 7-dehydrocholesterol by UVB radiation into previtamin D3, followed by thermal isomerization to vitamin D3. This inactive form of vitamin D is then converted into its active form, calcitriol, through hydroxylation reactions in the liver and kidneys.

Answer 3

[AI-generated answer — Step-by-Step Bot]

The synthesis of vitamin D from the skin involves a series of steps triggered by exposure to ultraviolet B (UVB) radiation from sunlight. Here is a step-by-step explanation of how vitamin D is made in our skin:

Step 1: UVB radiation exposure: When our skin is exposed to sunlight, specifically the UVB rays, it initiates the synthesis of vitamin D. It is important to note that UVB rays are only present in sunlight at certain times of the day and in specific geographic locations.

Step 2: Conversion of 7-dehydrocholesterol: In the epidermis, the outer layer of the skin, a molecule called 7-dehydrocholesterol is present. When UVB rays hit the skin, they penetrate the epidermis, reaching these 7-dehydrocholesterol molecules.

Step 3: Formation of previtamin D3: Upon exposure to UVB rays, 7-dehydrocholesterol undergoes a process known as photoisomerization or photolysis. This process converts 7-dehydrocholesterol into previtamin D3, also known as provitamin D3.

Step 4: Thermal isomerization: Previtamin D3 is not the active form of vitamin D. To become fully active, another process known as thermal isomerization occurs. In this step, the heat from the body converts previtamin D3 into vitamin D3 (cholecalciferol).

Step 5: Transport to the liver: Vitamin D3, synthesized in the skin, travels through the bloodstream to the liver, where it undergoes further metabolic processing.

Step 6: Hydroxylation in the liver: In the liver, vitamin D3 undergoes hydroxylation (the addition of a hydroxyl group) to form 25-hydroxyvitamin D3 [25(OH)D3], also known as calcidiol. This is the major circulating form of vitamin D in the bloodstream.

Step 7: Hydroxylation in the kidneys: Calcidiol, produced in the liver, moves on to the kidneys, where another hydroxylation reaction takes place. This step converts calcidiol into its active form called 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], also known as calcitriol.

Step 8: Receptor activation: Calcitriol interacts with specific receptors in various body tissues, including the intestines, bones, and immune cells. The binding of calcitriol to these receptors initiates a range of biological responses that regulate calcium and phosphorus metabolism, bone health, and the functioning of the immune system.

It is important to note that adequate sunlight exposure is necessary for the synthesis of vitamin D in the skin. However, other factors like the use of sunscreen, clothing coverage, skin pigmentation, geographic location, and time of day can affect the efficiency and amount of vitamin D produced in the skin. Ensure to balance sunlight exposure with proper sun protection measures to maintain optimal vitamin D levels.