Answer:
Varicose veins can best be described as veins cannot prevent the backflow of blood.
Explanation:
Varicose veins are a manifestation of venous insufficiency or peripheral vascular insufficiency.
Veins are blood vessels that, unlike arteries, are not able to contract, so they depend on gravity, muscle contractions and a system of valves to be able to carry blood to the heart.
<u>When the venous valves do not work, the blood is not transported properly, backflow occurs and is retained, producing dilation of the vein walls, which is characteristic of varicose veins</u>. In this case, veins cannot prevent the backflow of blood.
The other options are not correct because:
- <em>Varicose veins do not lose their ability to transport blood.
</em>
- <em>Veins cannot be used to transport blood from the heart.
</em>
- <em>Failure to adequately transport waste to the heart does not apply in this case.</em>
When the skin is exposed to ultraviolet rays, the skin produces a molecule that is turned into Vitamin D.
Sun is the source of ultraviolet rays important for Vitamin D production. Due to this reason, in the case of Vitamin D deficiency, it is recommended by doctor's to absorb sunlight by skin. The Vitamin D production occurs specifically by UV B rays rays which lie in the range of 290-315 nanometer.
The chemical 7-dehydrocholesterol absorbs these rays and convert to previtamin D3. Further, previtamin D3 isomerizes to Vitamin D. Other than sunlight, Vitamin D can be taken through diet. The sources include seafood like fish, fish oil, dairy products, beef liver etc. Vitamin D is required for bone and teeth formation, muscle contraction, immune system etc.
Learn more about Vitamin D -
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Answer:
Vaccinations are not always effective.
Explanation:
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Small Intestine, mainly Jejunum and Ileum