How is Vitamin D produced and metabolised in the body?
The body is provided with vitamin D in two ways; through the diet or through the exposure of skin to sunlight. Exposing the skin to sunlight is the main way the body produces vitamin D. 7-dehydrocholesterol is found in abundance in the upper layers of skin and when it is exposed to UV rays, specifically UVB rays, it is converted first to previtamin D3 and then into Vitamin D3 or cholecalciferol. Cholecalciferol then travels to the liver where it is combined with the vitamin D absorbed from the diet, and is converted to 25-hydroxyvitamin D3. From there the kidneys converted the 25-hydroxyvitamin D3 into 1.25-dihydroxyvitamin D3, the form of vitamin D that can be used by the body to maintain the correct calcium balance in the body.
Explain the role that the immune system's immune memory function plays in the effectiveness of vaccines.
When a person is vaccinated, their body is exposed to an inactive form of a certain pathogen. The body, thinking that it is under attack, begins to activate the immune response to destroy the intruder. Antigen specific antibodies are produced to fight off the intruder. Part of the job of the B-cells is to remember what intruders have invaded the body and what antibodies worked against them so the next time that intruder attacks, the immune response will be faster. Because the pathogen that the body is exposed to during vaccination is weakened, this gives the body a chance to prepare should the active form of the pathogen ever infect the body. Vaccines act as a kind of 'practice drill' so that if the body is exposed to the real pathogen, the immune system is prepared to fight back as quickly as possible.
Which of these phrases are correct? a) a good movie b) a English movie c) a honourable movie
b is correct. When the first sound of the word following the indefinite article is a vowel sound, the indefinite article is 'an'. The word following the indefinite article does not necessarily have to start with a vowel in order for 'an' to be the correct article. The word 'honour' for example, starts an 'h', which is a consonant, but the word begins with a vowel sound and so the correct article to use is 'an'.