Final answer:
The abbreviation for 'below the skin' is typically 'SC' or 'SQ,' not one of the provided options. The ectoderm gives rise to skin cells, and desquamation is the shedding of dead skin cells that helps prevent infections. The hypodermis does not supply blood vessels to the epidermis.
Step-by-step explanation:
The abbreviation for "below the skin" is not provided within the options you have given (a) ID, b) Derm, c) H, d) FS. The term for below the skin that is commonly used is 'subcutaneous,' which often gets abbreviated as 'SC' or 'SQ.'
Regarding your question about the skin cells, ectoderm is the correct answer (a) as it gives rise to the skin cells, along with other structures such as hair and nails. The epidermis and dermis are major layers of human skin, with the hypodermis lying below them, but it is not considered part of the skin.
Desquamation is the process by which dead skin cells are shed from the surface of the skin. This helps with preventing infections by regularly removing cells that may be infected or contain pathogens, keeping the skin's surface renewed and more resistant to bacterial and fungal invasions.
Lastly, the hypodermis is not the source of blood vessels in the epidermis. That would be not true, as the epidermis actually lacks blood vessels and gets nutrients via diffusion from the dermis underneath.