The dermis has dermal papillae which form projections that face upwards to

The dermis has dermal papillae which form projections

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- The dermis has dermal papillae which form projections that face upwards to interlock with the epidermis. This increases the surface area of the connection between the two layers. - Collectively the epidermal ridges of the epidermis and the dermal papillae of the dermis are called the Rete Apparatus . - Just beneath the dermis is another layer called the Hypodermis , but this is not technically part of the skin. The hypodermis is sometimes called the sub-cutaneous layer because it is beneath the skin. - The hypodermis contains a lot of blood vessels and adipose tissue. The sub-cutaneous/hypodermis region has larger blood vessels that branch off into smaller vessels (little capillary loops) which go all the way up to the epidermis. Heat can be radiated from the body through these little capillary loops. Skin color - is a result of epidermal pigmentation. There are two pigments primarily located in epidermal cells: 1. Carotene (found in orange vegetables). Keratinocytes are loaded carotene. If you are very fair skinned and you eat a lot of orange vegetables your skin will take on an orange color. 2. Melanin is a pigment located in cells found in the stratum basale called melanocytes . This pigment must be manufactured from an amino acid called tyrosine . There are little lipid membrane bound vesicles found in the melanocytes that contain two different things: Tyrosinase which is an enzyme activated by ultraviolet radiation that can convert tyrosine into melanin. Tyrosine which is an amino acid. Melanocytes pump the amino acid tyrosine into little vesicles called melanosomes which pump in the enzyme tyrosinase. Tyrosinase will convert tyrosine into melanin. Cytocrine Secretion - is a process by which melanosomes provide UV protection to other cells. Melanosomes (from melanocytes) are put into keratinocytes of the stratum spinosum to protect their nuclei from UV radiation. - Melanocytes in cytocrine secretion do NOT contain melanin because UV light does not reach the stratum spinosum. Without UV light, tyrosinase can not be activated to convert tyrosine to melanin. - However, if UV light does reach the stratum spinosum, melanosomes will form cytoplasmic extensions to move upward into the stratum spinosum. These cytoplasmic extensions will then pierce into cells and release melanosomes into the keratinocytes of the stratum spinosum. Melanosomes will then radiate around the nuclei and provide them protection from UV radiation. - As a second defense mechanism, melanosomes can also activate the enzyme tyrosinase to convert tyrosine into melanin. Melanin will then absorb the UV radiation to also protect the nuclei of the keratinocytes in the stratum spinosum. - Ultimately, by protecting the stratum spinosum, you protect the stratum basale beneath it. You do not want the stratum basale stem cells to get damaged by UV. Otherwise you will get skin cancer.
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