Integumentary System

• the nervous system is directly connected to the integumentary system through sensory receptors
• the 3 main layers of the skin are the epidermis, dermis and the subcutaneous/hypodermis
• the epidermis is avascular meaning it has no blood supply
• the epidermis has both living and dead cells
• epidermis is composed of 5 layers of cells known as strata
• the stratum basale is the deepest layer of the epidermis, where constant cell reproduction takes place (mitosis)
• the stratum basal is the closest layer of the epidermis to blood supply and receives nourishment from blood in the dermis layer
• the stratum basale is primarily composed of keratinocytes, but also contains melanocytes
• through mitosis, old cells are pushed upwards and off the surface of the skin, and newly made cells take their place
• the stratum spinosum is between the stratum basale and the stratum granulosum layers, and consists mostly of keratinocytes held together by sticky proteins called desmosomes
• The stratum spinosum helps make your skin flexible and strong
•  The stratum granulosum is between the stratum spinosum layer and the stratum lucidum layer. it has a grainy appearance due to further changes to the keratinocytes as they are pushed from the stratum spinosum
• in the stratum granulosum the cells become flatter, membranes thicken, generate large amounts of the protein "keratin". the organelles deteriorate and the cytoplasm is full of granules
• The stratum lucidum is between the stratum granulosum and the stratum corneum. It’s a thin, transparent layer of keratinocytes that are becoming less round and have a flatter shape. it is dense and rich in lipids
• the stratum lucidum is found only in the thick skin of palms, soles and digits. it is hairless
• the stratum corneum is the top layer of the epidermis. In the stratum corneum, keratinocytes become corneocytes
• the stratum corneum makes up 75% of the epidermis. it is a dry, dead layer which helps prevent dehydration of the underlying tissues and protection for the more delicate layers
• Corneocytes are strong, dead keratinocytes that protect you from harm, including abrasions, light, heat and pathogens
• The corneocytes eventually shed as new keratinocyte cells develop in the stratum basale layer and move through the other layers of skin. the cells can still be anchored to each other by desmosomes (which is why sunburn peels damaged epidermal layers in one sheet)
• the stratum corneum contains glycolipids in the extracellular space which helps keep water from easily entering or leaving your body
• most cells in the epidermis are keratinocytes but also present are melanocytes, dendritic cells and merkel cells
• melanocytes make melanin which is a pigment responsible for absorbing UV light and protecting the basale layer
• melanin protects from UV damage, if enough DNA in the cell is damaged the cell will die of or there is a risk of detrimental mutations (cancer)
• langerhans cells are a type of dendritic cell. they are part of the immune system and capture bacteria that gets through the superficial layers, and fight pathogens in the skin
• merkel cells detect light touch
• as cells move up through the epidermis they undergo the process of keratinisation. without the epidermis layer, you are prone to infection
• the dermis varies in thickness and is thicker on the palms/soles and thinner on eyelids and lips
• the dermis contains sebaceous glands, eccrine sweat glands, apocrine sweat glands, and hair follicles
• the dermis is made up of 2 layers known as the papillary and reticular layers
• the papillary layer is located below the epidermis and makes up 20% of the dermis
• the papillary layer contains endings of capillaries, lymph vessels and sensory neurons
• the papillary layer is a loose network of connective tissue and is highly vascular
• the papillary layer is an uneven surface that dovetails into basale layer above. this dovetailing is done so by dermal papillae which are finger-like projections (responsible for the fingerprint)
• the reticular layer makes up 80% of the dermis. it is densely packed with collagen and elastin fibres and provides skin with structure and elasticity
• the reticular layer contains sweat glands, sebaceous glands, hair follicles, blood vessels and nerves
• collagen gives strength and elastin allows skin to stretch and recoil
• sebaceous glands are connected to hair follicles and secrete sebum, they are mostly active during puberty
• sebum is an oily substance that acts as a lubtricant and antibacterial agent
• eccrine sweat glands are the major sweat glands of the body and found all over the skin, most numerously on the soles of the feet. they open onto the skins surface as a duct.
• the primary function of eccrine sweat glands is to cool the body down via thermoregulation