the skin makes up around 16% of total body weight making it the largest organ in the body although it's hard to imagine it as a single organ the skin along with its accessory structures like oil and sweat glands makes up the integumentary system the integumentary system protects the body from infections helps regulate body temperature and contains nerve receptors that detect pain sensation and pressure now the skin is divided into three layers the epidermis dermis and hypodermis the epidermis forms the thin outermost layer of skin underneath is the thicker dermis layer that contains the nerves and
blood vessels and finally there's the hypodermis which is made of fat and connective tissue that anchors the skin to the underlying muscle the epidermis itself is made up of multiple layers of developing corat ployes which are flat pancake shaped cells that are named for the Keratin protein that they're filled with keratin is a fibrous protein that allows karatinos sites to protect themselves from getting destroyed when you rub your hands through the sand at the beach catinos sites also make and secrete glycol lipids glyco meaning part sugar and lipid meaning part fat glycolipids help to prevent
water from easily seeping into and out of the body catinos sites start their life at the lowest layer of the epidermis called the stratum Bas or basil layer which is made of a single layer of stem cells that continually divide and produce new carattino sites these new carattino sites then migrate upwards to form the other layers of the epidermis the stratum Bas also contains another group of cells melanocytes which secrete a protein pigment or coloring substance called melanin melanin is actually a broad term that constitut several types of melanin found in people of differing skin
color these subtypes of melanin range in color from black to reddish yellow and their relative quantity Define a person's skin color when cartinos sites are exposed to the sun they send a chemical signal to the melanocytes which stimulates the melanocytes into making more melanin the melanocytes move the melanin into small Sachs called melanosomes and these get taken up by the newly formed corat sites melanin then acts as a natural sunscreen because its protein structure dissipates or scatters UVB light which if left unchecked can damage the DNA in the skin cells and lead to skin cancer
darker types of melanin and greater quantities of this kind of melanin are produced by individuals living close to the equator because they typically get more sun exposure however it's a fine balance because UVB light helps us generate vitamin D which is an important regulator of calcium absorption cortinos sites contain cholesterol derived molecules that are activated by UVB into Vitamin D as katos sites in the stum Bas mature and lose the ability to divide they migrate into the next layer called the strum spinosum which is about 8 to 10 cell layers thick cartinos sites in the
strum spinosum layer have proteins on the membrane that look like tiny spines these help the cells adhere to one another the stratum spinosum layer also has dendritic cells lurking around and these are star-shaped immune cells that are constantly patrolling looking for invading microbes the next layer up is the stratum granulosum which is 3 to 5 cell layers thick coratin oyes in this layer begin the process of koniz which is where the catinos sites flatten out and die and in this process they create the epidermal Skin Barrier to do this cortinos sites in the stratum granulosum
layer produce large amounts of keratin precursor proteins and glycolipids which remain within granules called cat Highland granules and Lamar granules respectively cat Highland granules eventually start to Aggregate and Crosslink forming enormous bundles of keratin within the karatinos site Lamar granules on the other hand get secreted and stick to the outer cell surface it forms a sort of cement between the cells making them more resistant to external forces in water loss over time the intracellular organel disintegrate so the cells flatten out and die coriz leads to development of the stratum lucidum layer which is two to
three cell layers thick of translucent dead kosy that have secreted most of their Lamar granul uals the stum lucidum is only found in thick skin like on the palms and soles of the feet because those are the areas that need Extra Protection the strum lucidum is absent in thin skin which covers the rest of the body and the other layers are thinner finally there's the stratum corium or the uppermost and thickest layer of the epidermis which is like a wall of 20 to 30 layers where the glycolipid acts like the cement and the dead kenized
cells of the bricks the dead coratin Ayes in this layer secrete natural antibiotics called defensin which poke holes in bacteria as new cartinos sites push up into the straum corneum older dead cells are shed forming skin flakes or dandruff now the dermis lies below the straum Bas of the epidermis and it's much thicker than the epidermis the dermis is divided into two layers a thin papillary layer below the stum Bas and a deeper reticular layer the papillary layer contains fibr blasts which produce a connective tissue protein called collagen the fiber blasts are arranged in finger-like
projections called pilli Each of which contains blood vessels and nerve endings one type of nerve ending found here is called a mner COR pusle and this is a dis shaped structure that detects fine touch and it allows you to know exactly where for example a feather touches your arm another type of nerve found in the pilli are called free nerve endings which are dendrites that detect pain the papillary layer also contains macras which capture pathogens that make it past the epidermis it's also the papillary layer that's responsible for fingerprints these are necessary for gripping and
sensing abilities of the fingers and feet and they make each of us as unique as snowflakes next is the reticular layer of the dermis which is even thicker than the papillary layer like the papillary layer however the reticular layer contains fibroblasts with scattered macroasia but the collagen in the reticular layer is packed very tightly together making it an excellent tissue support in addition fiber blasts in the reticular layer secrete elastin which is a stretchy protein that gives skin its flexibility the reticular layer also contains the Skin's accessory structures like oil and sweat glands hair follicles
lymphatic vessels and nerves and all of the blood vessels that serve these tissues one type of nerve ending found here is called a pacinian COR pusle and this is an onion-shaped structure that detects pressure or vibration and it allows you to feel when someone's grabbing your arm since the reticular layer contains lots of blood vessels and sweat glands it's also largely responsible for regulating temperature when body temperature rises like during a workout the nervous system makes these blood vessels dilate and makes the sweat glands secrete sweat dilation of blood vessels brings more blood closer to
the skin surface and that allows heat to get lost to the outside environment as sweat coats the skin surface it takes heat to evaporate so heat is slowly lost from the skin surface with every drop of sweat that evaporates away in the opposite situation when it's cold outside blood vessels con strict and that diverts blood flow away from the skin and there's no sweat so body heat is conserved finally there's the layer just below the dermis called the hypodermis or subcutaneous tissue this layer contains fat cells called atopos sites which help store most of the
fat in our body but also contains fiber blasts macrophases blood vessels nerves and lymphatics the hypodermis helps insulate deeper tissues provides padding to the body and anchors the skin to the muscle with connective tissue proteins like collagen all right as a quick recap the skin or the integumentary system is the largest organ of the body that has many important functions in physiology the integumentary system is divided into three major components including the epidermis dermis and hypodermis the epidermis is the most superficial layer and it's responsible for protection from pathogens and the environment for vitamin D
production and for giving the skin its color the dermis lies below the epidermis and controls temperature regulation and helps with sensation the hypodermis lies below the dermis and provides a point of attachment for the skin to the deeper muscles helping current and future clinicians Focus learn retain and Thrive learn more
