If you remember not long before the end of the year, I set myself a challenge which I didn't actually fully complete. That was to write up an 'assignment' on the skin. Lucky for me, it wasn't actually an assignment. But that's not to say that I didnt do a fair bit on notes on it, because I did. So basically, here are the notes that I have done. If you're not into the science of skin, maybe give this post a miss but you may be missing out on some interesting facts.
The skin is the largest organ of the body having 6 different functions: protection, immunity, sensation, heat regulation, absorption of vitamin D, and excretion of wastes, sweat, oil, etc. The skin has three different layers: The epidermis, the dermis and the hypodermis or subcutaneous layer. The skin is known as the integumentary system and it acts as a boundary fence and keeps all the bacteria from entering the body.
The epidermis itself is made up of 4 to 5 different layers. The stratum corneum is the layer that we see on the outside and it is constantly being rubbed off, the stratum lucidum which is only found on the soles of the feet and palms of the hands where hair follicles are not found, the stratum granulosum where the final stage of keratinisation is completed, the stratum spinosum being the thickest layer and plays a role in the strength of the skin, and lastly the stratum basal where new cells are produced to replace cells lost from the upper layers.
The dermis is the underlying layer and it is where collagen and elastin are found which is produced by the fibroblast cells. Collagen makes up for 70% of the dermis and give it’s fullness and toughness, as well as aiding in the skin’s healing process and assisting with stretching and contracting of the skin. Elastin is found in between the collagen fibres giving the skin elasticity and the ability to bounce back, this decreases which age creating ‘wrinkles’. The dermis is made up of two parts: the papillary layer and reticular layer. The papillary layer brings nutrients and oxygen and removes waste products and the reticular layer provides support and protection. Nerve endings are found in the dermis layer that generates sensation coming from the skin – touch, pressure or temperature.
The hypodermis or subcutaneous layer is made of fat cells known as adipocytes and loose connective tissue, rich in blood vessels, lymphatic vessels and nerve fibres. This layer acts as an energy reserve, when there is a lack of energy providing substances or intense effort the adipocytes can be put back into circulation. The hypodermis also participates passively in thermoregulation since fat is a heat insulator.
Hairs, sudoriferous glands (sweat), sebaceous glands (oil) and nails are all structures associated with the skin. Hair follicles, sudoriferous glands, and sebaceous glands are found in the dermis layer.
The hair follicle is a small structure containing the papilla, arrector pili muscle, sebaceous gland, blood vessels and lymphatic vessels. Hairs have three main roles to protect us from cold, heat and injury. The papilla is found at the base of the follicle and contains the blood supply which nourishes the hair. The arrector pili muscle is connected to the side of the follicle, the muscle contracts due to changes in temperature and causes ‘goose bumps.’ Sebaceous glands provide the sebum or oil which prevents dryness, helps in waterproofing the skin and has anti-fungal properties. Blood vessels are in the dermis and they transfer oxygen and nutrients to the papilla. Lymphatic vessels are intertwined with capillary networks in the dermis and without the vessel, our cardiovascular system would stop working and our immune response would be hopelessly impaired. The structure of the hair follicle is made up of keratin and combined in three different layers. The outer layer is the cuticle and is transparent. The middle layer is called the cuticle and contain the pigment that makes your hair colour, when there is a gradual fall of the melanin pigment, this is when hairs begin to ‘grey’. The medulla which is the central layer is absent in fine hair. Vellus hair is unpigmented hair and is less than 2cm long and covers the body. Terminal hair replaces the vellus hair on hair, armpits, beards, eyebrows and pubic areas at puberty. There are three stages of hair growth: anagen, catagen and telogen. Anagen is the growing stage and lasts for 2 to 6 years, this is the best time for removal. Catagen is the transition stage and lasts for 1 to 2 weeks and telogen is resting stage and last for 5 to 6 weeks before the hair falls out and a hair starts growing in the anagen stage.
Sudoriferous glands are sweat glands and there are two types of these glands: eccrine and apocrine. Eccrine are found everywhere on the body except the palms of hands and soles of feet. The sweat produced is 98% water and 2% sodium chloride and doesn’t have an offensive odour. Apocrine glands are only found in certain areas such as armpits and pubic regions and produces a sweat which is a milky fluid containing fat particles that bacteria can react to and product the unpleasant smell.
When I have done more notes I'll be sure to post Part 2 of Skin, The Largest Organ of the Body.