Skin, What is it?

The skin can be a complicating organ. It contains many parts that overlap and these parts can be associated with many names. This may not be a complete description. (See book).

7 FACTS ON YOUR SKIN ANATOMY

• 3 Structural layers: Epidermis, Dermis and Hypodermis
• 4 cell types: (Epidermis) Keratinocyte, Merkel cells, Melanocytes and Langerhan cells (Dermis) Fibroblast cells, Macrophage cells, Phagocytes and Mast Cells
• 2 glands: Sebaceous and Sudoriferous
• 4 main receptors: Mechanoreceptors, Thermoreceptors, Nociceptors and Proprioceptors
• 2 types of skin: Glabrous and hairy skin
• 3 proteins: Keratin, Collagen and Elastin
• 2 main appendages: Hair and Nails

3 MAIN FUNCTIONS OF YOUR SKIN

• Protection - The collagen provides strength and resistance to keep foreign bodies out
• Temperature Regulation - Our sweat production helps keep us cool,  this is also achieved with our blood vessels through vasoconstriction (narrowing) and vasodilation (widening)
• Sensation – Supplied with a network of nerve endings sensitive to touch and pain

The Epidermis is the upper, surface or outer, that is not sensitive and not vascular layer of our skin. It is thinner and made up of epithelial tissue. This layer has no blood vessels.

The Epidermis breaks down further into 5 layers:

• Stratum Corneum (also called the horny layer) this is our layer exposed to the environment. Our skin cells (Keratinocyte) end their journey here becoming flat, hard and dry. The cells become mostly keratin (a tough, fibrous and insoluble protein) at this point where the layer always sheds and is replaced. Keratin makes up about 95% of our epidermis. Keratinocyte main job is preventing water loss, but also provides protection from UV rays, heat and as the defense against viruses, parasites, fungi and bacteria.

Rubbing and pressure on this surface can cause the keratin to increase forming calluses to protect the skin.

• Stratum Lucidum (also called barrier layer) this inner layer of dead skin cells varying in shape. It has a smooth translucent appearance. This layer is only on the palms of our hands and soles of our feet where it is thicker.

Glabrous Skin is found with this layer, it is non-hairy. It contains no hair follicles.

• Stratum Granulosum (also called granular layer) the cells have a grainy appearance. Here skin cells transition towards the end of their journey they become larger as they take on more keratin.

• Stratum Spinosum (also called the squamous cell layer) It is here that a stage called mitosis takes place. The layer is several cells long. The cells have tiny fibrils connecting them together. Here is a center of reproduction. Cells found here are Keratinocytes and Langerhans cells. Langerhans cells are found in large numbers in this layer. They produce antigen.

The Malpighain Layer includes the Stratum Germinativum (lower) and the Stratum Spinosum (upper layer) together. This is where our nails extend.

• Stratum Germinativum (also called basal cell layer) this is the bottom layer of the epidermis. This layer is very thin at only one cell long. This layer contains fat at about 14 % and moisture at about 70%. Here cells divide and begin their journey taking about 28 days to reach the surface of our skin which we see.

The Melanocytes (cells) are somewhat cube shaped here. They are responsible for melanin (pigment where skin gets its color).

The cells are constantly going through mitosis. This layer is the beginning of the reproduction center. Merkel cell a receptor is found here and some areas in the mucosa. These receptors can easily be attacked and form malignant tumors.

Mucous Membranes: nostrils, lips of the mouth, eyelids, ears, genital area and anus.

Conditions Found Here:

The Dermis is the lower, bottom or inner sensitive and vascular layer of our skin. It is thicker and made up of mostly Collagen and Elastin. It also contains lymph vessels, hair follicles and glands.

The Dermis breaks down into 2 layers:

• Papillary Layer the thinner and superficial layer. Blood vessels provide nutrients for the epidermis. Phagocytes here help fight bacteria or other infections. It also contains lymphatic capillaries, nerve fibers and Meissner corpuscles (touch receptors).

• Reticular Layer is thicker and has elastin fibers which provide elasticity for movement and collagen fibers for strength and structure. It contains several cells and structures; our hair follicles, sebaceous glands (scalp, face, back and chest having a well-developed blood supply), apocrine and endocrine glands, blood vessels and nerve endings, meissner corpuscles and lamellar corpuscles which transmit sensations of touch and pressure.

Fibroblast cells here produce collagen and elastin which make up the main connective tissue. They play an important role in healing wounds.

Phagocytes can also be found here. They are a white blood cell in the immune system. They find and kill dangerous pathogenic cells.

Mast cells are also an immune cell here. They are loaded with histamine and heparin containing granules. Mast cells play a role in allergy and anaphylaxis.

Collagen is a protein that makes up about 75-80% of our skin. It is responsible for our skin's structure. As we age our cells produce less and this causes those wrinkles and fine lines.

Collagen is found in our tendons, ligaments and cartilage.

Elastin is a soluble protein in connective tissue. Like elastic it helps to snap back to it's original shape. Elastin is found in large blood vessels like the aorta and the lungs.

Hairy skin is the opposite of Glabrous skin. Hair in some form is found, mostly on the rest of our skin. For example: eyelashes, eyebrows and external ear. These hairs contain sensory nerves. We have all had something fall on our eyelashes. (Like the whiskers of a cat). These hairs serve a purpose.

The Sebaceous glands produce sebum an oily, waxy substance containing varies lipids (fats). Sebum is secreted on the skin surface by a duct in the hair follicle.

Conditions found here:

Dermatofibroma (benign skin bumps on legs)

Sebaceous cysts (contain sebum, an oil our body produces)

Dermoid cysts (contain hair or teeth)

Cellulitis (a bacterial infection of skin)

Rhytides (wrinkles)

Hypodermis (also called Subcutaneous Layer) is a loose fatty tissue with various thicknesses found in specific areas of the body. It gives our skin its shape. Here we find arteries that break down to capillaries as they travel up into the dermis. This layer connects our skin to bones and muscles. It provides fat storage serving as insulation and cushioning. The cells found here are the fibroblasts, adipose cells (store fat) and macrophages.

Macrophages are immune, kind of white blood cell actually a Phagocyte, that attacks foreign bodies (phagocytosis).

The Sudoriferous gland produces sweat (AKA Sweat gland) to cool our body temperature. They are small and tubular structures found in the Subcutaneous Layer. The sweat is released from our pores on the skin's surface.

The sweat/perspiration has a transparent colorless appearance. It is a fluid containing some fatty acids and mineral matter. When mixed with bacteria on the skin it can produce an unpleasant odor.

The human body has four main sensory skin receptors. These nerve endings are responsible for communicating to our brain.

Mechanoreceptors - sensations, such as applying pressure to a wound.

Thermoreceptors - temperature, such as putting our hand on a hot stove.

Nociceptors - pain, such as falling and scraping our knee.

Proprioceptors - location, such as keeping our balance while walking.

Hair and Nails are main appendages of our skin. They are also made up of keratin. Our hair and it's follicles make up the pilary system. Our nails are an extension of the Malpighian layer (epidermis).

Reference:

How the Body Works A Comprehensive Illustrated Encyclopedia of Anatomy General Editor Dr. Peter Abrahams Metro Books @2007 by Bright Star Publishing pic  Body Systems, How skin protects the body pgs. 416-417, Skin and nails pgs. 414-415  https://www.goodreads.com/book/show/16004050-how-the-body-works (book)

Modern Esthetics A Scientific Source for Estheticians Henry J Gambino, PhD Milady @1992 Delmar Ch 6 Skin Structure and Function pgs. 98-113

https://en.m.wikipedia.org/wiki/Cutaneous_receptor accessed 05/14/2020