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An in-depth look at how our skin functions

Updated on September 21, 2014

Did you know that your skin is the largest organ of your body? Clearly, it is not just a simple group of tissues covering your entire body; our skin is much more than that.

To start with, the skin is an organ associated with the nervous system. It monitors internal and external feelings and senses like warmth, stress and illness. In one way or another, it “talks” to your brain. Some experts even said that the skin is the “brain on the outside”.

Just imagine an eggshell which protects the yolk and the white inside. Similarly, your skin protects everything that it is capable of protecting from the foreign external objects like sunlight, insects and germs. At the same time, it keeps those which are from the inside from coming out just like water, blood and body organs. Furthermore, your skin enables you to perspire to maintain the appropriate body temperature of a human being. Not only that, your skin also serves as your channel for sensing things. When you touch a baby’s skin and the softness of his/her skin travels as a message to your brain. When you are nervous, your skin excretes sweat. Hence, your skin is a necessary and a very important organ in the human body. Not only does it tells you whether you feel hurt or cold but it also shows you how healthy and disciplined you are.

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The structure of our skin

If you can imagine a slightly flat cream cake slice with three main layers sandwiched together and lots of thinner ones within them, our skin is a bit like that. The human skin is composed of three main layers separated by thinner layers in between. Its three main layers are the epidermis, dermis and the subcutaneous fatty layer. Each layer will be thoroughly discussed on the succeeding paragraphs.

Epidermis

Epidermis comes from the Greek word epiderma; epi meaning over and derma which means skin. In a simple context, epidermis is the top most layer of the skin. It is a thin layer approximately about 1 mm or 1000 micrometers that covers your entire body from head to foot. The thickest areas can be found on the soles of your foot about 1.5mm; while the thinnest ones can be found on your eyelids with an estimated thickness of only 0.05mm. This area is known not to have any blood vessels; instead, it is nourished with blood through the small capillaries.

Skin cells, also called as keratinocytes, are produced all day, every day. Some dies, others develop and some are born in the five levels of the epidermis. It is said that these cells begin life at the bottom part of the epidermis and then eventually move up to the top surface as it matures and develop. By the time they reach the top most layer, it will die and will be stripped away soon from your skin. This process is known as exfoliation. Then, more “daughter” cells are on their way up and the cycle will repeat again. This process takes around more or less than a month – specifically 26-42 days. As you grow older, this process gradually slows down and dead cells began to stick to the top surface. This explains why older people usually have duller face as compared to young lads.

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cyhsanatomy1.wikispaces.com

The skin is considered to be an organ because it __________.

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Which part of the skin is the superficial layer of the epidermis consisting of dead cells that slough off?

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The structure of the epidermis

There are five layers at the bottom of the epidermis:

1. Basal layer or stratum basale. It is called “the factory of the skin.” It is where millions upon millions of skin are created every single day. The moment that they are created, this new cells are pushed upwards to penetrate to the top most part of the epidermis. Melanocytes or pigmentation cells, also begins here. The Melanin controls the color of your skin and hair; it also protects you from excessive sunlight. Lastly, the immune cells called Langerhans originate on this area. It serves as your first line of defense from foreign objects like bugs.

2. Spinous layer or stratum spinosum . These irregular shaped cells produce keratin. They produce the needed substance that makes up the skin, nails, and hair of a person.

3. Stratum granulosum. This is usually the busy area in the skin factory. It is where the keratin as well as the lipids and moisture-retaining ceramides are further developed.

4. Stratum lucidum. This usually associated with the following layer called stratum corneum. It can only be found in your palms and soles. The cells basically flatten and clump together to create an additional layer of protection where the cells encounter frequent frictions.

5. Horny layer or stratum corneum. This is the top most surface layer - think of the icing on a cake. The cells that can be found in this layer, called corneocytes, are estimated to be 25 to 30 layers dead and tightly packed along with lipids and proteins. Its thickness varies from 10 to 100 micrometers. This is the reason why the skin on areas like your eyelid is comparably more sensitive than those of your soles.

Technically speaking, corneocytes are dead during this period. However, they still contain some chemicals that enable them to act as a barrier and respond to the environment you are in. One of these chemicals is called the Natural Moisturizing Factor (NMF). This NMF promotes the absorption of water into corneocytes, thus, preventing the formation of cracks in between. This explains why healthy skin is smooth while unhealthy skin often feels and looks dry and rough. Hence, moisturizers often contain substances that rehydrate these corneocytes, acting like NMF in order to restore a smooth and healthy looking skin.

So what happens when the stratum corneum barrier got damaged? Usually, a “trans-epidermal water loss” (TEWL) occurs. Bad burns for example can cause massive water loss and these increases along with psoriasis, dermatitis, eczema, and others. Therefore, high trans-epidermal water loss would mean high chances of permeability. This would also mean an easier access of external irritants, like dust, to the epidermis.

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pH and the acid mantle of the skin

In case you are wondering what pH stands for, it means 'potential of hydrogen.' It is also known as 'acid/alkaline balance' and measures the hydrogen concentration of a particular substance. As you probably know, it is graded in a scale of 0 to 14; with 0 as the most acidic, 14 as the opposite, and 7 as the neutral. A human stomach generally has a pH of 1, the reason being is that your stomach needs enough amount of acid to break down the food you take. The 'acid mantle' which is the protective layer on your skin surface has a typical moderate level of pH which helps in killing bacteria and fungi. Many skin products claimed to be 'pH balanced', which simply means that these products have been processed to have a pH close to the ideal 5.5.

Dermis

The dermis is the middle layer that is connected to the epidermis through the “basement membrane,” a firm layer of soft tissue. This layer is thicker than that of the epidermis, which varies depending on the specific location in your body. Its thickness doubles as a person reaches the age between three and seven, and repeats during the puberty stage.

The dermis is responsible for keeping your skin toned and tight. To elaborate, the dermis layer is composed of collagen, one of the strongest proteins. Together with elastin, these two substances contain hyaluronic acid, a sticky substance that can hold water and is important for moisturizing. So what makes your skin sag? Aside from the natural factors like aging, other important and common causes are excessive exposure to sunlight, stress, unhealthy diet and the like.

Lastly, this layer has many sweat glands, follicles, nerves and blood vessels. This simply means that there is a great access of oxygen supply. Speaking of which, it also supplies oxygen to the epidermis.

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Sweat glands

Whilst most people don’t like to sweat, casual sweating is actually good and healthy. Sweating is somehow a mechanism for your body to moisturize your skin and regulate your body temperature. That explains why you always sweat all over your body when you are active, like doing some exercise. Not only that, these glands are also activated when you are terrified or nervous - remember your episodes of having a sweaty-palm or bullet sweats on your forehead. An average person has around two to four million sweat glands. There are currently two types of sweat glands, the eccrine and apocrine, both of which are created in the dermis layer.

The main difference between the eccrine and apocrine glands lies between their function and location to your body. To differentiate them further, eccrine glands are found all over your body while apocrine can be found on selected areas like under the armpits and around the genital area. Moreover, appocrine glands are mostly attached to hair follicles. Eccrine glands are more active and responsible for most sweat activities of a person; while apocrine glands are less active, but more concentrated - this explains why sweat in your underarms sometimes have foul odor. Another thing is eccrine glands often works independently, just think of yourself having a lot of sweat on your arms but not on your face. Apocrine glands, on the other hand, tend to work together, rare it is for a person who sweats on one underarm and not on the other isn’t it?

Follicles

Follicles are tube-like structures that sometimes contain a hair or not. It originates from the bottom of the dermis layer and extends up to the outer skin surface, often referred as pores. Connecting to these follicles are what referred to as sebaceous glands. These glands create the sebum, an oily substance that goes from the follicle up to the skin surface. In this area, if there is an increased production of sebum, acne begins to appear on our face, thorax, and back - if not treated at once, acne scar removal will be the next problem to face.

When you are surprised, cold or terrified, the arrector pill attached to your hair follicles contract, making them protrude a little bit. This event is called piloerection or better known as “goose bumps.” A quick side note, an indication of a healthy hair on the head is when it grows in an average .4mm length per day.

Subcutaneous layer or hypodermis

This is the bottom layer of the skin. It is comprised by adipose cells, nerves and blood vessels. Just like the dermis, subcutaneous layer varies in thickness. For example, this layer is thicker on your bottom, thinner on your neck, and completely absent on your eyelids. It helps your skin to be fatter, thus, helping you protect your bones and reserve an extra tank of energy. Furthermore, it also plays a role in synthesizing vitamin D on your skin after being exposed from sunlight. Hence, this layer is involved in creating healthy bones and teeth and improving your immune system.

Under normal circumstance, the human skin is roughly attached to a muscle and/or bone. In the event that the fatty layer excessively expands - say you gained a lot of weight - the fibers in the connective tissue are pulled tight, resulting to what is commonly known as cellulites.

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