Skin – Function, Anatomy, Structure, Layers, Glands and Their Arrangement

Skin – Function, Anatomy, Structure, Layers, Glands and Their Arrangement – Education Lecturer. Com -Skin is the outer layer that covers the body of a vertebrate. The skin consists of the epidermis, dermis, and hypodermis. The skin functions as a means of excretion due to the presence of sweat glands (sudoriferous glands) which are located in the dermis layer. The structure of the skin consists of the structure of the anatomical layers of the skin with different functions The parts of the skin are divided into three, namely the epidermis, the skin (dermis) and connective tissue lower.

As explained at the beginning, the skin consists of 3 parts, each layer of which is composed of several layers which have their own functions. So, here is an explanation of the parts of the skin.

Ari Skin (Epidermis)

The epidermis is the very thin outer part, the function of the epidermis is to protect body from various chemical substances found outside the body, protects the body from UV rays, protects the body from bacteria. The epidermis consists of two layers, the layers of the epidermis and their functions are as follows.

• Horn Layer / Stratum Cormeum

The horny layer is the outermost layer of the epidermis and is a dead layer so it peels easily, has no core and contains keratin. This layer will always be new, if it peels it will not hurt or bleed because there are no blood vessels and nerves.

• Characteristics of the Horn Layer 1. The outermost layer and is composed of dead cells
  2. Easy to peel
  3. It has no blood vessels and nerves so it doesn't hurt and doesn't bleed if the layer is peeled off.
• Malpighian layers

The Malpighian layer is the epidermis that is under the layer of horny skin. The Malpighian layer is composed of living cells that are always dividing. There are capillaries. The function of the capillary lining is to deliver nutrients. Living cells contain melanin. Melanin is a pigment that colors the skin and protects cells from damage caused by sunlight.

Melanin production will increase, if we get too much sunlight, our skin will become dark. Apart from melanin there is also keratin pigment. If the pigments keratin and melanin combine, the skin color will appear yellowish. If a person has no pigment, then this person is called an albino. Each person has different pigments so there are various skin colors such as olive, black, white and brown.

• Characteristics of the Malpighian Layer 1. Composed of living cells
  2. There are nerve endings
  3. There are pigments that are useful in providing color to the skin and protecting the skin from sunlight.

On the surface of the epidermis ( epidermis ) there are pores which house the oil glands and which grow hair, except for the epidermis which is found on the palms of the hands and feet which does not grow hair. The epidermis on the palms of the hands and feet has four layers. The layers on the palms of the hands and feet are as follows.

• Stratum Corneum
  The outermost layer of skin. Stratum corneum, the thickest layer on the soles of the feet and the thinnest layer on the forehead, cheeks and eyelids.
• Stratum Granulosum
  A layer containing two four cell layers united by a desmodom. These cells contain keratohyaline granules which have an influence on the formation of keratin in the upper layers of the epidermis.
• Stratum Lucidum
  A layer containing two to three layers of cells that do not have a nucleus which is usually found in thick skin, namely the palms of the hands and the heels of the feet.
• Germinal Stratum
  The cell layer contains one layer of actively dividing pyramidal cells that divide by mitosis to produce cells that migrate into the upper layers of the epidermis and ultimately to the surface skin.

Hide Skin (Dermis)

The hide or dermis is the second layer of skin. The boundary with the epidermis is lined with basement membrane. The dermis or hide layer is thicker than the epidermis. The dermis has elastic fibers which allow the skin to stretch when the person gets fat and the skin can sag when the person becomes thin.

Dermis Layers (Hide Skin)

In the inner layer of the dermis there are various layers, for more details as follows.

• Capillaries
  Functions to deliver nutrients/food substances to hair roots and skin cells.
• Sweat Glands (Glandula Sudorifera)
  It is spread throughout the skin and functions to produce sweat which is released through the skin pores.
• Oil Glands (Grandula Sebaceae)
  Functions to produce oil so that the skin and hair do not dry out and wrinkle.
• Hair Glands
  Has roots and hair shafts as well as hair oil glands. When we are cold and afraid, the hair on our body feels like it stands on end. This is because near the hair roots there are smooth muscles which have the function of holding the hair straight.
• Neural Bundles
  A collection of pain nerves, heat nerves, cold nerves and touch nerves.

Connective Tissue Under the Skin (Hypodermis)

The subcutaneous connective tissue is below the dermis. This tissue does not have a clear boundary with the dermis, as a benchmark for its boundary is where fat cells begin to appear. This layer of skin contains a lot of fat. The function of the lamak layer is to protect the body from impacts, as a source of reserve energy and to retain body heat.

Skin Anatomy

Skin is an organ that covers the entire outer surface of the body, it is the heaviest and largest organ of the body. The entire skin weighs around 16% of body weight, in adults around 2.7 – 3.6 kg and the area is around 1.5 – 1.9 square meters. The thickness of the skin varies from 0.5 mm to 6 mm depending on location, age and gender. Thin skin is located on the eyelids, penis, labium minus and skin on the medial part of the upper arm. Meanwhile, thick skin is found on the palms of the hands, soles of the feet, back, shoulders and buttocks. Embryologically, the skin originates from two different layers, the outer layer is the epidermis which is the epithelial layer that originates from the ectoderm while the inner layer that comes from the mesoderm is the dermis or corium which is a layer of tissue tie. (Ganong, 2008).

Epidermis

The epidermis is the thin, avascular outer layer of the skin. Consists of stratified squamous horny epithelium, containing melanocytes, Langerhans and Merkel cells. The thickness of the epidermis varies in various places on the body, thickest on the palms of the hands and feet. The thickness of the epidermis is only about 5% of the entire thickness of the skin. Regeneration occurs every 4-6 weeks. The epidermis consists of five layers (from the top to the deepest):

1. Stratum Corneum
2. Stratum Lucidum
3. Stratum Granulosum
4. Stratum Spinosum
5. Stratum Basale (Stratum Germinativum)

Dermis

It is the most important part of the skin which is often considered "True Skin". Consists of connective tissue that supports the epidermis and connects it to the subcutaneous tissue. The thickness varies, the thickest on the soles of the feet is around 3 mm.

The dermis consists of two layers:

1. Papillary layer; thin containing sparse connective tissue.
2. Reticular layer; thick consists of dense connective tissue.

Collagen fibers thicken and collagen synthesis decreases with age. The number of elastin fibers continues to increase and thicken, the elastin content of human skin increases approximately 5 times from fetus to adult. In old age, collagen crosses over in large quantities and elastin fibers decrease, causing the skin to lose its elasticity and appear to have many wrinkles. The dermis has a lot of blood vessel tissue.

The dermis also contains several epidermis derivatives, namely hair follicles, sebaceous glands and sweat glands. The quality of the skin depends on whether there are many epidermal derivatives in the dermis. Dermis function: supporting structure, mechanical strength, nutritional supply, resisting shearing forces and inflammatory response (Wasitaatmadja, 1997).

Subcutis

It is a layer under the dermis or hypodermis which consists of a layer of fat. This layer contains connective tissue that loosely connects the skin to the underlying tissue. The amount and size vary according to the region of the body and the nutritional state of the individual. Functions to support blood supply to the dermis for regeneration. Subcutis / hypodermis function: attached to the basic structure, heat insulation, calorie reserve, body shape control and mechanical shock absorber. (Wasitaatmadja, 1997).

Skin Structure

The skin consists of an outer layer called the epidermis and an inner layer or dermis layer. The epidermis does not contain blood vessels or nerve cells. The epidermis is composed of four layers of cells. From the inside to the outside, first is the stratum germinativum which functions to form the layer above it. Second, outside the germinal layer there is the stratum granulosum which contains a small amount of keratin which causes the skin to become hard and dry.

Apart from that, cells from the granulosum layer generally produce black pigment (melanin). The melanin content determines the degree of skin color, blackish or brownish. The third layer is a transparent layer called the stratum lucidum and the fourth layer (the outermost layer) is the horny layer called the stratum corneum.

The main constituent of the dermis is supporting tissue consisting of white fibers and yellow fibers. Yellow fiber is elastic/flexible, so the skin can expand. The stratum germinativum grows into the dermis to form sweat glands and hair roots. Hair roots are connected to blood vessels that carry food and oxygen, but they are also connected to nerve fibers.

At the base of each hair root, a muscle that moves the hair is attached. When cold or afraid, the hair muscles contract and the hair becomes erect. Inside the dermis there are fat deposits which function as a cushion to protect the inside of the body from mechanical damage.

Also Read: Plant Cells – Definition, Organelles, Functions and Structure

Skin Layer

• Epidermis: the epidermis is the outermost layer of tissue that functions as a protector or covers all organs. Epidermal tissue originates from protoderm. Once old, it can remain there or be damaged. If the epidermal tissue is damaged it will be replaced by cork. The amount of epidermal tissue is usually 1 layer but can also be more with varying shapes and sizes.
• Dermis: is a layer of skin consisting of blood vessels, oil glands, hair follicles, sensory nerve endings, and sweat glands. The blood vessels in this layer are so wide that they can accommodate around 5% of the blood in the entire body.
• Hypodermis: Hypodermis (connective tissue under the skin) is connective tissue located under the dermis layer, but the boundary between the hypodermis and the dermis is not clear. This layer is where fat is stored in the body, so it is often also known as the Lower Body Fat Layer. This fat functions to protect against impacts from hard objects, to maintain body temperature because fat can store heat, and as a source of reserve energy.
• Hair root (hair roots): root hairs are hairs or hairs in the form of fine fibers on plant roots, usually small in size and found on the sides of the main root or root branches. Root hairs are surface extensions of the root epidermis layer which function to optimize the absorption of water and nutrient minerals. The more root hairs, the greater the root surface area, allowing the plant to reach water and nutrient minerals in places far from where the plant grows.
• Hair follicles: Hair follicles or hair follicle is a small sac where the root of one strand of hair is located.
• Ecc sweat gland: Eccrine sweat glands or sweat glands regulate evaporation to cool the body at environmental temperatures increases what we know as sweat and removes the body's metabolic waste, mostly consisting of salt and urea.
• Hair shaft (hair shaft): Namely the part of the hair that is outside the skin, in the form of fine threads consisting of keratin / horn cells.
• Pore: On the outer surface of the skin there are pores (cavities) through which sweat comes out.
• Dermai papillae: Since the dermal papillae are located at the dermo-epidermal junction, one of their functions is to keep the dermis and epidermal layers connected. In other words, dermal papilla helps in strengthening dermal-epidermal connectivity. This is very important because the epidermis must depend on the dermis to improve blood circulation.
• Meisaner's corpuscle: are sensory nerve endings in the skin that are sensitive to touch.
• Free nerve ending: are nerve endings in the skin that are sensitive to stimulation, located around the hair roots.
• Reticular layer of dermis: made of thick collagen fibers arranged parallel to the surface of the skin. The reticular layer is denser than the papillary dermis, and strengthens the skin, providing structure and elasticity. It also supports other components of the skin, such as hair follicles, sweat glands, and sebaceous glands.
• Sabaceous (oil) gland (skin gland): are microscopic glands located just under the skin, whose function is to secrete oil and soap.
• Arrector pili muscle : small muscles attached to hair follicles. Contraction of these muscles causes the hair to stand up.
• Sensory nerve fibers: nerves that flow out from the brain and spinal cord to the muscles and glands to stimulate them.
• eccrine sweat glands: regulates evaporation to cool the body when the environmental temperature increases which we know as sweat and removes the rest of the body's metabolism mostly consists of salt and urea, even if we experience digestive disorders such as obstipation & constipation which causes When the excretion of feces or bowel movements is disturbed, the body will try to get rid of the remains of the body's metabolism through the sweat glands in the body skin surface.
• Pacinian corpuscle: nerve endings resembling a bulb (bulblike) or onion skin (because it is round and layered) are located in subcutaneous tissue of the skin, most commonly found in the palms of the hands, feet, joints and genitals, whose function is to detect tactile stimuli, pressure. These receptors are larger in size and fewer in number than Meissner and Merkel cells.
• Arteries: to provide oxygen and nutrients through the blood to all cells in the body
  veins = carry blood to the heart and send O₂ into the skin.
• Veins: to circulate blood throughout the surface of the skin.
• Adipose tissue: Adipose tissue is commonly known as body fat. Converting fat into usable fuel comes at a high cost, and the body must expends twice the energy to convert it into fuel compared to carbohydrates or proteins.
• Hair follicle receptor: Hair follicles are skin structures where hair grows. Their function is to make your hair stronger and your hair will look more beautiful.

Also Read: Functions and Parts of the Human Central Nervous System

Skin Function

Skin has many functions, which are useful in maintaining body homeostasis. These functions can be divided into protection, absorption, excretion, perception, body temperature regulation (thermoregulation), and vitamin D formation.

Protection function

The skin provides protection to the body in various ways as follows:

1. Keratin protects the skin from microbes, abrasion (friction), heat and chemicals. Keratin is a hard, rigid structure that is arranged neatly and tightly like bricks on the surface of the skin.
2. The released lipids prevent evaporation of water from the skin surface and dehydration; Apart from that, it also prevents the entry of water from the environment outside the body through the skin.
3. Oily sebum from the sebaceous glands prevents the skin and hair from drying out and contains bactericidal substances which function to kill bacteria on the surface of the skin. The presence of this sebum, together with sweat excretion, will produce an acid mantle with a pH level of 5-6.5 which can inhibit microbial growth.
4. Melanin pigment protects against the effects of harmful UV rays. In the basal stratum, melanocyte cells release melanin pigment to surrounding cells. This pigment is responsible for protecting genetic material from sunlight, so that genetic material can be stored properly. If there is a disruption in the protection by melanin, malignancy can occur.
5. Apart from that, there are cells that act as protective immune cells. The first are Langerhans cells, which represent antigens against microbes. Then there are phagocytic cells whose job is to phagocytose microbes that enter through keratin and Langerhans cells.

Absorption Function

Skin cannot absorb water, but it can absorb lipid-soluble materials such as vitamins A, D, E, and K, certain medications, oxygen and carbon dioxide. The skin's permeability to oxygen, carbon dioxide and water vapor allows the skin to take part in respiratory functions. Apart from that, some toxic materials can be absorbed, such as acetone, CCl₄, and mercury. Some medications are also designed to dissolve fats, such as cortisone, so they can penetrate the skin and release antihistamines at the site of inflammation.

The absorption capacity of the skin is influenced by the thickness of the skin, hydration, humidity, metabolism and type of vehicle. Absorption can take place through gaps between cells or through the openings of gland ducts; but more passes through the cells of the epidermis than through the openings of the glands.

Excretory function

The skin also functions in excretion through its two exocrine glands, namely the sebaceous glands and sweat glands:

• Sebaceous glands

Sebaceous glands are glands that are attached to hair follicles and release lipids known as sebum into the lumen. Sebum is released when the arrector pili muscle contracts, pressing on the sebaceous glands so that the sebum is released into the hair follicle and then onto the surface of the skin. Sebum is a mixture of triglycerides, cholesterol, proteins and electrolytes. Sebum functions to inhibit bacterial growth, lubricate and protect keratin.

• Sweat glands

Even though the stratum corneum is waterproof, around 400 mL of water can escape by evaporating through the sweat glands every day. A person who works indoors excretes an additional 200 mL of sweat, and for active people the amount is even more. Apart from releasing water and heat, sweat is also a means of excreting salt, carbon dioxide and two organic molecules resulting from protein breakdown, namely ammonia and urea.

There are two types of sweat glands, namely apocrine sweat glands and merocrine sweat glands.

1. Apocrine sweat glands are found in the axillary, breast and pubic areas, and are active at puberty and produce thick secretions with a distinctive odor. Apocrine sweat glands work when there are signals from the nervous system and hormones so that the myoepithelial cells around the glands contract and press on the apocrine sweat glands. As a result, the apocrine sweat glands release their secretions into the hair follicles and then onto the outer surface.
2. Merocrine (eccrine) sweat glands are found on the palms of the hands and feet. The secretions contain water, electrolytes, organic nutrients and metabolic waste. The pH level ranges from 4.0 – 6.8. The function of the merocrine sweat glands is to regulate surface temperature, excrete water and electrolytes and protects against foreign agents by making it difficult for foreign agents to attach and producing dermicidin, a small peptide with properties antibiotics.

Perceptual function

The skin contains sensory nerve endings in the dermis and subcutis. Ruffini's bodies in the dermis and subcutis respond to heat stimulation. Against the cold is played by the Krause bodies located in the dermis, Meissner's tactile bodies located in the dermis papillae play a role in touch, as do the Merkel bodies of Ranvier which are located in epidermis. Meanwhile, the pressure is played by the Paccini body in the epidermis. These sensory nerves are more numerous in erotic areas.

Body temperature regulation function (thermoregulation)

The skin contributes to regulating body temperature (thermoregulation) in two ways: sweating and adjusting blood flow in the capillaries. When the temperature is high, the body will sweat in large quantities and widen the blood vessels (vasodilation) so that heat will be carried out of the body. On the other hand, when the temperature is low, the body will sweat less and narrow the blood vessels (vasoconstriction) thereby reducing heat loss by the body.

Vitamin D Formation Function

Vitamin D synthesis is carried out by activating the 7 dihydroxy cholesterol precursor with the help of ultraviolet light. Enzymes in the liver and kidneys then modify the precursor and produce calcitriol, the active form of vitamin D. Calcitriol is a hormone that plays a role in absorbing dietary calcium from the gastrointestinal tract into the blood vessels.

Even though the body is able to produce vitamin D on its own, it does not meet the body's overall needs, so systemic administration of vitamin D is still necessary. In humans, the skin can also express emotions because of the blood vessels, sweat glands and muscles under the skin.

Color Formation in Skin

Skin color is influenced by two factors, namely epidermal pigmentation and capillary circulation in the dermis layer. Epidermal pigmentation is influenced by two pigments, namely carotene and melanin.

1. Carotene is a red-orange pigment that accumulates in the epidermis. Most commonly found in the stratum corneum in light-skinned people, as well as in fatty tissue in the dermis and subcutis layers. The discoloration caused by carotene is most visible in pale-skinned people, while it is difficult to see in dark-skinned people. Carotene can be converted into vitamin A which is necessary for epithelial maintenance and photoreceptor synthesis in the eye.
2. Melanin is a yellow-brown or black pigment produced by melanocytes. Melanocytes themselves are located between the basal cells and have extensions to the cells above them. The ratio of the number of melanocytes to basal cells varies, ranging from 1:20 to 1:4. The melanocyte Golgi apparatus forms melanin from tyrosine with the help of Cu and oxygen, then packages it into melanosome vesicles. These melanosomes will be delivered through the melanocytes and color the keratinized cells above them until they are degraded by lysosomes.

The number of melanocytes in both black and white people is the same, what is different is the activity and production of pigment (melanocytes). In people with pale skin, the transfer of melanosomes is only limited to the stratum spinosum, whereas in people with dark skin, melanosomes can be delivered to the stratum granulosum.

Blood circulation in the capillaries in the dermis also plays a role in determining skin color. Hemoglobin, whose function is to transport oxygen, is a pigment. When combined with oxygen, hemoglobin will be bright red, giving the capillaries a red color.

That's the discussion about Skin – Function, Anatomy, Structure, Layers, Glands and Their Arrangement Hopefully this review can increase your insight and knowledge, thank you very much for visiting. 🙂