Integumentary System

Part of the heat-liberating apparatus of the body

eccrine sweat gland

the protein in the epdiermis that thickens and protects the skin is

keratin

Eccrine sweat gland

most numerous sweat-producing gland in the skin

Sebaceous gland

oil-secreting gland in the dermis that is associated with hair follicles

Hair follicles

the sacs that hold the root of the hair fibers; sheath formed of both epithelial and connective tissues

Apocrine sweat gland

One of the large dermal exocrine glands located in the axilla and genital areas. Its secretion contains proteins and other substances that favor bacterial growth, causing odor

What factors contribute to wrinkles?

UV radiation, aging, hormonal changes, smoking, stress, eating unhealthy food

Cutaneous membrane

Also known as skin, it consists of the epidermis, dermis, and hypodermis

What is skin color influenced by?

Sin color is influenced by the presence of pigments, the degree of dermal circulation, and the thickness and degree of keratinization of the epidermis. Differences in skin pigmentations among individuals do not reflect different numbers of melanocytes, but instead different levels of synthetic activity. Melanocytes are usually distributed normally, it largely depends on if the cells can produce melanin.

Why do epidermal cells rely on the diffusion of nutrients and oxygen from capillaries within the dermis?

They lack local blood vessels. The cells with the highest metabolic demand are closest to the underlying dermis.

Collagen

Very strong and resist stretching but are easily bent or twisted

The framework of the dermis is composed of

connective tissue

The deeper layers of the epidermis are dominated by...

Keratinocytes, the body's most abundant epithelial cells. These cells form several layers (strata) and are continuously produced by stem cell divisions in the deepest layers and are shed at the exposed surface.

Major functions of integumentary system

- Protection of underlying tissue and organs against impact, abrasion, fluid loss, and chemical attack - Excretion of salts, water, and organic wastes by integumentary glands - Maintenance of normal body temperature through either insulation or evaporative cooling, as needed - Production of melanin, which protects underlying tissue from ultraviolet radiation - Production of keratin, which protects against abrasion and serves as a water repellent - Synthesis of vitamin D3, a steroid that is subsequently converted to calcitriol, a hormone important to normal calcium metabolism - Storage of lipids in adipocytes in the dermis and in adipose tissue in the hypodermis - Detection of touch, pressure, pain, and temperature stimuli, and the relaying of that information to the nervous system

There is often overlap between the epidermis and dermis when considering sensory receptors. Identify and describe the many sensory receptors of the skin.

- Tactile discs - Sensory neurons - Tactile corpuscles - Lamellated corpuscles (pacinian corpuscles)

Three layers of the dermis

1. Papillary 2. Reticular 3. Hypodermis

Five layers of the epidermis

1. stratum corneum 2. stratum lucidum 3. stratum granulosum 4. stratum spinosum 5. stratum basale

Melanin

A brown, yellow-brown, or black pigment produced by *melanocytes*, which are located in the stratum basale, squeezed between or deep to the epithelial cells. Melanocytes manufacture melanin from the amino acid tyrosine, and package it in intracellular vesicles called *melanosomes*.

Stratum granulosum

A layer of the epidermis that marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata. - Consists of 3 to 5 layers of keratinocytes. - By the time cells reach this layer, most have stopped dividing and have started making large amounts of keratin and keratohyalin. As these fibers develop, the cells grow thinner and flatter, and their membranes thicken and become less permeable.

Dermal papillae

A small, cone-shaped elevation at the base of the hair follicle filled with blood vessels (papilla: a nipple-shaped mound) and project into the epidermis. Like the epidermal ridges, it increases surface area for attachment.

Stratum spinosum

A spiny layer of the epidermis that provides strength and flexibility to the skin. - Consisted of 8 to 10 layers of keratinocytes bound together by desmosomes. - Look like miniature pincushions in standard histological sections. They look that way because the keratinocytes were processed with chemicals that shrank the cytoplasm but left the cytoskeletal elements with desmosomes intact. - Also contains *dendritic cells*, which participate in the immune response by stimulating a defense against (1) microorganisms that manage to penetrate the superficial layers of the epidermis and (2) superficial skin cancers.

Carotene

An orange-yellow pigment that normally accumulated in epidermal cells. It is most apparent in cells of s. corneum of light-skinned individuals, but it also accumulates in fatty tissues in the deep dermis and hypodermis.

Stratum corneum

At the outermost exposed surface of both thin and thick skin. Normally contains 15 to 30 layers of *keratinized cells*. - The dead cells in each layer of the stratum corneum remain tightly interconnected by desmosomes. - It takes 7 to 10 days for a cell to move from the stratum basale to the stratum corneum. - The dead cells generally remain the exposed stratum corneum for an additional two weeks before they are shed or washed away.

How does blood supply affect skin color?

Blood contains red blood cells filled with a red pigment hemoglobin. When bound to oxygen, hemoglobin is bright red giving capillaries in the dermis a reddish tint that is most apparent in lightly pigmented people.

Stratum lucidum

Clear, transparent layer of the epidermis under the stratum corneum. Located in the thick skin of the palms and soles, it separates the stratum corneum from deeper layers. - The cells are flattened, densely packed, largely devoid of organelles, and filled with the proteins keratin and *keratohyalin*. [These proteins were synthesized while the cells were in the underlying stratum granulosum. By the time they reach the stratum lucidum, they are dead and undergoing dehydration.]

Two most abundant fibers in dermis

Collagen and elastin Dermis can tolerate limited stretching. The elastic fibers provide flexibility, and the collagen fibers limit that flexibility to prevent damage to the tissue.

Integumentary system

Consists of the skin, mucous membranes, hair, and nail. It is the most accessible organ system, accounting for about 16% of our total body weight. It's surface, 1.5-2 square meters in area, is constantly worn away as a result of exposure to microorganisms, sunlight, and environmental chemicals. The integumentary system is where the body and the outside world come into contact, acting as a defense mechanism against the environment.

Reticular layer

Deeper layer of the dermis that supplies the skin with oxygen and nutrients. - Interwoven meshwork of dense irregular connective tissue containing both collagen and elastic fibers. - Bundles of collagen fibers extend superficially beyond the reticular layer to blend into those of the papillary layer, so the boundary between the two layers is indistinct. Collagen fibers of the reticular layer also extend into the deeper hypodermis. - Contain networks of blood vessels, lymphatic vessels, nerve fibers, and accessory organs such as hair follicles and sweat glands.

Epidermal ridges

Found in the deeper layers, they extend into the dermis and are adjacent to dermal projections called dermal papillae. Greatly increases the surface area for attachment, firmly binding the epidermis to the dermis.

Keratinocytes

Keratinocytes make up almost all the cells in the epidermis. Their name comes from the fact that they contain the structural protein keratin, which is also found in hair and nails. Keratin provides strength, flexibility, and toughness to the skin. New keratinocytes form at the bottom of the epidermis from dividing stem cells. As they migrate to the top of the epidermis, they increase keratin production and eventually stop dividing. The top layer of the epidermis consists of tightly packed dead keratinocytes that have lost their cell nucleus and other organelles. The skin owes most of its tough, waterproof barrier function to this top layer. These dead cells slough off easily and are replaced every 4 to 6 weeks by new keratinocytes that have migrated from the bottom of the epidermis to the top.

What is the relationship between lines of cleavage of skin and scarring?

Lines of cleavage - result from the arrangement of collagen and elastic fibers at any location in parallel bundles oriented to resist the forces applied to the skin during normal movement. A cut *parallel* to a cleavage = usually remain closed, heals with little scarring A cut at *right angles* to a cleavage = pulls open as severed elastic fibers recoil, results in greater scarring

Tactile corpuscles

Located in dermal papillae, these receptors are sensitive to light touch

Lamellated corpuscles (pacinian corpuscles)

Located in reticular layer, these receptors are sensitive to deep pressure and vibration

Melanocytes

Melanocytes make up only about 1% of the cells in the epidermis. They produce the pigment melanin, which gives skin its color. Melanocytes are not round or flattened like keratinocytes. They instead look more like nerve cells with their long projections. The long projections in melanocytes serve to deliver melanosomes—which are pigment-containing organelles—to keratinocytes. One melanocyte supplies many keratinocytes, in the same way that one nerve cell may interact with a large number of other nerve cells.

Transfer of melanosomes in dark-skinned VS light-skinned people

Melanosomes are transferrred via the long projections of the melanocytes, reaching the keratinocytes. Some of the melanosomes will then form a cap over the nucleus to absorb incoming UV rays. - Pale skin: this transfer occurs in the s. basale and s. spinosum. - Dark skin: the melanosomes are larger, and the transfer may occur in the s. granulosum as well; skin pigmentation is thus darker and more persistent.

Epidermis

Outer layer of skin, consists of stratified squamous epithelium. The epidermis protects the body from the elements, such as wind and ultraviolet (UV) radiation. It also serves as a barrier to keep bacteria and viruses out and water in. The epidermis is, however, a selective barrier, as some gases, such as oxygen, can pass through easily. One other important function of the epidermis is to produce vitamin D. Most cells in the epidermis are keratinocytes. Other cell types include melanocytes—skin cells that produce the pigment melanin—and different kinds of immune cells that defend the body against infection.

Papillary layer

Outermost layer of the dermis, directly underneath the epidermis. -Consists of highly-vascularized areolar tissue with all of the typical cell types within it. - Also contains capillaries, lymphatic vessels, and sensory neurons that supply the surface of the skin. - Gets its name from dermal papillae that project between epidermal ridges.

Elastin

Permit stretching and then recoil to their original length

Types of melanin

Pheomelanin: reddish-yellow Eumelanin: brown and black

Sensory neurons

Provide sensations of pain and temperature

The oldest epidermal cells are found in

S. Corneum

Tactile discs

Sensory receptor cells that detect pressure; monitor Merkel cells

Hypodermis layer

Separates skin from deeper structures. - Stabilizes position of the skin in relation to underlying tissues (such as skeletal muscles) while permitting independent movement. - An important site for storage of energy reserves due to adipose tissue.

MC1R

The MC1R protein sits on the surface of melanocytes and is activated by the melanocyte-signaling hormone (MSH) in the blood. Different versions of MC1R determine whether eumelanin or pheomelanin is produced

Stratum basale

The deepest layer of the epidermis consisting of stem cells capable of undergoing cell division to form new cells. - *Hemidesmosomes* attach the cells of this layer to the basal lamina that separates the epidermis from the areolar tissue of the adjacent papillary layer of the dermis. - *Basal cells*, or germinative cells, dominate, and they are stem cells whose divisions replace the more superficial keratinocytes that are lost or shed at the epithelial surface. - Skin surfaces that lack hair also contain specialized epithelial cells known as *Merkel cells* scattered among the basal cells. Merkel cells are sensitive to touch. When compressed, they release chemicals that stimulate sensory nerve endings.

The deeper layers of the epidermis consists of two main layers...

The epidermal ridges and dermal papillae

Keratization

The formation of protective, superficial layers of cells filled with keratin.

Dermis

The inner layer of the skin containing hair follicles, sweat glands, nerve endings, and blood vessels. It consists of a papillary layer of areolar tissue and a reticular layer of dense irregular connective tissue. Its function is to supply the epidermis with oxygen and nutrients from blood and to regulate body temperature. When it's hot, vessels in the dermis expand, exposing them more to the surface where they can radiate excess heat. When it's cold, vessels in the dermis constrict, which helps retain heat within the body. In addition, liquid sweat expelled from sweat glands cools the body as it evaporates. Sweating is also a way to get rid of some wastes produced in the body. Oil glands within the dermis secrete lipids that travel through the pores to the surface to lubricate and waterproof the skin.

Hypodermis

The layer of skin beneath the dermis, which serves as a storage repository for fat. (subcutaneous layer or superficial fascia) Separates the integument from the fascia around deeper organs. Functions mainly to insulate the body, provide a protective padding around internal organs, and store energy.

Cutaneous plexus

The network of arteries and veins connected to smaller vessels servicing tissues of the integumentary system

What three factors, in terms of melanin, vary from person to person?

Type of melanin, amount of melanin, and number of melanosomes *Although almost everyone has approximately the same number of melanocytes, the amount and size of the melanosomes and the amount of melanin within them can differ greatly. In general, more eumelanin-producing melanosomes will result in darker shades.

Thin vs Thick skin

Thick skin is only found in areas where there is a lot of abrasion - fingertips, palms and the soles of your feet. It contains a fifth stratum. It is about as thick as a standard paper towel (roughly 0.5 mm) Thin skin covers most of the body surface, contains four strata, and is about as thick as the wall of a plastic sandwich bag (roughly 0.08 mm) *Refer to the relative thickness of the epidermis, not to the integument (skin) as a whole

When does skin color turn blue?

When blood flow decreases and oxygen levels in the tissues decline. Hemoglobin will release oxygen and turn a darker red, which appears as a bluish color on the surface. - This is called cyanosis, which is most apparent in areas of very thick skin like the lips or beneath the nails.

When does skin color turn red?

When blood vessels are dilated, and blood flow is increased. - For example, when body temperature rises, the skin becomes flushed and red because the superficial blood vessels dilate so that the skin can act like a radiator and lose heat.

Arrector pili

tiny muscles attached to hair follicles that pull the hair upright during fright or cold (causing "goosebumps")