Anatomy and Physiology: The Integumentary System

Describe the general structure of hair.

Hairs (or pili) are made up of fused, dead keratinized epidermal cells and consists of the following: - shaft above the surface - a root that penetrates the dermis and subQ layer - cuticle - hair follicle - hair matrix - bulb (including papilla of the hair) The functions of hair include protection, decreasing heat loss, and sensing light touch.

Describe the structure of the hair follicle.

It is composed of two layers of epidermal cells, external and internal roots sheaths, surrounded by a connective tissue sheath. Surrounding the hair follicle are nerve endings called hair roots plexuses that are sensitive to touch. If a hair shaft is moved, the hair root plexus responds.

Explain the process of keratinization.

Keratinization, the replacement of cell contents with the protein keratin, occurs when cells move to the skin surface over a period of two to four weeks. As the cells move from one layer to the next, they accumulate more and more keratin. Eventually, the keratinized cells are sloughed off and replaced by underlying cells, which in turn, become keratinized.

What type of tissue makes up the epidermis?

Keratinized stratified squamous epithelium.

What is the role of keratinocytes, the cells which make up about 90 percent of the epidermis?

Keratinocytes produce the protein keratin, which is a tough, fibrous protein that helps protect the skin and underlying tissue from heat, microbes, and chemicals. Keratinocytes also produce lamellar granules, which release a waterproof sealant.

What is the role of Langerhans cells?

Langerhans Cells participate in immune responses mounted against microbes that invade the skin. They help other cells of the immune system recognize an antigen so that it can be destroyed. They are located in the stratum spinosum.

What is the role of melanocytes?

Melanocytes produce the pigment melanin, which contributes to skin colour and absorbs damaging ultraviolet (UV) light. Melanin can be either yellow-red or brown-black.

What is the role of Merkel cells?

Merkel Cells are also known as "tactile cells". They touch a sensory structure called a tactile (Merkel) disc and function in the sensation of touch. They are located in the stratum basale.

List the glands associated with the skin, and the products they secrete.

Skin glands are of three types as follows: Sebaceous (oil) glands usually are connected to hair follicles; they are absent in the palms and soles. Sebaceous glands produce sebum, which moistens hairs, waterproofs and softens the skin, and inhibits bacterial growth. Sudoriferous (sweat) glands are divided into apocrine and eccrine types. Both are coiled, tubular glands. Eccrine sweat glands help to regulate body temperature through evaporation and to eliminate wastes such as urea. Located throughout body, especially forehead, palms and soles. Located in the deep dermis with ducts going directly to surface of epidermis. Apocrine sweat glands are limited to the skin of the axilla (armpits), pubis, and areolae; their ducts open into hair follicles. Secretory portion located in the subQ layer. (Think APOCRINE --> ADULT --> open to hairs as in sebaceous glands) Ceruminous glands are modified sudoriferous glands that produce a waxy substance called cerumen. These glands are found in the external auditory meatus.

Name the layers of the skin; describe the structure of each; and name the general functions of the skin.

Structurally the skin consists of the following two parts: Epidermis—the superficial portion of the skin composed of epithelial tissue (keratinized stratified squamous epithelium). Dermis—the deeper layer of the skin primarily composed of connective tissue. The subcutaneous layer (Sub Q) or hypodermis lies deep within the dermis. It consists of areolar and adipose tissue. It serves as an area for fat storage, blood vessel passage, and pressure nerve endings.

Distinguish between the papillary layer and the reticular layer of the dermis, and locate the appropriate sensory receptor in each of these layers.

The dermis, composed of connective tissue containing collagen and elastic fibres, has two regions. The papillary layer is areolar connective tissue that contains fine elastic fibres; dermal papillae; corpuscles of touch (Meissner's corpuscles); and free nerve endings for sensations of heat, cold, pain, tickle, and itch. The deeper part of the dermis is the reticular region, which consists of dense, irregular connective tissue that contains bundles of collagen fibres and some elastic fibres. Between the fibres of the deeper part of the dermis are adipose cells, hair follicles, nerves, oil glands, and sweat glands. This layer also sometimes contains (but mostly in subQ) nerve endings called lamellated corpuscles which are sensitive to pressure. Epidermal ridges increase friction for better grasping ability, and provide the basis for fingerprints and footprints. Typically, the ridges reflect contours of the underlying dermis.

List the four/five layers of the epidermis.

The epidermis has four (thin skin) or five layers (thick skin), depending on the degree of friction and mechanical pressure applied to the skin. From the deepest to the most superficial, the layers of the epidermis are the following: stratum basale (stratum germinativum) stratum spinosum (cuboidal cells) stratum granulosum stratum lucidum (only in the palms and soles - thick skin) stratum corneum

Which four cell types make up the epidermis of the skin?

The epidermis is composed of stratified squamous epithelium and contains four principal types of cells: Keratinocytes Melanocytes Langerhans cells Merkel Cells

Describe the hair cuticle.

The hair cuticle is the outermost part of the hair shaft. It is a hard shingle-like layer of overlapping cells, some five to twelve deep. It is formed from dead cells which form scales that gives the hair shaft strength and do the best job of providing protection for it. IMAGE A

What is the muscle called that is connected hairs? Which glands release into hair follicles?

The smooth muscle called the arrector pili extends from the upper dermis to the side of the hair follicle. When contracted, hair stands on end. Sebaceous glands release into the hair follicles (and occasionally directly onto surface of skin).

Describe the functions of the various layers of the epidermis.

The stratum basale is the deepest layer of the epidermis and is composed of a single layer of columnar or cuboidal keratinocytes. It also contains some stem cells capable of undergoing cell division to form new cells. This layer is sometimes called the stratum germinativum to indicate its role in the formation of new cells. The stratum spinosum is the next layer of skin, where 8 to 10 layers of many-sided keratinocytes fit closely together. This layer provides strength and flexibility to the skin. The stratum granulosum marks the transition between the deeper, metabolically active strata and the dead cells of the more superficial strata. It consists of 3-5 layers of flattened keratinocytes undergoing apotosis. The presence of keratin is distinctive of this layer. This layer is also where a water repellent sealant forms between the cells via the secretions of lamellar granules. The stratum lucidum is present only in the fingers, palms, and soles and adds an extra layer of durability. It consists of 3-5 layers of flattened, dead, keratin-filled keratinocytes. The stratum corneum is the most superficial layer; it consists of 25-30 layers of dead cells which are continually shed and replaced. Lamellar granules in this layer make it water-repellent. Constant exposure to friction causes this layer to increase in depth by forming a callus, an abnormal thickening of the epidermis. "Californian Ladies Give Superb Backrubs"

Name the pigment responsible for skin and hair colour, and explain how people of different races (and skin colour) differ with respect to this pigment; and name the cell that produces it.

The wide variety of colours of skin is due to three pigments—melanin, carotene, and hemoglobin (in blood in capillaries)—in the dermis. Melanin causes the skin's color to vary from pale yellow to reddish brown to black. It is produced by MELANOCYTES. The number of melanocytes is generally constant, but pigment produced/transferred to keratinocytes is variable. UV light stimulates melanin production, which leads to tanning. Hemoglobin is the oxygen-carrying pigment in red blood cells. It can affect skin color, especially in light-skinned people (those with little melanin), depending on the oxygen content and amount of blood moving through the capillaries. Carotene is a yellow-orange pigment that is a precursor of vitamin A. It accumulates in the stratum corneum and fatty areas of the dermis when intake is excessive.

Discuss the functions of the skin.

Thermoregulation Protection through physical, chemical, and biological barriers. Cutaneous sensations including: - touch - pressure - vibration - tickle - heat - cold - pain Excretion and absorption Synthesis of Vitamin D

What is the role of lamellar granules?

These are produced by keratinocytes. Lamellar granules release a water-repellant sealant. They are mostly found in the "stratum granulosum". This lipid-rich secretion prevents loss of body fluids and entry of foreign materials.