The Integumentary System

1. The Integumentary System Anatomy / Physiology Mr. Atkinson’s Class Union Grove High School 2014-2015

2. Introduction • This most extensive organ system contains the skin and accessory structures, including hair, nails, glands (sweat and sebaceous), and specialized nerve receptors for stimuli (changes in internal or external environment) such as touch, cold, heat, pain, and pressure. Its functions include protection of internal structures, prevention of entry of disease-causing microorganisms, temperature regulation, excretion through perspiration, pigmentary protection against ultraviolet sunrays, and production of vitamin D. The body stores about half its fat in the underlying hypodermis.

3. Skin: Epidermal Layers • The skin is the largest organ of the body, with a surface area of 18 square feet. Its two main layers are the epidermis (outer layer) and dermis (inner layer). The epidermis has several strata (layers) that contain four cell types. • Keratinocytes produce keratin, a protein that gives skin its strength and flexibility and waterproofs the skin surface. • Melanocytes produce melanin, the dark pigment that gives skin its color. • Merkel's cells are involved with touch reception. • Langerhans' cells help the immune system by processing antigens (foreign bodies)

4. Skin: Epidermal Layers • The epidermis does not have a direct blood supply; all nutrients that feed these cells come from the dermis. Only the deepest cells of the stratum basale receive nourishment. The cells that are pushed away from this layer die. When the cells reach the skin surface, they are sloughed off in a process called desquamation. • During desquamation, keratinocytes are pushed toward the surface. These cells begin to produce the keratin that eventually will dominate their contents. When these cells reach the epidermis outer layer, they are little more than keratin-filled sacs. Millions of these dead cells are worn off daily, creating a new epidermis every 35 to 45 days.

6. Skin: Epidermal Layers • 1)Thestratum corneum, the outermost layer is thick with rows of dead cells. These cells contain soft keratin, which keeps the skin elastic and protects underlying cells from drying out. • 2) The stratum lucidumprotects against sun ultraviolet-ray damage. This thick layer appears only in frequently used areas such as palms of the hands and soles of the feet. Thick skin epidermis has all five strata. Thin skin covers thinner epidermal areas such as eyelids. Thin skin only has three or four of the five strata; it never has stratum lucidum or corneum. • 3) The stratum granulosum, the thin middle layer, initiates keratinization (production of keratin). This process starts the death of epithelial cells (the cell type that makes up skin). • 4) The next layer, the stratum spinosum, consists of spiny prickle cells that interlock to support the skin. • 5) The deepest layer of the epidermis, thestratum basale, is a single layer of cells resting on a basement membrane (layer between the dermis and epidermis). The stratum basale cells divide continuously. As new cells form, older ones are pushed toward the skin surface

7. Skin: Dermal Layers The Dermis, or "true skin," is the layer beneath the epidermis. Its major parts are • collagen (a protein that adds strength), • reticular fibers (thin protein fibers that add support), and • elastic fibers (a protein that adds flexibility). The dermis has two layers: • the papillary layer, which has loose connective tissue, and • the reticular layer, which has dense connective tissue. These layers are so closely associated that they are difficult to differentiate.

8. Dermis: Papillary Layer • The papillary layer lies directly beneath the epidermis and connects to it via papillae (finger-like projections). Some papillae contain capillaries that nourish the epidermis; others contain Meissner's corpuscles, sensory touch receptors. A double row of papillae in finger pads produces the ridged fingerprints on fingertips. Similar patterns in the ridged fingerprints on fingertips are on palms of the hands and soles of the feet. Fingerprints and footprints keep skin from tearing and aid in gripping objects.

9. Dermis: Reticular Layer • The reticular layer of the dermis also contains criss-crossingcollagen fibers that form a strong elastic network. This network forms a pattern called cleavage lines or Langer's lines. • Surgical incisions that are made parallel to cleavage lines heal faster and with less scarring than those made perpendicular. Parallel incisions disrupt collagen fibers less and require less scar tissue (cells that aid in healing) to close up a wound.

10. Dermis: Reticular Layer • The reticular layer also contains Pacinian corpuscles, sensory receptors for deep pressure. This layer contains sweat glands, lymph vessels, smooth muscle, and hair follicles, described in the discussion on hair follicles later in this overview.

11. Subcutaneous Layer: • The hypodermis (subcutaneous layer) lies beneath the dermis. Loose connective tissue such as adipose tissue (fat) insulates the body, conserving heat. It also contains blood vessels, lymph vessels, and the bases of hair follicles and sweat glands. The fat distribution in this layer gives the female form its characteristic curves.

12. The Integumentary System (Part II) • The integumentary system contains the skin, as well as associated structures such as fingernails, hair, and sensory receptors that enable humans to feel pressure, temperature, and pain.

13. Glands • In addition to these structures, it also produces sudoriferous (sweat) glands and sebaceous (oil) glands. • There are two types of sudoriferous glands (sweat glands) located in most of the body: eccrine glands are coiled ducts deep in the skin that connect to the surface; apocrine glands are found in areas such as the armpits. Eccrine glands secrete sweat, a mixture of 99 percent water and 1 percent salts and fats. In warm conditions with low humidity, perspiration (secretion of sweat) and evaporation cool the body.

14. Glands • Apocrine glands, are larger, deeper, and produce thicker secretions than eccrine glands. The secretions of the apocrine glands contain pheromones, substances that enable olfactory (sense of smell) communication with other members of the species. Unlike eccrine glands that respond to heat, apocrine glands respond to stressors by secreting sweat with a characteristic odor. This odor differs from the normal body odor resulting from secretions being decomposed by bacteria on the skin.

15. Glands • Ceruminous glands are modified apocrine glands in the external ear canal lining. They secrete cerumen (earwax), a sticky substance that is thought to repel foreign material.

16. Glands • Sebaceous glands (oil glands) are all over the body except on the palms of hands and soles of feet. The glands empty via ducts into the bases of hair follicles and secrete sebum (a mixture of fats, waxes, and hydrocarbons). Sebum keeps hair moist and prevents skin from drying. Sebaceous glands are numerous on the face and scalp. Increased hormone levels in the blood can produce excessive sebum, which can plug the gland and hair follicle, producing a skin disorder called acne.

17. Hair and Nails • Hair is composed of cornified threads of cells that develop from the epidermis and cover most of the body. Each hair has a medulla, cortex, and cuticle. The medulla in the center contains soft keratin and air. The cortex, the innermost thickest layer, has the pigment that gives hair color. The cuticle, the outermost layer, has cells that overlap like scales. Both the cuticle and cortex have hard keratin.

18. Hair and Nails • The hair root in a hair follicle is embedded beneath the skin. The hair shaft protrudes from the skin. Hair sheds and is replaced constantly during growth and rest phases. Hair has a protective function: for example, eyebrows keep sweat from running into the eyes, nose and ear hairs filter dust from the air, and scalp hairs protect against abrasion and overexposure to sun rays.

19. Hair and Nails • Hair follicles extend into the dermis; the deep ends expanded parts are called hair bulbs. A papilla (connective tissue protrusion that contains capillaries) protrudes into the hair bulb and provides nutrients for the growing hair. The hair follicle walls have an inner epithelial root sheath and an outer dermal root sheath. The epithelial root sheath has an inner and an outer layer that thins as it approaches the hair bulb. It becomes the matrix, the actively growing part of the hair bulb that produces the hair.

20. Hair and Nails • Arrectorpili muscles are smooth muscle cells attached to hair follicles. When they contract, they pull the hair into an upright position, causing skin dimples (goose bumps). The nervous system regulates these muscles; cold temperatures or fright can activate them.

21. Hair and Nails • Like hair, nails develop from the epidermis. These hard plates of keratinized cells are at the ends of fingers and toes. Nails appear pink because their translucency reveals the vasculartissue beneath. They aid in grasping objects, scratching, and protecting fingers and toes.

22. Hair and Nails • The components of the nail are the lunula, body, root, and free edge. The lunula is the white half-moon shaped part at the nail base. Both the body and free edge region that overhangs the end of the finger or toe are visible. The nail rests on the thick layer of epithelial skin called the nail bed. The root is hidden under skin folds. A thin layer of epithelium covers the nail during development; in the adult, it remains at the nail base only and is called the cuticle.

23. Skin Color • Skin color results from the presence of melanin, carotene (yellow to orange pigment), and underlying blood reflected through skin. Melanin keeps excessive ultraviolet rays from burning the skin. Exposure to sunlight causes the skin to produce more melanin, causing suntan, a temporary change in skin color. Melanin-rich cells continually move toward the surface, where they are sloughed. Too much sun is dangerous to skin; it increases the risk of cancer by affecting the genetic material of cells.

24. Skin Color • Variety of skin color is caused mainly by the number and distribution of melanocytes. Darker skin has more melanin that is produced by more melanocytes. However, the different skin colors among individuals and races do not reflect different numbers of melanocytes; instead, they show different kinds and amounts of melanin production by melanocytes. Oriental skin has a greater amount of carotene in the stratumcorneum, (uppermost layer of the epidermis) producing a yellowish tinge. Albinism is a condition where skin does not produce melanin and therefore has no color.