Chapter 5 - The Integumentary System Review

Papillary layer

consists of a highly vascularized loose, areolar connective tissue with all of the typical cell types within it.

Strata of the Epidermis

(from outer to inner) 1. Stratum Corneum 2. Stratum Lucidum 3. Stratum Granulosum 4. Stratum Spinosum 5. Stratum Basal

Sweat glands

- Eccrine sweat glands - Apocrine sweat glands

Functions of the Integumentary System

A. Protection B. Sensory C. Thermoregulation D. Synthesis E. Storage F. Excretion *secretes ear war

PIGMENATION

A. The color of one's skin is genetically programmed. However, increased pigmentation, or tanning, can result in response to ultraviolet radiation. B. Skin color is influenced by the presence of pigments in the epidermis: 1. Melanin = a brown, yellowish-brown, or black pigment produced by melanocytes. a. Melanocytes are located within the stratum basale, squeezed between or deep to the keratinocytes. Melanocytes manufacture melanin from the amino acid tyrosine, and package it in intracellular vesicles called melanosomes.

The Epidermis

A. The epidermis is formed of several layers called strata. 1. Thin skin, which 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). 2. Thick skin, which occurs on the palms of the hands and soles of the feet, possesses five strata. It is about as thick as a standard paper towel (roughly 0.50 mm). 3. Note that the terms "thick" and "thin" refer to the relative thickness of the epidermis, not the integument as a whole. 4. The cells in all of the layers of the epidermis, except the stratum basale, are called keratinocytes

The Hypodermis

(also known as the subcutaneous layer or superficial fascia) separates the integument from the fascia around the deeper organs. The hypodermis is composed of loose connective tissues like adipose and areolar connective tissue C. The hypodermis separates the dermis of the skin from deeper structures.

3 layers of The Integumentary System

- Epidermis - Dermis - Hypodermis

V. Accessory Organs of the Skin A. Hair and its associated structures

- Hair follicles: the internal root sheath, the external root sheath, and glassy membrane, Here a mass of epithelial cells forms a cap, called the hair bulb that surrounds a smaller hair papilla - The hair matrix is a clump of rapidly dividing basal cells that produce the hair. - Root hair plexus - Associated with each hair follicle is a bundle of smooth muscle cells called an arrector pili muscle

Parts of a Hair

- Hair shaft - Hair root - Cuticle - Cortex - Medulla

Parts of a nail

- Nail body - Nail bed - Nail root - Hyponychium - Eponychium - Lunula

Nails

- thick sheets of keratinized epidermal cells. - it protect the exposed dorsal surfaces of the tips of the fingers and toes. They also help limit distortion of the digits whey they are subjected to mechanical stress

4 types of Sensory receptors

1. Free Nerve Endings 2. Tactile discs 3. Tactile Corpuscles (Meissner's Corpuscle) 4. Lamellated Corpuscles (Pacinian Corpuscle)

VII. Age-related changes and Diseases/Disorders of the Integument A. Age-related changes alter the appearance of structure of the integument

1. Melanocyte activity declines, and in light skinned individuals, the skin becomes pale. With less melanin in the skin, people become more sensitive to sun exposure and more likely to experience sunburn. 2. Sebaceous gland secretions decreases with age and the skin becomes dry and often scaly. 3. The epidermis thins as germinative cell activity declines, and the connections between the epidermis and dermis weakens, making older people more prone to injury, skin tears, and skin infections. 4. The metabolic activity in the skin decreases as well. Synthesis of calcitriol (vitamin D3) decreases leading to muscle weakness and brittle bones. 5. The number of dendritic cells decreases to about half the levels seen at maturity. This reduction in cells may decrease sensitivity of the immune response and further encourage skin damage and infection. 6. The dermis becomes thinner and has fewer elastic fibers, making the integument weaker and less resilient. The results - sagging and wrinkling - are most pronounced in body regions with the most sun exposure. 7. Merocrine sweat glands become less active and with impaired perspiration processes, older people cannot lose hear at fast as younger people. Thus the elder are at greater risk of overheating in warm environments. 8. A reduction in dermal blood supply cools the skin, which can stimulate thermoreceptors and make a person feel cold even in a warm room. Reduced circulation and sweat gland function lessens their ability to lose body heat, which can cause their body temperature to soar dangerously high. 9. With declining levels of sex hormones, differences in secondary sexual characteristics with respect to hair distribution and body-fat distribution begin to fade. As a consequence, people age 90 - 100 of both sexes tend to look alike. 10. Hair follicles stop functioning or produce thinner, finer hairs. With decreased melanocyte activity, these hairs are gray or white.

The Dermis

A. The dermis lies between the epidermis and hypodermis. The dermis consists of two layers: 1. Papillary layer = consists of a highly vascularized loose, areolar connective tissue with all of the typical cell types within it. a. This layer also contains the capillaries, lymphatic vessels, and sensory neurons (called meissner's corpuscles) that supply the surface of the skin. b. The papillary layer gets its name from the dermal papillae that project between the epidermal ridges. c. This layer nourishes and supports epidermis. 2. Reticular layer = consists of an interwoven meshwork of dense irregular connective tissue containing both collagen and elastic fibers. a. Bundles of collagen fibers extend superficially to blend into those of the papillary layer and deeply to blend with the hypodermis. b. The collagen fibers provide strength while the elastic fibers provide flexibility. c. This layer restricts the spread of pathogens, stores lipid reserves, attaches skin to deeper tissues, possesses sensory receptors (like pacinian corpuscles), and contains blood vessels for temperature regulation.

Hemoglobin

The blood supply affects skin color because blood contains red blood cells filled with the red pigment

More characteristics of Epidermis

The deeper layers of the epidermis form epidermal ridges which extend into the dermis and are adjacent to the dermal projections called dermal papillae that project upward to the epidermis, like all other epithelia, the epidermis lacks local blood vessels, that is, they are avascular. Epidermal cells rely of the diffusion of nutrients and oxygen from capillaries within the dermis. As a result the cells with the highest metabolic demand are closest to the underlying dermis.

Stratum Granulosum

a. Consists of 3 - 5 cell layers where the keratinocytes appearance begins to change. The name stratum granulosum means "grainy layer". b. These cells become flattened, the plasma membrane becomes thickened, less permeable, and the organelles deteriorate. c. By the time the cells reach this layer, most have stopped dividing and have started making large amounts of keratin and keratinohyalin stored in numerous visible granules. d. Beyond this layer, there is no nutrient availability.

Stratum Spinosum

a. Consists of approximately 8 - 10 layers of keratinocytes bound together by desmosomes and microfilaments of pre-keratin. b. The name stratum spinosum, which means "spiny layer", refers to the fact that the cells look like miniature pincushions in standard histological sections. c. Large numbers of dendritic cells are found in this layer. These are specialized cells (sometimes called Langerhans cells) that participate in the immune response by stimulating a defense mechanism against 1) microorganisms that manage to penetrate the superficial layers of the epidermis and 2) superficial skin cancers.

Stratum Lucidum

a. In the thick skin of the palms and soles, a stratum lucidum separates the stratum corneum from deeper layers. b. The cells of this layer are flattened, densely packed, largely devoid of organelles, and filled with the proteins eleiden. c. By the time they reach the stratum lucidum, the cells are dead and undergoing dehydration

Stratum Corneum

a. Outermost layer of keratinocytes (sometimes called the "horny layer"). b. A broad zone of 15 - 30 layers of keratinized cells that accounts for up to three-quarters of the epidermal thickness. c. Keratinization is the formation of protective, superficial layers of cells filled with keratin. d. 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 in the exposed stratum corneum for an additional two weeks before they are shed or washed away

Stratum Basale

a. The deepest epidermal layer consisting of a single row of basal cells, or germinative cells, that are undergoing rapid mitotic divisions. These cells are sometimes called stem cells because their mitotic divisions replace the more superficial keratinocytes that are lost or shed at the surface. Basal cells are cuboidal in shape while keratinocytes are squamous shaped cells. b. 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. c. Approximately 10 - 25% of cells in this layer are melanocytes which produce melanin, a brown, yellowish-brown, or black skin pigment. d. In hairless skin, specialized cells called merkel cells exist in small numbers. These cells are sensitive to touch and when compressed, they release chemicals that stimulate sensory nerve endings

Eccrine sweat glands

also called merocrine sweat glands) are highly coiled glands that lie deep in the dermis of the palms, soles of the feet, and forehead. a. Eccrine gland secretions, commonly called sweat, are a hypotonic filtrate of the blood composed mostly of water (90%) and release by exocytosis. b. Once secreted by exocytosis (merocrine), the sweat travels via a duct to the surface of the skin where it opens into a funnel-shaped pore. c. Normal pH of sweat is between 4 and 6.

Carotene

an orange-yellow pigment that normally accumulates in epidermal cells. It is most apparent in cells of the stratum corneum of light-skinned individuals, but it also accumulates in fatty tissues in the deep dermis and hypodermis. Carotene is found in a variety of orange and yellow vegetables (sweet potatoes, carrots, squash).

Apocrine sweat glands

are largely confined to the axillary and anogenital areas. a. Larger than eccrine sweat glands and release their secretions into hair follicles. b. The secretions produced are similar to sweat but they also contain many organic compounds which can be metabolized by bacteria causing it to smell. c. Apocrine glands begin functioning at puberty.

Reticular layer

consists of an interwoven meshwork of dense irregular connective tissue containing both collagen and elastic fibers.

Burns

damage inflicted by intense heat, electricity, radiation or certain chemicals. a. First degree - superficial burn that affects only the epidermis. b. Second degree - goes deeper and affects both the epidermis and a portion of the dermis. c. Third degree - fully extends into the epidermis and dermis, destroying the tissue and affecting the nerve endings and sensory function. d. Fourth degree - even more severe, affecting the underlying muscle and bone.

Sebaceous glands

oil glands, produce sebum 1. Simple alveolar glands that are found all over the body except on the palms and the soles. Sebaceous follicles secrete onto skin surfaces located on the face, back, chest, nipples, and external genitalia. 2. Contractions of the arrector pili muscles squeeze the sebaceous gland and force the sebum (a mixture of triglycerides, cholesterol, proteins, and electrolytes) into the hair follicle and onto the surface of the skin. 3. These glands are the holocrine type, the cells fill up with oil then bust (lysis). 4. Sebum is secreted into a hair follicle, or occasionally a pore, or follicle, on the skin surface. Sebum softens and lubricates hair and surrounding skin and also has anti-bacterial properties. 5. Sebaceous glands tend to be inactive in childhood.