Integument Lecture Flashcards
Integument (Definition)
Skin and derivatives (hair, nails, glands, and specialized receptors)
Skin (cutis) *Definition and 3 types
Heaviest single organ of the body - 16% total body weight
composed of:
A. Epidermis - epithelial tissue - stratified squamous ep. -thinner than dermis
B. Dermis (or cornium) - connective tissue
C. “subcutaneous tissue” or “superficial fascia”
- beneath all this
- this may or may not be considered as part of the skin - but serves to bind the epidermis to subjacent tissues (loose C.T.).
Note: -epidermis is ectodermal derivative
-dermis is mesodermal derivative
Functions of Skin (7)
A. relatively impermeable to water - thus stops movement of most substances into, and loss of fluids out of the body.
B. functions as a receptor organ in continuous communication with environment.
C. protection from impact and friction injuries.
D. protection from U.V. rays - due to melanin - a pigment produced and stored in the epidermis.
E. active in process of thermoregulation - due to its glands, blood vessels, and adipose tissue.
F. excretes water and some salts via glands.
G. involved in synthesis of vitamin D for body’s use.
Epidermis (What it is and 5 layers from the dermis up)
- stratified squamous epithelium (keratinized)
- thickness of epidermis varies in different parts of the body, dependent on the amount of friction (e.g. palm and soles).
1. Stratum Basale
2. Stratum Spinosum
3. Stratum Granulosum
4. Stratum Lucidum
5. Stratum Corneum
Epidermis Layer: Stratum Basale (1st Layer)
Stratum Basale (Stratum Germinativum)
- columnar or cuboidal cells which rest on the basement membrane (dermal-epidermal junction)
- characterized by intense mitotic activity
- responsible for constant renewal of epithelium.
- note: human epidermis renewed approximately every 15-30 days.
- as cells age they move superficially into other layers.
Epidermis Layer: Stratum Spinosum (2nd Layer)
Stratum Spinosum
- cuboidal, polygonal, or slightly flattened cells
- in L.M. preparations may show a “prickle-studded” appearance due to processes (associated with Desmosomes) - thus the name “Spinosum”
- in areas of greater friction, this layer is thicker
Epidermis Layer: Stratum Granulosum (3rd Layer)
(named for Granules in cytoplasm)
- this layer may be absent or very thin in thin skin.
- cells die and nucleus breaks down - can be seen in various stages of degeneration.
- polygonal flattened cells with 2 characteristic types of cytoplasmic granules.
a. Keratohyaline Granules
- visible with L.M.
- not membrane bound - believed to eventually become part of keratin of Stratum Corneum.
b. Membrane Coating Granules
- visible with E.M.
- fuse to membrane and discharge substance into intercellular space. Believed to produce an “intercellular cement” that further prevents penetration of foreign materials.
Epidermis Layer: Stratum Lucidum (4th Layer)
- (means “clear”)
- usually only found in thick skin
- several layers of deal - non-nucleated translucent (thus the name) cells.
Epidermis Layer: Stratum Corneum (5th Layer)
- dead non-nucleated cells whose cytoplasm is filled with the darkly staining protein keratin.
- the outer portions of this layer are constantly being sloughed off.
- serves as a protective barrier to the living cells beneath.
Melanocytes (9 Details)
- *color of the skin is due mainly to pigment = melanin = dark brown pigment - produced by melanocytes = specialized cells of epidermis.
- found between epithelial cells and in the root of hair follicles.
- have round cell bodies with irregular extensions, which extend between cells present in the Basale and Spinosum layers.
- melanin is synthesized in melanocyte cell body and then transferred along cellular extensions to the contacted epithelial cells.
- even though melanin is synthesized in melanocytes it is stored in epithelial cell - thus these cells tend to have more of it.
- The number of melanocytes/unit area is not influenced by sex or race. Skin color differences are mainly due to a difference in the number of melanin granules in the epithelial cells.
- There is a wide variance in the distribution of the number of melanocytes in different areas of the skin. For example: the face and genital regions may contain high concentrations of cells while on the trunk there may only be about 1/2 as many per mm2.
- Tanning - 2-step process - protection from U.V. radiation.
a. preexisting melanin becomes more darkened due to a physiochemical reaction - and it is released into epithelial cell cytoplasm from granules.
b. rate of melanin synthesis by melanocytes is accelerated. - Carotene - less important pigment - found in the fatty areas of the dermis
Dendritic Cells (Langerhans Cells)
cells with dendritic-like processes that migrate into the epidermis and pick up antigens to be presented to lymphocytes as part of the body’s defense.
Dermis (cornium) *6-7 Details
A. Composed of connective tissue - just deep to epidermal epithelium.
B. Supports epidermis and binds it to deeper tissues.
C. Thickness varies according to location on the body.
- thickest on soles of feet - up to 3 mm
D. Outer surface of dermis is very irregular and presents many outgrowths (dermal papillae) - more numerous in areas subject to frequent pressure - believed to increase and reinforce derma-epidermal junction.
E. Contains a rich supply of B.V.’s, lymph vessels, and nerve endings.
F. Two rather indistinct boundaries:
1. Papillary Layer - outermost - thin - composed of loose C.T. - forms dermal papillae - Anchoring Fibrils extend from this layer to basal lamina of overlying epithelium.
2. Reticular Layer - thicker - irregular dense C.T.
*Age - causes collagen fibers to thicken in C.T. and collagen synthesis decreases. Elastic fibers steadily increase.
Epidermal Derivatives: Hairs (Pili) *11 Details
- thin keratinized structures - derived from invaginations of the epidermis.
- color, size, and disposition vary according to race, age, and sex.
- present almost everywhere on the body.
- follicles begin to form during the 3rd month.
- Lanugo - embryonic hair covering (5 or 6 months before birth). Lanugo is replaced by small lightly pigmented hairs called vellus hairs , which cover the entire body.
- larger more pigmented hairs are called terminal hairs (appear on scalp and on other regions after puberty). - -hair growth is discontinuous - periods of growth followed by periods of rest. Occurs at different times and rates over different parts of the body.
- Hair follicle - epidermal invagination resulting in a hair.
- Hair bulb - terminal dilation at hair’s base into which is inserted a terminal papilla (contains B.V.’s for hair’s nourishment).
- Hair Root - epidermal cells covering the terminal papilla.
- Shaft - portion continuing above the bulb and beyond the skin.
- Growth of Hair - cells of the bulb (matrix = germinal layer) differentiate into multiple cell types forming different layers in the hair follicle and these die and push superficially up and above the surface of the skin.
- *Arrector Pili Muscles - smooth muscle cells connecting the basement membrane surrounding the follicle (Glassy Membrane) to the Papillary layer of the dermis in oblique fashion. Produce erection of hair shaft (“goose-flesh”).
- *Hair color is due to melanocyte activity between hair root and dermal papilla – 3 pigment colors: black, brown, yellow - gray or white hair = lack of color.
Epidermal Derivatives: Nails *6 Details
- from modified epidermal cells
- cornified plates on the dorsal surfaces of the terminal ends of digits.
1. Nail bed - thickened epithelial surface on which the nail rests.
2. Nail itself is described as having a Nail body, free edge, and a nail root (embedded portion)
3. Lunula - crescent shaped white area near the root - no good explanation for presence.
4. Growth
a. occurs in nail root or proximal portion of the nail bed called the matrix.
b. as cells divide and differentiate they push the nail more distally out over the nail bed.
c. nail - tightly adherent and compact layer of keratinized epithelial cells.
Epidermal Derivatives: Glands (2 kinds associated with the skin) (6 Details, then 10 Details)
- Sebaceous (Oil) Glands
a. found on all parts of the body’s surface (with and without hair follicles).
b . the duct of which generally opens into the upper portion of a hair follicle. - in certain regions - penis, clitoris, and lips, these glands open directly onto the surface.
c. Holocrine Glands - cells differentiate and fill acini with rounded cells containing abundant fat (oil) droplets. These cells burst and secretion is gradually moved to the skin surface.
d. secretion product - Sebum - fats, cholesterol, proteins, and inorganic salts.
e. keep hair from drying and becoming brittle - also forms a protective film over the skin.
- prevents water loss.
- keeps skin soft and pliable.
f. Problem - Gland secretion is stimulated by sex hormones, which become more active at puberty. - Acne Blackhead - enlarged sebaceous gland - not dirt. - sebum - excellent bacterial medium - pimples or boils can result - increased occurrence during puberty.
- Sudoriferous (Sweat) Glands
a. present on almost all parts of outer body.
b. simple coiled tubular glands except in axilla - simple branched tubular.
c. secretory portion in dermis - surrounded by myoepithelial cells.
d. single excretory duct opening onto outside of epidermis.
e. merocrine glands.
f. contains mostly water, NaCl, Urea, Ammonia, and Uric Acid.
g. might have some limited excretory function.
h. Principle function is regulation of body temperature.
i. Most numerous on palms of hands and soles of feet.
j. Apocrine Sweat Glands - prevalent in lower forms but limited to axilla, genital and anal area, and areola of the nipple in man. Secrete protein containing milky secretion, which becomes strong smelling. Stimulated by adrenergic system (sexual excitement, fear, pain, etc.) but not by heat.
