Integumentary System

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Major layers of the epidermis and dermis, functions, structures of the integumentary system and their functions, and homeostatic responses to integumentary imbalances

What is the Integumentary System

The skin -- a complex set of organs that covers and protects body.

Name the organs that are involved in the integumentary system.

Skin, hair, nails, and sebaceous (sweat and oil) glands

Name the functions of the integumentary system

Waterproof, cushion, protect the deeper tissues, excrete waste, regulate temperature, provide sensory input and synthesize vitamin D.

How do the structures of the integumentary system relate to its functions?

Outer layer - epidermis has keratinized protective layer; second layer- dermis has secretion glands, blood vessels, hair follicles and receptors; third layer - subcutaneous has fatty cushion.

How do the structures of the integumentary system work together to maintain homeostasis in the body?

Provides protection, regulation of body temperature (sweat or shiver), sensory reception, water balance, synthesis of vitamins and hormones and absorption of materials.

The Skin

1.5-4.0 millimeters (mm), composed of two distinct regions, the epidermis and dermis

Epidermis

Composed of epithelial cells, is the outermost protective shield of the body. A keratinized stratified squamous epithelium consisting of 4 distinct cell types and 4 or 5 distinct layers.

Dermis

Makes up the bulk of the skin, is a tough leathery layer composed mostly of fibrous connective tissue. Only the dermis is vascularized.

Hypodermis (Superficial Fascia)

The subcutaneous tissue deep to the skin. It is not part of the skin, but it shares some of the skins protective functions. It is superficial to the tough connective tissue wrapping (fascia) of the skeletal muscles, consists mostly of adipose tissue. Functions: Anchors the skin to the underlying structures (mostly muscle), acts as a shock absorber.

Name the cells of the Epidermis

Keratinocytes, Melanocytes, Epidermal Dendritic cells (Langerhans' cells), and Merkel or tactile cells.

MNEMONIC: Keran Massaged ED Langerhan's Muscles Tactfully

Keratinocytes

Main role is to produce keratin, the fibrous protein that helps give the epidermis its protective properties.

Melanocytes

The spider-shaped epithelial cells that synthesize the pigment melanin, are found in the deepest layer of the epidermis. As melanin is made it is accumulated in membrane bound granules called melanosomes, that are moved along actin filaments by motor proteins to the ends of melanocytes processes. from there taken up by keratinocytes. Accumulate in superficial side of keratinocyte nucleus. (All humans have same number of melanocytes)

Epidermal Dendritic Cells

Arise from bone marrow and migrate to the epidermis. Also called Langerhans cells.

Functions: they ingest foreign substances and are key activators of the immune system.

Merkel or Tactile Cells

Are present at the epidermal-dermal junction. Shaped like a spiky hemisphere. Each cell is associated with a disclike sensory nerve ending. (touch receptors)

Layers of the Epidermis

Thick skin which covers the palms, fingertips, and soles of feet; Epidermis consists of 5 layers, or strata (bed sheets); superficial to deep: Stratum Corneum, Stratum Lucidum, Stratum Granulosum, Stratum Spinosum and Stratum Basale.
MNEUMONIC: Cora, Luci's Grandma, Spins Baseballs.

Layers of the Epidermis (b)

Superficial to deep: Stratum Corneum, Stratum Lucidum, Stratum Granulosum, Stratum Spinosum and Stratum Basale.

MNEUMONIC: Cora, Luci's Grandma, Spins Baseballs.

Stratum Corneum (Horny Layer)

20 to 40 cell layers of dead, flat keratinized, membranous sacs, accounts for up to 3/4s of epidermal thickness.

Functions: Protects from abrasion and penetration, Waterproofs, Barrier against biological, chemical, and physical assaults

Stratum Lucidum (Clear Layer)

Appears as a clear translucent band just above the stratum granuosum. 2 to 3 rows of flat, dead keratinocytes.

Stratum Granuosum (Granular Layer)

Thin layer that consists of 3 to 5 layers in which keratinocyte appearance changes drastically and the process of keratinization (in which the cells fill with the protein keratin) begins. Keratohyaline help form keratin in upper layers, and lamellated granules spew a water resistent glycolipid into the extracellular space slowing water loss across epidermis making the outter skin more tough.

Stratum Spinosum (Prickly Layer)

Several cell layers thick, cells contain a weblike system of intermediate prekeratin filaments attached to desmosomes. Keratinocytes appear to have spines and are scattered among abundant melanin granules and Langerhans' cells.

Stratum Basale (Basale Layer)

Deepest epidermal layer firmly attached to the dermis, Single row of stem cells, Also called stratum germinativum: cells undergo rapid division, Journey from basal layer to surface
Takes 25-45 days, 10 - 25% made of melanocytes

Dermis (b)

The second major skin region, is strong flexible connective tissue. Its cells are fibroblast, macrophages and occasional mast cells. Richly supplied with nerve fibers, blood vessels, and lymphatic vessels. Has two layers, papillary and reticular layers

Papillary Layer

Thin superficial layer is aerolar connective tissue, with fine interlaced mat of loosely woven collegen and elastic fibers. Has superior surface callled dermal papillae.

Dermal Papillae

Contain Capillary loops, Meissner's corpuscles (touch receptors), Free nerve endings (pain receptors). Indent overlying epidermis.

Reticular Layer

Accounts for 80% of the thickness of the dermis, it is coarse, irregularly arranged, and dense fibrous connective tissue. Collagen fibers provide strength and resiliency, Elastic fibers provide stretch-recoil properties.

Skin Color

Three pigments contribute to skin color: melanin, carotene, and hemoglobin.

Melanin

Made in the skin. A polymer made of tryosine amino acids. Range in colors from yellow to tan to reddish-brown to black. Its synthesis depends on an enzyme in melanocytes called tyrosinase and it passes from malanocytes to the basal keratinocytes.

Carotene

Yellow to orange pigment, that tends to accumulate in the stratum corneum and in fatty tissue of the hypodermis. Its color is most obvious in palms and soles of feet, where stratum corneum is the thickest.

Hemoglobin

The pinkish hue of fair skin, refects oxygenated hemoglobin in the blood cells circulating through dermal capillaries.

Name the Appendages of the Skin

The nails, sweat glands, sebaceous (oil) glands, hair follicles and hair.

Sweat Glands

Aka sudoriferous glands, are distributed all over the body, except nipples and parts of external genetelia. up to 3 million per person. Two types of glands, eccrine and apocrine.

Eccrine Sweat Glands

Secreting glands, are far more numerous and are abundant on palms, soles of feet and forehead. Each is a simple, coiled, tubular gland. Ducts connect to pores. Sweat: 99% water, NaCl, vitamin C, antibodies, dermcidin and metabolic wastes.

Apocrine Sweat Glands

Approx. 2000 of them are confined in axillary and anogenital areas. Release product by exocytosis. They are larger and lie deeper in the dermis, and ducts empty into hair follicles. Sebum: sweat + fatty substances and proteins. Functional from puberty onward (as sexual scent glands?)

Ceruminous Glands

Modified specialized apocrine glands found in the lining of the external ear canal. Secretion mixes with sebum and produces cerumen or earwax.

Mammary Glands

Secrete milk

Sebaceous (Oil) Glands

Simple branched alveolar glands that are found all over the body except in the thick skin of palms and soles. Small on body trunk and limbs but large on face neck and upper chest. Secrete oily substance called sebum. Most develop from hair follicles, Become active at puberty.

Sebum

Oily holocrine secretion. Bactericidal. Softens hair and skin.

Hair or Pili

Produced by hair follicles, consists of dead keratinized cells. 3 Layers of keratinized cells (medulla, cortex, cuticle)
Functions: Alerting the body to presence of insects on the skin, guards scalp against physical trauma, heat loss, and sunlight

Distribution: Entire surface except palms, soles, lips, nipples, and portions of external genitalia.

Contains hard keratin; more durable than soft keratin of skin
Hair pigments: melanins (yellow, rust brown, black)

Gray/white hair: decreased melanin production, increased air bubbles in shaft

Medulla

Central core of hair, consists of large cells and spaces. Soft keratin absent in fine hairs.

Cortex

A bulky layer surrounding the medulla, consists of several layers of flattened cells

Outermost Cuticle

Formed from a single layer of cells that overlap one another from below the shingles on a roof. Provides strength and helps keep inner layers tightly compacted.

Hair (image)

Cross section of a hair and hair follicle.

Hair Follicles

Longitudinal view of the hair bulb in the follicle from the epidermal surface into dermis. Two-layered wall: outer connective tissue root sheath, inner epithelial root sheath, Hair bulb: expanded deep end

Hair follicle receptor (root hair plexus)

Sensory nerve endings around each hair bulb. Stimulated by bending a hair

Arrector pili

Smooth muscle attached to follicle, Responsible for "goose bumps"

Vellus (Hair Type)

Pale, fine body hair of children and adult females.

Terminal (Hair Type)

Coarse, long hair of eyebrows, scalp, axillary, and pubic regions (and face and neck of males).

Hair Growth

Growth phase (weeks to years) followed by regressive stage and resting phase (1-3 months), Growth phase varies (6-10 years in scalp, 3-4 months in eyebrows)

Nail

Scalelike modification of the epidermis on the distal, dorsal surface of fingers and toes.

Functions of Integumentary System

1. Protection
2. Body Temperature Regulation
3. Cutaneous Sensation
4. Metabolic Functions
5. Blood Reservoir
6. Excretion

Protection

Three types of barriers:
1. Chemical (Low pH secretions (acid mantle) and defensins retard bacterial activity)
2. Physical/Mechanical (Keratin and glycolipids block most water and water- soluble substances limite penetration of skin by lipid-soluble substances, plant oleoresins (e.g., poison ivy), organic solvents, salts of heavy metals, some drugs)
3. Biological (Dendritic cells, macrophages, and DNA)

Body temperature regulation

~500 ml/day of routine insensible perspiration (at normal body temperature). At elevated temperature, dilation of dermal vessels and increased sweat gland activity (sensible perspirations) cool the body.

Cutaneous Sensations

Temperature, touch, and pain

Metabolic Functions

Synthesis of vitamin D precursor and collagenase
Chemical conversion of carcinogens and some hormones.

Blood Reservoir

The dermal vascular supply can hold up to 5% of body's blood volume.

Excretion

Limited amounts of nitrogenous wastes and salt are eliminated in sweat.

Skin Cancer

Most skin tumors are benign (do not metastasize). Risk factors: overexposure to UV radiation, frequent irritation of the skin. Some skin lotions contain enzymes in liposomes that can fix damaged DNA.

3 types: Basal Cell Carcinoma, Squamous Cell Carcinoma, Melanoma

Basal Cell Carcinoma

Least malignant, most common, Stratum basale cells proliferate and slowly invade dermis and hypodermis, Cured by surgical excision in 99% of cases.

Squamous Cell Carcinoma

Second most common, Involves keratinocytes of stratum spinosum. Most common on scalp, ears, lower lip, and hands. Good prognosis if treated by radiation therapy or removed surgically.

Melanoma

Most dangerous. Involves melanocytes. Highly metastatic and resistant to chemotherapy. Treated by wide surgical excision accompanied by immunotherapy.

Characteristics (ABCD rule)
A: Asymmetry; the two sides of the pigmented area do not match
B: Border exhibits indentations
C: Color is black, brown, tan, and sometimes red or blue
D: Diameter is larger than 6 mm (size of a pencil eraser)

Rules of Nines

Used to estimate the volume of fluid loss from burns.

First Degree Burns

Epidermal damage only, Localized redness, edema (swelling), and pain.

Second Degree Burns

Epidermal and upper dermal damage. Blisters appear.

Third Degree Burns

Entire thickness of skin damaged. Gray-white, cherry red, or black. No initial edema or pain (nerve endings destroyed). Skin grafting usually necessary.

Developmental Aspects: Fetal

Ectoderm - epidermis , Mesoderm - dermis and hypodermis , Lanugo coat: covering of delicate hairs in 5th and 6th month, Vernix caseosa: sebaceous gland secretion; protects skin of fetus.

Developmental Aspects: Adolescent to Adult

Sebaceous gland activity increases. Effects of cumulative environmental assaults show after age 30, Scaling and dermatitis become more common.

Developmental Aspects: Old Age

Epidermal replacement slows, skin becomes thin, dry, and itchy. Subcutaneous fat and elasticity decrease, leading to cold intolerance and wrinkles, Increased risk of cancer due to decreased numbers of melanocytes and dendritic cells.

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