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Human Anatomy & Physiology

Chapter 6: Skin & the Integumentary System

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II. 6.1 Skin & Its Tissues

A. Skin is an organ – one of the larger and more versatile of the body.

The Integumentary system consist of • the skin and• its accessory organs, such as

nailshair folliclessebaceous glandssweat glands

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II. 6.1 Skin & Its Tissues

B. The skin forms a barrier between ourselves & the outside; it is also vital in maintaining homeostasis. Functions include:• protective covering• helps with regulation of temperature• retards water loss (maintaining fluid & electrolyte balance)• houses sensory receptors• synthesizes biochemical (ex: vitamin D)• excretes small quantities of waste

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II. 6.1 Skin & Its TissuesC. Skin is considered an organ because it is made up of at least 2

different types of tissue; specifically, these tissues:• in the epidermis layer (this layer lacks blood vessels)

stratified squamous epithelium• in the dermis (thicker than the epidermis; contains hair follicles,

nerve fibers, sensory fibers, sweat & sebaceous glands)connective tissue (collagenous & elastic fibers) which gives skin elasticityepithelial tissue smooth muscle tissuenervous tissuevascular tissue (blood vessels which supply nutrients & helps regulate

body temperature)

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II. 6.1 Skin & Its Tissues

C. (continued)• the subcutaneous layer (not a true layer of skin) functions to bind

the skin to underlying organs – aka hypodermisconsist of loose connective tissue and adipose tissue

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II. 6.1 Skin & Its Tissues (see also p.114 in textbook)

D. Label skin illustration

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II. 6.1 Skin & Its TissuesE. Layers of the Epidermis

1. The stratum basal (aka stratum germinativum) is close to the nutrient supply of the dermis; it is made up of actively dividing cells, so its function is the production of new skin cells. • As new skin cells are produced they push upward; as they are moved upward (by

the production of newer cells) they die (lose the nutrient supply) and harden (become keratinized).

• The oldest skin cells are shed as younger cells are pushed upward. This loss of older cells and production of new cells is carefully balanced

2. The stratum corneum is a layer if dead, keratinized cells that provide “waterproofing” for the skin

Note: The stratum lucidium is found only in the palms of the hands & soles of the feet where the epidermis is thicker!!

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II. 6.1 Skin & Its TissuesF. Protection from UV radiation

E. 3. In areas where the skin is regularly subjected to rubbing or pressure, there is an increase in cell reproduction. This results in the formation of corns or calluses.

F. Deep layers of the skin are protected from ultraviolet radiation in sunlight by the pigment melanin.• Melanin is produced by specialized cells in the epidermis called melanocytes.• Melanin absorbs UV radiation preventing mutations of DNA in skin cells

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II. 6.1 Skin & Its TissuesG. Skin Color

1. Environmental factors that influence skin are sunlight, UV radiation, & X-rays which stimulate melanocytes to produce more melanin – resulting in darker skin

NOTE: all people have about the same number of melanocytes; skin color differences results from differences in the amount of melanin produced and the distribution of melanin granules.

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II. 6.1 Skin & Its TissuesG. Skin Color

2. Physiological factors that influence skin are:• blood in the dermal vessels

well-oxygenated blood is bright red (due to high concentration of hemoglobin) & can make the skin of fair-complexioned people appear pinkish

When hemoglobin concentration is low ( low blood oxygen concentration) the skin of fair-complexioned people appear bluish (aka cyanosis)

• diets high in β-carotene may turn skin orange-yellow• biochemical imbalances

such as build up of bilirubin which can cause a jaundiced (yellowish) appearance of skin

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II. 6.1 Skin & Its TissuesH. Dermis & Subcutaneous

LayerDermisThe boundary between the epidermis and dermis is uneven due to inward projections of epidermal ridges and resulting conical projections of the dermis (called dermal papillae) extending into the spaces between the epidermal ridges. Fingerprints form from these undulations of the skin.

Genes determine fingerprint patterns, but the patterns can change slightly as the fetus moves and the forming ridges are pressed against the uterine wall.

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II. 6.1 Skin & Its TissuesH. Dermis & Subcutaneous

LayerDermis (continued)The dermis • is the innermost layer of the skin• composed of collagenous & elastic fibers (these fibers decrease as you age

= wrinkles)• Contains the dermal blood vessels which supply nutrients to all skin cells &

help regulate body temperature

The collagenous & elastic fibers of the dermis are continuous with the subcutaneous layer

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II. 6.1 Skin & Its TissuesH. Dermis & Subcutaneous

LayerThis layer is composed of collagenous & elastic fibers and adipose tissue.• The adipose tissue acts as an insulator – decreasing

heat loss to the environment• This layer also contains the major blood vessels

supplying the skin & adipose tissues

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II. 6.1 Skin & Its Tissues; I. Skin Cancer: Cutaneous Carcinoma & Cutaneous Melanoma

Cutaneous Carcinoma (aka squamous cells or basal cell carcinoma)• Most common type of skin cancer• Originate from epithelial cells• Occurring most frequently in fair-skinned people regularly exposed to

sunlight; may result because normal peeling of sun-damaged skin (apoptosis) fails to occur• Arise from hard, dry, scaly growths that have reddish bases• Typically slow growing and can usually be cured completely by

surgical removal or radiation treatment

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II. 6.1 Skin & Its Tissues; I. Skin Cancer: Cutaneous Carcinoma & Cutaneous Melanoma

Cutaneous Melanoma• Develop from melanocytes (so these cancers are pigmented)• Exhibit a variety of colored areas: browns, black, gray, or blue• Irregular (versus smooth) outlines & may feel bumpy• Seem to be caused by short, intermittent exposures to high-

intensity sunlight (occasional blistering sunburns)• First spreads horizontally (more easily treated surgically);

eventually thickens & spreads into deeper tissue (becomes difficult to treat). Currently there are investigations into a type of gene therapy called cancer vaccine (stimulate immune system)

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III. 6.2 Accessory Organs of the SkinA: Nail The white, moon-shaped region at the base of

the nail (called the lunula) is the growing portion of the nail.

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III. 6.2 Accessory Organs of the Skin B: Hair• Each hair develops at the bottom

of a tube called a follicle which extends to the surface of the skin• At the base of the hair follicle is an

area of actively dividing epithelial cells called the hair root• The epithelial cells divide & push

earlier cells upward towards the skin; as they move away from the root, they die, become keratinized, & are a hair shaft

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Hair pigmentation: Dark = abundant melanin; Light / blonde = intermediate melanin;White = no melaninRed = pigment is trichosiderinGray = mixture of pigmented & unpigmented hair

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III. 6.2 Accessory Organs of the SkinC: Hair & Cold Temperature /

EmotionWhen stimulated by cold or emotional upset, the arrector pili contracts, causing the hair within the follicle to stand on end and a goose bump is formed. (WHY?)Note: when a muscle contracts, heat is releasedGoose bump (cutis anserine) & hair raising may be a vestigial reflex – animals look bigger = scare away predator

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III. 6.2 Accessory Organs of the SkinD: Sebaceous Gland

Sebaceous glands are usually associated with hair follicles • Are holocrine glands that secrete

an oily mixture of fatty material and cellular debris called sebum.• Sebum keeps the hair & skin soft,

pliable, & waterproof• Acne (acne vulgaris) is a disorder

of the sebaceous glands (overactive & inflamed glands become plugged)

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III. 6.2 Accessory Organs of the SkinE: Skin Section Diagram

Figure 6.1: A Section of Skin

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III. 6.2 Accessory Organs of the Skin F. Sweat GlandsSweat Glands are exocrine glands (ducts open onto surfaces)

Eccrine sweat glands• active throughout life; • respond to increase in body

temperature due to exercise or stress;• located on forehead, neck, &

back

Apocrine sweat glands• become active at puberty• Respond to elevated body

temperature, stress, fear, pain, & sexual arousal• most numerous in the axillary

region (air pit) and in the groin

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IV. Regulation of Body Temperature (set point = 98.6°F)Slight shifts in body temperature affects all metabolic activitiesTemperature > 37°C (or 98°F), the body needs to cool• heat from metabolically active cells is

transferred to blood in blood vessels• hypothalamus stimulates blood vessels

near surface of skin to dilate • at the same time, nervous system

stimulates sweat glands to produce sweat

• as sweat is evaporated heat is carried away, skin is cooled, blood in vessels near the skin is cooled

• cooled blood is circulated through system, hotter blood is brought to service

Temperature < 37°C (or 98°F), the body needs to warm• blood vessels of the skin

constrict, directing blood flow away from skin; this keeps heat near vital internal organs and restricts heat loss from skin

• nervous systems stimulates muscles to contract (which causes production of additional heat). We call this shivering!

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V. Healing of Wounds A: InflammationInflammation is the body’s response to injury and is meant to promote healing & wall off damage. The symptoms of inflammation are:• erythema (redness) is due to vasodilation that brings additional blood

to the area & increases permeability (forcing nutrient-containing fluid to leave the vessels & enter the tissue); nutrients needed for healing!• heat is a by-product of the increased metabolic activity as WBCs

attempt to fight off invaders• swelling is due to the increase of fluids in the area• pain is due to the pressure on nerve endings in the area (caused by

the swelling)

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V. Healing of Wounds B: Shallow vs Deep WoundsShallow wounds can be healed by an increased division of epithelial cells along the border of the wound until the break in the skin is healed.When a wound extends into the dermis or subcutaneous layer blood vessels break, • blood escapes into the wound, and a clot is formed. The clot forms a scab

that covers & protects the wound• fibroblasts migrate into area & form new collagenous fibers which bind the

wound together• as healing progresses, blood vessels extend beneath the scab, phagocytes

enter the area and remove dead cells & debris• damaged tissues are replaced, the scab shrinks & falls off. • Wound is healed