Skin and Its Tissues Chapter 06 Quiz

Chapter 06 Lecture Outline

• PowerPoint slides contain figures and tables, omitting notes.

Skin and Its Tissues

• Two or more tissue types grouped together, performing specialized functions, make up an organ.
• Skin is the largest organ in the body by weight.
• Another name for skin is the cutaneous membrane.
• Skin, along with its accessory structures (hair, nails, glands, and sensory receptors), constitutes the integumentary system.
• Skin is composed of several tissue types.
• Skin has two layers: epithelial tissue atop connective tissue.
• The outer layer is the epidermis.
• The deeper layer is the dermis.

Epidermis Tissues

• The outer layer is composed of stratified squamous epithelium.
• A basement membrane separates the epidermis from the dermis.
• The dermis is the thicker of the two skin layers, composed of connective tissue.
• The dermis contains collagenous and elastic fibers. (subcutaneous layer/hypodermis)
• The subcutaneous layer/hypodermis is beneath the dermis; acting as an insulating layer. This layer contains areolar and adipose connective tissue.
• The subcutaneous layer is not considered part of the skin.

Figure 6.1 Skin and Its Tissues

• Pictures are included of stratified squamous epithelium, dense irregular connective tissue, and adipose tissue.

Figure 6.2 Basic Structure of the Skin

• Diagram showing the epidermis, dermis, and subcutaneous layer.
• Components such as sweat glands, hair follicles, sebaceous glands, and nerve cells are identified within the dermis layer.

Epidermis

• Stratified squamous epithelium that rests on the basement membrane
• Lacks blood vessels
• Deepest layer, stratum basale, is nourished by blood vessels in the dermis
• Cells migrate toward the free skin surface, away from the nutrient supply.
• Keratinization: cells harden, dehydrate, and accumulate keratin as they move outward.
• Keratin is a tough, fibrous, waterproofing protein produced and stored in cells.
• Cells form a tightly packed stratum corneum outer layer, with desmosomes binding the cells together
• Stratum corneum cells slough off the skin surface.
• Thickest on palms and soles (0.8-1.4 mm), thinner elsewhere (0.07-0.12 mm).

Figure 6.3 Epidermis

• Diagram of the five layers of the epidermis:

  • Stratum corneum (outermost layer); dead keratinized cells.
  • Stratum lucidum (only in thick skin); palms and soles.
  • Stratum granulosum
  • Stratum spinosum
  • Stratum basale (deepest layer); mitotic layer.

• Function is to protect against water loss, harmful chemicals, mechanical injury, and pathogens.

Table 6.1 Layers of the Epidermis

• Details about each layer of the epidermis, including locations and characteristics.

Figure 6.4 Epidermis

• Melanocytes in the stratum basale produce melanin, the dark pigment that absorbs UV light and provides skin color.
• Melanin protects skin cells from UV light damage (DNA damage, fibroblast damage, and skin cancer).

Epidermis: Skin Color

• Factors affecting skin color:
  • Hereditary factors include the number of melanocytes and the amount and distribution of melanin granules. Albinos lack melanin.
  • Environmental factors include sunlight, UV light, and X-rays.
  • Physiological factors include oxygenation in the blood of dermal blood vessels (pinkish, cyanosis), vasodilation/vasoconstriction, and accumulation of carotene.

Clinical Application 6.1 Indoor Tanning and Skin Cancer

• Exposure to sunlight or tanning beds increases melanin production, darkening the skin.
• Tanning beds deliver high doses of UV radiation overwhelming the body's natural defense against skin cancer.
• Skin cancers (basal cell carcinoma and squamous cell carcinoma) arise from epithelial cells.
• Melanomas, arising from melanocytes, are the least common skin cancer but cause 80% of skin cancer deaths.

Dermis

• Inner layer of skin, average thickness is 1-2 mm.
• Contains dermal papillae between epidermal ridges that bind epidermis to underlying tissues.
• Contains connective tissue and muscle fibers.
• Contains nerve cell processes.
• Dermal blood vessels supply nutrients to skin cells.
• Contains hair follicles, sweat glands, and sebaceous glands.
• Contains sensory receptors (lamellar and tactile corpuscles).

Dermis Layers

• Papillary layer: Superficial layer composed of areolar connective tissue; thinnest layer; location of dermal papillae.
• Reticular layer: Deeper layer made of dense irregular connective tissue; thicker layer than the papillary layer.

Accessory Structures of the Skin

• Accessory structures extend into the dermis or hypodermis from the epidermis.
• Include hair follicles, nails, and skin glands (sweat and sebaceous).
• If accessory structures remain intact, the injured/burned dermis can regenerate.

Nails

• Protective coverings on ends of fingers and toes.
• Three parts: nail plate, nail bed, and lunula (most active growing region).

Figure 6.7 Hair Follicles

• Hair is found on all skin surfaces except palms, soles, lips, parts of external reproductive organs.
• A hair follicle is a tube-like depression from which hair develops, extending into the dermis or subcutaneous layer.
• Three parts of hair: hair bulb (dividing cells), hair root, and hair shaft (dead, keratinized cells).
• Hair follicles contain blood vessels to nourish hair.
• Hair color is related to the type and amount of melanin in the shaft produced by melanocytes.
• Arrector pili muscle (goosebumps) cause hair to stand erect.

Clinical Application 6.2 Hair Loss

• Common type of baldness is pattern baldness (androgenic alopecia), caused by lowered testosterone levels in men and estrogen levels in women.
• Progenitor cells are lacking in bald spots, but stem cells are present.
• Alopecia areata: autoimmune hair loss caused by antibodies attacking hair follicles.

Figure 6.9 Skin Glands: Sebaceous Glands

• Holocrine glands usually associated with hair follicles.
• Produce sebum (fatty material and cellular debris) which keeps hair and skin soft and waterproof.
• Excess sebum can result in acne and is absent on palms and soles.

Clinical Application 6.3 Acne

• Acne is a sebaceous gland disorder, common at puberty due to gland response to androgens.
• Acne occurs when sebaceous glands become clogged with sebum and epithelial cells. This provides an environment for anaerobic bacteria causing inflammation.
• Occurs in 80% of people between 11 and 30.
• Treatment involves Vitamin A derivatives, systemic antibiotics, salicylic acid, and benzoyl peroxide.

Figure 6.10 Skin Glands: Sweat Glands

• Also called sudoriferous glands, widespread in skin originating in deeper dermis or hypodermis.
• Eccrine (merocrine) glands are the most numerous and respond to body temperature.
• Apocrine sweat glands are located in axillary and groin areas; respond to emotions and pain.
• Other glands include ceruminous (ear wax) and mammary (milk).

Table 6.2 Skin Glands

• Description and function of each type of skin gland.

Skin Functions

• Protective covering (barrier against harmful substances, microorganisms).
• Prevents water loss.
• Contains sensory receptors.
• Excretes wastes.
• Helps produce vitamin D.
• Helps regulate body temperature.

Regulation of Body Temperature

• Important for maintaining metabolic rates, monitored by the hypothalamus.
• Set point is ~37 °C (98.6 °F).
• Skin plays a role in homeostatic mechanisms for temperature regulation.

Heat Production and Loss

• Heat is a product of cellular metabolism (skeletal and cardiac muscles, liver cells produce most heat).
• Methods of heat loss include radiation, conduction, convection, and evaporation (sweat changes to gas).
• Vasodilation of dermal blood vessels increases heat loss when the body is too hot.
• Vasoconstriction of deep blood vessels when the body is cold to conserve heat.

Figure 6.12 Body Temperature Regulation

• Diagram illustrating mechanisms for maintaining body temperature when it rises and when it falls.
• Signals to regulate the body temperature are sent through thermoreceptors to the hypothalamus (control center).

Problems in Temperature Regulation

• Hyperthermia: occurs when sweat cannot evaporate and heat from the air increases body temperature. Signs of hyperthermia include dry skin, weakness, dizziness, nausea, and rapid pulse.
• Hypothermia: unusually low body temperature resulting from extended cold exposure or illness. Signs of hypothermia include shivering, confusion, lethargy, loss of reflexes and consciousness.

Clinical Application 6.4 Elevated Body Temperature

• When the body loses the ability to regulate temperature in extremely hot environments, it can lead to hyperthermia.
• Raising the set-point (temperature range) of the body can be part of the immune system's defense mechanism to fight infections.
• Phagocytes release pyrogens in response to pathogens, increasing the set point and thus body temperature to destroy the pathogens.

Healing of Wounds and Burns

• Inflammation is a normal response to injury or stress. Blood vessels in affected tissues dilate, becoming more permeable.
• The damaged skin may become swollen, red, warm, or painful.

Cuts

• Shallow cuts (affecting only the epidermis) cause epidermal cells to divide more rapidly to fill gaps.
• Deep cuts (affecting dermis and subcutaneous layer) result in blood vessel breakage.
  • Blood creates a clot.
  • Clot and dried tissue form a scab.
  • Epithelial cells reproduce and fill the wound.
  • Fibroblasts produce collagen fibers to bind the wound.
  • Phagocytic cells remove dead cells and debris.
  • Excess collagen can form a scar.

Figure 6.13 Healing of a Wound

• Diagram of the healing process in wounds showing stages of healing.

Burns

• Burns are classified by tissue damage extent.
  • Superficial (first-degree) burns affect only the epidermis, causing redness, heat, and inflammation (sunburns).
  • Deep partial-thickness (second-degree) burns destroy the epidermis and some dermis and may blister.
  • Deep full-thickness (third-degree) burns destroy epidermis, dermis, and accessory structures. Healing occurs from the margin and often requires skin grafts.

Figure 6.15 Rule of Nines for Burn Patients

• A method for estimating the extent of burn injury by dividing the body surface into regions of 9% or multiples of 9.
• Estimations are used for fluid and electrolyte replacement and skin grafting.

Life-Span Changes

• Cell cycle slows; skin becomes scaly, age spots appear.
• Epidermis and dermis thin.
• Fat loss reduces; person feels cold.
• Skin wrinkles and sags.
• Sebaceous glands produce less oil. Skin becomes dry.
• Melanin production slows, hair whitens.
• Hair thins.
• Hair follicle numbers decline.
• Nail growth declines.
• Sensory receptors decline.
• Body temperature regulation less effective.
• Ability to produce vitamin D declines.