Chapter 4: Integumentary system (skin)

Under the Epithelial membranes

Cutaneous membranes, Mucous membranes, Serous membranes

Under the Connective tissue membranes

Synovial membranes

Functions of body membranes

Cover body surfaces. Line body cavities. Form protective sheets around organs.

Epithelial Membranes

simple organs also called covering and lining membranes

These Epithelial Membranes contain

Epithelial tissue layer, Connective tissue layer

Cutaneous membrane

= skin. Dry membrane, Outermost protective boundary

Construction of Epithelial Membranes

epidermis and dermis

Epidermis

is composed of keratinized stratified squamous epithelium

Dermis

is mostly dense (fibrous) connective tissue

Mucous membranes (mucosae)

Moist membranes. Line all body cavities that open to the exterior body surface. Adapted for absorption or secretion

Construction of Mucous membranes (mucosae)

Epithelium type depends on site. Loose connective tissue (lamina propria)

Serous membranes (serosae)

Line open body cavities that are closed to the exterior of the body. Occur in pairs, separated by serous fluid, with a visceral and parietal layer.

Construction of Serous membranes (serosae)

Simple squamous epithelium, Areolar connective tissue

Specific serous membranes

Peritoneum, Pleura, Pericardium

Peritoneum

Abdominal cavity,

Pleura

Around the lungs,

Pericardium

Around the heart

Synovial membranes

Loose areolar connective tissue only (no epithelial tissue). Line fibrous capsules surrounding joints (Line bursae, Line tendon sheaths). Secrete a lubricating fluid to cushion organs moving against each other during muscle activity.

Integumentary system consists of the

Skin (cutaneous membrane), Skin appendages, Sweat glands, Oil glands, Hair, Nails

Functions of the Integumentary System

Insulates and cushion deeper body organs. Protects the entire body. Aids in loss or retention of body heat as controlled by the nervous system. Aids in excretion of urea and uric acid. Synthesizes vitamin D.

Integumentary System protects the entire body from

Mechanical damage (bumps and cuts), Chemical damage (acids and bases), Thermal damage (heat or cold), Ultraviolet (UV) radiation (sunlight), Microbes (bacteria), Desiccation (drying out)

Two kinds of tissue compose the skin

Epidermis, Dermis

Hypodermis (subcutaneous layer)

▪ Anchors the skin to underlying organs ▪ Not technically part of the integumentary system ▪ Composed mostly of adipose tissue ▪ Serves as a shock absorber and insulates deeper tissues.

Epidermis

—outer layer ▪ Capable of being hard and tough ▪ Stratified squamous epithelium ▪ Keratinocytes (the most common cell) produce a fibrous protein called keratin ▪ Avascular ▪ Composed of five layers (strata)

Summary of layers of the epidermis from deepest to most superficial

▪ Stratum basale ▪ Stratum spinosum ▪ Stratum granulosum ▪ Stratum lucidum (thick, hairless skin only) ▪ Stratum corneum

Stratum basale (stratum germinativum)

▪ Deepest layer of epidermis ▪ Lies next to dermis ▪ Wavy borderline with the dermis anchors the two together ▪ Cells undergoing mitosis ▪ Daughter cells are pushed upward to become the more superficial layers. Stem cells are actively dividing; some newly formed cells become part of the more superficial layers.

Stratum spinosum

▪ Cells become increasingly flatter and more keratinized. Cells contain thick bundles of intermediate filaments made of pre-keratin.

Stratum granulosum

Cells are flattened, organelles are deteriorating; cytoplasm full of granules.

Stratum lucidum

▪ Formed from dead cells of the deeper strata. ▪ Occurs only in thick, hairless skin of the palms of hands and soles of feet.

Stratum corneum

▪ Outermost layer of epidermis ▪ Shingle-like dead cells are filled with keratin (protective protein prevents water loss from skin).

Melanin

is a pigment produced by melanocytes. ▪ Color is yellow to brown to black. ▪ Melanin accumulates in membrane-bound granules called melanosomes. ▪ Amount of melanin produced depends upon genetics and exposure to sunlight.

Melanocytes

are mostly in the stratum Basale of the Epidermis.

Epidermal dendritic cells

Alert and activate immune cells to a threat (bacterial or viral invasion)

Merkel cells

Associated with sensory nerve endings. Serve as touch receptors called Merkel discs

Structure of the Skin

Dermis

▪ Connective tissue ▪ Underlies the epidermis

Two layers of the dermis

Papillary layer (upper dermal region), Reticular layer (deepest skin layer)

Papillary layer (upper dermal region)

contain projections called dermal papillae ▪ Indent the epidermis above ▪ Many projections contain capillary loops, and others house pain and touch receptors ▪ On palm and sole surfaces, papillae increase friction and gripping ability ▪ Fingerprints are identifying films of sweat.

Reticular layer (deepest skin layer)

▪ Blood vessels ▪ Sweat and oil glands ▪ Deep pressure receptors (lamellar corpuscles)

Other dermal features

▪ Cutaneous sensory receptors ▪ Phagocytes ▪ Collagen and elastic fibers ▪ Blood vessels

Three pigments contribute to skin color

Melanin, Carotene, Hemoglobin

Melanin

▪ Yellow, reddish brown, or black pigments

Carotene

▪ Orange-yellow pigment from some vegetables

Hemoglobin

▪ Red coloring from blood cells in dermal capillaries ▪ Oxygen content determines the extent of red coloring

Redness (erythema)

—due to embarrassment, inflammation, hypertension, fever, or allergy

Pallor (blanching)

—due to emotional stress (such as fear), anemia, low blood pressure, impaired blood flow to an area

Jaundice (yellow cast)

—indicates a liver disorder

Bruises (black and blue marks)

—hematomas

Appendages of the Skin

▪ Cutaneous glands are all exocrine glands ▪ Sebaceous glands ▪ Sweat glands ▪ Hair ▪ Hair follicles ▪ Nails

Sebaceous (oil) glands

▪ Located all over the skin except for palms and soles ▪ Produce sebum (oil) ▪ Makes skin soft and moist ▪ Prevents hair from becoming brittle ▪ Kills bacteria ▪ Most have ducts that empty into hair follicles; others open directly onto skin surface ▪ Glands are activated at puberty

Sweat (sudoriferous) glands

▪ Produce sweat ▪ Widely distributed in skin

Two types of sweat (sudoriferous glands)

1. Eccrine glands 2. Apocrine glands

Eccrine glands

▪ Open via duct to sweat pores on the skin's surface ▪ Produce acidic sweat (Water, salts, vitamin C, traces of metabolic waste) ▪ Function in body temperature regulation.

Apocrine glands

▪ Ducts empty into hair follicles in the armpit and genitals ▪ Begin to function at puberty ▪ Release sweat that also contains fatty acids and proteins (milky or yellowish color) ▪ Play a minimal role in body temperature regulation

Hair

▪ Produced by hair follicle ▪ Root is enclosed in the follicle ▪ Shaft projects from the surface of the scalp or skin ▪ Consists of hard keratinized epithelial cells ▪ Melanocytes provide pigment for hair color ▪ Hair grows in the matrix of the hair bulb in stratum basale

Hair anatomy

▪ Central medulla ▪ Cortex surrounds medulla ▪ Cuticle on outside of cortex (Most heavily keratinized region of the hair)

Hair follicle

▪ Composed of an epithelial root sheath and fibrous sheath

Dermal region

provides a blood supply to the hair bulb (deepest part of the follicle)

Arrector pili muscle

connects to the hair follicle to pull hairs upright when we are cold or frightened

Nails

▪ Heavily keratinized, scalelike modifications of the epidermis ▪ Lack of pigment makes nails colorless

▪ Stratum basale

extends beneath the nail bed, which is responsible for growth

Parts of a nail

▪ Free edge ▪ Body is the visible attached portion ▪ Nail folds are skin folds that overlap the edges of the nail; the cuticle is the proximal edge ▪ Root of nail is embedded in skin ▪ Growth of the nail occurs from nail matrix.

Athlete's foot

▪ Caused by fungal infection (Tinea pedis) ▪ Itchy, red peeling skin between the toes

Boils (furuncles) and carbuncles

▪ Caused by inflammation of hair follicles ▪ Carbuncles are clusters of boils caused by bacteria

Cold sores (fever blisters)

▪ Caused by human herpesvirus 1 ▪ Blisters itch and sting

Contact dermatitis

▪ Caused by exposure to chemicals that provoke allergic responses ▪ Itching, redness, and swelling of the skin

Impetigo

▪ Caused by bacterial infection ▪ Pink, fluid-filled raised lesions around mouth/nose

Psoriasis

▪ Triggered by trauma, infection, hormonal changes, or stress ▪ Red, epidermal lesions covered with dry, silvery scales that itch, burn, crack, or sometimes bleed

Burns

▪ Tissue damage and cell death caused by heat, electricity, UV radiation, or chemicals ▪ Result in loss of body fluids and infection from the invasion of bacteria. Estimated using the rule of nines

Associated dangers of burns

▪ Protein denaturation and cell death ▪ Dehydration and electrolyte imbalance ▪ Circulatory shock

Rule of nines

▪ Body is divided into 11 areas for quick estimation ▪ Each area represents about 9 percent of total body surface area. ▪ The area surrounding the genitals (the perineum) represents 1 percent of body surface area

First-degree burn (superficial burn)

▪ Only epidermis is damaged ▪ Skin is red and swollen

Second-degree burn (partial-thickness burn)

Epidermis and superficial part of dermis are damaged ▪ Skin is red, painful, and blistered ▪ Regrowth of the epithelium can occur

▪ Third-degree burn (full-thickness burn)

▪ Destroys epidermis and dermis; burned area is

Painless ▪ Requires skin grafts, as regeneration is not possible ▪ Burned area is blanched (gray-white) or black

Fourth-degree burn (full-thickness burn)

▪ Extends into deeper tissues (bone, muscle, tendons) ▪ Appears dry and leathery ▪ Requires surgery and grafting ▪ May require amputation

Criteria for deeming burns critical (if any one is met)

▪ Burns affect the airways ▪ Circumferential (around the body or limb) burns have occurred

Over 30 percent of body

has second-degree burns

Over 10 percent of the body

has third- or fourth-degree burns

Third- or fourth-degree

burns of the face, hands, or feet, or genitals

Homeostatic Imbalances of Skin

Skin cancer

▪ Most common form of cancer in humans ▪ Most important risk factor is overexposure to ultraviolet (UV) radiation in sunlight and tanning beds

Cancer can be classified two ways

Benign and Malignant

Benign

means the neoplasm (tumor) has not spread

Malignant

means the neoplasm has invaded other body areas.

Most common types of skin cancer

▪ Basal cell carcinoma ▪ Squamous cell carcinoma ▪ Malignant melanoma

Basal cell carcinoma

▪ Least malignant and most common type of skin cancer ▪ Arises from cells in stratum basale that are altered so that they can no longer make keratin ▪ Lesions appear as shiny, dome-shaped nodules that develop a central ulcer.

Squamous cell carcinoma

▪ Believed to be induced by UV exposure ▪ Arises from cells of stratum spinosum ▪ Lesions appear as scaly, reddened papules that gradually form shallow ulcers ▪ Early removal allows a good chance of cure ▪ Metastasizes to lymph nodes if not removed

Malignant melanoma

▪ Most deadly of skin cancers, but accounts for only 5 percent of skin cancers ▪ Arises from melanocytes ▪ Metastasizes rapidly to lymph and blood vessels ▪ Detection uses ABCDE rule for recognizing melanoma.

A

Asymmetry (Two sides of pigmented mole do not match)

B

Border irregularity (Borders of mole are not smooth)

C

Color (Different colors in pigmented area)

D

Diameter (Spot is larger than 6 mm in diameter)

E

Evolution (One or more of the ABCD characteristics is evolving)

Lanugo

a downy hair, covers the body by the fifth or sixth month of fetal development but disappears by birth

Vernix caseosa

an oily covering, is apparent at birth

Milia

small white spots, are common at birth and disappear by the third week

Acne

may appear during adolescence

Youth

skin is thick, resilient, and well hydrated

Aging

skin loses elasticity and thins