Chapter 4: Skin and Body Membranes

Functions of body membranes

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

Classified According to Tissue Types

- Epithelial Membranes: Cutaneous membranes, Mucous membranes, Serous membranes.
- Connective tissue membranes: Synovial membranes

Cutaneous Membrane

- Cutaneous membrane = skin
- Dry membrane (sweat & oil glands)
- Outermost protective boundary
- Superficial epidermis is composed of keratinized stratified squamos epithelium.
- Underlying dermis is mostly dense, fibrous connective tissue.

Mucous Membranes

- Surface epithelium type depends on site (stratified squamos epithelium can be found in the mouth and the esophagus while simple columnar epithelium is found int he rest of the digestive tract.)
- Lamina propria: underlying loose connective tissue
- Lines all body cavities that open to the exterior body surface.
- Most membranes adapted for absorption of secretion.

Serous Membranes (Serosa)

- Surface is a layer of simple squamos epithelium
- Underlying layer is a thin layer of areolar connective tissue
- Lines open body cavities that are closed to the exterior of the body
- Serous memebranes occur in pairs separated by serous fluid. (Visceral layer covers the outside of the organ. Parietal layer lines a portion of the wall of ventral body cavity.)

Specific Serous membranes

- Peritoneum: Abdominal cavity
- Pleura: Around the lungs
- Pericardium: Around the heart.

Synovial Membrane

- Connective tissue only
- Lines fibrous capsules surrounding joints (like the bursae and tendon sheaths)
- Secretes a lubricating fluid.

Integumentary System

- Skin (cutaneous membrane)
- Skin derivatives: sweat glands, oil glands, hair, and nails.

Skin (Integument) Functions

Protects deeper tissues from:
- Mechanical damage like bumps
- Chemical damage (acids/bases)
- Bacterial damage
- UV radiation (sunlight)
- Thermal damage (extreme heat/cold)
- Desiccation (drying out) (Keratin protects the skin from water loss.)
- 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
- Cutaneous sensory receptors detect touch, temperature, pressure, and pain.

Epidermis

- Outer layer of skin
- Stratified squamos epithelium
- Cornified or keratinized (hardened by keratin) to prevent water loss.
- Avascular
- Most cells are keratinocytes

Dermis

- Dense connective tissue
- Underneath epidermis.
- 2 layers: Papillary and Reticular
- Where glands and hair follicles are.

Hypodermis

- Deep to dermis (meaning underneath dermis)
- Not technically part of the skin
- Anchors skin to underlying organs
- Composed mostly of adipose tissue
- Serves as a shock absorber and insulates deeper tissue.

Layers of the Epidermis (Deep to superficial)

1. Stratum Basale
2. Stratum Spinosum
3. Stratum Granulosum
4. Stratum Lucidum
5. Stratum Corneum

Stratum Basale

- or 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

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.

Melanin

- Pigment (melanin) produced by melanocytes
- Colour is yellow to brown to black
- Melanocytes are mostly in the stratum basale
- Melanin accumulates in membrane-bound granules: melanosomes
- Amount of melanin produced depends upon genetics and exposure to sunlight.

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

Papillary Layer

- Upper dermal region
- Projections called dermal papillae
- Some contain capillary loops
- Others house pain receptors (free nerve endings) and touch receptors
- Fingerprints are identifying films of sweat

Reticular Layer

- Deepest skin layer
- Blood vessels
- Sweat and oil glands
- Deep pressure receptors (lamellar corpuscles)

Overall Dermis Structure

- Collagen and elastic fibers located throughout the dermis
- Collagen fibers give skin its toughness
- Elastic fibers give skin elasticity
- Blood vessels play a role in body temp. and regulation
- Nerve supply sends messages to the CNS.

Melanin

- Yellow, reddish brown, or black pigments

Carotene

- Orange-yellow pigment from some vegetables

Hemoglobin

- Red colouring from blood cells in dermal capillaries
- Oxygen content determines the extent of red colouring.

Erythema

- redness
- due to embarrassment, inflammation, hypertension, fever, or allergy.

Blanching

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

Jaundice

- Yellowing
- Liver disorder

Bruises

- Black and blue marks
- hematomas

Sebacous Glands

- Produces sebum (oil)
- Lubricant for skin
- Prevents brittle skin
- Kills bacteria
- Most have ducts that empty into hair follicles; others open directly onto skin surface
- Glands activate at puberty

Sweat glands

- Produce sweat. (Thank you captain obvious)
- Widely distributed in skin

Eccrine Glands

- Open via duct to pore on skin surface
- Produce Sweat
- sudoriferous gland

Apocrine glands

- Ducts empty into hair follicles
- Begin to function at puberty
- Release sweat that also contains fatty acids and proteins (milky or yellowish color)
- Sudoriferous glands

Sweat

- Composed of water, salts and vitamin C, some metabolic waste, fatty acids and proteins (apocrine only.)
- Functions to help dissipate excess heat, excrete waste products, and the acidic nature inhibits bacteria growth.
- Odor is from bacteria

Hair

- Produced by hair follicle
- Root enclosed in follicle
- Shaft projects from surface of the scalp/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 (is the most heavily keratinized region of the hair.)

Hair Follicle

- Dermal and epidermal sheath surrounding hair root

Arrector Pili Muscle

- Smooth muscle
- Pulls hair upright when person is cold or frightened.

Nails

- Scale-like modifications of the epidermis (are heavily keratinized)
- Stratum basale extends beneath the nail bed (is responsible for growth)
- Lack of pigment makes them colorlesss

Nail Structures

- Free edge
- Body is the visible attached portion
- Nail folds are skin folds that overlap the edges of the nail
- Growth occurs from nail matrix
- Root of nail is embedded in skin
- Cuticle is the proximal nail fold that projects onto the nail body.

Tissue repair (wound healing) occurs in two ways:

1. Regeneration: Replacement of destroyed tissue by the same kind of cells
2. Fibrosis: Repair by dense (fibrous) connective tissue (scar tissue.)

Inflammation

- Capillaries become permeable
- Clotting proteins migrate into the area from the bloodstream
- A clot walls off the injured area

Granulation Tissue forms

- Growth of new capillaries
- Phagocytes dispose of blood clot and fibroblasts
- Rebuild collagen fibers

Burns

- Tissue damage and cell death caused by heat, electricity, UV radiation, or chemicals.
- Associated dangers are dehydration, electrolyte imbalance, and/or circulatory shock
- Results in loss of body fluids and invasion of bacteria

Rule of Nines

- Way to determine the extent of burns
- Body is divided into 11 areas for quick estimation
- Each area represents about 9% of total body surface area.
- The perineum represents 1% of body surface area

Body Surface Area Percentages

- Anterior and posterior head and neck = 9%
- Anterior and posterior upper limbs = 18%
- Anterior and posterior trunk = 36%
- Anterior and posterior lower limbs = 36%

First-Degree Burns

- Partial-Thickness burn
- Only epidermis is damaged
- Skin is red and swollen

Second-Degree Burn

- Partial-Thickness burn
- Epidermis and upper dermis are damaged
- Skin is red with blisters

Third-Degree Burns

- Full-Thickness burn
- Destroys entire skin layer; burned area is painless.
- Requires skin grafts
- Burn is gray-white or black.

Burns are considered critical if ...

- Over 25% of body has second-degree burns
- Over 10% of body has third-degree burns
- There are third-degree burns of the face, hands, or feet.

Athlete's Foot

- tinea pedis
- fungal infection

Boils and carbuncles

- bacterial infection

Cold sores

- caused by virus (herpes simplex virus-1 specifically)

Contact dermatitis

- Exposures cause allergic reaction

Impetigo

- Caused by bacterial infection (Staphylococcus aureus or Streptococcus pyogenes specifically)
- Rash that kids usually get. Contagious.

Psoriasis

- Cause is unkown
- Triggered by trauma, infection, or stress
- Itchy, scaly, rash

Skin Cancer

- Cancer: abnormal cell mass
- Either benign (nonspreading) or malignant (moves to other parts of body)
- skin cancer is the most common type of cancer.

Metastasizes

- cancer moves to other parts of the body

Basal Cell Carcinoma

- Least malignant
- Most common type
- Arises from stratum basale

Squamos Cell Carcinoma

- Metastasizes to lymph nodes if not removed
- Early removal allows a good chance of a cure.
- Believed to be sun-induced
- Arises from stratum spinosum

Malignant Melanoma

- Most deadly
- Cancer of melanocytes
- Metastasizes rapidly to lymph and blood vessels
- Detection uses ABCD rule

ABCD Rule

- A = Asymmetry (Two sides of pigmented mole do not match.)
- B = Border Irregularity (Borders of mole are not smooth.)
- C = Colour (Different colorus in pigmented area.)
- D = Diameter (Spot is larger than 6mm/the size of a pencil eraser.)

Developmental Aspects of Skin

-In youth, skin is thick, resilient, and well hydrated
-With aging, skin loses elasticity and thins
-Skin cancer is a major threat to skin exposed to excessive sunlight
-Balding and/or graying occurs with aging; both are genetically determined; other factors that may contribute include drugs and emotional stress

During the fifth and sixth months of development, a fetus is covered with a downy type of hair called

lanugo

By the time the infant is born, it has usually shed this hairy cloak, and instead its skin is covered with an oily coating called

the vernix caseosa

• This white, cheesy-looking substance, produced by the sebaceous glands, protects the baby’s skin while it is floating in its water-filled sac inside the mother.

• The newborn’s skin is very thin, and blood vessels are easily seen through it. As the baby grows, its skin becomes thicker, and more subcutaneous fat is deposited.

During adolescence, the skin and hair become oilier as sebaceous glands are activated, and acne may appear. Acne usually subsides in early adulthood, and the skin reaches its optimal appearance when we are in our twenties and thirties. Then visible changes in the skin begin to appear…..

as it is continually assaulted by abrasion, chemicals, wind, sun, and other irritants and as its pores become clogged with air pollutants and bacteria. As a result, pimples, scales, and various kinds of dermatitis (der″mah-ti′tis), or skin inflammation, become more common.

As we continue to age, the amount of subcutaneous tissue decreases, leading to sensitivity to cold. The skin also…..

becomes drier (because of decreased oil production), and as a result, it may become itchy and bothersome. .

Hair loses its luster as we age, and by age 50 the number of hair follicles has dropped by one-third and continues to decline, resulting in hair thinning….

and some degree of baldness, or alopecia (al″o-pe′she-ah), in most people.

• Many men become bald as they age, a phenomenon called male pattern baldness. A bald man is not really hairless—he does have hairs in the bald area. But, because those hair follicles have begun to degenerate, the vellus (vell = wool) hairs are colorless and very tiny (and may not even emerge from the follicle).

• Another phenomenon of aging is graying hair.

Thinning of the skin, another result of the aging process, makes it more susceptible to……

bruising and other types of injuries.

• The decreasing elasticity of the skin, along with the loss of subcutaneous fat, allows bags to form under our eyes, and our jowls begin to sag.

When the cause of these conditions is not genetic…..

hair loss is usually not permanent.