Skin & Body Membranes Part 2

Stratum Corneum

consists on average of 25 to 30 layers of flattened dead keratinocytes

● aka HORNY LAYER

● Complete differentiation of granular cells results in stacked layers of

anucleate, flattened cornified/keratinized cells

● mechanical protection

● protect deeper layers from injury and microbial invasion

● “barrier activity”- waterproof barrier of the epidermis

Dermal-Epidermal Junction

● basement membrane zone

● ATTACH DERMIS TO EPIDERMIS to each other and

to provide resistance against external shearing forces

● SUPPORT for the epidermis

● semipermeable barrier

• MELANOCYTES

• MERKEL CELLS

• LANGERHANS CELLS OR BIRBECK GRANULES

3 Types Non-keratinocytes of the Epidermis

MELANOCYTES

are neural crest-derived, PIGMENT-

SYNTHESIZING dendritic cells that reside

primarily in the basal layer

○ 8% of total cells in the epidermis

○ VITILIGO : autoimmune depletion of

melanocytes

VITILIGO

autoimmune depletion of melanocytes

MERKEL CELLS

are slow-adapting type I mechanoreceptors

○ least numerous

○ located in sites of HIGH-TACTILE SENSITIVITY

○ hairy skin and in the glabrous skin of the digits, lips,

regions of the oral cavity, and the outer root sheath

of the hair follicle

LANGERHANS CELLS OR BIRBECK GRANULES

ANTIGEN PRESENTING & PROCESSING

CELLS

○ reduced in the epidermis of patients with certain

conditions, such as psoriasis, sarcoidosis, and

contact dermatitis;

○ they are functionally impaired by UV radiation,

especially UVB

Dermis

A major structural element of the skin

● site of VASCULAR, LYMPHATIC AND NERVE NETWORKS

● has great tensile strength (resists pulling or stretching forces).

● provides skin’s pliability and elasticity

● responsible for thermal regulation

● essential to the survival of the epidermis

● cells present in the dermis include predominantly fibroblasts, with some

macrophages, and a few adipocytes

• the upper papillary dermis

• deeper reticular dermis

Two Major Regions of the Dermis

the upper papillary dermis

■ Nipplelike bumps

■ Tactile receptors

■ 1/5 of the thickness

deeper reticular dermis

■ Elastic fibers

■ Forms most of dermis

■ Attached to Subcutaneous Layer

CUTANEOUS VASCULATURE

Made up of Blood Vessels

● provide NUTRITION for the skin tissue

● temperature and blood pressure regulation, wound

repair, and numerous immunologic events

● penetrate the subcutaneous fat and enter the deep

reticular dermis

Lymphatics

● IMPORTANT in regulating pressure of the interstitial fluid

○ by resorption of fluid released from vessels

○ clearing the tissues of cells, proteins, lipids, bacteria, and degraded

substances

● Lymph flow
ARTERIAL PULSATIONS

○ larger-scale muscle contractions and movement of the body

○ backflow prevented by bicuspid-like valves within the vessels

CUTANEOUS NERVES AND RECEPTORS

sensory fibers alone (free nerve endings)

● specialized structures (corpuscular receptors) function as

receptors of touch, pain, temperature, itch, and mechanical

stimuli

● Receptors are particularly DENSE IN HAIRLESS areas such as

the areola, labia, and glans penis

● arise segmentally from spinal nerves

Meissner's corpuscles

Mechanoreceptors:

“Touch” receptors

Near the Surface of the skin

Pacinian corpuscle

ONION-SKIN Appearance

RAPIDLY adapting mechanoreceptors

“Vibration” and “Pressure” stimuli

Hypodermis

“subcutis”

● INSULATION

● mechanical integrity

● containing the larger source vessels and nerves

● Under the skin, not part of the skin

DERMATOMES

Area of the skin that is supplied by a Spinal Nerve

Functions of the skin

FUNCTION & TISSUE LAYER

Permeability barrier - Epidermis

Protection from pathogens - Epidermis, Dermis

Thermoregulation - Epidermis, Dermis, Hypodermis

Sensation - Epidermis, Dermis, Hypodermis

UV Protection - Epidermis

Wound repair/regeneration - Epidermis, Dermis

Physical Appearance - Epidermis, Dermis, Hypodermis

Appendages of the skin

• Hair follicles

● Sebaceous glands

● Nails

● Sweat glands

Hair

is composed of columns of dead, keratinized epidermal cells bonded

together by extracellular proteins.

Shaft

is the superficial portion of the hair, which projects above the surface

of the skin.

Root

is the portion of the hair deep to the shaft that penetrates into the

dermis, and sometimes into the subcutaneous layer.

medulla, cortex, and cuticle of the hair.

The shaft and root of the hair both consist of three concentric layers of cells:

Inner medulla

which may be lacking in thinner hair, is composed of two

or three rows of irregularly shaped cells.

Middle cortex

forms the major part of the shaft and consists of elongated cells.

Cuticle of the hair

the outermost layer, consists of a single layer of thin, flat cells that are the most heavily keratinized.

Hair follicle

Surrounding the root of the hair is the _______________ .

Epithelial Root Sheath

which is made up of an external root sheath and an internal root sheath, together referred to as an _______________ .

External Root Sheath

is a downward continuation of the epidermis.

Internal Root Sheath

is produced by the matrix and forms a cellular tubular sheath of epithelium between the external root sheath and the hair.

Dermal Root Sheath

The dense dermis surrounding the hair follicle is called the ____________ .

Bulb

The base of each hair follicle and its surrounding dermal root sheath is an onion-

shaped structure.

This structure houses a nipple-shaped indentation, the papilla of the hair, which

contains areolar connective tissue and many blood vessels that nourish the growing

hair follicle.

The bulb also contains a germinal layer of cells called the hair matrix.

Depilatory

A Substance that removes hair. It dissolves the protein in the hair shaft, turning it into a gelatinous mass that can be wiped away. Because the hair root is not affected regrowth of the hair occurs.

Electrolysis

An Electric current is used to destroy the hair matrix so the hair cannot regrow.
Laser treatments may also be used to remove hair.

HAIR GROWTH

Each hair follicle goes through a growth cycle, which consists of a growth stage, a regression stage,

and a resting stage.

growth (anagen) stage

During the ______________ cells of the hair matrix divide. As new cells from the hair matrix are added to the base of the hair root, existing cells of the hair root are pushed upward, and the hair grows longer. While the cells of the hair are being pushed upward, they become keratinized and die.

regression (catagen) stage

Following the growth stage is the ________________, when the cells of the hair matrix stop

dividing, the hair follicle atrophies (shrinks), and the hair stops growing.

Resting (telogen) stage

After the regression stage, the hair follicle enters a ___________________. Following the resting

stage, a new growth cycle begins.

Scalp Hair

• is in the growth stage for 2 to 6 years, the regression stage for 2 to 3

weeks, and the resting stage for about 3 months.

• At any time, about 85% are in the growth stage.

• Normal hair loss in the adult scalp is about 70–100 hairs per day.

• Both the rate of growth and the replacement cycle may be altered by illness, radiation

therapy, chemotherapy, age, genetics, gender, and severe emotional stress

Sebaceous Glands

Oil glands are simple, branched acinar glands.

● With few exceptions, they are connected to hair follicles.

• The secreting portion of a sebaceous gland lies in the dermis and usually opens into the neck of a hair follicle. In some locations, such as the lips, glans penis, labia minora, and tarsal glands of the eyelids, sebaceous glands open directly onto the surface of the skin.

• Absent in the palms and soles, sebaceous glands are small in most areas of the trunk and limbs, but large in the skin of the breasts, face, neck, and superior chest.

Sebum

Sebaceous glands secrete an oily substance called __________, a mixture of

triglycerides, cholesterol, proteins, and inorganic salts.

Acne

• is an inflammation of sebaceous glands that usually begins at puberty, when the sebaceous glands are stimulated by androgens.

• Occurs predominantly in sebaceous follicles that have been colonized by bacteria, some which thrive in the lipid sebum.

• The infection may cause a cyst or sac of connective tissue cells to form which can destroy and displace epidermal cells. This is called Cystic Acne.

Nails

● are plates of tightly packed, hard, dead, keratinized epidermal cells that form

a clear, solid covering over the dorsal surfaces of the distal portions of the

digits.

● Each nail consists of a nail body, a free edge, and a nail root.

● The nail body (plate) is the visible portion of the nail. It is comparable to the

stratum corneum of the general epidermis, with the exception that its

flattened, keratinized cells fill with a harder type of keratin and do not shed.

Nails body appears pink

Most of the ____________ because of blood flowing through the capillaries in the

underlying dermis.

Free Edge

is the part of the nail body that may extend past the distal end of the digit. The free

edge is white because there are no underlying capillaries.

Nail Root

is the portion of the nail that is buried in a fold of skin. The whitish, crescent-shaped

area of the proximal end of the nail body is called the lunula (little moon).

Whitish

It appears ____________ because the vascular tissue underneath does not show through due to a

thickened region of epithelium in the area.

Hyponychium, or nail bed

Beneath the free edge is a thickened region of stratum corneum called the

____________________, which secures the nail to the fingertip.

eponychium or cuticle

is a narrow band of epidermis that extends from and

adheres to the margin (lateral border) of the nail wall. It occupies the proximal border of

the nail and consists of stratum corneum.

Nail matrix

The proximal portion of the epithelium deep to the nail root is the ___________, where

cells divide by mitosis to produce growth.

Nail Development

● Nail growth occurs by the transformation of superficial cells of the matrix into nail cells.

● The growth rate of nails is determined by the rate of mitosis in matrix cells, which is

influenced by factors such as a person’s age, health, and nutritional status.

● The average growth in the length of fingernails is about 1 mm (0.04 in.) per week.

● The growth rate is somewhat slower in toenails.

SWEAT GLANDS

● aka Sudoriferous Glands

● 3-4 million in number

● release sweat, or perspiration, into hair follicles or onto the skin

surface through pores

● 2 Types: Eccrine & Apocrine

ECCRINE SWEAT GLANDS

● aka Merocrine Sweat Glands

● Simple coiled tubular glands

● Much more common

● Distribute throughout the skin of most regions of the body, especially in the

skin of the forehead, palms, and soles

● sweat produced by eccrine sweat glands (about 600 mL per day) consists of

water, ions (mostly Na and Cl), urea, uric acid, ammonia, amino acids,

glucose, and lactic acid.

● help regulate body temperature through evaporation

● Eccrine sweat glands start to function soon after birth

APOCRINE SWEAT GLANDS

● also simple, coiled tubular glands

● found mainly in the skin of the axilla (armpit), groin, areolae (pigmented

areas around the nipples) of the breasts, and bearded regions of the face in

adult males.

● secretion via Exocytosis

● secretory portion of these sweat glands is located mostly in the subcutaneous

layer

● the excretory duct opens into hair follicles

● apocrine sweat is slightly viscous and appears milky or yellowish in color

● apocrine sweat glands do not begin to function until puberty.

PATHOLOGIC SKIN DISEASES

● URTICARIA

● ACUTE INFLAMMATORY DERMATOSES

○ ECZEMA

○ ERYTHEMA MULTIFORME

● VERRUCAE

● SUPERFICIAL FUNGAL INFECTIONS

● ACNE VULGARIS

● BURNS

● SKIN CANCER

URTICARIA

○ Hives or wheals

○ Due to increased microvascular permeability

ECZEMA

○ Greek word “eczema” meaning to “boil over”

○ Red, papulovesicular, oozing, crusted lesions

○ Can be categorized into

■ Allergic

■ Atopic

■ Drug-related

■ Photoeczematous

ERYTHEMA MULTIFORME

○ Uncommon, self-limited, “multiform” lesions

○ Macules, papules, vesicles, bullae

clinical and pathologic manifestations of the

inflammatory response

● Rubor - redness

● Tumor- swelling

● Calor- warmth

● Dolor- pain

● Functio laesa- loss of

function

Rubor

Redness

Tumor

Swelling

Calor

Warmth

Dolor

Pain

Functio Laesa

Loss of Function

Infection of the skin

● VERRUCAE (WARTS)

● SUPERFICIAL FUNGAL INFECTIONS

● ACNE VULGARIS

VERRUCAE (WARTS)

○ Common in children and adolescents, and occurs at any age

○ Direct contact transmission

○ Self-limited (6months- 2 years)

SUPERFICIAL FUNGAL INFECTIONS

○ Confined to the Stratum Corneum

○ Caused primarily by Dermatophytes

○ Grow in soil and on animals

ACNE VULGARIS

○ Middle to late teenage years

○ M<F

○ Physiologic hormonal

variations

○ Alteration in hair follicles,

particularly sebaceous glands

BURNS

damage to your body's tissues caused by heat, chemicals, electricity,

sunlight, or radiation

Thermal burns

Hot metals, scalding liquids, steam, and flames, when

coming into contact with the skin, can cause thermal burns.

Radiation burns

prolonged exposure to UV rays of the sun, or to other

sources of radiation such as X-ray.

Chemical burns

strong acids, alkalines, detergents, or solvents coming into

contact with the skin or eyes.

Electrical burns

These burns are from electrical current, either alternating

current (AC) or direct current (DC).

Types of Degree Burn

● First-degree (superficial) burns

● Second-degree (partial thickness) burns

● Third-degree (full thickness) burns

● Fourth-degree burn

First-degree (superficial) burns

○ only the epidermis, or outer layer of skin.

○ red, painful, dry, and with no blisters.

○ Mild sunburn is an example.

Second-degree (partial thickness) burns

○ epidermis and part of the dermis layer of skin.

○ red, blistered, and may be swollen and painful.

Third-degree (full thickness) burns

○ destroy the epidermis and dermis.

○ damage the underlying bones, muscles, and

tendons.

Fourth-degree burn

○ bones, muscles, or tendons are also burned

○ The burn site appears white or charred. There is

no feeling in the area since the nerve endings are

destroyed.

Types of Skin cancer

● SQUAMOUS CELL CARCINOMA

● BASAL CELL CARCINOMA

SQUAMOUS CELL CARCINOMA

○ 2nd most common tumor on SUN-EXPOSED areas in older people

○ DNA damage due to UV light

○ M<F, Invade the basement membrane of the DEJ

BASAL CELL CARCINOMA

○ Most common invasive cancer

○ Slow growing, rarely metastasize

○ In SUN-EXPOSED areas

○ PEARLY papules

○ Dilated subepidermal Blood vessels

(telangiectasias)