Integumentary System

Integumentary System

Largest organ in body, ~16% of body weight, and is the first line of defense

Skin functions

Protect tissue and organs from shock, excretes salts, water, and wastes, maintains body temperature, makes vitamin D3 (a steroid) which is converted to calcitriol, and storage of nutrients- lipids stored in adipocytes in dermis and subcutaneous layer

2 major part of integumentary System

Cutaneous membrane and accessories

Epidermis (cutaneous membrane)

epithelia does not have blood vessels; consists of stratified Squamous epithelial cells

Dermis (cutaneous Membrane)

under laying area of connective tissue; has a lot of blood vessels.

Subcutaneous Layer

A layer deeper than dermis and is also called “hypodermis” which is not part of cutaneous membrane.

Accessories

Hair, nails, exocrine glands, arrector pili muscles, et al

Keratinocytes

body’s most abundant epithelia cells (by shape they are Squamous cells). Cells produced at deepest layer and shed at superficial layer

Types of skin layering

Thick skin has 5 layers (palms of hands and soles of feet) and thin skin has 4 layers

Thick skin layers

Stratum germinativum (stratum basal; deepest), s. spinosum, s. granulosum, s. lucidum (not found in thin skin), and s. corneum (superficial)

Thin skin layers

Stratum germinativum (basal; deepest), s.spinosum, s. granulosum, and s. corneum (superficial)

Epidermal skin layers

Stratum means one layer; strata means two + layers

Stratum germinativum (stratum basal)

This is the deepest layer and is attached to the basal lamina with hemidesmosomes. Basal lamina separates epithelia from connective tissue and has epidermal ridges which extends into dermis which increases contact area between two places increasing attachment strength

Germinativum cells ( cell type of stratum basal)

Called basal cells and are found throughout stratum germinativum are “stem cells” which replace the cells lost in the upper layers

Merkel Cells ( cell type of stratum basal)

Are sensitive to touch (pain receptors); when compressed by pressure they release chemicals that stimulate nerves

Melanocytes ( cell type of stratum basal)

Produce brown pigment due to sunlight are found in stratum germinativum. They are also found in the middle layer of the eye ( the urea) and product melanin for eye color. Little to no melanin = blue eyes and lots of melanin = brown eyes. Can migrate widely in the embryo so cancer can metastasize very easily and are mostly fatal.

Stratum basal (cont)

Ratio of melanocytes to stem cells vary based on body location (1:4 to 1:20). Fair skinned humans have melanocytes in stratum basal and spinosum; dark skinned humans have them in stratum basal, spinosum and granulosum

Ultraviolet rays

From the sun and penetrates the skin and damage melanocytes DNA by producing thymine-thymine dimers.

Enzyme tyrosinase

People that lack this which is required for melanin production are known as an albino

Carotene

Orange/yellow pigment in the epidermis. Comes from carrots and squash and is converted to vitamin A (important to eyes and epithelia), accumulates in epidermal cells; primarily stratum corneum of light skinned individuals

Melanin

A brown, yellow brown or black pigment produced by melanocytes in epidermis. Abinos lack melanin.

Melanocytes

they are located in stratum germinativum and make melanin from AA tyrosine. Protects against UV radiation. UV damages DNA causes skin cancer like malignant cancer and melanoma

Hemoglobin

Transports oxygen looks red when attached to O2. Bright red = more oxygen, dark red= less oxygen. When attached to CO2 vessels look blue and when blood supply is dermis is reduced the skin becomes “pale”

Jaundice

Liver unable to excrete bile so yellow pigment accumulates in body causing skin and eyes to turn yellow; occurs in newborns and can be easily cured by placing under a UV lamp

Stratum Spinosum

Each time one stem cell divides into two daughter cells, the daughter cells is pushed from S. germinativum to Stratum spinosum. Have 8-10 layers of cells which are attached by desmosomes

Dendritic (langerHans) Cells

Involved in immune response, are found in stratum Spinosum and they defend against microorganism that penetrate skin and attack superficial skin cancers

Startum Ganulosum

Called the “grainy layer”; this strata has 3-5 layers of keratinocytes. When cells reach this layer they have quit dividing and start to make protein keratin. Keratin is also found in hair/nails

Stratum Lucidum

Known as the clear layer and is found only in thick layer of skin on palms of hands and soles of feet. Cells are flattened, densely packed and filled w/keratin

Stratum Corneum

Constitues that expose areas of both thick and thin skin. Most superficial layer; “corn” means “horn”. 15-30 layer is keratinized cells. Keratinization or “cornifcation” is the formation of a protective layer of cells w/keratin, it takes 15-30 days for cell to move from stratum germinativum to Stratum corneum. Dead cells remain on top of it for two more weeks until pushed to skin surface and lost. Desmosomes keep dead cells attached

Insensible perspiration

is H2O resistant but not H2O proof. One point H2O lost by evaporation each day through skin

Sensible Perspiration

Produced by sweat glands (merocrine glands)

Endocrine functions and skin

Hormones coordinate with the integumentary system

Steroid hormones (endocrine functions)

glucocorticoids loosen cell connection between keartinocytes and thus reduce skin as a barrier to microbes

Thyroid hormones (endocrine functions)

maintains normal blood flow to skin

Sex hormones (Endocrine function)

Causes cell division which increases epidermal thickness and accelerates wound repair; increase number of dendritic cells for defense against pathogens

Growth hormones (Endocrine function)

increases fibroblast activity and collagen production; promotes wound repair

Epidermal Growth factor (ECF) -Growth hormone

Made in salivary glands promotes division of cells in stratum germinativum and stratum spinosum. Accelerates keratin production and stimulates epidermal repair after injury.

Vitamin D3 (Endocrine function)

Can be obtained from two sources sunlight and diet

Vitamin D3 through sunlight

causes a cholesterol related steroid (7 dehydrocholesterol) to be converted into cholecalciferol (D3) in epidermis. The D3 enters capillaries and goes to liver where it’s converted into an intermediary product. The intermediary product is converted into colcitriol. Calcitriol causes calcium and phosphate absorption which is needed for bone growth.

Vitamin D3 through Diet

Can be obtained from fis, fish oils and shellfish. D3 is absorbed in the intestines, then into the capillaries and passed to the liver. This is why they put vitamin D in milk because a lot of people do not get out in the sunlight enought to produce D3

Basal cell carcinoma (skin cancers)

malignant cancer found in stratum germinativum (most common form of cancer) due to UV radiation. Virtually no metastasis so most people survive

Malignant melanoma (skin cancer)

caused by cancerous melanocytes; metastasize via lymphatic system. Early detection prior to metastasis person has 99% change of surviving 5 years. Section after metastasis person has 14% chance of surviving 5 years.

Dermis

Located between the epidermis and hypodermis; contains collage and elastin. Subdivided into two layers. Also has blood vessels, lymph vessels, and nerve fibers.

Collagen

Is strong and flexible

Elastin

Stretches then recoils

Papillary layer (layer of dermis)

Superficial; consists of areola tissue and contains capillaries, lymph vessels and sensory neurons.

Reticular layer (layer of the dermis)

Deeper layer; consists of dense irregular tissue with collagen and elastin. Contains same things as papillary layer but also has sweat glands and hair follicles which extend into dermis.

Dermatitis

Inflammation of the skin primarily in the papillary layer due to chemicals or radiation.

Papilary layer sensory nerve

The major sensory neurons of this layer is the tactile corpuscles

Reticular layer sensory neurons

Major sensory neuron for this layer is lamellated corpuscles.

Dermal Circulation

If blood supply gets interrupted to the epidermis or dermis you can get an ulcer (shedding of epithelium)

Bed sores (pressure sores)

Also called decubitus ulcers affect bed ridden people by killing epidermal cells and then removes the barrier to infection by bacteria.

Merkel Cells (nerve cells in epidermis)

Located here so bed sores affect these cells sending intense pain stimuli to CNS. They are monitored by tactile discs; provided pain and temperature stimuli.

Dermis nerve supply

Has Merkel Cells and tactile corpuscles in dermal papillae for light touch stimuli and lamellated corpuscles for pressure or vibration.

Subcutaneous Layer

Not part of integumentary System. Contains areola and adipose tissue which accumulates in, in neck, arm, lower back and buttocks for men and for women in breast, hips, thighs and buttocks. Has blood vessels good place for injections.

Lines of Cleavage

Formed by the collagen and elastin finbers in the dermis and hypodermis; lines are parallel to the forces for each location. Important for wound healing. Parallel to cleavage better healing and less scarring, perpendicular to cleavage more scarring.

Hair

Covers most of body (exceptions are lips, palms of hands and soles of feet, external genitalia). Non-living structures produced by hair follicles; estimated 2.5 million hairs.

Hair blub (part of hair follicle)

mass of epithelial cells which surrounds hair papilla; cells in the hair bulb form the hair.

Hair papilla (part of hair follicle)

Connective tissue containing capillaries and nerves

Hair root (part of hair follicle)

anchors hair to skin

Hair Shaft (part of hair follicle)

Part of hair we see on surface. Is made up of dead cells full of the protein keratin.

Cuticle (part of hair follicle)

Outer surface of the shaft and covers the “cortex” an intermediate layer which covers the medulla which is the core of the hair.

Hair color

Comes from pigment “melanin”; with age pigment productions decreases causing hair to become gray.

Lanugo (Embryo)

Hair formed after 3 months on embryo then are shed before birth; helps to warm embryo

Vellus Hairs (Adult)

“peach fuzz” smaller, shorter delicate hair which covers body surface

Terminal Hairs (Adult)

large coarse hair found on head, armpits, eyebrows and eyelashes

Hair Functions

serves to protect and warm scalp, assists in sensory stimuli and provides as a signal of rage.

Root Hair plexus

Nerves surround the base so you can feel wind blow

Arrector pile

Muscle that causes hair to stand up due to fear (goosebumps) or rage

Sebaceous glands (exocrine gland)

Called oil glands and released by holocrine secretion through rupture of the secretory cells. Produces sebum an oily lipid that coats hair and inhibits bacteria

Typical sebaceous glands

secrete into hair follicles

Sebaceous Follicles

secrete into skin surface

Sweat gland (exocrine gland)

also called “sudoriferous glands”; released by merocrine Secretion

Apocrine sweat glands

really uses a merocrine Secretion but name has not changed. Influenced by hormones and bacteria use the sweat as a nutrient source which in thrue produces an odor.

Merocrine sweat glands

Found in most parts of body. Produces watery secretion with electrolytes, thermoregulated the body , and controlled by nervous system.

Mammary glands

produces milk; apocrine secretion

Cerumious glands

sweat glands in ears, sweat combines with secretions from sebaceous glands nearby to form wax (“cerumen”); apocrine secretion

Nail body

Main portion of nail; covers area known as “nail bed”

Nail root

Where growth starts

Free edge

distal portion of nail body; area that is cut

Eponychium

portion of stratum corneum extends over nail at nail root (also called the cuticle)

Hyponychium

area of thickened stratum corneum under free edge

lateral nail grooves

depressions on each side of the nail

Lateral nail folds

ridges on each side of the nail

Lunula

pale, crescent shape area at proximal part of nail body

Blood vessels

may be obscured near cuticle and make lunula “moon”

Function of nails

Protect tips of fingers and toes, supports digits during physical stree, and con be used as a diagnostic medical tool

Medical conditions of the integumentary system

Nails become yellow if have AIDS or thyroid gland problems.

Psoriasis

Rapid cell division of stem cells in stratum germinativum

Incision (Repair of skin due to injury)

Cut

Abrasion (Repair of skin due to injury)

scrape

Step one (Repair of skin due to injury)

injury (cut or scrape) to skin causes bleeding to occur, blood clots to stop bleeding, mast cells detect injury and trigger an immune response

Step two (Repair of skin due to injury)

Scab formed over injury, cells from stratum germinativum move into area. Blood flow to region increases bringing more phagocytic cells. Epithelial cells will migrate underneath the wound

Step three (Repair of skin due to injury)

Scab undermined by epidermal cells to start repair; fibroblasts produce meshwork of “fiber” over top of injury creating scar tissue

Step four (Repair of skin due to injury)

Scab disappears; fibroblasts continue to create scar tissue that will raise the overlapping epidermis higher than original skin

Granulation tissue

Combination of blood clot, fibroblasts, capillary network

Keloid

Thickened area of scar tissue which has a shiny surface

Aging

Epidermis thins, number of Langerhans cells decrease, D3 production drops, number of melanocytes decrease, gland activity reduces, blood supply to skin decreases, collagen decreases making skin thinner and weaker, elastic decreases making skin less tight more wrinkled, and moisture decrease making skin drier