integumentary system

What does the Integumentary system consist of

Skin, hair, nails, glands

Structure of skin

2 main regions

• epidermis

• dermis

epidermis

superficial region

• epithelial tissue and is avascular

• keratinized stratified squamous epithelium

• made up of 4/5 layers → thick skin contains 5 layers and is found in high abrasion areas and soles of feet → thin skin has 4 layers

4 cells found in epidermis

1. keratinocytes

2. melanocytes

3. dendritic(langerhans)

4. tactile (merkel)

keratinocytes

most abundant cell type that arise from deepest layer of epidermis

tightly connected by desmosomes

Millions slough off every day

melanocytes

spider shapes cells located in deepest epidermis

produce pigment melanin which is packaged into melanosomes - melanosomes are transferred to keratinocytes where they protect nucleus from UV damage

dendritic cells

star shapes macrophages that patrol deep epidermis

• part of the immune system

tactile cells

attached to sensory nerve endings

dermis

underlies epidermis

Mostly fibrous connective tissue and flexible connective tissue, vascular

• cells include fibroblasts, macrophages and occasionally mast cells and wbc

• Contains nerves, blood vessels and lymphatic vessels

• Fibres in matrix bind body together

• contains epidermal hair follicles, oil glands, and sweat glands

• 2 layers: papillary and reticular

papillary layer

superficial layer of areolar tissue, consisting of loose, interlacing collagen and elastic fibres and bv

loose fibres allow phagocytes to patrol for microorganisms

dermal papillae: superficial region of dermis that sends fingerlike projections up into epidermis

• projections contain capillary loops, free nerve endings, and touch receptors (tactile corpuscles, aka meissner’s corpuscles)

In thick skin, dermal papillae lie on top of dermal ridges, which give rise to epidermal ridges

– Collectively, ridges are called friction ridges

• Enhance gripping ability

• Contribute to sense of touch

• Sweat pores in ridges leave unique fingerprint pattern

reticular layer

• Makes up 80% of dermal thickness

• Consists of dense fibrous connective tissue → many elastic fibers provide stretch recoil properties → collagen fibers provide strength and resiliency → bind water, keeping skin hydrated

• Cutaneous plexus: network of blood vessels between reticular layer and hypodermis

• ECM contains pockets of adipose cells

• Cleavage (tension) lines

• flexure lines

Cleavage (tension) lines

in reticular layer are caused by many collagen fibers running parallel to skin surface

– Externally invisible

– Important to surgeons because incisions parallel to

cleavage lines heal more readily

Flexure lines of reticular layer

are dermal folds at or near joints

– Dermis is tightly secured to deeper structures

– Skin’s inability to slide easily for joint movement causes deep creases

– Visible on hands, wrists, fingers, soles, toes

5 layers of epidermis

1. stratum basale

2. stratum spinosum

3. stratum granulosum

4. stratum lucidum

5. stratum corneum

stratum basale

• deepest of all

• firmly attached to dermis

• consists of a single row of stem cells that are mitotic, producing 2 daughter cells each time → one daughter cell journeys from basal to surface (25-45 days to reach). The cell dies as it moves towards surface→ other cell remains in stratum basale as stem cell

• layer aka stratum germinativum bc of active mitosis

• 10-25% of layer also composed of melanocytes

stratum spinosum (prickly layer)

• several layers thick

• cells contain weblike system of intermediate prekeratin filaments attached to desmosomes → allows them to resist tension and pulling

• keratinocytes in this layer appear spikey so they’re called prickle cells

• scattered among keratinocytes are abundant melanosomes and dendritic cells

stratum granulosum (granular layer)

• thin layer of flattened cells

• cell appearance changes → nuclei and organelles disintegrate → keratinization begins - cells accumulate keratohyaline granules that help keratin fibers in upper layers → cells also accumulate lamellar granules, a water resistant glycolipid that slows water loss

• cells above this layer die → too far from dermal capillaries to survive

stratum lucidum (clear layer)

• found only in thick skin

• consists of thin, translucent band of 2 to 3 rows of clear, flat, dead keratinocytes

stratum corneum

• several rows of flat, anucleated, keratinized dead cells

• accounts for ¾ of epidermal thickness

• though dead, cells still function to prevent water loss, protect deeper cells from environment, protect from abrasion and penetration, act as a barrier against chemical, biological and physical assaults

apoptosis

cells change by going through controlled cell death

dead cells slough off at a rate of 50,000 cells/min

3 pigments contribute to skin colour

1. melanin

2. carotene

3. hemoglobin

melanin

Only pigment made in skin; made by melanocytes

• Made from amino acid tyrosine

• Packaged into melanosomes that are sent to shield DNA of keratinocytes from damaging UV sunlight

The more sun, the more need for protective shield, the more melanin will be produced

Skin color differences are due to amount and colour of melanin

Freckles and pigmented moles are local accumulations of melanin

carotene

yellow to orange pigment (obtained from carotene rich foods).

most obvious in palms and soles

accumulates in stratum corneum and hypodermis

hemoglobin

pinkish hue of fair skin where the colour of hemoglobin shows through

cyanosis

Blue skin color: low oxygenation of hemoglobin

pallor

blanching or pale

• anemia, low bp, fear, anger

erythema

redness

• fever, hypertension, inflammation, allergy

jaundice

yellow cast

-liver disorders

bruises

blue and black marks

• aka ecchymoses or hematomas are a result of clotted blood beneath skin

• as clot is broken down colour of the bruise changes

hair

Consists of dead keratinized cells

• None located on palms, soles, lips, nipples, and portions of external genitalia

• Functions:

– Warn of insects on skin

– Hair on head guards against physical trauma

– Protect from heat loss

– Shield skin from sunlight

structure of a hair

Hairs (also called pili): flexible strands of dead, keratinized cells

• Produced by hair follicles

• Contains a harder keratin than skin

– Hard keratin is tougher and more durable, and cells do not flake off

• Regions:

– Shaft: area that extends above scalp, where keratinization is complete

– Root: area within scalp, where keratinization is still going on

Hair pigments are made by melanocytes in hair follicles

– Combinations of different melanins (yellow, rust, brown, black) create all the hair colors

 Red hair has additional pheomelanin pigment

 Gray/white hair results when melanin production decreases and air bubbles accumulating in shaft

3 parts of hair shaft

1. medulla: central core of large cells and air spaces

2. cortex: several layers of flattened cells surrounding medulla

3. cuticle: outer layer consisting of overlapping layers of single cells

structure of a hair follicle

Extends from epidermal surface to dermis

• Hair bulb: expanded area at deep end of follicle

• Hair follicle receptor (or root hair plexus): sensory nerve endings that wrap around bulb

– Hair is considered a sensory touch receptor

• Wall of follicle composed of:

– Peripheral connective tissue sheath

 Derived from dermis

 Also called fibrous sheath

– Glassy membrane: thickened basal lamina

– Epithelial root sheath

 Derived from epidermis

Hair matrix:

actively dividing area of bulb that produces hair cells

• As matrix makes new cells, it pushes older ones upward

Arrector pili:

small band of smooth muscle attached to follicle

• Responsible for “goose bumps”

Hair papilla

dermal tissue containing a knot of capillaries that supplies nutrients to growing hair

vellus hair

pale, fine body hair of children and adult females

terminal hair

coarse, long hair

• Found on scalp and eyebrows

At puberty

• Appear in axillary and pubic regions of both sexes

• Also on face and neck of males

hirsutism

In women, ovaries and adrenal glands produce small amounts of androgens (male sex hormones), but tumors on these organs can cause abnormally large amounts of androgens – Ex: polycystic ovary syndrome

Can result in excessive hairiness, called hirsutism, as well as other signs of masculinization

alopecia

hair thinning in both sexes after 40

baldness

Genetically determined and sex-influenced condition

Male pattern baldness caused by follicular response to DHT (dihydrotestosterone)

nails

• Scale-like modifications of epidermis that contain hard keratin

• Act as a protective cover for distal, dorsal surface of fingers and toes

• Consist of free edge, nail plate, and root

• Nail bed is epidermis underneath keratinized nail plate

Nail matrix

thickened portion of bed responsible for nail growth

nail folds

skin folds that overlap border of nail

Eponychium

nail fold that projects onto surface of nail body – Also called cuticle

Hyponychium

area under free edge of plate that accumulates dirt

• Nails normally appear pink because of underlying capillaries

• Lunule: thickened nail matrix, appears white

nail disease

Nail appearance can help in diagnosing some diseases such as:

• Thickened yellow nails can be due to a fungal infection of nail

• koilonchya also called “spoon nail” – an outward concavity of the nail may signal iron deficiency

sweat glands

sudoriferous glands

All skin surfaces except nipples and parts of external genitalia contain sweat glands

– About 3 million per person

• Two main types

– Eccrine (merocrine) sweat glands

– Apocrine sweat glands

eccrine (merocrine) sweat glands

• most numerous type

• abundant on palms, soles and forehead

• Ducts connect to pores

• Function in thermoregulation by releasing sweat

– Regulated by sympathetic nervous system

• Sweat is mostly water with salts, vitamin C, antibodies, dermcidin (microbe-killing peptide) and metabolic wastes

apocrine sweat glands

Confined to axillary and anogenital areas

Secrete viscous milky or yellowish sweat that contains fatty substances and proteins

– Bacteria break down sweat, leading to body odor

• Begin functioning at puberty

– Function unknown but may act as sexual scent gland

Other modified apocrine glands

• Ceruminous glands: lining of external ear canal; secrete cerumen (earwax)

• Mammary glands: secrete milk

sebaceous glands

Widely distributed, except for thick skin of palms and soles

Most develop from hair follicles and secrete into hair follicles

• Relatively inactive until puberty

– Stimulated by hormones, especially androgens

• Secrete sebum

– Oily holocrine secretion

– Bactericidal (bacteriakilling) properties

– Softens hair and skin

acne

Acne is usually an infectious inflammation of the sebaceous glands, resulting in pimples (pustules or cysts)

• Whiteheads are blocked sebaceous glands

– If secretion is oxidized, whitehead becomes a blackhead

• Overactive sebaceous glands in infants can lead to seborrhea, known as “cradle cap”

– Begins as pink, raised lesions on scalp that turn yellow/brown and flake off

functions of skin

Sensations

Thermoregulation

UV protection

Protection

Prevent h2o loss

Immunity

Vitamin D

chemical barrier

Skin secretes many chemicals which have anti-microbial properties, such as:

 Sweat

 Cells secrete antimicrobial defensin

 Sebum

– Acid mantle: low pH of skin retards bacterial multiplication

– Melanin provides a chemical barrier against UV radiation damage

physical barrier

Flat, dead, keratinized cells of stratum corneum, surrounded by glycolipids, block most water-soluble substances

– Some chemicals have limited penetration of skin

 Lipid-soluble substances

 Plant oleoresins (e.g., poison ivy)

 Organic solvents (acetone, paint thinner)

 Salts of heavy metals (lead, mercury)

 Some drugs (nitroglycerin)

biological barriers

- Epidermis contains phagocytic cells

 Dendritic cells of epidermis engulf foreign antigens and activate immune response

– Dermis contains macrophages

 Macrophages also activate immune response

organic solvents and stuff clinical app

if organic solvents or heavy metals pass through skin and enter blood, multiple organ systems can be devastated which can be lethal

– Examples:

 Kidneys can shut down

 Brain can be damaged

 Absorption of lead can result in anemia and neurological defects.

• Care must always be used when handling organic solvents or heavy metals

– Should never be touched with bare hands

body temp regulation

Under normal, resting body temperature, sweat glands produce unnoticeable sweat

– Called insensible perspiration

• If body temperature rises, dilation of dermal vessels can increase sweat gland activity to produce an increase of noticeable sweat

– Called sensible perspiration; designed to cool body

• Cold external environment

– Dermal blood vessels constrict

– Skin temperature drops to slow passive heat loss

metabolic functions

Skin can synthesize vitamin D needed for calcium absorption in intestine and other important health benefits

• Chemicals from keratinocytes can inactivate some carcinogens

• Keratinocytes can activate some hormones

– Example: convert cortisone into hydrocortisone

• Skin makes collagenase, which aids in natural turnover of collagen to prevent wrinkles

blood reservoir

Skin can hold up to 5% of the body’s total blood volume

• Skin vessels can be constricted to shunt blood to other organs, such as an exercising muscle

excretion

Skin can secrete limited amounts of nitrogenous wastes, such as ammonia, urea, and uric acid

sweating can cause salt and water loss

skin cancer

Risk factors

– Overexposure to UV radiation

– Frequent irritation of skin

• Three major types of skin cancer

– Basal cell carcinoma

– Squamous cell carcinoma

– Melanoma

basal cell carcinoma

Least malignant and most common, does not metastasize

Stratum basale cells proliferate and slowly invade dermis and hypodermis

Cured by surgical excision in almost all cases

squamous cell carcinoma

- Second most common type; can metastasize

– Involves keratinocytes of stratum spinosum

– Usually is a scaly reddened papule on scalp, ears, lower lip, or hands

– Good prognosis if treated by radiation therapy or removed surgically

melanoma

Cancer of melanocytes; is most dangerous type because it is highly metastatic and resistant to chemotherapy

– Treated by wide surgical excision accompanied by immunotherapy

– Key to survival is early detection: ABCD rule

 A: asymmetry; the two sides of the pigmented area do not match

 B: border irregularity; exhibits indentations

 C: color; contains several colors (black, brown, tan, sometimes red or blue)

 D: diameter; larger than 6 mm (size of pencil eraser)

burns

Tissue damage caused by heat, electricity, radiation, or

certain chemicals

– Damage caused by denaturation of proteins, which destroys cells

Immediate threat is dehydration and electrolyte imbalance

– Leads to renal shutdown and circulatory shock

• To evaluate burns, the Rule of Nines is used

– Body is broken into 11 sections, with each section representing 9% of body surface (except genitals, which account for 1%)

– Used to estimate volume of fluid loss

when are burns considered critical

Burns are considered critical if:

– >25% of body has second-degree burns

– >10% of body has third-degree burns

– Face, hands, or feet bear third-degree burns

treatment for burns

- Debridement (removal) of burned skin

– Antibiotics

– Temporary covering

– Skin grafts

1st degree burn

Epidermal damage only

– Localized redness, edema (swelling), and pain

2nd degree burn

Epidermal and upper dermal damage

– Blisters appear

3rd degree burn

Entire thickness of skin involved (referred to as full-thickness burns)

 Skin color turns gray-white, cherry red, or blackened

 No edema is seen and area is not painful because nerve endings are

destroyed

 Skin grafting usually necessary