The Integumentary System PDF

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The Integumentary System (2nd Exam) Integumentary System Consists of: 

Skin

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Hair

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Nails

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Sweat glands

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Sebaceous (oil) glands

Functions: 

Protection: a physical and chemical barrier to abrasion, invasion, dehydration, and UV light

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Temperature regulation: produces sweat, which reduces body temperature

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Stimulus Perception: nerve endings detect touch, temperature, pressure, etc.

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Excretion: perspiration serves to eliminate bodily wastes

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Synthesis of Vitamin D: conversion of type of cholesterol into vitamin D happens in the epidermis

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Blood/water reservoir: the dermis is extensively vascular and stores large volumes of blood until needed elsewhere

Structure: 

The skin consists of two distinct regions: o

Epidermis 

Most superficial region

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Consists of Keratinized stratified squamous epithelium

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Is avascular (lacking blood vessels) ALL EPITHELIUM US AVASCULAR

o

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Dermis 

Underlies the epidermis

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Thick, fibrous connective tissue layer

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Is vascular (contains blood vessels)

The subcutaneous layer just deep to the skin is the Hypodermis (not part of the skin) o

Not considered a part of the skin, but shares some functions

o

Also known as the “superficial fascia”

o

Made of adipose and areolar tissue

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Acts to anchor the skin to underlying muscles

o

Serves as a shock absorber and insulator

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Contains Pacinian corpuscles, which are nerve endings sensitive to pressure changes

Epidermis 

Cells of the epidermis: o

o

1) Keratinocytes 

Produce the fibrous protein Keratin that gives the skin its waterproof, protective properties

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Make up most cells of the epidermis

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Tightly connected by desmosomes

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Surface keratinocytes are dead, and millions fall off every day

2) Melanocytes 

Located in the deepest epidermis (base layer)

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Produce the protein Melatonin, which is the primary contributor to skin color 

Packaged into melanosomes, which are transferred to keratinocytes and help to protect their nuclei from UV damage

 o

3) Langerhans cells (dendritic cells) 

o

Macrophages that patrol the deep epidermis as part of the immune system

4) Merkel cells (tactile cells) 

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The tanner is the more protection you have

Sensory receptors that sense touch

The epidermis is made up of 4 or 5 distinct layers: o

1) Stratum Basale (strat - various layers) 

Deepest layer (base layer)

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Consists of a single layer of mitotic that move towards the surface of the skin to replace dead cells that have been shed

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o

o

Consists also of 10-25% Melanocytes, actively producing Melatonin

2) Stratum Spinosum (spinning layer) 

Several cell layers thick, made of spikey looking prickle cells, beginning to produce keratin

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Also find scattered melanosomes and dendritic cells

3) Stratum granulosum 

Four to six layers of flattened cells

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Cells start to lose nuclei and organelles as nourishment source gets further away

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Cells begin to accumulate keratin granules

4) Stratum lucidum

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Found only in thick skin (palms and pedal surface)

5) Stratum corneum 

Many tows of flat, anucleated, keratinized dead cells

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Accounts for three-quarters of epidermal thickness

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Functions to protect deeper cells, prevent water loss, prevent abrasion/penetration, and act as a physical barrier What layer is dividing all the other cells? Stratum Basale

Dermis 

Strong, flexible connective tissue layer

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Cells include fibroblasts, macrophages, and occasional mast cells and white blood cells

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Fibers within the matrix bind in the body together o

Makes up the “hide” that is used to make leather

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Contains nerves, blood vessels, and lymphatic vessels

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Contains epidermal hair follicles, oil glands, and sweat glands

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The dermis is composed of two layers: o

1)Papillary layer 

Made of areolar connective tissue with loose collagen and elastic fibers, and blood vessels

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Contains fingerlike regions where the dermis projects up into the epidermis, called Dermal papillae 

Dermal papillae contain capillaries, free nerve endings, and Meissner’s corpuscles (touch receptors)

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

o

Collectively ridges are called friction ridges 

Enhance gripping ability

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Contribute to sense of touch

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Sweat pores in ridges leave unique fingerprint pattern

2) Reticular layer 

Makes up ~80% of dermal thickness

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Consists of coarse, dense fibrous connective tissue 

Many Elastic fibers provide stretch-recoil properties

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Collagen fibers provide strength and resiliency o

Bind water, keeping skin hydrated

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

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Extracellular matrix contains pockets of adipose cells

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Cleavage (tension) lines in reticular layer are caused by many collagen fibers running parallel to skin surface

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Externally invisible

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Important to surgeons because incisions parallel to cleavage lines heal more readily

Flexure lines of reticular layer are dermal folds at or near joints

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Dermis is tightly secured to deeper structures

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

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Visible on hands, wrists, fingers, soles, toes

Skin color 

Three pigments contribute to skin color o

1) Melanin 

Only pigment made in skin; made by Melanocytes in the stratum Basale 

Packaged into melanosomes that are sent to Keratinocytes to shield DNA from sunlight

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Sun exposure stimulates melanin production

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Two forms: reddish yellow to brownish black

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All humans have same number of keratinocytes, so color differences are due to amount and form of melanin

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o

Freckles and pigmented moles are local accumulations of melanin

2) Carotene 

Yellow to orange pigment

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Most obvious in palms and soles

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Accumulates in stratum corneum and hypodermis

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Can be converted to vitamin A for vision and epidermal health

3) Hemoglobin 

Oxygen carrying pigment in blood that gives skin pinkish hue

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Pinkish hue of fair skin is due to lower levels of melanin 

Skin of Caucasians is more transparent, so color of hemoglobin shows through

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Skin color is a blend of the 3 pigments as influenced by Genetics and Environment

Hair 

Consists of dead keratinized cells

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

Functions: 

Warn of insects on skin

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Hair on head guards against physical trauma

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Protect from heat loss

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Shield skin from sunlight

Structure of a hair: 

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

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Produced by hair follicles

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Contains Hard keratin, not like soft found in skin o

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

Regions: o

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

o

Three parts of hair shaf: 

Medulla: central core of large cells and air spaces (inside of the hair)

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Cortex: several layers of flattened cells surrounding medulla (Outside)

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Cuticle: outer layer consisting of overlapping layers of single cells

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

Structure of a hair follicle:

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Extends from epidermal surface to dermis

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Hair Bulb: expanded area at deep end of follicle

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

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Hair matrix: actively dividing area of bulb that produces hair cells o

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Hair is considered a sensory touch receptor

As matrix makes new cells, it pushes older ones upward

Arrector pili muscle: small band of smooth muscle attached to follicle o

It contracts and pulls hair up/out from skin in response to cold/fright 

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Responsible for “goose bumps”

Hair Papilla o

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

Nails 

Scale-like modifications of epidermis that contain hard keratin

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

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Consist of free edge, nail plate, and root

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Nail bed is epidermis underneath keratinized nail plate

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Structure: o

Nail Matrix: thickened portion of bed responsible for nail growth

o

Nail folds: skin folds that overlap border of nail

o

Eponychium: nail fold that projects onto surface of nail body 

o

Also called Cuticle

Hyponychium: area under free edge of plate that accumulates dirt

o

Nails normally appear pink because of underlying capillaries 

Lunule: thickened nail matrix, appears white

Glands 

1) Sebaceous glands- (oil) exocrine glands usually found in association with a hair follicle. They secrete by the holocrine method o

Their secretion is called Sebum, it is a mixture of cholesterol, fats, and cell fragments which serve to protect from drying and inhibit bacterial growth

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2) Sudoriferous glands - (sweat) a mixture of water, salts and organic waste o

Sweat functions to eliminate wastes and to regulate body temperature.

o

Found on all skin surfaces except nipples and part of genitalia 

About 3 million per person

o

Contract upon nervous system stimulation to force sweat into ducts

o

Two main types: 

A) Eccrine (merocrine) (most kind) 

Most numerous type

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Abundant on palms, soles, and forehead

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Ducts connect to pores

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Function in Thermoregulation o

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Regulated by sympathetic nervous system

Their secretion is Sweat o

99% water, salts, vitamin C, antibodies, dermcidin (microbe-killing peptide), metabolic wastes

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B) Apocrine 

Confined to axillary and anogenital areas

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

Bacteria break down sweat, leading to body odor

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Larger than eccrine sweat glands with ducts emptying into hair follicles

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Begin functioning at puberty

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Modified apocrine glands o

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

o

Mammary glands: secrete milk

Skin Cancer 

Most skin tumors are Benign (not cancerous) and do not spread (metastasize) o

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Tumors that are cancerous are Malignant tumors

Risk factors: o

Overexposure to UV radiation

o

Frequent irritation of skin

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Some skin lotions contain enzymes that can repair damaged DNA

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Three major types of skin cancer o

o

1) Basal Cell Carcinoma 

Least malignant and most common

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Stratum Basale cells proliferate and slowly invade dermis and hypodermis

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Cured by surgical excision in 99% of cases

2) Squamous Cell Carcinoma

o

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Second most common type; can metastasize

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Involves Keratinocytes of stratum spinosum

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

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Good prognosis if treated by radiation therapy or removed surgically

3) Melanoma 

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

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Treated by wide surgical excision accompanied by immunotherapy

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Key to survival is early detection: ABCD rule A. Asymmetry: the two sides of the pigmented area do not match B. Border; 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 o

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Immediate threat is dehydration and electrolyte imbalance o

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Damage caused by denaturation of proteins, which destroys cells

Leads to renal shutdown and circulatory shock

To evaluate burns, the Rule of Nines is used o

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

o

Used to estimate volume of fluid loss

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Burns can be classified by severity: o

First-degree 

Epidermal damage only 

o

Localized redness, edema (swelling), and pain

Second-degree 

Epidermal and upper dermal damage 

Blisters appear

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First- and second-degree burns are referred to as Partial-thickness burns because only the epidermis and upper dermis are involved

o

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Third-degree 

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

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

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

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Skin grafting usually necessary

Burns are considered critical if: o

>25% of body has second-degree burns

o

>10% of body has third-degree burns

o

Face, hands, or feet bear third-degree burns

Treatment includes: o

Debridement (removal) of burned skin

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Antibiotics

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Temporary covering

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Skin grafts...