A&P Integumentary System

Structure included in the Integumentary System

Skin, Hair, Nails, Sweat Glands, and Sebaceous (oil) glands

How many distinct regions are in the skin

2: Epidermis and Dermis

What is the third region that is not a part of the skin but shares some functions

Hypodermis, or subcutaneous tissue.

Epidermis

The superficial region consisting of epithelial tissue. Avascular

Dermis

Underlies the epidermis. Made of mostly fibrous connective tissue, vascular.

Hypodermis (superficial fascia)

Subcutaneous layer deep to skin. Made of mostly adipose tissue that absorbs shock and insulates. Anchors skin to underlying structures: mostly muscles.

1

Dermal Papillae

2

Sweat Pore

3

Eccrine Sweat Gland

4

Arrector Pili Muscle

5

Sebaceous (oil) gland

6

Hair follicle

7

Hair root

8

Dermal vascular plexus

9

Adipose Tissue

10

Hair follicle receptor (root hair plexus)

11

lamellar corpuscle

12

Sensory nerve fiber with free nerve endings

13

Subcutaneous Tissue (Hypodermis: not part of Skin)

14

Reticular Layer

15

Dermis

16

Papillary Layer

17

Epidermis

18

Hair Shaft

What is the epidermis mostly made up of

Keratinized Stratified squamous epithelium

Four cell types found in the epidermis

Keratinocytes, Melanocytes, Dendritic (Langerhans) cells, Tactile (Merkel) cells

Keratinocytes

• Produce fibrous keratin (protein that gives skin its protective properties)

• Major cells of epidermis

• Tightly connected by desmosomes

• Millions slough off every day

Melanocytes

• Spider-shaped 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 (Langerhans) cells

• Star-shaped macrophages that patrol deep epidermis

  • Are key activators of immune system

Tactile (Merkel) cells

Sensory receptors that sense touch

In thin skin epidermis contains how many layers?

4: Stratum basale, stratum spinosum, stratum granulosum, stratum corneum

How many layers are found in thick skin?

5: the stratum lucidum is found between the stratum granulosum and the stratum corneum

Where is thick skin found

High-abrasion areas such as hands and feet

Which layer is the deepest of all epidermal layers

Stratum basale (basal layer): is firmly attached to the dermis

What is the make up of thee stratum basale

• Consists of a single row of stem cells that actively divide (mitotic), producing two daughter cells each time

  • One daughter cell journeys from basal layer to surface, taking 25–45 days to reach surface

    • Cell dies as it moves toward surface

  • Other daughter cell remains in stratum basale as stem cell

What is the stratum basale also know as

Layer also known as stratum germinativum because of active mitosis

What type of cell makes up 10-25% of the stratum basale

melanocytes

Characteristics of the stratum spinosum

• Several cell 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 are called prickle cells

• Scattered among keratinocytes are abundant melanosomes and dendritic cells

How many cells thick is the stratum granulosum?

Four to six cells thick but these cells are flattened making the layer thin

What changes occur in the appearance of cells found in the stratum granulosum?

• Cells flatten, nuclei and organelles disintegrate

• Keratinization begins

  • Cells accumulate keratohyaline granules that help form keratin fibers in upper layers

• Cells also accumulate lamellar granules, a water-resistant glycolipid that slows water loss

Why do cells found above the stratum granulosum die?

They are too far from dermal capillaries to facilitate access of nutrients from the bloodstream

What is the stratum lucidum?

• Found only in thick skin

• Consists of thin, translucent band of two to three rows of clear, flat, dead keratinocytes

• Lies superficial to the stratum granulosum

What is the stratum corneum?

• 20–30 rows of flat, anucleated, keratinized dead cells

• Accounts for three-quarters of epidermal thickness

What functions do the dead cells making up the stratum corneum maintain?

• Protect deeper cells from the environment

• Prevent water loss

• Protect from abrasion and penetration

• Act as a barrier against biological, chemical, and physical assaults

How do cells change?

Cells change by going though apoptosis (controlled cell death)

• Dead cells slough off as dandruff and dander

• Humans can shed ~50,000 cells every minute

What type of tissue and cells make up the dermis?

• Strong, flexible connective tissue

• Cells include fibroblasts, macrophages, and occasionally mast cells and white blood cells

• Fibers in matrix bind body together

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

What structures can be found in the dermis?

• Contains nerves, blood vessels, and lymphatic vessels

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

How many layer make up the dermis (what are they called)

Two layers: Papillary and Reticular

What is the papillary layer?

• Superficial layer of areolar connective tissue consisting of loose, interlacing collagen and elastic fibers and blood vessels

• Loose fibers allow phagocytes to patrol for microorganisms

• Dermal papillae

What are the dermal papillae found in the papillary layer

• superficial region of dermis that sends fingerlike projections up into epidermis

  • Projections contains capillary loops, free nerve endings, and touch receptors (tactile corpuscles, also called 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

What is the Reticular Layer?

• Makes up ~80% of dermal thickness

• Consists of coarse, dense fibrous connective tissue

  • Many elastic fibers provide stretch-recoil properties

  • Collagen fibers provide strength and resiliency

    • Bind water, keeping skin hydrated

• Cutaneous plexus

• Extracellular matric

What is the cutaneous plexus in the reticular layer

network of blood vessels between reticular layer and hypodermis

What is contained in the reticular layer’s extracellular matrix

Pockets of adipose cells

What causes cleavage (tension) lines in reticular layer

• many collagen fibers running parallel to skin surface

  • Externally invisible

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

What are flexure lines in the reticular layer

• 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

What causes striae or stretch marks

Extreme stretching of skin can cause dermal tears that leave silvery white scars

What causes blisters?

Acute, short-term traumas to skin can cause

What are blisters

fluid-filled pockets that separate epidermal and dermal layers

What are the three pigments that contribute to skin color?

Melanin, Carotene, Hemoglobin

Key characteristics about Melanin

• Only pigment made in skin; made by melanocytes

• Made from amino acid tyrosine by tyrosinase

• 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

• Two forms: reddish yellow to brownish black

• Skin color differences are due to amount and form of melanin

• Freckles and pigmented moles are local accumulations of melanin

How does excessive sun exposure damage skin

• Elastic fibers clump, causing skin to become leathery

• Can depress immune system and cause alterations in DNA that may lead to skin cancer

• UV light destroys folic acid

  • Necessary for DNA synthesis, so insufficient folic acid is especially dangerous for developing embryos

• Photosensitivity is increased reaction to sun

  • Some drugs (e.g., antibiotics, antihistamines) and perfumes cause photosensitivity, leading to skin rashes

What is the pigment carotene?

• Yellow to orange pigment

• Most obvious in palms and soles 

• Accumulates in stratum corneum and hypodermis

• Can be converted to vitamin A for vision and epidermal health

What is the pigment Hemoglobin?

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

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

Examples of alterations in skin cancer that can indicate disease

• Cyanosis

  • Blue skin color: low oxygenation of hemoglobin

• Pallor (blanching or pale color)

  • Anemia, low blood pressure, fear, anger

• Erythema (redness)

  • Fever, hypertension, inflammation, allergy

• Jaundice (yellow cast)

  • Liver disorders

Alterations in skin color that can indicate disease

• Bruises (black-and-blue marks)

  • Also referred to as ecchymoses or hematomas, are a result of clotted blood beneath skin

  • As clot is broken down, color of bruise changes

• Brown or black “necklace” or bruises

  • Hyperpigmented dark areas in axillae and around neck may be a sign of insulin resistance and elevated blood glucose levels

What is hair/pili made of?

• flexible strands of dead, keratinized cells

  • Produced by hair follicles

• Contains hard keratin, not like soft keratin found in skin

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

Where is hair not located?

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

What are the functions of hair?

• Warn of insects on skin

• Hair on head guards against physical trauma

• Protect from heat loss

• Shield skin from sunlight

Regions of the hair

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

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

What are the three parts of hair shaft?

• Medulla: central core of large cells and air spaces

• Cortex: several layers of flattened cells surrounding medulla

• Cuticle: outer layer consisting of overlapping layers of single cells

How are hair pigments mad 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 replace melanin in shaft

What is the 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

What is the wall of a 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

What is the hair matrix

• actively dividing area of bulb that produces hair cells

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

What is the arrector pili

•  small band of smooth muscle attached to follicle

  • Responsible for “goose bumps”

What is the 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

Hair growth

• Nutrition and hormones affect hair growth

• Follicles cycle between active and regressive phases

  • Average 2.25 mm growth per week

  • Lose 90 scalp hairs daily

Homeostatic imbalance of androgens in women

• 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

• In many cases, no clinical problem is found

Alopecia

hair thinning in both sexes after age 40

True baldness

• Genetically determined and sex-influenced condition 

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

Telogen effluvium (TE)

•  is abrupt hair thinning caused by an abundance of hair follicles entering resting phase at same time

  •  Can be due to stress-induced factors such as: hormonal changes, surgery, severe emotional trauma, or crash dieting

Other causes or thinning and/or texture change:

• Drugs (ex: antidepressants, chemotherapeutic drugs)

• Hypothyroidism

• Protein-deficient diets

Nail key information

• Scalelike 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

Nail Color

• Nails normally appear pink because of underlying capillaries

  • Lunule: thickened nail matrix, appears white

• Abnormal color or shape can be an indicator of disease

Instances when nail appearance can help in diagnosing some diseases

• Yellow-tinged may indicate respiratory or thyroid gland disorder

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

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

• Beau’s lines – horizontal lines across nails may indicate severe illnesses such as uncontrolled diabetes, heart attack or cancer chemotherapy

Basic Information of Sweat Glands

• Also called 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

• Contain myoepithelial cells

  • Contract upon nervous system stimulation to force sweat into ducts

Multicellular exocrine glands mode of secretion

• Merocrine: most secrete products by exocytosis as secretions are produced (sweat, pancreas)

• Holocrine: accumulate products within, then rupture (sebaceous oil glands)

• Apocrine: accumulate products within, but only apex ruptures; whether this type exists in humans is controversial (maybe mammary cells?)

Eccrine (Merocrine) Sweat Glands

• Most numerous type

• Abundant on palms, soles, and forehead

• Ducts connect to pores

• Function in thermoregulation

  • Regulated by sympathetic nervous system

• Their secretion is sweat

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

• Larger than eccrine sweat glands with ducts emptying into hair follicles

• Begin functioning at puberty 

  • Function unknown but may act as sexual scent gland

Modified Apocrine Glands

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

• Mammary glands: secrete milk

Sebacious (Oil) 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

What is sebum

• Oily holocrine secretion

• Bactericidal (bacteria-killing) properties

• Softens hair and skin

What causes acne?

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

  • Associated with Propionibacterium acne infection

• Whiteheads are blocked sebaceous glands

  • If secretion is oxidized, whitehead becomes a blackhead

What causes “cradle cap”?

• 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