apk2100c chapter 5 - the integumentary system

The integumentary system

1. skin

2. accessory organs

Skin (integument)

• largest organ of body

Accessory organs

• hair

• nails

• oil and sweat glands

Regions of skin

• epidermis (top layer)

• dermis (deep to epidermis)

• hypodermis (underneath, not technically part of the skin - association with layers on top)

Gross Structure of the Skin and Underlying Anatomy

• epidermis then dermis

• hypodermis (has lot of adipose tissue)

Functions of skin

• thermoregulation

• protection

• sensory reception

• excretion

• vitamin D production

thermoregulation

• vessels, capillaries

• ability to sweat

• disipate heat

protection

natural physical barrier from external vs internal

sensory reception

lots of nerve endings that will sense signals

(tactile, pressure, cold temp, etc.)

excretion

certain solutes, salts, water content can leave the body

vitamin d production

happens in the skin

epidermis

• Most superficial layer

• avascular

• keratinized stratified squamous epithelium (hard)

• contains 4 principal cells

  • keratinocytes - over 90 percent

  • melanocytes - pigment

  • langerhans cells (dendritic cells) - immune function

  • merkel cells (tactile epith cells) - pressure, touch, tactile senses

avascular

• no blood vessels ( in epidermis )

Thin skin

• keratinized stratified squamous ET

• areas of skin where little friction develops

• most of body

• FOUR epidermal layers

• thin epidermis

Thick skin

• areas where friction commonly develops

• palms, feet, fingertips

• FIVE epidermal layers

• thick/larger epidermis (keratinized layer)

Stratum

layer

Stratum basale (TE)

• Thin epidermis

• Most basal layer → Deepest epidermal layer

• One row of actively mitotic cells (keratinocytes)

  • A lot of cell division happening

  • pushing up → bumping cells upward

• Melanocytes (produced melanin) → deposits melanin into keratinocytes

• see dendritic cells - touch sensation

Melanocytes

dictates skin pigment - produces melanin

Stratum spinosum (TE)

• thin epidermis

• several layers of keratinocytes unified by desmosomes

• cells contain thick bundles of intermediate filaments made of pre-keratin

  • tonofilaments

• pushed up from basale

Statum granulosum (TE)

• Thin epidermis

• one to five layers of flattened cells

• organelles deteriorating

• cytoplasm full of lamellar granules (release lipids - makes skin waterproof) and keratohyaline granules

Stratum corneum (TE)

• thin epidermis

• most superficial layer

• 20-30 layers of dead cells → flat membranous sacs filled with keratin

• glycolipids in extracellular space

Layers of thin epidermis

Does the thick epidermis have the same layers as the thin epidermis?

Has all four, but one extra layer called the stratum lucidum

• stratum corneum = more thicker in thick epidermis

Stratum lucidum

• only in thick epidermis

• slightly translucent

• thin, clear layer of dead skin cells

Epidermis is replaced how often?

Every month

ex. tanning (epidermis)

ex. tattoo = deposited into deeper skin (places that hav blood vessels)

What are the 3 pigments that impart varying colors and tones to skin and hair?

Melanin (produced in hair and skin)

Carotene (orange color - baby eating carrots)

Hemoglobin (in blood, red color)

Two types of melanin

• Pheomelanin

• Eumelanin

Pheomelanin

• imparts yellow to red colors

• particularly noticeable in hair

Eumelanin

• impacts a brown to black color (overrides of pheomelanin)

Number of melanocytes for everyone is…

the same

Why are there color differences (although there is the same number of melanocytes)?

Due to the amount of pigment produced (melanin) and transferred to keratinocytes

Light skin

• melanocytes producing less melanin

• melanin clumped near nucleus

• breaks down quickly

Dark skin

• Melanocytes produce more melanin

• melanin spread through keratinocytes

• breaks down slowly (harder)

Abundant pheomelanin in hair

Minimal eumelanin in skin

Abundant eumelanin in skin and hair

Moderate pheomelanin and eumelanin in skin

Abundant eumelanin in hair

How do melanocytes produce protein (melanin)?

• Takes the amino acid tyrosine and converts it to melanin

• Melanocytes transfer melanin granules into keratinocytes

• melanin keratocytes like to surround itself around nucleus (shield against UV rays)

What do melanin place itself between?

The sun and the cell’s nucleus

• melanin granules act as shield against UV rays to prevent cancer

Albinism

• Cannot produce any melanin due to a genetic disorder

• Inability to produce the tyrosinase enzyme

• translucent hair, skin, and eyes → can have visual issues

• display pink or red eyes → due to hemoglobin in blood vessels

What tissue is in the dermis

Mostly connective tissue → very tough

What structures are in the dermis?

• blood vessels → vascular region of skin

• lymphatic vessels

• nerves

Regions of dermis

Papillary layer of the dermis = superficial → areolar loose connective tissue proper

Reticular (network) layer of the dermis = deeper → dense irregular connective tissue proper

Papillary layer of dermis

superficial → areolar loose connective tissue proper

Reticular layer of dermis

deeper → dense irregular connective tissue proper

swirling pattern of collagen fibers

what is dermal papillae

Feature of dermis

• small projections of papillary dermis into overlying epithelium above

dermal papillae function

• Enhances surface area for nutrients/gas exchange (to go up to the epidermis that is avascular)

• Strengthens the dermal-epidermal junction → tightly bound

• does NOT make fingerprints

Epidermal ridges

• Ridges are part of fingerprints

• dermal papillae don’t match the epidermal ridges

Dermal ridges

Form fingerprints

Underlying mounds of tissue and protrudes upward

Cleavage lines

• Separations or less dense regions of collagen bundles (space between bundles) in the reticular dermis

• create an invisible cleavage line in the skin

• Incisions made along lines heal more quickly and gape less than incisions made across (important for surgery)

• run longitudinally

Hypodermis

Not a part of the skin (below the skin)

Subcutaneous layer of CT

What is hypodermis made of?

Mostly adipose tissue loose CT proper

• varies in thickness

• cushion and padding

• protects underlying structures, insulates, and stores energy

What does the hypodermis contain?

Large blood vessels, lymphatic vessels, and nerves whose branches extend into dermis

Cutaneous sensation (how do we feel things with our skin)

• many sensory structures embedded in the dermis (nerve endings)

• some free endings - sensory structures derived from the epidermis

  • hair follicles

  • sweat glands

  • oil glands

• some structures are from underlying nerves, which transmit information to the CNS

• in epidermis so you can detect pain right away

Appendages of skin

• derived from epidermis but mostly located in dermis

  • nails

  • hair and hair follicles

  • sebaceous (oil) glands

  • sweat glands

Nails

• scale like modification of epidermis containing dead keratinocytes full of HARD keratin

Superficial nail structures

• free edge of the nail

• lunule

• lateral nail fold

• nail plate

• eponychium (cuticle)

free edge of nail

part you cut off

nail plate

directly over digit of nail

pink part of nail - transparent due to dead keratinocyte so see blood

lunule

half moon shape white area

only visible part of the nail matrix - cells proliferating for nail growth (thick) → highly mitotic cells

lateral nail fold

around nail and will turn into the cuticle (eponychium)

eponychium

cuticle

Deep nail structures

• nail bed

• phalanx (bone of fingertip)

• nail root

Nail bed

• made up of epidermal cells under nail plate

Nail root

• covers the nail matrix

Hair

• flexible columns of dead keratinocytes full of HARD keratin

shaft of hair

above the surface

root of hair

below surface

Hair medulla

inner core

Hair cortex

around medulla

Hair cuticle

superficial layer

hair follicle

• Sheath around the hair

• made up of external and internal root sheath

external root sheet

• most superficial to hair

• derived from the stratum basale

internal root sheath

• closest to hair

• just outside of hair cuticle

• derived from stratum corneum of the epidermis

  • invaginates downward to turn into this

Hair bulb

• End of hair root - enlarged

• Has a connective tissue papilla = blood vessels come into matrix

• matrix cells = highly mitotic allowing for hair growth

Arrector pili muscle - hair

Directly attached to the hair follicle

This muscle contracts, pulling hair up = goosebumps

Smooth muscle - involuntary

Sebaceous gland

Body’s natural moisturizer

produces oil = sebum

Product dumped into the hair follicle

Sebum

• Keeps hair/skin soft

• protects against brittle hair/skin

• Protects the epidermis from cracking

• Collects dirt/dust

• impedes water loss across the skin

Where do we have sebaceous glands?

Located everywhere except plantar and palmar regions (palms of hand and soles of feet)

Glassy membrane

Outside of the root sheath of hair

Thin transparent tissue

Anchors self to basement membrane

Types of hair

• straight (circle cross section)

• wavy

• curly (oval cross section)

What are the two types of sweat glands (sudoriferous)

Eccrine sweat glands

Apocrine sweat glands

Eccrine sweat glands

• palms, soles, forehead (predominantly)

• true “sweat”; watery

• thermoregulatory function

• duct opens directly onto skin surface

Apocrine sweat glands

• axillary, anal, genital areas only

• duct opens to the hair follicle (similar to sebaceous) + mixes with sebum/stuff

  • dumps into hair follicle

• milky “sweat”

• body odor

• no thermoregulatory function