A & P exam 2

integument is made up of 2 main sections

epidermis and dermis

epidermis

• sits on top of the dermis

• superficial layer

• epithelial tissue (has to sit on top of CT)

• avascular - no blood vessels

• thinner

dermis

• deeper layer underneath the epidermis

• fibrous CT

• vascular- has blood vessels

• thicker

subcutaneous layer

• also known as hypodermis

• deep to the skin

• shares some of the skin's functions

• adipose tissue- shock absorption and insulation

• anchors the skin due to underlying structures (skeletal muscles)

cells within epidermis

• mainly consists of keratinized stratified squamous epithelium tissue

4 cell types within the epidermis

• keratinocytes

• melanocytes

• dendritic cells

• tactile cells

cells of the epidermis

mainly consists of keratinized stratified squamous epithelium (protection)

keratinocytes

• produce keratin

• Keratin is a fibrous protein that gives skin its protective properties

• connected by desmosomes

• we slough off millions a day

melanocytes

• produce melanin pigment and packages into melanosomes

• found in deepest layer of epidermis

• stellate-shaped cells

• melanosomes are transferred to keratinocytes to help protect the cell from UV damage

dendritic cells

• macrophage cells help to activate the immune system

• found deep within the epidermis

tactile cells

sensory receptors for touch

layers of epidermis

4-5 layers (strata), depending on skin thickness

1. stratum basale

2. stratum spinosum

3. stratum granulosum

4. stratum lucidum*

5. stratum corneum

Thick skin

5 layers

Thin skin

4 layers

stratum basale

• deepest epidermal layer, firmly attached to the dermis

• single row of stem cells (mitotic cells) that are at the basal layer (alive)

• 10-25% of cells are melanocytes

stratum spinosum

• several layers thick

• prickly

• keratinocytes in this layer have a spiky appearance

• Melanosomes and dendritic cells are scattered throughout

stratum granulosum

• 4-6 layers of flattened cells

• organelles disintegrate

• keratinization has begun

• cells accumulate water-resistant glycolipid

• last layer of living cells

• above this layer, cells begin to die due to increased distance from dermal capillaries

keratinization

• glycoprotein that is water-resistant

• shield cell

stratum lucidum

• only found in THICK skin

• 2/3 layers of translucent, dead keratinocytes

• superficial layer to granulosum

• found in heel of foot, palm of hands, etc

stratum corneum

• many rows of flat, anucleated, dead keratinocytes

• ¾ of epidermal thickness

• still has function despite being dead cells (acts as a barrier from environment and prevents water loss)

Dermis

• strong fibrous connective tissue

• bind body tg and make up our hide (leather)

• mainly fibroblasts and macrophages

• nerves and blood vessels

• hair follicles, oil, and sweat glands

two layers that make up dermis:

• papillary (what epidermis sits on)

• reticular

papillary layer

• areolar CT w interlacing collagen and elastic fibers

• Superficial region contains dermal papillae (fingerlike projections) extending towards the epidermis (bc epidermis has no blood supply, so that’s how it gets oxygen and nutrients)

• Papillary contains capillary loops, nerve endings, and touch receptors

• in thicker skin, dermal papillae gives rise to epidermal ridges (friction ridges)

Increases gripping ability, contributes to sense of touch, and leaves unique fingerprint patterns, which are enhanced by sweat pores

reticular layer

• 80% of the dermis thickness

• composed of dense irregular CT

• elastic fibers, collagen fibers, and binds to h20 to maintain skin hydration

• contains dermal plexus

• collagen fibers form cleavage tension lines when running parallel to the skin’s surface

• near joints, the deep dermis forms flexure lines, where the deep dermis is tightly secured to deeper structures

cleavage lines

• represent separation between underlying collagen fiber bundles in reticular dermis

• surgical incisions running parallel to cleavage lines heal better than those made across them

flexure lines

• form where dermis is closely attached to underlying structures

hypodermis

• subcutaneous tissue

• hypodermic injections (subQ)

• highly vascular

• mostly adipose

functions:

• energy reservoir

• thermal insulation (keeps us warm)

• padding/cushioning

skin color

• melanin, made by melanocytes, gets packed into melanosomes and then transferred to keratinocytes

• Protects keratinocyte DNA from UV damage

• darker skin = more melanin production

• Carotene: yellowish-orange pigment that you can get from carrots, and it accumulates in the stratum corneum

• hemoglobin: pinkish hue of fair skin due to low levels of melanin and blood gets close to skins surface

basal layer of epidermis

most alive cells

superficial layer of epidermis

most dead cells (near stratum corneum)

hair

• flexible strands of dead, keratinized cells

• produced by hair follicles

• Keratin in hair is tougher/harder than keratin in skin

• hair shaft- above skin

• hair root- within skin

functions

• thermoregulation

• protect from sun

• sensation

• facial expression

structure of hair follicle

• hair root sits within hair follicle

• deep end of hair follicle is known as hair bulb

• The follicular wall has 3 layers folded down from the epidermis to the dermis

• hair papilla extends into hair bulb and contains knot of capillaries which supplies nutrients to hair growth

• actively dividing area within hair bulb (hair matrix)

• new cells push old cells upward

structure of hair shaft

• cuticle- outer layer of hair (single cells)

• cortex- layers of flattened cells surrounding the medulla

• medulla- central core containing large cells and air spaces (making it light)

structure of hair follicle

• each hair bulb is surrounded by sensory nerve endings

• The arrector pili is a smooth muscle attached to each hair follicle

• hair pigments are made by melanocytes at the base of hair follicle

• pigment transferred to cortical cells

• genetics determine differences in melanin structure

• more melanin = darker hair

• decreased melanin = gray/white hair

types of hair and hair and hair growth

• Languo- fine, unpigmented hair, downy hair: appears in last trimester (babies have this in utero to keep them warm)

• vellus- pale, fine body hair, hair of children: primary human hair (all hair on children)

• terminal hair- darker, coarser hair (eyebrows, lashes, armpit etc.)

• vellus hair transitions into terminal hair

Nails

• scale-like, modified stratum corneum containing hard keratin

• protective cover for the distal, dorsal digital surface

• nail matrix is thickened portion of nail bed responsible for nail growth (alive)

exocrine glands

• glands that secrete secretions onto a surface

• merocrine sweat gland

• apocrine sweat gland

• sebaceous gland

sweat glands

1. merocrine gland- smaller

2. apocrine gland- larger, secretes onto hair follicle

• contain myoepithelial cells that contract when stimulated by nervous system to squeeze secretions out of gland

merocrine (eccrine) gland

• secrete onto skin surface

• palms, soles, forehead

• small and simple

• function in thermoregulation

• secrete sweat (99% water)

apocrine glands

• confined to areas of terminal hair (axillary and anogenital)

• secrete onto hair follicle

• larger than eccrine gland

• secrete more viscous, milky sweat leading to body odor

• function begins at puberty

• two modified apocrine glands:

• ceruminous (ear wax)

• mammary (breast milk)

sebaceous oil gland

• most secrete into hair follicles

• mostly inactive until puberty

• secretes sebum (oily bacterial secretion that softens hair and skin)

functions of skin

protection

• chemical barrier

•