A&P Lab 1 (Chapter 5)

The Integumentary System

What is the anatomical term for skin?

Cutaneous membrane

What is the 2 main layers of the skin?

1. Epidermis (on top)

2. Dermis (beneath, separated by a basement membrane)

What layers sits below both the Epidermis (top) and Dermis (beneath epidermis)?

Hypodermis (which secures skin to deeper muscle and bone via loose connective and adipose tissue)

What are the 6 accessory structures of the skin?

1. sweat glands

2. sebaceous glands

3. hair follicles

4. nails

5. sensory receptor

6. arrector pili muscles

The Epidermis

• avascular (has no blood vessels)

• cells receive oxygen and nutrients by diffusion from vessels in the deep dermis

• The dominant cell type is the keratinocyte, which produces keratin (a tough, fibrous protein that gives the skin strength)

• As keratinocytes migrate upward, they fill with keratin, harden, and eventually die, forming the protective outer surface.

• The epidermis is separated into 4-5 strata (layers) which allows the skin to keep recycling and building new protective barriers

What is avascular?

having no blood vessels

what is the dominant cell type of the epidermis?

keratinocyte

What do keratinocytes produce? What is Keratin?

keratin; a tough, fibrous protein giving the skin strength

What are the 5 epidermal strata (layers) (deep to superficial)?

1. Stratum Basale

2. Stratum Spinosum

3. Startum Granulosum

4. Stratum Lucidum

5. Stratum Corneum

(REMEMBER: Before Sun, Get Lotioned Completely)

What layer is the deepest layer?

Stratum Basale

• Single row of stem cells on the basement membrane

• Most mitotically active, continuously producing new keratinocytes to push upward to the surface to replace the dead surface cells.

  • Examples of these cells are melanocytes, tactile epithelial cells, and keratinocyte stem cells

What do melanocytes do?

produces melanin and the pigment (from the melanin) protects the underlying keratinocytes DNA from UV-radiation

What are the Tactile Epithelial cells? (in Basale)

sensory receptors that are paired with small neurons from the dermis

• detect light touch concentrated in the finger tips, lips, base of hairs.

What are Keratinocyte cells? (in basale)

• source of all cells populating the layers

• where vitamin D synthesis begin

• (whether this layer (basale) survives during an injury, determines whether skin can regenerate on its own)

Which layer is the thickest layer? (Hint: cell shape looks like spines)

Stratum Spinosum (10-14 layers)

• Cells are still alive and mitotically active

• Contains immune cells (phagocytes)

• Contains Dendritic epidermal cells (immune phagocytes) that patrol for pathogens and protect skin and deeper tissues

Which layer has 3-5 layers?

stratum granulosum (3-5 layers)

• Contains prominent cytoplasmic granules with keratin bundles and lipid-based substances

• Hydrophobic lipids are secreted and create a waterproof barrier

  • This lipid release cuts off nutrient supply, and the cell begins to die

Which layer is primarily thin but is only thick on the palms and soles (feet)?

stratum lucidum

• thin, clear layer of dead keratinocytes found only on thick skin

• ONLY thick in the palms and soles

• provides protection

Which layer is the outermost layer?

stratum corneum

• multiple layers of dead, flattened keratinocytes packed with keratin; primary barrier

• This layer is the primary physical and chemical barrier between the body and the outside world

Whats the difference between thick and thin skin?

Thick skin

• found ONLY on palms and soles

• all FIVE epidermal layers

• VERY THICK stratum corneum (the outermost layer)

• MANY skin glands

Thin skin

• covers MOST of the body

• ONLY FOUR epidermal layers (No stratum lucidum - primarily thin skin but only thick on the palms and soles)

• Includes hair follicles and sebaceous glands

A callus forms in either skin type when repetitive pressure stimulates the production of extra stratum corneum layers

What is the second major layer of the skin?

The dermis

The Dermis

• Highly vascular (has blood vessels) connective tissue beneath the epidermis

• Supplies blood to the avascular (has no blood vessels) epidermis

• divided into 2 sub-layers:

  • Papillary Layer

  • Reticular layer

What are the 2 sub-layers of the dermis?

Papillary Layer

• Thinner, more superficial

• Loose connective tissue

• Houses tactile corpuscles (Messiner’s) for light touch detection

  • Concentrated in fingertips, lips, and face

Reticular Layer

• Deeper, thicker

• Dense irregular connective tissue (collagen bundles provide strength)

• Contains lamellar corpuscles (Pacinian) for deep pressure and vibration

  • + Blood vessels, sweat glands, hair follicles, and sebaceous glands and adipose tissue

Injuries and Fingerprints on the Dermis layer

Injury requiring sutures

• The reticular dermis provides the tensile strength (pulling and stretching) needed to hold wound edges together

  • Sutures only anchored in the epidermis layer CANNOT resist tearing forces from multiple directions

    • Proper anchoring into the reticular dermis minimizes scarring and ensure effective wound closure

Fingerprints

• The ridges visible on fingertips are created by the interface between dermal papillae (small upward projections) and the overlying epidermis.

• Sweat pores open along these epidermal ridges, depositing a thin film that creates residual fingerprints when you touch a surface.

How is skin color determined?

melanin

What does melanin produce?

melanocytes (in the stratum basale - the deepest layer)

What does melanin do? What are the 2 UV exposure trigger responses?

it absorbs UV radiation and protects the DNA of dividing keratinocytes from UV radiation

• UV exposure triggers 2 responses:

  • immediate response: existing melanin in keratinocytes is oxidized, causing rapid darkening

  • delayed response: UV damage to melanocyte DNA stimulates new melanin production; develops slowly but lasts longer

  • Ex(s):

    • Freckles: localized increase in melanin production (more melanin, same # of melanocytes)

    • Moles (nevus): localized proliferation of melanocytes (more melanocytes, not just more melanin)

    • albinism (melanocytes present but fail to produce melanin; high UV-related DNA damage risk)

How are burns classified?

by depth and tissue damage

• Critical variable is whether the stratum basale survives as this determines whether the skin can regenerate on its own or requires a skin graft

First degree burn

• damage to the epidermis ONLY

• skin appears red and painful; no blistering because the dermis is intact

• stratum basale is unaffected, meaning the skin will regenerate completely without scarring

• ex. sunburn

Superficial second-degree burn

• epidermis and papillary dermis are damaged

• blistering occurs as fluid leaks from damaged papillary capillaries

• painful due to nerve endings remaining intact in the dermis

• stratum basale may be partially spared

• if enough viable cells survive along the basement membrane, regeneration without a skin graft is possible

Deep second degree burn

• damage extends into the reticular dermis (beginning to destroy accessory structures - hair follicles, sweat glands)

• still painful if some nerve endings survive.

• Regeneration is less reliable, and grafting may be needed, depending on the extent

Third degree burns

• the entire dermis is destroyed (including nerve endings, blood vessels, and accessory structures - hair follicles and sweat glands)

• painless at the center because the nerve endings that transmit pain no longer exist

• The stratum basale is completely gone and skin cannot regenerate on its own. grafting is required.

What are the 4 accessory structures?

hair, sweat glands, sebaceous (oil) glands, and nails

Integumentary Accessory Structure: Hair

• covers the entire body except thick skin regions, the lips, and parts of the external genitalia

• both parts are composed of stratified squamous keratinized epithelial cells

  • shaft: the visible portion projecting above the skin surface; made of columns of dead keratinized cells

  • root & hair bulb: embedded in the dermis; surrounded by a sensory neuron detecting hair movement

    • the root is enclosed in a hair follicle with an epithelial and dermal root sheath.

    • The hair bulb contains the hair matrix, which is the site of actively dividing keratinocytes producing new hair.

  • Arrector Pili: smooth muscle attached to the dermal root sheath; contraction pulls hair upright, causing goosebumps

what 2 glands are comprised of the accessory structure, sweat glands?

1. eccrine gland

• opens directly onto the skin surface

• location: found all over the body surface (most numerous in palms and soles)

• produces water and electrolyte-based substance

  • sebaceous glands: produce sebum, an oily secretion that lubricates hair and skin - found everywhere besides the palms and soles

2. apocrine gland

• opens into hair follicles

• location: concentrated in areas like the underarms and groin

• produces a lipid-rich substance

Nails

• hard keritanized structures at digit tips

• The nail plate includes visible nail body and nail root under the skin

• growth occurs at the nail matrix beneath the nail root

• The proximal nail fold produces the eponychium (cuticle); the distal free edge is secured by the hyponychium. Nails contain no melanocytes and are mostly translucent; the lunula (the proximal white half-moon) represents visible keratin accumulation from the matrix below.