The Integumentary System 5 The Integumentary System

Integumentary System 1 8 2 9 3 7 Get the skinny here….. 4 5 6

The Skin = The Cutaneous Membrane Skin (Integument) The Skin = The Cutaneous Membrane Consists of three major regions Epidermis – outermost superficial region (stratified squamous epithelial tissue) - lacks blood supply. Dermis – middle region (dense irregular connective tissue with muscle & nervous tissue) - collagen & elastic fibers - binds the epidermis to underlying tissues Hypodermis or subcutaneous layer (superficial fascia) – deepest region (adipose tissue with nervous tissue & blood vessels) - Binds dermis to organs and blood vessels

Integumentary Functions Overall Function: Maintaining Homeostasis (what else?) Temperature regulation Protection of underlying tissues. Retardation of water loss Sensory Reception Synthesizing certain chemicals Excreting wastes.

Integumentary Functions Memory Tool WeT PETS – Visualize a dog with these features: Water bowl: Reduce water loss Petting the dog: Touch Guard dog: Protection Dog doo: Excretion Panting: Temperature regulation Food bowl: Synthesis of needed molecules Good dog, Dermo!!

Covers 7600 sq. cm in average adult. 7% of body weight. The Largest Organ Covers 7600 sq. cm in average adult. 7% of body weight. Varies in thickness- .5 mm to 2 mm. Composed of many tissues: Hair Epithelial Nerves Adipose Smooth Muscle Blood Glands

Epidermis Hair shaft Pore Dermal papillae (papillary layer of dermis) Meissner's corpuscle Free nerve ending Reticular layer of dermis Sebaceous (oil) gland Dermis Arrector pili muscle Sensory nerve fiber Eccrine sweat gland Pacinian corpuscle Hypodermis (superficial fascia) Artery Vein Hair root Adipose tissue Hair follicle Eccrine sweat gland Hair follicle receptor (root hair plexus) Figure 5.1

Epidermis Composed of keratinized stratified squamous epithelium, consisting of four distinct cell types and four or five layers Cell types include keratinocytes (squamous cells), melanocytes, Merkel cells, and Langerhans’ cells Outer portion of the skin is exposed to the external environment and functions in protection

Cells of the Epidermis (Listed in order of importance!) Keratinocytes – produce the fibrous protein keratin, which makes the skin waterproof (most common cell of epidermis - squamous) Melanocytes – produce the brown pigment melanin (causes skin color for UV protection – amoeboid shape) Merkel cells – function as touch receptors in association with sensory nerve endings Langerhans’ cells – epidermal macrophages that help activate the immune system (amoeboid shape and activity)

Cells of the Epidermis Figure 5.2b

Layers of the Epidermis Stratum Basale Stratum Spinosum Stratum Granulosum Stratum Lucidum Stratum Corneum Deep Superficial

Layers of the Epidermis

A Mnemonic for the Layers of the Epidermis: Corneum Lucidum Granulosum Spinosum basale BS Grows Lots of Corn!!

Layers of the Epidermis Two major processes occur in the epidermis: mitosis and keratinization Mitosis occurs in the deepest layer (stratum basale), where new cells are continually formed to replace old, dead cells that have sloughed off of the most superficial layer (stratum corneum) Keratinization occurs in the intermediate layers, as the cells age and accumulate large quantities of the protein keratin, becoming a waterproof protective layer in the stratum corneum when the cells die Figure 5.2b

Layers of the Epidermis: Stratum Basale (Basal Layer) Deepest epidermal layer firmly attached to the dermis C onsists of a single row of the youngest keratinocytes C ells undergo rapid division (mitosis), hence its alternate name, stratum germinativum

Layers of the Epidermis: Stratum Spinosum (Spiny Layer) As the young cuboidal keratinocytes begin to form keratin fibers, the lengthening fibers stretch the cell membranes, forming spiny projections Cells joined together by desmosomes

Layers of the Epidermis: Stratum Spinosum (Prickly Layer) C ells contain a weblike system of intermediate filaments attached to desmosomes Desmosomes: anchoring junctions between cells – they connect cells securely in areas subjected to stress, like skin and cardiac muscle Intermediate filaments stretch across the interior of the cell from one desmosome to another, forming part of the cytoskelton Melanin granules and Langerhans’ cells are abundant in this layer C ell membranes

Layers of the Epidermis: Stratum Granulosum (Granular / Grainy Layer) Thin; three to five cell layers in which drastic changes in keratinocyte appearance occurs Keratohyaline and lamellated granules accumulate in the cells of this layer – gives the cells a granulated, or spotty, appearance

Layers of the Epidermis: Stratum Lucidum ( Clear Layer) Thin, transparent band superficial to the stratum granulosum Consists of a few rows of flat, dead keratinocytes Clear because nuclei, organelles, & membrane no longer visible Present only in thick skin (palms and soles)

Layers of the Epidermis: Stratum C orneum (Horny Layer) Outermost layer of completely keratinized cells Accounts for three quarters of the epidermal thickness Functions include: Waterproofing Protection from abrasion and penetration Rendering the body relatively insensitive to biological, chemical, and physical assaults

Layers of the Epidermis Figure 5.2b