Chapter 5 The Integumentary System Part A

Objectives List functions of the skin List & describe cell structure of the different layers of the skin Write the process of keratinization in your own words Describe the principle of skin color Identify and label skin structures on diagram and model Match and select from a given list with 100% accuracy List: The three types of burns Their degrees of severity Be able to estimate the extent of damage

Functions of the Integumentary System Protection: Chemical, physical, and mechanical barrier Body temperature regulation is accomplished by: Dilation of dermal vessels (cooling) Constriction of dermal vessels (warming) Increasing sweat gland secretions to cool the body Cutaneous sensation: Exoreceptors sense touch and pain

Functions of the Integumentary System Metabolic functions Synthesis of vitamin D in dermal blood vessels Blood reservoir: Skin blood vessels store up to 5% of the body’s blood volume Excretion Elimination of water and salts Elimination of limited amounts of nitrogenous wastes

Skin (Integument) The skin consists of two distinct regions Epidermis: Outermost superficial region Dermis Middle region below the epidermis The hypodermis (superficial fascia) Subcutaneous layer deep to skin Shares some protective functions with skin Not part of the skin

Reticular layer of dermis Hair shaft Pore Dermal papillae (papillary layer of dermis) Epidermis 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, Consists of: Four distinct cell types Four or five layers (in palm & Sole) Cell types include: Keratinocytes, Melanocytes, Merkel cells, Langerhans’ cells Avascular: Nutrients move by diffusion thru tissue fluid from the dermis Outer portion of the skin is exposed to the external environment ; it functions in protection

Cells of the Epidermis: Keratinocytes Most abundant cell type Arise from the continuously dividing deep layer “the stratum basale” Produce the protective fibrous protein keratin Pushed upward by newly formed cells underneath Become dead keratin-containing bags at the skin free surface

Cells of the Epidermis: Melanocytes Spider-shape epithelial cells Found in the deepest layer of the epidermis Produce membrane-bound melanin granules (melanosomes) Melanosomes are moved along melanocyte processes to nearby keratinocytes Melanin granules accumulate into pigment shields on the superficial side of keratinocyte nuclei These pigment shields protect the melanocytes nuclei (DNA) from the damaging effect of UV

Cells of the Epidermis: Langerhans’ Cells Star shaped cells Also called epidermal dendritic cells Arise in the bone marrow and migrate to the epidermis Have a phagocytic function Also help activate the immune system Extend processes among keratinocytes forming a network

Cells of the Epidermis: Merkel Cells Occasional cells present at the epidermal-dermal junction Spiky hemisphere in shape Each cell is intimately associated with a disc-like sensory nerve ending The cell-nerve combination is called Merkel disc Merkel disc functions as a sensory receptor for touch

Layers of the Epidermis Figure 5.2b

Stratum Basale (Basal Layer) Epidermis Layers: Stratum Basale (Basal Layer) Deepest epidermal layer Firmly attached to the dermis Consists of a single row of the youngest keratinocytes Cells are in rapid division, hence the layer is named, (stratum germinativum) 10-25% of this layer are melanocytes Occasional Merkel cells are also found

Layers of the Epidermis Figure 5.2b

Stratum Spinosum (Prickly Layer) Epidermis Layers: Stratum Spinosum (Prickly Layer) This layer is several cell layers thick Cells contains bundles of intermediate filaments made of pre-keratin Melanin granules are scattered among keratinocytes Langerhans’ cells are most abundant Keratinocytes look spiny “prickled” due to: The shrinking of the cells during tissue preparation while dismosomes are holding tight

Layers of the Epidermis Figure 5.2b

Stratum Granulosum (Granular Layer) Epidermis layers: Stratum Granulosum (Granular Layer) Thin - three to five cell layers keratinocyte appearance drastically changes here: Cells flatten Nuclei and organelles begin to disintegrate Cells accumulate two types of granules: Keratohyaline granules: Help form keratin in upper layer Lamellated granules: Release waterproof glycolipid extracellularly Cells “toughen” due to thickening of cytoplasm

Layers of the Epidermis Figure 5.2b

Stratum Lucidum (Clear Layer) Epidermis Layers: Stratum Lucidum (Clear Layer) Present only in thick skin (palm & sole) Thin, transparent band Above the stratum granulosum Consists of a few rows of flat, dead keratinocytes

Stratum Corneum (Horny Layer) Epidermis Layers: Stratum Corneum (Horny Layer) Outermost layer of keratinized cells Accounts for 75% of the epidermal thickness Functions include: Waterproofing (exracellular glycolipid) Protection from abrasion and penetration (keratin & thick membrane) Relative insensitivity to biological, chemical, and physical assaults

Layers of the Epidermis Figure 5.2b

Dermis (hide) Second major skin region Made of: Richly supplied with: Strong, flexible connective tissue (no epithelium) Sweat & oil glands and major portions of hair follicles reside here (although all are epidermal in origin) Richly supplied with: nerve fibers blood vessels lymph vessels

Dermis (cont’d) Cell types found in the dermis include: Fibroblasts Macrophages Mast cells (occasionally) White blood cells The dermis is composed of two layers: Papillary: thin superficial (loose areolar) Reticular: thick deeper (dense irregular)

Layers of the Dermis: Papillary layer Areolar connective tissue with collagen and elastic fibers Superiorly is thrown into projections called dermal papillae Various dermal papillae contain: Capillary loops Meissner’s corpuscles (touch receptos) Free nerve endings (pain receptors)

Layers of the Dermis: Papillary layer cont’d. On the palms and soles, dermal papillae lie atop larger mounds called dermal ridges Dermal ridges cause formation of epidermal ridges Epidermal ridge patterns are unique and determined genetically Sweat pores open along epidermal ridge crests An individual’s fingertips leave identifying film of sweat called (fingerprints)

Reticular layer of dermis Hair shaft Pore Dermal papillae (papillary layer of dermis) Epidermis 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

Layers of the Dermis: Reticular Layer Accounts for approximately 80% of dermis thickness Made of dense irregular connective tissue Collagen fibers add strength and resiliency to the skin Elastin fibers provide stretch-recoil properties Contains less dense regions called cleavage or tension lines (important for surgeons) that run in: Longitudinal patterns in the skin of the head and limbs Circular patterns around the skin of the trunk and neck

Hypodermis (Superficial Facia) Subcutaneous layer deep to the skin Stores fat (shock absorber) Functions as an insulator Anchors skin to underlying structures (usually muscles) Composed of: Adipose tissue Areolar connective tissue

Biol2401.5039 Break Slide 09/ 24/’12