The Integumentary System u Definition u Organizational Features u Characteristics of the dermis u Characteristics of the epidermis u Types of skin u Skin color u Accessory skin structures: hair, glands, nails

What is the Integumentary System? u Skin: - about 10% of our body weight - functions of skin: - protection (abrasion, shocks, chemical bacteria) - temperature regulation - sensation - excretion - vitamin D production (important to normal Calcium metabolism) u Accessory Structures - hair - glands - nails

Non-physiological Importance of the Integumentary System

Organizational Features of Skin u Composed mainly of epithelial and connective tissues. u Organized into two main layers: epidermis and dermis u The skin rests on the hypodermis

Features of the Hypodermis The hypodermis attaches skin to underlying muscle and bone. - the hypodermis is composed of loose CT - fibers: mainly collagen - cells: fibroblasts, adipocytes, macrophages - the hypodermis is a major site of fat deposition - fat serves as insulation, protection, energy storage - good vascular supply in the hypodermis

Characteristics of the dermis u The dermis connects the skin to the hypodermal layer u It is composed mainly of dense irregular CT: - fibers: collagen, with some elastic & reticular - cells: fibroblasts, macrophages u The dermis contains the nerves, vessels, and glands of the skin u Two layers: reticular and papillary

Characteristics of the Epidermis u Composed of stratified squamous keratinized epithelium u Major cell type: keratinocyte (produces keratin) - keratin has a high sulfur content - disulfide bonds form - forms sheets due to crosslinking - very insoluble in water - hard to digest (Other cell types: melanocytes, Langerhans cells) u Epidermal layer is thinner than dermis u Contains no blood vessels u Separated from the dermis by a basement membrane

The Five Stages (strata) of the Epidermis u Cells divide in the deepest stage; they die and are pushed up into more superficial stages. u The five stages are (from superficial to deep): - stratum corneum - stratum lucidum - stratum granulosum - stratum spinosum - stratum basale

The Five Stages (strata) of the Epidermis u Stratum basale: site of cell proliferation. Deepest, thin layer. Cells joined by desmosomes. u Stratum spinosum: Cells appear spiny. They begin to fill with keratin, some cell division takes place. u Stratum granulosum: Thin, dark layer (2 to 5 cells thick). Cells contain dark protein granules. They begin to die here. u Stratum lucidum: Thin, clear layer. Keratin remains, dark protein granules are lost. Not present in all skin types. u Stratum corneum: dead squamous cells joined by desmosomes. Cells are cornified. Layers of stratum corneum constantly flake off of skin.

The Five Stages (strata) of the Epidermis str. basale str. spinosum str. granulosum str. lucidumstr. corneum

Types of Skin: Thick versus Thin u Skin is characterized as thick or thin, based on thickness of the epidermis. u Thick skin has all five strata, thin skin may lack stratum lucidum. u Thick skin: - found in areas of high friction (palms, soles of feet, etc.) - the papillae of the dermis form parallel ridges u Thin skin: - found wherever thick skin isn’t - no parallel ridges formed by dermis - hair is only found on thin skin

Determinants of Skin Color u Skin colored is determined and influenced by: - the abundance of skin pigments - the amount of blood circulating though the skin - the thickness of the stratum corneum

Skin Pigments u The major skin pigment is melanin (brown pigment) - produced by melanocytes - absorbed by keratinocytes - amount produced by melanocytes varies - genetic factors - exposure to the sun u Other substances can cause pigmentation: - carotene (from food, like carrots) - disease (jaundice)

Accessory Skin Structures: Hair Hair: a characteristic of all mammals - dense hair covering most of the body is called fur - the color of hair is determined by pigment (melanin) - two types of hair: terminal and vellus - terminal: long, thick, pigmented - vellus: short, fine, unpigmented

Accessory Skin Structures: Hair Why do humans need hair? - display? - insulation? - protection against friction? - protection against foreign substances? - dispersion of glandular secretions? - evolutionary remnant?

Structure of Hair u Hair consists of a shaft (above skin), root, and bulb u The hair grows within a hair follicle u Hair is composed of hard keratin (lots of sulfur) u In cross section, hair has three layers: medulla, cortex, and cuticle u Hair is associated with sebaceous glands, sweat glands, and arrector pili muscle shaft root bulb medulla cortex cuticle arrector pili sebaceous gland

Accessory Skin Structures: Glands There are two categories of glands associated with the skin to consider: u sebaceous glands: - produce sebum (oily) - duct ends in a hair follicle - provides oil to the skin and hair u sweat glands: - merocrine: produce sweat; open onto skin surface - apocrine: produce organic secretion (scent), open into hair follicles

Accessory Skin Structures: Nails u Found at distal ends of the digits u Consist of proximal nail root, distal nail body u Functions: - protect the ends of the digits - aid in grasping, manipulating objects - defense (scratching) - display (female)

Next Lecture..... The Skeletal System