Integumentary SystemChapter 6 Sections 1 & 2

Objectives• Describe what constitutes an organ, and name the large organ of the integumentary system• Discuss the functions of the skin• Describe the structure of the layers of the skin• Summarize the factors that determine skin color

Introduction• Review: two or more tissues grouped together to perform

specialized functions constitutes an organ• The skin is the largest organ in the body by weight• The skin and its accessory structures together make up the integumentary system• Skin is composed of several types of tissues such as,

stratified squamous epithelium, dense irregular connective, and adipose tissues (see figure 6.1 p.180)• It is a versatile organ of the body and vital in maintaining

homeostasis

Characteristics & Functions of the Skin• It prevents harmful substances and microorganism from

entering the body• It lessens water loss by diffusion from deeper tissues• It regulates body temperature• It houses sensory receptors• Contains epidermal dendritic cells or Langerhans cells

which initiated the immune response to phagocytize harmful microorganisms

• It excretes small amounts of waste• Some skin cells produce the vitamin D precursor, which when

exposed to sunlight changes to an inactive form of vitamin D.

Skin & its Tissues• The skin, also known as the cutaneous membrane, has

two distinct layers:• The epidermis• The dermis

The Epidermis• The outer layer of the skin• It’s a thin layer, averaging 0.07-0.12 mm thick• Composed of stratified squamous epithelium• It lacks blood vessels• Can have five distinct layers• Stratum corneum• Stratum lucidum• Stratum granulosum• Stratum spinosum• Stratum basale

The Epidermis Overall

Stratum corneum• Is the outermost layer• Consists of many layers of keratinized, dead epithelial

cells that are flattened and non-nucleated• Keratinization is the process of older skin cells, called

keratinocytes, thickening and developing many desmosomes while hardening at the same time• Keratin is a tough, fibrous, waterproof protein that is

stored in those cells

Stratum lucidum• Found between the stratum corneum and stratum

granulosum on the soles of your feet and the palms of your hands• Cells appear clear• Nuclei, organelles and cell membranes are no longer

visible• This layer is missing where the skin is thinner

Stratum granulosum• Found beneath the stratum corneum• Consists of 3-5 layers of flattened cells that contain

shrunken fibers of keratin and shriveled nuclei

Stratum spinosum• Lies beneath the stratum granulosum• Composed of many layers of cells with centrally located,

large, oval nuclei, and developing fibers of keratin• Cells become flattened as new layers develop

Stratum Basale• The deepest layer of the epidermis• Consists of a single row of cuboidal or columnar cells • Can grow and divide because the cells receive nutrients

from the nearby dermis layer• Also contains melanocytes

The Epidermis Overall

Melanocytes• Are specialized cells that produce the dark pigment melanin

from the amino acid tyrosine in organelles called melanosomes• Melanin provides skin color and absorbs UV radiation in

sunlight• They lie in the stratum basale of the epidermis• The number of melanocytes is the same for all human

regardless of racial origins• It is the amount of melanin produced that determines how

dark your skin is, as well as, genetic factors and environmental factors

The Dermis• The boundary between the dermis and the epidermis is

uneven• Two distinct layers:• Dermal papilla• Dermis

Dermal papilla (Papillary Layer)• Are cone-shaped and extend from the dermis layer into

the uneven ridges of the epidermis• Composed of areolar connective tissue• They increase the surface area where epidermal cells

receive oxygen and nutrients from the capillaries• They are found all over in the skin of the body, but are

most abundant in the hands and feet• They form friction ridges that leave a patterned

impression better known as a fingerprint

Dermis layer (Reticular Layer)• Composed of dense irregular connective tissue with a

tough collagenous fibers and elastic fibers embedded in a gel-like ground substance• The network of these fibers, give skin its toughness and

elasticity• The dermis on average is 1.0-2.0 mm thick• On the eyelids it is 0.5 mm• On the soles of the feet it is 3.0 mm• Also contains: muscle fibers, accessory structures, nerve

cell processes, and sensory receptors

The Dermis