Integumentary System
Chapter 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