The Integumentary System
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Definition
Organizational Features
Characteristics of the dermis
Characteristics of the epidermis
Types of skin
Skin color
Accessory skin structures: hair,
glands, nails
What is the Integumentary System?
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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)
Accessory Structures
- hair
- glands
- nails
Non-physiological Importance of the
Integumentary System
Organizational Features of Skin
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Composed mainly of epithelial and connective tissues.
Organized into two main layers: epidermis and dermis
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
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The dermis connects the skin to the hypodermal layer
It is composed mainly of dense irregular CT:
- fibers: collagen, with some elastic & reticular
- cells: fibroblasts, macrophages
The dermis contains the nerves, vessels, and glands of the skin
Two layers: reticular and papillary
Characteristics of the Epidermis
Composed of stratified squamous keratinized epithelium
 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)
 Epidermal layer is thinner than dermis
 Contains no blood vessels
 Separated from the dermis by a basement membrane
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The Five Stages (strata) of the Epidermis
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Cells divide in the deepest stage; they die and are pushed
up into more superficial stages.
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
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Stratum basale: site of cell proliferation. Deepest, thin
layer. Cells joined by desmosomes.
Stratum spinosum: Cells appear spiny. They begin to fill
with keratin, some cell division takes place.
Stratum granulosum: Thin, dark layer (2 to 5 cells thick).
Cells contain dark protein granules. They begin to die
here.
Stratum lucidum: Thin, clear layer. Keratin remains, dark
protein granules are lost. Not present in all skin types.
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. lucidum
str. basale
str. corneum
str. spinosum
str. granulosum
Types of Skin: Thick versus Thin
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Skin is characterized as thick or thin, based on thickness of
the epidermis.
Thick skin has all five strata, thin skin may lack stratum
lucidum.
Thick skin:
- found in areas of high friction (palms, soles of feet, etc.)
- the papillae of the dermis form parallel ridges
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
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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
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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
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
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Hair consists of a shaft
(above skin), root, and bulb
The hair grows within a hair
follicle
Hair is composed of hard
keratin (lots of sulfur)
In cross section, hair has
three layers: medulla,
cortex, and cuticle
Hair is associated with
sebaceous glands, sweat
glands, and arrector pili
muscle
shaft
medulla
cortex
root
bulb
cuticle
arrector
pili
sebaceous
gland
Accessory Skin Structures: Glands
There are two categories of glands associated with the skin to
consider:
 sebaceous glands:
- produce sebum (oily)
- duct ends in a hair follicle
- provides oil to the skin and hair
 sweat glands:
- merocrine: produce sweat; open onto skin surface
- apocrine: produce organic secretion (scent), open
into hair follicles
Accessory Skin Structures: Nails
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Found at distal ends of the digits
Consist of proximal nail root, distal nail body
Functions:
- protect the ends of the digits
- aid in grasping, manipulating objects
- defense (scratching)
- display (female)
Next Lecture.....
The Skeletal System