Transcript Chapter 6 Skin and its Appendages

Chapter 6
Skin and its Appendages
Introduction
• Skin (integument) is body’s largest organ
• Approximately 1.6 to 1.9 m2 (17-20 ft2)
• 0.05 - 0.3 cm thick
• ~9 pounds...7 - 15% of Body Weight
• Self-repairing and protective boundary
• Integumentary system describes the skin
and its appendages
– Hair
– Nails
– skin glands
One Square Inch Contains
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20 Blood Vessels
65 Hairs & Hair Muscles
78 Nerves
78 Sensors for Heat
13 Sensors for Cold
160 Sensors for Pressure
• 100 Sebaceous/Oil
Glands
• 1300 Nerve Endings
• 19,500,000 Cells
• 500,000 Cells Dying &
Being Replaced
Structure of the Skin
• Cutaneous membrane
• Two primary layers
– Epidermis
• Outermost, thinner layer
• Epithelial layer
– Dermis
• Inner, thcker layer
• Vascular connective tissue
– Joined by dermal-epidermal junction (Figures 6-1 and 6-2)
• Subcutaneous layer
– Hypodermis (superficial fascia)
• Fat and areolar tissue
Structure of the Skin
• Thin Skin
– Covers most of body surface
– Refers to epidermal layer only
– 0.5 – 5 mm thick
• Thick Skin
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Contains all five layers of epidermis
Stratum corneum is especially noticeable
Dermal papillae
No hair
Soles and palms
4 to 5 mm thick
Figure 5.1
Structure of the Skin
• Epidermis
– Cell types
• Keratinocytes
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constitute over 90% of cells present
principal structural element of the outer skin
Filled with tough, fibrous protein called keratin
Arranged in layers
Most important cells in the epidermis
Structure of the Skin
• Epidermis
– Cell types
• Melanocytes
– pigment-producing cells (5% of the total)
– contribute to skin color (melanin)
– filter ultraviolet light
Structure of the Skin
• Epidermis
– Cell types
• Langerhans cells
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dendritic (branched) antigen-presenting cells (APCs)
play a role in immune response
Defense mechanism for the body
Originate in bone marrow
Trigger immune reactions, epidermal macrophages
Structure of the Skin
• Epidermis (cont.)
– Cell layers
• Stratum germinativum (growth layer)—describes the
stratum spinosum and stratum basale together
– Stratum basale (base layer)
» single layer of columnar cells
» only these cells undergo mitosis, then migrate
through the other layers until they are shed
– Stratum spinosum (spiny layer)
» cells arranged in 8 to 10 layers with desmosomes
that pull cells into spiny shapes
» cells rich in RNA
Structure of the Skin
– Cell layers (cont.)
• Stratum granulosum (granular layer)
– cells arranged in two to four layers and filled with keratohyalin
granules
– where keratinization begins
– two to four layers deep
– contain high levels of lysosomal enzymes
• Stratum lucidum (clear layer)
– cells filled with keratin precursor called eleidin
» serves to block water penetration or loss
– absent in thin skin
• Stratum corneum (horny layer)
– most superficial layer
– dead cells filled with keratin (barrier area)
Structure of the Skin
– Cell layers (cont.)
• Stratum corneum (horny layer)
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Dead squamous filled with keratin cells on the skin’s surface
Keratinocytes held together by desmosomes
Thick cell membranes resistant to chemical
Keratinization
Hyperkeratosis
Functions
» Waterproofing
» Protection from abrasion and penetration
» Rendering the body relatively insensitive to biological,
chemical, and physical assaults
Figure 5.2b
Quick Check
• Identify the two main or primary layers of skin.
What tissue type dominates each layer?
• The terms thin and thick skin refer to which
primary layer of skin? How do thin and thick
skin differ?
• Identify the two main cell types found in the
epidermis.
• List the five layers or strata of the epidermis.