1. Chapter 6 Skin and its Appendages

2. Introduction 0.05 - 0.3 cm thick
Skin (integument) is body’s largest organ
Approximately 1.6 to 1.9 m2 (17-20 ft2)
cm thick
~9 pounds % of Body Weight
Self-repairing and protective boundary
Integumentary system describes the skin and its appendages
Hair
Nails
skin glands

3. One Square Inch Contains
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

4. 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

5. Structure of the Skin Thin Skin Thick Skin Covers most of body surface
Refers to epidermal layer only
0.5 – 5 mm thick
Thick Skin
Contains all five layers of epidermis
Stratum corneum is especially noticeable
Dermal papillae
No hair
Soles and palms
4 to 5 mm thick

6. Figure 5.1

8. Structure of the Skin Epidermis Cell types Keratinocytes
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

9. Structure of the Skin Epidermis Cell types Melanocytes
pigment-producing cells (5% of the total)
contribute to skin color (melanin)
filter ultraviolet light

10. Structure of the Skin Epidermis Cell types Langerhans cells
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

11. 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

12. 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)

13. Structure of the Skin Cell layers (cont.)
Stratum corneum (horny layer)
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

14. Figure 5.2b

17. 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.