1. Functions Layers Throughout Life
Integumentary System
Functions
Layers
Throughout Life

2. Integumentary System Cutaneous membrane (skin) – our largest organ
Accounts for 7% of body weight
Divided into two distinct layers
Epidermis
Dermis
Accessory structures
Subcutaneous layer (hypodermis)

3. Functions Of The Integument
Cushions and insulates deeper organs
Protects body from abrasion, trauma, chemicals, pathogens, temperature extremes and UV rays
Excretion and secretion
Contains sensory receptors associated with nerve endings
Synthesis and storage of nutrients (vitamin D3)

4. Integumentary Structures
Components of the Integumentary System
Figure 5-1

5. Skin Structures

6. The Epidermis- Four Main Cell Types
Melanocytes - found in basal layer, manufacture and secrete pigment
Merkel cells - basal layer, attached to sensory nerve endings
Keratinocytes – Arise from deepest layer of epidermis to stratum spinosum
Produce keratin – a tough fibrous protein
Produce antibodies and enzymes
Keratinocytes are dead at skin's surface
Langerhans cells - stratum spinosum, part of immune system macrophage-like

7. The Epidermis Stratified squamous epithelium
Several distinct cell layers
Thick skin—five layers on palms and soles
Thin skin—four layers on rest of body

8. Layers of The Epidermis
Stratum corneum
Most superficial layer
Dead, flattened (squamous) cells
Abundant keratin - Keratinized (cornified) tough, water-resistant protein
Protects skin against abrasion and penetration
Stratum lucidum (clear layer)
Occurs only in thick skin – palms and soles
Composed of a few rows of flat, dead keratinocytes

9. Layers of The Epidermis
Stratum granulosum (grainy layer)
Consists of keratinocytes
Tonofilaments
Keratohyaline granules – help form keratin
Lamellated granules – contain a waterproofing glycolipid
Stratum spinosum (spiny layer)
“Spiny” appearance caused by artifacts of histological preparation
Contains thick bundles of intermediate filaments (tonofilaments)
Resist tension
Contain protein prekeratin
Contains star-shaped Langerhans cells

10. Layers of the Epidermis
Stratum basale
Deepest layer of epidermis
Attached to underlying dermis
Stem cells actively divide
Merkel cells – associated with sensory nerve ending
Melanocytes – secrete the pigment melanin

11. Epidermal Cells and Layers of the Epidermis
Figure 5.3

12. Sources of Skin Color Melanocytes Carotene Hemoglobin - blood pigment
Make melanin from tyrosine
Melanin provides UV protection
Gives reddish-brown to brown-black color
Carotene
Contributes orange-yellow color
Provided from diet (carrots and tomatoes)
Hemoglobin - blood pigment
Caucasian skin contains little melanin
Allows crimson color of blood to show through

13. Dermis Second major layer of the skin
Provides mechanical strength, flexibility, and protection for underlying tissues
Highly vascular and contains a variety of sensory receptors that provide information about the external environment
Two layers
Papillary layer – includes dermal papillae
Reticular layer - deeper layer – 80% of thickness of dermis
Flexure lines - creases on palms

14. Layers of the Dermis Papillary layer Reticular layer
Underlies epidermis
Named for dermal papillae
Aerolar connective tissue
Supports, nourishes epidermis
Provides sensory nerves, lymphatics, and capillaries
Reticular layer
Tough, dense, fibrous layer
Dense irregular connective tissue
Collagen fibers - limit stretch
Elastic fibers - provide flexibility
Blends into papillary layer (above)
Blends into subcutaneous layer (below)

15. Dermal Components Epidermal accessory organs
Cells of connective tissues proper
Communication with other organ systems
Cardiovascular
Lymphatic
Nervous
Sensation
Control of blood flow and secretion

16. Subcutaneous Layer - Hypodermis
Composed of loose connective tissue - areolar and adipose
Stabilizes skin position
Loosely attached to dermis
Loosely attached to muscle
Contains many fat cells
Provides thermal insulation
Cushions underlying organs
Safely receives hypodermic needles

17. The Skin Throughout Life
Epidermis
Develops from embryonic ectoderm
Dermis and hypodermis
Develop from mesoderm
Melanocytes
Develop from neural crest cells

18. The Skin Throughout Life
Fetal skin
Well formed after the fourth month
At 5-6 months
The fetus is covered with lanugo (downy hairs)
Fetal sebaceous glands produce vernix caseosa

19. The Skin Throughout Life
Middle to old age
Skin thins and becomes less elastic
Shows harmful effects of environmental damage
Skin inflammations become more common