1. Skin and Membranes
Chapter 6

2. Learning Objectives Lesson 6.1: Skin and Membranes
Classify, compare the structure of, and give examples of each type of body membrane.
Describe the structure and function of the epidermis and dermis.
List and briefly describe each accessory organ of the skin.
List and discuss the five primary functions of the integumentary system.

3. Learning Objectives Lesson 6.1: Skin and Membranes (Cont.)
List and briefly describe the three most common types of skin cancer.
Classify burns and describe how to estimate the extent of a burn injury.

4. Body Membranes Classification of body membranes (Figure 6-1)
Epithelial membranes
Composed of epithelial tissue and an underlying layer of connective tissue
Connective tissue membranes
Composed largely of various types of connective tissue
The term membrane refers to a thin, sheetlike structure that may have many important functions in the body.

5. Types of Body Membranes
Figure 6-1, A: Epithelial membranes include cutaneous membrane (skin), serous membranes, and mucous membranes.
Figure 6-1, B: Connective tissue membranes include synovial membranes.

6. Body Membranes (Cont.) Epithelial membranes Cutaneous membrane: Skin
Serous membranes: Simple squamous epithelium on a connective tissue basement membrane
Types
Parietal layer: Line walls of body cavities
Visceral layer: Cover organs found in body cavities
Examples
Pleura: Parietal and visceral layers line walls of thoracic cavity and cover the lungs
Peritoneum: Parietal and visceral layers line walls of abdominal cavity and cover the organs in that cavity
Three types of epithelial tissue membranes: cutaneous, serous, and mucous.
Cutaneous membrane is primary organ of integumentary system.

7. Body Membranes (Cont.) Epithelial membranes Serous membranes Diseases
Pleurisy: Inflammation of the serous membranes that line the chest cavity and cover the lungs
Peritonitis: Inflammation of the serous membranes in the abdominal cavity that line the walls and cover the abdominal organs
A serous membrane is composed of two distinct layers of tissue.

8. Body Membranes (Cont.) Epithelial membranes Mucous membranes
Line body surfaces that open directly to the exterior
Produce mucus, a thick secretion that keeps the membranes soft and moist
Mucous membranes contain an epithelial layer and a fibrous connective tissue layer.
The term mucocutaneous junction is used to describe the area where the skin and mucous membranes meet.

9. Body Membranes (Cont.) Connective tissue membranes
Do not contain epithelial components
Produce a lubricant called synovial fluid
Examples are the synovial membranes in the spaces between joints and in the lining of bursal sacs
Connective tissue membranes are smooth and slick.
Connective tissue membranes reduce friction between opposing surfaces of bones in movable joints.

10. The Skin
Structure (Figure 6-3): Two primary layers called epidermis and dermis
Epidermis
Outermost and thinnest primary layer of skin
Composed of several layers of stratified squamous epithelium
Stratum germinativum: Innermost layer of cells that continually reproduce; new cells move toward the surface (Figure 6-4)
As cells approach the surface, they are filled with a tough, waterproof protein called keratin; eventually cells flake off
Stratum corneum: Outermost layer of keratin-filled cells
The skin is the largest organ of the body.
The skin is one of the most important organs of the body.
The skin is also known as the cutaneous membrane and is composed of the epidermis and dermis.

11. The Skin (Cont.) Structure
Skin pigment: Deepest epidermal layer is responsible for production of pigment, which gives color to the skin
The brown pigment melanin is produced by specialized cells in this layer
Blisters are caused by breakdown of union between cells or primary layers of skin
The amount and type of melanin in your skin depends first on the skin color genes you have inherited; however, other factors such as sunlight exposure can modify this hereditary effect.

12. Microscopic View of the Skin
Figure 6-3: The epidermis is raised at one corner to reveal the ridges in the dermis.

13. Photomicrograph of the Skin
Figure 6-4: New cells of the epidermis are produced in stratum germinativum.
The deep region of the skin is the dermis.
Courtesy Edward Reschke.

14. The Skin (Cont.) Structure Dermal-epidermal junction Dermis
Specialized area between two skin layers
Dermis
Deeper and thicker of the two primary skin layers and composed largely of connective tissue
Upper papillary layer of dermis characterized by parallel rows of tiny bumps called dermal papillae
Ridges and grooves in dermis form pattern unique to each individual
Basis of fingerprinting
Improves grip for tool use and walking
The deeper cells of the epidermis are packed tightly together.

15. The Skin (Cont.) Structure Dermis
Deeper reticular layer of dermis filled with network of tough, interlacing, collagenous and stretchable elastic fibers
Number of elastic fibers decreases with age and contributes to wrinkle formation
Dermis also contains nerve endings, muscle fibers, hair follicles, sweat and sebaceous glands, and many blood vessels
The subcutaneous tissue is sometimes called the superficial fascia or hypodermis.

16. Accessory Organs of The Skin
Hair, nails, and skin receptors
Hair (Figure 6-5)
Soft hair of fetus and newborn is called lanugo
Hair growth requires epidermal tubelike structure called hair follicle
Hair growth begins from hair papilla
Hair root lies hidden in follicle and visible part of hair called shaft
Arrector pili is specialized smooth muscle that produces “goose bumps” and causes hair to stand up straight
The human body is covered with millions of hairs.
A few areas of the skin are hairless – the lips, palms of hands, and soles of feet.

17. Hair Follicle
Figure 6-5 shows a hair follicle and its related structures.

18. Accessory Organs of The Skin
Hair, nails, and skin receptors
Nails (Figure 6-7)
Produced by epidermal cells over terminal ends of fingers and toes
Visible part is called nail body
Root lies in a groove and is hidden by cuticle
Crescent-shaped area nearest root is called lunula
Nail bed may change color with change in blood flow
Nails are classified as sensory organs.
Under the nail lies a layer of epithelium called the nail bed.

19. Structure of Nails Figure 6-7, A: Fingernail viewed from above.
Figure 6-7, B: Sagittal section of fingernail and associated structures.

20. Accessory Organs of The Skin
Hair, nails, and skin receptors
Skin receptors (Figure 6-3)
Specialized nerve endings: Make it possible for skin to act as a sense organ
Lamellar corpuscle (Pacini corpuscle): Capable of detecting pressure
Tactile corpuscle (Meissner corpuscle): Capable of detecting light touch
Skin receptors relay messages to the brain concerning sensations like touch, pain, and pressure.
Burn injuries destroy skin receptors.

21. Skin Receptors
Two skin receptors are visible in Figure 6-3: the tactile (Meissner) corpuscle and the lamellar (Pacini) corpuscle.

22. Accessory Organs of the Skin
Skin glands
Types
Sweat or sudoriferous
Sebaceous
Sweat or sudoriferous glands
Eccrine sweat glands
Most numerous, important, and widespread of the sweat glands
Produce perspiration or sweat, which flows out through pores on skin surface
Function throughout life and assist in body heat regulation
Two types of skin glands: sweat (sudoriferous) and sebaceous.
Eccrine sweat glands are the most numerous, important, and widespread of the sweat glands.
Sweat assists in the elimination of waste products.
Pinpoint-size openings on the skin are called pores.

23. Accessory Organs of the Skin (Cont.)
Skin glands
Sweat or sudoriferous glands
Types
Apocrine sweat glands
Found primarily in the skin in the axilla (armpit)
Larger than eccrine glands
Thicker secretion
Sebaceous glands
Secrete oil for the hair and skin
Grow where hairs grow
Tiny ducts open into hair follicles
Sebum secretion increases during adolescence
Instead of watery sweat, apocrine glands secrete a thicker secretion.
Odor from apocrine gland secretion is caused by the contamination/decomposition of the secretion by skin bacteria.
When sebum secretion increases during adolescence, it is stimulated by the increased blood levels of the sex hormones.
Sebum secretion often darkens and forms into a blackhead (comedo).

24. The Skin (Cont.) Functions of the skin
Protection; first line of defense against:
Infection by microbes
Ultraviolet rays from sun
Harmful chemicals
Cuts and tears
Temperature regulation
Skin can release almost 3000 calories of body heat per day
Mechanisms of temperature regulation
Regulation of sweat secretion
Regulation of flow of blood close to the body surface
The most important functions of the skin are protection, temperature regulation, sense organ activity, excretion, and synthesis of vitamin D.
The skin is also called the cutaneous membrane.
When blood supply increases, skin reddens.

25. The Skin (Cont.) Functions of the skin Sense organ activity Excretion
Skin functions as an enormous sense organ
Receptors serve as receivers for the body, keeping it informed of changes in its environment
Excretion
Body rids itself of wastes
Excess vitamins, drugs, and hormones can be excreted onto the skin by sweat
Synthesis of vitamin D
Occurs when skin is exposed to ultraviolet light
Vitamin D is critically important to good health
The skin’s millions of nerve endings serve as antennas or receivers for the body.
Excretion can influence amounts of certain ions and waste products present in blood.
Recent research has shown how important vitamin D is, which emphasizes the importance of this skin function.

26. Skin Cancer Most common types (Figure 6-8) Causes Kaposi sarcoma (KS)
Squamous cell carcinoma
Basal cell carcinoma
Malignant melanoma
Causes
Genetic predisposition
Sun's ultraviolet (UV) radiation damages skin cell deoxyribonucleic acid (DNA), causing mistakes during mitosis
Kaposi sarcoma (KS)
First appears as purple papules
The three most common types of skin cancer are squamous cell carcinoma, basal cell carcinoma, and malignant melanoma.
Exposure to sunlight is the most important factor in causing skin cancer.
Kaposi sarcoma is also known as human herpes virus 8 (HHV8).

27. Skin Cancer Lesions
Figure 6-8: Examples of skin cancer lesions. A, Kaposi sarcoma. B, Squamous cell carcinoma. C, Basal cell carcinoma. D, Malignant melanoma.
A: From Rakel R: Textbook of family medicine, ed 7, Philadelphia, 2007, Saunders.
B: From Goldman L, Ausiello D: Cecil textbook of medicine, ed 23, Philadelphia, 2008, Saunders.
C: From Noble J: Textbook of primary care medicine, ed 3, Philadelphia, 2001, Mosby.
D: From Townsend C, Beauchamp RD, Evers BM, Mattox K: Sabiston textbook of surgery, ed 18, Philadelphia, 2008, Saunders.

28. Skin Cancer (Cont.) Squamous cell carcinoma Basal cell carcinoma
Common type of skin cancer
Slow growing
Lesions begin as painless, hard, raised nodules
Will metastasize
Basal cell carcinoma
Most common type of skin cancer
Originates in cells at base of epidermis, often on upper face
Lesions begin as small raised areas that erode in center, bleed, and crust over
Less likely to metastasize than other skin cancer types
If not treated, squamous cell carcinomas will eventually spread and infect other organs or areas of the body.

29. Skin Cancer (Cont.) Malignant melanoma
Most serious form of skin cancer
May develop from benign, pigmented moles or excess UV radiation
Incidence in the United States is increasing
ABCDE rule of self-examination (Table 6-1)
Benign moles should be checked regularly for warning signs of melanoma.
Adults who had more than two blistering sunburns before the age of 20 have much greater risk of developing melanoma.

30. Malignant Melanoma
Use the ABCDE rule when checking for signs of malignant melanoma.

31. Burns
Treatment and recovery or survival depend on total area involved and severity or depth of the burn
Body surface area is estimated using the “rule of nines” (Figure 6-9) in adults
Body is divided into 11 areas of 9% each
Additional 1% located around genitals
Burns aren’t just caused by fires or contacting a hot surface.
Overexposure to UV light or contact with a harmful chemical can cause burns.

32. Courtesy Barbara Cousins.
The “Rule of Nines”
Figure 6-9: Dividing the body into 11 areas of 9% each helps to estimate the amount of skin surface burned in an adult.
Courtesy Barbara Cousins.

33. Burns (Cont.) Classification of burns (Figure 6-10)
First-degree (partial-thickness) burns
Only the surface layers of epidermis involved
Second-degree (partial-thickness) burns
Involve the deep epidermal layers and always cause injury to the upper layers of the dermis
An example of a first-degree burn is a typical sunburn.
With second-degree burns, complete destruction of the dermis does not occur; scarring is common.

34. Burns (Cont.) Classification of burns
Third-degree (full-thickness) burns
Characterized by complete destruction of the epidermis and dermis
May involve underlying muscle and bone
Risk of infection is increased
Fourth-degree (full-thickness) burns
Extends below subcutaneous tissue and reaches muscle or bone
May occur as result of high-voltage electrical burns
Third-degree burns are initially insensitive to pain but intense pain is soon experienced.
Fourth-degree burns may require skin grafting or amputation of limbs.

35. Classification of Burns
Figure 6-10: Thickness of the damaged skin is one way to classify burns. A, First-degree burn. B, Second-degree burn. C, Third-degree burn.
A: From Kliegman RM: Nelson textbook of pediatrics, ed 20, Philadelphia, 2016, Elsevier.
B and C: Courtesy Dr. Richard L Judd, Dwight D Ponsell, from Mosby’s first responder, ed 2, St Louis, 1988, Mosby.

36. Questions?