Chapter 4 Skin and Body Membranes



Chapter 4 Skin and Body Membranes

I. Body membranes

• Classification of body membranes

A. Epithelial membranes

1. cutaneous membranes – skin – composed of stratified squamous epithelium. – exposed to air, dry membrane

2. mucous membrane - lines all body cavities open to the exterior (ex: respiratory, digestive, urinary etc.) – wet or moist membranes - continuously bathed in secretions. -–function – absorption, secretion, some produce mucus.

3. Serous membrane – lined body cavities that are closed to exterior (except dorsal body cavity and joint cavities). –occur in pairs

a. parietal layer – lines a specific portion of the wall of ventral body cavity.

b. Visceral layer – covers outside of organ in that cavity. *serous fluid – between serous layers. –allows organs to slide easily across cavity walls.

c. Specific serous membranes

1. peritoneum – surrounds organs in abdominal cavity.

2. Pleura – around lungs

3. Pericardium – around heart

B. connective tissue membrane

1. synovial membranes – connective tissue – no epithelial tissue. –lines fibrous capsules surrounding joints. – function – provide a smooth surface and secrete a lubrication fluid.

II. Integumentary system (skin)

A. functions of skin – protective (see table 4.1)

1. Structure – composed of two kinds of tissue

2. Epidermis – composed of stratified squamous epithelium – can keritanize the skin becoming hard and tough.

3. Dermis – dense connective tissue. *They fit firmly together but may be separated to form a blister. Under epidermis and dermis is the subcutaneous tissue – mostly adipose. –not part of skin but anchors skin.

B. Epidermis – avascular – does not have a blood supply of its own.

1. layers of epidermis

a. Stratum Germinativum (Basale)– constantly undergoing cell division. Closest to dermis. – new cells pushed upward, become flatter, full of keritan and die. – die because they are unable to get adequate nutrients and oxygen because of lack of blood supply.

b. 3 superficial layers – stratum granulosum, stratum spinosum, stratum lucidum.

c. Stratum corneum – outermost layer 20 to 30 cells thick. – dead cells filled w/keritan. – function – protects deeper cells from outer environment.

* new epidermis every 35 to 45 days.

2. Melanin – a pigment found in melanocytes. (yellow to brown to black.) - found in stratum germinativum. – tanning occurs when sunlight stimulates melanocytes to produce more melanin. – Freckles and moles form when melanin is accumulated in one spot.

C. Dermis – 2nd main section of skin.

- dense fibrous connective tissue in two major divisions:

1. papillary layer – upper dermal region. (uneven w/ finger-like projections on superior surface.) - called dermal papillae.

a. blood supply and nerves reach into dermal papillae.

b. Pattern of dermal papillae determine fingerprints of each person.

c. Sweat glands in fingers cause you to leave fingerprints on everything touched.

2. reticular layer – deepest skin layer.

a. contains blood vessels, sweat glands, oil glands.

b. Many phagocytes (cells that engulf foreign bodies) to eat bacteria that penetrate the epidermis.

c. Contains collagen and elastic fibers (gives skin moisture and elasticity) – w/ age less fibers and collagen; skin sags and wrinkles.

d. Dermis has a good supply of blood vessels. Helps regulate body temperature.

e. Decubitus ulcers - bedsores – blood supply is restricted to skin. Cells die, skin breaks, cracks, permanent damage may result.

D. Skin color –

Three pigments contribute to skin color:

1. amount and kind of melanin (yellow, reddish brown, black)

2. amount of carotene deposited in stratum corneum and subcutaneous tissue.

3. Amount of oxygen bound to hemoglobin (pigment in RBC) in dermal blood vessels.

- cyanosis – skin appears blue – when hemoglobin is poorly oxygenated. (in dark skinned people cyanosis is visible in mucous membranes and nail beds.)

4. skin color signaling disease –

a. redness – fever, allergy etc.

b. pallor or blanching – pale , fever, anger, anemia, low blood pressure, impaired blood flow.

c. Jaundice (yellow cast) – liver disorder.

d. Black and blue marks – bruises – blood has collected in tissue and out of circulation.

E. Appendages of Skin – cutaneous glands, hair, hair follicles and nails.

1. cutaneous glands- exocrine glands – release their secretions on the surface of the skin.

a. sebaceous glands (oil) – found all over skin except palms and under feet. – usually empty into hair follicle, some directly on surface.

- sebum – mixture of oily substances and cell fragments.

- Blackheads – dried sebum, darkens.

- Whiteheads – sebum clogging up sebaceous gland’s duct.

b. sweat glands – (sudoriferous glands) (over 2.5 million per person.)

1. eccrine glands – produce sweat all over body.

- efficient in heat regulating in body.

- Sweat mostly salt, water, some metabolic wastes.

2. apocrine sweat glands – axillary and genital areas of body. – ducts empty into hair follicles. – secretions contain fatty acids and proteins, salt, water, etc. – odorless until bacteria on skin surface use protein secreted as nutrients for growth, takes on musky smell. – play a minimum role in thermoregulation. – function unknown.

2.Hair and hair follicles

a. function – shielding eyes, remove foreign bodies from respiratory tract, insulation.

b. Hair – produced by hair follicle

1. flexible epithelial structure

2. root – enclosed in follicle.

3. Scalp – projecting from skin.

4. Hairbulb – area where hair is formed by division of germinal epithelial cells.

5. Cells kertanize and die.

6. Mostly protein, mostly dead.

7. Layers of hair –

a. cuticle – outer layer

b. cortex – middle layer

c. medulla – center of hair

8. Melanocytes in hair bulb determine hair color.

9. Shape of hair shaft determines type of hair Ex: wavy, straight, or curly.

10. Arrector pilli muscle – muscle connecting hair to dermis. – when cold or frightened muscle contracts forming “goosebumps”.

3. Nails – figure 4.7 pg 104 – nails are dead cells.

F. Homeostatic Imbalances of skin

1. Infections and Allergies

a. athlete’s foot – resulting from fungus infection.

b. Boils, carbuncles – inflammation of hair follicles.

c. cold sores – fever blister – caused by herpes virus.

d. Contact dermatitis – itching redness swelling (exposed to chemicals, allergic response).

e. Impetigo – caused by staphlococcus infection.

f. Psoriasis – red skin covered by dry, silvery scales.

2. Burns – tissue damage and cell death caused by heat, electricity, UV, chemicals.

a. body loses fluids

1. rule of nine – divides body into 11 sections, 9 % each to determine % of body burned.

b. infection occurs

c. type of burns

1. 1st degree burns –only epidermis is damage. (sunburn usually).

2. 2nd degree burns – epidermis and upper dermis damage. – regrowth may occur

3. 3rd degree – destroy entire thickness of skin – full thickness burns. Regeneration not possible – skin grafting must occur.

d. considered critical if :

1. over 25% of body 2nd degree

2. over 10% of body 3rd degree

3. 3rd degree on face, hands, or feet.

3. Skin Cancer -

a. basal cell carcinoma – the least malignant and most common skin cancer. Cells in the stratum germinativum no longer honor the boundary between epidermis and dermis. They invade the dermis and subcutaneous tissue. Appear mostly on sun-exposed areas of the face and appear as shiny, dome shaped nodules. – Full cure is the rule of 99% of the cases when surgically removed.

b. Squamous cell carcinoma – arises from the cells of the stratum spinosum. Appears as a scaly reddened elevated area. Appears most often on the scalp, ears, hands and lower lip. It will spread to the lymph nodes in untreated. Complete cure is possible if it is surgically removed in time.

c. Malignant melanoma - a cancer of melanocytes. – Only about 5% of the skin cancers. Often deadly. Pigmented areas appear spontaneously. It usually appears as a spreading brown to black patch that metastasized rapidly to surrounding lymph and blood vessels. Chance for survival is helped by early detection.

d. ABCD rule –

A. asymmetry

B. border irregularity

C. color

D. diameter

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