Skin & Body Membranes

Chapter 4

FACTS ABOUT THE SKIN

• Called the Integument: means covering.

• Covers entire body.

• Wt. Approximately 9 pounds.

• 7% of total body wt.

Facts Cont.Every square centimeter of skincontains: -70cm of Blood Vessels-55cm of nerves (230 sensory receptors) -100 sweat glands-15 oil glands-1/2 million cells dying and are constantly being replaced.

I. Classification of Body Membranes

A. Epithelial Membranes

• Epithelial sheet• Underlying layer of connective tissue

1. Cutaneous Membrane

• Skin• Keratinizing stratified squamous

epithelium• Anchored by dense fibrous CT

2. Mucous Membranes

• Epithelium varies• Underlying loose CT• Lines all cavities open to exterior

3. Serous Membranes

• Layer of simple squamous• Layer of areolar CT• Lines body cavities closed to exterior• Made of two layers

– Parietal: lines cavity– Visceral: cover outside of organs in cavity

• Serous fluid in between layers• Decrease friction

Figure 4.1 Classes of epithelial

membranes

B. Connective Tissue Membranes

• Synovial Membranes: soft areolar CT– No epithelial cells– Line fibrous capsules

surrounding joints– Provide smooth

surface & secrete lubricating fluid

II. Integumentary System

A. Basic Skin Functions

• Mechanical Damage: keratin toughens cells– Pressure receptors alert nervous system to

possible damage

• Chemical damage: keratinized cells relatively impermeable– Pain receptors alert nervous system

• Bacterial Damage: secretions are acidic & inhibit bacteria– Phagocytes ingest foreign substances &

pathogens

• Ultraviolet radiation: melanin produced by melanocytes offer protection

• Thermal Damage: heat, cold, & pain receptors

• Desiccation: keratin in cells reduce evaporation

• Heat loss: activating sweat glands– Allowing blood to flush into skin capillary

beds

• Heat retention: reducing flow of blood into skin capillary beds

• Excretion of urea & uric acid in sweat• Modified cholesterol molecules in skin

converted to vitamin D by sunlight

B. Types of Nerve Endings

• Cutaneous sensory receptors - (exteroceptors) - respond to stimuli outside the body.–Meissners Corpuscles in

dermal papillae - sense gentle touch and feel in the skin

–Pacinian receptors - deeper dermis - deeper pressure

–Root Hair Plexuses - wind in the hair

–Bare nerve endings - sense cold, heat etc.

C. Structure of the Skin

• Most superficial: Epidermis• Second Layer: Dermis• Hypodermis: not actual skin but is

known as the fat layer of the skin.–Underneath the dermis–Mostly fat, insulate and absorb shock–Anchors skin to underlying structures

Epidermis: 4 Cell types

1. Keratinocytes: main structural cell…new epidermis every 35-45 days Produce Keratin: fibrous protein used

for protection.

2. Melanocytes: give skin color, accumulate on superficial side of keratinocytes.

3. Langerhans cells: macrophages of the immune system.

4. Merkel Cells: Combines• with nerve receptors to form • Merkel disc which is sensitive • to touch.

5 layers of Epidermis

(pg. 100 fig. 4.3)

1. Stratum Basale (Basal Layer) -Mostly young Keratinocytes,

-One cell layer thick

2. Stratum Spinosum (Spiny Layer)- Mostly Langerhans cells that surround keratinocytes that are flat and prickly.-Keratinocytes in this layer contain tonofilaments:

-Thick bundles of tension fibers

3. Stratum Granulosum (Granular

Layer) -3-5 Layers of Keratinocytes

-Tough Layer -Water resistant, to slow water loss from the body

4. Stratum Lucidum (Clear Layer) -Only present in thick skin -Mainly 2-3 rows of Keratinocytes

5. Stratum Corneum (Horny Layer) -Outermost layer, mostly dead

keratinocytes or keratin filled cells

-20-30 layers thick, thickest layer

- prevent abrasion and penetration

-Waterproofing from environment

-Protects deeper cells

Dermis: 2nd Layer of Skin

• Hide of our skin• Richly supplied with nerves, blood & lymph

vessels.• Cell types are mostly macrophages &

fibroblasts.• House major portion of hair follicles, oil and

sweat glands.

The dermis has 2 major layers

1. Papillary Layer: connect epidermis to dermis

- Contain the majority of blood vessels. - Form identifying finger and foot prints.

2. Reticular Layer - 80% of the Dermis - Dense irregular connective

tissue - Form cleavage lines: skin

heals better when an incision is made along these lines.

- If overstretched such as in pregnancy, dermal tears form striae or sretchmarks.

- Blister: Separation of Epidermis from Dermis, fluid filled.

D. SKIN COLOR

3 PIGMENTS CONTRIBUTE TO SKIN COLOR

1. MELANIN

-Color ranges: yellow - reddish brown - black

-More melanin the darker the color. Freckles and moles are local

accumulation of melanin. -Sun exacerbates melanin

buildup

2. CAROTENE

Color range: yellow - orange.

Found in certain plants: carrots, rich sources of Vitamin A.

Most found in the palms and soles.

3. HEMOGLOBIN• Color range: - Pale: caused

by lack of blood.• Yellow: caused by build up of

bile in the blood (Jaundice).• Blue: cyanosis, lack of oxygen• Pink: Normal hue

•Bronze: Addisons disease,

metallic appearance

•Blue: Lack of Oxygen (cyanosis).

•Redness: Erythema, blushing,

inflammation, or hypertension.

•Bruises: blood has escaped & clotted in tissue spaces

E. APPENDAGES OF THE SKIN

1. HAIR AND HAIR FOLLICLES

- Hair (Pili): made of keratin

Shaft: projects from the skin Root: embedded in skin, depending on shape signifies, straight or curly hair.

- Hair pigment depends on melanocytes located in follicle

- Hair Follicles (pg. 105 fig. 4.7) - contains hair root - Nerve endings - Knot of capillaries: papilla,

to supply nutrients - Bundle of smooth muscle:

arrector pili: raiser of hair.

2. Distribution of Hair growth

Fine Vellus: fine body hair of children or females

Terminal hair: course scalp hair and eyebrows - grow in response to sex

hormones, the more testosterone the more terminal hair

Alopecia: hair loss, as we get older new hairs do not replace old hairs as quickly.

Male patterned baldness: genetic and sex-influenced condition

3. Nails

Hard keratin

4. Sweat Glands

• sudoriferous glands• -Cover entire skin surface except for

nipples, and parts of external genitalia.• 2.5 million per person

08/02/98

Types of Sweat Glands

• Eccrine: most numerous– location: palms, soles of feet, forehead– secretion: sweat

• 99% water, salts, nitrogenous wastes• acidic pH 4-6

–purpose: temperature regulation– emotion induced sweating, we have no

control

• Apocrine: –Location: axillary, genital areas–Size: Larger than eccrine glands–Secretions: same as eccrine plus fatty

deposits and protein.• - Has foul odor when fats and

proteins are decomposed (body odor)

• -Begin to function at puberty

5. Sebaceous (oil) glands

• Location: all over the body except for palms and soles of feet.

• Secretion: Sebum, oily substance• Function: smooth and soften hair and

skin and slows water loss during dry weather.

• Acne: active inflammation of gland–Bacteria

• Blocked duct: Whitehead is formed if this oxidizes and dries it

becomes a blackhead• Seborrhea: (Cradle Cap)

– in infants is over secretion of sebaceous glands

III. Homeostatic Imbalances

A. Burns

• Partial thickness burns - 1st and 2nd degree

• Full thickness burns - 3rd degree

1. Problem with burns

• Fluid and electrolyte imbalance• Shock• Infection

2. Treatment

• Dependent on percentage of burn calculated by the Rule of nines.– pg. 108 fig. 4.11

• Fluid and electrolyte replacement• Antibiotics• Supportive care• Debridment of eschar(burned skin)• Grafting

B. Skin Cancer

1. Basal Cell Carcinoma–most common, least malignant, slow

growth–Pearly edge–99% cure rate with early excision

2. Squamous Cell Carcinoma

• In keratinocytes of the stratum spinosum• Scaly red papule (round elevated)• rapid growth, meets to lymph• Good cure rate if caught early and

radiation is followed through.

3. Malignant Melanoma

• CA of Melanocytes• Most dangerous• Accounts for about 5% of Skin CAs• Little chance of survival, better if caught

early• Tx is surgical excision with

chemotherapy

4. American Cancer Society

• ABCD rule for examination of skin CA

A - Asymmetry

B - Border irregularity

C - Colors different

D - Diameter is larger than 6mm (pencil eraser)