BIO 210
CHAPTER 6
SKIN AND ITS APPENDAGES: SUPPLEMENT 1
I. INTRODUCTION TO THE INTEGUMENTARY SYSTEM
A. STRUCTURE
- Organs Include Skin (Integument), Hair, Nails and Skin Glands
(Sweat and Sebaceous)
- Hair, Nails, and Skin Glands AKA Appendages of Skin
B. PRIMARY FUNCTION: Protection
II. THE SKIN (CUTANEOUS MEMBRANE)
A. STRUCTURE
1. PRIMARY LAYERS ‑ 2
a. EPIDERMIS
1. FEATURES
‑ Outer, Thinner Layer of Skin
‑ Tissue Type: Membranous Epithelium (Stratified Squamous Epithelium ‑ Keratinized)
2. CELL TYPES ‑ 3
a.
KERATINOCYTES
‑ Most Numerous and Important Cells in the Epidermis
‑ Filled with (or in the Process of Becoming Filledwith) Keratin (Keratinization)
‑ Keratin: Strong Protein; Protects and Waterproofs the Skin
‑ Keratinization: Process by Which Cells in the Epidermis Become Filled with Keratin and Moved to
the Skin's Surface (Cells Die in the Process)
b.
MELANOCYTES
‑ Produce Melanin
‑ Functions of Melanin
1) Responsible for Color of Skin, Hair, and Eyes
2) Filters UV Light
c.
3.
a.
LANGERHAN'S CELLS
‑ Provide Defense against Foreign Invaders (Work with the Immune System)
CELL LAYERS ‑ 5 (Listed Superficial to Deep)
STRATUM CORNEUM
‑ "Hardened Layer": Cells in this Layer are Totally Filled with Keratin (Replaces the Cytoplasm)
‑ Known as the Barrier Area
‑ Cells at the Surface of this Layer are Dead
b.
STRATUM LUCIDUM
‑ "Clear Layer": Cells in this Layer have a Clear Appearance (Keratin Precursor)
‑ Only Present in Thick Skin
c.
STRATUM GRANULOSUM
‑ "Granular Layer": Cells in this Layer are Filled with Granules (Keratin Precursor)
‑ Keratinization Begins in this Layer
d.
STRATUM SPINOSUM
‑ "Spiny Layer": Cells in this Layer Have an Irregular Shape (Plasma Membranes Modified
To Hold Tightly Together)
‑ Rich in RNA (Preparation for Keratinization)
e.
4.
STRATUM BASALE
‑ "Base Layer": The Innermost Layer of Epidermis
‑ Mitosis Occurs in this Layer
EPIDERMAL GROWTH AND REPAIR
a. TURNOVER (REGENERATION) TIME
‑ Time Required for Epithelial Cells to Form in the Stratum Basale & Migrate to the Skin's Surface
‑ Average Turnover Time = 35 Days (Maintains a Constant Skin Thickness)
- Application: Shortened Turnover Time Results in Formation of Callus
b.
EPIDERMAL PROLIFERATING UNIT (EPU)
‑ Each Group of 8‑10 Basal Cells Along with the Vertical Columns of Cells Above
(Up to the Skin's Surface)
‑ Epidermis Grows in Units ‑ Not as a Whole
5.
DERMAL ‑ EPIDERMAL JUNCTION
‑ The Union Between the Epidermis and the Dermis
‑ A Basement Membrane
‑ Functions:
‑ Tightly "Glues" the Epidermis to the Dermis
‑ Provides Support for the Epidermis
‑ Serves as a Partial Barrier Between the Epidermis and the Dermis
b.
1.
DERMIS
FEATURES
‑ Inner, Thicker Layer of Skin
‑ Tissue Type: Connective Tissue
‑ Called "True Skin" (Thicker and Gives Strength to Skin)
2.
STRUCTURES PRESENT IN THE DERMIS
a.
SENSORY RECEPTORS
‑ Specialized Nerve Endings for Hot, Cold, Pressure,Pain, and Touch
(Skin Functions as a Sense Organ)
MUSCLE FIBERS ‑ 2 Types
1. SKELETAL
‑ Located Only in the Dermis of the Face and Scalp
‑ Function: Voluntary Movement of the Face and Scalp
b.
2. SMOOTH ‑ ARRECTOR PILI MUSCLES
‑ The Most Abundant of the 2 Types of Muscle Fibers
‑ Form Arrector Pili Muscles
‑ Produces "Goose Bumps"
c. HAIR FOLLICLES
‑ Tubes That Hold Hairs (More Detail with Hair)
d. SWEAT, SEBACEOUS GLANDS
‑ Skin Glands (More Detail with Skin Glands)
e.
3.
BLOOD VESSELS
‑ The Dermis Contains an Extensive Network of Blood Vessels That Play an Important Role in
Regulation of Body Temperature
LAYERS ‑ The Dermis has 2 Layers
a. PAPILLARY LAYER (DERMAL PAPILLAE/FINGERPRINTS)
‑ Thin Superficial Layer of Dermis
‑ Folded ‑‑‑> Folds Known as Dermal Papillae ‑‑‑>
Forms Fingerprints (Thick Skin)
b.
RETICULAR LAYER (LANGER'S LINES/CLEAVAGE LINES)
‑ Inner, Thicker Layer of Dermis
‑ Contains Many Protein Fibers (Collagenous and Elastic)
‑ Collagenous Fibers:
‑ Most of the Fibers are this Type
‑ Form Langer's/Cleavage Lines (Pattern Unique to Each Individual)
‑ Surgical Incisions Should be Made Parallel to Langer's Lines for Better Wound Healing
‑ Elastic Fibers:
‑ If Overstretched and Torn, Forms "Stretch Marks"
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2.
SUBCUTANEOUS LAYER (HYPODERMIS; SUPERFICIAL FASCIA)
‑ Tissue Type: Connective Tissue (Loose Areolar and Adipose)
B.
1.
SKIN COLOR
PRIMARY DETERMINANT: AMOUNT OF MELANIN PRODUCED
- The Primary Determinant of Skin Color is the Amount of Melanin Produced By Melanocytes (Not the Number
of Melanocytes)
- How Melanocytes Produce Melanin:
- They Convert an Amino Acid (Tyrosine) into Melanin (The Process is Regulated By an Enzyme)
- They Then Transfer the Melanin to Other Cells in the Epidermis
2. FACTORS THAT AFFECT MELANIN PRODUCTION
- What Determines the Amount of Melanin Produced by Melanocytes?
a. HEREDITY (DNA/Genes) - The Most Important Factor That Determines the Amount of Melanin Produced
By Melanocytes
- 4-6 Pairs of Genes Control How Much Melanin Melanocytes Will Produce
- However, There Are Several Factors That Can Modify the Effect of Heredity
b. SUNLIGHT
- Prolonged Exposure to Sunlight Causes Melanocytes to Increase Their Production of Melanin and Skin to
Darken (A Protective Mechanism – Melanin Protects Skin Cells From UV Light)
c. HORMONES
- The Secretion of Certain Hormones From the Anterior Pituitary Gland (MSH, ACTH) Increases the
Production of Melanin
- Normally the Secretion of These is Carefully Regulated By Genes and Negative Feedback Mechanisms;
However, Under Certain Abnormal Conditions (Disease) the Secretion of These Hormones May Increase,
Causing Skin to Darken
d. AGE - Increasing Age May Cause Melanocytes to Decrease Their Production of Melanin (The
Converting Enzyme Becomes Less Active); Responsible for Graying Hair, Blotchy Coloring Of Skin
3.
CHANGES IN SKIN COLOR UNRELATED TO MELANIN PRODUCTION
- Other Factors (Besides the Production of Melanin) Can Cause Skin Color to Change. These Changes in Skin
Color Tend to Be Temporary and Are Best Seen in Fair-Skinned Individuals
a. AMOUNT OF BLOOD FLOW TO THE SKIN
- The Amount of Blood Flow to the Skin at a Given Time Can Change the Color of the Skin
- Example: If Some Condition Causes Skin Blood Vessels to Dilate and Therefore Increases Blood Flow to the
Skin (i.e. Exercise), Skin Appears Pinker in Color
b. AMOUNT OF OXYGEN IN THE BLOOD
- The Amount of Oxygen in the Blood at a Given Time Can Change the Color of the Skin
-Example: If Red Blood Cells Are Carrying Less Oxygen Than Normal (i.e., May Occur in Certain Respiratory or
Cardiovascular Diseases), Skin May Appear Bluish in Color
C.
FUNCTIONS OF SKIN
1.
PROTECTION - The Major Function of Skin
a. FROM…?
Invasion By Microorganisms, Harmful Chemicals (D/T the Design of the Epidermis)
Dehydration (D/T Keratin)
UV Light (D/T Melanin)
Mechanical Injury (D/T the Design of the Dermis – Thicker, Stronger Than the Epidermis)
b. SURFACE FILM
1. DEFINITION/COMPONENTS
- A Thin Film of Materials That Covers the Skin’s Surface
- Consists of Secretions From Sweat and Sebaceous Glands As Well As Dead Epithelial Cells
2.
-
2.
FUNCTIONS
Barrier
Antibacterial/Antifungal (D/T Chemical Components)
Lubricates (D/T Oil)
Hydrates (D/T Sweat)
Buffers (D/T Chemical Components)
SENSATION
- Skin Functions as a Sense Organ for the Sensations of Hot, Cold, Pressure, Pain, and Touch
- D/T Sensory Receptors in the Dermis
3. MOVEMENT WITHOUT INJURY
- Skin Allows Body Growth and Movement of the Body Without Injury to Underlying Tissues and Organs
D/T Elasticity of the Dermis and SQ Layer
4. EXCRETION
- Skin Functions as an Excretory Organ D/T Sweat Glands Located in the Dermis
5. VITAMIN D PRODUCTION (ENDOCRINE FUNTION)
- Skin Assists in the Production of Vitamin D
- Mechanism: Precursor Compound in Skin Cells Activated By UV Light à Transported By Blood to Liver,
Kidney à Converted to Vitamin D (Needed for Calcium Absorption)
- This is Skin’s Endocrine Function (Vitamin D Classifies Loosely as a Hormone)
6. IMMUNITY
- Skin Works With the Immune System to Defend Against Microorganisms
- D/T Langerhans Cells in the Epidermis and Phagocytes
7. HOMEOSTASIS OF BODY TEMPERATURE
- Skin Helps to Maintain Constant Body Temperature (Sweat Glands and Blood Vessels)
a. BASIC PRINCIPLE
To Maintain a Constant Body Temperature: Heat Production Must Equal Heat Loss
b. HEAT PRODUCTION: FROM FOOD CATABOLISM
Nutrient Catabolism yields Energy : 1) Chemical (ATP)
2) Heat (Released)
RELATES TO ACTIVITY
Increased Activity  Increased Catabolism  Increased Heat Production
- Cells That Are the Most Active and Produce the Most Heat: Liver, Skeletal Muscle
c. HEAT LOSS – 80% Occurs Through the Skin FROM EVAPORATION AND RADIATION
- Evaporation - Vaporization of Liquid (Requires Heat Energy)
- Example: Evaporation of Sweat
- Most Impt. Way Heat Loss Occurs in Hot Temps.
- Radiation - Heat Transfer (Warmer à Cooler) Without Direct Contact Between 2 Objects
- Example: Dilation of Blood Vessels in the Dermis
Most Impt. Way Heat Loss Occurs in Cool Temps.
d. HOMEOSTATIC CONTROL OF BODY TEMPERATURE
1. MECHANISM INVOLVED WHEN BODY TEMPERATURE INCREASES
2. MECHANISM INVOLVED WHEN BODY TEMPERATURE DECREASES
D. BURNS
1. DEFINITION ‑ Injury/Death of Skin Cells
2. SEVERITY DETERMINED BY:
a. DEPTH
1. FIRST DEGREE BURN (PARTIAL THICKNESS BURN)
‑ Involves Epidermis
- typical Sunburn (Minor Pain, Redness, Peeling; No Blistering or Scarring)
2. SECOND DEGREE BURN (PARTIAL THICKNESS BURN)
‑ Involves Epidermis and Upper Dermis
‑ Characterized by Severe Pain, Blistering,Swelling, and Scarring
3. THIRD DEGREE BURN (FULL THICKNESS BURN)
‑ Involves Destruction of Both the Epidermis and Dermis; May Involve Deeper Tissues
- Characterized by Severe Scarring, No Pain (Destruction of Nerve Endings)
b. EXTENT
1. "RULE OF PALMS"
‑ Palm Size of Victim is Approximately 1% of Body Surface
2. "RULE OF NINES"
‑ Divides the Body's Surface into %'s Based on 9
3. OTHER (SPECIAL CIRCUMSTANCES)
III. APPENDAGES OF THE SKIN
A. HAIR
1. STRUCTURE
a. HAIR ROOT- Hidden Portion of the Hair (Lies in Hair Follicle)
b. HAIR SHAFT‑ Visible Portion of the Hair
c. HAIR FOLLICLE & GERMINAL MATRIX
- Hair Follicle
- Tubelike, Holds Hair Root
- Formation: Cells from the Epidermis Push Down into the Dermis
- Follicle Wall: 2 Layers
1) Outer: Dermal Root Sheath
2) Inner: Epithelial Root Sheath
- Germinal Matrix
- Cap-shaped Cluster of Cell at Bottom of Hair Follicle
- Forms the Hair (Mitosis and Keratinzation)
d. HAIR PAPILLA
- Dermis that Protrudes into the Germinal Matrix
- Contains Blood Vessels
e. CORTEX AND MEDULLA OF HAIR
- Medulla: Inner Core of the Hair
- Cortex: Outer Portion of the Hair (Cells Contain Melanin and Keratin)
- Cuticle: Covers Cortex
f. SEBACEOUS GLANDS - Oil Glands; Part of Hair Follicle - Secrete Sebum Directly into Follicle
- Functions of Sebum: 1) Lubricates Skin, Hair & 2) Antifungal
- Located in Dermis in All Areas Except Palms and Soles
2. FUNCTION
‑ Body Hair: No Apparent Function
‑ Head Hair: Mainly Cosmetic; Some Protection
‑ Other Hairs (i.e., Eyelashes, Nose Hairs): Protection
B. NAILS
1. NAIL BODY
- Visible Portion of the Nail
- Composed of Cells Completely Filled with Hardened Keratin
2. NAIL BED
- Lies Below Nail Body
- Composed of Epidermis
3. ROOT
- Hidden Portion of the Nail
4. LUNULA
- Moon-shaped, White Portion of the Nail Body that Lies Closest to the Root
- Cells Beneath the Lunula Form Nails and are Responsible for Nail Growth (Mitosis and Keratinzation)
C. SKIN GLANDS - Microscopic Glands that Lie in the Dermis
1. SWEAT GLANDS
- Most Numerous of the Skin Glands
- 2 Types
a. ECCRINE
- Most Numerous Sweat Glands
- Smallest Sweat Glands
- Lie in the Dermis in Most of the Body (Esp. Numerous in Palms, Soles, Forehead, Upper Torso)
- Secrete Perspiration that is Clear, Thin, Watery onto Skin’s Surface
- Function T/O Life
b. APOCRINE
- Largest of Sweat Glands
- Limited Distribution
- Secrete Perspiration that is Thick, Yellowish into Hair Follicles
- Secretion Assoc. with Odor
- Begin to Function at Puberty
2. SEBACEOUS GLANDS (Prev. Discussed)
3. CERUMINOUS GLANDS
- Special Type of Sweat Gland (Modified Apocrine)
- Located in External Ear Canal
- Secrete Sweat (into Hair Follicles/onto Skin Surface) in External Ear Canal
- Cerumen: Mixture of Sweat (Ceruminous Glands) and Oil (Sebaceous Glands);
Maintains Moisture (Ear Canal); Can Harden/Block Canal