ANS 331: Integumentary System
I. Skin--The Integument
A. Largest Organ
B. Composed of all four tissue types
C. Functions:
1. Protection
2. Prevents desication
3. Assists in maintenance of body temperature
4. Excretory Function
5. Sensory Organ
6. Synthesis of Vitamin D
7. Storage of Nutrients
D. Composed of Three Layers
1. Epidermis
2. Dermis
3. Hypodermis
II. Epidermis
A. Keratinized Stratified Squamous Epithelium
1. Outer Keratinized Cells are dead.
2. Avascular
B. Other Epidermis Cells
1. Keratinocytes
a. Primary Epithelial Cells
b. Produce Keratin--Tough, fibrous, waterproof protein
c. Found on Basement Membrane between Epidermis and Dermis
d. Loss nucleus, organelles and cytoplasm
as they migrate to surface
--Become a lifeless sheet of keratin
2. Melanocytes
a. Pigment cells
b. Found in Deep Layers of Epidermis
c. Absorbed by Keratinocytes to protect them from UV Light
3. Langerhan's Cells
a. Macrophages of Skin
4. Merkel Cells
a. Associated with nerve endings at Basement Membrane
b. Play a role in sensation of touch.
C. Layers of Epidermis (Inside to Out)
1. Stratum Germativum (S. Basale)
a. Basal Layer
2. Stratum Spinosum
a. Spiny Layer
3. Stratum Granulosum
a. Granular Layer
b. Missing in Hairy animals
4. Stratum Lucidum
a. Clear Layer
b. Only found in thickest layers of skin
5. Stratum Corneum
a. Horny Layer
III. Dermis
A. Dense Irregular Connective Tissue
1. Fibers
a. Collagen, Elastin, and Reticular
2. Cells
a. Fibroblasts, Adipocytes, and Macrophages
B. Also contains:
1. Hair Follicles
2. Nerve Endings
3. Glands
4. Smooth Muscle
5. Blood Vessels
6. Lymphatics
C. Hide of Animal
1. Makes up biggest portion of skin
D. Two Layers
1. Papillary
a. Contain Dermal Papillae
i. Interdigitation of basement membrane between Epidermis and Dermis
ii. Keep these two layers together
b. Capillaries
i. Nourish and remove waste products from Epidermis
ii. Temperature Control
c. Nerve Endings
i. Nociceptors
ii. Touch Receptors (Meissner's Corpuscles)
iii. Temperature Receptors
2. Reticular Layers
a. Tough, and Fibrous Layer
IV. Hypodermis
A. Subcuteneous Layer
1. Permits skin to move freely
B. Areolar Connective Tissue
1. Adipose
2. Blood and Lymphatic Vessels
3. Nerves
C. Pressure Receptors
1. Vater-Pacinian Corpuscle
V. Pigmentation of Skin
A. Caused by melanin granules
in cytoplasmic extensions of melanocytes
B. Controlled by MSH from Pituitary
C. Protects keratocytes from UV light
VI. Related Structures of the Integument
A. Hair
1. Function: Temperature Regulation
2. Hair Strands and Follicles
a. Shaft
--Visible part of hair
b. Root
--Portion of hair buried under skin
c. Follicle
i. Invagination of the epidermis that extends
into the dermis or even hypodermis
ii. Parts:
1. Hair Bulb
--Deepest expanded part of hair follicle
2. Papilla
--Base of Bulb
--Mound of Dermal cells
--Vascular
3. Matrix
--Covers papilla
--Rapidly dividing epithelial cells
--Cells become keratinized as the lose contact
with nutrition provided by papilla
4. Wall of Follicle
--Three layers
a. Internal Epithelial Root Sheath
b. Outer Epithelial Root Sheath
c. Dermal (C.T.) Root Sheath
iii. Animals with Fur have compound follicles
1. Multiple hair strands emerge from Epidermal orfice (pore)
a. As many as 15
b. One primary hair
--Guard or Cover Hair
--Longer
c. Multiple secondary hairs
--Satellite hairs
--Shorter
d. Hair Strand
i. Medulla
--Soft keratin
ii. Cortex
--Hard keratin
iii. Cuticle
--Hard keratin
--Single layer--Shingled
--Prevent from matting (Most animals)
--Wool animals: Cuticle raised
to hook onto each other
e. Root Hair Plexus
i. Surround hair root as touch receptors
3. Growth Cycle of Hair
a. Three phases
i. Anagen
--Growth Phase
ii. Catagen
--Transition Phase
iii. Telogen
--Quiescent phase
--Ends with hair loss
a. Shedding
b. Telogen Effluvium
4. Hair Color
a. Due to Melanin in Cortex and Medulla
5. Types of Hair
a. Primary, Guard Hairs
b. Secondary, Wool-type Hairs
c. Tactile Hairs
--Whiskers
6. Arrector Pili Muscle
a. Controls hair angle
--Implantation Angle
b. Functions:
a. Heat Regulation
b. Defense--Sympathetic Response
c. Sebacous gland secretion
B. Glands
1. Sebaceous Glands
a. Located in Dermis
b. Most empty into hair follicle
c. Some empty directly to skin
i. Mucocutaneous junctions
1. Lips
2. Labia vulvae
3. Penis
4. Prepuce
5. Anus
6. Eyelids
d. Produce Sebum in Holocrine manner
i. Lanolin in Sheep
e. Arrector Pili muscle compresses glands to push sebum
into the hair follicle
f. Moisturizes and Waterproofs Skin and Hair
2. Sweat Glands
a. Two types of sweat glands
i. Apocrine
ii. Eccrine
iii. Both considered merocrine
b. Eccrine
i. Typical of humans, but sparse among
domestic animals
ii. On foot pads of dogs and cats
--Provide a moist surface for
better traction
c. Apocrine
i. Horses, cattle, sheep, dogs, cats
ii. Composition, volume, stimulus,
and function vary among species
iii. Mixes with sebum
--Provides protective cover
--Responsible for animal odor
(bacterial flora)
iv. Heat loss function
--horse>cattle>sheep>dogs>cats>swine
C. Claws and Dewclaws
1. Claws
a. Outer coverings of distal digits
b. Functions:
i. Traction
ii. Defense
iii. Catching Prey
c. Retractable in Felines (except Cheetah)
2. Dewclaws
a. Remains of digits/hooves
D. Hoof
1. Mass of horny keratin
a. Rests on Corium
i. Attaches to periostium of bone
ii. Modified Dermis
b. Outer hoof is epidermis
2. Hoofed animals called ungulates
3. Ruminants and pigs have two weight bearing hooves
a. Third and Fourth digit
b. Second and Fifth digit/hooves are dewclaws
4. Horses have one weight bearing digit
a. Third digit
b. Other digits form Ergots and Chestnuts
c. Parts:
i. Wall
ii. Sole
iii. Frog
E. Horns
1. Mass of horny Keratin
a. Epidermal
2. Stucturally similar to hair
3. Corium binds periostium
4. Found in females and males
a. Most farm animal are dehorned
or naturally polled
b. Dehorning is permanent
5. Antlers
a. Found only in males
b. Are dermal in origin and arise as bony protuberances from skull.
c. Will fall off and grow again
~~~~~Revised
10/7/03~~~~~ TAW