1. CH. 8: The skin and its Accessory structures
INTEGUMENTARY SYSTEM
CH. 8: The skin and its Accessory structures

2. SKIN INTRO ________ organ of the body
ACCESSORY ORGANS: hair, sweat glands, sebaceous glands, nails
FUNCTIONS OF THE SKIN:
-Barrier against invasion of microorganisms
-Protects underlying structures from injury
-Prevents the body from drying out
-Maintains and regulates body temp
-Receptor for senses: touch, heat, cold, pressure, pain
-Disposes of waste products

3. Skin’s Composition EPIDERMIS
_____________: Outer, thinner layer, visible to the naked eye
Made of 5 layers of __________ __________ epithelial tissue  
- from deepest to most superficial:

4. LAYERS
1) STRATUM __________ – basal layer; cells continuously multiply and are pushed to outer layer until they die and are sloughed off; continuous process
2) STRATUM __________ – spinous layer; cells in this layer are shrunken and spaced apart; thick in areas that are susceptible to wear and tear
3) STRATUM __________ – granular layer; granules in the cytoplasm of cells are visible; cells are beginning to die; not present in all areas (esp in hairy skin); keratinization begins
4) STRATUM __________ – clear layer; cells are closely packed and clear; not always present (esp in hairy skin), but when it is, it is found in areas of wear and tear
5) STRATUM __________ – horny layer; cells are flat, lifeless, and cornified (keratinized); cells are overlapping, dry; give horns, hooves, beaks, and hair their strength; dead cells are continuously sloughed

5. DERMIS HYPODERMIS inner, thicker layer of skin
made of dense, fibrous connective tissue that contains blood vessels and nerves
also contains hair, involuntary muscle, sebaceous glands, sweat glands, and sensory receptors 
HYPODERMIS
Layer under the dermis also called subcutis/subcutaneous layer
consists of fatty (adipose) tissue
allows the skin to move without tearing

6. SKIN THICKNESS
thickest in areas of _______ & ________ (footpads, forehead, dorsal neck, dorsal thorax, rump, base of tail)
thin skinned areas: pinna of the ear, axillary, inguinal, scrotal, periorbital, and perianal regions

7. Hair, covers most animals as a thick coat…
Many animals have fur coats rather than hair coats; fur is a short, fine, soft hair.
Three types of hair:
Primary Hair
Secondary Hair
Tactile Hair

8. hair PRIMARY (#1)– “__________” hair, top coat
stiff, but with a smooth appearance
water runs off the coat of the animal without chilling the animal
SECONDARY (#2)– “___________”hair, undercoat
soft, shorter, thin, wavy

9. HAIR _____________ - thicker and longer than primary hair
found around the face
grow from hypodermis or superficial muscle layer
Each hair is innervated, allowing them to be touch receptors
EX: cat whiskers (vibrissa – any large tactile hair)

10. Hair develops from the ______ ______, which is located inside the hair follicle.
Hair _____________ is what is visible
_______________ __________– bundles of involuntary muscle that are attached to hair follicles
hair stiffens when the muscle contracts
plays a part in the fight or flight response
_______________ – hair along the neck and back that is raised when an animal needs to increase its size during a fight
HAIR

11. Hair growth 2 ARRANGEMENTS FOR HAIR GROWTH:
_____________ – primary hairs grow from separate follicles (cows, horses)
_____________________ – 2-5 primary hairs grow from each follicle (dogs, cats) and are surrounded by clusters of secondary hairs; all are growing from a common pore

12. HAIR color peaks every spring and fall
THERMAL REGULATION is affected by HAIR COLOR
light colored coats are cooler in hot, sunny climates
________________– individual hairs have several bands of light and dark pigments with black tips
________________ – process of losing hair
peaks every spring and fall
affected by photoperiod, temperature, nutrition, hormones, genetics, health

13. GLANDS SWEAT GLANDS (sudoriferous glands)
organs that excrete sweat to cool the body
dogs and cats sweat very little amounts that is usually masked by the hair coat; horses can sweat in much larger amounts
panting, slobbering, and smearing saliva on their coats helps to dissipate the heat

14. SWEAT GLANDS ____________ GLANDS – found throughout the body
secrete strong-smelling substance into follicles
often line the external ear canal and over-secretion can lead to otitis externa
______________ GLANDS – coiled structure whose duct emerges on the skin surface
produce watery sweat
found only on the footpads and between the nostrils in the dog

15. SWEAT GLANDS Continued
________________ GLANDS – secrete SEBUM (fatty lubricant)
which lubricates the skin and hair
waterproofs the coat
gives the coat a glossy sheen
spreads sweat
slows bacterial growth
acts as a territory marker
absent on foot pads and nose

16. SEBACEOUS GLANDS EXAMPLES
___________ GLANDS – on lips of cats, marks territory
___________ GLANDS – produce a strong odor that makes female goats attracted to male goats during breeding season.
Located caudomedially to the horns
_____ _____ - pouches at 4/5 and 7/8 o’clock. Foul smelling secretion that is expressed during defecation and serves as a territory marker

17. CERUMINOUS GLANDS
modified sweat glands located in the external ear canal
secrete earwax (aka _______________)

18. NAILS, CLAWS, HOOVES
modified epidermal structures of the distal phalanges
used for protection, scratching, digging, or defense in battle
dermis contains nerves and blood vessels
all have a WALL, SOLE, and PAD, but with variations

19. NAILS, CLAWS, HOOVES ___________ = hoof or claw
___________ = underside of hoof or claw
flaky in small animals
abundant surface area in horses
__________= finger tip
small animals have individual digit pads, metacarpal and metatarsal pads, and a carpal pad
horses have a _________ that pads the hoof and acts as a shock absorber with the bulbs

20. DEWCLAWS serve no practical purpose
(are often removed in dogs)
usually found on front legs in small animals, but can also be found on hindleg
dogs can be “double dewclawed”
required in Great Pyrenees
look like miniature hooves in ruminants

21. CHESTNUTS, ERGOTS CHESTNUTS ERGOT vestigial carpal and tarsal pads
flattened, oval masses of horn in the horse
found on the medial surface of the legs just proximal to the carpus and at the distal end of the tarsus
ERGOT
vestigial metacarpal/metatarsal pads
small mass of horn in a patch of hair on the palmar/plantar aspect of the horse’s fetlock

22. HORN
permanent structure of keratinized epithelium that grows continuously after birth and originates from the frontal bone
never branched and are never shed
Hornless breeds of species that can have horns are called POLLED
Shape of horn is determined by breed, sex, age
male horns are usually larger
cattle horns are located in temporal position, sheep and goats are in a parietal position
goat horns grow caudally
sheep horns are curled

23. ANTLERS grow from the skull, but are made of bone instead of keratin
shed and regrown every year, becoming more complicated in structure
Each year the horns are initially covered in VELVET which is soft hairy skin that produces the antler. The velvet is rubbed off as the skin dies and the bony process is exposed. Once the antler is exposed it begins to lose blood supply and is eventually shed.

24. Questions?