16.0 INTEGUMENT
Upon completion of this lecture, students will be able to:
a) Define and use properly the following words: Skin, Epidermis, Stratum basale,
Hemidesmosomes, Stratum spinosum, Stratum granulosum, Keratohyalin granules,
Keratin tonofilaments, Corneum, Stratum lucidum, Stratum corneum, Keratinized,
Epidermal cells, Keratinocytes, Melanocytes, Melanin granules, Langerhans cells,
Merkel's cells, Dermis or corium, Papillary Dermis, Dermal papillae, Epidermal pegs,
Reticular dermis, Panniculus, Epidermal appendages, Hair follicles, Simple follicle,
Compound follicle , Glassy membrane, External root sheath, Internal root sheath,
Cuticle, Cortex, Medulla, Cutaneous plexus, Hair bulb, Arrector pili muscle, Guard hair
(primary), Wool hair (secondary), Sensory hair, Sinus hairs (whiskers), Tylotrich hairs ,
Hair cycle, Anagen, Catagen, Telogen, Feather, Quill, Vane, Barb, Barbules, Sebaceous
glands, Holocrine secretions, Sweat glands, Apocrine sweat secretion, Merocrine sweat
secretion, Perianal glands, Anal glands, Anal sacs, Circumanal glands.
b) Describe and associate basic structure/function for the following: all structures listed
above.
c) Identify by microscopy: arrector pili muscle, compound follicle, corium, cuticle, dermal
papilla, dermis, epidermal peg, epidermis, external root sheath, feather, guard hair, hair
bulb, Hypodermis, internal root sheath, keratin, keratinocytes, keratohyalin granules,
melanin, melanocytes, papillary dermis, quill, reticular dermis, sebaceous gland, sensory
hair, simple follicle, sinus hair, stratum basale, stratum corneum, stratum granulosum,
stratum lucidum, stratum spinosum, sweat gland.
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INTEGUMENT
I.
GENERAL INFORMATION
A. Skin
1. Epidermis
2. Dermis or corium (hoof and claw)
3. Hypodermis
B. Derivative structures
1. Appendages
a. hair, nails, claws, hooves, horns, antlers, feathers, comb, wattle
C. Glands
1. sebaceous, sweat, mammary
II.
SKIN
A. EPIDERMIS
1. Epidermal Layers
a. Stratum basale
i. a single layer of cells on the basal lamina
ii. intense mitotic activity provides continual renewal of epidermis
iii. hemidesmosomes
b. Stratum spinosum
i. cuboidal to squamous cells filled with tonofilament bundles
(extend to desmosomes)
ii. desmosomes firmly bind cells together
iii. spiny appearance is due to fixation shrinkage away from the
desmosomes
iv. also capable of mitosis
v. 2-5 cells thick (thicker layer in hairless regions)
c. Stratum granulosum
i. flat polygonal cells containing basophilic granules
ii. keratohyalin granules are precursors of keratin (tonofilaments
bound by the substance contained in keratohyalin granules)
iii. 1-4 cell layers thick
iv. hard keratin found in hair, feathers, hooves (contains disulfide
bonds)
v. soft keratin found in the outer layer of cells (corneum) in most skin
surfaces.
vi. membrane-coating granules are released intercellularly to form a
water barrier
d. Stratum lucidum
i. layers of translucent squamous cells (organelles are absent)
ii. limited to thick epidermis (footpad, nose, teat)
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e. Stratum corneum
i. many layers of flat enucleated cornified cells (corneocytes) that
slough from the skin
ii. keratinized (keratin replaces organelles) or non-keratinized skin
(dead cells are sloughed before cellular organelles disappear and
keratin is formed)
iii. lipid functions as a permeability barrier
2. EPIDERMAL CELLS
a. KERATINOCYTES
i. cells that become keratinized
b. MELANOCYTES
i. derived from neural crest cells during development of the embryo
ii. not easily recognized in H&E (best to use Gold method)
iii. found between keratinocytes in the basal layer (forms
desmosomal junctions)
iv. long cytoplasmic extensions project into invagination of
keratinocytes of the basale and spinosum
v. Melanin granules are released by cytocrine secretion and taken
up by keratinocytes
vi. melanin granules accumulate over the nucleus
vii.the number of granules determine skin color
viii. hair color and skin is due to different amounts of melanin and the
type of amino acids
ix. red hair contains more cysteine than black hair.
x. Factors stimulating melanin deposition:
1. sunlight, inflammation, irradiation, and hormones (MSH,
ACTH, steroids)
c. LANGERHANS CELLS
i. stellate cells with dendritic processes
ii. found throughout the epidermis (seen only with Gold staining)
iii. derived from bone marrow
iv. form a web-like screen to trap antigens
v. processes antigens for presentation to lymphocytes
vi. a non-phagocytizing macrophage (mononuclear phagocytic
series)
vii.Migrate to local lymph nodes to present antigen to T & B cells
d. MERKEL'S CELLS
i. Neuroendocrine cells
ii. slow adapting mechanoreceptors
iii. paracrine role in epidermal structure
D. DERMIS OR CORIUM
1. Papillary Dermis
a. Connective tissue zone that supports and binds the epidermis
b. Rich supply of blood and lymph vessels, nerves and smaller collagen
bundles
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c. Thin loose connective tissue (reticular fibers, fibroblasts, mast cells,
macrophages, lymphocytes; sometimes difficult to tell where Papillary
stops and Reticular starts)
d. Dermal papillae - irregular projections into the epidermis (provides
cushion); mostly prominent in thick skin such as foot pad and palmar
surfaces
e. Epidermal pegs - interdigitations with the dermal papillae
2. Reticular dermis
a. thicker zone than the papillary dermis
b. large bundles of Type I collagen are found in a woven pattern
c. collagen mutations cause connective tissue diseases that affect the skin
and skeleton in domestic animals (loose, tight, or fragile skin)
d. mostly dense irregular with some loose connective tissue
e. attaches skin to muscle and fascia
f. Panniculus - area containing large numbers of adipose cells (cushion digital pads)
II.
EPIDERMAL APPENDAGES
A. HAIR
1. TYPES OF HAIR FOLLICLES
* thin shafts of keratinized epithelium
* derived from an epidermal invagination
a. SIMPLE FOLLICLE
i. has one primary hair)
b. COMPOUND FOLLICLE
i. usually has one primary hair & several secondary hairs (up to 15)
2. PARTS OF THE HAIR
a. FOLLICLE
i. continuous with the epidermis
ii. thick basal lamina (glassy membrane)
iii. External root sheath - all layers of the epidermis
iv. Internal root sheath - cells surrounding the hair shaft up to
sebaceous glands
v. cuticle - cuboidal cells that become enucleated and flatten to form
keratinized shingles over the hair
vi. cortex - keratinized fusiform cells that contain melanin granules
vii. medulla - keratinized cuboidal cells separated by spaces in the
center of large hairs only.
viii. cutaneous plexus supplies capillary net around follicles and
glands
b. HAIR BULB
i. terminal dilation of the hair follicle as an epidermal peg
ii. dermal papilla is the vascularized basal invagination
iii. stratum basale active in mitosis to provide for hair growth
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c. ARRECTOR PILI MUSCLE
i. smooth muscle bundles in oblique angle
ii. connecting the follicle CT sheath to the papillary dermis
iii. innervated to provide erection of hair shaft
3. TYPES OF HAIR
a. GUARD HAIR (PRIMARY)
i. compound follicles that have a common opening
ii. the principal hair (guard) is larger in diameter
iii. primary follicle root is deep within the dermis
iv. this is the predominant type in horses, cow, and certain dogs
b. WOOL HAIR (SECONDARY)
i. secondary hair of the compound follicles
ii. smaller in diameter - has no medulla
iii. more shallow follicle
iv. predominant in sheep, cats
c. SENSORY HAIR
i. Sinus hairs (whiskers)
a. follicles surrounded by blood sinuses and free nerve
endings
ii. Tylotrich hairs
a. distributed throughout hair coat for mechanical reception
4. THE HAIR CYCLE
a. Anagen
i. period of mitotic activity in the bulb which produces growth;
regrowth occurs in about 130 days
b. Catagen
i. A transitory period when the hair bulb becomes a solid mass of
keratinized cells
c. Telogen
i. A resting, non.growing stage (weeks to months); a secondary
germ center forms at the base
5.0.
OTHER INFORMATION ON HAIR
A. Shedding of hair is either synchronized (whole body) or mosaic (each follicle has own
rhythm).
B. The Hair Cycle is influenced by:
1. light, pregnancy, disease states
2. Steroids tend to prolong telogen
3. Thyroxin shortens telogen (hypothyroidism causes "alopecia" or lack of hair)
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6.0
FEATHER
A. Quill - develops within the follicle and contains vascular components of the dermal
papilla
B. Vane - continuation of the quill above the skin surface
C. Barb - lateral projections from the vane
D. Barbules - parallel projections from the barb; the tips hook opposing barbules
E. Down feathers do not have barbules, but have very thin barbs
7.0
GLANDS ASSOCIATED WITH SKIN
A. SEBACEOUS GLANDS
1. several acini open into a common short duct at the head of the hair follicle
2. holocrine secretions
i. he cells fill with fat droplets; the nuclei become pycnotic; the cells die and
release sebum onto the skin surface
B. SWEAT GLANDS
1. Apocrine sweat secretion is predominant type in domestic species
i. well developed in the horse, less in other species, absent in birds
ii. opens to the skin surface
2. Merocrine sweat secretion (mucous or serous)
i. only in selected areas such as footpads (Eccrine Sweat Glands
C. PERIANAL GLANDS
1. Anal glands
i. sweat glands in submucosa of anal canal
ii. (dog, cat, pig)
2. Anal sacs
i. paired diverticula of anus
ii. apocrine sweat (dog)
iii. sebaceous (cat)
iv. carnivore and rodents
3. Circumanal glands
i. mass of large acidophilic cells near anal sac (sebaceous-like)
ii. problem in dogs
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