Max's House
Integumentary System - Part 1: Hair Coat
The integument (skin) of the cat has unique properties regarding coat color, skin pigmentation, inflammatory response, - and specialized integumentary structures. The skin and hair coat condition is an indicator of general health or internal disease. Research regarding the feline integument is specific but is less voluminous than that available for some other domestic species,
The skin functions as an enclosing barrier, preventing the loss of water, electrolytes, and macromolecules. In addition, it prevents entry of potentially injurious agents (e.g., chemical, physical, and microbiologic agents). The flexibility and elasticity of the skin allow motion. Skin produces hair and claws, plays an important role in temperature regulation, and functions as a reservoir for electrolytes, water, vitamins, fat, carbohydrates, proteins, and other materials. The epitheliocytes, intraepidermal macrophages (Langerhans cells), and lymphocytes of the skin play a role in immunoregulation. The melanocytes produce pigmentation, which determines coat and skin color and helps protect the cat from solar radiation. The skin surface and resident organisms provide protection from bacterial and fungal invasion, Skin is a primary sense organ for touch, pressure, pain, itch, heat, and cold. Lastly, the skin functions as an excretory organ and aids in blood pressure control and possibly vitamin D metabolism.
Hair is important in thermal insulation and sensory perception and also plays an important role as a barrier against chemical and physical injury to the skin.
HAIR COAT
Coat Types
The shorthair cat is the fundamental "wild" type, and this coat type is dominant. The longest primary hairs of a longhair cat may be three times as long as those of a shorthair cat. Mutant hair coat types, such as the curly coat in the Devon Rex and Cornish Rex and the wirehair coat seen in the American Wirehair breed, have been perpetuated as breed characteristics.
Three types of hairs have been described in the cat based on the gross appearance of the primary and two types of secondary (or undercoat) hairs:
1 . Primary, or guard, hairs are the thickest hairs and are straight and taper evenly to a fine tip.
2. Awn, or secondary, hairs are thinner and possess a subapical swelling below the hair tip.
3. Down hairs, also a type of secondary hair, are the thinnest hairs and are evenly crimped or undulated.
Primary and secondary hairs are medullated in the cat. The cat does not possess lanugo, or nonmedullated, hair: In the classic coat types, secondary hairs are more numerous than primary hairs, occurring in a 10: 1 ratio dorsally and a 24: 1 ratio ventrally. The Cornish Rex lacks primary hairs, and the Devon Rex has primary hairs that resemble secondary hairs. Both breeds have problems with genetic pattern alopecia (hair loss) involving the chest, abdomen, and shoulders and a predilection for molting of the coat at times of estrus, pregnancy, or stress. The symmetric alopecia that results may be mistaken for an endocrine dermatosis.
Coat Colors
All of the coat type genes are inherited independently of those for color. The only case of linkage definitely established in the cat is the sex linkage of the orange gene "0" resulting in female, but not male, calicos, This means that all color varieties may be found with each coat type and each body type or conformation. However, not all possible combinations are recognized by cat breed registration groups or have necessarily been produced by breeders.
All cats, whatever their coloring, are genetically tabbies, possessing the mackerel (narrow, vertical, gently curving stripes), Abyssinian (solid, agouti pattern), or blotched (classic, larger patches) tabby genes. The mackerel (tiger-striped) tabby is the true wild type, for this pattern is derived from the domestic cat's wild ancestors. The tabby is a complex color built up from two component patterns, one superimposed on the other, that are governed by separate sets of genes. The underlying pattern is called agouti and is a universal gray camouflaging pattern found in many mammal species. It is composed of hairs with a bluish base and black tip separated by yellow banding. Solid black and white cats are called selfcolored cats. The genetic difference between a tabby and a true self-colored cat is that the latter is nonagouti in constitution. The honagouti genes remove the yellow bands across the hairs in the light areas of the tabby pattern so that the color of these hairs merges with the darker stripes to make a uniform color.
The completely white cat results from the possession of the dominant "W" gene, but behind the white exterior may lie literally any color genotype (e.g., self-colored, tabby, or bicolored). The white haired cat is not a true albino. Although the "W" gene is generally all dominant, it does seem to vary somewhat in its masking ability. In the white cat, deafness may affect one or both ears, and although this is more common in cats with blue eyes, it can also appear in those with orange eyes, The deafness, which results from degeneration of the cochlea, is irreversible and commonly begins 4 to 6 days after birth.
Coat Growth
The hairs of the coat grow from follicles associated with the dermis.
Hairs do not grow continuously but rather in cycles. Each cycle consists of a growing
phase (anagen), during which the follicle is actively producing hair; a transitional
period (catagen); and a resting period (telogen), when the hair is retained in the
follicle as a dead, or "club," hair that is subsequently lost.
Mean hair growth is about 295 µm/day for primary hairs and about 260 µm/day for
secondary hairs. Cats may have twice as many hairs per cubic millimeter on the abdomen as
on the dorsum. Cats are unusual among domestic species in having a fully haired scrotum.
Hair replacement in cats is mosaic in pattern and predominantly responsive to photoperiod
and possibly to ambient temperature. Cats that spend significant periods outdoors in
colder climates will shed noticeably twice a year (spring and fall). Normal indoor cats
shed all year long.
Hair follicle activity is maximal in the summer and minimal in the winter. In summer,
about 30% of the primary hairs and 50% of the secondary hairs are in telogen. In winter
these percentages increase to about 75% and 90%, respectively. Therefore, cats are more
easily epilated in the winter.
The barbed tongue and the forepaws are the main instruments of grooming for the cat.
The time devoted to grooming varies from none to one third or more of the waking hours.
Grooming is not just a matter of personal hygiene, as licking stimulates the glands of the
skin that keep the coat waterproof. Grooming is also a necessary part of temperature
regulation in the cat, as evaporation of sweat is ineffective because of the fur. The
other practical function served by grooming is removal of loose hair, debris, and
parasites from the fur.
The pathogenesis of trichobezoar (hairball) formation in cats is unknown, although
some investigators postulate that a disorder of gastric motility is responsible.
Tactile Hairs (Whiskers)
Tactile hairs (pili tactiles) are substantially thicker than normal guard hairs and
protrude beyond these. These long sensory hairs also extend three times deeper into the
dermis than primary follicles. The tactile hair follicle is surrounded by a fibrous
capsule and is richly supplied with a venous (blood) sinus. In the walls of the venous
sinus are nerve endings that are responsive to the movement of the tactile hair, which is
amplified by wave action of the surrounding blood (tactile bodies). Most tactile hairs
are-found on the face, principally on the upper lip and around the eyes, although others
are scattered on the lower lip, chin, and elsewhere on the head and carpus. They are named
according to location (e.g., pili tactiles labiales maxillares). The tactile hairs of the
carpal region are found on the caudal antebrachium and carpus. These are especially
sensitive to touch and are a characteristic feature of carnivores that use their forelegs
for grasping prey.
The slightest movement of tactile hairs, even by air currents, stimulates the nerve
endings and provides information on the cat's immediate surroundings. The attached mm.
arrectores pilorum move the tactile hairs, and the hair can be "put on the
alert" when required.
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