Skin and coat
Skin Skin seals the body from the outside, protecting it from physical injury and excessive fluid loss. You may think that canine skin helps to regulate body temperature. Well, in humans sweat glands play a crucial role in regulation of the body temperature, but in dogs this task is mostly performed by the tongue. Different receptors are embedded in dog skin that provide their tactile sense. The skin consists of three layers on top of each other. The outer most layer of skin is called the epidermis. It consists of dead, keratinized cells that are continually replaced. The layer below is called dermis. It contains mostly blood vessels and nerves, as well as glands, muscles and follicles (sacks enclosing the root of the hair). The last skin layer is called subcutis, which consists of fibrous tissue and allows a certain degree of mobility against the underlying bone and muscle tissue. Coat A dog’s body is almost entirely covered with hair, with the only exceptions being the nose and the paws. A canine overcoat is usually rougher than the undercoat located below. And hair is constantly growing and may shed throughout the year. Length, density and color of the coat vary with breed. Some parts of the body (i.e. loin and arm pits) may have have a thinner coat than others. External factors that influence the growth of the coat may be temperature, season and daylight as well as intrinsic factors, i.e. the sexual cycle. Diet can also have a huge influence on the quality of the coat, which can be related to the especially the supply, of vitamins, essential fatty acids, proteins etc. The amount of grooming a dog recieves and the condition of the dog's environment are also influential factors. Hair growth The cycle of hair growth is divided into three phases: During the first phase, known as the anagen phase, new hair is created and grows inside the follicle, a tube-like invagination of the skin. The part of the hair located below the skin is called the root, which contains a bulb at its end. Located directly below the bulb is the papilla - a fibrous capsule inside the dermis, which is also enclosed by the follicle. This is where cell-budding takes place creating new hair substance, thus producing hair growth. Once the hair has grown to its full length, growth stops. During the second phase, known as the catagen phase, the papilla contracts and pushes the hair follicle out. The hair itself is not growing while the follicle is shortening. During the last phase (telogen phase) the papilla regenerates and the follicle starts to produce a new hair foilicle, that ejects the old hair lodged above.