View source for Small Animal Dermatology Q&A 07

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'''A photomicrograph of a cross section of a hair bulb is shown.'''

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<FlashCard questions="3">
|q1=What are the stages of the hair cycle, and what are the most common patterns of growth in dogs and cats?
|a1=
There are three stages or cycles in hair growth. 
#The first is anagen, or the growing phase. During this time the hair follicle is actively producing hair. The anagen hair is characterized by a well-developed dermal papilla that is covered or ‘capped’ by the hair matrix.
#The second stage is catagen, or a transition stage between active growth and rest. This hair is characterized by retraction toward the surface. The catagen hair follicle is shortened in length and smaller. The most characteristic feature of a catagen hair is the replacement of inner root sheath by trichilemmal keratinization.
#During telogen, or the resting stage, the hair stops growing and is retained in the hair follicle as a dead hair. A telogen hair is characterized as a small hair, approximately one-third the length of the anagen hair. Hairs continue to grow until they reach a preset length and then enter the resting phase. The hair will remain in this state until a new hair starts to grow, pushes the old hair out, and the old hair is shed. <br><br>
Hairs in dogs and cats are replaced in a mosaic pattern with peaks of hair loss/replacement in the spring and fall. The other two most common replacement patterns are seasonal and waves.
|l1=Hair - Anatomy & Physiology
|q2=What factors influence hair growth in animals?
|a2=
The hair cycle of animals is controlled by a number of factors including: 
*photoperiod, 
*ambient temperature, 
*health, 
*genetics (i.e. breed and species), 
*nutrition, 
*hormones, and 
*local factors that directly influence the growth of hair follicles. <br>
The most important of these factors are photoperiod and ambient temperature.
|l2=Hair - Anatomy & Physiology#Control of hair growth
|q3=Describe the basic anatomy of a hair follicle.
|a3=
Hair follicles are divided into three major anatomical regions: the infundibulum, isthmus, and the inferior segment. 
#The infundibulum or pilosebaceous region consists of the area from the opening of the sebaceous duct to the surface of the skin. 
#The isthmus consists of the area between the opening of the sebaceous duct and the attachment of the arrector pili muscle. 
#The inferior segment extends from the attachment of the arrector pili muscle to the dermal hair papilla.
|l3=Hair - Anatomy & Physiology#Hair and hair follicle anatomy
</FlashCard>

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