term | characterisitics |
Dermis | Middle layer of skin, consists of collagenous connective tissue, holds other components together, cushions body, contains: sensory nerves, hair follicles, sebaceous glands, sweat glands |
Epidermis | Top layer of skin, consists of: stratum corneum (top keratinized skin cells to prevent dessication), stratum lucidum (usually where exposed to lot abrasion), stratum granulosum, stratum spinosum, stratum basale (constant cell production migrates up) |
Hypodermis | Bottom layer of skin, contains: adipocytes (energy reserve, thermoregulation/ insulation) |
Sebaceous glands | oil, associated with hair follicles to keep moist and waterproof |
sweat glands | Eccrine: not associated with hair, function at birth, produce thin sweat for evaporative cooling, most common on palms and soles, Apocrine: near hair follicles, begin at puberty, create viscous sweat, |
scent glands | modified sweat or sebaceous glands, produce scents may be pheromonal, not all pheromones from scent glands |
Mammary glands | specialized epidermal, # and location vary through different species |
Hair growth types | Angora: continuous growth, long may be shed
Definitive: grows to certain length and stops, shed and replaced |
Hair functional type: Vibrissae | : long, stiff, enervation at base, all mammals but humans, definitive |
Hair functional type: Guard hair | outer layer hair/fur, spines (large & stiff for protection, definitive), bristles (firm, angora, manes lions and horse), awns (most common, definitive) |
Hair functional type: Underhair | Wool: angora, thick, soft, curly, Fur: short, soft, hairs close together, definitive, Velli: short, fine, velvety, gone after birth for many, gone as mature |
Hair anatomy | Medulla: center of hair, sometimes hollow, solid, alternating, Cortex: thickest layer, outside medulla, inside cuticle, Cuticle: outer layer, scale-like pattern, can be ID character |
Hair color | 2 types melanin pigment: Pheomelanin (shades red & yellow), Eumelanin (shades black & brown), Albinism: no pigment from genetic mutation, Melanism: all black from genetic mutation, pigments secreted at base of hair as develop |
Hair color patterns | Agouti: different bands of color from base to tip, Countershading: top and bottom animal different colors (most common in (semi)arboreal), Cryptic coloration: match habitat, Disruptive coloration: spots/ stripes break up outline of animal, warning colors |
Molt | Periodic replacement of definitive growth, Post-juvenile (once), annual (once/year), seasonal (commonly 2X/year often with color change), generally done over weeks |