4,503
edits
Changes
Jump to navigation
Jump to search
Equine Integumentary System - Horse Anatomy (view source)
Revision as of 15:22, 19 November 2012
, 15:22, 19 November 2012→Hair
The hair follicle originates from a peg of epidermal cells that grows down into the underlying dermis, where it forms a hair cone over a piece of dermis called the '''dermal papilla'''. The papilla provides the blood and nerve supply for the growing hair. From the hair cone, the cells keratinise and form a hair. As the hair grows up through the epidermis to the skin's surface, the cells at the point of the cone die, forming a channel, the hair follicle.
The hair follicle originates from a peg of epidermal cells that grows down into the underlying dermis, where it forms a hair cone over a piece of dermis called the '''dermal papilla'''. The papilla provides the blood and nerve supply for the growing hair. From the hair cone, the cells keratinise and form a hair. As the hair grows up through the epidermis to the skin's surface, the cells at the point of the cone die, forming a channel, the hair follicle.
===Hair Types===
====Guard Hairs====
These are generally '''stiff and straight''' and form the outer haircoat of an animal. They are uniformly distributed across the skin surface and give the haircoat a '''smooth appearance'''. The smoothness of the coat is important in allowing '''rain to fall from the surface''' without penetrating deeper to the epidermis and causing loss of body temperature. The oily coating of the haircoat comes from the secretions of the sebaceous glands in the epidermis, associated with the hair follicle. This also contributes to the '''‘waterproofing’''' of the haircoat. Each hair consists of an outer cuticle, with a cortex and innermost medulla. It is composed of highly keratinised, dead epithelial cells, with the arrangement into the 3 layers conferring flexibility.
The '''''arrector pili''''' muscle is attached to the proximal end of the follicle and the dermis close to the point at which the hair is externalised. Involuntary contraction of this muscle in cold ambient temperatures causes '''erection of the hairs to trap warm air against the skin''', thus providing [[Thermoregulation in Skin - Anatomy & Physiology|insulation]]. This can also be induced by the ‘fight or flight’ mechanism of the '''sympathetic nervous system'''.
Modifications of the guard hairs in horses include the coarse hair of the mane, tail and the tufts of hair ('feathers') around the fetlock region.
====Wool Hairs====
These are thin, wavy, soft hairs that form the '''undercoat of animals'''. They are often much more numerous than the tough guard hairs and usually shorter. Their number increases in '''winter''' when they serve to keep the body warm.
===Tactile Hairs====
Tactile hairs are associated with a sensory function and are much '''thicker and stiffer''' than other hairs. They are mainly found on the face and can also be referred to as '''''whiskers''''' or '''''vibrissae'''''. Their '''follicles are much deeper''' into the hypodermis than guard or wool hairs and possess a '''venous sinus and nerve endings with mechanoreceptors'''. During embryonic development, they appear before other hair types.
These hairs are mostly found on the '''face, near the eyes and on the upper lip'''.
====Tylotrich Hairs====
These large hair follicles are '''rapidly adapting mechanoreceptors'''. They may be present anywhere on the body. These structures consist of a single large hair, surrounded by neurovascular tissue at the level of the sebaceous gland.
==Skin Glands==
==Skin Glands==
==Mammary Glands==
==Mammary Glands==
==Digit==
==Digit==