The equine foot includes the hoof, dermis, first, second and third phalanges and associated structures. The hoof itself is the cornified layer of the epidermis, lacking the stratum granulosum and stratum lucidum. It is important to understand the histology of the hoof because a disease involving the epithelium of the foot, called laminitis, is the most devastating clinical disease of the foot.

The peculiar histology of the hoof is formed from special relationships between the dermis (or corium) and the overlying epidermis. In some places, the dermal papillae and epidermal pegs are confluent forming apparent layers, i.e., they are laminar or consist of lamellae; in other places they are more typical. It is this lamellar interaction between the epidermis and dermis that gives the hoof its strength.

The Equine Hoof

The wall of the hoof is that part of the hoof which is visible when the foot is on the ground, and it can be divided into three layers. From outside to inside, they are the stratum externum (tectorium), the stratum medium, and the stratum internum (lamellatum).

hoofdiagram1&2F.jpg (49029 bytes)

 

 

 

 


hoofdiagram3F.jpg (19905 bytes)

The Wall of the Hoof

  • The stratum externum or tectorium is an extension of the perioplic epidermis and is composed of cornified eipithelial cells which appear as a soft, white, shiny material. This tissue attaches the hoof to the epidermis of the skin of the foot.
  • The stratum medium or coronary epidermis is composed of prominent tubular and intertubular horn, and this layer comprises the bulk of the wall of the hoof.

  • The stratum internum or stratum lamellatum is the epidermis in the laminar region.

Stratum Lamellum

It is made of nontubular horn which fuses with stratum medium and helps hold the wall to the foot. In this region, the dermal papillae and epidermal pegs form elongated ridges oriented perpendicular to the ground. These ridges are formed from primary and secondary laminae - the secondary laminae being oriented at close to a right angle to the primary laminae. There are about 600 primary laminae and about 100-200 secondary laminae for each primary lamina. This system of interdigitating primary and secondary laminae provides the tight bond between the wall of the hoof and the underlying dermis. Thus, damage to the laminae leads to disruption of this interdigitating system which results in separation of the hoof wall from the dermis and phalanx beneath it.

 

hoofhisto1F.jpg (30818 bytes)
Histological section of fetal hoof.  Note the interdigitation of the epidermis and the underlying dermis in the region called the stratum lamellatum

hoofhisto2F.jpg (32858 bytes)
Higher magnification of 
the stratum lamellatum.  
A= Primary epidermal lamina;
B= Primary dermal lamina

Laminitis (acute laminar degeneration) is an inflammation of the laminae within the hoof. Many pathophysiologic mechanisms are thought to cause laminitis, among them vasoconstriction within the digit, perivascular edema, arteriovenous shunting of blood at the level of the coronary band, venoconstriction and microthombosis. These lead to less than normal perfusion of blood to the digit resulting in ischemia, edema and eventually necrosis of the laminae.

Copyright 2002 Charlotte L. Ownby
Histology Part 2 Index