Laminae are what bind the hoof wall to the foot bone. They are an example of tissue that is at once durable and vulnerable. They transfer from hoof wall to P3 (foot bone),and vice versa, all the force generated between horse and earth. At times this is a tremendous load. The laminae successfully carry out this task with apparent ease.
The laminae of the horny wall are called epidermal or insensitive laminae. They are made of nonliving keratinized cells. The laminae which interlock with the epidermal laminae are called dermal or sensitive laminae. The dermal laminae are living tissues with a perfuse vascular system.
The surface area produced by this system is huge considering the space it occupies.
The brown stuff is horn (insensitive) and the red stuff is flesh (sensitive).
This process of artery becoming vein is called anastomosis. To anastomose is to communicate, in a liquid sort of way. Arteries and veins can communicate at larger branches as well. This is by way of shunts or AVAs (arterio venous anastomoses). The horse's foot has a circulatory autoregulation system. By opening and closing AVAs to periodically flush greater amounts of blood through the foot it can stay warm in extreme cold conditions. This autoregulatory system may be important both in preventing founder and in causing laminitis.
Laminitis is not fully understood at this time. There are several theories about it's etiology. My field experience leaves me firmly convinced that inflammation is the most important factor in most cases. In those cases where inflammation was controlled, so was the pathology controlled.
The horse has primary and secondary laminae. The larger primary laminae have secondary laminae around their edges. I haven't counted the laminae, but those who have say there are approx. 600 primary laminae in the average horse's hoof.
Lamellar circulation consists of a dense vascular network. Arteries branch out becoming smaller in diameter until at their smallest diameter they are called capillaries. They then become larger as they branch back into larger vessels now called veins.