Bones and Their Development

What are bones important for? And how do they achieve this?

They act as mineral reservoirs for calcium and phosphorus, containing 99% of the body’s calcium and 80% of the phosphate along with 2/3 of the sodium the bones act as a perfect reservoir controlling the levels of these elements in the blood. 0.5% of calcium is exchangeable but plays a massive role in regulating plasma calcium. The bone acts as an ion exchange column which contributes to stability of blood levels in conjunction with the kidneys in something called a homeostatic function. Bones have a massive metabolic flow therefore can easily monitor and exchange elements with the blood. When a lack of diet containing these minerals occurs the bone can release chemicals of these nutrients so the body is still well fed. If blood calcium is allowed to get high or low then muscles and nerves will stop functioning

They manufacture red blood cells through use of the bone marrow which consists mainly of hematopoietic tissue. Stem cells in the red bone marrow called hemocytoblasts are the key building block behind everything formed in the blood. If one of these hemocytoblasts commits to becoming a proerythroblast it will develop into a red blood cell. “Million red blood cells are made every second in a process that takes 2 days, that’s a lot of blood cells.

They act as support columns by being the essential building blocks of a house. Without bones they would be a floppy mess on the floor. With over 200 bones standing strong together like pillars for attachment they are the main frame base of a horse or any animal. Except for maybe jellyfish…. All stemming from the spinal cord which offers a strong foundation for extension the skeleton uses a variety of bone classifications to form a stable base for which to attach muscles, tendons and ligaments to create the locomotive animal.

They act as levers for movement by what was previously discussed. The shape and structure allows attachment of soft tissues to be the power behind the horse. With aid of sesamoid bones changing angles and articulations the tendons work perfectly in conjunction with these long bones to move the horse effortlessly.

Finally they provide protection for vital organs, the skull protects the brain and ribs protect, heart, lungs, liver, kidneys, stomach etc… Without this the horse would be vulnerable to any knock or bump.

How does your horses cannon bone grow from a foal to mature?

Limbs are developed from a mass of cartilage. The 3rd metacarpal is a long bone. Long bones grow in length from a growth plate called the epiphyseal cartilage. Long bones such as the 3rd metacarpal consist of 3 parts. The middle section of it is called the diaphysis, this is a hollow tube made from cancellous bone, and in here is the production factory for red blood cells. At either end of the bone is an epiphysis, they create what is known as the articular surface for the bone. In the growing foal, the diaphysis and epiphyses are centres of bone formation. Bone formation or, ossification, itself takes place by a process of endochondral ossification in which soft cartilage cells are transformed into hard bone cells. Between the diaphysis and epiphysis is a metaphyseal growth plate. (Only at the distal end) This allows the bone to grow in length. When a bone reaches a point where it no longer needs to grow the growth plates close up as ossification occurs to become joined as one. Keeping the proportion and correct shape as growth occurs can also be called bone modelling. This modelling is vitally important as the horse is getting older because of the work it will be expected to do as it grows. Without this the horse could suffer under the intense workload humans can put their horses under. As much as a bone can stop growing when it reaches a certain age bone remodelling never stops as technically it is repairing any breaks or damage a bone can suffer. This occurs by osteoclasts taking away old bone and replacing it with new bone made by osteoblasts and turn it into osteocytes, The osteoblasts are found in the periosteum which is a thin layer lining the outside of the bone except the articular surfaces. The osteocytes are found within the endosteum. The osteocytes that produce bone are able to harden this bone into osteoclasts through supplying the bone with minerals, calcium and phosphorus in a process known as ossification. All of which these things are supplied to through arteries that travel through bones using the medullary cavity and drop of important nutrients in the diaphysis where they pick up red blood cells that are being made there to help carry other minerals around the body in a giant circle.

What are the differences between the cannon bone and Shannon bone?

The 3rd metatarsal differs from the 3rd metacarpal because it is roughly one sixth longer in any given horse. it has a much more cylindrical shaft being very prominent dorsally. It tapers down towards the distal extremity and it has a more triangular proximal articular surface with a non-articular area in the centre. On the dorsal lateral surface is a shallow grove for the metatarsal artery with the medial side showing a finer grove for the metatarsal vein. On the plantar surface the nutrient foramen which is sometimes doubled is placed higher than that of a metacarpal. Proximal extremity is wider dorsal to plantar. On the dorso medial side is a rough ridge for insertion of the tendon from the peroneus tertius muscle. The pedal bone is slightly pointier in the hind as it gives a better shape to spring off from where as the fronts are rounded for more weight bearing

What are the proximal and distal Sesamoids?

The sesamoid bones are irregular shaped bones found within the leg and have several key functions.

The functions of the sesamoids is to extend the articular surface of joints, change angle of attachments for tendons to improve efficiency and to form a Scutum when lubricated for a smooth passage for tendons. You get two proximal sesamoids on each leg, they are located on the palmar surface of the third metacarpal on the distal extremity. Together they provide a groove for the digital flexor tendons so efficiency increases due to angle change. They form a Scutum and increase articular surface of the fetlock forming an important part of the suspensory apparatus. The abaxial surface gives attachment to a series of collateral ligaments and the dorsally extending branches of the suspensory which is what makes it such a strong compact joint.

The distal sesamoid or navicular bone which gets its name from the naval word ship is transversely elongated and articulates with the distal end of the middle phalanx as well as the distal phalanx. The DDFT glides over the palmar/plantar surface which is opposite to the articulations, being separated from the bone by a navicular bursa. The surface under the bursa is cartilage covered. The proximal and distal borders separating the articular and flexor surfaces are grooved and have larger foraminae.