internalanatomy

The Dog's Internal Anatomy:

Part 1 - Skeletal

Richard Delgado |

The dog's skeletal, muscular, and nervous systems are actually pretty similar to our own. They are mammals, just like us, and they share some of the same characteristics. Of course, they are four-legged, they do not sweat, they have a tail, and differ in many other ways, but the systems are alike.

Mammal structures are made up of bone, muscle, nerves, tendons, and ligaments. These all work together to make up the structure of the body and are what contribute to the motor functions.

I will be describing the make-up and the function of these structures, starting with bone in this part one issue.

Bone
Let me start with the skeletal system. Now, there are three different hormones that work to regulate the Calcium level in a dog's body fluids, which you do not need to know the names of. Another important hormone is responsible for bone develop while dogs are in utero, or developing in the uterus.

I want to make this learning experience as user friendly as possible, so I will not bore you with scientific names and other long terms, unless I feel it is necessary. Even then, I will keep it simple and describe everything.

Bone Structure
Calcium, as we all know, is what makes bone so hard, but it is also vital to other functions in a mammal, our dog's being mammals. Phosphorus is another important mineral that makes up bone.

Bone is actually rather lightweight material. Bone is made up of protein fibers called collagen, which mainly extend along the lines of tensional force. Collagen is weight for weight just as strong as steel. Calcium salts and phosphorus deposit themselves within these fibers. This mineral build-up is what gives bone its strength and rigidity. It is the collagen fibers that give bone its great tensile strength, while the calcium salts give bone its compressional strength.

The rigid skeleton is what provides protection for your dog's vital organs, allows the dog to have locomotion, and supports your dog's weight against gravity. However, when stresses such as excess weight are applied, the bone is placed under more pressure. Other stresses can include jumping up and down from high places, excessive running, and other high impact activities. These are contributing factors to bone and joint diseases found in dogs.

Bone has two types in dogs and other mammals. Cortical bone, or compact bone, makes up the outer layer of most bones, and makes up about 80% of the bone in the body. The other type of bone is called trabecular bone, or otherwise known as spongy bone. This type of bone makes up the other 20% of bone in the body. The spongy bone is found inside the compact bone.

Osteocytes are the bone cells that are found in compact bone. They have a low surface to volume ratio, and receive nutrients from tiny canals within the compact bone. These canals are called Haversian canals, which contain blood vessels which transport blood and nutrients to compact bone.

The spongy bone is made up of spicules, or plates. It is highly metabolic, has a high surface to volume ratio, with many bone cells sitting on the plate surface. Spongy bone gets its nutrients by diffusion through from the ECF. That is, the nutrients pass from the body's extracellular fluid into the bone.

So, you can see that bone is a living tissue. Blood and nutrients flow in and out of bone, regulated by the body to maintain a constant level of minerals, blood, nutrients, and so on.

Bone Growth
I will talk about growth of long bones, which grow differently than the skull. I am focusing on a dog's legs because this is what we are concerned with here. I want to teach you about your dog's vulnerable structures when it comes to leg and joint problems common in dogs.

Long bones grow by first forming a cartilage base. Remember, that bone is made up of a protein called collagen. Ossification then occurs, that is, minerals bind to the cartilage, forming actual bone. The ossification process is what forms skeletal bone as we know it.

The ends of long bones are where growth occurs. Epiphyses or epiphyseal plates are formed at the ends of the shaft of long bones. These plates separate the ends from the rest of the shaft of the bone.

Growth occurs as long as the plates are present. Once the plates are closed, growth stops and the newly formed bone length is now part of the shaft of the bone. Hormones regulate the growth in width of the bone.

While bone growth is taking place, these areas of soft bone are vulnerable to injury, especially in the carpal (wrist) and stifle (knee).

Bone Formation and Resorption
Just because bones stop growing does not mean they become inactive. Far from it. Remember how blood and nutrients are transported to both types of bone? These systems are always present in bone.

Old bone does get constantly replaced and new bone formed, but the length of the bone will not change. This process is called resorption and formation. Resorption refers to the process of removal of old bone cells and re-assimilating them into the body. Formation, of course, refers to the process of forming new bone cells.

Bone marrow forms the cells that are responsible for the resorption and formation process. The cells that are responsible for eroding and resorbing old bone cells are called osteoclasts. The cells that are responsible for forming new bone cells are called osteoblasts.

Osteoblasts secrete collagen and other proteins, and various other substances to form bone. These cells eventually turn into Osteocytes. Remember these? Osteocytes are the cells that make up compact bone. Do you see how this works now?

Conclusion
I have tried to explain the skeletal structure of a dog in a way that you will understand it and have more knowledge in this area. I hope that I have succeeded. There is so much that occurs in your dog's system that this is just barely the tip of the iceberg.

This information is crucial to understanding why it is so important to never let your dog, young or old, jump to and from high places, or otherwise place great stresses on their bodies.

While the proteins and minerals that make up bone are unbelievably strong, damage can occur.

Injuries can slow or impede the natural processes in their body to repair themselves. Some injuries may go unnoticed and not come up until later years. By then, it is too late. Please regulate your dog's play and activities. For more information on keeping your dog healthy and feeling youthful, please visit the Pet Care 4 Our Animals website.

The Dog's Internal Anatomy

Part 2 Muscles, Tendons, Ligaments, And Joints

Richard Delgado

For the next topic of the dog's musculo-skeletal system, I will be talking about four things. I will go over the muscles, tendons, ligaments, and joints. These four tissues help tie together the skeletal system, which supports the animal, and allows movement.

Muscles
Muscles are what gives your dog movement. There are a lot of other systems that also contribute, but it is the contraction and relaxation of muscle that gives mechanical movement to the skeletal system, allowing dogs to walk, run, wiggle their noses, etc.

There are three different types of muscle in the mammalian body. There is Skeletal muscle, Cardiac muscle, and Smooth muscle. Cardiac muscle is just what it sounds like. This is heart muscle which has well-developed cross-striations throughout the muscle. Heart muscle beats rhythmically on its own due to Pacemaker Cells in the Myocardium which discharge and cause the involuntary heartbeat.

The Myocardium is just the thickest middle layer of the heart wall and Pacemaker Cells are just cells that set and keep a pace within the heart.

Smooth muscle also contains these pacemaker cells, but these beat at an irregular rhythm. Smooth muscle does not have any cross-striations, and is found in the internal organs of mammals, and are also involuntary.

Next comes the skeletal muscle. This is what I will be concentrating on. Skeletal muscle requires voluntary thought processes, which triggers nerve impulses, which then triggers muscle movement.

Skeletal muscle is attached to the skeleton by tendons. I will talk about these in a minute. Muscles allow movement of the skeleton to occur by contracting and relaxing. Muscles do not expand and push, they can only contract and pull. This is why there are muscles on each side of a bone. They are called Antagonistic Muscle Pairs. For example, one muscle contracts and pulls to bend the leg, the other contracts and pulls to straighten it out.

These are the basics of muscle, and from here on out things get very complicated. I will keep it simple, so here are just a few other things to know about muscle.

Skeletal muscle is made up of individual muscle fibers, that taken together, form the muscle structure. Each muscle fiber runs in a parallel line between the tendons, and most muscle fibers both begin and end at the tendons. The way that these muscle fibers are arranged makes the contractile force additive, that is, when contraction occurs, the force along the line of muscle adds up as more force occurs.

There are three main proteins that make up the contractile mechanism in skeletal muscle. They are Myosin-II, Actin, and Tropomyosin. Tropomyosin is further made up of three subunits.

I will try to generalize what happens in muscle when contraction occurs. This process is very complex, so remember, this is just a layman's explanation.

Skeletal muscle is made up of thin filaments and thick filaments. The contraction of muscle occurs when the thin filaments slide past the thick filaments. The so called "power stroke" occurs by what I would call a lever action. A lever from the thin filament detaches from the thick filament, moves down the thick strand, re-attaches, then flexes and pulls the strand shorter. The distance moved is just a few nanometers, but when hundreds or thousands of these lever actions occur all along the muscle filaments, considerable shortening of the muscle occurs.

I hope I explained that in a way that you can understand, because you can spend months studying just the mechanism of contraction and relaxation of muscle.

There are two types of muscle fibers in the dog's body. These are Type I and Type II fibers. The different fiber types are found in different types of muscle. Red muscle is mostly made up of Type I fibers and are darker, respond slowly and have long latency, and are responsible for maintaining posture. These are long, slow contractions.

White muscles contain mostly Type II fibers and are responsible for fine, skilled movements. They have short twitch durations.

One last tidbit about muscle is that dog skeletal muscle has the ability to exert 3 to 4 kilograms of tension per square centimeter of cross-sectional area. This is also true for human skeletal muscle.

Tendons and Ligaments
The information that I have about tendons and ligaments will be brief. Tendons are what attach the muscles to the bone, and Ligaments are what attach bone to bone. They are both very tough and fibrous. They can take a lot of stress, but once they sustain an injury, tendons and ligaments heal slowly. If they are allowed to rest, they can regain their strength and motion. But if the injury is ignored, and more damage continues to occur, it will result in obvious pain. Without rest and treatment, tendons and ligaments will never regain their original strength or range of motion.

Tendons are made up mostly of collagen protein, along with other proteins. They have a poor blood supply, and when they suffer injury, they are difficult to treat, and often do not heal well.

Ligaments are similar to tendons in structure, but attach bone to bone.

Changes in the mechanical motion of a limb also affects changes the tendons and ligaments. When tendons and ligaments are gradually placed under increasing stress, they can adapt and become stronger and more flexible. This occurs in athletic dogs and dogs that perform daily work such as herding, pulling sleds, and other activities. When dogs gradually work up to a certain work level, the tendons and ligaments adapt as well.

When your dog lays around all day, and all week, then you take them to the park to play fetch on the weekend, your dog is placing great stress on their tendons and ligaments when they are suddenly running hard, making quick turns, and putting compressional stress on their entire skeletal system.

Stretching out your dog's muscles before any type of exercise, and making sure that they are warmed up before any activity will help decrease any chances of injury or damage on the cellular level. Take time to stretch out your dog's legs by taking each limb, moving it in all directions, and holding it in place for a few seconds.

For example, grab one of your dog's front legs and stretch it all the way out, and hold for a few seconds. Then stretch it all the way in the other direction and hold. Repeat this a few times. Make sure to stretch his leg at the elbow and the wrist as well. Repeat this for all limbs. Then walk your dog for at least 10 minutes before any activity to make sure he is warmed up and will not be working with "cold" muscles.

Another stressful situation placed on your dog is when you have them jump in or out of your vehicle with cold muscles. As described above, this places stress on your dog's entire skeletal system. Over time, this will cause problems such as arthritis and hip dysplasia. Young puppies should never, ever be allowed to jump or run before they are at least one year old. To see the reason why, refer to part 1 of this series, The Dog's Internal Anatomy: Part 1- Skeletal at the Pet Care 4 Our Animals website.

In order to reduce stress on your dog from jumping in and out of your vehicle, or on and off of your bed or couch, read about how to increase your dog's longevity and keep him youthful.

Joints
A joint is simply the place where two bones meet. Each end of the bone is covered by a layer of cartilage called articular cartilage. The entire joint structure is covered by a joint capsule called the articular capsule. This capsule is lined on the inside by the synovial membrane, which produces joint fluid, called synovial fluid. The synovial fluid provides lubrication for the bone, muscle, ligament, and tendon at that joint.

This is a generalization, because there are many different types of joints depending on their location in the dog body, and their structure and purpose. What I have described above is called a synovial joint, which is a freely moving joint. Note that the two bones are separated by a cavity.

Synovial joints are further divided into two different types. A Hinge Joint is a freely moving joint that can only bend in one direction, such as the knee. A Ball-and-Socket Joint will allow rotaional movement and can move in all planes. An example of this would be the hipbone joint.

There are also two other types of joints. One, called Fibrous Joints are immovable joints. These joints hold bone together tightly, such as in the skull. The skull consists of many bones that do not move.

The other type of joint is called a Cartilaginous Joint. These joints allow some movement and are found mostly in the vertebral column. Each vertebrae is divided by a cartilaginous joint, which provides protection and cushion between vertebrae. Continual jumping up and down from high places can cause damage to these joints, and lead to back problems in dogs.

Richard Delgado brings his 15 years of pet care experience to the internet community to teach all dog lovers to properly care for their dogs. His current website Pet Care 4 Our Animals at http://www.4ouranimals.com focuses on the care and prevention of dog joint diseases. Sign up for his monthly newsletter at newsletter@4ouranimals.com.
Published At: www.Isnare.com Permanent Link: http://www.isnare.com/?aid=9525&ca=Pets