Chapter Two...General Canine Anatomy & Physiology

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    In this chapter the canine anatomy and physiology will be discussed in terms of developing a better “touch” when massaging a pet.

    The nine principal systems of the body are:
    Skeletal- the bone structure of the dog
    Muscular- the movement structure of the dog
    Nervous- the responsive structure of the dog: the brain, the spinal cord, and the network of intersecting nerves.
    Circulatory- the blood supply for the dog: heart, lungs, pulmonary arteries, arteries, pulmonary veins, veins, lymphatic capillaries, capillaries, lymphatics (fight viral and bacterial infections), and lymph nodes.
    Respiratory- the oxygen supply for the dog: the nose, mouth, trachea, pharynx, bronchial tubes, bronchioles and the lungs.
    Endocrine- the hormonal and body chemistry supply for the dog: the hypothalamus, pituitary, thyroid, pancreas, adrenals, liver, kidneys, spleen, ovaries and testes.
    Reproductive- the sexual and maternal parts of the dog: for the male: the testicles, accessory glands and ducts, and the external genital organ; for the female: the ovaries, oviducts, uterus, vagina and external genitalia.
    Digestive or Alimenary Canal- the nutrient supply and waste removal system for the dog: the mouth, pharynx, esophagus, stomach, small and large intestine, colon, rectum and anus.
    Urinary- the toxin and waste removal system for the dog: kidneys, ureters, bladder, urethra, and penis or vulva.
    Understanding the skeletal, musculature and principal systems of the dog will give you the building blocks needed to address concerns or issues with those areas of an ailing pet.

    Getting to know the superficial anatomy of the canine is of foundational importance to being able to navigate the canine structure. Superficial massage deals mostly with the musculoskeletal (muscles, connective tissues and skeletal structure) system and the neurological system as these induce the body’s movement, so we will begin there.

    Landmark and Superficial Anatomy
    Knowing the points of the canine form is one of the building blocks to finding your way and mapping the structure of the dog. Using your hands and your mind to feel the dog’s body for major muscle mass, bony landmarks and points of reference such as their shoulder and hip angulation, feeling for areas of elevated heat, spots of fluid build-up or tension, all the while thinking about what you are feeling physiologically, will be your starting point for every massage. As well, watching the dog’s superficial anatomy as it walks or runs, or stretches or sleeps around you will also help you find clues to areas where help may be needed to alleviate pain or immobility. As massage givers, we must use our eyes, our hands, and our minds to inspect the animal and to find answers to the questions that are not answerable by the dog.


    The Integumentary System
    Clearly the first line of physical contact we have with the dog is with its skin and coat. The integumentary system is another word for the skin and fatty tissue layers.
    These are the medium through which we work in order to get to the deeper musculature, joints, tendons and ligaments beneath. The integumentary system is the organ system that protects the body from damage, comprising the skin and its appendages (including hair, scales, feathers, hoofs, and nails). The integumentary system has a variety of functions; it may serve to waterproof, cushion, and protect the deeper tissues, excrete wastes, and regulate temperature, and is the attachment site for sensory receptors to detect pain, sensation, pressure, and temperature. In most terrestrial vertebrates with significant exposure to sunlight, the integumentary system also provides for vitamin D synthesis. The integumentary system is the largest of the body's organ systems. Canine skin (integumentary) is composed of a minimum of 3 major layers of tissue: the epidermis; dermis; and hypodermis. The epidermis forms the outermost layer, providing the initial barrier to the external environment. Beneath this, the dermis comprises two sections, the papillary and reticular layers, and contains connective tissues, vessels, glands, follicles, hair roots, sensory nerve endings, and muscular tissue. The deepest layer is the hypodermis, which is primarily made up of adipose tissue. Substantial collagen bundles anchor the dermis to the hypodermis in a way that permits most areas of the skin to move freely over the deeper tissue layers.
    The integumentary system has multiple roles in homeostasis. All body systems work in an interconnected manner to maintain the internal conditions essential to the function of the body. The skin has an important job of protecting the body and acts as the body’s first line of defense against infection, temperature change, and other challenges to homeostasis. Functions include:
    • Protect the body’s internal living tissues and organs
    • Protect against invasion by infectious organisms
    • Protect the body from dehydration
    • Protect the body against abrupt changes in temperature, maintain homeostasis
    • Help excrete waste materials through perspiration
    • Act as a receptor for touch, pressure, pain, heat, and cold
    • Protect the body against sunburns by secreting melanin which is limited in its ability for canines as they do not produce melanin as people do and are there for at a much higher risk of sunburn and skin cancer
    • Generate vitamin D through exposure to ultraviolet light
    • Store water, fat, glucose, and vitamin D
    • Maintenance of the body form
    • Formation of new cells from stratum germinativum to repair minor injuries


    The Skeletal System
    The skeleton of an animal is its framework. Much as the framework for a home or building, it comprises a strong safety or protective system for the softer or weaker tissues and organs of the animal. The skeleton defines the animals overall size and shape as it is the frame around which the animal’s muscles are formed and hold tight to. The canine skeleton is made up of these primary bone groups:
    The skull and facial bones are comprised of the nasal, frontal, parietal jaw bones, and the mandible.


    The spine is comprised of 7 cervical bones across the neck, 13 thoracic bones across the shoulders and mid-back, 7 lumbar bones of the lower back across the croup and loin, and 3 fused sacral vertebrae which comprise the lower loin and the base of the tail. After this are the caudal bones numbering from an average of 20-23 which comprise the tail. These can number depending on the breed of dog and if the dog’s tail has been surgically altered.
    The rib cage is comprised of 13 pairs of ribs that spring from the thoracic vertebrae and curve both forward and downward where they meet at the sternum bone, or breastbone under the dog. Not all of the ribs come all the way to the point where they connect with the sternum, about half of them curve around the abdomen of the dog and end in a secondary shorter rib bone which is attached to the larger main rib by a small section of cartilage to allow for flexibility and stretch at the mid-point of the dog.
    The final rib, called the floating, last, or 13th rib, is a short and finer bone with a well-rounded curve. This bone is one of the most commonly injured bones of the dog’s midsection during a side collision. Such injury can create small lumps and dips in the rib at the point where the injury occurred.
    The forelegs and front angulation carries about 6o% of the dog’s overall weight. This area is comprised 2 thoracic limbs which are in turn made up of the scapula or shoulder blade, the humerus or upper arm, the radius (think “right up top”) and the ulna (think “under”), the carpus bones- which are the larger bones of the wrist or pastern area, the metacapus which are the larger bones on the top of the foot and the knuckle bones, and the phalanges, which are the bones of the toes.
    The hind legs and rear angulation is comprised of two pelvic limbs. These are in turn made up by the pelvis- which is created by the ilium, ischium, and pubis bones. The legs are comprised of the femur, the tibia (“think on top”), fibula, the hock or tarsus bones- which are made up of seven tarsal bones that create the point of the hock and the larger bones of the ankle or pastern area, the metatarsals which are the larger bones and knuckles of the top of the foot, and the phalanges or toe bones.

    The Bones
    Bones are the building blocks of the skeletal system and have an amazing range or sizes and shapes. Bones are the hardest body tissues second only to the teeth- which are also bones but covered with enamel. Bones are made of minerals, mostly of calcium, and are able to withstand extreme pressure and tension. Each bone is covered by a protective membrane called the periosteum. This tissue not only protects each bone, but also serves as a point of attachment for joints and ligaments which in turn hold all of the bones together in their needed places. When the periosteum is injured, bone malformation or bone growths may occur. The surface of the bone where rotation or articulation occurs will be covered with a thick hyaline cartilage which helps to cushion as a shock absorber and provides for smooth movement thereby reducing friction.
    The longer bones of the body are mainly the levers of the limbs and they also are the main weight supporters. The shorter and smaller bones of the body are found primarily in complex joints and provide more of the flexibility points and ease joint concussion. The flat bones of the body- such as the ribs, pelvis, and shoulder blades are primarily found surrounding organs and are providing safety for them, as well as large surface areas for major muscle groups to adhere to. Both the long bones and the flat bones of the body have a central cavity called the medullary cavity, which produces special and vital bone marrow.


    The Joints
    Joints are the meeting place and intersection of two bones. The joints of the body permit bone articulation or movement and work to produce motion. Movement of the dog is created by contraction of the dog’s muscle and the articulation of the joint for that area of muscle.
    There are two types of joints; fibrous or cartilaginous which are fixed and lack a joint cavity- such joints are found in the sacroiliac, the pelvis and the skull, and the synovial joints. The synovial joints are most common and those are found throughout the body where movement occurs between two bones such as the shoulder, hips, and the legs.
    The cartilage on the end of each bone that comprises a joint is there to reduce friction, absorb shock and to create a smooth rotation surface. On the synovial joints, there are joint capsules or capsular ligaments. The inner layer of the capsular wall is made of a delicate layer of synovial membrane which creates a viscous or lubricating fluid known as synovial fluid.
    Joints can provide 4 main types of movement: flexion or bending, extension or stretching, abduction or drawing away from the middle of the body, and adduction or drawing back to the center, and rotation.


    The Ligaments & Tendons
    Tendons are connective tissue which links muscle to bones. Tendons are made up of dense white fibrous tissue similar to ligaments, and they attach to the periosteum or membrane surrounding the bone and blend with them due to their similar collagen make up. There are two types of ligaments- the tendon of origin; connects the muscle to the less movable bone, and the tendon of insertion; which attaches the muscle to a more movable bone- these work so that upon muscular contraction, the insertion is brought closer to the origin. Tendons can come is varying lengths and are most commonly round but can also be flattened. Tendons are incredibly strong and do not usually rupture. Tendons can do what is termed “stress up”, whereby they sometimes can remain contracted after heavy exercise. While massaging these areas can stretch and loosen long term tension, inflamed tendons are at risk of being overstretched and strained. Tendons are protected by sheaths called tendon bursa. If this sheath is repeatedly irritated, it can accumulate excess fluid and create soft swellings. By massaging these swellings and applying cold presses, we can gain circulation to the area and help dissipate the inflammation.

    The Canine Stifle Joint
    Ligaments are made of collagen which is a fibrous protein found in all connective tissue. Ligaments are bands of thick tissue which connects one bone to another.
    Several groups of ligamentous structures help provide flexibility and safety to the spinal column, neck, pelvis and legs. Ligaments are limited in their blood supply. Blood circulation to ligaments is limited and due to less blood flow to these tissues, when a sprain happens to a joint, it takes longer to heal than a sprain upon a muscle.
    The purpose of the ligaments surrounding joints is to prevent excessive or abnormal range or motion or hyperextension, to and to resist lateral torque or twisting. Ligaments are very tough but have little contraction ability and are only somewhat elastic. Due to this they must work along with the muscles. If they are overstretched or repeatedly stretched, they will weaken and can lose their strength. This in turn allows for repeated spraining and joint instability or hyperextension. When this happens, surgical repair is needed to recover its full tensile strength.

    The Muscles

    The canine muscular system provides the power to the skeletal structure. There are three types of muscles; the cardiac, smooth and involuntary. The cardiac muscles are those which create the heart. The involuntary or autonomic muscles work in the digestive, urogenital, respiratory and circulatory systems. The skeletal muscles of the canine form, which number more than 700, are predominately voluntary and work to create the dog’s movement.
    There are at least two types of muscle fiber; slow twitch fibers (ST), and fast twitch fibers (FT). ST fibers have strong endurance qualities and need oxygen to do their job- they are thereby aerobic fibers. A good supply of blood is needed to bring them their needed oxygen, and to remove waste products from them which are created during exercise. FT fibers are anaerobic and do not require oxygen to work. They are able to deliver quick effort as that required for a fast burst of speed. These muscles are only able to perform for a short amount of time. The rate of ST to FT muscle fibers is genetically inherited. This means that through selective breeding which has developed all the dog breeds available to us today, the characteristics associated with any one certain breed of dog will also have the accompanying relation of muscle fibers, but this will be determined not only by their breed group, but also per what the sire and dam bring to the mix when they create offspring. In example, a Greyhound will have a different ratio of fibers when compared to any other breed, such as the Bassett Hound, but some Greyhounds may have more or less FT or ST fibers when compared to another Greyhound from difference lineage; the same for the Bassett Hound.
    Regardless of the FT and ST ratio, a muscle is comprised of a fleshy part and two tendons which adhere the muscle to the bone- one at either end of the muscle belly. The muscle belly is the part of the muscle that contracts in response to a nerve command. What occurs during a muscle contraction is that the muscle fibers fold in on themselves and this shortens the muscle, similar to the pleats of an accordion or the folds in a fabric window blind. The muscle belly is made up of many muscle fibers arranged into bundles with each bundle wrapped inside of connective tissue or fascia. Each fascia supports and completely covers and separates the individual muscle bundle, as well as the entire muscle itself. This individual bundle arrangement, with additional support to the entire muscle, creates the most support, strength and flexibility for each individual muscle within its muscle group.

    Skeletal Muscles
    Since massage most directly is effective via the skeletal muscle groups, we will learn about these first. Muscles come in all shapes and sizes; some are thin some are bulky and a variety of lengths as well. These muscles all work together to provide a dog its grace and power.
    These muscles work in 3 different methods; concentric contraction, isometric contraction, and eccentric contraction. Isometric contraction occurs when a muscle contracts without causing any movement- such as during standing when it secures stability.
    Concentric contraction occurs when a muscle contracts and shortens thereby causing articular movement- such as forward or backward movement. Eccentric contraction happens when a muscle gradually releases as it elongates- this assists in helping regular movement to not be jerky, and to help cushion shock absorption during the landing phase of jumping.
    Skeletal muscles are highly elastic and have strong contractile power. They respond to motor nerve impulses and as a result the contraction mechanism is a generated process. The release process of a muscle is not a generated process but it is instead a relaxing of the muscle as a result of the cessation of the motor nerve impulses that originally asked the muscle to contract.
    Muscles are equipped with two types of sensory nerve endings: the Gogli apparatus and the muscle spindle. The Gogli apparatus nerve endings send feedback impulses to the brain as to the whereabouts of the muscle; this process is referred to as proprioception. These nerve endings are located where the muscle and the tendons join.
    The muscle spindle nerve endings prevent overstretching of the muscle fibers. As its name implies, the nerve fiber coils around the entire length of the muscle bundle. When reaching a given length, spindle fires nerve impulses that trigger a fast reflex motor nerve reaction to induce immediate contraction of the muscle fibers; this helps prevent overstretching and potential tearing of the muscle fibers- this is a safety mechanism.

    Understanding scar tissue, spasms, stress points and tears
    When a muscle develops a contracture, this means the muscle remains contracted and could result in a spasm. When this contracture happens, relaxation of the muscle cannot occur and pain and restriction or immobility of the muscle will occur. When a muscle overstretches a spasm usually occurs. A spasm is a violent contraction of the muscle in response to the stretching or trauma to it, thereby the muscle cannot lose its rigidity. A microspasm or stress point is a small spasm occurring in only a few muscle fibers within the muscle bundle. Microspasms have a cumulative effect over time that results in a full spasm.
    Sometimes when a muscle is stretched past its limits a tear in the muscle fibers can occur. This causes immediate spasms within the muscle and speeds inflammation to the site of the injury in the body’s natural attempt to immobilize the injury. As part of the healing process, new connective tissues are laid down in an irregular pattern within the muscle fibers which results in scarring. This scar tissue reduces the muscle’s ability to attain its original tensile strength, elasticity and flexibility. Massage therapy is incredibly helpful in the case of lessening scar tissue following an injury by applying kneading and friction after proper warm up of the tissues. Stretching is also a wonderful technique to reduce and prevent the formation of scar tissue.
    A heavily exercised muscle will often form light inflammation within its fibers. This is a normal process for promoting the building of additional muscle fibers. It is often seen in the early phases of training or in growing dogs. It is important to keep this inflammation under control in order to avoid the formation of scar tissue. This is another advantage to massage therapy for active dogs. To keep inflammation down, cold hydrotherapy and deep massage techniques will stir up blood circulation and thereby bring new oxygen and nutrients to promote healing and break down scar tissue.
    As a result of heavy exercise, a stress point can develop close to the origin tendon of the muscle. A stress point is a small spasm in the muscle fiber. You can keep a dog free of stress points by using stress point therapy.
    Another side effect of heavy training is the formation of trigger points. A trigger point is a combination of lactic acid buildup (a byproduct of exertion of a muscle) and motor nerve ending irritation mostly found in the muscle belly. Trigger points can be found in any muscle of the body and massage techniques can keep a dog free of them.
    Study all of the muscles thoroughly. Understanding the interrelation of all of the components of the musculoskeletal system will contribute greatly to your expertise and skillful ability with understanding problems and purposeful, effective massage of needy areas.

    The Nervous System
    The nervous system is comprised of the brain, spinal cord, sensory and motor nerves. This system controls all body functions including both voluntary and involuntary functions. It governs all commands to the body both internal and those from external catalysts. The central nervous system is comprised of two systems; the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Massage does not directly affect the CNS, but it is indirectly affected through the PNS.
    The peripheral nervous system works to convey nerve impulses through the motor (or afferent) nerves that carry information from the CNS to the body parts, and from the body parts to the CNS. These nerves exit through the spinal column and the spinal vertebrae. When massage is applied, it greatly influences the peripheral system through applied rhythm and pressure that comes from our hands and bodies.

    Each of the nerve tissues are comprised of many filaments that are very susceptible to pressure. Such as when heavy trauma happens, where significant pressure is applied to a nerve, impulses can actually stop traveling through it. The swelling that often accompanies trauma, is nature’s way of immobilizing or splinting an affected area, and while this works naturally and effectively, it also usually causes loss nerve sensation. The after effect of prolonged loss of sensory nerve impulses to an area of muscles, usually causes degeneration and eventual shrinkage of the tissue in the immediate area as a result of lost motor nerve impulses from the central nervous system to the traumatized body part. As an example, this is in part what happens when the muscle of an arm or leg is casted, or when dysplasia is advanced.
    The Autonomic Nervous System (ANS) governs and maintains a stable environment for the overall functioning of the nervous system. The ANS governs the vital organs and all of their functions as they related to every one of the other principal systems of the dog- breathing, digesting, eliminating, and circulation. The ANS also is the circuitry board for the locomotion skills and smoothness of movement of the body during action. Within the ANS there are two major divisions; the sympathetic and parasympathetic which both originate within the brain.

    The Sympathetic Division
    This system is the body’s response systems to danger, stress, anger and physical arousal. It governs increasing the heart and respiration rates, it governs the rate of blood flow needed for activity or alert response. It helps the animal to spring into action due to threat, emergency or excitement that is associated with the animal “fight or flight” mechanism.


    The Parasympathetic Division
    Stimulation of this system happens when the body is not in action- as during sickness, sleep or resting, or for digestion and elimination. It also sees to continued circulation and respiration, immune response and reproduction functions during these times of inactivity. The stimulation of this system promotes relaxation and the vegetative functions of the body.





    The Canine Lymph and Glandular System
    The lymphatic system consists of lymph nodes and lymph vessels. The main function here is to transport and store white blood cells. White blood cells are the main line of defense against disease and infection. The lymphatic system is a complex and vital system primarily responsible for the transportation of lymph and for participating in many immune functions of the body. The lymphatic system occurs throughout the body and is made up of small glands called lymph nodes, which are connected to each other by a series of vessels called lymphatics. Other important organs in this system include the bone marrow, spleen, thymus and gut-associated lymphoid tissue (GALT), which is the lymphatic tissue associated with the gastrointestinal (GI) tract. The lymphatic system is located throughout the body and has many components:
    Lymph nodes or glands are small round, oval or bean-shaped structures that are located at various locations throughout the body. The lymph nodes are connected to each other by a series of vessels called lymphatics, which carry lymph from place to place. Some lymph nodes lie along the surface of the body (along the neck, under the arms, in the groin, behind the knees), while others lie deep within the body (chest and abdomen). The bone marrow lies within the central shaft of bones, primarily the long bones of the body. The spleen is located near the stomach in the left forward part of the abdomen. The thymus is located in the front part of the chest cavity, between the trachea (windpipe) and the ribs. The GALT is made up of lymph tissue scattered throughout the GI tract including the tonsils and intestines. Lymph is a milky fluid that flows throughout the system. It contains proteins, fats and a type of white blood cell called lymphocytes. Lymph is collected from the fluid of various tissues and eventually is returned to the blood circulatory system. The lymphatic system provides another route by which fluid can flow from distant tissues back into the blood stream, one that is separate from capillaries and veins. It also carries proteins and other substances away from tissues that cannot be removed or transported directly into the blood system.

    Similar to the blood circulatory system, the lymphatic system is comprised of fine channels that lie adjacent to the blood vessels. These lymphatic vessels eventually merge into a rather large vessel called the thoracic duct. As the lymph is carried from distant parts of the body, it is collected into larger and larger vessels until the vessels all converge in the chest and deposit the lymph in the large vein (cranial vena cava) leading to the right atrium of the heart.

    The lymph moves through the lymphatic vessels toward the lymph nodes. The lymph nodes lie at varying points along the course of the lymphatic chain and can form clusters in some areas of the body. Lymph nodes have a dense fibrous outer coating, called a capsule and are filled with white blood cells and spaces containing lymph fluid. Several types of white blood cells predominate in the lymph nodes, particularly lymphocytes, plasma cells, and macrophages.

    The bone marrow consists of connective tissue, the cells of which form a delicate meshwork within the marrow cavity. The marrow cavity is permeated by numerous thin-walled blood vessels. Within the spaces of this tissue, the immature and adult stages of different blood cells exist.

    The spleen is the largest body of lymphatic system. It is a dark red organ that is supplied with numerous blood vessels. A tough capsule of fibrous tissue covers the spleen. The splenic "pedicle" is located along one surface and serves as the entry and exit point for blood vessels. The internal structure of the spleen consists of:
    Red pulp – areas for red blood cell storage and for the trapping of immune proteins called antigens
    White pulp – areas of special immune response cells called lymphocytes and reticuloendothelial cells
    Marginal zone – an area that separates the white and red pulp and helps to filter the blood

    The thymus is an organ that varies in size depending on the age of the individual. It is largest in young animals and shrinks to a very small size in the adult.

    GALT is present throughout the gastrointestinal tract. Peyer's Patches are aggregates of lymphoid tissue found in the small intestine and are a type of GALT.
    The lymphatic system has several very important functions:

    • absorbing excess fluid from tissues and returning it to the bloodstream
    • absorbing fat from the gastrointestinal tract
    • transporting white blood cells and certain proteins
    • playing an important role in the immune system, particularly in the production of antibodies (immunoglobulins).

    The lymphatic system filters and removes debris from the tissues of the body. Cells produce proteins and waste products. The lymph absorbs these products and carries them away from the tissues because they are often too large to be effectively absorbed and removed by the bloodstream.
    The lymphatic system, functioning along with the circulatory system, absorbs nutrients from the small intestines. A large portion of digested fats is absorbed via the lymphatic capillaries. Fat absorbed from the small intestinal lymphatic capillaries or lacteals is termed chyle.
    The lymph nodes filter out cellular waste products and foreign material in the lymph fluid, including potentially dangerous infectious particles like bacteria and viruses. They trap material received from the lymphatic vessels and provide a site for white blood cells to mount an immune response. They act as a barrier against the entrance of these foreign substances into the bloodstream.
    The chief function of the bone marrow is the production of various red and white blood cells.
    The spleen is an integral part of the immune system and it filters abnormal cells from the blood. It also helps make and store blood cells.
    The thymus is a very important part of the immune system in the newborn. It is the site where the earliest immune cells are made and where immune functions take place in the young animal.
    GALT's main function is to provide immunologic defenses at the surface of certain areas of the body, such as the tonsil and the lining of the intestinal tract. These are areas where the body is often exposed to foreign materials and infectious agents.