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5.4: Structure of Bone - Biology


Roasted Bone Marrow

Do you recognize the food item in the top left of this photo in Figure (PageIndex{1})? It’s roasted bone marrow, still inside the bones. It’s considered a delicacy in some cuisines. Marrow is a type of tissue found inside many animal bones, including our own. It’s a soft tissue that in adults may be mostly fat. You’ll learn more about bone marrow and other tissues that make up bones when you read this concept.

Bones are organs that consist primarily of bone tissue, also called osseous tissue. Bone tissue is a type of connective tissue consisting mainly of a collagen matrix that is mineralized with calcium and phosphorus crystals. The combination of flexible collagen and hard mineral crystals makes bone tissue hard without making it brittle.

Bone Anatomy

There are several different types of tissues in bones, including two types of osseous tissues.

Types of Osseous Tissue

The two different types of osseous tissue are compact bone tissue (also called hard or cortical bone) tissue and spongy bone tissue (also called cancellous or trabecular bone).

Compact bone tissue forms the extremely hard outside layer of bones. Cortical bone tissue gives bone its smooth, dense, solid appearance. It accounts for about 80 percent of the total bone mass of the adult skeleton. Spongy bone tissue fills part or all of the interior of many bones. As its name suggests, spongy bone is porous like a sponge, containing an irregular network of spaces. This makes spongy bone much less dense than compact bone. Spongy bone has a greater surface area than cortical bone but makes up only 20 percent of bone mass.

Both compact and spongy bone tissues have the same types of cells, but they differ in how the cells are arranged. The cells in the compact bone are arranged in multiple microscopic columns, whereas the cells in the spongy bone are arranged in a looser, more open network. These cellular differences explain why cortical and spongy bone tissues have such different structures.

Other Tissues in Bones

Besides cortical and spongy bone tissues, bones contain several other tissues, including blood vessels and nerves. In addition, bones contain bone marrow and periosteum. You can see these tissues in Figure (PageIndex{2}).

  • Bone marrow is a soft connective tissue that is found inside a cavity, called the marrow cavity. There are two types of marrow in adults, yellow bone marrow, which consists mostly of fat, and red bone marrow. All marrow is red in newborns, but by adulthood, much of the red marrow has changed to yellow marrow. In adults, red marrow is found mainly in the femur, ribs, vertebrae, and pelvic bones. Red bone marrow contains hematopoietic stem cells that give rise to red blood cells, white blood cells, and platelets in the process of hematopoiesis.
  • Periosteum is a tough, fibrous membrane that covers the outer surface of bones. It provides a protective covering for cortical bone tissue. It is also the source of new bone cells.

Bone Cells

As shown in Figure (PageIndex{3}), bone tissues are composed of four different types of bone cells: osteoblasts, osteocytes, osteoclasts, and osteogenic cells.

  • Osteoblasts are bone cells with a single nucleus that make and mineralize bone matrix. They make a protein mixture that is composed primarily of collagen and creates the organic part of the matrix. They also release calcium and phosphate ions that form mineral crystals within the matrix. In addition, they produce hormones that also play a role in the mineralization of the matrix.
  • Osteocytes are mainly inactive bone cells that form from osteoblasts that have become entrapped within their own bone matrix. Osteocytes help regulate the formation and breakdown of bone tissue. They have multiple cell projections that are thought to be involved in communication with other bone cells.
  • Osteoclasts are bone cells with multiple nuclei that resorb bone tissue and break down bone. They dissolve the minerals in bone and release them into the blood.
  • Osteogenic cells are undifferentiated stem cells. They are the only bone cells that can divide. When they do, they differentiate and develop into osteoblasts.

Bone is a very active tissue. It is constantly remodeled by the work of osteoblasts and osteoclasts. Osteoblasts continuously make new bone, and osteoclasts keep breaking down bone. This allows for minor repair of bones as well as homeostasis of mineral ions in the blood.

Microscopic Anatomy of The Compact Bone

The basic microscopic unit of bone is an osteon (or Haversian system). Osteons are roughly cylindrical structures that can measure several millimeters long and around 0.2 mm in diameter. Each osteon consists of lamellae of compact bone tissue that surround a central canal (Haversian canal). The Haversian canal contains the bone's blood supplies. The boundary of an osteon is called the cement line. Osteons can be arranged into woven bone or lamellar bone. Osteoblasts make the matrix of bone which calcifies hardens. This entraps the mature bone cells, osteocytes, in a little chamber called lacunae. The osteocytes receive their nutrition from the central (Haversian) canal via little canals called canaliculi. All of these structures plus more are visible in Figure (PageIndex{4}).

Types of Bones

There are six types of bones in the human body based on their shape or location: long, short, flat, sesamoid, sutural, and irregular bones. You can see an example of each type of bone in Figure (PageIndex{5}).

  • Long bones are characterized by a shaft that is much longer than it is wide and by a rounded head at each end of the shaft. Long bones are made mostly of compact bone, with lesser amounts of spongy bone and marrow. Most bones of the limbs, including those of the fingers and toes, are long bones.
  • Short bones are roughly cube-shaped and have only a thin layer of cortical bone surrounding a spongy bone interior. The bones of the wrists and ankles are short bones.
  • Flat bones are thin and generally curved, with two parallel layers of compact bone sandwiching a layer of spongy bone. Most of the bones of the skull are flat bones, as is the sternum (breast bone).
  • Sesamoid bones are embedded in tendons, the connective tissues that bind muscles to bones. Sesamoid bones hold tendons farther away from joints so the angle of the tendons is increased, thus increasing the leverage of muscles. The patella (knee cap) is an example of a sesamoid bone.
  • Sutural bones are very small bones that are located between the major bones of the skull, within the joints (sutures) between the larger bones. They are not always present.
  • Irregular bones are those that do not fit into any of the above categories. They generally consist of thin layers of cortical bone surrounding a spongy bone interior. Their shapes are irregular and complicated. Examples of irregular bones include the vertebrae and the bones of the pelvis.

Feature: Reliable Sources

Diseased or damaged bone marrow can be replaced by donated bone marrow cells, which help treat and often cure many life-threatening conditions, including leukemia, lymphoma, sickle cell anemia, and thalassemia. If a bone marrow transplant is successful, the new bone marrow will start making healthy blood cells and improve the patient’s condition.

Learn more about bone marrow donation, and consider whether you might want to do it yourself. Find reliable sources to answer the following questions:

  1. How does one become a potential bone marrow donor?
  2. Who can and who cannot donate bone marrow?
  3. How is a bone marrow donation made?
  4. What risks are there in donating bone marrow?

Review

  1. Describe osseous tissue.
  2. Why are bones hard but not brittle?
  3. Compare and contrast the two main types of osseous tissue.
  4. What non-osseous tissues are found in bones?
  5. List four types of bone cells and their functions.
  6. Identify six types of bones, and give an example of each type.
  7. True or False. Spongy bone tissue is another name for bone marrow.
  8. True or False. Periosteum covers osseous tissue.
  9. Compare and contrast yellow bone marrow and red bone marrow.
  10. Which bone is mostly made of cortical bone tissue?

    A. Pelvis

    B. Vertebrae

    C. Femur

    D. Carpal

  11. a. Which type of bone cell divides to produce new bone cells?

    b. Where is this cell type located?

  12. Where do osteoblasts and osteocytes come from, and how are they related to each other?

  13. Which type of bone is embedded in tendons?

  14. True or False. Calcium is the only mineral in bones.

Explore More

Watch this entertaining and fast-paced Crash Course video to further explore bone structure:

Check out this video to learn more about bone remodeling:


5.4: Structure of Bone - Biology

Bones are considered organs because they contain various types of tissue, such as blood, connective tissue, nerves, and bone tissue. Osteocytes, the living cells of bone tissue, form the mineral matrix of bones. There are two types of bone tissue: compact and spongy.

Compact Bone Tissue

Compact bone (or cortical bone) forms the hard external layer of all bones and surrounds the medullary cavity, or bone marrow. It provides protection and strength to bones. Compact bone tissue consists of units called osteons or Haversian systems. Osteons are cylindrical structures that contain a mineral matrix and living osteocytes connected by canaliculi, which transport blood. They are aligned parallel to the long axis of the bone. Each osteon consists of lamellae, which are layers of compact matrix that surround a central canal called the Haversian canal. The Haversian canal (osteonic canal) contains the bone’s blood vessels and nerve fibers (Figure 1). Osteons in compact bone tissue are aligned in the same direction along lines of stress and help the bone resist bending or fracturing. Therefore, compact bone tissue is prominent in areas of bone at which stresses are applied in only a few directions.

Figure 1. Compact bone tissue consists of osteons that are aligned parallel to the long axis of the bone, and the Haversian canal that contains the bone’s blood vessels and nerve fibers. The inner layer of bones consists of spongy bone tissue. The small dark ovals in the osteon represent the living osteocytes. (credit: modification of work by NCI, NIH)

Practice Question

Which of the following statements about bone tissue is false?

  1. Compact bone tissue is made of cylindrical osteons that are aligned such that they travel the length of the bone.
  2. Haversian canals contain blood vessels only.
  3. Haversian canals contain blood vessels and nerve fibers.
  4. Spongy tissue is found on the interior of the bone, and compact bone tissue is found on the exterior.

Spongy Bone Tissue

Whereas compact bone tissue forms the outer layer of all bones, spongy bone or cancellous bone forms the inner layer of all bones. Spongy bone tissue does not contain osteons that constitute compact bone tissue. Instead, it consists of trabeculae, which are lamellae that are arranged as rods or plates. Red bone marrow is found between the trabuculae. Blood vessels within this tissue deliver nutrients to osteocytes and remove waste. The red bone marrow of the femur and the interior of other large bones, such as the ileum, forms blood cells.

Figure 2. Trabeculae in spongy bone are arranged such that one side of the bone bears tension and the other withstands compression.

Spongy bone reduces the density of bone and allows the ends of long bones to compress as the result of stresses applied to the bone. Spongy bone is prominent in areas of bones that are not heavily stressed or where stresses arrive from many directions. The epiphyses of bones, such as the neck of the femur, are subject to stress from many directions. Imagine laying a heavy framed picture flat on the floor. You could hold up one side of the picture with a toothpick if the toothpick was perpendicular to the floor and the picture. Now drill a hole and stick the toothpick into the wall to hang up the picture. In this case, the function of the toothpick is to transmit the downward pressure of the picture to the wall. The force on the picture is straight down to the floor, but the force on the toothpick is both the picture wire pulling down and the bottom of the hole in the wall pushing up. The toothpick will break off right at the wall.

The neck of the femur is horizontal like the toothpick in the wall. The weight of the body pushes it down near the joint, but the vertical diaphysis of the femur pushes it up at the other end. The neck of the femur must be strong enough to transfer the downward force of the body weight horizontally to the vertical shaft of the femur (Figure 2).


Principles of Bone Biology

Principles of Bone Biology is the essential resource for anyone involved in the study of bones. It is the most comprehensive, complete, up-to-date source of information on all aspects of bones and bone biology in one convenient source. Written and published in less than one year, it will become an indispensable resource for any scientific or medical library. This, second edition, details countless advances over the past five years, both by updating old chapters and providing additional material. It takes the reader from the basic elements of fundamental research to the most sophisticated concepts in therapeutics.

Principles of Bone Biology is the essential resource for anyone involved in the study of bones. It is the most comprehensive, complete, up-to-date source of information on all aspects of bones and bone biology in one convenient source. Written and published in less than one year, it will become an indispensable resource for any scientific or medical library. This, second edition, details countless advances over the past five years, both by updating old chapters and providing additional material. It takes the reader from the basic elements of fundamental research to the most sophisticated concepts in therapeutics.

Key Features

The most current and timely source of information about the biology and pathology of bone
Provides succinct coverage of the subject
Contributors include over 200 of the most respected researchers in the field
Extensive table of contents and index for easy reference
Easy-to-read and highly informative to both the newcomer and the initiated to the field
Spans the spectrum from molecular biology to in vivo pharmacology
Complete bibliography with each entry fully referenced for additional background reading
First edition was selected by Doody Publishing as one of the 250 Best Health Science books published in 1996

The most current and timely source of information about the biology and pathology of bone
Provides succinct coverage of the subject
Contributors include over 200 of the most respected researchers in the field
Extensive table of contents and index for easy reference
Easy-to-read and highly informative to both the newcomer and the initiated to the field
Spans the spectrum from molecular biology to in vivo pharmacology
Complete bibliography with each entry fully referenced for additional background reading
First edition was selected by Doody Publishing as one of the 250 Best Health Science books published in 1996


Bone Development

Intramembranous ossification stems from fibrous membranes in flat bones, while endochondral ossification stems from long bone cartilage.

Learning Objectives

Distinguish between intramembranous and endochondral ossification

Key Takeaways

Key Points

  • The ossification of the flat bones of the skull, the mandible, and the clavicles begins with mesenchymal cells, which then differentiate into calcium-secreting and bone matrix-secreting osteoblasts.
  • Osteoids form spongy bone around blood vessels, which is later remodeled into a thin layer of compact bone.
  • During enchondral ossification, the cartilage template in long bones is calcified dying chondrocytes provide space for the development of spongy bone and the bone marrow cavity in the interior of the long bones.
  • The periosteum, an irregular connective tissue around bones, aids in the attachment of tissues, tendons, and ligaments to the bone.
  • Until adolescence, lengthwise long bone growth occurs in secondary ossification centers at the epiphyseal plates (growth plates) near the ends of the bones.

Key Terms

  • osteoid: an organic matrix of protein and polysaccharides, secreted by osteoblasts, that becomes bone after mineralization
  • endochondral: within cartilage
  • chondrocyte: a cell that makes up the tissue of cartilage
  • diaphysis: the central shaft of any long bone

Development of Bone

Ossification, or osteogenesis, is the process of bone formation by osteoblasts. Ossification is distinct from the process of calcification whereas calcification takes place during the ossification of bones, it can also occur in other tissues. Ossification begins approximately six weeks after fertilization in an embryo. Before this time, the embryonic skeleton consists entirely of fibrous membranes and hyaline cartilage. The development of bone from fibrous membranes is called intramembranous ossification development from hyaline cartilage is called endochondral ossification. Bone growth continues until approximately age 25. Bones can grow in thickness throughout life, but after age 25, ossification functions primarily in bone remodeling and repair.

Intramembranous Ossification

Intramembranous ossification is the process of bone development from fibrous membranes. It is involved in the formation of the flat bones of the skull, the mandible, and the clavicles. Ossification begins as mesenchymal cells form a template of the future bone. They then differentiate into osteoblasts at the ossification center. Osteoblasts secrete the extracellular matrix and deposit calcium, which hardens the matrix. The non-mineralized portion of the bone or osteoid continues to form around blood vessels, forming spongy bone. Connective tissue in the matrix differentiates into red bone marrow in the fetus. The spongy bone is remodeled into a thin layer of compact bone on the surface of the spongy bone.

Endochondral Ossification

Endochondral ossification is the process of bone development from hyaline cartilage. All of the bones of the body, except for the flat bones of the skull, mandible, and clavicles, are formed through endochondral ossification.

Process of endochondral ossification: Endochondral ossification is the process of bone development from hyaline cartilage. The periosteum is the connective tissue on the outside of bone that acts as the interface between bone, blood vessels, tendons, and ligaments.

In long bones, chondrocytes form a template of the hyaline cartilage diaphysis. Responding to complex developmental signals, the matrix begins to calcify. This calcification prevents diffusion of nutrients into the matrix, resulting in chondrocytes dying and the opening up of cavities in the diaphysis cartilage. Blood vessels invade the cavities, while osteoblasts and osteoclasts modify the calcified cartilage matrix into spongy bone. Osteoclasts then break down some of the spongy bone to create a marrow, or medullary cavity, in the center of the diaphysis. Dense, irregular connective tissue forms a sheath (periosteum) around the bones. The periosteum assists in attaching the bone to surrounding tissues, tendons, and ligaments. The bone continues to grow and elongate as the cartilage cells at the epiphyses divide.

In the last stage of prenatal bone development, the centers of the epiphyses begin to calcify. Secondary ossification centers form in the epiphyses as blood vessels and osteoblasts enter these areas and convert hyaline cartilage into spongy bone. Until adolescence, hyaline cartilage persists at the epiphyseal plate (growth plate), which is the region between the diaphysis and epiphysis that is responsible for the lengthwise growth of long bones.


Localization and function

Annexins are generally cytosolic proteins, with pools of both a soluble form and a form stably or reversibly associated with components of the cytoskeleton or proteins that mediate interactions between the cell and the extracellular matrix (matricellular proteins). Some, such as annexins A11 and A2, have been found in the nucleus under particular circumstances [25, 26]. In certain instances, annexins may be expressed at the cell surface, despite the absence of any secretory signal peptide for example, annexin A1 translocates from the cytosol to the cell surface following exposure of cells to glucocorticoids [27], and annexin A2 is constitutively expressed at the surface of vascular endothelial cells where it functions in the regulation of blood clotting [28]. The expression level and tissue distribution of annexins span a broad range, from abundant and ubiquitous (annexins A1, A2, A4, A5, A6, A7, A11) to selective (such as annexin A3 in neutrophils and annexin A8 in the placenta and skin) or restrictive (such as annexin A9 in the tongue, annexin A10 in the stomach and annexin A13 in the small intestine).

The presence of multiple annexins in all higher eukaryotic cell types suggests fundamental roles in cell biology [5], even though prokaryotes and yeasts appear to tolerate their absence, but the apparent functional diversity within the family remains perplexing. The development of knockout mice has provided insight into the functions of annexins A1, A2, A5, A6 and A7. Loss of ANXA1 leads to changes in the inflammatory response and the effects of glucocorticoids [29], whereas the ANXA2 knockout mouse has defects in neovascularization and fibrin homeostasis [30]. The ANXA5 and ANXA6 knockout mice have subtler phenotypes and need further investigation [31, 32], and two independently derived ANXA7 null mutant mouse strains are either embryonic lethal [33] or show changes in calcium homeostasis [34]. The diversity of phenotype in the annexin knockout mice is consistent with these proteins having largely independent functions. Roles for annexins that have been established from studies using cultured cells are not always reflected in phenotypic abnormalities in the corresponding knockout mice, suggesting that functional redundancy may, in some instances, obscure the full range of functions of these multifunctional proteins. In mice that lack an overt phenotype, there is now the opportunity to test molecular theories of annexin function, such as the proposed calcium channel activity of annexin A5.


Formation, structure, and function of extra-skeletal bones in mammals

This review describes the formation, structure, and function of bony compartments in antlers, horns, ossicones, osteoderm and the os penis/os clitoris (collectively referred to herein as AHOOO structures) in extant mammals. AHOOOs are extra-skeletal bones that originate from subcutaneous (dermal) tissues in a wide variety of mammals, and this review elaborates on the co-development of the bone and skin in these structures. During foetal stages, primordial cells for the bony compartments arise in subcutaneous tissues. The epithelial–mesenchymal transition is assumed to play a key role in the differentiation of bone, cartilage, skin and other tissues in AHOOO structures. AHOOO ossification takes place after skeletal bone formation, and may depend on sexual maturity. Skin keratinization occurs in tandem with ossification and may be under the control of androgens. Both endochondral and intramembranous ossification participate in bony compartment formation. There is variation in gradients of density in different AHOOO structures. These gradients, which vary according to function and species, primarily reduce mechanical stress. Anchorage of AHOOOs to their surrounding tissues fortifies these structures and is accomplished by bone–bone fusion and Sharpey fibres. The presence of the integument is essential for the protection and function of the bony compartments. Three major functions can be attributed to AHOOOs: mechanical, visual, and thermoregulatory. This review provides the first extensive comparative description of the skeletal and integumentary systems of AHOOOs in a variety of mammals.

Fig. S1. The skull of a mature male sika deer (Cervus nippon).

Fig. S2. The skull of a mature female sika deer (Cervus nippon).

Fig. S3. Developing antlers with velvet on the surface in a mature male Persian fallow deer (Dama mesopotamica).

Fig. S4. Ossicones in the giraffe (Giraffa camelopardalis).

Fig. S5. The ossicones of a mature male okapi (Okapia johnstoni).

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.


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Chinsamy-Turan has provided an immense service to the field with the publication of this book.

-- Kristina Curry Rogers ― Trends in Ecology and Evolution

Of interest to a wide audience of biologists, the core readership [is] vertebrate paleontologists, each of whom should have a copy.

-- Tim J. Fedak and Brian K. Hall ― Quarterly Review of Biology

A must-read for anybody interested in the biology of one of the most fascinating animals in the history of our planet.

-- Luis M. Chiappe ― Nature

An irreplaceable manual for all students working in this field.

-- Magdalena Borsuk-Bialynicka ― Acta Palaeontologica Polonica

Chinsamy-Turan's accessible, engaging book contains enough personal reflections and professional opinions to keep readers enthralled.

-- James R. Spotila ― Bioscience

A valuable addition to the library of anyone who thirsts for every bit of knowledge available about these Mesozoic saurians.

-- Lynne M. Clos ― Fossil News: Journal of Avocational Paleontology

Provides a compelling, if not universal, view of dinosaur physiology that is certain to attract serious consideration and attention.

-- Matthew F. Bonnan ― Journal of Vertebrate Paleontology

Particularly strong on describing what bone is, how it is studied microscopically, and what it is capable to telling us.

-- Kevin Padian ― Progressive Palaeontology

At last! An entire book devoted to one of the most recently developed and hottest techniques for the study of dinosaurs and other ancient animals. The author has devoted her career to the study of the histology of fossil bone. She comprehensively surveys a body of literature that begins more than a century ago but is up-to-the-minute as well. She skillfully introduces the student to the basics of the subject but also presses toward the limit of what the technique can tell us about the fascinating topics of growth and physiology of extinct animals. She describes the work of others with fairness but leaves no doubt as to her opinions about the shortcomings of widely cited studies. She writes with clarity and vigor and has presented a book that will be widely read by paleontologists of all levels and leanings.

-- Peter Dodson, University of Pennsylvania

Book Description

"A must-read for anybody interested in the biology of one of the most fascinating animals in the history of our planet."―Luis M. Chiappe, Nature


Apoptosis

The mature bone is always remodeling: the old bone is resorbed and replaced with new bone. A team of osteoblasts and osteoclasts move along the bone, dissolving and rebuilding. What happens to the cells when they have finished rebuilding an area of bone? The osteoclasts and most of the osteoblasts undergo a process called apoptosis, or cell suicide. They are not killed. There is no lack of oxygen or nutrients. There are no toxic materials. Instead, there are genes in the cell which can be activated, causing the cell to disintegrate. These genes (of course) are carefully regulated within the cell. The factors that regulate apoptosis are currently under investigation. Some are related to estrogens, or to interleukins. Medications which could modify apoptosis have the potential for treating or preventing osteoporosis.


Skeletons & Bones Science Lesson

Have you ever seen a house or a building while it is being built? If so, you may have noticed long wooden or steel beams being constructed before the outside walls are added.

These beams make up the framework of the building, very much like the way that your bones form your skeleton.

Both frames provide shape, strength, and protection – your bones for your body and the beams for the building. However, unlike the framework in a house, bones are alive!

Your bones will continue to grow inside your body until you are around 25 years old!

Bones can also repair themselves. Small cracks form in bones all the time from bumping into objects and doing strenuous activities like running and jumping.

But these cracks are rarely noticed by us because they are repaired quickly by special bone cells called osteoclasts (say OS-TEE-O-CLASTS) and osteoblasts (say OS-TEE-O-BLASTS).

These cells also repair major breaks in the bone. A doctor may need to help set the broken bone in place, but the bone will usually heal itself in about 6-8 weeks.

Bones are very strong, but are also amazingly lightweight!

Bones are wrapped in a thin covering called the periosteum (say PER-EE-OS-TEE-UM). The periosteum supplies nutrients to the bones to keep them strong and healthy. Beneath this is a hard layer called compact bone. It provides most of the strength for the bone.

Inside the bone is a “spongy” material. It has lots of holes and gaps in it to make your bones lightweight and also allow for the production of red blood cells.

Based on their shape, bones can be classified as long, short, flat, or irregular.

(FYI: bone fossils give us clues about animals that may have lived long ago.)

Long bones are easy to spot because they are longer than they are wide. Finger bones, arm bones, and leg bones are all good examples of long bones.

Short bones tend to look like a cube. The bones in your wrists and ankles are short bones.

Flat bones are thin and look flattened. Examples include the sternum (the bone down the middle of your chest that your ribs are connected to), shoulder blades, and the pelvic (hip) bones. Irregular bones have weird shapes and can be found all over the body. The bones in the spinal column are irregularly shaped.

Since bones cannot bend without breaking, something else is needed to allow your body to move – joints.

A joint is where two or more bones meet and allows movement between those bones. How much movement can occur depends on the type of joint. Here are some different joints that exist in your body:

  • Hinge joint: To demonstrate a hinge joint, open a door and then close it. Notice where the door is attached to the wall and the movement is occurring. This is called a hinge and is very similar to how the joints in your fingers move (not the joints attaching your fingers to your palm though). Bend your fingers. Notice how the knuckles only allow the sections of your fingers to move inward towards your palm – not side-to-side or backwards. Your knees are another example of hinge joints.
  • Saddle joint: This joint works like a hinge joint but has slightly more flexibility. A prime example of a saddle joint is where your thumb meets your palm. It can move forward and backward and side to side, allowing you to grasp objects between your thumb and fingers.
  • Pivot joint: This joint allows rotating movement. The two bones in your forearm connected to your elbow form a pivot joint. To see how this works, open a door using a door knob. Notice how not just your hand, but the whole lower part of your arm rotates to twist the knob.
  • Ball and socket joint: To demonstrate how this joint works, make a fist with one hand, and then cover it with the other. Notice how the fist can move freely in a full circle. A ball and socket joint works the same way – it allows the part that fits into the joint to move without restraint. Ball and socket joints are in your shoulders and your hips and have the most flexibility of any type of joint. On a side note, most animals that walk on four legs, like dogs and cats, don’t have shoulders with ball and socket joints. This is because the flexibility of ball and socket joints makes the shoulder and arm bones less stable. These animals have shoulder joints that are more similar to hinge joints to increase their stability and allow them to run very fast on all four legs.

Congenital diseases

Certain congenital and developmental bone diseases occur in the dog. Examples include the following:

Numerous other developmental abnormalities of joints may affect young dogs, such as aseptic necrosis of the head of the femur, dislocation of the knee cap (patella), and elbow dysplasia.

Osteomyelitis

Osteomyelitis is an inflammation of bone that is usually caused by a bacterial infection. Infections of the bone may also arise with certain fungal infections and in the presence of bone implants, such as bone plates and pins.

Nutritional disorders

Trauma. Trauma to bones is perhaps the most common skeletal disorder encountered in the dogs, especially dogs allowed to roam free. Dogs that are injured through falls, automobile accidents or fights can experience a variety of bony fractures and dislocations.


Watch the video: Introduction to Bone Biology (January 2022).