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6.3: Bone Structure

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  • Learning Objectives

    • Identify the anatomical features of a bone
    • Define and list examples of bone markings
    • Describe the histology of bone tissue
    • Compare and contrast compact and spongy bone
    • Identify the structures that compose compact and spongy bone
    • Describe how bones are nourished and innervated


    Gross Anatomy of Bone

    The structure of a long bone allows for the best visualization of all of the parts of a bone (Figure \(\PageIndex{1}\)). A long bone has two parts: the diaphysis and the epiphysis. The diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone. The hollow region in the diaphysis is called the medullary cavity, which is filled with yellow marrow. The walls of the diaphysis are composed of dense and hard compact bone.

    Figure \(\PageIndex{1}\): Anatomy of a Long Bone.A typical long bone shows the gross anatomical characteristics of bone.


    The medullary cavity has a delicate membranous lining called the endosteum (end- = “inside”; oste- = “bone”), where bone growth, repair, and remodeling occur. The outer surface of the bone is covered with a fibrous membrane called the periosteum (peri- = “around” or “surrounding”). The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone. Tendons and ligaments also attach to bones at the periosteum. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints (Figure \(\PageIndex{2}\)). In this region, the epiphyses are covered with articular cartilage, a thin layer of cartilage that reduces friction and acts as a shock absorber.

    Figure \(\PageIndex{2}\): Periosteum and Endosteum.The periosteum forms the outer surface of bone, and the endosteum lines the medullary cavity.

    Flat bones, like those of the cranium, consist of a layer of diploë (spongy bone), lined on either side by a layer of compact bone (Figure \(\Pageindex{3}\)). The two layers of compact bone and the interior spongy bone work together to protect the internal organs. If the outer layer of a cranial bone fractures, the brain is still protected by the intact inner layer.

    Figure \(\PageIndex{3}\): Anatomy of a Flat Bone.This cross-section of a flat bone shows the spongy bone (diploë) lined on either side by a layer of compact bone.

    Bone Markings


    Table \(\PageIndex{1}\)

    Bone Markings
    Marking Description Example
    Articulations Where two bones meet Knee joint
    Head Prominent rounded surface Head of femur
    Facet Flat surface Vertebrae
    Condyle Rounded surface Occipital condyles
    Projections Raised markings Spinous process of the vertebrae
    Protuberance Protruding Chin
    Process Prominence feature Transverse process of vertebra
    Spine Sharp process Ischial spine
    Tubercle Small, rounded process Tubercle of humerus
    Tuberosity Rough surface Deltoid tuberosity
    Line Slight, elongated ridge Temporal lines of the parietal bones
    Crest Ridge Iliac crest
    Fossa Elongated basin Mandibular fossa
    Fovea Small pit Fovea capitis on the head of the femur
    Sulcus Groove Sigmoid sulcus of the temporal bones
    Canal Passage in bone Auditory canal
    Fissure Slit through bone Auricular fissure
    Foramen Hole through bone Foramen magnum in the occipital bone
    Meatus Opening into canal External auditory meatus
    Sinus Air-filled space in bone Nasal sinus
    Figure \(\PageIndex{4}\): Bone Features.The surface features of bones depend on their function, location, attachment of ligaments and tendons, or the penetration of blood vessels and nerves.

    Bone Cells and Tissue


    Although bone cells compose a small amount of the bone volume, they are crucial to the function of bones. Four types of cells are found within bone tissue: osteoblasts, osteocytes, osteogenic cells, and osteoclasts (Figure \(\PageIndex{5}\)).

    Figure \(\PageIndex{5}\): Bone Cells.Four types of cells are found within bone tissue. Osteogenic cells are undifferentiated and develop into osteoblasts. When osteoblasts get trapped within the calcified matrix, their structure and function changes, and they become osteocytes. Osteoclasts develop from monocytes and macrophages and differ in appearance from other bone cells.




    Table \(\PageIndex{2}\)

    Bone Cells
    Cell type Function Location
    Osteoblasts Bone formation Growing portions of bone, including periosteum and endosteum
    Osteocytes Maintain mineral concentration of matrix Entrapped in matrix

    Compact and Spongy Bone


    Compact Bone

    Compact bone is the denser, stronger of the two types of bone tissue (Figure \(\PageIndex{6}\)). It can be found under the periosteum and in the diaphyses of long bones, where it provides support and protection.




    Spongy (Cancellous) Bone


    Figure \(\PageIndex{7}\): Diagram of Spongy Bone.Spongy bone is composed of trabeculae that contain the osteocytes. Red marrow fills the spaces in some bones.

    Skeletal System: Paget’s Disease


    While some people with Paget’s disease have no symptoms, others experience pain, bone fractures, and bone deformities (Figure \(\PageIndex{8}\)). Bones of the pelvis, skull, spine, and legs are the most commonly affected. When occurring in the skull, Paget’s disease can cause headaches and hearing loss.

    Figure \(\PageIndex{8}\): Paget's Disease.Normal leg bones are relatively straight, but those affected by Paget’s disease are porous and curved.




    Blood and Nerve Supply

    The spongy bone and medullary cavity receive nourishment from arteries that pass through the compact bone. The arteries enter through the nutrient foramen (plural = foramina), small openings in the diaphysis (Figure \(\PageIndex{9}\)). The osteocytes in spongy bone are nourished by blood vessels of the periosteum that penetrate spongy bone and blood that circulates in the marrow cavities. As the blood passes through the marrow cavities, it is collected by veins, which then pass out of the bone through the foramina.


    Figure \(\PageIndex{9}\): Diagram of Blood and Nerve Supply to Bone.Blood vessels and nerves enter the bone through the nutrient foramen.

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    Watch this video to see the microscope features of a bone.

    Chapter Review

    A hollow medullary cavity filled with yellow marrow runs the length of the diaphysis of a long bone. The walls of the diaphysis are compact bone. The epiphyses, which are wider sections at each end of a long bone, are filled with spongy bone and red marrow. The epiphyseal plate, a layer of hyaline cartilage, is replaced by osseous tissue as the organ grows in length. The medullary cavity has a delicate membranous lining called the endosteum. The outer surface of bone, except in regions covered with articular cartilage, is covered with a fibrous membrane called the periosteum. Flat bones consist of two layers of compact bone surrounding a layer of spongy bone. Bone markings depend on the function and location of bones. Articulations are places where two bones meet. Projections stick out from the surface of the bone and provide attachment points for tendons and ligaments. Holes are openings or depressions in the bones.

    Bone matrix consists of collagen fibers and organic ground substance, primarily hydroxyapatite formed from calcium salts. Osteogenic cells develop into osteoblasts. Osteoblasts are cells that make new bone. They become osteocytes, the cells of mature bone, when they get trapped in the matrix. Osteoclasts engage in bone resorption. Compact bone is dense and composed of osteons, while spongy bone is less dense and made up of trabeculae. Blood vessels and nerves enter the bone through the nutrient foramina to nourish and innervate bones.

    Review Questions

    Q. Which of the following occurs in the spongy bone of the epiphysis?

    A. bone growth

    B. bone remodeling

    C. hematopoiesis

    D. shock absorption

    Answer: C

    Q. The diaphysis contains ________.

    A. the metaphysis

    B. fat stores

    C. spongy bone

    D. compact bone

    Answer: B

    Q. The fibrous membrane covering the outer surface of the bone is the ________.

    A. periosteum

    B. epiphysis

    C. endosteum

    D. diaphysis

    Answer: A

    Q. Which of the following are incapable of undergoing mitosis?

    A. osteoblasts and osteoclasts

    B. osteocytes and osteoclasts

    C. osteoblasts and osteocytes

    D. osteogenic cells and osteoclasts

    Answer: C

    Q. Which cells do not originate from osteogenic cells?

    A. osteoblasts

    B. osteoclasts

    C. osteocytes

    D. osteoprogenitor cells

    Answer: D

    Q. Which of the following are found in compact bone and cancellous bone?

    A. Haversian systems

    B. Haversian canals

    C. lamellae

    D. lacunae

    Answer: C

    Q. Which of the following are only found in cancellous bone?

    A. canaliculi

    B. Volkmann’s canals

    C. trabeculae

    D. calcium salts

    Answer: C

    Q. The area of a bone where the nutrient foramen passes forms what kind of bone marking?

    A. a hole

    B. a facet

    C. a canal

    D. a fissure

    Answer: A

    Critical Thinking Questions

    Q. If the articular cartilage at the end of one of your long bones were to degenerate, what symptoms do you think you would experience? Why?

    A. If the articular cartilage at the end of one of your long bones were to deteriorate, which is actually what happens in osteoarthritis, you would experience joint pain at the end of that bone and limitation of motion at that joint because there would be no cartilage to reduce friction between adjacent bones and there would be no cartilage to act as a shock absorber.

    Q. In what ways is the structural makeup of compact and spongy bone well suited to their respective functions?

    A. The densely packed concentric rings of matrix in compact bone are ideal for resisting compressive forces, which is the function of compact bone. The open spaces of the trabeculated network of spongy bone allow spongy bone to support shifts in weight distribution, which is the function of spongy bone.


    articular cartilage
    thin layer of cartilage covering an epiphysis; reduces friction and acts as a shock absorber
    where two bone surfaces meet
    (singular = canaliculus) channels within the bone matrix that house one of an osteocyte’s many cytoplasmic extensions that it uses to communicate and receive nutrients
    central canal
    longitudinal channel in the center of each osteon; contains blood vessels, nerves, and lymphatic vessels; also known as the Haversian canal
    compact bone
    dense osseous tissue that can withstand compressive forces
    tubular shaft that runs between the proximal and distal ends of a long bone
    layer of spongy bone, that is sandwiched between two the layers of compact bone found in flat bones
    delicate membranous lining of a bone’s medullary cavity
    epiphyseal plate
    (also, growth plate) sheet of hyaline cartilage in the metaphysis of an immature bone; replaced by bone tissue as the organ grows in length
    wide section at each end of a long bone; filled with spongy bone and red marrow
    opening or depression in a bone
    (singular = lacuna) spaces in a bone that house an osteocyte
    medullary cavity
    hollow region of the diaphysis; filled with yellow marrow
    nutrient foramen
    small opening in the middle of the external surface of the diaphysis, through which an artery enters the bone to provide nourishment
    cell responsible for forming new bone
    cell responsible for resorbing bone
    primary cell in mature bone; responsible for maintaining the matrix
    osteogenic cell
    undifferentiated cell with high mitotic activity; the only bone cells that divide; they differentiate and develop into osteoblasts
    (also, Haversian system) basic structural unit of compact bone; made of concentric layers of calcified matrix
    perforating canal
    (also, Volkmann’s canal) channel that branches off from the central canal and houses vessels and nerves that extend to the periosteum and endosteum
    fibrous membrane covering the outer surface of bone and continuous with ligaments
    bone markings where part of the surface sticks out above the rest of the surface, where tendons and ligaments attach
    spongy bone
    (also, cancellous bone) trabeculated osseous tissue that supports shifts in weight distribution
    (singular = trabecula) spikes or sections of the lattice-like matrix in spongy bone

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