Systems Biology
Bones are composed of a mixture of organic and inorganic materials, specifically, a collagen protein matrix and a mineral portion of inorganic hydroxyapatite crystals. These materials organize into osteons, consisting of rings of lamellae surrounding a central Haversian canal. Volkmann's canals connect adjacent osteons, while lacunae between the lamellae house mature osteocytes interconnected by canaliculi. Bones generally consist of an outer compact bone layer with spongy bone inside. Long bones have an elongated diaphysis full of marrow, and a spongy bone-filled epiphysis at either end. The metaphysis lies between them, with the epiphyseal plate enabling growth during childhood.
Other important components include tendons, which attach muscle to bone, and ligaments, connecting bone to bone to form joints. Joints can be moveable or immovable depending on their function. Cartilage comes in three varieties: hyaline, fibrous, and elastic. Hyaline cartilage, the most prevalent type, covers the ends of joints providing cushioning. Fibrous cartilage is rigid, while elastic cartilage is flexible and can be found in structures like the ears and epiglottis.
Lesson Outline
<ul> <li>Bone Structure and Composition</li> <ul> <li>Chemical composition of bone</li> <ul> <li>About one third is organic material (mainly proteins)</li> <li>Two thirds is inorganic material (such as hydroxyapatite crystals and water)</li> </ul> <li>Microscopic features of bones</li> <ul> <li>Osteons (structural unit of bone)</li> <ul> <li>Rings of bony matrix called lamellae</li> <li>Haversian canals (central canals) contain blood vessels, lymph vessels, and nerves</li> <li>Volkmann's canals (transverse canals) connect adjacent osteons</li> </ul> <li>Lacunae</li> <ul> <li>Small spaces between lamellae</li> <li>House mature bone cells (osteocytes)</li> </ul> <li>Canaliculi</li> <ul> <li>Small canals that transport nutrients and waste</li> <li>Connect osteocytes to Haversian and Volkmann's canals</li> </ul> </ul> <li>Macroscopic features of bones</li> <ul> <li>Two types of osseous tissue: compact bone and spongy bone</li> <ul> <li>Compact (cortical) bone</li> <ul> <li>Strong and rigid, found on the outsides of bones</li> <li>Comprised of osteons</li> </ul> <li>Spongy (trabecular or cancellous) bone</li> <ul> <li>Porous and found in inner parts of bones</li> <li>Bone matrix forms spongy trabeculae filled with bone marrow</li> <li>Good for shock absorption</li> </ul> </ul> <li>Long bones</li> <ul> <li>Has diaphysis (elongated shaft) and epiphysis (end of the bone)</li> <li>Metaphysis is the transitional area between epiphysis and diaphysis</li> <li>Epiphyseal plate or growth plate allows for longitudinal growth of the bone</li> </ul> </ul> <li>Connective tissues related to bones</li> <ul> <li>Tendons attach muscle to bone</li> <li>Ligaments connect bone to bone, forming joints</li> <li>Joints can be movable or immovable</li> </ul> <li>Cartilage</li> <ul> <li>Flexible and lacks blood supply or nerves</li> <li>Three types: hyaline, fibrous, and elastic</li> <ul> <li>Hyaline cartilage: most prevalent, covers joints and involved in endochondral ossification</li> <li>Fibrous cartilage: rigid, forms structures like intervertebral discs</li> <li>Elastic cartilage: flexible, forms structures like ears and epiglottis</li> </ul> </ul> </ul> </ul>
Don't stop here!
Get access to 71 more Systems Biology lessons & 8 more full MCAT courses with one subscription!
FAQs
Compact bone, also known as cortical bone, is dense and solid, forming the outer layer of bones. It provides support and strength to the bone. Spongy bone, or trabecular bone, is less dense and has a porous, honeycomb-like structure. It is found inside the ends of long bones and in the inner layer of flat bones, such as the skull. Spongy bone is lighter and helps with shock absorption.
Collagen is a protein that makes up about 30% of bone composition and provides the bone with its tensile strength and flexibility. Hydroxyapatite crystals, on the other hand, are mineralized inorganic compounds that contribute to the hardness and rigidity of the bone. They make up about 65-70% of the bone matrix. Together, collagen and hydroxyapatite crystals provide bone with its unique combination of strength and flexibility, which is essential for supporting the body and withstanding various types of physical stress.
Osteons, also known as Haversian systems, are the basic structural units of compact bone. Each osteon contains a central Haversian canal, which is surrounded by concentric layers of bone matrix called lamellae. Osteons are aligned parallel to the long axis of the bone for optimal support and strength. They also contain small spaces, called lacunae, that house bone cells called osteocytes. Osteons are essential in the rebuilding and remodeling processes of bones and play a vital role in bone support and strength.
Haversian canals, located in the center of each osteon, are responsible for providing blood supply, nutrients, and nerve connections to the bone cells. These canals run vertically through the bone and are interconnected by transverse channels called Volkmann's canals. Volkmann's canals also connect the Haversian canals to the periosteum (the outer bone membrane) and the endosteum (the inner bone membrane). Together, Haversian and Volkmann's canals form a vascular network in compact bone, which is essential for bone health and maintenance.
Lacunae are small spaces within the bone matrix that house osteocytes, the mature bone cells responsible for maintaining bone tissue. Canaliculi are microscopic channels connecting adjacent lacunae, allowing the osteocytes to communicate and exchange nutrients and metabolic waste products. This arrangement allows for efficient nutrient delivery and waste removal, as well as the transmission of mechanical signals throughout the bone, which is crucial for overall bone health and maintenance.
MCAT® is a registered trademark of the Association of American Medical Colleges. The United States Medical Licensing Examination (USMLE®) is a joint program of the Federation of State Medical Boards (FSMB®) and National Board of Medical Examiners (NBME®). NAPLEX® is a registered trademark of the National Association of Boards of Pharmacy. PANCE© is a registered trademark of the National Commission on Certification of Physician Assistants. NCLEX® is a registered trademark and service mark of the National Council of State Boards of Nursing, Inc. None of the trademark holders are endorsed by nor affiliated with Sketchy or this website.
