Chapter 12 Flashcards
Bones are
Rigid mineralized structure that help perform five major roles in the body
The 5 major roles bones help perform in the body
Support
Protection
Movement
Mineral storage
Hematopoiesis
Bones are often called ——
There are —— bones in the humans body
- bones are often called Osseous tissue
- 80 axial, 126 appendicular (206)
The five shape categories of bones
Long bones
Short bones
Flat bones
Irregular bones
Sesamoid bones
Diaphysis
Main shaft-like portion, hollow, cylindrical and thick with compact bone
Epiphyses
At distal and proximal ends of the bone that provide points of muscle attachments and stability to joints
Articulate cartilage
Thin layer of hyaline cartilage
Periosteum
Dense, white fibrous membrane that covers bone (except joint surfaces)
Medullary cavity
“Marrow cavity”
Endosteum
Thin, fibrous membrane that covers the medullary cavity
Compact bone
External table: compact bone around the external (distal) cortex
Internal table: compact bone around the internal (proximal) cortex
Diploe: the region between the external and internal tables, which is composed of cancellous bone
Bones differ in?
Both size and shape
They also differ in the amount and proportion of two main types of bone:
Cortical (cortex-> outside) - dense and solid bone, primarily around the edge (outer layer) of bone structures
Cancellous - “spongy born”/ “trabecular bone”
- a network of thin branched crossbeams, which provide structural support of bone structures, primarily found in the center
Compact bone constitutes about —— of the total bone mass in adult bones
- compact bone constituents about 80% of total bone mass in adults
- cylinder-shaped structural units “Haversian systems”
- Each osteon surround a Central Canal: delivers nutrient and removes wastes from the metabolically active, but imprisoned, bone cells
Structures of the osteon:
Lamellae:
Concentric lamellae: cylinder-shaped layers of calcified matrix in the osteon
Interstitial lamellae: layers of calcified matrix between osteons
Circumferential lamellae: lamellae that run along the inner circumference and outer circumference of a bone
Structures of the osteon
Lacunae: smalls spaces in bone matrix that contain tissue fluid and bone cells
Canaliculi: ultra-small canals that radiate in all directions from the lacunae and connect them to teach other and to the central canal
Central Canal: “Osteonal canal”/ “Haversian canal” - lined with endosteum and contains blood vessels,, lymphatic vessels and nerves
Bones are held together by and critical for what
Bones are held together by ligaments
Critical structures for support, movements and maintaining homeostasis
Bone to bone
Bone to muscle
Bone to bone = ligaments (Sprains)
Bone to muscle - tendons (strains)
The three bone cells
Osteoblast:
- “Bone-building” cells -> synthesize and secrete an organic matrix called osteoid
- collagen strands in the osteoid serve as a framework for the formation of hydroxyapatite crystals, which mineralizes the bone tissue
Osteoclast:
- “Bone-destroying” / “Bone-reabsorbing” cells
- Giant multinucleate cells which are responsible for the active erosion of bone minerals (hydrochloric acid (HCL) and collagenase)
Osteocyte:
- “mature cells”
- mature no dividing osteoblasts that have become surrounded by matrix and now lie within Lacunae
Cancellous bone consists of?
Cancellous bone consists of about 20% of total bone mass
- They contain no osteons but instead consist of crisscrossing bony branches called trabeculae (“trabecular bone”)
Fractal -> cancellous bone
They appear random, but they are more complex in orientation
Trabeculae are actually arranged along liens of ——
Arranged along lines of stress
- their size and orientation will there differs between individual bones according to the nature and magnitude of the applied load
- the direction of stresses created by the weight of the body
Wolff’s law
- developed from the German Anatomist and surgeon Julius Wolff
- “bone in a healthy person or animal will adapt to the loads under which it is placed”
Wolff’s law -> loading
- if loading on a particular bone increases, the bone will removal itself over time to become stronger to resist the sort of loading
- inversely, if the loading on a bone decreases, the bone will become less dense and weaker due to the lack of the stimulus to continued remodeling.
- osteopenia & osteoporosis
Myeloid tissue
Type of soft, diffuse connective tissues, often called bone marrow
Two types of myeloid tissue
Red bone marrow: prominent in children and infants -> responsible for the production of red blood cells (RBCs)
Yellow bone marrow: prominent in older adults -> is a regular of hematopoietic stem cells being replaced with adipocytes
Chondrocyte
- product the tough, rubbery ground substance of cartilage
- found in the lacuna ,similar to osteocytes
Perichondrium
A connective tissue membrane that surrounds the cartilage mass
Hyaline cartilage tissue
- hyalos = glass
- the most prevalent type of cartilage
- found in support rings of the respiratory tract and covering the ends of bones
Fibrocartilage tissue
- strongest and most durable type of cartilage
- matrix is rigid and filled with a dense packing of strong white collagen fibers
- found in intervertebral disks and in the knee joint (menisci)
Elastic cartilage joint
- contains few collagen fibers but large number of very fine elastic fibers
- providing flexibility
- found in the ear and larynx
Articulation:
- a point of contact between the bones “joints”
- joints may be classified into three major categories by using either structural of functional schemes
Structural
- according to the type of connective tissue
- fibrous
- cartilaginous
- synovial
Functional
- according to the degree of movement they permit
- synarthroses
- amphiarthroses
- diathroses
Fibrous joints (synarthroses)
- held together by fibrous connective tissue (type and amount will vary based on their articulation)
- joints are immovable
- the three subtypes: syndesmoses, sutures, gomphoses
Amphiarthroses
- joints that are articulated through either hyaline cartilage or fibrocartilage
- offer limited movement, in certain circumstances
- the two subtypes: synchondroses, symphyses
Diarthroses
- the body’s most mobile, numerous and anatomically complex joints (freely movable joints)
- the three main groups: uniaxial (hinge and pivot), biaxial (saddle and condyloid), multiracial (ball-and-socket, gliding)
Diarthroses -> uniaxial
- synovial joints that permit movement around only one axis and in only one plane
- hinge joints: those in which the articulating ends of the boned form a hinge-shaped unit (only back and forth movements); flexion and extension
- Pivot joints: those in which a projection of one bone articulates with a ring or notch or another bone
Diarthroses -> biaxial
- synovial joints that permit movement around two perpendicular axes in two perpendicular planes
- Saddle joint: those in which the articulating ends of the bone resemble reciprocally shaped miniature saddles (allows joints to swing in an arch)
- condyloid joints: ellipsoidal joints, those in which a condyle fits into an elliptical socket
Diathroses -> multiaxial
- synovial joints that permit movements around three or more axes and in three or more planes
- Ball-in-socket joints: a ball-shaped head of one bones fits into a concave depression on another, thereby allowing the first bone to move in many directions
- Gliding joints: characterized by relatively flat articulating surfaces that allow limited gliding movements along various axes.
Diarthroses seven structures
Joint capsule: sleeve-like extension of the periosteum of each articulating bone
Synovial membrane: moist, slippery membrane that lines the inner surface of the joint capsule
Articular cartilage: thin layer of hyaline cartilage covering and cushioning the articular surfaces of bones
Joint cavity: small space between articulating surfaces of the bones of the joint
Menisci (articular disk): pads of fibrocartilage located between the articulating ends of the bones in some Diarthroses
Ligament: strong cords of dense, white fibrous tissue
Bursae: a closed pillow-like structure, which consists of a synovial membrane filled with synovial fluid
Ligaments
Attach bone to bone in a synovial joint (ACL -> anterior cruciate ligament in the knee)
Tendons
Attach muscle to bone (Achilles tendon)
Both tendons and ligaments are what
Composed of tough connective tissue containing collagen (strong, flexible)
- muscles further stabilize joints
Osteogenesis
- the forming of new bone
Endochondral ossification
- “bone formation in cartilage”
Intramembranous ossification
- bones formed within fibrous membrane
- occurs within the flat bones
Bone development in the embryo
- Early fetal development: cartilage model forms (formed by chondroblasts)
- later fetal development: osteoblasts replace cartilage with bone
- childhood: primary and secondary ossification sites formed
- adolescence: elongation at growth plates
Hormone regulation
- preadolescence: growth hormone stimulates bone lengthening
- early adolescence: estrogen and testosterone stimulate bone lengthening
- late adolescence: estrogen and testosterone cause replacement of cartilage growth plates with bone
Intramembranous ossification
- occurs within connective tissue membrane
- Osteogenic stem cells -> osteoblasts
Ossification centers:
- clusters of differentiated osteoblasts
- secreting matrix material and collagenous fibers
- bones develop sheets fibrous connective tissue
Endochondral ossification
- occurs within cartilage, with bone formation spreading from end to end
- cartilage develops periosteum
- bones is deposited by osteoblast, which differentiate from stem cells on the inner surface of the periosteum
- primary ossification center: develops when blood vessels enter the rapidly changing cartilage model at the midpoint of the diaphysis
- secondary ossification center: develops in the epiphysis
Bone remodeling
- bone is constantly being broken down and reformed
- as much as 18% of bone is recycled each year
- this remodeling is regulated by hormones:
- parathyroid hormone:
- PTH secretion increases when blood levels of Ca++ fall; stimulates osteoclasts to secrete more bone-dissolving enzymes- calcitonin: calcitonin secretion increases when blood levels of Ca++ are high; stimulates osteoblasts to add calcium and phosphate to bone
Sprains
- stretched or torn ligaments
- heal slowly (few cells and poor blood supply)
Bursitis and tendinitis
- inflammation of bursae or tendons
Arthritis
Osteoporosis
- inflammation of joints
- osteoarthritis
- rheumatoid arthritis
Osteoporosis: excessive bone loss
Osteoclasts do what
They break down
Osteoblasts do what
Build up
