bones chapter 6

Osteoporosis is a rare hereditary bone disorder that causes bone to be come overly dense can be presented in three different forms osteoporosis tarda, congenital and marble bone.

Osteopenia- loss of ossification (bone density ) bones get thin and weaker apart of getting old

Gigantism- over production of growth hormones before puberty

Acromegaly- cartilages growth and changes in the soft tissue that lead to enlargement,mainly happen in adulthood

Osteosarcoma - bone cancer most common malignancy in adolescent child

60-75 survival rate. Symptoms present at night around knee

Swings sarcoma- mostly children and adolescents 50% mortality rate with chemo, radiation and surgery.

Osteoma-noncancerous (benign) bone tumor in children and adolescents remove with laser photocoagulation

There’s 206 bones in the body

The skeletal system divides into two axial and appendicular

The axial system is the support system for the body consist of the head, neck, back and chest

The appendicular is anything that attach to the axial.

Proximal- closer

Distal- further

Functions of the skeletal systems is to provide support for attachment of soft tissues, storage of minerals, calcium, regulated blood serum ca+ levels, red marrow production, and protect underlying organs

Sutural  bones- between flat bones of skull, jigsaw puzzle shaped

Irregular bones-short flat with ridged surfaces examples are pelvis, several bones in the skull

Short bones- boxlike in appearance, short bones examples carpal and tarsal bones

Flat bone- thin parallel surfaces, examples are skulls, parietal bone,sternum and ribs

Long bone-long and slender examples are femurs, tibia, and humerus as they mature ostpeclast enlarge medullary cavity osteons form Around blood vessels in compact bones.

Seamoid bones- small round and flat, located in kneecap, hand and feet

Depression opening-sites where blood vessels of nervers lie alongside or penetrate the bone

Projections opening- form where muscles, tendons and ligaments attach, where bones form joints.

Diaphysis- tubular or long shaft

Epiphysis- end of the bone on both sides, where bones join with other bones.

Metaphysis- where the epidhysis and diaphysis meet

Osteocytes- one mature bone cell held in a lacuna, they cannot divide and a lacuna will always have no more than one osteocytes the main job is to maintain protein and mineral content of the surrounding matrix and help repair damage bones.

Dense matrix - contain calcium salt

Osteoblasts- form new bones and grow healing existing bones through a process called osteogenesis ,absorb and remove bone matrix

Osteoblasts surround by bone, then they become osteocytes and come from osteoprogenitor

Osteoid- matrix produced by osteoblasts but not yet calcified to form bone.

Osteoclasts- break down old or damaged bones to make space for new ones. Come from the same stem cells that produce monocytes and macrophages.

osteolysis is the breakdown and loss of bone tissue

Pth increase osteoclast activity

osteoprogenitor cells are stem cells that differentiate into osteoblasts, and osteoprogenitor cells themselves originate from mesenchymal stem cells

Bone homeostasis is the synergic balance between osteoblasts (builders) and osteoclasts (breakers), ensuring constant renewal and strength of bone tissue.

Structure of compact bone below

Osteon is the basic unit that has central canal

concentric lamellae form one at a time during the creation of an osteon in compact bone.

Perforating canals- opposite directions

perpendicular to the central canal

Spongy bone has a mesh like open matrix called trabeculae which is  avasuclar, space between trabeculae is filled with red bone marrows that make red blood cells and have blood vessels, giving nutrients to osteocytes

Weight bearing bones are centrally located in the body and support and distribute the body's weight include bones such as femur, tibia and ulna

Periosteum is made out of an outer fibrous layer and inner layer the cellular layer it cover all bones except parts enclosed in joint. Almost all your bones are covered by the periosteum. It supplies them the blood they need, and helps them grow and heal

The function of periosteum is to isolate bone from surrounding tissues.

The endosteum is a thin, vascular membrane that lines the inner surface of bones Also where the medullary cavity  central canals, and the surfaces of spongy bone is located

Endochondral ossification is a process of bone formation that involves the replacement of hyaline cartilage with bone tissue. Hyaline cartilage is a type of cartilage that is found in many parts of the body, including the joints, ribs, and growth plates

Endochondral ossification is the process of replacing cartilage with bone to form the skeleton’s long bones.

Endochondral ossification steps

Step 1 - hyaline chondrocytes near the center of the bone begin to enlarge,.

Step 2. There will now be distinguishing features of epiphysis, diaphysis, metaphysis.

Step 3. Blood blasts its way into the medullary cavity, making it the primary ossification center.

Endochondral Ossification

Step 4. now bone becomes longer & thicker

Step 5. At the epiphysis, blood vessels give a blood supple & osteoblasts build it up & calcify it, making it the secondary ossification center

Step 6. trabecula are seen in the epiphysis with cartilage surrounding it.

Appositional growth enables bones to increase in both length and thickness. During this process, compact bone thickens and strengthens the long bones through the formation of circumferential lamellae. It involves adding new bone tissue to the bone’s outer surface, while osteoclasts simultaneously break down old bone tissue.

The epiphyseal line marks the area where bone growth once occurred. During growth, this area contains cartilage known as the epiphyseal plate (or growth plate), which allows bones to lengthen. Once growth is complete—typically after puberty—the cartilage is replaced by bone, forming the epiphyseal line. When this line appears, it indicates that bone growth in length has stopped

During puberty (and throughout childhood), the epiphyseal plate — also called the growth plate — is open and made of cartilage. This is where new bone is formed, allowing bones to grow longer.

After puberty, when growth in height stops, the cartilage in the plate is gradually replaced by bone. What remains is the epiphyseal line, a thin remnant that marks where the growth plate used to be.

if osteoblast activity is higher, bones become thicker and stronger; if osteoclast activity dominates, bones may become thinner or weaker. The balance between these two cells controls bone growth, thickness, and overall shape.

he hormone calcitriol is produced in the kidneys and helps the body absorb calcium and phosphorus from the digestive tract. Its synthesis requires cholecalciferol, also known as vitamin D₃

Vitamin A, which stimulates osteoblast activity, Vitamin K, which helps synthesize bone proteins, and Vitamin D, which aids in calcium absorption, all work together to support and maintain healthy bone growth and development

Bones are composed of approximately 67% inorganic components and 33% organic components:

  • Inorganic components (67%) — these give bone its hardness and strength:

    • Calcium: 39%

    • Phosphate: 17%

    • Carbonate: 9.8%

    • Sodium: 0.7%

    • Magnesium: 0.5%

    • Potassium: 0.2%

  • Organic components (33%) — mostly collagen fibers, which provide flexibility and resilience to the bone structure.

If blood calcium levels drop by more than 30%, muscle cells and neurons in the brain become unresponsive.

If levels drop by more than 50%, it can lead to death.

Calcium homeostasis is maintained by the hormones calcitonin and parathyroid hormone (PTH).

Parathyroid Hormone (PTH): Produced by parathyroid glands → raises blood calcium by stimulating bone breakdown, increasing intestinal absorption, and reducing kidney excretion.

Calcitonin: Produced by thyroid glands  parafollicular cells (clear cells)→ lowers blood calcium by inhibiting bone breakdown and increasing kidney excretion.

Bleeding-Produces a clot (fracture hematoma)

Endosteum and periosteum cells divide and move to the fracture site.

Calluses form to stabilize the break:

  • External callus: cartilage and bone around the fracture

  • Internal callus: develops inside the medullary cavity

Osteoblasts replace the central cartilage of the external callus with spongy bone.

Osteoblasts and osteocytes continue remodeling the fracture for up to a year, gradually reducing bone calluses.

Osteopenia

  • Early bone demineralization (starts ~ages 30–40)

  • Bone loss per decade: Women ~8%, Men ~3%

  • Most affected areas: Epiphyses, vertebrae, jaws

  • Consequences: Fragile limbs, reduced height, tooth loss

Osteoporosis

  • Severe loss of spongy bone, usually later in life due to reduction in estrogen

  • Impairs normal function

  • Prevalence over age 50: Women 29%, Men 18%

Compression fracture-jumping from high height compressed  vertebrae

Epiphyseal fracture- in child before puberty, if not fix bone will not grow correctly

Green stick fractures-A partial fracture where the bone bends and cracks, but does not break completely. Older and younger audiences can be affected

Cole’s fracture- Fracture of the distal radius near the wrist,elderly fall on outstretch arm

Potts fracture- Fracture of the distal fibula and/or tibia involving the ankle soccer