Saladin A&P Chapter 7

Bone Marrow

Soft tissue that occupies the medullary cavity of a long bone or the spaces amid the trabeculae of spongy bone

Stages of healing 3

callus formation (3) soft callus of fibrocartilage replaced by hard callus of bone in 6 weeks

Growth Ceases

when epiphyseal plate "closes" anabolic steroids may cause premature closure of growth plate producing short adult stature

Other Factors

20 or more hormones, vitamins & growth factors not well understood

Healing Time

8 - 12 weeks, longer in elderly

Matrix of Osseous Tissue Inorganic Matter

85% hydroxyapatite (crystallized calcium phosphate salt) 10% calcium carbonate other minerals (fluoride, sulfate, potassium, magnesium)

Bone Growth and Remodeling Notes

A mature bone however, grows only by the appositional mechanism. Because osteocytes have little room as it is and none to spare for the deposition of more matrix. The only way an adult bone can grow is to add more osseous tissue to the surface.

Endochondral Ossification

A process by which a bone develops from a pre-existing model composed of hyaline cartilage. Begins at the 6th week of fetal development and continues into the early 20's.

Endosteum

Endosteum is the internal surface of the bone, while the periosteum is the external surface covering of the bone.

General Features of Bones

Enlarged ends (epiphyses) are spongy bone covered with a layer of compact bone enlarged to strengthen joint & provide for attachment of tendons and ligaments

General Features of Bones

Epiphyseal plate or line depends on age.

Epiphyseal plate:

Epiphyseal plate: in children and adolescents and epiphyseal plate of hyaline cartilage separates the marrow spaces of the epiphysis and diaphysis. The epiphyseal plate is a zone where the bones elongate by a growth process. There are no ephiphyseal plates in adults.

Physiology of Osseous Tissue

Even after a bone is fully formed, it remains a metabolically active organ with many rolls to play including its own maintenance, growth, and remodeling. It also exchanges minerals with the tissue fluid and helps to maintain calcium homeostasis.

Structure of a Flat Bone

External/internal surfaces of flat bone are composed of compact bone.

Pott

Fracture at the distal end of the tibia, fibula, or both: common sports injury

Fracture Types - Colles

Fracture of the distal end of the radius and ulna; common in osteoporosis

Bone Marrow - Gelatinous

Gelatinous marrow of old age yellow marrow replaced with reddish jelly

Bone Growth and Remodeling

Grow and remodel themselves throughout life growing brain or starting to walk athletes or history of manual labor have greater density & mass of bone Cartilage grows by both appositional & interstitial growth Non-mature bones increase in length by interstitial growth of epiphyseal plate (adding more matrix internally) Bones also increase in width by appositional growth (adding more matrix to the surface) osteoblasts lay down matrix in layers parallel to the outer surface & osteoclasts dissolve bone on inner surface if one process outpaces the other, bone deformities occur(osteitis deformans)

Carpopedal Spasm

Hypocalcemia causing overexcitability of nervous system and muscle spasm of hands and feet

Bone Marrow notes

In young to middle aged adults most of this red marrow turns to fatty yellow bone marrow. Yellow marrow no longer produces blood. In adults red marrow is limited to the vertebrae... (see line 3 under RBM)

Bones make up skeletal system

Individual bones are made up of bone tissue, marrow, cartilage, and periosteum.

Two methods of ossification (prior to birth)

Intramembranous Endochondral

Intramembranous Ossification Notes

Mesenchyme is embryonic connective tissue. When this tissue condenses into a sheet the cells of this sheet enlarge and differentiate into osteogenic cells Osteoblasts deposit an organic matrix called osteoid tissue, calcium phosphate is deposited in the matrix and some osteoblasts get trapped in the lacunae and differentiate into osteocytes. This process gives rise to a sandwich-like arrangement of spongy bone between two surface layers of compact bone.

Metaphysis & Secondary Ossification Center

Metaphysis is cartilagenous material that remains as growth plate between medullary cavity & secondary ossification centers in the epiphyses.

Structure of a Flat Bone

Middle layer is spongy bone (diploe). No marrow cavity.

Hypercalcemia

excessive calcium binding to cell surface makes sodium channels less likely to open, depressing nervous system

Bone Marrow - Yellow

fatty marrow of long bones in adults

Stages of healing 1

fracture hematoma (1) broken vessels form a blood clot

Fracture Types - Linear

fracture parallel to long axis of the bone.

Closed Reduction

fragments are aligned with manipulation & casted

Stress Fracture

is a break caused by abnormal trauma to a bone car accident, fall, athletics, etc

Orthopedics

prevention & correction of injuries and disorders of the bones, joints & muscles

Calcitonin Functions

reduces osteoclast activity by as much as 70% in 15 minutes - so osteoclasts liberate less calcium from the skeleton. increases the number & activity of osteoblasts

Stages of healing 4

remodeling (4) occurs over next 6 months as spongy bone is replaced with compact bone

Calcitriol (Activated Vitamin D)

Abnormal softness of the bones is called rickets in children and osteomalacia in adults

Compact Bone - Osteon (haversian system)

Basic structural unit cylinders of tissue formed from layers (lamellae) of matrix arranged around central canal holding a blood vessel collagen fibers alternate between right- and left-handed helices from lamella to lamella osteocytes connected to each other and their blood supply by tiny cell processes in canaliculi

Secondary Ossification Center

Begin to form in the epiphyses near time of birth Same stages occur as in primary ossification center result is center of epiphyseal cartilage being transformed into spongy bone Hyaline cartilage remains on joint surface as articular cartilage and at junction of diaphysis & epiphysis (epiphyseal plate) each side of epiphyseal plate has a metaphysis

Healing of fractures notes

Blood vessels are broken at the fracture site. Blood clots. Blood vessels grow into the clot and a soft callus of fibrocartilage forms. Mineral deposition hardens the soft callus and converts it to a hard callus of spongy bone. Osteoclasts remove excess tissue from the had callus and the bone eventually resembles its original appearance.

Structure of a Flat Bone

Blow to the skull may fracture outer layer and crush diploe, but not harm inner compact bone.

Puberty Bone Growth

Bone growth especially rapid at puberty hormones stimulate proliferation of osteogenic cells and chondrocytes in growth plate adolescent girls grow faster than boys & reach their full height earlier (estrogen has stronger effect) males grow for a longer time

Bone and Bone Tissue

Bone/osseous tissue - connective tissue with a matrix hardened by minerals (calcium Phosphate)

Calcitriol (Activated Vitamin D)

Calcitriol behaves as a hormone (blood-borne messenger) Calcitrol is a form of Vit. D. produced by the sequential action of the skin, liver and kidneys. It is called a vitamin as it is added to the diet in fortified milk for people who do not get enough sunlight to initiate Vit. D. synthesis in the skin.

Functions of Calcium

Calcium is needed for communication between neurons, muscle contraction, blood clotting & exocytosis 99% of calcium is in the bones. Calcium and phospate is also found in the blood

Ion Imbalances

Calcium phosphate homeostasis depends on calcitriol, calcitonin & Parathyroid hormone (PTH)

Ion Imbalances

Changes in phosphate concentration have little effect Changes in calcium can be serious hypocalcemia is deficiency of blood calcium causes excessive excitability of nervous system leading tomuscle spasms, tremors or tetany hypercalcemia excessive calcium binding to cell surface makes sodium channels less likely to open, depressing nervous system

Endochondral Ossification

Chondrocytes at the primary ossification center die and blood vessels penetrate the bony collar and invade. The primary ossification center then becomes the primary marrow cavity as various stem cells and blood fills the central cavity.

Treatment of Fractures

Closed reduction, open reduction internal fixation (ORIF), traction, eletrical stimulation, orthopedics

Histology of Compact Bone

Collagen fibers corkscrew down the matrix of a given lamella in a helical arrrangement like the threads of a screw. They alternate between right and left handed helices from lamella to lamella. This enhances the strength of bone. The perforating canals or volkmann canals cross the matrix and feed into the central canals. The innermost osteocytes around each central canal receive nutrients from these blood vessels. They also receive waste from their neighbors and convey them to the central canal for removal by the bloodstream.

Matrix of Osseous Tissue

Combination provides for strength & resilience minerals resist compression; collagen resists tension bone adapts to tension and compression by varying proportions of minerals and collagen fibers

Mineral Resorption Braces

Dental braces reposition teeth, creating greater pressure on the bone on one side of the tooth and less on the other side increased pressure stimulates osteoclasts; decreased pressure stimulates osteoblasts to remodel jaw bone

Matrix of Osseous Tissue

Dry weight is 1/3 organic & 2/3 inorganic matter.

Bone as a tissue

Dynamic tissue that continually remolds itself

Estrogen Replacement Theories

ERT slows bone resorption, but best treatment is prevention -- exercise & calcium intake (1000 mg/day) between ages 25 and 40 Therapies to stimulate bone deposition are still under investigation

Electrical Stimulation

Electrical stimulation is used on fractures that take longer than 2 months to heal

The Metaphysis Zones

It exhibits 5 histological zones of transformation from cartilage to bone (We begin with farthest from the marrow cavity). Zone of reserve cartilage Hyaline cartilage, no transformation into bone. Zone of cell proliferation Chondrocytes multiply and line up. Zone of cell hypertrophy Enlargement of chondrocytes. Zone of calcification Temporary calcification of cartilage. Zone of bone deposition Death of chondrocytes; bone deposition; trabeculae forming

Calcitriol (Activated Vitamin D) Function

Its function is to raise the blood calcium concentration. Increases small intestine to absorb calcium weakly promotes urinary reabsorption of calcium ions so less calcium is lost in the urine promotes osteoclast activity to raise blood calcium concentration to the level needed for bone deposition

General Features of Bones

Joint surface covered with articular cartilage (lubrication)

Long Bone

Long bones include the humerus, ulna, femur, tibia and fibula. Spongy bone is found at the edges of long bone.

Long Bone

Long bones serve as rigid levers that are acted upon by the skeletal muscles to produce body movement.

Intramembranous Ossification Process

Mesenchyme (embryonic connective tissue) condenses into a sheet of soft tissue transforms into a network of soft trabeculae osteoblasts gather on the trabeculae to form osteoid tissue (uncalcified bone) calcium phosphate is deposited in the matrix transforming the osteoblasts into osteocytes osteoclasts remodel the center to contain marrow spaces & osteoblasts remodel the surface to form compact bone mesenchyme at the surface gives rise to periosteum

Mineral Deposition

Mineralization is crystallization process in which ions (calcium, phosphate & others) are removed from blood plasma & deposited in bone tissue

Osteoporosis

Most common bone disease. Bone lose mass and become brittle due to loss of both organic matrix and minerals. risk of fracture of hip, wrist & vertebral column lead to fatal complications such as pneumonia widow's (dowager's) hump is deformed spine

Mineral Deposition Notes

Now we are going to talk about the physiology of mature osseous tissue. Most tissues have inhibitors to prevent calcification. Calcium phosphate crystals do not form unless the product of calcium and phosphate concentration in the tissue fluids reaches a critical value called the solubility product.

The formation of bone is called

Ossification or osteogenesis

Osteoblasts

Osteoblasts form and help mineralize organic matter of matrix

Osteocytes

Osteocytes (mature bone cells) are osteoblasts that have become trapped in the matrix they formed cells in lacunae connected by gap junctions inside canaliculi signal osteoclasts & osteoblasts about mechanical stresses

Cells of Osseous Tissue Proccess

Osteocytes are strain sensors , when they detect a strain in the bone they communicate this information to osteoblasts; they are a mature bone cell. Osteblasts then deposit bone where needed Osteoclasts remove bone.

Osteogenic Cells

Osteogenic cells reside in endosteum, periosteum or central canals arise from embryonic fibroblasts and become only source for new osteoblasts multiply continuously & differentiate into osteoblasts in response to stress or fractures

Cells of Osseous Tissue

Osteogenic cells, osteoblasts, and osteocytes

Compact Bone

Perforating canals or Volkmann canals vascular canals perpendicularly joining central canals Circumferential or outer lamellae

Long Bone

Periosteum and articular cartilage. Compact and spongy bone. endosteum. Yellow Marrow.

Functions of Phosphate

Phosphate is a component of DNA, RNA, ATP, phospholipids, & acid-base buffers 85% - 95% of phosphate is in the bones. Calcium and phospate is also found in the blood

Endochondral Ossification Process

Primary ossification center forms in cartilage model chondrocytes near the center swell to form primary ossification center matrix is reduced & model becomes weak at that point Some cells of the perichondrium become osteoblasts, which produce a bony collar The bony collar acts like a splint it also cuts off diffusion of nutrients and hastens their death (becomes periosteum

Mineral Resorption Process

Process of dissolving bone & releasing minerals into the blood performed by osteoclasts "ruffled border" hydrogen pumps in the cell membrane secrete hydrogen ions into the space between the osteoclast & the bone chloride ions follow by electrical attraction hydrochloric acid with a pH of 4 dissolves bone minerals an enzyme (acid phosphatase) digests the collagen

General Features of Bones

Shaft (deaphysis) is cylinder of compact bone containing marrow cavity (medullary cavity) & lined with endosteum (layer of osteogenic cells and reticular connective tissue)

Achondroplastic Dwarfism

Short stature but normal-sized head and trunk long bones of the limbs stop growing in childhood but other bones unaffected

Intramembranous Ossification

Produces flat bones of skull & clavicle

Endochondral Ossification

Produces most other bones. i.e. vertebrae, pelvic bones and bones of the limbs

Bone Marrow - Red

Red marrow looks like thick blood mesh of reticular fibers and immature blood cells hemopoietic means produces blood cells found in vertebrae, ribs, sternum, pelvic girdle and proximal heads of femur and humerus in adults

General Features of Bones

Remainder of bone covered with periosteum outer fibrous layer of collagen fibers continuous with tendons or perforating(Sharpey's) fibers that penetrate into bone matrix inner osteogenic layer important for growth & healing

Calcitonin

Secreted by C cells of the thyroid gland when blood calcium concentration rises too high Important role in children, but little effect in adults calcitonin deficiency is not known to cause any disease in adults may be useful in reducing bone loss in osteoporosis

Parathyroid Hormone

Secreted by the parathyroid glands found on the posterior surface of the thyroid gland Released when calcium blood level is too low Injection of low levels of PTH can cause bone deposition Calcitrol: and as discussed calcitrol raises the level of calcium in the blood.

Spongy Bone

Spongelike appearance formed by rods and plates of bone called trabeculae spaces filled with red bone marrow Trabeculae have few osteons or central canals no osteocyte is far from blood of bone marrow Provides strength with little weight trabeculae develop along bone's lines of stress

Cells of Osseous Tissue

Stem cells, osteoclast. Osteoclasts develop in bone marrow ; each osteoclast is formed by the fusion of several stem cells, so they are unusually large. They break down bone.

Functions of skeletal system

Support, protection, movement, blood formation, mineral reservoir, pH balance and detoxification.

Ion Imbalances Notes

Tetany is the inability of a muscle to relax. Tetany begins as calcium concentration falls to 6mg/dL. At 4mg/dL the muscles of the larynx contract. Hypercalcemia: at 12mg/dL and higher hypercalcemia causes depression of the nervous system, emotional disturbances, muscle weakness, sluggish reflexes and sometimes cardiac arrest.

Wolff's Law of Bone

The architecture of a bone is determined by the mechanical stresses placed upon it, and the bone thereby adapts to withstand those stresses.

Primary Ossification Center

The first sign of Endochondral ossification is the multiplication and swelling of chondrocytes near the center of the model which is called the primary ossification center. There is the formation of the supportive bony collar.

Primary Ossification Center & Marrow Space

The first sign of Endochondral ossification is the multiplication and swelling of chondrocytes near the center of the model which is called the primary ossification center. There is the formation of the supportive bony collar. Invasion of the model by blood vessels and creation of a primary marrow space.

The Metaphysis

The region of transition from cartilage to bone at each end of the primary marrow cavity is called a metaphysis. This is where cartilage in converted into bone and it is responsible for bone elongation and a person's increase in height.

Fractures are classified by

Their structural characteristics -- causing a break in the skin, breaking into multiple pieces, etc or after a physician who first described it

Traction

Traction is not used in elderly due to risks of long-term confinement to bed hip fractures are pinned & early walking is encouraged

Blood Vessels of Compact Bone

You can see the concentric lamellae that encircle a haversian canal. An osteon or haversian system is the central canal and its lamellae. The skeleton receives half a liter of blood per minute.

Pathological Fracture

a break in a bone weakened by some other disease bone cancer or osteoporosis

Mineral Deposition - Ectopic Ossification

abnormal calcification may occur in lungs, brain, eyes, muscles, tendons or arteries (arteriosclerosis)

Parathyroid Hormone Functions

binds to osteoblasts causing them to release osteoclast-stimulating factor that stimulates osteoclast multiplication & activity promotes calcium resorption by the kidneys promotes calcitriol synthesis in the kidneys inhibits collagen synthesis and bone deposition by osteoblasts

Fracture Types - Greenstick

bone is bent on one side and has incomplete fracture on opposite side.

Matrix of Osseous Tissue Organic Matter

collagen, glycosaminoglycans, proteoglycans & glycoproteins

Hypocalemia

deficiency of blood calcium causes excessive excitability of nervous system leading tomuscle spasms, tremors or tetany

Stages of healing 2

granulation tissue (2) fibrous tissue formed by fibroblasts & infiltrated by capillaries

Mineralization Process

osteoblasts produce collagen fibers that spiral along the length of the osteon in alternating directions fibers become encrusted with minerals hardening matrix ion concentration must reach the solubility product for crystal formation to occur & then positive feedback forms more

Open Reduction Internal Fixation

surgical exposure & repair with plates & screws