HA: Chapter 5

process

any projection or bump

Bone remodeling

- coordinated removal and replacement of bone tissue by osteoclasts and osteoblasts Functions: • Change bone shape and adapt to environment • Replace old/damaged bone • Release mineral stores

The skeletal system

-Bones are dynamic organs that consist of several tissue types Made up of: •Osseous Tissue • Connective Tissues: Cartilages, Ligaments, Other (for skeletal stabilization)

Bone types

-flat bones: frontal bone, ribs, scapula, parietal lobe, sternum -long bones; humerus, clavicle, radius, ulna, femur, -irregular bones; vertebra -short bones; carpals compact lining and spongy inside -sesamoid bones; reduce friction, look like peddles. forms inside the tendon; patella

Calcium homeostasis: decrease in calcium

-parathyroid glands release parathyroid hormone (PTH) -PTH stimulates Calcium release from bones by osteoclast and reabsorption. Also, increase the calcium uptake in the kidneys and intestines. all of these cause calcium levels in the blood to rise and bring back to homeostasis

Calcium homeostasis: increase in calcium

-thyroid gland releases calcitonin that stimulates calcium deposition in bone and reduces calcium uptake in the kidneys and brings calcium level down

sinus or antrum

a chamber within the bone, normally filled with antrum

trochanter

a large rouge projection

line

a low ridge

sulcus

a narrow groove depression

neck

a narrower connection between the epiphysis and diaphysis

meatus or canal

a passageway through the surface of a bone

spine

a pointed process

crest

a prominent ridge

tuberosity

a rouge projection

foramen

a rounded passageway for nerves and blood supply

fossa

a shallow depression

tubercle

a small rounded projection

facet

a small, flat articular surface

condyle

a smooth rounded articular process

trochlea

a smooth, grooved articular process shaped like a pulley

ramus

an extension of bone making an angle to the rest of the structure

Cartilage

dense connective tissue in joints, rib cage, nose, ear -reduces friction by providing a smooth surface for the movement of two articulating bone

fissure

elongated cleft

openings

foramen, fissure, meatus or canal, sinus or antrum

process formed for articulation of adjacent bones

head, neck, condyle, trochlea, and facet

bone remodeling and maintenance

resting bone--> osteoclast resorption of bone--> reversal, mononuclear cells make it nice and smooth---> matrix deposition involve osteoblast secrete the bone matrix--->mineralization osteoblast becomes osteocytes

ligament

short bands of tough fibrous connective tissue connects bone to other bone

head

the expanded articular end of an epiphysis, often separated from the shaft by a narrower neck

process formed where ligaments and tendons attach

trochanter, tuberosity, tubercle, crest, line, spine

Epiphysis bone type

• (ends of the long bones) • Contains bone marrow

Diaphysis bone type

• (shaft of the long bones) • The medullary cavity of this type contains bone marrow

Bone growth and development

• Before six weeks of development, the skeleton is hyaline cartilage • Cartilage cells will be replaced by bone cells or replacing tissue with bone is called ossification • Osteogenesis: Bone formation • Calcification: The deposition of calcium ions into the bone tissue

Endochondral ossification step 2

• Blood vessels grow around the edges of the cartilage • Perichondrium differentiates into osteoblasts to lay down bone to form osteon • Perichondrium converts into peritoseum • Formation of bone collar: Thin layer of compact compact bone around the shaft of cartilage

Endochondral ossification step 1

• Chondrocytes near the center of the diaphysis increase in size • Surrounding matrix begins to calcify • Chondrocytes die and disintegrate due to lack of nutrients • Formation of cavities within the cartilage

two types of bone

• Compact bone (aka cortical bone) • Spongy bone (aka cancellous/trabecular bone)

Endochondral ossification step 6

• Epiphyses filled with spongy on bone • Formation of epiphyseal cartilage (epiphyseal plate) Between epiphysis and diaphysis • Osteoblasts invade shaft side of epiphyseal cartilage, replacing cartilage with bone at same rate that epiphyseal cartilage enlarges. Enlargement pushes epiphysis away from diaphysis - length of bone increase

FACTORS AFFECTING BONE REMODELING & GROWTH

• Essential nutrients: ex. Calcium, Phosphorous, Magnesium, Sodium. must be maintained • Vitamins: ex. Vitamin A, Vitamin C, Vitamin D • Hormones: ex. Parathyroid (releases stored minerals), calcitonin (matrix deposition), sex hormones

Endochondral ossification step 3

• Increased blood supply: Capillaries and osteoblasts migrate into the heart of cartilage, invading spaces left by chondrocytes • Primary ossification center: 1. Cartilaginous matrix is replaced by spongy bone produced by osteoblasts 2. Localized medially and moves toward ends

Intramembranous ossification

• Involved in the development of clavicle, mandible, skull, and face

• Endochondral ossification

• Involved in the development of limbs, vertebrae, and hips

Periosteum

• Lines outside of bone Functions: - Protects - Attaches to fascia; for muscle attachemnt - Attachment site for circulatory & nervous supply

Osteocytes cells

• Mature bone cells in bone matrix • maintain and monitor the protein and mineral content of the surrounding matrix. • directs both the release of calcium from bone to blood and the deposition of calcium salts in the surrounding matrix. • occupy small chambers, called lacunae, that are sandwiched between layers of calcified matrix. These matrix layers are known as lamellae • These sandwiched layers form tiny circles called osteons . These circles form canals that carry blood vessels and nerves through the bone. • Channels called canaliculi radiate through the matrix from lacuna to lacuna and toward free surfaces and adjacent blood vessels that interconnect the osteocytes situated in adjacent lacunae. • tight junctions provide a route for the diffusion of nutrients and waste products from one osteocyte to another across gap junctions.

Endosteum

• Osteogenic Connective • Lines medullary cavity • One cell thick -When osseous tissue surrounds another tissue

Endochondral ossification step 5

• Secondary Ossification: Migration of capillaries and osteoblasts into epiphysis centers -blood vessel iniciates the process. • Present at birth; Femur, Tibia, and Humerus

Endochondral ossification step 4

• Shaft filled with spongy bone • Osteoclasts create medullary cavity • Bone of shaft becomes thicker • Cartilage of metaphyhsis invaded by osteoblasts Produces bone columns • Further growth: Increase in length and Diameter enlargement

Endochondral ossification steps

• Steps 1 - 4 : initiation of ossification in developing bone • Steps 5 - 7 : increasing length of developing bone

Functions of the skeleton

• Support: structural support • Protection: Delicate tissues and organs are often surrounded by skeletal elements. The ribs protect the heart and lungs, the skull encloses the brain, the vertebrae shield the spinal cord, and the pelvis cradles delicate digestive and reproductive organs. • Movement • Blood Cell Production: by red marrow, produced blood cells, white cells, and platelets, which fills the internal cavities of many bones • Mineral Storage/Homeostasis: calcium & phosphorus

Bones (Osseous Tissue)

• Supporting connective tissue • Specialized cells consisting of osteoprogenitor cells, osteoblasts, osteocytes, and osteoclasts • Bone linings: Periosteum (outer); separates it from surrounding tissues and Endosteum (inner); lines inner bony surfaces • Has a solid matrix due to the deposition of calcium salts around the protein fibers.

Epiphyseal plate bone type

• The line separating the diaphysis and epiphysis • Consists of cartilage until skeletally mature

Metaphysis bone type

• The widened portion of the diaphysis where bone is added during growth

Osteoprogenitor cells

• are flattened or squamous-shaped stem cells termed • are found in the innermost layer of the periosteum and in the endosteum lining the medullary cavities. • stem cells, who's devision produce osteoblasts. The ability to produce additional osteoblasts becomes extremely important after a bone is cracked or broken. • produce matrix • When activity increases, bones become stronger and more massive.

Endochondral ossification step 7

• decrease rate of epiphyseal cartilage enlargement • increase rate of osteoblast activity closes the Epiphyseal • then the Epiphyseal cartilage gets narrower and narrower; eventually disappears • all that is left is epiphyseal line • Epiphyseal plate remains cartilaginous until skeletal maturity (depends on bone) 18-20 • Articular cartilage: Thin cap of original cartilage exposed to joint cavity. Prevents damaging bone‐to‐bone contact within joint

Compact bone

• is for protection, its dense and Made up of osteons • Consists of: • Central canal: contain blood vessels that surround the osteon • Canaliculi: interconnect the lacunae of an osteon and form a branching network that reaches the central canal. allows for communication • Osteocytes: are arranged in circular layers around a central canal, or Haversian canal, which contains the blood vessels that supply the osteon. • Lamellae: form a series of concentric rings, resembling a "bull's-eye" target, around the central canal. The collagen fibers spiral along the length of each lamella, and variations in the direction of spiraling in adjacent lamellae strengthen the osteon as a whole. -Interstitial lamellae fill in the spaces between the osteons in compact bone. -the circumferential lamellae form the outer and inner surfaces of the shaft

Osteoclasts

• large, multinucleate cells found at sites where bone is being removed. • secrete acids through a process involving the exocytosis of lysosomes. The acids dissolve the bony matrix and release amino acids and the stored calcium and phosphate. This erosion process, called osteolysis, increases the calcium and phosphate concentrations in body fluids. • are always removing matrix and releasing minerals, when they remove calcium salts faster than osteoblasts deposit them, bones become weaker.

Osteoblasts cells

• secrete osteoid, the organic components of the bone matrix. • are responsible for the production of new bone • respond to a variety of different stimuli, including mechanical and hormonal, to initiate osteogenesis. • if it becomes surrounded by matrix, it differentiates into an osteocyte.

Spongy bone

• spaced, Arranged in parallel strut, branching plates called trabeculae • Trabeculae form a network • Is why bones are lightweight, the branching trabeculae give it strength despite its relatively light weight. -has bone marrow

The Matrix of the bone

• the tissue surrounding the cell is composed of Calcium phosphate • The calcium phosphate interacts with calcium hydroxide to form crystals of hydroxyapatite used to form small plates along side ground substance proteins that make bone hard • these crystals incorporate calcium carbonate, and ions such as sodium, magnesium, and fluoride to resist compression. • has collagen fibers, which contribute tensile strength to bone. Collagen fibers are tough, flexible and provide an organic framework for the formation of mineral crystals.