Bones and Skeletal Tissues (Chapter 6) Flashcards
Basic Structure of Skeletal Cartilage
Chondrocytes in lacunae; Matrix, Avascular
Structure/Function of Perichondrium
Dense irregular CT; structurally similar to a capsule; surrounding cartilage contains blood vessels and nerves; restrains cartilage when compressed
Hyaline Cartilage Structure and Location
Scattered chondrocytes in lacunae; no visible fibers in matrix; Articular, costal, respiratory, nasal
Elastic Cartilage Structure and Location
Scattered chondrocytes in lacunae; branching elastic fibers in matrix allows for flexibility; external ear, epiglottis
Fibrocartilage Structure and Function
Rows of chondrocytes in lacunae; parallel collagen fibers that withstand heavy pressures; intervertebral discs, meniscus, pubic symphysis
Appositional Growth
Derived from chondroblasts in perichondrium; New cartilage laid down on top of pre-existing cartilage
Interstitial Growth
Derived from chondrocytes within pre-existing lacunae; Occurs within pre-existing cartilage; Growth plates in long bones
Axial Skeleton
Along midline of body
Appendicular Skeleton
Appendages and points of attachment to body
Long Bones
Are longer than wide
Short Bones
Cube-shaped
Flat Bones
Plate-like
Irregular Bones
Odd-shaped
Sesamoid (Circular Bones)
Atypical short bones that are formed within tendons which allow tendons to slide
Functions of Bone
Support: provide body framework and attachment sites for tendons; Protection: internal organs from injury; Movement: skeletal muscle contractions pull on bones via tendons that allow movement of the body and its parts; Mineral Storage: stored as salts in bone which are released into blood as needed; Triglyceride (Fat) Storage: stored in adipose CT; Blood Cell Formation: hematopoiesis
Periosteum
Surrounds bone not covered by articular cartilage; Contains blood vessels and nerves
Outer Layer
Dense irregular CT (attachment site for tendons and ligaments)
Inner Layer
Osteogenic Cells: which are derived from mesenchyme (mitotic) which develop from osteoblasts; Osteoblasts: form new bone by producing matrix and fibers; Osteoclasts: degrade bone and are formed by fusion of multiple macrophages (huge and multinucleate)
Functions of Periosteum
Increases bone width; Assists in repair and nourishment of bone; Attachment site of tendons and ligaments
Endosteum
Lines yellow bone marrow cavities, central canals in bone, and covers bony spicules/trabeculae in spongy bone; Composed of a single layer of osteogenic cells, osteoblasts, and osteoclasts within a thin layer of reticular CT
Epiphysis
Distal and proximal ends of long bones; Contains spongy bone surrounded by compact bone and articular cartilage
Epiphyseal Line
Region where epiphysis joins diaphysis; Site of lengthwise bone growth during childhood/adolescence; Hyaline cartilage transitions bone in adult
Diaphysis
Between epiphyses; Compact bone surrounding medullary cavity proper
Articular Cartilage
Thin layer of hyaline cartilage; Covers ends of long bones; Functions include decreasing friction and absorbing shock
Marrow Cavities
Spaces housing bone marrow; Found within spongy bone; Within marrow cavities of all developing fetal bones
Red Bone Marrow
Function: hematopoiesis; Composition: developing blood cells, adipocytes, fibroblasts, and macrophages within reticular CT framework
Yellow Bone Marrow
Composition: primarily adipocytes (adipose CT) and a few blood cells; Function: store triglycerides as energy reserves
Flat Bone Structure
Organization: compact bone surrounding spongy bone; CT Coverings: periosteum, endosteum which lack diaphysis and epiphyses; Marrow cavities: only in red bone marrow
Single Osteon
Lamellar Bone; Organization: concentric tubes of bony matrix, collagen fibers and mineral salts which are oriented in opposite directions in adjacent lamellae, ability to withstand twisting forces associated with movement of body; Central Canal: vertical passageway
Volkmann’s (Perforating Canals)
Horizontal passageways; Connect with central canals and medullary cavities; Blood vessels, lymphatics, and nerve fibers from periosteum to endosteum
Osteocytes Lacunae
Found within small cavities between lamellae which is surrounded by tissue fluid; mature bone cells surrounded by matrix; Amitotic
Canaliculi
Radiate from lacunae; Contains slender cytoplasmic processes of osteocytes bathed by tissue fluid; Allow communication between adjacent osteocytes via gap junctions; Allows passage of nutrients, O2, wastes, and CO2 between osteocytes and central canal
Interstitial Lamellae
Areas of bony tissue between osteons; Represent fragments of older osteons; Partially destroyed by bone rebuilding or growth
Circumferential Lamellae
Deep to periosteum or lies beneath endosteum, encircling marrow cavities; Withstand twisting of bone due to external forces
Microscopic Anatomy of Spongy Bone
20% of human skeleton; Organized along lines of mechanical stress; Honeycomb of trabeculae which support and protect red bone marrow; No osteons present and no central canals; Lamellae are arranged irregularly
Organic Components
Osteogenic Cells (mitotic stem cells); Osteoblasts (mitotic bone forming): secretes fibers and matrix); Osteocytes (amitotic trapped in matrix): maintain daily metabolism of bone, strain sensors communicate to osteoblasts/clasts to start bone remodeling; Osteoclasts (amitotic break down bone matrix): lots of lysosomes and osteoids (35% of matrix which are secreted by osteoblasts)
Inorganic Components
Mineral Salts: calcium phosphate, mineralize within spaces between collagen fibers -> accumulate around collagen fibers which contributes to hardness of bone; Calcification of Bony Matrix: Collagen must be present in order for calcification of bone and provides flexibility to bone
Endochondral Ossification
Forms all bones from base of skull down, begins during 8th-9th week of fetal development, replaces hyaline cartilage skeleton with a bony skeleton, requires break down of cartilage prior to ossification
First Step of Endochondral Ossification
New blood vessels infiltrate perichondrium which is converted to a periosteum
Second Step of Endochondral Ossification
Mesenchymal Cells develop into osteogenic cells which develop into osteoblasts
Third Step of Endochondral Ossification
Osteoblasts from the periosteum secrete and form bony matrix in which a bone collar forms around a diaphysis
Fourth Step of Endochondral Ossification
Chondrocytes enlarge which provides signal for cartilage matrix to calcify and harden
Fifth Step of Endochondral Ossification
Chondrocytes begin to die
Sixth Step of Endochondral Ossification
Cartilage begins to deteriorate and is replaced by increasing amounts of bony tissue
Seventh Step of Endochondral Ossification
Hyaline cartilage remains at epiphyses and at epiphyseal plate
Eight Step of Endochondral Ossification
Blood vessels from periosteum invade internal spaces and form spongy bone
Ninth Step of Endochondral Ossification
Diaphysis elongates and osteoclasts form medullary cavity
Tenth Step of Endochondral Ossification
Secondary ossification centers develop in epiphyses at birth due to invasion by new blood vessels
Intramembranous Ossification
Begins during 8th week of development and bone is laid down between 2 sheet-like layers of mesenchyme, forms bones of skull and clavicles
First Step of Intramembranous Ossification
Ossification centers form when mesenchymal cells cluster and become osteogenic cells which develop into osteoblasts
Second Step of Intramembranous Ossification
Osteoid is secreted by osteoblasts which is mineralized
Third Step of Intramembranous Ossification
Spongy bone is formed when osteoid is laid down around blood vessels which starts formation of trabeculae
Fourth Step of Intramembranous Ossification
Mesenchyme forms periosteum for newly formed bone
Soft Spots
Allow flexibility of skull during childbirth and allows rapid brain growth during infancy
Resting Zone
Small scattered chondrocytes which are closest to epiphysis; Function: anchor epiphyseal plate to epiphysis; Chondrocytes in this region do not function in bone growth
Proliferation Zone
Columns of mitotic chondroblasts; Secrete cartilaginous matrix and collagen fibers; Push epiphysis from diaphysis and bone lengthens
Hypertrophic Zone
Older chondrocytes enlarge and lacunae enlarge; Matrix between lacunae begins to erode and provides a signal for cartilage calcification to begin
Calcification Zone
Only a few cells in thickness; Cartilage matrix calcifies and chondrocytes die; Forms spicules of calcified cartilage at junction of epiphysis/diaphysis
Ossification Zone
Occurs in diaphysis region; Osteoclasts degrade calcified cartilage; Osteoblasts invade from marrow of spongy bone; Replaces calcified cartilage with bony tissue
Appositional Growth in Width of Bones
Osteoblasts within periosteum secrete matrix onto bone surface; Osteoclasts from endosteum degrade bone lining medullary cavity; Osteoblast activity is slightly greater than osteoclast activity; Bones are thicker and stronger
Regulation of Bone Growth
GH (growth hormone): stimulates activity at epiphyseal plate, promotes cell division, protein synthesis, and osteoblast activity; TH (thyroid hormone): controls GH activity, assures proper proportions of bone growth; Estrogens and Testosterones: increase osteoblast activity, growth spurts, estrogen ultimately shuts down bone growth at epiphyseal plates
Bone Remodeling
Involves two processes: bone resorption and deposition; Associated with periosteum and endosteum; Remodeling cells: osteoclasts and osteoblasts
Bone Remodeling Function
Renews bone before deterioration sets in and fractures occur; Redistribution of bone along lines of mechanical stress; Heals injured bone
Osteoblast and Osteoclast Function
Blast: build compact bone at periphery; Clast: reabsorb spongy bone and build new bone marrow
First Step of Bone Resorption
Osteoclasts attach to surface of bone and form a leak proof seal
Second Step of Bone Resorption
Secrete lysosomal contents (pH 4.5-5.5) which digest matrix and a pocket forms beneath osteoclast: Acids dissolve mineral salts to soluble forms, enzymes digest osteoid and cells found in bone (organic components)
Third Step of Bone Resorption
Ca+2 and other minerals are released from bone
Fourth Step of Bone Resorption
Osteoclasts perform endocytosis, transcytosis, and exocytosis: tissue fluid enters capillaries
Fifth Step of Bone Resorption
Osteoclasts under apoptosis when no longer needed
First Step of Bone Deposition
A new bone matrix is formed by osteoblasts; Osteoblasts remove Ca+2 and PO4-2 from blood via mechanism
Second Step of Bone Deposition
Deposit fibers and matrix which then leads to calcification of matrix
Third Step of Bone Deposition
Become osteocytes when completely surrounded by matrix
Hormonal Regulation of Bone Modeling: Decreased Ca+2 in blood
Detected by cells in parathyroid gland which releases PTH (parathyroid hormone): increases osteoclast activity and increases Ca+2 in blood
Hormonal Regulation of Bone Modeling: Increased Ca+2 in blood
Detected by parafollicular cells in thyroid: increase osteoblast activity which inhibits osteoclast activity and decreases Ca+2 in blood
Mechanical Stress on Bone
Bones become stressed when weight bears on them or muscles pull on them; Bones grow or remodel in response to stresses which applies to both compact and spongy bone
First Step of Mechanical Stress
Mechanical stress is usually off center and bone tends to bend slightly
Second Step of Mechanical Stress
Bending compresses one side and stretches the other
Third Step of Mechanical Stress
Deformed bone pushes fluid containing ions through canaliculi and gap junctions between cellular processes
Fourth Step of Mechanical Stress
Creates electrical current detected by osteocytes which releases chemical messengers to stimulate bone deposition
Fracture Classification
Simple (skin not pierced) vs Compound (skin is pierced); Complete (broken into 2 parts) vs Partial (broken lengthwise but not separated); Spiral (bone is twisted and break is ragged)
First Step of Bone Repair: Hematoma Formation
Bone breaks and blood vessels tear and blood is released into space between break; Blood clots in space between break and forms hematoma; Area becomes inflamed and swollen; Damaged bone cells die; Within 6-8 hours of injury
Second Step of Bone Repair: Fibrocartilage Callus Formation
Macrophages and osteoclasts removed dead cells and damaged tissues; Fibroblasts from periosteum produce collagen fibers that reconnect broken ends; Chondroblasts fill space with fibrocartilage: Within 3 weeks of injury
Third Step of Bone Repair: Bony Callus Formation
Osteoblasts convert fibrocartilage to spongy bone: Within 3-4 months of injury
Osteoarthritis
Breakdown of joint’s cartilage, bones rub against each other causing discomfort
Osteomalacia
Body doesn’t get or absorb sufficient amounts of calcium and phosphate
Osteopenia or Osteoporosis
Increased breakdown of bone
Rickets
Low levels of vitamin D fail to control levels of calcium and phosphate. Blood levels of these minerals decrease which causes body to release hormones that then release calcium and phosphate from bones. Bones become soft and weak
Paget’s Disease
Chronic disorder of bone remodeling process. Bones formed by this abnormal process of excessive breakdown and formation are often abnormal, enlarged, less dense than normal bone, brittle, and prone to breakage
Achondroplasia
Disorder of bone growth that results in dwarfism. Genetic disorder; it is inherited as an autosomal dominant trait. It is caused by a mutation in fibroblast growth factor receptor 3 (FGFR3)
Osteomyelitis
Occur through Staphylococcus bacteria infecting bone; Can be caused by another infection, deep wounds, and direct contamination of the bone by external sources
Osteosarcoma
Rare malignant tumor arising in bone by bone producing immature bone by unknown cause
Osteogenesis Imperfecta
Brittle bone disease; osteogenesis imperfect (O1) is a congenital disease, caused by a defect in the gene that produces certain types of collagen, autosomal disease
Hypercalcemia
Too much calcium present in blood cause by hyperparathyroidism (PHTP) due to excess parathyroid hormone (PTH) being released by parathyroid glands
