Histology: Bone & Cartilage

Extracellular fluid (nutrients & metabolites) are found within canaliculi (huge contribution to body ECF, 1.3 L of 5-6 L total) Osteocytes respond to reduced mechanical stress by secreting what which destroy bone through rapid, transient (relative to osteoclasts) mechanism called what?

MMPs (matrix metalloproteinases) Osteocytic osteolysis

*In bones with a substantial weight-bearing function, the trabecular pattern is arranged to provide what?

Maximum resistance to the physical stresses to which that bone is normally subjected

A slender, pointed usually hard body

Spicule

Where does appositional growth take place?

"At the edge" of the cartilage mass (i.e., between the cartilage proper and the surrounding perichondrium)

What is the prescribe treatment for osteoporosis?

*Denosumab

When does osteoporosis occur? Loss of bone mass leads to loss of strength, making the bones brittle and weak

*The rate of bone resorption exceeds the rate of bone formation

What is endosteum composed of?

1. A monolayer of osteoprogenitor cells 2. Osteoblasts

Intramembranous ossification requires: 1. 2. 3.

1. A well-vascularized primitive connective tissue 2. Bone formation is not preceded by the formation of a cartilage 3. An aggregate of mesenchymal stem cells differentiates directly into osteoid-producing osteoblasts

What is the basic architecture of bone composed of?

1. An outer cortical or compact bone 2. An inner trabecular or spongy zone - Cortical bone forms a rigid outer shell that resists deformation, - Inner trabecular meshwork provides strength of acting as a complex system of internal struts - The spaces between the trabecular meshwork are occupied by bone

Components of osteoid: 1. 2. 3.

1. Type 1 collagen - 90% of the protein in bone which binds 2. *Osteocalcin and osteonectin, calcium binding proteins (raise local Ca++ conc.) 3. Alkaline phosphatase (ALP)

Osteoblasts are exclusively located at the surface of the bone. - Flattened (inactive) or - Cuboidal to columnar (active) - Lots of rER and secretory vesicles *Synthesize and secrete the organic matrix of bone 1. 2. 3. 4. Vesicles are exocytosis to form what?

1. Collagen type 1 2. Proteoglycans 3. GAGs 4. Glycoproteins Osteoid (uncalcified/unmineralized bone matrix)

Fibrocartilage is a combination of what? 1. 2.

1. Dense regular connective tissue Type I collagen Contains blood vessels 2. Hyaline cartilage Type II collagen *No perichondrium (doesn't need because of blood vessels in connective tissue) *Only cartilages that don't have perichondrium are fibrocartilage and articular hyaline cartilage

How long bones grow In length 1. In width 2. *Osteoblasts from the periosteum lay down new bone around the outside

1. Endochondral ossification 2. Appositional growth

What are the 2 layers of perichondrium?

1. Fibrous layer 2. Chondrogenic layer

What 2 disorders are responsible for the majority of dwarfism cases? 1. - Also known as pituitary dwarfism can be treated through replacement therapy 2. - "Without cartilage formation" but really affects bone more than cartilage - Sporadic mutation in 80% of cases - Caused by a mutation in fibroblast growth receptor 3 (FGFR3) - In normal development, FGFR3 has a negative regulatory effect on bone growth - In achondroplasia, the mutated form of the receptor is constitutively active and this leads to severely shortened bones

1. Growth hormone deficiency 2. Achondroplasia

What are the 3 major forms of cartilage?

1. Hyaline cartilage 2. Elastic cartilage 3. Fibrocartilage

Bone remodeling (or bone metabolism) is a lifelong process where: 1. 2.

1. Mature bone tissue is removed from the skeleton (a process called bone resorption), and 2. New bone tissue is formed (a process called ossification or new bone (tissue not a totally new bone) formation)

What is the principal function of periosteum and endosteum? 1. 2. 3.

1. Nutrition 2. Repair 3. Growth of bone

What are the 4 cells and their functions involved in bone formation?

1. Osteogenic cell: Stem cell 2. Osteoblast: Matrix-synthesizing cell responsible for bone growth 3. Osteocytes: Mature bone cell that maintains the bone matrix 4. Osteoclast: Bone-reabsorbing cell

Cells of Bones (4 Types) 1. What differentiates into osteoblasts? 2. What secretes the matrix? 3. When osteoblasts are surrounded by matrix, they become quiescent and are now called what? The spaces osteocytes occupy are known as lacunae. 4. What are multinucleated giant cells derived from fused bone marrow precursors (monocytes) and are responsible for bone resorption and remodeling?

1. Osteoprogenitor cells 2. Osteoblasts 3. Osteocytes 4. Osteoclasts

What does the periosteum consist of?

1. Outer layer of dense fibrous connective tissue, which merges with ligaments and other connective tissues 2. Inner cellular layer containing osteoprogenitor cells that have the potential to differentiate into osteoblasts

What are the 4 functions of cartilage?

1. Support of soft tissues 2. Act as a shock absorber (resists compression) 3. Free-sliding surface for joints (smooth surface) 4. As a template for growth of long bones- The embryonic skeletons forms first as cartilage, then parts of it are transformed into bone

Extracellular matrix accounts for 95% of the total cartilage volume. It consists of an organized and dense network of thin collagen fibers embedded in a concentrated solution of proteoglycans 1. 2. 3.

1. Water: 70-80% of the ECM 2. Collagen: 10-20% of the ECM predominantly *collagen type 2 3. Proteoglycans (PG) 10-15% Composed of subunits called glycosaminoglycans (GAGs)

5 distinct zones during endochondral ossification 1. This zone contains normal resting hyaline cartilage? 2. In this zone, chondrocytes undergo rapid mitosis, forming distinctive looking stacks. 3. It is during this zone the chondrocytes undergo hypertrophy (become enlarged). Chondrocytes contain large amounts of glycogen and begin to secrete alkaline phosphatase. 4. In this zone, chondrocytes are either dying or dead, leaving cavities that will later be invaded by bone-forming cells. Chondrocytes here die when they can no longer receive nutrients or eliminate wastes via diffusion. This is because the calcified matrix is much less hydrated than hyaline cartilage *different from mineralization. 5. Osteoprogenitor cells invade the area and differentiate into osteoblasts, which elaborate matrix that becomes calcified on the surface of calcified cartilage. This is followed by resorption of the calcified cartilage/calcified bone complex (by osteoclasts/chrondroclasts)

1. Zone of resting cartilage (reserve zone) 2. Zone of proliferation 3. Zone of maturation/hypertrophy 4. Zone of calcification 5. Zone of ossification

Ground substance: 1. Serve as hydroxyapatite crystal nucleation sites 2. 3.

2. Glycosaminoglycans (hyaluronan, chondroitin sulfate, keratan sulfate) 3. Glycoproteins (osteocalcin, osteonectin, osteopontin)

Endochondral Ossification 1. Hyaline cartilage 2. Bony collar forms around part of cartilage- blocks oxygen flow to underlying cartilage 3. Cartilage calcifies and starts to due under bone collar (Dark grey) 4. As cartilage deteriorates in this region and is removed, which opens spaces, blood vessels invade the now empty spaces *bringing in what that now can form bone? Note: the mature osteoclasts can also resorb cartilage (some sources call them chondroblasts) 5. Bone starts to form on calcified cartilage, forms what?

4. Bringing oxygen and osteogenic cells 5. "Primary ossification center"

What type of growth results from the differentiation of *perichondrial cells? Occurs when chondrogenic cells in the inner layer of the perichondrium undergo mitotic division and begin to synthesize matrix. As matrix secretion continues, the chondroblasts drift away from the perichondrium, eventually becoming trapped within matrix lakes of their own manufacture. As matrix secretion continues, the chondroblasts drift away from the perichondrium, eventually becoming trapped within matrix lakes of their own manufacture. When matrix secretion subsides, the chondroblasts become mature chondrocytes. These chondrocytes can divide a couple of more times when they do, this is called what?

Appositional growth Interstitial growth

What is an inflammation of the joints that can affect one or multiple joints? More than 100 different types.

Arthritis

What is hyaline cartilage absent of perichondrium and covers the end of long bones to form synovial joints. It has changing orientations of the lacunae and isogenous groups at different depth in the cartilage, which reflect the orientations of the collagen fibers in the matrix.

Articular cartilage

What are circulating levels of ATP used for clinically?

As a marker of osteoblast activity

What specialized type of connective tissue functions to provide protection for internal organs such as the brain, heart, lungs, bladder, and reproductive organs? Provides supporting framework for the body such as long bones for limbs or facial skeleton for the face. Enables body movement in conjunction with the muscles and the nervous system. Produces blood cells (hematopoiesis) within the medullary cavity of long bones and cancellous bone. Provides calcium and phosphorus reserve for the body. Provides detoxification for storing heavy metals in the bone tissues. Provides sound transduction in the middle ear via the ossicles: malleus, incus, stapes.

Bone *Bone is a dynamic tissue that constantly changes shape in relation to the stresses place upon it

What does cartilage always lack?

Blood vessels (but it is usually but not always) surrounded by a dense connective tissue perichondrium that is vascularized, lymphatics, and nerves

Excessive growth hormone can lead to what 2 diseases?

Gigantism, acromegaly

What enzyme is released by the thyroid gland, binds to the calcitonin receptor on *osteoclasts and *reduces the activity of their bone resorbing function?

Calcitonin

The skeleton serves as the calcium reservoir for the body and contains 99% of the body's calcium in crystals of hydroxyapatite. - Blood calcium is usually quite stable because of a constant interchange between blood calcium and bone calcium Mechanism for raising blood calcium: 1) Calcium ions are mobilized from hydroxylapatite crystals to insterstitial fluid- *Happens mainly in what type of bones? Easier to release calcium from younger, more lightly calcified lamellae (that exist even in adult bone)

Cancellous bone

1. The osteoclasts releases hydrogen ions through the action of what enzyme? Through the ruffled border into resorptive cavity, acidifying and aiding dissolution of the mineralized bone matrix. 2. Several hydrologic enzymes cathepsins and matrix metalloproteinases (MMP), are released by lysosomes to digest the organic components of the matrix

Carbonic anhydrase

Except in young children, damaged cartilage undergoes slow and often incomplete degeneration. *Mainly because of what? *In contrast, bone is heavily vascularized, and heals very well The cartilage that does regenerate after damage, is due to chondrogenic cells coming from the perichondrium. In extensively damage areas, and occasionally in small areas, the perichondrium produces a scar of dense connective tissue instead of forming new cartilage.

Cartilage avascularity

What condition occurs when the external portion of the ear suffers a blow, blood clot, or other collection of fluid under the *perichondrium? This separates the cartilage from the overlying perichondrium that supplies its nutrients, causing the cartilage cells to die and resulting in the formation of fibrous tissue (scar tissue) in the overlying skin. As a result, the outer ear becomes permanently swollen and deformed, resembling a cauliflower. The condition is most common among wrestlers, mixed martial artists and rugby players; usually a cauliflower ear is the result of repetitive injuries.

Cauliflower ear

What does cartilage tissue consist of? Chondrocytes account only for 3% of the total cartilage volume Chondrocytes are surrounded by extracellular matrix that they secrete and remove

Cells (chondroblasts, chondrocytes), and extracellular matrix

Formation of cartilage during embryonic development: 1. At the site of chondrogenesis, mesenchymal cells round out and proliferate, and differentiates into what?

Chondroblasts

The fibers are primarily what type of collagen?

Collagen type 1

Fibers are 90-95% of what type of collagen?

Collagen type I Small amounts of type V, III, XI, XIII collagens can be found

Flexible fibers embedded in rigid ground substance. Steel bars are analogous to what? Cement is analogous to what? If mineral removed, bone is too bendable. If collagen removed, bone is too brittle.

Collagen type I (33%) Hydroxyapatite Ca5(PO4)3(OH) (66%)

1. Intramembranous ossification *The bone is formed directly by what?

Condensation of mesenchyme rather than from a cartilage model

Insufficient growth hormone can lead to what?

Dwarfism

What cartilage is found in structures subjected to repeated deformation or vibration? Found in the external ear, epiglottis, and some small cartilages of the larynx. Each elastin molecule in the network has multiple random-coil domains which expand and contract; this allows the entire network to stretch and recoil like a rubber band

Elastic cartilage

During embryonic development, most of the skeleton is first formed of cartilage. Cartilage cells are capable of dividing (mitosis) unlike mature bone cells, which are enclosed in a solid matrix. The cartilage model can grow as rapidly as the fetus does. Beginning at the third month and through prenatal development, the cartilage is gradually replaced by bone. This is called what?

Endochondral Ossification

Formation of bone in an embryo What pattern of formation is characterized by the replacement of cartilage by bone? Most bones of the body are formed in this way including long bones.

Endochondral ossification

The internal marrow cavity and the trabeculae are lined with what specialized thin connective tissue?

Endosteum

*What does bone stain on H&E?

Eosinophilic, pink on H&E

What is responsible for the growth in length of bone and disappears at adulthood, causing bone growth to cease. In adults, who have stopped growing, the plate is replaced by an epiphyseal line? Epiphyseal closure occurs at different times in different bones and is complete in all bones by about age 20 ,

Epiphyseal cartilage with epiphyseal plates

What cells compose most of the fibrous layer?

Fibroblasts

In the perichondrium, what are the outer cells and what are the cells closest to the layer of cartilage?

Fibroblasts Chondroblasts

What cartilage is the strongest of the cartilages, blends the strength of the dense connective tissue with that of cartilage? "Islands of hyaline cartilage floating in a sea of connective tissue"

Fibrocartilage

What is the connective tissue and microscopic blood vessels that form on the surfaces of a wound during the healing process?

Granulation tissue

Bone fractures are typically treated by restoring the fractured pieces of bone to their natural position (if necessary), and maintaining those positions while the bone heals. In the healing of a bone fracture, what forms before the bone? In embryological endochondral ossification, what forms the template for bone formation?

Fibrocartilage Hyaline cartilage

*What is ALP responsible for?

For the crystallization of CaPO4 around the type 1 collagen matrix

If more pressure is put on a bone than it can stand, it will split or break. Although broken bone and bone break are common colloquialisms for a bone fracture, break is not a formal orthopedic term. A break of any size is called what? Common causes of bone fractures: - Fall from a height - Motor vehicle accidents - Direct blow - Child abuse - Repetitive forces, such as those caused by running, can cause stress fractures of the foot, ankle, tibia, or hip

Fracture

Osteoblasts begin to form what with other osteoblasts?

Gap junctions There are many more gap junctions in osteocytes

What disease is caused by the overproduction of pituitary growth hormone (GH) (aka somatotrophin) causes excessive growth at the epiphyseal plate*? In children, what is the condition called? In adults after the growth plates have closed, it is called what? Children develop great stature Adults develop deformed bones

Gigantism Acromegaly

What is the tissue fibroblasts begin to lay down between 4 & 10 days after the fracture occurs? The granulation tissue forms a 'scaffold' between the two fragments, from which the formation of a soft callus can begin.

Granulation tissue

In adjacent lamellae, the collagen fibers are oriented in different directions. *The presence of large numbers of lamellae with differing fiber orientations provides the bone with what?

Great strength, despite its light weight

Each osteon consists of concentric layers, or *lamellae, of compact bone tissue that surround a central canal, know as the what? Center of cylinder contains the neurovasculature to provide the nutrient supply to the bone tissue. Osteon follow a gentle spiral around the long axis of the bone. 1 cm of cortical bone displays many thousands of osteons

Haversian canal

In trabecular bone, blood vessels run through bone marrow spaces, supply oxygen etc. that pass into canaliculi, and feed osteocytes in lacunae inside trabeculae. In compact bone, what specialized delivery system is required to meet the metabolic requirements of osteocytes trapped in compact bone?

Haversian system

What causes necrosis of osteocytes- lack of oxygen?

Hematoma

In areas of bone undergoing resorption, osteoclasts lie within enzymatically etched depressions in the matrix known as what?

Howship's lacunae

Fibrocartilage is located in areas where support and tensile strength are required. A tissue intermediate between dense connective tissue and hyaline cartilage. Fibrocartilage has only very limited distribution in the body: annul is fibrosis of the IV disc, pubic symphysis, & menisci of knee joint What type of cartilage is contained in costal cartilages? IV discs contain what type of cartilage? The pubic symphysis contain what type of cartilage?

Hyaline cartilage Fibrocartilage Fibrocartilage

*Elastic cartilage is essentially similar to what type of cartilage? *These provide greater flexibility to this type of cartilage What does elastic cartilage contain? Elastic cartilage contains an abundant network of elastic fibers. Elastic fibers have a yellowish tint to them, so in fresh tissue elastic cartilage will appear somewhat yellow while hyaline cartilage will appear clear or bluish-white.

Hyaline cartilage plus elastic fibers Contains type II collagen Contains perichondrion

What is the mineralized ground substance?

Hydroxyapatite (Ca10)(PO4)6(OH)2

This division of chondrocytes is basis for what type of growth of cartilage?

Interstitial grow up

What type of growth is characterized by mitotic division of pre-existing chondrocytes? Occurs when chondrocytes divide mitotically into clusters of daughter cells each secreting a small amount of matrix. Less important of the two ways, occurs during early phase of cartilage formation.

Interstitial growth

1. Compact bone is remodeled within an osteon 2. Osteoclasts hollow out at the center, then osteoblasts lay back new bone 3. The new bone is likely to be at a slightly different angle than in old osteons, eventually forms what?

Interstitial lamellae

Formation of bone in an embryo What pattern of formation is characterized by flat bones of the skull and mandible. "Soft spots" that help the fetal skull pass through the birth canal later become ossified forming the skull?

Intramembranous ossification

Cartilage structure What is the term for a cluster of chondrocytes originating from one single progenitor cell? Territorial matrix (a thin rim surrounds lacunae) *More basophilic which indicates a high concentration of newly synthesized GAGs Interterritorial matrix (appears more eosinophilic)

Isogenous group

Formation of cartilage during embryonic development: 2. Subsequently the chondroblasts begin to synthesize and secrete matrix into the extracellular space entrapping themselves within what? They become further separated by the formation of additional matrix, and the cells are now called what?

Lacunae Chondrocytes

Osteoprogenitor cells are derived from what type of cells of bone and bone marrow? When new bone is not required, these cells are quiescent. They are flat, inconspicuous, have a pale staining oval nucleus and sparse cytoplasm. Bone-lining cells resemble fibroblasts. Osteoprogenitor cells are activated (become osteoblasts) following fracture, growth or in various disorders of bone. Are located in the periosteum and in the endosteum.

Mesenchymal cells (MSC)

During bone growth by endochondral ossification, the cartilage must grow (as the child grows) by cell division. Then the cartilage must do what?

Must die and then be replaced by bone

Where does interstitial growth occur?

Occurs "in the middle" of the mass of cartilage 1. Epiphyseal plates of long bones (Helps to increase length of long bones) 2. Articular cartilage *growth must come from within because there is no perichondrium to add cells by apposition all growth Elsewhere in the body, interstitial growth becomes less pronounced after embryonic development, as the matrix becomes increasingly rigid from the cross-linking of matrix molecules. Cartilage then only increases in girth by apposition all growth

Where is trabecular bone remodeled? As with compact bone, the exact direction of bone formation depends on the stresses applied to the bone white it is forming.

On the bone surface

What is the most common type of arthritis? Sometimes called a degenerative joint disease or "wear and tear" arthritis. Results from breakdown of joint cartilage and underlying bone. Causes: Previous joint injury, abnormal joint or limb development, and inherited factors. Risk is greater in those: Who are overweight, have one leg of a different length, and have jobs that result in high levels of joint stress.

Osteoarthritis

What secrets osteoids?

Osteoblasts

What are very large cells in the macrophage family that are multinucleated with 5-50 nuclei and are derived from blood precursors (monocytes) that fuse together? Very vigorous motile cells with acidophilic cytoplasm have lots of lysosomes, have lots of mitochondria, well developed rER and Golgi.

Osteoclasts (bone-reabsorbing cells)

What are mature bone cells derived from osteoblasts that became trapped in lacunae within the calcified matrix? - Are flat almond shaped cells with reduced RER & Golgi - Radiating from lacuna are *canaliculi (tunnel-like spaces) that house cytoplasmic processes of osteocytes (called *filopodia) - Gap junctions form between ends of processes allowing movement of ions and small molecules

Osteocytes

What is the most commonly found cell in mature bone tissue? These cells are simply osteoblasts trapped in the matrix that they secrete. Can live as long as the organism itself (half-life of 25 years). *They do NOT divide. Although these cells have reduced synthetic activity and (like osteoblasts) are capable of mitotic division, *they are actively involved in the routine turnover of bone matrix, through various mechanosensory mechanisms.

Osteocytes

The empty space surrounding osteocytes is the result of enzymatic degradation of bone matrix by MMPs. Increased mechanical stress activates molecular mechanisms similar to those found in the matrix producing osteoblasts (why weight-bearing exercise increases bone density) *Thus, the osteocytes are responsible for reversible remodeling of their pericanalicular and perilacunar bone matrix. This process is called what?

Osteocytic remodeling

What is the organic component of bone called? (Before it is mineralized). Constitutes ~50% of bone volume and ~15% of bone weight Bone consists of what?

Osteoid Consist of fibers and ground substance

What is a functional subunit of cortical bone? Cylinders of 100-259 micrometer diameter and 3-5mm in length.

Osteon

What is an extremely rare inherited disorder that is also know as *marble bone disease and *Albers-Schonberg disease? Caused by defective osteoclasts function (they lack ruffled borders) Results in overgrowth, thickening, and hardening of bones Can obliterate bone marrow cavities, depressing blood cell formation and causing anemia and lack of white blood cells. The exact genetic defect is unknown, however, deficiency of what enzyme?

Osteopetrosis "stone bone"

Remodeling responds to functional demands of the mechanical loading. These processes also control the reshaping or replacement of bone following injuries like fractures but also micro-damage, which occurs during normal activity. In the first year of life, almost 100% of the skeleton is replaced. In adults, remodeling proceeds at about 10% per year. *An imbalance in the regulation of bone remodeling's two sub processes, bone resorption and bone formation, results in many metabolic bone diseases, such as what?

Osteoporosis

What is the most common type of bone disease that leads to a reduction in the mass of bone per unit volume to a level below that's required for adequate mechanical support function?.

Osteoporosis

Cartilage is avascular. Cartilage can develop from chondrogenic precursors where oxygen is low (actually won't form where oxygen is high) *In contrast, bone is heavily vascularized and for bone to develop from osteogenic precursors requires what? *What (bringing oxygen) must already exist in close proximity BEFORE bone will start to form?

Oxygen Blood vessels

What hormone is released by the parathyroid gland and binds to the PTH receptor on *osteoblasts? They stop production of osteoid and instead secrete factors that promotes osteoclastic resorption of bone, raising calcium? Osteoclasts have receptors for calcitonin (from thyroid gland), but not for parathyroid hormone.

Parathyroid hormone (PTH)

What are the 2 enzymes that regulate blood calcium?

Parathyroid hormone (PTH) raises low blood calcium Calcitonin lowers high blood calcium

Formation of cartilage during embryonic development: 3) At the same time, the mesenchymal cells of the periphery condense to form a fibrous sheath around the newly formed cartilage, known as what?

Perichondrium

What if the fibrous sheet of dense connective tissue that covers cartilage? Rich in fibroblasts, in differentiated mesenchymal stem cells (chondrogenic precursor cells), blood vessels, nerves, lymphatic vessels

Perichondrium

The exterior of long bones is covered with a connective tissue membrane called what?

Periosteum

What is the first bone tissue to appear in embryonic development and bone repair? Woven bone is produced when osteoblasts produce osteoid rapidly - Abundant osteocytes - Haphazard organization of collagen fibers (weak bone) - Low mineral content - This bone is remodeled and replaced by what?

Primary (immature, woven) bone Secondary bone

What does intramembranous ossification produce?

Produces flat bones of skull and clavicle

What do sex hormones promote?

Promote bone formation; stimulate ossification of epiphyseal plate

Death of osteocytes (by trauma, senescence, or apoptosis) results in what?

Resorption of matrix by osteoclasts

Deficiency of vitamin D leads to what 2 diseases?

Rickets and osteomalacia

What disease is a result of a deficiency in vitamin D which causes newly formed bone not to properly calcify/mineralize? Vitamin D stimulates the synthesis of which 2 bone glycoproteins? What do they bind? The vitamin D receptor also is a transcription factor for proteins required to import calcium from the intestines. *In children this results in what? *In adults, this results in what? Major problem in pregnant women because fetus requires Ca++

Rickets, osteomalacia Osteocalcin and osteopontin, which bind hydroxylapatite to collagen type 1 and integrins on bone cells Rickets Osteomalacia (adult rickets)

What bone replaces primary bone, is found in adults, has an organized lamellar disposition of collagen, is composes of parallel or concentric lamellae of collagen, and whose matrix is calcified (strong bone)?

Secondary (mature, lamellar) bone

Osteoporosis is caused by a drop in estrogen in women after menopause and a drop in testosterone in men. Women over age 50 and men over age 70 have a higher risk for osteoporosis. Osteoclasts are inhibited by what?

Sex hormone

What are connective tissue consisting of bundles of strong collagenous fibers (type I) connecting periosteum to bone? They are part of the outer fibrous layer of the periosteum to the bone. They are part of the outer fibrous layer of the periosteum.

Sharpey's fibers (aka bone fibers, or perforating fibers)

Collagen has high concentration of GAGs (glycosaminoglycans) and proteoglycans, which interact with collagen and elastic fibers. ~75% of the wet weight of cartilage is water, which helps it to resist compression What is responsible for high water content of cartilage?

Sulfated GAGs have a negative charge makes them absorb mainly Na+ ions, water follows salt!

What is a joint in which the opposing bony surfaces are covered with a layer of hyaline cartilage or fibrocartilage? This articular hyaline cartilage is bathed in synovial fluid produced by the synovial membrane that lines the walls of the cavity. *What does articular cartilage lack? It receives its oxygen and nutrients from the synovial fluid that bathes it.

Synovial joint Perichondrium

Why do osteoblasts need gap junctions?

To transfer oxygen and ions through osteocytes Can transfer through a chain of ~10 cells

What are cancellous/spongy bone made of?

Trabeculae

Anastomosing bony spicules in cancellous bone which form a meshwork of intercommunicating spaces that are filled with bone marrow

Trabeculae of bone

What does the perichondrium harbor?

Vascular supply for avascular cartilage

Haversian (central) canals carry blood vertically. What canals carry blood horizontally or obliquely?

Volkmann's canal