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Questions and Answers

What is the primary function of osteoclasts in bone tissue?

  • To degrade bone and maintain calcium homeostasis (correct)
  • To form new bone during growth
  • To lay down unmineralized matrix
  • To monitor and maintain bone matrix

Which type of cartilage is most abundant in the human body?

  • Elastic cartilage
  • Fibrocartilage
  • Hyaline cartilage (correct)
  • Articular cartilage

What type of bone is described as being longer than it is wide?

  • Flat bone
  • Irregular bone
  • Long bone (correct)
  • Short bone

What is the function of the periosteum?

<p>Covers external bone surfaces except at joints (A)</p> Signup and view all the answers

Which component of bone matrix is primarily responsible for its tensile strength?

<p>Collagen fibers (A)</p> Signup and view all the answers

What type of cartilage growth occurs from the inside out?

<p>Interstitial growth (D)</p> Signup and view all the answers

Which type of cartilage is found in the vertebral discs due to its compressibility and strength?

<p>Fibrocartilage (A)</p> Signup and view all the answers

What is the role of osteocalcin in the body?

<p>Regulates insulin release and glucose metabolism (C)</p> Signup and view all the answers

What type of bone is formed directly from cartilage during fetal development?

<p>Endochondral bone (D)</p> Signup and view all the answers

What type of cells are osteoprogenitor cells?

<p>Undifferentiated stem cells (D)</p> Signup and view all the answers

Where is red bone marrow primarily found in adults?

<p>Around the trabeculae of certain bones (B)</p> Signup and view all the answers

Which statement about the medullary cavity in long bones is true?

<p>It contains yellow marrow in adults (A)</p> Signup and view all the answers

What is the primary cause of osteomalacia in adults?

<p>Inadequate calcium in diet (D)</p> Signup and view all the answers

What is the primary effect of parathyroid hormone (PTH) when blood calcium levels decrease?

<p>Stimulation of osteoclasts to resorb bone (D)</p> Signup and view all the answers

According to Wolff's law, how does bone respond to mechanical stress?

<p>Thickens and becomes stronger in areas of high pressure (B)</p> Signup and view all the answers

What happens to bone density in women after menopause?

<p>It decreases due to lower estrogen levels (D)</p> Signup and view all the answers

What is the first step in the bone repair process after a fracture occurs?

<p>Creation of the hematoma (B)</p> Signup and view all the answers

What does a fibrocartilaginous callus consist of during bone healing?

<p>Macrophages and cartilage cells (D)</p> Signup and view all the answers

What occurs during the bony callus formation stage of bone repair?

<p>Cartilage dies and is replaced with bone (B)</p> Signup and view all the answers

Why might astronauts experience weaker bones?

<p>Lack of mechanical stress due to microgravity (A)</p> Signup and view all the answers

What must happen for effective bone remodeling to occur after a fracture?

<p>The fracture must be immobilized (C)</p> Signup and view all the answers

What is the initial structure formed by osteoblasts during intramembranous ossification?

<p>Ossification center (D)</p> Signup and view all the answers

In which region of the epiphyseal plate are chondrocytes actively dividing?

<p>Active region (C)</p> Signup and view all the answers

What is the result of hyper-secretion of growth hormone during adolescence?

<p>Gigantism (B)</p> Signup and view all the answers

What happens to the initial spongy bone during the formation of the medullary cavity?

<p>It is broken down by osteoclasts (D)</p> Signup and view all the answers

Which condition is characterized by the epiphyseal plate closing after a growth spurt?

<p>Sex hormone influence (A)</p> Signup and view all the answers

Which of the following processes primarily occurs at the outer surface of the bone during appositional growth?

<p>Osteoblast activity (D)</p> Signup and view all the answers

What is the role of osteoclasts during bone growth?

<p>Resorbing old bone tissue (D)</p> Signup and view all the answers

What is the primary effect of testosterone on the male skeleton?

<p>Inducing epiphyseal plate closure later than in females (D)</p> Signup and view all the answers

Which hormone controls the activity at the epiphyseal plate?

<p>Growth hormone (C)</p> Signup and view all the answers

What structure develops from the periosteum during intramembranous ossification?

<p>Compact bone (B)</p> Signup and view all the answers

Which of the following is true during secondary ossification in epiphyses?

<p>Spongy bone is retained and actively growing cartilage remains (D)</p> Signup and view all the answers

What type of growth is characterized by increasing the volume of the bone from within?

<p>Interstitial growth (D)</p> Signup and view all the answers

What is the significance of maintaining calcium levels in the body?

<p>It's critical for muscle contraction and nerve function (C)</p> Signup and view all the answers

Study Notes

Functions of Bones

  • Support: Provides structural support for the body and protects internal organs.
  • Protection: Shields the central nervous system; skull protects the brain, and vertebrae protect the spinal cord, while the rib cage encases thoracic and upper abdominal organs.
  • Attachment Points: Serves as attachment points for skeletal muscles via tendons.
  • Storage: Stores essential minerals and fat; yellow marrow located in adult bones.
  • Blood Cell Formation: Hematopoiesis occurs in red bone marrow, responsible for producing blood cells.
  • Hormone Production: Osteocalcin plays a role in regulating insulin release, glucose homeostasis, and energy expenditure.

Cartilage and Skeletal Formation

  • Initial Skeleton: Composed of cartilage and connective tissue fibers before ossification.
  • Characteristics of Cartilage: Strong, resilient, flexible, and mainly composed of water; lacks nerve supply and blood vessels, encased by perichondrium containing blood vessels.

Types of Cartilage

  • Hyaline Cartilage: Most prevalent type, containing spherical chondrocytes and collagen; examples include articular, costal, respiratory, and nasal cartilages.
  • Elastic Cartilage: Similar to hyaline but with more elastic fibers, making it more flexible; found in the external ear and epiglottis.
  • Fibrocartilage: Contains rows of chondrocytes interspersed with thick collagen bands; offers great tensile strength and is found in areas bearing weight, such as vertebral discs and knee joints.

Cartilage Growth

  • Appositional Growth: New cartilage forms on the surface of existing cartilage, increasing thickness.
  • Interstitial Growth: Growth occurs within the cartilage as cells divide and secrete new matrix, increasing length.

Bone Tissue

  • Skeletal Structure: Divided into axial (skull, vertebral column, ribs) for protection and appendicular (limbs and girdles) for movement.
  • Bone Shapes:
    • Long bones: Longer than wide (e.g., limb bones).
    • Short bones: Cube-shaped (e.g., wrist and ankle bones).
    • Flat bones: Thin, flat, and curved (e.g., sternum, ribs).
    • Irregular bones: Unclassified shapes (e.g., vertebrae).

Gross Anatomy of Bone

  • Bone Composition: All contain outer compact bone and inner spongy bone.
  • Compact Bone: Appears smooth and solid; spongy bone has open spaces filled with marrow.
  • Membranes: Surrounded by periosteum (external covering) and endosteum (internal covering).
  • Vascularization: Involves nutrient arteries and veins for blood supply to the bone structure.

Microscopic Anatomy

  • Osteon: Fundamental structural unit of compact bone; composed of lamellae organized to withstand stress.
  • Central Canals: Host nerves and blood vessels, while perforating canals connect with neighboring osteons.

Hematopoietic Tissue

  • Blood Formation: Found in long and flat/irregular bones; red marrow is present in infants and adults, where it converts to yellow marrow with age.
  • Red Marrow Functionality: Converts to yellow marrow over time; can revert during instances of anemia or blood loss.

Cellular Composition of Bone

  • Osteoprogenitor Cells: Stem cells that divide to produce osteoblasts or remain undifferentiated.
  • Osteoblasts: Immature bone-forming cells that secrete unmineralized matrix (osteoid).
  • Osteocytes: Mature bone cells responsible for monitoring bone matrix and responding to mechanical stress.
  • Osteoclasts: Bone-reabsorbing cells that help remodel bones and maintain calcium homeostasis.

Chemical Composition of Bone

  • Organic Components: Include cells and osteoid; sacrificial bonds in collagen offer resilience.
  • Inorganic Components: Primarily mineral salts like calcium phosphate that provide strength.

Bone Ossification

  • Types of Ossification:
    • Endochondral Ossification: Most common, replaces cartilage with bone tissue; initiated by the formation of a bone collar at about nine weeks of fetal development.
  • Stages of Endochondral Ossification:
    • Formation of bone collar and primary ossification center in the diaphysis.
    • Development of a cavity within the diaphysis as cartilage calcifies and cells die off.### Bone Development and Ossification
  • Matrix within the primary ossification center (POC) deteriorates, creating a cavity in the diaphysis.
  • Cartilage outside the bone continues to grow, supported by the bone collar which prevents collapse under weight.
  • Initial spongy bone formation occurs in the diaphysis around the third month of gestation when the periosteal bud invades the cavity, containing nutrients and various cell types.
  • Osteoblasts create matrix around the calcified cavity, leading to initial trabecular bone formation.
  • Formation of the medullary cavity begins at birth, where initial spongy bone is resorbed by osteoclasts and replaced by medullary cavity.
  • Secondary ossification begins in epiphyses, with spongy bone retained while actively growing cartilage persists.

Intramembranous Ossification

  • Involves bone formation from a fibrous membrane with no cartilage involved.
  • Begins with mesenchymal cells differentiating into osteoblasts, forming an ossification center.
  • Osteoblasts lay down osteoids which calcify, trapping them to form osteocytes.
  • Blood vessels invade calcified matrix, leading to the creation of trabeculae known as woven bone.
  • Periosteum formation occurs as mesenchyme condenses, creating a fibrous layer; compact bone replaces some spongy bone with red marrow development.

Bone Growth

  • Length growth occurs through interstitial growth at the epiphyseal plate which has three regions: active, resting, and hypertrophy.
  • Active regions divide and lay down new matrix, pushing epiphyses away from diaphysis.
  • Cartilage is calcified and replaced, with growth continuing into adolescence until epiphysis and diaphysis fuse at the epiphyseal plate closure.
  • Width growth is appositional; osteoblasts secrete new matrix under periosteum while osteoclasts break down tissue internally to maintain thickness.

Hormonal Regulation of Bone Growth

  • Growth hormone, released by the anterior pituitary gland, regulates epiphyseal plate activity.
  • Excess growth hormone leads to gigantism, while insufficient levels cause dwarfism.
  • Sex hormones (estrogen and testosterone) influence growth spurts during puberty; estrogen leads to earlier closure of epiphyseal plates in females, while testosterone influences male skeletal features.

Bone Remodeling

  • Continuous process of bone deposition (new formation) and resorption (breakdown), vital for calcium homeostasis.
  • Parathyroid hormone (PTH) increases osteoclast activity when blood calcium levels drop, enhancing bone resorption to release calcium into the bloodstream.
  • Wolff’s Law asserts that bones strengthen in response to mechanical stress, leading to denser and thicker areas where pressure is higher.
  • Bone density can decrease after menopause due to lower estrogen levels.

Bone Repair Process

  • Requires immobilization of the fracture site to initiate repair.
  • Hematoma formation occurs at fracture site, with new blood vessels bringing in macrophages and chondroblasts to form fibrocartilaginous callus.
  • Bony callus formation replaces cartilage with bone; remodeling is necessary for normal stress adaptation.
  • Hyaline cartilage and epiphyseal plates persist into adulthood, crucial for ongoing skeletal function.

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