Chapter 6

FOSSIL CROCODILE

• Araripesuchus patagonicus

• Topic focusing on bone tissues and the skeletal system.

Functions of the Skeletal System

• Support: Provides framework for the body.

• Protection: Encloses vital organs like the heart, brain, and lungs.

• Movement: Works with muscles to facilitate body movement.

• Mineral Storage and Homeostasis: Stores minerals such as calcium and phosphate.

• Blood Cell Formation (Hemopoiesis): Houses red bone marrow that produces red blood cells (RBC), white blood cells (WBC), and platelets.

• Fat Storage: Bones store fat as yellow bone marrow.

The Skeletal System – Bone Tissue

• Composed of:

  • Bone tissue

  • Cartilage

  • Dense connective tissue

  • Adipose tissue

  • Blood/vascular connective tissue

  • Nervous tissue

Bone Shapes

• Short bone: Small, cube-like; examples include wrist and ankle bones.

• Flat bone: Plate-like; examples include cranium, hip, and ribs.

• Long bone: Long and thin; examples include arm and leg bones.

• Irregular bone: Complex shape; examples include vertebrae and facial bones.

• Sesamoid bone: Bones wrapped inside a tendon; example includes patella.

• Sutural bone: Bones located between cranial bones.

Bone Markings

• Surface features of bones that help in:

  • Naming of bone parts

  • Indicating muscle and ligament attachments

  • Indicating passageways for blood vessels and nerves

  • Providing landmarks for physicians

General Description of Bone Markings

• Elevations and Projections:

  • Process: A term for any projection.

  • Ramus: Extension of a bone making an angle with the rest of the structure.

  • Trochanter: A large, rough projection.

  • Tuberosity: A smaller, rough projection.

  • Tubercle: A small, rounded projection; Crest: A prominent ridge; Line: A low ridge; Spine: A pointed or narrow process.

  • Head: Expanded articular end of an epiphysis.

  • Neck: Narrow connection between epiphysis and diaphysis.

  • Condyle: Smooth, rounded articular process.

Depressions and Openings

• Trochlea: Grooved articular process shaped like a pulley.

• Facet: Small flat articular surface.

• Fossa: Shallow depression.

• Sulcus: Narrow groove.

• Foramen: Rounded passageway for blood vessels/nerves; Canal: duct or channel.

• Meatus: Passageway through a bone; Fissure: Elongated cleft or slit; Sinus: Chamber within a bone filled with air.

Bone Structure

• Diaphysis: Shaft of a long bone; primarily compact bone tissue.

• Epiphysis: End of a long bone; primarily spongy bone tissue filled with red bone marrow.

• Metaphysis: Area between diaphysis and epiphysis, including the cartilaginous epiphyseal plate before puberty.

• Medullary Cavity: Cavity in the diaphysis filled with yellow bone marrow.

Bone Structure

• Periosteum: Dense connective tissue covering outer surface of the long bone; facilitates muscle attachment and helps with bone growth and repair.

• Endosteum: Lining of the medullary cavity; aids in growth and repair of bone.

Bone Tissue

• Connective tissue composed mainly of dispersed cells within a solid extracellular matrix.

Bone Cells

• Four types of bone cells:

  • Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts; located in endosteum and deeper periosteum.

  • Osteoblasts: Immature bone cells that secrete extracellular matrix (collagen fibers and calcium salts).

  • Osteocytes: Mature bone cells formed by osteoblasts trapped in the matrix; maintain bone tissue.

  • Osteoclasts: Modified white blood cells that dissolve bone tissue, releasing calcium into the blood.

Extracellular Matrix

• Collagen Fibers: Provide flexibility.

• Salts: Such as calcium phosphate and calcium carbonate, providing strength.

Types of Bone Tissue

• Compact Bone:

  • Comprises 80% of bone mass; makes up most of diaphysis.

  • Characterized by dense structure; consists of osteons, each containing a central canal with blood vessels and nerves, surrounded by concentric rings of bony matrix (lamellae).

• Spongy Bone:

  • Composed of trabeculae (plates) with spaces that house red bone marrow involved in hemopoiesis.

Blood Supply to a Bone

• Involves branches from nutrient arteries and veins and connections to superficial osteons, including various vessels supplying different bone areas.

Bone Formation

• Ossification: Process of bone formation originating from mesenchymal tissue in a fetus.

• Two methods:

  • Intramembranous Ossification: Formation of bone within mesenchymal membranes; forms flat bones.

  • Endochondral Ossification: Replacement of hyaline cartilage mold with osseous tissue; forms most bones.

Bone Formation – Intramembranous Ossification

• Involves development processes including ossification center formation, calcification, trabecular formation, and periosteum development, ultimately leading to compact bone tissue.

Bone Formation - Endochondral Ossification

• Involves forming a cartilage model, primary ossification centers, medullary cavity formation, secondary ossification center development, and articular cartilage formation.

Bone Growth

• Interstitial Growth: Increases length of bone; occurs in fetus, childhood, and puberty.

• Appositional Growth: Increases thickness; continues post-puberty.

Bone Remodeling

• Continuous cycle of resorption (via osteoclasts) and deposition (via osteoblasts) that allows healing and adaptation to stress.

Factors Affecting Bone Growth & Remodeling

• Minerals: Calcium, phosphorous, magnesium, fluoride, iron, manganese.

• Vitamins:

  • Vitamin C (collagen production).

  • Folic Acid and Vitamin B (protein production).

  • Vitamin A (stimulates osteoblasts).

• Hormones:

  • Human growth hormone (promotes growth via osteoblast stimulation).

  • Thyroid hormones (promote bone growth).

  • Sex hormones (stimulate growth initially but later lead to epiphyseal plate ossification).

Bone Fractures

• Types of Fractures:

  • Closed (simple), Open (compound), Comminuted, Greenstick, Impacted, Pott’s fracture, Colle’s fracture, Stress fractures.

Bone Fracture Repair

• Involves 1. Production of fracture hematoma, 2. Formation of fibrocartilage callus, 3. Production of bony callus, 4. Bone remodeling.

Calcium Homeostasis

• Crucial for normal body functions, such as blood coagulation and muscle contraction, with bones serving as the primary storage site.

Hormonal Regulation of Calcium Levels

• Parathyroid Hormone (PTH): Increases blood calcium via stimulating osteoclasts.

• Calcitonin (CT): Decreases blood calcium levels by inhibiting osteoclasts and stimulating bone deposition.

Impact of Aging on Bones

• Increased age leads to decreased bone density and brittleness, particularly in menopausal women, via changes in hormonal levels and reduced protein synthesis.

Osteoporosis

• Characterized by decreased bone mass, predominantly affecting menopausal women; prevention includes hormone replacement therapy and sufficient calcium intake.

Clinical Applications

• Various conditions related to bone growth and disorders include giantism, pituitary dwarfism, acromegaly, Marfan’s syndrome, achondroplasia, osteogenesis imperfecta, osteomalacia, osteosarcoma, and osteomyelitis.