Bone Tissue Lecture 2 Flashcards
Bone Blood Supply Overview
- Rich in blood supply due to high metabolic activity and constant remodeling.
- Blood supply is crucial for maintaining structural integrity and providing nutrients.
Arteries and Veins
Four major arteries and veins supply bone tissue:
- Periosteal arteries/veins
- Nutrient artery/vein
- Metaphyseal arteries/veins
- Epiphyseal artery/vein
Periosteal Arteries/Veins
- Enter through Volkmann’s canals.
- Supply blood to and from the outer portion of compact bone and periosteum.
Nutrient Artery/Vein
- Enter through the nutrient foramen in the diaphysis.
- Supply blood to the inner portion of compact bone and proximal spongy bone.
Metaphyseal Arteries/Veins
- Enter at the metaphysis portion.
- Supply blood to the metaphysis and red bone marrow.
Epiphyseal Artery/Vein
- Enter at the epiphysis portion.
- Supply blood to the epiphysis and red bone marrow.
Bone Remodeling
Process
- Lifelong process
- Mature bone tissue is replaced by new bone tissue.
Bone Remodeling
Purpose
- Maintains structural integrity
- Strengthens high-stress areas
- Controls reshaping after injuries
- Repairs micro-damage
- Maintains blood calcium homeostasis.
Bone Remodeling
Bone Resorption
- Osteoclasts break down bone matrix.
- Removes collagen and minerals, releasing calcium into the blood.
Bone Remodeling
Bone Deposition
- Osteoblasts create new bone ECM.
- Lay down osteoid, the organic bone component.
- Deposit minerals, mainly calcium, from the blood.
Bone Remodeling
Simultaneous Processes
- Resorption and deposition work together.
- Respond to stress on the bone.
- Wolff’s Law: bone is added where needed and removed where not.
Factors Affecting Bone Growth
Minerals
Calcium, phosphorus, fluoride, magnesium, manganese.
Factors Affecting Bone Growth
Vitamins
- Vitamin A promotes osteoblasts.
- Vitamin C for collagen.
- Vitamin D aids calcium absorption.
- Vitamin K & B12 for bone proteins.
Factors Affecting Bone Growth
Hormones
- Thyroid hormones (T3 & T4) promote bone growth.
- GH stimulates IGFs for growth.
- Sex hormones affect bone growth/remodeling.
- Hormones in calcium homeostasis (calcitonin, PTH).
Calcium Functions
- Essential for nerve and muscle functioning.
- Key in blood clotting.
- Important for various body chemical reactions.
Calcium Regulation
- Calcium levels must be tightly controlled (8.5 - 10.5 mg/dL).
Deviations can be fatal: - Hypercalcemia (>10.5 mg/dL) ➡️ Cardiac arrest.
- Hypocalcemia (<8.5 mg/dL) ➡️ Respiratory arrest.
Calcium Regulation Locations
Bone:
Resorption increases blood Ca2+.
Deposition decreases blood Ca2+.
Kidney:
Reabsorption increases blood Ca2+.
Decreased reabsorption decreases blood Ca2+.
Gastrointestinal Tract:
Absorption increases blood Ca2+.
Decreased absorption decreases blood Ca2+.
Calcium Regulating Hormones
- Calcitonin: Decreases blood Ca2+.
- Parathyroid Hormone (PTH): Increases blood Ca2+.
- Calcitriol (Vitamin D): Increases blood Ca2+.
Calcitonin
- Produced by thyroid gland’s parafollicular cells.
- Decreases blood Ca2+.
- Antagonistic to PTH and calcitriol.
Calcitonin Mechanism
- Decreases bone resorption.
- Inhibits osteoclasts, favoring osteoblasts.
- Decreases kidney Ca2+ reabsorption.
- More Ca2+ excreted, lowering blood Ca2+.
Parathyroid Hormone (PTH)
- Produced by parathyroid glands.
- Increases blood Ca2+.
- Antagonistic to calcitonin, synergistic to calcitriol.
PTH Mechanism
- Increases bone resorption.
- Activates osteoclasts, favoring bone breakdown.
Kidney actions:
* Increases Ca2+ reabsorption.
* Activates calcitriol.
PTH Regulation
Controlled by negative feedback.
Calcitriol
- Produced in skin from UV-activated cholesterol.
- Increases blood Ca2+.
- Antagonistic to calcitonin, synergistic to PTH.
Calcitriol Mechanism
- Increases intestinal Ca2+ absorption.
- Boosts blood Ca2+ levels.
Fractures
- Any break in the bone.
- Types vary by severity, location, and cause.
Open Fractures (Compound)
- Definition: bone ends protrude through the skin.
- Complications: infection, non-union.
- Treatment: surgery, antibiotics.
Closed Fractures (Simple)
- Definition: bone ends don’t pierce the skin.
- May not need surgery depending on displacement.
Comminuted Fractures
- Bone broken in multiple places forming fragments.
- Requires surgery with internal/external fixation.
Greenstick Fractures
- Incomplete, one side broken, other bent.
- Common in children due to more organic material.
Impacted Fractures
- One bone end driven into the other.
- Common in car accidents.
Transverse & Oblique Fractures
- Transverse: perpendicular to bone length.
- Oblique: broken on an angle.
Spiral Fractures
- Looks like a corkscrew around the bone.
- Occurs due to a twisting motion.
Pott’s Fractures
- In distal fibula with ankle sprain.
- Serious injury to distal tibial articulation.
Colles’ Fractures
Distal radius fracture, distal part displaced upwards.
Avulsion Fractures
- Small piece of bone attached to tendon or ligament pulled away.
- Common in young athletes.
Stress Fractures
- Microscopic fissures due to repetitive strenuous activities.
- Commonly missed by x-rays.
Growth Plate Fractures
Break in child/teen growth plate can result in limb deformities.
Vertebral Compression Fractures (VCF)
- Vertebrae fracture, compressed into wedge shape.
- Often in osteoporosis or trauma.
Osteoporosis
- “Porous bone.”
- Loss of bone mass with deteriorating bone microarchitecture.
- Bone resorption > bone deposition.
- Caused by: hormones, diet, exercise, drugs, genetics.
- More common in elderly and women.
Osteomalacia & Rickets
- Failure of bones to calcify.
- In children, Rickets; in adults, Osteomalacia.
- “Soft bones” due to calcium deficiency.
- Vitamin D, sunlight, diet deficiency.
- Rickets causes bowing, fractures; osteomalacia affects bone mineral ratio.
- Both caused by vitamin D deficiency.
Formation of Fracture Hematoma (Reactive Phase)
Fracture repair step 1
- Exposed blood vessels clot at fracture.
- Circulation stops, nearby bone cells die.
- Inflammation from dead cells.
- Phagocytes and osteoclasts remove debris.
Fibrocartilaginous Callus Formation
Fracture repair step 2
- Fibroblasts lay down collagen fibers.
- Chondrocytes produce fibrocartilage.
- Callus formation.
- Lasts about 3 weeks.
Bony Callus Formation
Fracture repair step 3
- Osteogenic cells become osteoblasts.
- Convert fibrocartilage into spongy bone trabeculae.
- Joins living and dead portions of bone fragments.
- Lasts around 3-4 months.
Bone Remodeling
fracture repair step 4
- Osteoclasts resorb remaining dead bone fragments.
- Compact bone replaces spongy bone.
- Occurs around the periphery.
X-Ray or Radiography
- Electron beams pass through objects.
- Soft tissue and air are translucent or black.
- Dense objects like bone, metals appear grey or white.
Radiolucent: Less dense, lets x-rays through.
Radiopaque: Dense, resists x-rays.
DEXA Scan (Dual X-Ray Absorptiometry)
- Measures bone density.
- Tracks bone loss and diagnoses osteoporosis.
Bone Scan
- Radioactive tracer taken up by living bone tissue.
- Scanning device detects high or low activity.
- Hot Spots: Indicate higher metabolism (e.g., cancer).
- Cold Spots: Indicate healed fractures, arthritis.
- Most useful bone imaging method due to efficiency, accuracy, and reduced radiation.
