BIO 141-The Skeletal System and Bone Tissue-Chapter 6

Bone Growth: Appositional Growth

Growth in thickness

Two Principle Effects on Bone:

1. Loss of calcium and other minerals from bone matrix (demineralization) -very rapid in women 40-45 as estrogen levels decrease. -In males, begins after 60. 2. A decreased rate of protein synthesis.

Developmental Anatomy

5th week: limb bud 6th week: hand or foot plate, cartilaginous 7th week: ossification begins 8th week: upper and lower limbs

Normal Plasma Level

9-11mg/100mL

Fracture and Repair of the Bone

A fracture is any break in a bone. Classified by: -Severity of the break -Shape/position of fracture line

Osteogenesis

Bone formation

Rickets

Bowed legs, skull, rib cage, and pelvic deformity.

Comminuted Fracture

Broken ends of bones are splintered, fragments loose.

Histology of Bone Tissue

Calcification: -Fiber framework -Crystallization results in hardening of the tissue. -Osteosblasts: bone building cells.

Small Changes in Blood Levels Calcium can be Serious:

Cardiac arrest if to high Respiratory arrest if too low

Long Bone Structure

Central cavity: medullary cavity Red marrow: blood production Endosteum: marrow cavity lining Periosteum: vascular surface covering Articular cartilage: surfaces of each epiphysis Epiphysis: enlarged ends

Osteoporosis

Decreased bone mass resulting in porous bones.

CT (Calcitonin)

Decreases calcium levels by: -inhibiting osteoclasts -increase bone formation by osteoblasts

Pott's Fracture

Distal Fibular Fracture (Fracture in the ankle)

Colles' Fracture

Distal Radial Fracture (Fracture in the wrist)

Spongy Bone

Found in the ends of long bones and inside flat bones: -Pelvis -Sternum -Parts of the skull -Ribs

Bone Growth: Interstitial Growth

Growth in length: epiphyseal plate; consists of four zones: -Zone of resting cartilage: anchor growth plate to bone. -Zone of proliferating cartilage: rapid cell division. -Zone of hypertrophic cartilage: cells enlarge and remain in columns. -Zone of calcified cartilage: dead chondrocytes, extracellular matrix calcified, osteoclasts dissolve calcified matrix, and osteoblasts form bone over calcified cartilage.

PTH (Parathyroid Hormone)

Increases blood calcium by: -Stimulating osteoclasts -Stimulating calcitrol formation

Two Types of Ossification That Occur:

Intramembranous ossification: formation of bone directly from or within fibrous connective tissue membranes. Endochondrial ossification: formation of bone from hyaline cartilage models (most bones)

Osteomalacia

Lack of Vitamin D

Development of Bone Tissue

Mesenchymal cells (only in fetal development) transform into chondroblasts.

Stress Fracture

Microscopic fissures from repeated strenuous activities.

Closed Fracture

No break in the skin.

Factors Affecting Growth

Nutrition: -Vitamin C for collagen formation -Vitamin K and B12 for protein synthesis. Sufficient levels of specific hormones: -insulin-like growth factor -promotes cell division at epiphyseal plate

Greenstick Fracture

One side broken, other side bends

Impacted Fracture

One side of the fracture driven into the interior of the other side.

Bone

Osseous tissue. Connective tissue: widely spaced cells separated by matrix.

4 Types of Cells in Bone Tissue

Osteogenic: starts with Osteoblasts: stem cell; creates new bone Osteocytes: maintain bone Osteoclasts: break down bone tissue

Hormonal Abnormalities

Oversecretion of hGH during childhood produces giantism. Undersecretion of hGH or thyroid hormone during childhood produces short stature. Lack of estrogen receptors on cells grow taller than normal.

Treatments fro Fractures

Reduction: brought into alignment. -Closed Reduction: manual manipulation -Open Reduction: surgical with internal fixation devices.

Bone Remodeling

Remodeling is the ongoing replacement of old bone tissue by new bone tissue. -Old bone is constantly destroyed by osteoclasts. -New bone is constructed by osteoblasts. -Several hormones and calcitrol control bone growth and bone remodeling. (estrogen)

Open (Compound) Fracture

Skin broken.

Compact Bone

Strongest form Under periosteum Resists stresses produced by weight and movement. Connect to periosteum by: -Transverse canals -Longitudinal (central) canals Osteon Structure: -Concentric lamella: rings of calcified matrix -Lacunae: spaces between rings -Caniliculi: fluid filled canals radiating from lacunae -Osteocytes: bone cells inside caniliculi.

Functions of the bone and the skeletal system

Support: -Soft tissues -Provide attachment points Protect: -Internal organs Assist in movement: -Muscles pull on bones Mineral Homeostasis: -Store minerals (Calcium and Phosphate) Blood cell production: -Red bone marrow (hemopoiesis) Triglyceride storage: -Yellow bone marrow (energy source)