Chapter 6: Skeletal System

two characteristics of skeletal cartilage

no blood vessels or nerves

perichondrium

layer of dense connective tissue surrounding cartilage like a girdle

function of the perichondrium

• helps cartilage resist outward expansion

• contains blood vessels for nutrient delivery to cartilage

cells that make up cartilage

chondrocytes

three types of cartilages

Appositional and Interstitial growth

two ways that cartilage grows

seven important functions of bones

support, protection, movement, mineral and growth factor storage, blood cell formation, triglyceride (fat) storage, and hormone production

Hematopoiesis

blood cell formation that occurs in red marrow cavities of certain bones

Osteocalcin

secreted by bones to regulate insulin secretion, glucose levels, and metabolism

long bones, short bones, flat bones, irregular bones

four types of bones (shape)

compact bone

dense outer layer on every bone that appears smooth and solid

spongy bone

made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae

periosteum

white, double-layered membrane that covers external surfaces except joints

endosteum

• delicate connective tissue membrane covering internal bone surface

• covers trabeculae of spongy bone

fibrous layer and osteogenic layer

two layers of periosteum membrane

Fibrous Layer

outer layer of periosteum, formed by dense irregular connective tissue consisting of Sharpey’s fibers that secure to bone matrix

Osteogenic Layer

inner layer of periosteum, contains primitive osteogenic stem cells - contains nerve fibers and blood vessels

osteogenic cells, osteoblasts, osteocytes, bone-lining cells, and osteoclasts

five major cell types found in bone tissue

Osteogenic Cells

• mitotically active stem cells in periosteum and endosteum

• some differentiate into osteoblasts or bone-lining cells when stimulated

Osteoblasts

bone forming cells that secrete unmineralized bone matrix called osteoid - actively mitotic

Osteocytes

• mature bones in lacunae that no longer divide

• maintain bone matrix and act as stress or strain sensors

Bone-lining cells

(periosteal cells and endosteal cells) flat cells on bone surfaces believed to also help maintain matrix

Osteoclasts

giant, multinucleate cells that function in bone resorption - breakdown of bone

Resorption

breakdown of the bone

Spongy bone

this type of bone there are no osteons present, but trabeculae contain irregularly arranged lamellae and osteocytes interconnected by canaliculi

components of Osteoid

ground substance and collagen fibers- contribute to tensile strength and flexibility of bone

Hydroxyapatites (mineral salts)

inorganic component of bones - consist mainly of tiny calcium phosphate crystals in and around collagen fibers - responsible for hardness and resistance to compression

Ossification

process of bone tissue formation

month 2

formation of bony skeleton begins in month ______ of development

Endochondral ossification

bones form by replacing hyaline cartilage (cartilage bones)

Intramembranous ossification

bone develops from fibrous membrane (membrane bones)

1. bone collar forms around diaphysis of cartilage model

2. Central cartilage in diaphysis calcifies, then develops cavities

3. Periosteal bud invades cavities, leading to formation of spongy bone

4. Diaphysis elongates, and medullary cavity forms

5. epiphyses ossify

5 steps in process of ossification

primary ossification center

endochondral ossification begins at the _________ in center of shaft

parathyroid hormone (PTH) and Calcitonin

two types of hormonal controls in bone remodeling

Calcitonin

this is produced (hormonal response) then there are high levels of blood calcium

Parathyroid hormone (PTH)

this is produced (hormonal response) then there are low levels of blood calcium

hypocalcemia

a medical condition where there are low levels of calcium in the blood

hypercalcemia

a condition where there is too much calcium in the blood, usually due to excessive bone resorption

Wolff’s law

a theory that descibes how bones adapt to mechanical stress - Bones in healthy animals remodel themselves to become stronger when they are subjected to increased loading. This process is called bone remodeling

Comminuted, Compression, Spiral, Epiphyseal, Depressed, and Greenstick

six most common types of fractures

Comminuted

a type of fracture when the bone fragments into three or more pieces

Compression

a type of fracture where the bone is crushed

Spiral

a type of fracture where a ragged break occurs when excessive twisting forces are applied to a bone - common sports fracture

Epiphyseal

a type of fracture where the epiphysis separates from the diaphysis along the epiphyseal plate

Depressed

a type of fracture where broken bone portion is pressed inward - typical skull fracture

Greenstick

a type of fracture where the bone breaks incompletely

Osteomalacia

disease of poorly mineralized bones

• calcium salts not adequately desposited

• results in soft, weak bones

Rickets

osteomalacia of children - vitamin D deficiency or insufficient diertary calcium

Osteoporosis

a group of diseases in which bone resorption > deposit - bone mass declines

Risk factors for osteoporosis

aged, postmenopausal women, insufficient exercise, diet lacking calcium and protein, smoking, genetics, hormone-related conditions, and consumption of alcohol or certain medications

calcium, vitamin D supplements, weight-bearing exercise, and hormone replacement therapy

ways to treat osteoporosis

calcium in diet, reduce consumption of carbonated beverages and alcohol, and weight-bearing exercise

ways to prevent osteoporosis

bone formation exceeds resorption

compare bone formation and resorption in children and adolescents