chapter 6: bone tissue

what is bone tissue made up of?

(5 main ones)

cartilage

dense connective tissue

epithelium

adipose tissue

blood forming tissue

what is bone tissue?

a continual flex of breaking down old bone and building new bone

functions of bone tissue include:

support

protection

assistance with movement

mineral homeostasis

red bone marrow producing RBC, WBC, and platelets

yellow bone marrow storing triglycerides

what does mineral homeostasis release?

Ca(2+) = calcium

PO4(2-) = phosphate

structure of bone include:

diaphysis

metaphysis

epiphysis

articular cartilage

periosteum

medullary cavity

endosteum

what are the bone cells?

osteogenic (progenitor) cells

osteblasts

osteocytes

osteoclasts

what is the function of osteogenic cells?

produce daughter cells through miotic division that will become osteoblasts

osteoblasts

helps build new bone tissue and matrix

osteocytes

mature cells of osteoblasts and exchanges waste and nutrients with blood

how do osteoblasts turn into osteocytes?

osteoblasts secret a matrix and entrap themselves in the collagen they make which become osteoblasts

osteoclasts

50 or more fused monocytes

releases powerful enzymes that breaks down bone in a process called resorption

compact bone characteristics

provides protection and support

80% of skeleton

contains osteons

osteonic canal

concentric lamellae

lacuna

canaliculi

spongy bone characteristics

makes up majority of flat, short, and irregular bones

20% of skeleton

protects red bone marrow

arranged at lines or stress to reduce stress and forces

where does spongy and compact bone get its nourishment from?

the medullary blood supply

true or false : bone grows away from blood supply

false, bone grows around its blood supply

what is osteogenesis and what are the 2 types?

process where bone forms

intramembraneous ossification

endochondral ossification

what is intramembraneous ossification?

bone formed through the differentiation of mesenchymal cells in fibrous connective tissue

steps of intramembraneous ossification

mesenchymal cells differentiate (mesenchymeosteogenic cells become osteoblasts and secretes matrix of osteoid)

osteoblasts turn into osteocytes matrix calcifies

matrix develops into trabeculae to form spongy bone

outer mesenchyme condenses forming the periosteum

what is the endrochondral ossification?

bone is formed from a cartilaginous model (eventually ossified)

what are the steps of endochondral ossification?

mesenchymal cells turn into chondroblasts which produces a model of future bone out of hyaline cartilage (including perichondrium surrounding it)

chondroblasts turn into chondrocytes interstitial and apositional growth continues

chondrocytes in the mid region hypertrophy (increase in size) leading to some bursting and their content lowers pH leading to calcification

nutrient artery stimulates osteogenic cells of the perichondrium to increase into osteoblasts which secretes a periosteal bone color and the region grows into a primary ossification center with the remnants of cartilage being transformed into trabeculae

primary ossification proceeds inward from the outside of the bone

as blood vessels enter the epiphysis a secondary ossification center is formed and ossification here proceeds outward from the center

this leaves an articulating surface of cartilage as well as an epiphyseal plate

4 zones of bone growth

bone grows along the epiphyseal lining in 4 zones

zone of resting cartilage

zone of proliferating cartilage

zone of hypertrophic cartilage

zone of calcified cartilage

zone of resting cartilage

anchors epiphyses

zone of proliferating cartilage

divides chondrocytes

zone of hypertrophic cartilage

chondrocytes increase in size

zone of calcified cartilage

dead calcified chondrocytes

osteoclasts move in dissolving matrix

osteoblasts beging creating new matrix

Insulin growth factors

Promotes cell division at the epiphyseal plate

Human growth factor

Stimulates insulin growth factor

Thyroid (T3&T4)

Contains thyroxine and helps promote bone growth by stimulating osteoblasts

Low thyroxine

Cretinism

High thyroxine

Microcephaly

Insulin

From pancreas affects growth and promotes bone growth by increasing synthesis of bone proteins

Sex steroids

Estrogen and androgens cause growth spurts and causes the epiphyseal to seal

Bone resorption

Removal of minerals and collagen fibers from bone by osteoclasts

Bone deposition

Addition of minerals and collagen fibers to bone by osteoblasts

What is the process of bone resorption?

Osteoclasts attach to endosteum and periosteum to form a leak proof seal at edges of ruffled border → releases lysosomal enzymes and acids into sealed pockets → enzymes digest fibers or organic substances while acids dissolve bone mineral → interstitial fluid and products of bone resorption diffuse into nearby capillaries and can be used for new bone formation

How do bones grow (appositional or interstitial)?

Appositional

Periosteal cellosteoblasts

Forms a matrix and ridges of matrix forms a groove for periosteal blood vessels

Ridges meet to form central canal

Osteoblasts form new concentric lamellae to periosteal BV

Osteomyelitis

Bone infection

Compound fracture

Bone pierces through the skin

Simple fracture

Bone doesn’t break the skin

Comminuted fracture

Bone breaks into 2 or more pieces (fragments)

Green stick fracture

Partial fracture on one side where the bone bends (mostly in young kids)

Impacted fracture

One end of the bone is forcefully driven into the other

Potts fracture

Fracture at distal end of the fibula

Colles fracture

Fracture at distal end of radius

Stress fracture

Tiny fissures caused by strenuous exercise

Fracture repair

Fracture hematoma forms (clot)

Phagocytes clean up area of cellular debris

Granular tissues (procallus eventually turns into fibrocartilage callus) which holds the ends of broken bone together

Conversion of fibrocartilagenous callus into spongy bone of bony callus to its nearly original form

Why is calcium important?

Neural functions

Enzymatic reactions

Blood clotting

Muscle contractions

Calcium level range

9-11

What does high Ca result in and what does low Ca result in?

High - cardiac arrest

Low - respiratory arrest

What is calcium regulated by?

Hormones, specifically parathyroid hormone (secreted by parathyroid gland)

Calcium homeostasis process

Low calcium is detected by parathyroid glands → gene in parathyroid cell detects intracellular increase → PTH synthesis increases and more PTH is released in blood

Presence of higher PTH levels increases number and activity of osteoclasts which increases bone resorption → PTH stimulates formation of calcitrol (promotes absorption from GI → blood)

Calcitonin

Hormone acts when calcium levels rise

How is calcitonin secreted?

By the parafollicular cell of thyroid gland

What is the role and function of calcitonin?

Inhibits activity of osteoclasts and speeds up deposition of calcium in bone formation to decrease blood calcium levels

Osteoporosis

Decreased bone mass and increased risk of fracture

Osteomalacia

Vitamin D deficiency (leads to weak bones)