Bone Cells & Tissue

cells, tissue, growth, diseases

What are the cell types of the bone?

osteocytes, osteoblasts, osteoclasts, and osteogenic cells

osteocytes

mature osteoblasts that cannot divide and are entrapped in hardened bone matrix and they sense stimuli and send signals to osteoblast and osteoclasts to begin remodeling or repair process

osteoblasts

helps form new bone by secreting substances that make up bone matrix

osteogenic cells (osteoprogenitor cells)

stem cells that produce cells that differentiate into osteoblasts and are important in fracture repair

osteoclasts

remove and remodel bone matrix that is unwanted or unhealthy and are multinucelated

bone matrix

1/3 of bone weight is collagen fibers and 2/3 of weight is calcium phosphate

tensile strength

collagen fibers in bone matrix make bone highly resistant to stretching forces

compressional strength

calcium salts allow bones to resist strong squeezing forces

torsional strength

bone lacks ability to endure twisting

What are the two types of bone tissue?

spongy bone and compact bone

spongy bone

light and porous, found in the ends of long bones and middle of most other bones surrounded by compact bone, consists of latticework of bone (trabeculae) that adds strength but no weight, and has no blood vessels but the marrow found in trabeculae supplies nutrients

compact bone

dense and solid which offers strength which is why it forms the shafts of the long bone and outer surfaces of bone. consists of many canals and passages that contain and serve blood vessels

periosteum

wraps the superficial layer of compact bone and isolates bone from surrounding tissue, acts as a route for blood and nervous supply, and actively participates in bone growth and repair

endosteum

cellular layer lining medullary cavity, is active during bone growth, repair, and remodeling, covers spongy bone, lines central canals, and consist of simple layer of osteogenic cells

bone marrow

a type of soft tissue that fills the medullary cavity of long bone and spaces of spongy bones

red bone marrow

in charge of producing red blood cells

yellow bone marrow

replaces red bone marrow and is saturated with fat so it no longer produces red blood cells and can change back into red marrow in severe cases

Ossification

forms of bone development for either fibrous connective tissue or cartilage

intramembranous ossification

ossification of fibrous connective tissue and begins with stem cells differentiating into osteoblasts which then deposit bone matrix

endochondral ossification

bone evolves from cartilage and begins when osteoblasts replace chondrocytes and coat diaphysis in a thin layer of bone creating a ring that begins to calcify

bone lengthening

grows for a fixed period of time and occurs at epiphyseal plate

bone widening and thickening

happens throughout lifespan and occurs when osteoblasts in periosteum lay down new layers of bone around the outside of the bone while osteoclasts dissolve inner bone tissue widening marrow cavity

remodeling

osteoclasts remove matrix and reduce mass of little used bones (repairs minor traumas and contributes to homeostasis and leads to projections and surface markings)

What does the maintenance of bone density depend on?

balance of work between osteoclasts (reabsorption) and osteoblasts (ossification)

osteoporosis

condition where bones lose so much mass they become extremely brittle and minor stress can cause a fracture

pituitary growth failure

inadequate growth hormone, abnormally short bones

marfan’s syndrome

inherited metabolic condition that causes excessive cartilage formation at epiphyseal cartilages that results in a very tall person with long, slender limbs and cause cardiovascular problems

gigantism

overproduction of growth hormone before puberty and is commonly cause by a pituitary tumor

acromegaly

overproduction of growth hormone after epiphyseal plate closes leading to bones becoming thicker instead of longer

Calcium in the body

calcium and phosphate ions are absorbed in the intestines and is then lost in the urine. normals levels lead to balance of osteoblasts and osteoclasts

What is the response to low calcium ion levels in blood?

Parathyroid Gland Response

Parathyroid Gland Response

Bone response: mature osteoclasts break down bone matrix releasing stored calcium ion

Intestinal response: increased rate of calcium ion absorption

Kidney response: increased production of calcitriol and increase calcium ion reabsorption

What is the response to high calcium ion levels in blood?

Thyroid gland response

Thyroid Gland Response to high calcium ion levels

Bone response: osteoclasts stop; osteoblast continue to deposit calcium ions in bone matrix

Intestinal response: decreased rate of calcium ion absorption

Kidney response: decreased calcium ion reabsorption (more lost in urine)