Physiology skeletal system + directional terms

Bone Marrow

Found in the hollow sections of bone, and in spongy bone

• Red – Primarily responsible for new blood cells of all varieties

• Yellow – Primarily responsible for producing/storing fat, producing bone tissue/cartilage, and producing red blood cells during emergencies

Both – house stem cells

Osteoblasts

Cells that produce new bone tissue, these cells are responsible for ossification. They secrete enzymes that dissolve the bone matrix, releasing calcium and phosphate into the bloodstream.

Osteocytes

They are matured osteoblasts that have become entrapped within the bone matrix. They form when an Osteoblast finishes its job. While trapped, they monitor the health of the bone.

Osteoclasts

cells that break down and reabsorb bone tissue when needed. They make space for osteoblasts to create new bone tissue in areas that are growing or need repair. If osteoblasts are builders, osteoclasts are your bones' demolition crew. (think “remodeling” a house)

Osteogenic cells

Stem cells that can develop into osteoblasts. Osteogenic cells differentiate and develop into osteoblasts which, in turn, are responsible for forming new bones.

Ossification

The process of bone formation. Our bones actually start as cartilage

1.Starting around the center, Osteoblasts produce bone tissue while the cartilage is digested simultaneously. This process progresses outwardly

1. Blood vessels (among other things) form in the new  canals, and allow various bone cells to transfer in/out

2. Mineralization occurs afterwards 

Calcium Regulation

• Your body must maintain the correct balance of calcium between bones and blood

  • Osteoblasts need Ca to make new bone tissue

  • Bone tissue needs Ca to remain strong

  • Blood needs Ca to deliver to nerves/muscles so that they function properly

  • Osteoclasts provide an increase of Ca when they break bone tissue down

Hormone and Calcium regulation

• Hormones PTH and calcitonin work to maintain a balance between those needs

• When blood Ca levels fall, PTH works to bring it back up by

  • Having osteoclasts break down bone tissue for Ca ⇒ send to blood

  • Telling the body to ingest/retain more Ca

• When blood Ca levels rise, calcitonin works to bring it back down by

  • Preventing osteoclasts from breaking down bone ⇒ keeps Ca in bones

  • Telling the body to excrete more Ca

  • Stimulating the transference of blood Ca to bones*

superior

above; or more towards the head

inferior

below; or way from the head

anterior

towards the front; towards the belly

posterior

towards the back

medial

closer to the midline of body or structure

lateral

further from the midline of body structure

proximal

nearer to the point of attachment

distal

further from point of attachment

superficial

towards, or on the surface

deep

away from the surface of the body