Bone Function
Bones are also involved in blood cell formation. Blood cells are originally formed through hematopoiesis in the yolk sac. Hematopoiesis (blood cell production) is then performed in the marrow. There are two types of marrow: red and yellow.
Red marrow functions in the formation of red blood cells, white blood cells, and platelets. It is found in the spongy bone. Spongy bone is most commonly found in the skull, ribs, sternum, clavicle, vertebrae and pelvis.
Yellow marrow occupies the cavities of most bones and is responsible for fat storage.
Storage Functions of Bone
Inorganic minerals and salts are stored in the inorganic matrix of bone. Calcium phosphate is the most common form and is very important in many metabolic processes. Extra calcium is stored in bone for the body to utilize when needed. When blood levels of calcium are low, calcium is released from the bone to increase blood calcium levels. The body works to maintain consistent blood calcium levels and will sacrifice calcium density in order to maintain blood calcium levels – the blood calcium has higher priority.
Bones also store magnesium, sodium, potassium and carbonate. Bones can also store harmful materials, such as lead.
Questions:
What is the term for red blood cell production? _________________________________________
What type of bone is hematopoiesis performed in? ______________________________________
Name several bones with spongy bone? _______________________________________________
What function does yellow marrow perform? ___________________________________________
Where is yellow marrow located? ____________________________________________________
What else does red marrow produce __________________________________________________
The most common storage form of calcium in the bone is called ___________________________ .
The body uses bones as a calcium reservoir so that it can maintain _____________ calcium levels.
Is the body willing to severely deplete bone calcium for the blood? Yes or No? _______________
Why do you think it is willing to do this? ______________________________________________
What is the term for decreased bone density? ___________________________________________
Since lead is accumulated in bones and very dense, would lead show up on an x-ray Y/N ________
Control of Calcium in the Blood and Bone
The body works to maintain calcium levels within a small range for homeostasis. If calcium levels begin to rise, receptors in the thyroid gland trigger the thyroid to release calcitonin. Calcitonin is a hormone that travels through the bloodstream and into bone to activate osteoblasts. Osteoblasts absorb calcium from the blood and deposit it into the bone. This process decreases blood calcium levels and increases bone calcium storage levels. When blood calcium levels return to normal, the thyroid gland stops releasing calcitonin; which shuts off the osteoblasts and stops calcium storage.
When blood calcium levels are too low, receptors in the parathyroid gland sense the drop of blood calcium. The parathyroid gland releases parathyroid hormone which travels through the bloodstream to the bone. There it triggers osteoclasts to break down bone and release calcium into the bloodstream to raise calcium levels. When calcium levels return to normal the parathyroid hormone stops releasing parathyroid hormone, which shuts off the release of calcium from the bone.
Questions:
For homeostasis, does the body care about blood or bone calcium levels? _____________________
Which gland has receptors for measuring high calcium levels? ______________________________
What hormone does it release? _______________________________________________________
What cell does that hormone act on? __________________________________________________
What does that cell do when activated? ________________________________________________
What stops that cell from functioning? _________________________________________________
What gland measures low calcium levels? ______________________________________________
What hormone does the gland release? _________________________________________________
What cell does the hormone act on? ___________________________________________________
What does activating this cell produce? ________________________________________________
Tougher Questions:
What would happen if you did not have a thyroid gland? __________________________________
What would happen if you did not have a parathyroid gland? _______________________________
What would happen if osteoblasts did not respond to calcitonin? ____________________________
What would happen if your kidneys were losing large amounts of calcium per day. Much more than you are consuming in your diet? __________________
Would this produce a net loss of calcium out of the body Yes/No ___________________________
How would your body respond? _____________________________________________________
How long would your body continue stealing calcium from the bone to maintain blood levels? _________________________________
Would this create a higher risk of stress fractures? ________________________________________
What would need to be done to resolve the problem? _____________________________________