Bone - 1 -- VTPP 435

Bone - 1 -- VTPP 435

What stimulates Bonegrowth

Load Force

How does bone grow?

grows vertically and elongates to keep its shape

Trabecular Bone

forms a lattice calcified lattice of bone matrix

Osteoclast

-multi nucleus
-differentiate from macrophages that are derivatives of bone marrow white blood cell
-have ruffled border

Osteocyte

-most long lived cell in human body
-senses mechanical load
-located in a lacuna
-are in rings

Canaliculi

-connection from osteocyte to osteoblast and nerves and vessels
-sends info about load or force

RANK L

-created and released by osteoblasts to ramp up osteoclast activity
-binding makes osteoclasts differentiate

Osteoblast

-follow osteoclasts to make bone
-have PTH receptors
-derived from mesenchymal cells

1,25 (OH)2 Vitamin D3 Active Form

1) hydroxylated in liver to 25-(OH)2 Vitamin D
2) hydroxylated in kidney to 1,25-(OH)2 Active Form
-1 alpha hydroxylate in kidney controlled by PTH
-vitamin D acts on small intestine to absorb Ca2+ & PO43-

Parathyroid Hormone (PTH)

-activates osteoblast/osteocyte to release RANKL
-acts on intestines, kidneys and bone

Calcitonin

-peptide hormone
-made in thyroid
-inhibits osteoclast
-stimulated by increased Ca2+

Ca2+ Sensing Receptor

-sensor on Parathyroid of high Ca2+
-inactivated due to lack of Ca2+ --> increased PTH
-is a GCPR Receptor

G protein-coupled receptor (GCPR)

1) Signal binds to GCPR & ativates G-protein
2) G-protein turns on adenylyl cyclase
3) Adenylyl cyclase converst ATP --> cAMP
4) cAMP turns on Protein Kinase A
5) Protein Kinase A phosphorylates other proteins to cause a change

4 Main Ca2+ Functions

1) Muscle Contraction
2) Neurotransmitter & Hormone Release
3) Exocrine Secretion
4) Enzyme Activation

Parathyroid Hormone Receptor (PTHR)

-made in kidney and bone cells
-expressed by osteoblasts