Gary Carlson  
Medical and Biological Illustration

Osteoclasts remove excess bone by etching away at the bone surface. When they become overactive, osteoporosis may occur. [source]

Adipocytes, or fat cells, greatly increase in size over time as lipid droplets accumulate within the cytoplasm.  [source]

Schematic representation of neurotransmitters crossing between neurons showing the action of a drug for treating Alzheimer’s disease.[source]

Boney remodeling is a chronic process of replacement with minimal change in the gross shape of the bone structure. Osteoblasts and osteoclasts together are referred to as bone remodeling units. They work in concert together, coordinated via paracrine signaling by the osteoblasts. The constant remodeling allows for calcium homeostasis and the repair of microscopic daily stressors. The histology slide show demonstrates bone remodeling with osteoclasts resorbing one side of a bony trabecula and osteoblasts depositing new bone on the other side.

Three words of Piaget’s disease of bone:

  1. Excess activity of osteoclasts, destroying the bone. Shortly after the osteoblasts hurry to try to fix the bone, although haphazardly. The end result is a mozaic pattern of lamellar bone (the buzz word).
  2. Increased ALP (Alkaline Phosphatase) level in combination with a NORMAL calcium and phosphate. By the way, hydroxyproline is also elevated (FYI).
  3. Osteosarcoma. Risk is increased in patients with Paget’s disease of bone.

Image: Uploaded for Wikimedia Commons by user Laughlin Dawes.

Osteoclasts (shown) resorb bone over a period of weeks, and are especially active during periods of rapid remodeling (eg, after menopause). Because osteoclasts work faster than osteoblasts, the rate of bone loss may outpace the rate of bone production. During these periods, the newly produced bone is at increased risk for fracture because it is less densely mineralized, collagen has not matured, and resorption sites are temporarily unfilled.

Trabecular and Cortical Bone

Previously unknown by me, there are apparently two types of bone; trabecular and cortical.

Trabecular bone is often found within the inside of bones. It is characterized by a spongy appearance and is full of holes. It is in here that the bone marrow resides. In addition to the above functions and possessing a relatively light mass, the trabecular bone also serves to function as a reservoir of calcium and releases said element readily when the body runs low.

Cortical bone is the outer layer of bone. It is highly dense and accounts for the majority of the skeleton’s mass.

It is this conbination of cortical and trabecular bone that keeps the skeleton light and maintains the motility that humans possess.

Fun fact: the human skeleton is synthesized by special cells known as osteoclasts. These cells are responsible for renewing and maintaining the skeleton. The human skeleton is replaced, cell by cell, every ten years or so.

Got milk?

Here is a few things from my personal notes. Regarding Calcium homeostasis. Please note: there is more mechanisms of actions that can regulate Calcium such as : sympathetic/parasympathetic tone, alpha-1 receptors etc.

Increase in Ca+ will stimulate the Thyroid Gland to secrete Calcitonin in which will trigger the Kidneys to increase secretion of Ca+ and will also inhibit osteoclast activity. 

A decrease in Ca+ will trigger the Parathyroid Gland to secrete PTH in which will do the following; Stimulate osteoclast activity, Increase Ca+ reabsorption via- Kidneys , Increase in Calcitrol synthesis which will stimulate a increase in absorption of Ca+ by the digestive tract.

Black tea substance may treat bone loss

TOKYO :  Japanese researchers have found that a substance in black tea may be effective for treating osteoporosis, a disease that causes bones to become weak and brittle.
The team, including Keizo Nishikawa, assistant professor at Osaka University, found that theaflavin-3, or TF-3, a substance in black tea, blocks an enzyme – DNA methyltransferase – that increases osteoclasts, cells that destroy…

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The role of MicroRNAs in Osteoclasts and Osteoporosis.

The role of MicroRNAs in Osteoclasts and Osteoporosis.

RNA Biol. 2014 Nov 2;11(11):1355-1363

Authors: Tang P, Xiong Q, Ge W, Zhang L

Osteoclasts are the exclusive cells of bone resorption. Abnormally activating osteoclasts can lead to low bone mineral density, which will cause osteopenia, osteoporosis, and other bone disorders. To date, the mechanism of how osteoclast precursors differentiate into mature osteoclasts remains elusive. MicroRNAs (miRNAs) are novel regulatory factors that play an important role in numerous cellular processes, including cell differentiation and apoptosis, by post-transcriptional regulation of genes. Recently, a number of studies have revealed that miRNAs participate in bone homeostasis, including osteoclastic bone resorption, which sheds light on the mechanisms underlying osteoclast differentiation. In this review, we highlight the miRNAs involved in regulating osteoclast differentiation and bone resorption, and their roles in osteoporosis.

PMID: 25692234 [PubMed - as supplied by publisher]

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