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The osteoblast    is the bone cell responsible for forming new bone and is found in the growing portions of bone, including the periosteum and endosteum. Osteoblasts, which do not divide, synthesize and secrete the collagen matrix and calcium salts. As the secreted matrix surrounding the osteoblast calcifies, the osteoblast become trapped within it; as a result, it changes in structure and becomes an osteocyte    , the primary cell of mature bone and the most common type of bone cell. Each osteocyte is located in a space called a lacuna and is surrounded by bone tissue. Osteocytes maintain the mineral concentration of the matrix via the secretion of enzymes. Like osteoblasts, osteocytes lack mitotic activity. They can communicate with each other and receive nutrients via long cytoplasmic processes that extend through canaliculi    (singular = canaliculus), channels within the bone matrix.

If osteoblasts and osteocytes are incapable of mitosis, then how are they replenished when old ones die? The answer lies in the properties of a third category of bone cells—the osteogenic cell    . These osteogenic cells are undifferentiated with high mitotic activity and they are the only bone cells that divide. Immature osteogenic cells are found in the deep layers of the periosteum and the marrow. They differentiate and develop into osteoblasts.

The dynamic nature of bone means that new tissue is constantly formed, and old, injured, or unnecessary bone is dissolved for repair or for calcium release. The cell responsible for bone resorption, or breakdown, is the osteoclast    . They are found on bone surfaces, are multinucleated, and originate from monocytes and macrophages, two types of white blood cells, not from osteogenic cells. Osteoclasts are continually breaking down old bone while osteoblasts are continually forming new bone. The ongoing balance between osteoblasts and osteoclasts is responsible for the constant but subtle reshaping of bone. [link] reviews the bone cells, their functions, and locations.

Bone Cells
Cell type Function Location
Osteogenic cells Develop into osteoblasts Deep layers of the periosteum and the marrow
Osteoblasts Bone formation Growing portions of bone, including periosteum and endosteum
Osteocytes Maintain mineral concentration of matrix Entrapped in matrix
Osteoclasts Bone resorption Bone surfaces and at sites of old, injured, or unneeded bone

Compact and spongy bone

The differences between compact and spongy bone are best explored via their histology. Most bones contain compact and spongy osseous tissue, but their distribution and concentration vary based on the bone’s overall function. Compact bone is dense so that it can withstand compressive forces, while spongy (cancellous) bone has open spaces and supports shifts in weight distribution.

Compact bone

Compact bone is the denser, stronger of the two types of bone tissue ( [link] ). It can be found under the periosteum and in the diaphyses of long bones, where it provides support and protection.

Diagram of compact bone

A generic long bone is shown at the top of this illustration. The bone is split in half lengthwise to show its internal anatomy. The outer gray covering of the bone is labeled the periosteum. Within the periosteum is a thin layer of compact bone. The compact bone surrounds a central cavity called the medullary cavity. The medullary cavity is filled with spongy bone at the two epiphyses. A callout box shows that the main image is zooming in on the compact bone on the left side of the bone. On the main image, the periosteum is being peeled back to show its two layers. The outer layer of the periosteum is the outer fibrous layer. This layer has a periosteal artery and a periosteal vein running along its outside edge. The inner layer of the periosteum is labeled the inner osteogenic layer. The compact bone lies to the right of the periosteum and occupies the majority of the main image. Two flat layers of compact bone line the inner surface of the ostegenic periosteum. These sheets of compact bone are called the circumferential lamellae. The majority of the compact bone has lamellae running perpendicular to that of the circumferential lamellae. These concentric lamellae are arranged in a series of concentric tubes. There are small cavities between the layers of concentric lamellae called lacunae. The centermost concentric lamella surrounds a hollow central canal. A blue vein, a red artery, a yellow nerve and a green lymph vessel run vertically through the central canal. A set of concentric lamellae, its associated lacunae and the vessels and nerves of the central canal are collectively called an osteon. The front edge of the diagram shows a longitudinal cross section of one of the osteons. The vessels and nerve are visible running through the center of the osteon throughout its length. In addition, blood vessels can run from the periosteum through the sides of the osteons and connect with the vessels of the central canal. The blood vessels travel through the sides of the osteons via a perforating canal. The open areas between neighboring osteons are also filled with compact bone. This “filler” bone is referred to as the interstitial lamellae. At the far right of the compact bone, the edge of the spongy bone is visible. The spongy bone is a series of crisscrossing bony arches called trabeculae. There are many open spaces between the trabeculae, giving the spongy bone its sponge-like appearance.
(a) This cross-sectional view of compact bone shows the basic structural unit, the osteon. (b) In this micrograph of the osteon, you can clearly see the concentric lamellae and central canals. LM × 40. (Micrograph provided by the Regents of University of Michigan Medical School © 2012)

Questions & Answers

This app should be updated too much as there is very little information for some topics.I hope you will consider my information....
aman Reply
adenohypophysis is made up of what type of cells and what is the name of those cells?
Mannu Reply
armstrong Reply
motor root of the trigeminal nerve
what is the nervous system about
what passes through foramen ovale?
Farah Reply
what are the organelles of a cell
Amina Reply
muscular system
nucleus ribosome Golgi body call membrane cytoplasm
these are the cellular components that functions to provide energy,remove waste and cell division
Organelles of the cell are: Mitochondria,Ribosome,golgi apparatus, nucleus, secretory granules, nuclear e t c
how can we maintain the internal living things
Choolwe Reply
how many seconds does a human will stop if you sneeze
Kharl Reply
1 sec not specific
physiology of vision
Sudipta Reply
Can pure water become gel like?
ovie Reply
what is Homeostasis
Laura Reply
It is the ability of an organism to co ordinate it's internal environment so as to achieve balance in all areas
what is anatomy
Sandra Reply
what is physiology
The study of how the body works
the branch of biology dealing with the functions and activities of leaving organisms and their parts including all physical and chemical processes
the study of human body . phicically and chemically it's called anotomy physiology
the branch of biology dealing with the functions and activities of living organisms
which vein do we inject to give infusions
it is the scientific study of the body structure
What Choolwe Muselitata said is the definition of anatomy
Physiology can also be described as the way in which a living organism or bodily part functions
Anotomy is the science which we humen body of structure and function know as the anotomy
study of the body funtion and structure
functional study of the body
it is the study about the functions of body organs
what are the vital sign procedure
jeniffer Reply
You start the TPR then BP after explaining the procedure to the patient and your requirements ready.
which type of vein to you inject to give infusions?
how long do u take radial pulse
Flavian Reply
1 minute
You can take it for 15 seconds , the number you got you multiply wth 2
but in the aspect of the multiplying that isn't right
radial pulse kya hai?
for more accurate values you must do the 1 minute
1 minute.
60 seconds
1 minute
yes @sabina
What is homeostasis
Winter Reply
Homeostasis is the state of relative stability of the body's environment
what are fluids
fluid is a substance that has no fixed shape and yield easily to external pressure
Difference between hemostasis and homeostasis
Hemostasis is blocking or stopping blood flow from a damaged blood vessel by coagulation of that vessel or obstructing it.
Homeostasis is a balanced state. An equilibrium. The body does this by regulating itself by using hormones and neurotransmitters to keep chemicals balanced within the body.
Examples of site of homeostasis
For example, to much calcium in the blood would stimulate the release of calcitonin from the thyroid gland. Calcitonin will decrease calcium levels by depositing it into the skeleton. This is known as bone deposition, a homeostatic mechanism. Parathyroid hormone is the opposite to calcitonin.
There are a lot of homeostatic mechanisms in the body. Insulin and glucagon is another one. These two regulate glucose (sugar) levels in the blood. High glucose levels would cause insulin from the pancreas beta cells. Insulin lowers blood sugar. Glucagon increases blood sugar
what is the function of spleen
Bankole Reply
It filtrate and store the blood
it helps fight pathogens
old RBC are recycled in spleen and platelets and WBC are stored there
spleen is also called as graveyard of rbc
It control laughing
combing with stomach , it regulates digestion
In vertebrates, including humans, a ductless vascular gland, located in the left upper abdomen near the stomach, which destroys old red blood cells, removes debris from the bloodstream, acts as a reservoir of blood, and produces lymphocytes.

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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