MCAT Biology : Types of Bone Cells

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

Example Question #1 : Types Of Bone Cells

__________ function to synthesize bone tissue and __________ function to reabsorb bone tissue.

Possible Answers:

Osteoblasts . . . osteoblasts

Osteoblasts . . . osteoclasts

Osteoclasts . . . osteoclasts

Osteoclasts . . . osteoblasts

Correct answer:

Osteoblasts . . . osteoclasts

Explanation:

Bones consist of two types of cells that regulate bone growth: osteoblasts and osteoclasts. Osteoblasts lay down collagen and other important organic substances that are required to synthesize bone tissue, whereas osteoclasts reabsorb existing bone tissue. The activity of both cells is important for repair, growth, and maintenance of bone tissue.

Note that a third type of cell, osteocytes, is also found in bone, but does not play as much of an active role in maintaining bone structure.

Example Question #1 : Types Of Bone Cells

Several tests reveal that a unknown hormone reverses the effects of parathyroid hormone. What can you conclude about this unknown hormone?

Possible Answers:

It decreases osteoblast activity and increases blood calcium levels

It decreases osteoblast activity and decreases blood calcium levels

It decreases osteoclast activity and increases blood calcium levels

It decreases osteoclast activity and decreases blood calcium levels

Correct answer:

It decreases osteoclast activity and decreases blood calcium levels

Explanation:

The question states that the unknown hormone has the opposite effect of parathyroid hormone. Recall that parathyroid hormone functions to increase blood calcium levels; therefore, this unknown hormone must decrease blood calcium levels.

When blood calcium levels increase due to parathyroid hormone, osteoclasts in bones break down the bone matrix and release the calcium into the blood. This means the activity of the unknown hormone must inhibit the activity of osteoclasts to decrease blood calcium levels. This hormone is most likely released to prevent bone loss.

The unknown hormone in this question would most likely be calcitonin. Calcitonin decreases blood calcium levels and is very important in menopausal and pregnant women who have a higher risk of having excessive bone loss.

Example Question #12 : Bone

A researcher takes a sample of bone tissue and observes a cell under a microscope. He notices that the cell is in the process of breaking down its nuclear membrane. Based on this information, what can the researcher conclude about this cell?

Possible Answers:

The cell can be either an osteoblast or an osteoclast

The cell is an osteoclast

The cell cannot be an osteoblast or an osteoclast

The cell is an osteoblast

Correct answer:

The cell cannot be an osteoblast or an osteoclast

Explanation:

The question states that the cell is breaking down its nuclear membrane. Recall that the nuclear membrane is broken down during prophase of mitosis or prophase I of meiosis; therefore, the cell must be undergoing either mitosis or meiosis. One of the key characteristics of osteoblasts, osteocytes, and osteoclasts is that they do not undergo mitosis. Also, remember that only germ cells undergo meiosis. Since the observed cell is undergoing a division, the researcher can conclude that the cell is not an osteoblast or an osteoclast.

Osteogenic cells, however, can undergo mitosis. Osteogenic cells are cells that differentiate into osteoblasts. Once differentiated, the osteogenic cells can no longer undergo mitosis.

Example Question #3 : Types Of Bone Cells

Which cells are responsible for building bone?

Possible Answers:

Osteomites

Osteoclasts

Marrow

Osteoblasts

Myofibrils

Correct answer:

Osteoblasts

Explanation:

Osteoblasts form bone by crystalizing calcium phosphate around collagen.

Example Question #2 : Types Of Bone Cells

A normally active man is in a coma after a major car accident. He remains hospitalized until he wakes up three weeks later. After waking, he finds himself unable to return immediately to his previous activity level. Tests show that he has experienced a decrease in muscle tone and bone mass.

During the man's hospitalization, which of the following cells was likely most active?

Possible Answers:

Cell activity did not change

Osteoclasts 

Osteoblasts 

Myoblasts

Correct answer:

Osteoclasts 

Explanation:

Osteoclasts are responsible for bone resorption and osteoblasts are responsible for bone re-formation. While bed-ridden, this man will have a decrease in osteoblast production since he was not moving during the three weeks he was in a coma. His osteoclast production, however, would probably stay the same as it was before the accident (and therefore the man would experience atrophy during his time of being immobile).

Example Question #6 : Types Of Bone Cells

Parathyroid hormone (PTH) is responsible for increasing blood calcium levels in the body. Which cell in the bones would be stimulated by PTH in order to increase blood calcium levels?

Possible Answers:

Osteocytes

Osteoclasts

Macrophages

Osteoblasts

Correct answer:

Osteoclasts

Explanation:

Osteoclasts are responsible for resorbing bone matrix and releasing key minerals, including calcium, back into the bloodstream. They are stimulated by parathyroid hormone when blood calcium levels are low.

Osteoblasts build bone matrix and later differentiate into osteocytes, which preserve the bone tissue.

Example Question #7 : Types Of Bone Cells

Which of the following would increase blood calcium concentration?

Possible Answers:

Increasing osteoclast activity

Increasing calcitonin levels in the blood

Decreasing parathyroid hormone levels in the blood

Increasing osteoblast activity

Correct answer:

Increasing osteoclast activity

Explanation:

This question requires a strong understanding of factors affecting bone resorption and bone re-formation.

Bone re-formation takes place when osteoblasts use calcium and phosphate from the blood to form bone. Calcitonin stimulates osteoblasts to form bone. Parathyroid hormone (PTH), on the other hand, stimulates bone resorption and causes osteoclasts to break down bone, causing blood calcium and phosphate levels to increase.

Of the possible answers, only increased osteoclast activity would result in higher blood calcium levels. Increased osteoblast activity, decreased parathyroid hormone, and increased calcitonin would all result in lower blood calcium levels.

Example Question #3 : Types Of Bone Cells

Which of the following cell types would be inhibited in the event of hypercalcemia?

Possible Answers:

Osteoclasts

Osteocytes

Hematopoietic stem cells

Osteoblasts

Osteogenic cells

Correct answer:

Osteoclasts

Explanation:

In the event of hypercalcemia the body has elevated blood calcium levels. As a result, osteoclasts, which are responsible for the resorption of bone matrix and the release of calcium into the bloodstream, would experience reduced function.

Osteoblasts, in contrast, help to synthesize bone and would be stimulated by high blood calcium levels to remove calcium from the blood and sequester it in bone. Osteocytes, sometimes known as osteogenitor cells, are the progenitor cells to osteoblasts.

Example Question #4 : Types Of Bone Cells

After a bone fracture, what cells function to repair the damage of the injury?

Possible Answers:

Osteoclasts

Osteocytes

Osteodentins

Osteons

Osteoblasts

Correct answer:

Osteoblasts

Explanation:

After a fracture, osteoblasts—bone forming cells—start to produce new bone through the process of osteogenesis. They produce compact bone and fuse the bone segments together.

An osteocyte is a mature bone cell. Osteoclasts are cells that dissolve the bony matrix. An osteon is a unit of hard bone with embedded osteocytes that surround a central (Haversian) canal containing a capillary. Osteodentin is calcification resembling bone that forms very rapidly in response to trauma, such that cells and blood vessels are incorporated. 

Example Question #10 : Types Of Bone Cells

 What structure serves to connect different Haversian canals and provides a means for communication and nutrient transport?

Possible Answers:

Osteoarterials

Trabeculae

Volkmann canals

Lymph vessels

Canaliculi 

Correct answer:

Volkmann canals

Explanation:

Volkmann canals connect different Haversian systems, allowing the osteocytes within their lacuna to communicate via chemical and cellular signalling.

Canaliculi form a "spiderweb" of tiny channels to facilitate communication between osteocytes within a single Haversian system, but do not permit communication between different osteons.

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