bone development

A doctor oberves a teenager who noticed that one of his legs is about two inches longer than the other. He also sees that the patient had broken one of his legs when he was 8 years old, but the patient's notes don't indicate which leg. What conclusion is the doctor likely to come to?

• The patient broke the shorter leg on the diaphysis.

• The patient broke the shorter leg on the epiphyseal plate.

• The patient broke the longer leg on the epiphyseal plate.

• The patient broke the longer leg in the diaphysis.

Answer explanation

The epiphyseal plate is the site of longitudinal growth in bones. The patient likely broke the leg along the plate, which caused it to grow less than the other leg.

Which of the following is true relating cartilage to the skeletal system?

• Cartilage is not found in joints and vertebral discs

• Cartilage is an intermediate that is stiffer than muscle, but softer than bone

• There are two types of cartilage

• Cartilage has the ability to regenerate

Answer explanation

Cartilage is a flexible, avascular connective tissue. It is less flexible than muscle, but softer and more flexible than bone. These properties make it an ideal candidate for joints, providing a medium between the muscles and bones that enact forces on the joint. Cartilage is found on the epiphyses of long bones and between certain bones, such as vertebrae, to cushion the motion of the joints.

Due to its avascular nature, cartilage does not easily regenerate. It is formed by chondroblasts (cartilage cells) in a chondrin matrix. In endochondral ossification, cartilage can be used as a precursor to bone, but will never be formed as a result of bone breakdown. Finally, there are three types of cartilage: elastic cartilage, hyaline cartilage, and fibrous cartilage.

The diaphysis is able to grow in length because of thin layers of cartilage cells located in which of the following regions?

• Haversian canal

• Epiphyseal plate

• Periosteum

• Marrow

Answer explanation

Thin layers of cartilage cells in the epiphyseal plate enable the diaphysis (bone shaft) to grow in length. The epiphyseal line forms when growth stops and ossification occurs, permanently fusing the diaphysis and epiphysis.

The periosteum is a tough connective tissue sheath that covers the outer surface of bones. The medullary cavity is a hollow cylinder inside the diaphysis. The medullary cavity contains bone marrow, which contains blood cells in different stages of development. The Haversian canals perforate bony structure and contain blood vessels, lymph vessels, and nerves. 

What type of bone cell is responsible for resorbing bone tissue?

• Lacunae

• Osteocytes

• Osteoclasts

• Osteoblasts

Answer explanation

Osteoclasts are bone cells that are responsible for resorbing—or breaking down—bone tissue. Osteoblasts, on the other hand, deposit bone tissue.

Cartilage is not a type of bone cell at all; it is a type of connective tissue consisting of chondrocytes suspended in an avascular matrix. Lacunae are small cavities within the bone matrix that house osteocytes; osteocytes are mature bone cells.

How do bones maintain a functional weight as they grow?

• Osteocytes create new Haversian systems to limit the bone weight

• Osteocytes form long fibers around the medullary cavity

• Osteoclasts lining the medullary cavity remove interior layers of matrix

• Osteoblasts secrete acidic compounds, which dissolve some of the adjoining matrix

Answer explanation

Osteoclasts dissolve bony matrix and repatriate calcium as the bone grows. This expands the meduallary cavity and maintains a manageable mass for the bones, while allowing the body to recycle valuable calcium deposits.

Where are osteocytes located?

• Beneath the periosteum

• Throughout the hydroxyapatite matrix

• The lacunae of Haversian systems

• the lining of the medullary cavity

Answer explanation

Osteoytes, the long-lived star-shaped cells found in established bones, are primarily found within Haversian systems—the target-shaped tubes of bone matrix. They are encased in a bubble of interstitial fluid known as a lacuna.

An adolescent girl is suffering from reduced longitudinal bone growth in her humerus. Which of the following bone regions should be examined closely in order to determine the cause of the growth deficiency?

• The periosteum

• The diaphysis

• The epiphyseal plate

• Articular cartilage

Answer explanation

Longitudinal bone growth occurs at the epiphyseal plate through the process of endochondral ossification. Cartilage cells undergo rapid mitosis in this region forming the structure that is later replaced by bone tissue.

In childbirth, the child’s skull is flexible due to fontanelles, or soft regions that are composed of connective tissue. Through what process does the connective tissue of the infant’s skull become bone?

• Intramembranous ossification

• Bony secretion

• Endochondral ossification

• Compact bone resorption

Answer explanation

Intramembranous ossification is the process in which bones are formed within dermal tissue. This process is responsible for forming the flat bones of the skull, as well as the clavicle. Other bones of the body are formed by the process of endochondral ossification, in which cartilage is replaced by bone tissue.

what causes rickets

• vitamin D deficiency

• vitamin c deficiency

• calcium deficiency

• phosphate deficiency

you a examine a 3o year old man who had fracture of the tibia one month ago and find out there is pus oozing from the fracture site. what could be the cause

• osteoporosis

• osteomyelitis

• osteomalacia

• osteogenesis

Answer explanation

osteomyelitis is Infection of the bone with charactristic pus from the fracture site.

osteoporosis is In this condition bone mass (the amount of bone tissue) is

reduced because its deposition does not keep pace with

resorption. osteomalacia caused by deficiency

of vitamin D which promotes calcification of bone

and absorption of calcium in the small intestine.