Gross Anatomy of Bones - Structure of a Long Bone: Videos & Practice Problems

Long bones consist of two epiphyses (wider ends) and a diaphysis (shaft). The epiphysis contains spongy bone and is covered with articular cartilage for smooth joint movement. The diaphysis is made entirely of compact bone and houses the medullary cavity filled with yellow marrow. The metaphysis connects the epiphysis and diaphysis, featuring the epiphyseal plate, crucial for bone growth during puberty. Nutrient foramina allow blood vessels and nerves to enter the bone, ensuring its vitality and function.

Overview of Long Bones

Long bones are characterized by their unique structure, consisting of two ends known as epiphyses and a central shaft called the diaphysis. Each long bone has an epiphysis at both ends, which is the wider part of the bone. For example, the femur, the longest bone in the body, illustrates this structure well. The epiphysis is primarily composed of spongy bone on the inside, surrounded by a layer of compact bone on the outside. At the joints, the epiphysis is covered with articular cartilage, which provides a smooth surface for joint movement, reducing friction and preventing painful bone-on-bone contact.

The diaphysis, or shaft of the long bone, is distinctively made entirely of compact bone, making it thicker and stronger than the compact bone found at the epiphyses. This solid structure is crucial for supporting the weight of the body and withstanding stress during movement. Inside the diaphysis lies the medullary cavity, which is filled with yellow marrow in adults. This design, resembling a hollow pipe, optimizes the strength-to-weight ratio of the bone, allowing for both durability and lightness.

Connecting the epiphysis and diaphysis is the metaphysis, a region where the two structures meet. Within the metaphysis is the epiphyseal plate, commonly referred to as the growth plate, which is a line of hyaline cartilage that facilitates the lengthening of long bones during growth. This growth occurs until the end of puberty, after which the epiphyseal plate transforms into the epiphyseal line, a remnant of compact bone indicating that growth has ceased.

Understanding these components is essential for grasping how long bones develop and function. The epiphysis, diaphysis, and metaphysis each play critical roles in the overall structure and growth of long bones, contributing to the skeletal system's strength and flexibility.

Gross Anatomy of Bones - Structure of a Long Bone Example 1

Forensic analysis can utilize skeletal remains to estimate the age of an individual by examining specific structures within the metaphysis of long bones. The metaphysis is the widened end of a long bone, where the epiphyseal plate (or line) is located. This structure plays a crucial role in bone growth, particularly in children, where it is primarily composed of cartilage. As individuals mature, this cartilage is gradually replaced by compact bone, allowing forensic scientists to determine age based on the state of the epiphyseal plate.

In children, the epiphyseal plate is predominantly cartilage, which is less visible on X-rays. This cartilage facilitates the lengthening of bones during growth. As individuals transition into adolescence, the epiphyseal plate remains visible but begins to thin, indicating a slowdown in growth. In this stage, the line separating the diaphysis (the shaft of the bone) from the epiphysis (the end part of the bone) is still present, but the space is reduced as growth continues to decelerate.

By the time an individual reaches adulthood, the epiphyseal plate has completely ossified into compact bone, resulting in the absence of any visible space on X-rays. This transformation signifies the cessation of growth, marking a critical point in skeletal development. Understanding these changes in the epiphyseal plate across different life stages is essential for forensic scientists when estimating the age of skeletal remains.

During a skiing accident, Jean-Luc breaks the shaft of his humerus. What is the anatomically correct term for the portion of the bone that he broke?

• A. Metaphysis
• B. Epiphysis
• C. Diaphysis
• D. Articular Cartilage

Answer: (C)

Osgood-Schlatter disease is a painful condition that affects the proximal end of the tibia (a long bone) just distal to the knee. It primarily affects athletically active children between the ages of 10 and 14. The condition develops when the patellar tendon places strain on this area of the tibia as the area is not as stable as other regions of the bone in children this age. Why would this region not be as stable as other regions of the tibia?

• A. The medullary cavity does not fully develop until adulthood, meaning the yellow marrow would not provide shock absorption.
• B. The spongy bone of the epiphysis would not have fully calcified so the bone in that area would not be as hard.
• C. Articular cartilage is not fully formed until adulthood meaning there would be more stress in the joint.
• D. Children in this age are going through a growth spurt meaning there is a significant amount of cartilage in the epiphyseal plate.

Answer: (D)

Nerves and Blood Supply

Understanding the gross anatomy of bone, particularly the structure of long bones, involves recognizing the essential roles of nerves and blood supply. Bone is a living, dynamic tissue that requires a robust vascular and nervous system to function effectively. The outer layer of bone, known as compact bone, is dense and relatively impenetrable, necessitating specific entry points for blood vessels and nerves.

The primary entry point for these structures is the nutrient foramen, a small macroscopic hole typically located in the diaphysis (the shaft) of long bones. While most diaphyses contain a single nutrient foramen, there can be instances where more than one exists. This foramen allows the nutrient artery to enter the medullary cavity, supplying blood to the bone and the yellow marrow within. Conversely, the nutrient vein exits through this foramen, carrying deoxygenated blood away from the bone.

Inside the diaphysis, blood vessels and nerves branch out from the nutrient foramen, spreading throughout the medullary cavity to ensure adequate nourishment and signaling to the bone tissue. In contrast, the metaphysis and epiphysis regions of long bones feature multiple smaller holes, referred to as foramina, which accommodate the vascular and nervous supply in areas where spongy bone is present. This pattern is consistent across various bone types, not just long bones, where compact bone surrounds spongy bone.

In summary, the nutrient foramen serves as a critical conduit for the nutrient artery and vein, along with nerves, facilitating the essential blood supply and innervation of bone tissue. Understanding these anatomical features is vital for comprehending how bones maintain their health and functionality.

Gross Anatomy of Bones - Structure of a Long Bone Example 2

In this section, we explore the anatomy of a long bone, focusing on key components that contribute to its structure and function. The articular cartilage is a smooth tissue that covers the epiphysis at the joints, providing cushioning and reducing friction during movement. This cartilage is crucial for joint health and mobility.

Next, we identify compact bone, which forms the dense outer layer of the bone, providing strength and support. It is found both in the epiphysis and along the entire shaft, known as the diaphysis. The diaphysis is the long, tubular section of the bone that houses the medullary cavity.

The medullary cavity is the hollow center of the diaphysis, which contains bone marrow and is essential for the production of blood cells. Surrounding the bone is the periosteum, a protective connective tissue layer that plays a role in bone growth and repair.

Within the diaphysis, we also find the nutrient foramen, a small opening that allows blood vessels and nerves to enter the medullary cavity. The nutrient artery is the specific blood vessel that passes through this foramen, supplying essential nutrients to the bone.

Finally, the spongy bone is located within the epiphyses, characterized by a porous structure that helps reduce the weight of the bone while maintaining strength. This arrangement is vital for the overall functionality of long bones, allowing them to support weight and withstand stress during physical activities.

What problems would arise if a bone lacked a nutrient foramen?

• A. Bones would lose their tensile strength.
• B. The periosteum would not adhere to the bone properly.
• C. The articular cartilage would not form.
• D. Bones would lose blood supply and nerves.

Answer: (D)

Which bone structure is most closely associated with the perforating fibers?

• A. Nutrient Foramen.
• B. Periosteum.
• C. Medullary Cavity.
• D. Epiphyseal Plate.

Answer: (B)

Achondroplasia is the most common form of dwarfism. A person with this condition will have short arms and legs but a normal sized head and trunk. Achondroplasia literally means 'without cartilage formation'. Why would a disorder that affects cartilage formation lead to dwarfism?

• A. Cartilage is more prevalent in the limbs as there are more articulating joints in the arms and legs.
• B. Long bones grow in length at the epiphyseal plate, which is composed of cartilage until puberty.
• C. Long bones are covered with articular cartilage at joints. A lack of cartilage at the joint would inhibit growth.
• D. Without cartilage, the medullary cavity would not form properly shortening the diaphysis.

Answer: (B)

Where would you be more likely to find red marrow and why?

• A. The nutrient foramen, red marrow produces blood cells, and the nutrient foramen contains blood vessels.
• B. The endosteum, red marrow produces blood cells, and the endosteum contains progenitor bone cells.
• C. The epiphysis, red marrow is found in spongy bone, and spongy bone is found in the epiphysis.
• D. The diaphysis, the medullary cavity of the diaphysis is filled with marrow.

Answer: (C)

Here’s what students ask on this topic:

What are the main structural components of a long bone?

A long bone consists of two main parts: the epiphyses and the diaphysis. The epiphyses are the wider ends of the bone, containing spongy bone and covered with articular cartilage for smooth joint movement. The diaphysis, or shaft, is made entirely of compact bone and houses the medullary cavity filled with yellow marrow. The metaphysis connects the epiphysis and diaphysis and features the epiphyseal plate, crucial for bone growth during puberty. Nutrient foramina allow blood vessels and nerves to enter the bone, ensuring its vitality and function.

What is the function of the epiphyseal plate in long bones?

The epiphyseal plate, also known as the growth plate, is a line of hyaline cartilage located in the metaphysis of long bones. It is crucial for bone growth during puberty, allowing the bone to increase in length. As a person matures and reaches the end of puberty, the epiphyseal plate transitions into the epiphyseal line, converting to compact bone and ceasing further growth in length.

How does the structure of the diaphysis contribute to the strength of long bones?

The diaphysis, or shaft, of a long bone is made entirely of compact bone, which provides significant strength and rigidity. The compact bone forms a thick, solid outer layer, while the medullary cavity inside is hollow and filled with yellow marrow. This pipe-like structure offers an optimal strength-to-weight ratio, making the bone strong yet not overly heavy. Engineers have found that this design, similar to a hollow rod, provides excellent structural integrity.

What is the role of nutrient foramina in long bones?

Nutrient foramina are small holes located in the diaphysis of long bones, allowing blood vessels and nerves to enter the bone. These foramina are essential for supplying the bone with nutrients and oxygen, ensuring its vitality and function. The nutrient artery brings blood into the medullary cavity, while the nutrient vein carries blood out. In the metaphysis and epiphysis, several smaller foramina serve a similar purpose, facilitating the distribution of blood and nerve supply throughout the bone.

What is the difference between the epiphysis and diaphysis of a long bone?

The epiphysis and diaphysis are distinct parts of a long bone. The epiphysis is the wider end of the bone, containing spongy bone and covered with articular cartilage for smooth joint movement. In contrast, the diaphysis is the tubular shaft made entirely of compact bone, housing the medullary cavity filled with yellow marrow. The epiphysis is involved in joint articulation and growth, while the diaphysis provides structural support and strength to the bone.