There are four types of bone: long bones, short bones, flat bones, and irregular bones. Long bones are longer than they are wide, with spongy bones at both ends and a cavity filled with bone marrow in the shaft. The femur of an adult male is about 19 inches long and a bit under an inch in diameter.
The proximal end of the femur the part closest to the heart is the head of the femur. The head of the femur is a ball that makes up part of the hip joint.
It allows the leg to move at all angles. Below the head of the femur is the neck and the greater trochanter. The greater trochanter attaches to tendons that connect to the gluteus minimus and the gluteus medius muscles. These muscles pull the leg to help with walking and running.
This is known as an extension of the leg or the hip. Below the greater trochanter is the lesser trochanter, situated at the base of the neck of the femur. The lesser trochanter is the part of the femur attached to a pair of muscles that help flex the thigh lift the leg forward. Below the lesser trochanter is the gluteal tuberosity, which is where the gluteus maximus is attached.
The main shaft of the femur is known as the body of the femur. The distal end of the femur is where it connects with the patella knee cap and the bones of the lower leg, the tibia, and fibula. The distal end of the femur has a saddle that rests on the top of the tibia. It has rounded edges on either side of the knee joint, known as the condyles. The depression between the condyles is called the patellar groove.
Inside the body of the femur is the medullary cavity, which contains bone marrow. At the ends of the femur are areas of compact bone, which is solid and does not contain marrow. Surrounding the compact bone is spongy bone, which has lots of small cavities dispersed throughout it. The neck and head of the femur contain spongy bone. The femur is the primary bone of the leg. It supports the weight of the body on the leg and is capable of carrying 30 times the weight of the body.
The femur provides the ability for articulation and leverage for the leg. Articulation allows for standing, walking, and running. The femur is the primary bone of the leg and all other leg bones are attached to the distal portion of the femur. The medullary cavity contains red bone marrow, which is involved in the production of red blood cells. Over time, red bone marrow is replaced by yellow bone marrow, which helps to store fat.
Blood flow in the femur is hard to measure. It is a significant amount, so much so that a needle inserted into the spongy bone can be used to infuse enough fluid into the bloodstream to offset shock or dehydration. Fractures are the most common condition of the femur. It takes a lot of force to break a femur, although certain areas of the femur are more susceptible.
The neck of the femur is the most vulnerable to fracture. Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and knees.
Figure reviews bone classifications with their associated features, functions, and examples. Bones can be classified according to their shapes. Long bones, such as the femur, are longer than they are wide. Short bones, such as the carpals, are approximately equal in length, width, and thickness. Flat bones are thin, but are often curved, such as the ribs. Irregular bones such as those of the face have no characteristic shape.
Sesamoid bones, such as the patellae, are small and round, and are located in tendons. What are the structural and functional differences between a tarsal and a metatarsal? Structurally, a tarsal is a short bone, meaning its length, width, and thickness are about equal, while a metatarsal is a long bone whose length is greater than its width.
Functionally, the tarsal provides limited motion, while the metatarsal acts as a lever. What are the structural and functional differences between the femur and the patella?
Structurally, the femur is a long bone, meaning its length is greater than its width, while the patella, a sesamoid bone, is small and round. Functionally, the femur acts as a lever, while the patella protects the patellar tendon from compressive forces. 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. The differences between compact and spongy bone are best explored via their histology. 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 is the denser, stronger of the two types of bone tissue Figure 6. It can be found under the periosteum and in the diaphyses of long bones, where it provides support and protection.
The microscopic structural unit of compact bone is called an osteon , or Haversian system. Running down the center of each osteon is the central canal , or Haversian canal, which contains blood vessels, nerves, and lymphatic vessels. As described earlier, canaliculi connect with the canaliculi of other lacunae and eventually with the central canal. This system allows nutrients to be transported to the osteocytes and wastes to be removed from them. Like compact bone, spongy bone , also known as cancellous bone, contains osteocytes housed in lacunae, but they are not arranged in concentric circles.
The trabeculae may appear to be a random network, but each trabecula forms along lines of stress to provide strength to the bone. The spaces of the trabeculated network provide balance to the dense and heavy compact bone by making bones lighter so that muscles can move them more easily. In addition, the spaces in some spongy bones contain red marrow, protected by the trabeculae, where hematopoiesis occurs.
Watch this video to see the microscopic features of a bone. Skip to main content. Chapter 6: The Skeletal System. Search for:. Bone Classification and Structure Learning Objectives Classify bones according to their shapes Describe the function of each category of bones. Identify the anatomical features of a bone Describe the histology of bone tissue Compare and contrast compact and spongy bone Identify the structures that compose compact and spongy bone.
Bone Classifications Bone classification Features Function s Examples Long Cylinder-like shape, longer than it is wide Leverage Femur, tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges Short Cube-like shape, approximately equal in length, width, and thickness Provide stability, support, while allowing for some motion Carpals, tarsals Flat Thin and curved Points of attachment for muscles; protectors of internal organs Sternum, ribs, scapulae, cranial bones Irregular Complex shape Protect internal organs Vertebrae, facial bones Sesamoid Small and round; embedded in tendons Protect tendons from compressive forces Patellae.
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