Once you arrive on scene, you notice a relatively young woman who appears to be in moderate distress. She is lying in bed complaining of pain throughout her back, neck, and legs. She appears to be breathing normally, with no wounds, injuries, or signs of life threats at the moment. Initially, there doesn’t seem to any cause or explanation for the patient’s pain.
The fiancé tells you that the she has been complaining of increasing back pain for the last four months, and when he came home from work today he found her in bed – she told him that she couldn’t walk anymore. The patient denies any form of trauma, including assault, falls, or any heavy lifting.
As you begin to perform a physical assessment of the patient, you tell your partner to bring a stretcher board and set up the equipment. Examination reveals a pulse of 112 beats per minute, a blood pressure of 116/78, respirations of 28 breaths a minute, with normal temperature. The skin is pink, warm, and dry. There are no obvious body deformities, injuries, wounds, or signs of swelling. A 3-lead ECG reads a normal sinus rhythm. The patient is fully alert and oriented and is able to respond to verbal commands. Your partner returns with the stretcher board and a cervical collar. You put the cervical collar on, and with the help of your partner, log-roll the patient onto the stretcher board. The crew helps load the patient into the ambulance. Once in the ambulance, you perform a more detailed assessment of the patient, and repeat the vital signs. You brainstorm possible causes of her agonizing yet obscure pain. Taking into account her young age and lack of external injury, you consider likely systemic possibilities and potential health conditions that could be a cause for her pain. You set up an IV and start the patient on two liters of oxygen via nasal cannula. You continue to obtain a full history and health report from the patient, as your partner transports with urgency…
■Introduction
The primary structure of the skeletal system is composed of 206 bones buried deep in muscles and other soft tissues, providing the stable framework that supports the entire human body. It should be directly noted that bones are technically regarded as organs.
However, some academic texts and professors will refer to bones as tissue. Bones are comprised of osseous tissue, or bone tissue, as well as other types of tissue: connective tissue, epithelium, and nervous tissue that collectively work together and function as a single unit, which is the very definition of an organ.
Moreover, bones are living organs – they continuously adapt and aid the body in responding to varying environments. Nevertheless, our discussion of the skeletal system will begin with an overview of its function, followed by a classification of the types of bone, based on examination of their structure.
From there, we will examine the microscopic structure of bone and analyze bone development, growth and the aging process. Once we cover this groundwork, we will then investigate specific bones and their organization in the human skeleton. We will conclude our studies with an overview of joints, or articulations, and the integration of the skeletal system with other organ systems of the human body.
Figure 4-1 Human skeleton.
■Functions of the Skeletal System
The skeletal system provides five distinct functions1:
•Support
•Protection
•Movement
•Storage (mineral homeostasis)
•Hematopoiesis
The bones of the skeletal system provide a supporting framework for the whole body; all of the soft tissues in the body use the bones as a scaffold from which to suspend. The bones also serve as a protective barrier for the body’s most vital structures; for example – the skull protects the brain, while the sternum and ribs protect the heart and lungs.
Bones aid in the mechanics of movement. While muscles provide the force via contraction, the bones provide the vehicle for the movement. Muscles are attached to bones, and during contraction, they shorten, pulling on the bones and moving them. Bones also perform a significant role in the storage and maintenance of certain metabolic functions, such as calcium and phosphate regulation.
Figure 4-2 Red blood cells.
Lastly, bones are responsible for one of the most vital physiological processes in the body. That process is called hematopoiesis, or blood cell formation. Blood cell production is carried out in the red bone marrow, a soft connective tissue found deep inside the medulla, or center, of specific bones.
■Classification of Bones
Six different types of bones are defined and named according to their shape2:
•long bones
•short bones
•flat bones
•sesamoid bones
•sutural bones
•irregular bones
Examples of long bones are the humerus (bone of the upper arm), and the femur (bone of the upper leg).
Short bone examples include the carpals (wrist bones) and the tarsals (ankle bones).
Examples of flat bones can be seen in the skull, such as the frontal bone or in the pelvis, such as the ilium.
Sesamoid bones are small, rounded bones implanted with a tendon (a type of connective tissue that attaches skeletal muscles to bones); the most easily recognizable one being the patella, or knee cap.
Sutural bones are small and flat bones that sit between the flat bones of the skull; they vary in size and number.
Finally, irregular bones are bones that cannot be classified as any other type of bone and have varying shapes that can be found in the vertebrae, or spinal bones and in the skull, such as the sphenoid and ethmoid bones.
We will take a thorough look at the structural components of a long bone, which will allow us to recognize all of the fundamental characteristics of the entire collection of bones.
Bone structure (gross)
Gross anatomy defines a branch of anatomy focusing on macroscopic (large enough to be observed by the naked eye) structures of organs and tissues.
Seven main components to the gross structure of a long bone are discussed below:
•Diaphysis – shaft; the cylindrical mid-section of a long bone,3 constructed out of solid compact bone (discussed later). It is dense, hard, and extremely strong.
•Medullary cavity – the hollow area inside and deep to the diaphysis of a bone. It contains yellow bone marrow, the fatty, inactive form of marrow found in the adult skeleton.
•Epiphysis – the outer ends of bone, constructed of spongy bone, which houses red bone marrow, the active form of marrow that is responsible for hematopoiesis. The epiphysis is also the location of secondary ossification during development (discussed later).
•Periosteum – A thick, strong, outer fibrous membrane that covers most of a long bone, except for the ends of joint surfaces.
•Endosteum – A thin, interior membrane of connective tissue that lines the medullary cavity.
•Articular cartilage – a thin layer of cartilage that covers the ends of bones, at the outermost regions of the epiphysis; they function like shock absorbers that cushion the ends of bones, where a joint is formed.
•Physis