Anatomy and physiology

Chapter 20 Anatomy and physiology





KEY POINTS























SKELETAL SYSTEM


The skeletal system is made up of bones and joints that work together with muscles and ligaments to provide a framework for the body (Fig. 20.1).





BONES


Bone is hardest of all connective tissue found in the human body and is formed by a process of ossification which takes place in two ways. The first is intramembranous ossification, where connective tissue is replaced by calcium phosphate, and this occurs in the skull. The second is intracartilaginous ossification, where hyaline cartilage is replaced by calcium phosphate, and this occurs almost throughout the skeleton.


Bone tissue comprises spongy/cancellous or compact bone. Microscopic structure of bone consists of Haversian systems arranged in concentric circles of lamellae (layers), which surround the Haversian canals. Each Haversian canal contains blood and lymphatic vessels and nerves. In compact bone, these Haversian systems and lamellae are packed closely together with very little space between them. In spongy bone there are fewer Haversian systems and the Haversian canals are larger with bigger gaps between the lamellae. These spaces help to reduce the weight of the bone. Bone marrow, consisting of both yellow and red marrow, fills the spaces created by the gaps.


Bone tissue is dependent on nutrients such as calcium, phosphorous and vitamins C and D for growth and repair. Exercise affects the growth and repair of bone and muscle by stimulating blood supply and circulation.




Functions of bone







Bones are classified into the following types (Table 20.1):







Table 20.1 Classification of bone



























Shape Description Location in the body
Long bones Length is greater than width

Short bones Equal in length, breadth and thickness Wrist (carpal bones), ankle (tarsal bones)
Flat bones Usually more curved and thin than flat; e.g. the curved bones of the skull protect the brain Skull, chest (scapula, ribs, sternum), pelvis
Irregular bones These do not have any of the above-mentioned shapes, hence ‘irregular’ Axial skeleton, both shoulder and pelvic girdle and vertebrae
Sesamoid bones Small bones that are found embedded in certain tendons connecting muscle to bone Knee (the commonest sesamoid bone is the patella), but may also be seen on images of the hand, wrist and foot)



JOINTS


A joint forms at a point where two bones and cartilages meet or where adjacent bones and cartilages are joined. Although bone gives the body protective structure and muscles provide the ability to move, it is actually the joints that provide the mechanism by which movement takes place. Radiographic contrast can sometimes be injected into a joint space (e.g. in the glenoid cavity of the shoulder) to visualise any underlying pathology. This procedure is known as an arthrogram.



Classification


A joint can be classified according to the range of movement it provides or by its articular surface structure. All joints in the body can be classified as shown in Table 20.2; however, certain areas of the body may have a combination of two joints; for example the temporomandibular joint (TMJ) comprises gliding and pivot joints.


Table 20.2 Classification of joints



















Type of joint Structure Description of movement, with examples
Fibrous




Cartilaginous




Synovial Have lubricated articular cartilage between bones giving smooth, free movement in a range of directions







CARDIOVASCULAR SYSTEM


This system forms the transport network for the body.




THE HEART


The heart is a muscle that acts as a pump and provides the energy and force to keep blood circulating throughout the body. Blood is circulated via a closed transport system; that is, oxygenated blood leaves the heart via arteries, passes through a tiny network of capillaries where transfer of oxygen and nutrients take place, and then deoxygenated blood returns to the heart via the veins.




Structure


The heart and the great vessels are surrounded and supported by a protective covering called the pericardium. The pericardium is a fibroserous sac that is attached to the sternum, diaphragm and great vessels by connective tissue.


The heart wall is made up of three layers of tissue (Fig. 20.3):






The pericardium consists of two layers of tissue. The outer layer is a tough fibrous layer that serves to protect the heart wall and secure its position within the thorax. The inner layer is a serous layer. This serous pericardium is furtherdivided into an outer parietal layer, which forms the inner lining of the fibrous pericardium, and an inner visceral layer that forms the outer covering of the heart (also known as epicardium). Between these layers is a potential space, called the pericardial cavity. This contains serous fluid, which allows for flexibility in the movement of the heart during contraction and relaxation phases (heartbeats), thus reducing friction during these movements.


The myocardium is a thick layer of cardiac muscle lying between the pericardium and the inner endocardium. It has two layers of cardiac muscle arranged in a spiral form and it is this muscular arrangement that gives the heart its squeezing ability.


The endocardium is a thin fibrous layer made up of endothelial cells and connective tissue. It lines the inner surface of the heart walls and continues as the inner lining of the great vessels that emerge and leave from the heart.


Blood supply to heart wall is via the left and right coronary arteries and venous return is via the coronary sinus and cardiac veins.








RESPIRATORY SYSTEM


The thorax is probably the most frequently imaged body part in radiology departments today because a single chest X-ray is sometimes sufficient to make a diagnosis and determine the overall health of a patient. The mechanism of breathing (inspiration and expiration) occurs within this system. It functions as a series of passages through which air travels from the outside (atmosphere) to the inside(lungs). In addition, this system contributes to wider ranging functions of voice production, coughing and sneezing.





Feb 20, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Anatomy and physiology
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