Microanatomy, Physiology of Bone & Joints

Transcription

1 Microanatomy, Physiology of Bone & Joints The Skeleton There are 206 bones in the human body. The bones that are required in this syllabus are the cranium, mandible, clavicle, sternum, scapula, ribs, humerous, vertebrae, radius, ulna, ilium (pelvis), carpals, metacarpals, phalanges (fingers), sacrum, femur, patella, tibia, fibula, tarsals, metatarsals and phalanges (toes). There are two main parts of the skeleton. These are the appendicle skeleton and the axial skeleton. The appendicular skeleton is made up of the pectoral girdle, pelvic girdle and the limbs. The axial skeleton consists of the skull, ribs, sternum and vertabral column The function of the Skeleton 1. To protect delicate organs (e.g. brain - cranium). 2. To provide shape and support to the body (e.g. the firm construction of the thorax which permits breathing). 4. To manufacture blood cells and 5. Storage of minerals such as calcium and phosphate and to store fat 6. To allow body movements Bones 1. Long Bones - like bones of the arm (radius, humerous) and the bones in legs(femur) they are effective leavers which facilitate movement. 2. Short Bones - these small bones as in foot (tarsel bones) and wrists (carpal bones) are strong

2 and capable of resisting compressive forces. 3. Flat Bones - these bones usually have a protective function and include ribs, pelvis and cranium. 4. Irregular Bones - such as spinal vertebrae and the scapula and they have a variety of functions. Construction of Long Bones Diaphysis A tube of compact bone which has great strength and rigidity. The cavity is known as the medullary and in an adult that is filled with yellow bone marrow. Epiphysis A spongy material. There to absorb compressive forces. It is spongy or cancellous bone and is filled with red bone marrow. Epiphyseal Plate Where longitudinal growth takes place. Articular Cartilage or Hyaline Covers the joint surface of a bone and is made up of hyaline cartilage. Bluish - white matrix tissue. The matrix is solid, smooth, firm and resilient. Cells appear in groups forming a cell nest. Form at the joints between two bones e.g. knee.

3 Periosteum The periosteum covers the rest of the bone (it is like a tough skin). It is fused to the bone the muscle tendons are attached to the periosteum. The periosteum also has a nerve and blood supply which provides nutrition to the bone. Compact Bone Consists of thousands of collagen based structure called HAVERSIAN SYSTEM. It consists of a central canal surrounded by concentric ring shaped calcium based plates called lamellae. Spongy or Cancellous Bone A honey comb appearance in a criss-cross matrix of bone tissue called trabeculae. Red bone marrow fills the tiny space.

4 Bone Cells Bone may seem to be stable and unchanging, but in fact, bone is constantly being remodeled. Bone remodeling is triggered by a need for calcium in the extracellular fluid, but it also occurs in response to mechanical stresses on the bone tissue. To understand bone remodeling, and the factors that lead to pathological problems with bone, you need to know about three cell types found in bone. Osteoblasts are bone-forming cells. They are connective tissue cells found at the surface of bone. They can be stimulated to proliferate and differentiate as osteocytes. Osteocytes are bone cells. Osteocytes manufacture type I collagen and other substances that make up the bone extracellular matrix. Osteocytes will be found enclosed in bone. Osteoclasts are bone-resorbing cells ("-clast" means to break; osteoclasts break down bone). They are large, multinucleate cells that form through the fusion of precursor cells. Unlike osteoblasts, which are related to fibroblasts and other connective tissue cells, osteoclasts are descended from stem cells in the bone marrow that also give rise to monocytes. Ossification The process of the bone formation is called ossification. Bone is formed by two types of ossification: endochondral and intramembranous. Endochondral ossification is the transformation of cartilaginous material into bone. Most of the skeletal bones are developed by this ossification process which continues till a person is fully grown. The epiphyseal plate (growth plate) usually ossifies through teenage years until the body is fully grown. Intramembranous ossification is the transformation of fibrous connective tissue in sheet like layers to form bone tissue. This most commonly found in the flat bones of the skull.

5 Joints and Joint Movement Fibrous bone united by intervening fibrous tissue e.g. skull and pelvis Cartilaginous United by intervening cartilage e.g. vertebral column and pubic bone Synovial six major types: ball & socket hinge condyloid saddle gliding pivot Most Complex Joint = Synovial Joint The Synovial Capsule

6 Types: Ball and Socket Joint The head of the bone articulates with the socket of another. The movement in all axis and planes. e.g. hip, shoulder Hinge Joint The projection of one bone fits into the groove of another. Flexion and extension movements only. Movement in one axis and plane of movement. e.g. elbow Pivot Joint The end of one bone protrudes into a "sleeve" or ring composed of bone of another bone. Rotation of one bone (radius) around its own long axis against the other bone (ulna). e.g. Radius to ulna, vertebrae Condyloid Joint The oval end of one bone fits into complementary cavity of another. Moderate movement, flexion and extension, adduction and abduction. e.g. wrist Saddle Joint Each surface has concave and convex areas (saddle) movement similar to condyloid but a greater range of movement of axis. e.g. carpal to metacarpal of thumb Gliding Joint The flat surface of one slips over the other. Very small range of movement. No rotation around axis. e.g. tarsals and carpals, vertebrae Joint Movement: Basic movement of the body can be described using the following terms. Flexion Bending a body part or decreasing the angle between the parts. Extension Straightening a body part to increase the angle between the parts.

7 Abduction Moving a part of the body away from the midline. Adduction Moving a part of the body towards the midline. Inversion Turning the foot so that the sole faces inwards. Eversion Turning the foot so that the sole faces outwards. Supination Turning the hand so the palm faces upwards. Pronation Turning the hand so the palm faces downwards. Rotation Turning the body part on the axis. Full rotation is not possible in a human due to restrictions of muscles, blood vessels and nerves (e.g. turning the head from side to side). Circumduction A combination of movement which result in a cone-like movement (e.g. arm circles).

8 The Knee Figure 1: Right Knee Although the knee joint may look like a simple joint, it is one of the most complex. Moreover, the knee is more likely to be injured than is any other joint in the body. We tend to ignore our knees until something happens to them that causes pain. As the saying goes, however, "an ounce of prevention is worth a pound of cure." If we take good care of our knees now, before there is a problem, we can really help ourselves. In addition, if some problems with the knees develop, an exercise program can be extremely beneficial. Figure 2: Right Knee

9 The knee is essentially made up of four bones. The femur, which is the large bone in your thigh, attaches by ligaments and a capsule to your tibia. Just below and next to the tibia is the fibula, which runs parallel to the tibia. The patella, or what we call the knee cap, rides on the knee joint as the knee bends. When the knee moves, it does not just bend and straighten, or, as it is medically termed, flex and extend. There is also a slight rotational component in this motion. This component was recognized only within the last 50 years, which may be part of the reason people have so many unknown injuries. The knee muscles which go across the knee joint are the quadriceps and the hamstrings. The quadriceps muscles are on the front of the knee, and the hamstrings are on the back of the knee. The ligaments are equally important in the knee joint because they hold the joint together. You may have heard of people who have had ligament tears. Problems with ligaments are common. In review, the bones support the knee and provide the rigid structure of the joint, the muscles move the joint, and the ligaments stabilize the joint. Figure 3: Cross Sectional View of Right Knee The knee joint also has a structure made of cartilage, which is called the meniscus or meniscal cartilage. The meniscus is a C-shaped piece of tissue which fits into the joint between the tibia and the femur. It helps to protect the joint and allows the bones to slide freely on each other. There is also a bursa around the knee joint. A bursa is a little fluid sac that helps the muscles and tendons slide freely as the knee moves. To function well, a person needs to have strong and flexible muscles. In addition, the meniscal cartilage, articular cartilage and ligaments must be smooth and strong. Problems occur when any of these parts of the knee joint are damaged or irritated.

10 CRUCIATE LIGAMENTS Figure 4: Right Knee There are two cruciate ligaments located in the center of the knee joint. The anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL) are the major stabilizing ligaments of the knee. In figure 4, on the lateral view, the posterior cruciate ligament prevents the femur from sliding forward on the tibia (or the tibia from sliding backwards on the femur). In the medial view, the anterior cruciate ligament prevents the femur from sliding backwards on the tibia (or the tibia sliding forwards on the femur). Most importantly, both of these ligaments stabilize the knee in a rotational fashion. Thus, if one of these ligaments is significantly damaged, the knee will be unstable when planting the foot of the injured extremity and pivoting, causing the knee to buckle and give way.