Skeletal+System+MV

Molly Vaughn 6 October 2008 Human Biology

Skeletal System 1. What are the four main functions of the skeleton? (p. 208) - The skeleton supports the body. The bones of the legs support the entire body when we are standing, and bones of the pelvic girdle supports the abdominal cavity. - The skeleton protects soft body parts. The bones of the skull protect the brain; the rib cage protects the heart and lungs. The vertebrae protect the spinal cord, which makes nervous connections to all the muscles of the limbs. - The skeleton produces blood cells. All bones in the fetus have red bone marrow that produces blood cells. In the adult, only certain bones produce blood cells. - The skeleton stores minerals and fat. All bones have a matrix that contains calcium phosphate, a source of calcium ions and phosphate ions in the blood. Fat is stored in yellow bone marrow. - The skeleton, along with the muscles, permits flexible body movement. While articulations (joints) occur between all the bones of limbs.

2. What is the difference between cartilage and bone? (p.208) - Compact bone is highly organized and composed of tubular units called osteons. In a cross section of an osteon, bone cells called osteocytes lie in lacunae, which are tiny chambers arranged in concentric circles around a central canal. Matrix fills the space between the rows of lacunae. Tiny canals called canaliculi run through the matrix, connecting the lacunae with one another and with the central canal. The cells stay in contact by strands of cytoplasm that extend into the canaliculi. Osteocytes nearest the center of an osteon exchange nutrients and wastes with the blood vessels in the central canal. These cells then pass on the nutrients and collect wastes from the other cells via the gap junctions. Compared with compact bone, spongy bone has an unorganized appearance. It contains numerous thin plates separated by unequal spaces. Although, this makes spongy bone lighter than compact bone, spongy bone is still designed for strength. Just as braces are used for support in the buildings, the trabeculae follow lines of stress. The spaces of spongy bone are often filled with red bone marrow, a specialized tissue that produces all types of blood cells. The osteocytes of spongy bone are irregularly placed within the trabeculae, and canaliculi bring them nutrients from the red bone marrow. - Cartilage is not as strong as bone, but it is more flexible because the matrix is gel-like and contains many collagenous and elastic fibers. The cells, called chondrocytes, lie within lacunae that are irregularly grouped. Cartilage has no nerves, making it well suited for padding joints when the stresses of movement are intense. Cartilage also has no blood vessels, making it slow to heal. The three types of cartilage differ accordingly to the type and arrangement of fibers in the matrix. Hyaline cartilage is firm and somewhat flexible. The matrix appears uniform and glassy, but actually it contains a generous supply of collagen fibers. Hyaline cartilage is found at the ends of long bones, in the nose, at the ends of the ribs, and in the larynx and trachea. Fibrocartilage is stronger than hyaline cartilage because the matrix contains wide rows of thick, collagen fibers. Fibrocartilage is able to withstand both tension and pressure, and it forced where support is of prime importance-in the disks located between the vertebrae and also in the cartilage of the knee. Elastic cartilage is more flexible than hyaline cartilage because the matrix contains mostly elastin fibers. This type of cartilage is found in the earflaps and the epiglottis.

3. Why is vitamin D important to bone growth? How do we get vitamin D? (p. 212) - The importance of bone growth is signified by the involvement of several hormones in bone growth. A hormone is a chemical messenger, produced by one part of the body, which acts on a different part of the body. Vitamin D is formed in the skin when it is exposed to sunlight, but it can also be consumed in the diet. Milk, in particular, is often fortified with vitamin D today. In the kidneys, vitamin D is converted to a hormone that acts on the intestinal tract. The chief function of vitamin D is intestinal absorption of calcium. In the absence of vitamin D, children can develop rickets, a condition marked by bone deformities including bowed long bones. Growth hormone directly stimulates growth of the epiphyseal plate, as well as bone growth in general. However, growth hormone will be somewhat ineffective if the metabolic activity of cells is not promoted. Thyroid hormone, in particular, promotes the metabolic activity of cells. Too much growth hormone during childhood can produce excessive growth and even gigantism, while too little can cause dwarfism. Too much GH produces gigantism in youths prior to epiphyseal fusion and acromegaly in adults following epiphyseal fusion. Adolescents usually experience a dramatic increase in height, called the growth spurt, due to an increase level of sex hormones, which apparently stimulate osteoblast activity to the point that the epiphyseal plates become “paved over” by the faster growing bone tissue, within one or two years of the onset of puberty.

4. Insert an image of a skeleton. You will need to know the location of the following bones. Skull: Frontal bone- in the middle of the skull Parietal bone- on the back left side of the skull Temporal bone- on the lower left side of the skull Occipital bone- on the bottom middle of the back of the skull Zygomatic bone- the cheekbone Maxilla- the bone right under your nose Mandible- the bottom of your mouth (jaw) Pectoral girdle: Clavicle- the stop of the shoulder Scapula- on the left and right side of the back Upper limb: Humerus- the top bone in the arm Ulna- the right bone in the bottom of the arm Radius- the left bone in the bottom of the arm Carpals- wrist bones Metacarpals- knucklebones Phalanges- finger bones Rib Cage: Sternum- in the middle of the rib cage Ribs- surrounding the lungs Costal cartilages- the ribs Pelvic girdle: Coaxyl bones- the top two bones in the pelvis Sacrum- the bones right before the bottom of the spine between the pelvis Coccyx- the bottom of the spine Lower limb: Femur- the first long bone in the leg Patella- the kneecap Tibia- the right bone in the leg Fibula- the left bone in the leg Tarsals- the big toe Metatarsals- the bones right before the toes Phalanges- the toes