Grooming Grooming serves a number of purposes. It is health related in that the activity cares for the skin, feathers, or fur.Grooming also serves a social function. Between members of a community, grooming reduces stress, communicates and signals social status, spreads pheromones, achieves thermoregulation or pain relief, increases or decreases arousal, self-stimulates, and prevents sexually transmitted diseases. As grooming is similar through the various levels of animal taxa, it has been conjectured that grooming behavior is evolutionarily ancient. Most animals (mammals, birds, and insects) groom by moving their limbs over their own bodies or mouthing or licking their bodies. In some birds, sandbathing is quite common. With fish, a species with no limbs, it is not uncommon to see them rubbing or simply moving against rocks, branches, or sand, generally accomplishing what a sandbath does for a bird. A bird preening its feathers, a cat licking its paws, or a bear brushing his back against a tree truck are all self-grooming. This is where the animal, alone, takes care of the grooming behavior without help from another animal. However, mutual grooming is quite common. In mammalian species, this is a form a display behavior, which helps to cement the social bonds between members of the group. Yet another kind of cleaning behavior, called cleaning symbiosis, occurs between certain species of fish and shrimp. Here, one species will eat the parasites off another species. The cleaner gets food, the recipient remains debrisand parasite-free.
Bone Composition, Development, and Remodeling Between 66 and 70 percent of bone is an inorganic mineral composite made of calcium phosphate and calcium carbonate, which is mostly hydroxyapatite. Much of the remainder of bone is the fibrous protein collagen. This mineral and protein together are called the bone matrix. Within the bone matrix are the three types of specialized cells which ensure its formation, remodeling as is needed, and continuity throughout life. The first cell type, the osteoblast, produces the bone matrix and surrounds itself with it, synthesizing collagen and stimulating mineral deposition. The second cell type, the osteocyte, is a branched cell that becomes embedded in bone matrix, is interconnected, and acts in the control of the mineral balance of the body. Finally, the osteoclast cells destroy the bone matrix whenever it is remodeled during skeleton growth or the repair of bone breaks and bone fractures. The stepwise conversion of cartilage into bone begins when the chondrocytes of hyaline cartilage enlarge and arrange themselves in rows. This is followed by the synthesis of collagen fibers, and mineral deposition around them. Just below the inner surface of the periosteum a vascular membrane- the perichondrium-forms and supplies the osteoblasts needed for bone formation. Simultaneously, osteoclasts excavate layers through the bone layer and set the stage for the formation of additional bone. All the bones in the bodies of the vertebrates change their sizes and shapes as these organisms pass through their lives. The processes involved are collectively called remodeling. An example of such change is the growth of the long bones in circumference as the limbs grow from puberty to adulthood. In the course of such bone growth the periosteum provides the osteoblasts required to deposit bone matrix around the bone exterior and to calcify it. At the same time the endosteumderived osteoclasts often dissolve bone in the interior, thus enlarging the marrow cavity. Remodeling in such cases occurs in response to biosignals including those caused by increases in the need for bone to bear additional weight or to anchor increased muscle mass. Conversely, inactivity and the lack of exercise can result in remodeling which produces diminished bone mass. The complex changes involved in bone remodeling are also controlled by vitamin D and hormones originating in the pituitary gland, the thyroid gland, and the parathyroid glands. Abnormalities in bone growth and remodeling are associated with a great many bone diseases, ranging from rickets to bone cancer.
