and that of the tissue fluid, usually favoring fluid absorption by the blood capillaries. Compare colloid osmotic pressure. oocyte (OH-oh-site) In the development of an egg cell, any haploid stage between meiosis I and fertilization.
oogenesis (OH-oh-JEN-eh-sis) The production of a fertilizable egg cell through a series of mitotic and meiotic cell divisions; female gametogenesis. ophthalmic (off-THAL-mic) Pertaining to the eye or vision; optic.
opposition A movement of the thumb in which it touches any fingertip of the same hand. optic Pertaining to the eye or vision. orbit The eye socket of the skull. organ Any anatomical structure that is composed of at least two different tissue types, has recognizable structural boundaries, and has a discrete function different from the structures around it. Many organs are microscopic and many organs contain smaller organs, such as the skin containing numerous microscopic sense organs. organelle Any structure within a cell that carries out one of its metabolic roles, such as mitochondria, centrioles, endoplasmic reticulum, and the nucleus; an intracellular structure other than the cytoskeleton and inclusions. organic Pertaining to compounds of carbon. origin The relatively stationary attachment of a skeletal muscle. Compare insertion. osmolality (OZ-mo-LAL-ih-tee) The molar concentration of dissolved particles in 1 kg of water. osmolarity (OZ-mo-LERR-ih-tee) The molar concentration of dissolved particles in 1 L of solution. osmoreceptor (OZ-mo-re-SEP-tur) A neuron of the hypothalamus that responds to changes in the osmolarity of the extracellular fluid. osmosis (oz-MO-sis) The net diffusion of water through a selectively permeable membrane. osmotic diuresis (oz-MOT-ic DY-you-REE-sis) Increased urine output due to an increase in the concentration of osmotically active particles in the tubular fluid. osmotic pressure The amount of pressure that would have to be applied to one side of a selectively permeable membrane to stop osmosis; proportional to the concentration of nonpermeating solutes on that side and therefore serving as an indicator of solute concentration. osseous (OSS-ee-us) Pertaining to bone. ossification (OSS-ih-fih-CAY-shun) Bone formation. osteoarthritis (OA) A chronic degenerative joint disease characterized by loss of articular cartilage, growth of bone spurs, and impaired movement; occurs to various degrees in almost all people with age.
osteoblasts Bone-forming cells that arise from osteogenic cells, deposit bone matrix, and eventually become osteocytes. osteoclasts Macrophages of the bone surface that dissolve the matrix and return minerals to the extracellular fluid. osteocyte A mature bone cell formed when an osteoblast becomes surrounded by its own matrix and entrapped in a lacuna. osteon A structural unit of compact bone consisting of a central canal surrounded by concentric cylindrical lamellae of matrix. fig. 7.4
osteoporosis (OSS-tee-oh-pore-OH-sis) A degenerative bone disease characterized by a loss of bone mass, increasing susceptibility to spontaneous fractures, and sometimes deformity of the vertebral column; causes include aging, estrogen hyposecretion, and insufficient resistance exercise. ovary The female gonad; produces eggs, estrogen, and progesterone. ovulation (OV-you-LAY-shun) The release of a mature oocyte by the bursting of an ovarian follicle. ovum Any stage of the female gamete from the conclusion of meiosis I until fertilization; a primary or secondary oocyte; an egg. oxidation A chemical reaction in which one or more electrons are removed from a molecule, lowering its free energy content; opposite of reduction and always linked to a reduction reaction. oxytocin (OT) (OCK-see-TOE-sin) A hormone released by the posterior pituitary gland that stimulates labor contractions and milk release.
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