Calcium in biology

Calcium ions (Ca²⁺) play a pivotal role in the physiology and biochemistry of organisms and the cell. They play an important role in signal transduction pathways, where they act as a second messenger, in neurotransmitter release from neurons, in contraction of all muscle cell types, and in fertilization. Many enzymes require calcium ions as a cofactor, those of the blood-clotting cascade being notable examples. Extracellular calcium is also important for maintaining the potential difference across excitable cell membranes, as well as proper bone formation.

Calcium levels in mammals are tightly regulated, with bone acting as the major mineral storage site. Calcium ions, Ca²⁺, are released from bone into the bloodstream under controlled conditions. Calcium is transported through the bloodstream as dissolved ions or bound to proteins such as serum albumin. Parathyroid hormone secreted by the parathyroid gland regulates the resorption of Ca²⁺ from bone, reabsorption in the kidney back into circulation, and increases in the activation of vitamin D₃ to Calcitriol. Calcitriol, the active form of vitamin D₃, promotes absorption of calcium from the intestines and the mobilization of calcium ions from bone matrix. Calcitonin secreted from the parafollicular cells of the thyroid gland also affects calcium levels by opposing parathyroid hormone; however, its physiological significance in humans is dubious.

CA2

CA2, CA-2 or CA II may refer to :

Adams CA-2

The Adams CA-2 is a single seat, low-wing, American ultralight aircraft that was designed by Frank Griffith of Corning Aircraft around 1992 and was available as plans for amateur construction until 1999. In 1999, Hummel Aviation of Bryan, Ohio began offering the design. Although the design was well received, plans were no longer listed as being available from Hummel Aviation as of 2007.

In 2011, Adams Aeronautics Company of Dallas, Georgia, took over sales and support of the CA-2 design.

Development

The design goals of the CA-2 described a plans-built aircraft for the US FAR 103 Ultralight Vehicles category, including a maximum 254 lb (115 kg) empty weight. The CA-2 was also intended to be one of the lowest cost ways of obtaining an ultralight aircraft. These goals were met and the resulting aircraft has an empty weight of 250 lb (113 kg), when equipped with a 28 hp (21 kW) Rotax 277 engine. At the time it entered the market, the airframe construction cost was estimated to be US$1600 and the total completion cost US$5000–6000. The price for the plans, consisting of 40 sheets of 11"X17" (28 X 43 cm), was US$150 in 2011.