Given a question and a context passage, generate the answer having the word or phrase from the context passage. Here, the answer should be a shortest continous span from the passage.

Context: From the outside, the skin looks plain and simple, as you can see in Figure 16.5. But at a cellular level, theres nothing plain or simple about it. A single square inch of skin contains about 20 blood vessels, hundreds of sweat glands, and more than a thousand nerve endings. It also contains tens of thousands of pigment-producing cells. Clearly, there is much more to skin than meets the eye! For a dramatic introduction to the skin, watch this video: MEDIA Click image to the left or use the URL below. URL: The skin is only about 2 mm thick, or about as thick as the cover of a book. Although it is very thin, it consists of two distinct layers, called the epidermis and the dermis. You can see both layers and some of their structures in Figure 16.6. Refer to the figure as you read about the epidermis and dermis below. The epidermis is the outer layer of skin. It consists almost entirely of epithelial cells. There are no blood vessels, nerve endings, or glands in this skin layer. Nonetheless, this layer of skin is very active. It is constantly being renewed. How does this happen? 1. The cells at the bottom of the epidermis are always dividing by mitosis to form new cells. 2. The new cells gradually move up through the epidermis toward the surface of the body. As they move, they produce the tough, fibrous protein called keratin. 3. By the time the cells reach the surface, they have filled with keratin and died. On the surface, the dead cells form a protective, waterproof layer. 4. Dead cells are gradually shed from the surface of the epidermis. As they are shed, they are replaced by other dead cells that move up from below. The epidermis also contains cells called melanocytes. You can see a melanocyte in Figure 16.7. Melanocytes produce melanin. Melanin is a brown pigment that gives skin much of its color. Everyones skin has about the same number of melanocytes per square inch. However, the melanocytes of people with darker skin produce more melanin. The amount of melanin that is produced depends partly on your genes and partly on how much ultraviolet light strikes your skin. The more light you get, the more melanin your melanocytes produce. This explains why skin tans when its exposed to sunlight. The dermis is the inner layer of skin. It is made of tough connective tissue. The dermis is attached to the epidermis by fibers made of the protein collagen. The dermis is where most skin structures are located. Look again at Figure pain, pressure, and temperature. If you cut your skin and it bleeds, the cut has penetrated the dermis and damaged a blood vessel. The cut probably hurts as well because of the nerve endings in this skin layer. The dermis also contains hair follicles and two types of glands. You can see some of these structures in Figure 16.8. Hair follicles are structures where hairs originate. Each hair grows out of a follicle, passes up through the epidermis, and extends above the skin surface. Sebaceous glands are commonly called oil glands. They produce an oily substance called sebum. Sebum is secreted into hair follicles. Then it makes its way along the hair shaft to the surface of the skin. Sebum waterproofs the hair and skin and helps prevent them from drying out. Sweat glands produce the salty fluid known as sweat. Sweat contains excess water, salts, and other waste products. Each sweat gland has a duct that passes through the epidermis. Sweat travels from the gland through the duct and out through a pore on the surface of the skin. You couldnt survive without your skin. It has many important functions. In several ways, it helps maintain homeostasis. The main function of the skin is controlling what enters and leaves the body. It prevents the loss of too much water from the body. It also prevents bacteria and other microorganisms from entering the body. Melanin in the epidermis absorbs ultraviolet light. This prevents the light from reaching and damaging the dermis. The skin helps maintain a constant body temperature. It 
 Question: __major organ of the integumentary system
skin

Context: Ca2+ is a ubiquitous intracellular messenger responsible for controlling numerous cellular processes including fertilization, mitosis, neuronal transmission, contraction and relaxation of muscles, gene transcription, and cell death. At rest, the cytoplasmic Ca2+ concentration [Ca2+]i is approximately 100 nM, but this level rises to 500-1,000 nM upon activation. In osteoblasts, the elevation of [Ca2+]i is a result of an increase in the release of Ca2+ from endoplasmic reticulum and/or extracellular Ca2+ influx through voltage gated Ca2+ channels. Many of the cellular effects of Ca2+ are mediated by the Ca2+ binding protein, calmodulin (CaM). Upon binding up to four calcium ions, CaM undergoes a conformational change, which enables it to bind to specific proteins eliciting a specific response. Calmodulin kinase II (CaMKII) is a major target of the Ca(2+)/CaM second messenger system. Once bound to Ca(2+)/CaM, the multimeric CaMKII is released from its autoinhibitory status and maximally activated, which then leads to an intraholoenzyme autophosphorylation reaction. Calcineurin (Cn) is another major target protein that is activated by Ca(2+)/CaM. Cn is a serine-threonine phosphatase that consists of a heterodimeric protein complex composed of a catalytic subunit (CnA) and a regulatory subunit (CnB). Upon activation, Cn directly binds to, and dephosphorylates nuclear factor of activated T cells (NFAT) transcription factors within the cytoplasm allowing them to translocate to the nucleus and participate in the regulation of gene expression. This review will examine the potential mechanisms by which calcium, CaM, CaMKII, and Cn/NFAT control osteoblast proliferation and differentiation. 
 Question: Which calcium/calmodulin dependent protein phosphatase is involved in the activation of the family of NFAT transcription factors (Nuclear Factors of Activated T cells)?
can

Context: The heat that is used for geothermal power may come to the surface naturally as hot springs or geysers, like The Geysers in northern California. Where water does not naturally come to the surface, engineers may pump cool water into the ground. The water is heated by the hot rock and then pumped back to the surface for use. The hot water or steam from a geothermal well spins a turbine to make electricity. Geothermal energy is clean and safe. The energy source is renewable since hot rock is found everywhere in the Earth, although in many parts of the world the hot rock is not close enough to the surface for building geothermal power plants. In some areas, geothermal power is common (Figure 1.1). In the United States, California is a leader in producing geothermal energy. The largest geothermal power plant in the state is in the Geysers Geothermal Resource Area in Napa and Sonoma Counties. The source of heat is thought to be a large magma chamber lying beneath the area. Where Earths internal heat gets close to the surface, geothermal power is a clean source of energy. In California, The Geysers supplies energy for many nearby homes and businesses. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: 
 Question: where does geothermal energy come from?

earths internal heat