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" This table was adapted with permission from B. Alberts, D. Bray, J. Lewis, M. Raff, K. Roberts, and J. D. Watson (1983). "Molecular Biology of the Cell." Garland Publishing Co., New York.

" This table was adapted with permission from B. Alberts, D. Bray, J. Lewis, M. Raff, K. Roberts, and J. D. Watson (1983). "Molecular Biology of the Cell." Garland Publishing Co., New York.

FIGURE 1-15 Model of human erythrocyte membrane. Speculative model based on the human erythrocyte major glycoprotein oligo-meric complex. Phosphatidylserine and phosphatidylglycerol (solid circles) are distributed asymmetrically. Abbreviations: GP, glyco-phorin; III, component 3; IVa, component 4.1; IVb, component 4.2; V, component 5 or actin; VI, component 6 or GP-3-D; VII, component 7; Sp, spectrin. Reproduced from Nicholson, G. L. (1982). In "Biological Regulation and Development" (R. F. Goldberger and K. R. Yama-moto, eds.), Vol. 3A, p. 222. Plenum, New York.

FIGURE 1-15 Model of human erythrocyte membrane. Speculative model based on the human erythrocyte major glycoprotein oligo-meric complex. Phosphatidylserine and phosphatidylglycerol (solid circles) are distributed asymmetrically. Abbreviations: GP, glyco-phorin; III, component 3; IVa, component 4.1; IVb, component 4.2; V, component 5 or actin; VI, component 6 or GP-3-D; VII, component 7; Sp, spectrin. Reproduced from Nicholson, G. L. (1982). In "Biological Regulation and Development" (R. F. Goldberger and K. R. Yama-moto, eds.), Vol. 3A, p. 222. Plenum, New York.

Figure 1-13 depicts an endocrine system involving the CNS, hypothalamus, adenohypophysis, and ultimate target organs. Here, external or internal signals are often mediated by the limbic system or some other system of the brain, and an electrical signal is generated within the CNS that is ultimately delivered to the hypothalamus, where it is transduced into a chemical messenger—the releasing hormones of the

Figure 1-13 depicts an endocrine system involving the CNS, hypothalamus, adenohypophysis, and ultimate target organs. Here, external or internal signals are often mediated by the limbic system or some other system of the brain, and an electrical signal is generated within the CNS that is ultimately delivered to the hypothalamus, where it is transduced into a chemical messenger—the releasing hormones of the

mone is normally (in the absence of an endocrine disease related to hormone secretion) strictly related to the organism's perceived "need" for the biological response^) generated by the hormone in question. The "need" for any hormone will be determined by the physiological set point for that endocrine system. Thus, a characteristic feature of most endocrine systems is the existence of a feedback loop that limits or regulates the secretion of the hormonal messenger. There are two general categories of endocrine feedback systems: those involving the CNS and the hypothalamus and those where the function achieved by the hormone (elevated blood glucose, elevated serum Ca2+, etc.) directly feeds back upon the endocrine gland that secretes the hormones.

Figure 1-12 depicts a schematic diagram of a peripheral feedback system analogous to that utilized by PTH and l,25(OH)2D3 to maintain a normal serum Ca2+ level in the range 9.5-10.5 mg/100 ml of serum. When serum Ca2+ falls, PTH secretion is stimulated and the secreted PTH initiates, at distal target organs, a biological response^) that elevates serum Ca2+. In the event that the serum Ca2+ rises above 10.5 mg/100 ml of serum, there is a feedback signal to the parathyroid gland that represses the secretion of PTH (see Chapter 9 for additional details).

FIGURE 1-16 Model of a fluid mosaic membrane showing distribution and mobility of cell membrane receptors. (A) Integral transmembrane glycoproteins occur in a domain of the membrane of different lipid composition; a glycosaminoglycan molecule is shown associated with the carbohydrate side chains of the glycoproteins. (B) Aggregation of some of the glycoproteins stimulates the attachment of cytoskeletal components: microfilaments (MF) and microtubules (MT) to peripheral membrane components on the cytoplasmic surface are shown. Other unattached integral membrane proteins are capable of lateral motion. Reproduced from Nicholson, G. L. (1982). In "Biological Regulation and Development" (R. F. Goldberger and K. R. Yamamoto, eds.), Vol. 3A, p. 225. Plenum, New York.

FIGURE 1-16 Model of a fluid mosaic membrane showing distribution and mobility of cell membrane receptors. (A) Integral transmembrane glycoproteins occur in a domain of the membrane of different lipid composition; a glycosaminoglycan molecule is shown associated with the carbohydrate side chains of the glycoproteins. (B) Aggregation of some of the glycoproteins stimulates the attachment of cytoskeletal components: microfilaments (MF) and microtubules (MT) to peripheral membrane components on the cytoplasmic surface are shown. Other unattached integral membrane proteins are capable of lateral motion. Reproduced from Nicholson, G. L. (1982). In "Biological Regulation and Development" (R. F. Goldberger and K. R. Yamamoto, eds.), Vol. 3A, p. 225. Plenum, New York.

Mitotic chromosome

Histories

Histories

FIGURE 1-17. Schematic model of a chromosome. The DNA double helix is wrapped around a core of histone proteins to form a nucleosome; altogether the DNA of a single human chromosome is estimated to have approximately 1 million nucleosomes. The nucleosomes, in turn, aggregate to create a very ordered structure termed the "chromatin fiber." The resulting chromatin fibers, which are approximately 30 nm in diameter, condense to create clustered, looped regions that create the chromosome. Each chromosome is composed of two chromatids. This figure was adapted from Becker, W. M., and Deamer, D. W. (1991). "The World of the Cell," 2nd edition. The Benjamin / Cummings Publishing Co., Menlo Park, CA.

Chromatin fiber

FIGURE 1-17. Schematic model of a chromosome. The DNA double helix is wrapped around a core of histone proteins to form a nucleosome; altogether the DNA of a single human chromosome is estimated to have approximately 1 million nucleosomes. The nucleosomes, in turn, aggregate to create a very ordered structure termed the "chromatin fiber." The resulting chromatin fibers, which are approximately 30 nm in diameter, condense to create clustered, looped regions that create the chromosome. Each chromosome is composed of two chromatids. This figure was adapted from Becker, W. M., and Deamer, D. W. (1991). "The World of the Cell," 2nd edition. The Benjamin / Cummings Publishing Co., Menlo Park, CA.

adenohypophysis (see the legend to Figure 1-13 for additional detail).

D. Oncogenes and Hormones

It has become clear that there is a close link between endocrinology and certain forms of cancer. A cancer cell may be described as a cell that has escaped the normal constraints of physiological regulation that maintain the function of that cell within the normal boundaries of the homeostatic state. The "escape" can involve the oncogenic production by the cancer cell of excess or altered forms of a hormone or its receptor. An oncogene is a gene related to cancer. The presence of this oncogenic hormone and / or oncogenic receptor can then totally distort the regulated state of the cell;

this may contribute to the aggressive properties of a tumor. This is particularly so if the oncogene product is an analog of a cellular growth factor that stimulates growth of the tumor. These complex details are considered further in Chapter 20.

Cure Tennis Elbow Without Surgery

Cure Tennis Elbow Without Surgery

Everything you wanted to know about. How To Cure Tennis Elbow. Are you an athlete who suffers from tennis elbow? Contrary to popular opinion, most people who suffer from tennis elbow do not even play tennis. They get this condition, which is a torn tendon in the elbow, from the strain of using the same motions with the arm, repeatedly. If you have tennis elbow, you understand how the pain can disrupt your day.

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