6.5 The neurotransmitters histamine and serotonin: a role for chemical signalling between neurons of

As in all other regions of the brain, the integration of physiological change in the hypothalamus, conducted by the dialogue between many thousands of nerve cells, is the result of transmissions across chemical synapses. The functions of the hypothalamus are therefore dependent upon neurotransmission by a number of different chemical mediators and are critically dependent on the balance between their respective activities. Monoamine neurotransmitters (histamine and serotonin) operate in subgr
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6 Conclusion

There is much more to living in polar regions than insulation against the cold. Food may be very scattered both in space and in time and breeding must be tightly synchronized to seasons and food availability. Some of the most spectacular examples of natural obesity and efficient regulation of appetite are found among polar animals. The study of such species not only demonstrates that it is possible to remain healthy and active when very obese and during prolonged fasting, it also helps us to
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3.2 Small babies

Development continues in the womb until birth, which, in humans, is about 38 weeks after conception. (The often quoted duration of pregnancy of 40 weeks is based on pregnancy beginning on the first day of the last menstrual period.) The duration of the period of development before birth, called gestation, is highly variable. It is not possible to determine its full range in the UK, because medical intervention usually prevents pregnancies going beyond about two weeks after the due date, or te
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2.2 Vitamin A

Activity 4

Look back at Table 1 and identify the foods that contain vitamin A. On the basis of this information, try to predict where vitamin A is stored in the human body.

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Acknowledgements

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All other materials included in this unit are derived from content originated at the Open University.

1. Join the 200,000 studen
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1.4.2 The functional group approach

It is the classification of functional groups that simplifies the study of organic chemistry (the chemistry of compounds that contain carbon). With many millions of known organic compounds, and more being added by the day, it would be hopeless if their properties could not be systematised in some way. It turns out that a given functional group usually has the same chemical properties whatever carbon chain it is bonded to, so once the general properties of each functional group are known, all
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1.4.1 Salicylic acid

The structural formula of salicylic acid, 2.1, looks quite complicated. However, it becomes less daunting if you unpack it a bit. One of the first things to do when confronted with an unfamiliar structure is to check that all the valencies are correct (four for carbon, two for oxygen and one for hydrogen). If any atoms have the wrong valency, it follows that there is a mistake somewhere and the molecule does not exist as drawn. It looks OK for the structure of salicylic acid. You proba
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1.2.4 Fertilization

Now that we have considered the production of gamete cells, including the process of meiosis, we can examine the next stage of reproduction, the process of fertilization, which occurs inside the female's reproductive tract. As fertilization occurs, the successful sperm stops swimming and a change takes place in the egg cell membrane, which prevents any other sperm from fusing with it. The nucleus of the sperm cell is injected into the cytoplasm of the egg cell. The chromosomes of the fertiliz
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2.2 Persistent currents lead to constant magnetic flux

An important consequence of the persistent currents that flow in materials with zero resistance is that the magnetic flux that passes through a continuous loop of such a material remains constant. To see how this comes about, consider a ring of metal, enclosing a fixed area A, as shown in Figure 6a. An initial magnetic field B0 is applied perpendicular to the plane of the ring when the temperature is above the critical temperature of the material from which the rin
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2.1 Zero electrical resistance

In this section we shall discuss some of the most important electrical properties of superconductors, with discussion of magnetic properties to follow in the next section.

The most obvious characteristic of a superconductor is the complete disappearance of its electrical resistance below a temperature that is known as its critical temperature. Experiments have been carried out to attempt to detect whether there is any small residual resistance in the superconducting state. A sensitive t
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Optional reading

Debates about the relationship between science, citizenship and democracy continue to influence public policies related to science communication and public engagement in science. In part, these debates involve discussions about scientific and other ways of knowing. For an introduction to these issues, see Irwin (1999).

This premise, of exchanging information and learning from others, is also relevant to your communication with other expert scientists. As a research student you will lear
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5: Other forms of potential energy

It is worth emphasising that the gravitational energy (or gravitational potential energy, to give it the full name) of an object increases when it moves in the opposite direction to the gravitational force (i.e. when it moves upwards). This relationship between energy and force does not apply only to gravity. For many forces, motion against the force (that is, in the opposite direction to the force) allows energy to be stored, and this energy can be reclaimed when the obj
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3.2 Number of progeny

Female guppies begin to breed as soon as they become mature at about three months old; they then produce clutches of eggs, most of which become fertilized, at roughly one-month intervals until they die or become too old. Clutches vary in size from one to 40 eggs; the average clutch contains about 10 eggs. Thus, female guppies produce a large number of offspring during their lives, far more than can survive to maturity.

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3.5.2 Link checking sites

The World Wide Web contains millions of web pages. Many of these pages are impossible to read, even though many existing web pages will reference them: your browser will usually return with some message such as ‘Error 404 Page not Found’ when you try to access them. Error 404 is a standard message returned by web servers when a non-existent page is accessed. It is also the telephone area code for Atlanta in the United States; you will occasionally hear technical staff referring to non-exi
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3.2 Utility theory

Utility theory is based on this assumption of rationality and describes all decision outcomes (financial and otherwise) in terms of the utility (or value) placed on them by individuals. Within this framework, decisions can be understood in terms of rationally ordered levels of utility attached to different outcomes.

Bazerman (2001, pp.3–4), for example, describes a formally rational decision process for arriving at a decision with the greatest expected utility in the following terms:<
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Studying mammals: The opportunists
Many mammals are food specialists, with complex adaptations that gear them toward a particular food source. So how do the omnivores survive and prosper without these fancy evolutionary features? This unit examines the physiology, diet and strategies of some of these opportunistic feeders. It is the sixth unit in the ‘Studying mammals’ series. Fir
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Animals at the extremes: The desert environment
Animal life has adapted to survive in the most unlikely and inhospitable habitats. This unit looks at the surprisingly diverse desert climates throughout the world and mammals, birds, lizards and amphibians that survive there. It splits these animals into three groups according to their strategy for survival: evaders, evaporators and endurers, then discusses how these strategies work on a biochemical and physiological level.Author(s): Creator not set

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Understanding the environment: Flows and feedback
There is increasing recognition that the reductionist mindset that is currently dominating society, rooted in unlimited economic growth unperceptive to its social and environmental impact, cannot resolve the converging environmental, social and economic crises we now face. The primary aim of this unit is to encourage the shift away from reductionist and human centred thinking towards a holistic and ecological worldview.Author(s): Creator not set

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Understanding the environment: Complexity and chaos
There is increasing recognition that the reductionist mindset that is currently dominating society, rooted in unlimited economic growth unperceptive to its social and environmental impact, cannot resolve the converging environmental, social and economic crises we now face. The primary aim of this unit is to encourage the shift away from reductionist and human centred thinking towards a holistic and ecological worldview.Author(s): Creator not set

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