3.4 The Eddington Limit

Thus the observations require that a luminosity of around 100 times that of the entire Milky Way Galaxy be generated within a region with a diameter only about 1000 times that of the Earth's orbit! (A truly amazing statement.)

The most obvious mechanism for generating such enormous luminosity within such a tiny region of space is an accretion process, but instead of perhaps more familiar compact stars with masses ~M
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2 Black holes: a reminder

You may have previously met the formation of a black hole at the end of the life of a massive star. Accreting black holes, which were formed in this way, are members of close binary star systems.

A black hole is formed when self-gravity causes material to collapse to such high densities that the escape speed (or escape velocity) reaches the speed of light. Using Newtonian dynamics we can calculate the magnitude of the escape velocity from planet Earth (mass M E
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1 Evolution versus creation: science and non-science

Science aims to extend our understanding of natural phenomena through testing of explanatory hypotheses by reference to hard evidence. It is not concerned with ideas that cannot be tested in this way, such as subjective opinions (for example, what is good or evil, beautiful or ugly) or religious beliefs (about, say, ‘the meaning of life’ and the existence of gods or spirits), though we will return to ideas like this at the end of this unit. The remit of science was eloquently summarised b
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1.3.3 A breeding experiment: stage two

We now turn to the second stage of the breeding experiment, but this time we will follow the phenotypes and genotypes simultaneously. The purple (Gg) grains of the F1 generation are planted and when these have developed into mature F1 plants they produce male and female flowers. These F1 plants are crossed with each other, as shown in Figure 8. The fertilised ovules develop into grains borne on cobs, and these grains are the beginning of the second f
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3.5 Muscle

There are different sorts of muscle in the body and they have different functions. Skeletal muscles are the muscles that, for example, are used for movement in your arms and legs.

Skeletal muscles store glucose as glycogen (Figure 4) and are able to use glucose as a fuel. Insulin stimulates muscles to take up glucose, and w
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3.2 Pancreas

The pancreas is a structure (an organ) that lies towards the back of the abdomen, the part of the body between the chest and the pelvis (hips). The abdomen contains the stomach, liver, spleen, pancreas, intestines and other structures. The pancreas is near the liver and the spleen (Figure 1) and opens into the small intestine.
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3.1 Introduction

The main role of glucose within the body is as a fuel but it also contributes to the fabric (tissue) by attaching to proteins. In people without diabetes, the blood glucose levels are kept within very narrow limits. The body does not allow them to become too high or too low. Several parts of the body are involved in this process. Some are large, for example the liver, and some are very small, such as the cells within the pancreas. Cells are small building blocks of the body and cannot
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2 What is diabetes?

Diabetes mellitus is a condition in which the glucose level in the blood is higher than it should be. The word ‘diabetes’ comes from the Greek word for ‘siphon’. A siphon is a way of removing liquid, and diabetes is used to describe disorders that remove liquid from the body, resulting in excessive thirst and the production of large amounts of urine. There are two forms of diabetes, diabetes mellitus and diabetes insipidus, of which diabetes mellitus is the more common. The wor
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1 Defining diabetes

This unit introduces the parts of the body and processes involved in the development of diabetes. Type 1 and Type 2 diabetes are similar but distinct conditions and, for doctors, it is not always easy to decide which type of diabetes someone has. Does this matter, and is one type of diabetes worse than the other? There are many misconceptions about diabetes among health care professionals and the population in general. We hope this unit will help you to explore and clarify your ideas about di
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Introduction

This unit introduces parts of the body and processes involved in the development of diabetes.

This unit is from our archive and is an adapted extract from Diabetes care (SK120) which is no longer taught by The Open University. If you want to study formally with us, you may wish to explore other courses we offer in this subject area.


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Acknowledgements

Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence.

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

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14 Unit questions and answers

Note: Question 1 is included in Section 3.

Question 2


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6.4 Taking the image

Activity 12

Now watch this video clip of a patients lungs being imaged, called a VQ (ventilation quotient) scan. What are the two different types of acquisitions used called? What radioactive substance is used for each acquisition, and why
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6.3.2 Crystal

Almost all modern gamma cameras use (thallium-doped) sodium iodide (NaI) as the scintillation crystal. A gamma photon interacts with the crystal to produce many photons of visible light.

Sodium iodide is hygroscopic so cannot be left exposed to the air. The front surface is coated with a low atomic number metal that allows the gamma photons to pass through. The rear surface is covered with a transparent coating so that the visible photons can pass through to the photomultiplier tubes.
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6.3.1 Collimator

Without a collimator, gamma rays from all directions would be collected by the crystal and no useful image could be obtained. Gamma rays cannot be focused by a lens but a collimator consisting of a series of holes in a lead plate can be used to select the direction of the rays falling on the crystal. Most collimators in use today are parallel hole collimators. A parallel hole collimator is shown schematically in Author(s): The Open University

6.2 Producing the radioactive substance (elution)

In the radiopharmacy Tc-99m is produced in a generator.

Mo-99, a product of the fission of uranium, is isolated from a nuclear reactor and absorbed on to an alumina column in the generator. When a saline solution is passed over the column, ion exchange results in the production of sodium pertechnetate. This can then be chemically manipulated to form a variety of compounds. The removal of the technetium by the passage of saline is known as elution.

Conveniently, the optimum interva
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5 Ultrasound

Ultrasound imaging uses acoustic waves, rather than ionizing radiation, to form an image. The principle is rather like radar; a pulse of ultrasound (1–15 MHz) is sent out from the transducer and reflected from tissue boundaries. Measurement of the time taken for the pulse to return allows the distance to the reflecting boundary to be calculated.

The important parameter determining the amount of reflection is known as the acoustic impedance (Z) of the tissue and is the product o
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2.2 The kinkajou

LoM describes this tree dweller as a relative of the raccoon. It belongs to the order Carnivora and is one member of a family generally referred to as procyonids [p. 170], or more commonly the raccoon family. You'll be aware that some members of this family – for example, coatis [p. 174] – are omnivores. As you'll see in the video sequence below, coatis are more typically found in the undergrowth and leaf litter, rather than high up in the trees. (If you need to remind yourself of the lif
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7 The threat of extinction

DA ends his book by writing eloquently of the dangers of extinction faced by mammals, from habitat loss as we exploit our environment to produce more and more food, for our growing population. However bleak the picture, there is still time and opportunity to save mammal species from extinction. Although bison in the USA and Canada were reduced to barely 1000 individuals in 1900, their numbers have now risen to well over 150 000 thanks to the efforts of First Nation indigenous peoples, and ran
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4 Who were the ancestors of Homo?

Fossil evidence supports Darwin's view that humans and apes evolved from an ape-like ancestor and, furthermore, suggests that the ape line diverged from the Homo line at least five million years ago (Figure 1). From our current knowledge of the fossils available to us, the evolutionary tree in
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