3.6.2 Experiencing the pregnancy If a woman does find herself pregnant, what can she expect? Pregnancy is a time of enormous physical and emotional changes, and these are often difficult to cope with. To begin with, the physical effects of early pregnancy can be extremely unpleasant. The nausea and vomiting of morning sickness can be very severe, and although in many women the symptoms abate after a while, in others they persist right through the pregnancy. Sickness is thought to be due to the high levels of progestogen circ
3.4.2 Compaction and adhesion Around the time of the 8- to 16-cell division, the conceptus undergoes a morphological (shape) change, called compaction, in which the cells fatten on each other, and the outlines of individual cells become hard to distinguish. This stage, sometimes referred to as a morula, from the Greek word for mulberry, is shown in Figure 17i. At this stage it is hard to see individual cells; in fact, unless the cells are separated by various laboratory treatments, it is not possible to see the two
4.4 Hormonal control of sperm production The most important hormone involved in controlling sperm production is a steroid called testosterone. This is produced in the testis itself, by the Leydig cells (see Figure 12a). The testosterone is released from the Leydig cells between the tubules, and taken up by the neighbouring Sertoli cells. The Leydig cells are stimulated to make testosterone by two other hormones, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are both produced by the pituitary gland and
1.3.4 Surgical methods of contraception Surgical methods are by and large the most drastic and irreversible ones, ranging from castration to relatively untraumatic tube-tying. Because of the psychological and physiological side-effects, surgical removal of the testes or ovaries is not generally carried out for contraceptive reasons alone, although these operations may be carried out for other reasons, such as the presence of malignant tumours. Any kind of surgical sterilization can be physiologically traumatic for a woman, as it in
1.3.2 Chemical contraceptives These methods rely to a large extent on an understanding of the physiology of the reproductive process. They are targeted at preventing the production or release of gametes, i.e. the sex cells – sperm and eggs – which need to fuse to produce a new individual. To date, most effort in this area has been directed towards preventing a woman from ovulating, i.e. releasing an egg, although more recently trials have begun on ‘male pills’ which block sperm production. Ovulation i
Introduction This unit is from our archive and it is an adapted extract from Human Biology and Health (SK220) which is no longer in presentation. If you wish to study formally at The Open University, you may wish to explore the courses we offer in this curriculum area
. This unit looks at the human being in the context of an individual life cycle, examining some of the processes that
Acknowledgements Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit: This content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence. See Terms and Conditions. Figure 1 Copyright ©
Figures
3.4.7 Induced earthquakes Some reservoirs cause earthquakes to occur. This is perhaps not so surprising, as earthquakes are caused by stress in rocks, and the addition of a large mass of water in a reservoir on top of the rocks at the Earth's surface stresses the rocks and can trigger an earthquake. Not all reservoirs induce earthquakes: it is in general only the larger reservoirs, or the deeper ones (over 100m deep), and only if the reservoir is built in an earthquake area, releasing stress already stored in t
3.4.4 Sediment filling The lifetime of reservoirs can vary greatly. Many reservoirs have lasted for over a hundred years, but some may be useful for only a much shorter period—fifty years or so — not because of the general deterioration of the dam as it gets older, but because sediment accumulates in the reservoir. Rivers carry large amounts of mud, silt and sand in suspension, particularly during floods, and when a river enters a reservoir it slows down and the sediment carried in suspension is deposited on th
3.3 Dams To economize on constructional materials and costs, it is desirable to build a dam at a narrow part of a valley so that the dam can be kept as short as possible. The quantity of constructional materials needed to build dams, and their cost, can be enormous. The Aswan High Dam, built during the 1960s, cost £400 million for a 1.2 km dam. Though shorter than the Aswan High Dam, the longest dam in Britain, the Kielder Dam in Northumberland (Author(s):
2 River flow The total land area drained by a river system, including all its tributaries, is called a river catchment. The water in a river comes not only from direct precipitation, springs and overland flow (i.e. water flowing across the ground surface, excluding that in streams and rivers; this is rare in temperate vegetated areas) but also from the underground flow of water, directly to the river. Part of this underground flow is interflow, that part of infiltration which moves th
4 Groundwater movement Groundwater flows underground in response to elevation differences (downwards) and pressure differences (from areas of high pressure to areas of low pressure). Near the water table, this means that groundwater usually flows ‘downhill’, i.e. from a higher level to a lower level, just as it would on the surface. The difference in energy between two points that are l metres apart horizontally on a sloping water table is determined by the difference in height (h) between them (<
3.6.2 The JAK–STAT pathway Another important protein kinase pathway is the JAK–STAT pathway. Cytokines (Section 2.2), are frequently used for signalling between cells of the immune system. Cytokine-induced signal transduction cascades are often direct pathways to the nucleus for switching on sets of genes. Janus kinases (JAKs, named after the two-faced Roman god) are a particular
1.6 Fibrous proteins Most of the proteins described so far have been globular proteins. There are, however, some distinctive features that characterise fibrous proteins and we present here a general overview of these. Elongated fibrous proteins frequently play a structural role in the cell. They do not readily crystallise but tend to aggregate along their long axis to form fibres. X-ray diffraction studies of these fibres, in contrast to analysis of protein crystals, provides only very limited information on the
Introduction Proteins are the ‘doers’ of the cell. They are huge in number and variety and diverse in structure and function, serving as both the structural building blocks and the functional machinery of the cell. Just about every process in every cell requires specific proteins. Let us begin by listing some of the basic cellular processes and the role that proteins play. Chemical catalysis Enzymes, which are responsible for catalysing biological
7.5 Emission from spiralling electrons: synchrotron radiation In the very first reading (Activity 1) we encountered the term ‘non-thermal’ describing the spectrum of light emitted from AGN. In this subsection we will learn more about the most important type of non-thermal radiation: synchrotron emission. When a charged particle moves in the presence of a magnetic field it experiences a Lorentz force, which produces an acceleration whose direction is perpendicular to both the magnetic field line and the velocity of the particle,
5 The Scopes monkey trial This section was written by Gary Slapper. In 2007, Professor Michael Reiss, a Church of England priest and the head of science at London's Institute of Education, said that it is becoming more difficult to teach evolution in schools because of the spread of creationism. Similar debate has long been burning in the United States. Also in 2007, a creationist museum opened near Cincinnati, where children in animal skins play amid model dinosaurs, suggesting they once coexisted and th
1.6 Summary The number of chromosomes is characteristic of each species and can vary enormously between species. Sexual reproduction always includes two distinctive processes: the production of gametes, which involves meiosis, and fertilisation. The two processes are accompanied by changes in the chromosome number, from diploid to haploid and from haploid to diploid, respectively. Genetics is based on the concept of the gene as the unit of inheritance. A particular phenotypic character is det
2 The biology of prions The increasing interest in kuru during the 1950s and 1960s had the effect of stimulating research into TSEs in humans and other animals. Summarise, in general terms, the possible causes of disease in animals. 6 Thermoregulation and mammalian fur A coat of profuse mammalian body hair is commonly called fur. Fur provides insulation, which is a property that one first thinks of as useful for mammals to help retain body heat. Fur is a unique and fundamental feature of mammals, though not all living species possess it.
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Question 12
