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Time: 20 hours
Level: Introductory
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 Introduction Resource- This unit looks at the human being in the context of an individual life cycle, examining some of the processes that contribute to the formation of a new person. After a brief discussion of historical ideas...
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- 1 What is development? Resource
- In this unit we begin to look at the human being in the context of an individual life cycle, examining some of the processes that contribute to the formation of a new person. This is the first time that...
| | | | | 2 How has the human population grown?
- 2 How has the human population grown? Resource
- For most of human history there have been relatively few people in the world. Figure 2 shows that only over the last 50 years have numbers really shot up, and that, at the turn of the century, the population...
| | | | | 3 Artificial contraception
- Decoupling sex and reproduction Resource
- Humans have separated sex and reproduction: unlike other species, we can enjoy sexual intercourse even (or especially) at times when fertilization is not possible. Many sexual encounters are casual, and...
- 3.1 Chemical contraceptives Resource
- 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...
- 3.2 Mechanical methods of contraception Resource
- While hormone-containing pills represent a very sophisticated kind of contraceptive, mechanical contraceptives are a straightforward idea: they act by preventing sperm and egg from meeting. Mechanical...
- 3.3 Surgical methods of contraception Resource
- 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...
- 3.4 Natural methods of contraception Resource
- Many people with particular religious beliefs are fundamentally opposed to the use of artificial methods of contraception. In the developing world, where, as you saw above, the population is frequently...
- Summary of Section 3 Resource
- Many people wish to limit the number of their offspring, and so resort to contraceptive measures.
| | | | | 4 Preparing for conception
- 4.1 Why are cells different? Resource
- Now let us go on with our story and assume that we have decided the time is right to have a baby. The primary requirement for conception is that healthy gametes should be produced. We shall therefore look...
- 4.2 The reduction of chromosome number: meiosis Resource
- If you look at the chromosomes shown in Figure 8 you will see that they have been lined up in pairs. The members of each pair are of similar shape and size, and unlike the members of other pairs. At a...
- 4.3 Gamete production in men Resource
- A sexually mature man is producing sperm all the time at a rate of around 300–600 per gram of testis per second. This provides the 500 million or so which are released at each ejaculation. But the formation...
- 4.4 Hormonal control of sperm production Resource
- 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...
- 4.5 Gamete production in women Resource
- It is time now to turn to the question of how female gametes – eggs – are made. There are substantial differences between sperm and eggs, and consequently their production pathways are very different.
- 4.6 Hormonal control of egg production Resource
- As you can see from the preceeding section, hormones play a crucial role in the maturation of the oocyte. Figure 3 showed you how levels of oestogen and progestogen vary throughout the menstrual cycle,...
- 4.7 Factors affecting fertilization Resource
- It is useful at this stage to summarize the main factors involved in a successful fertilization. First and foremost, fertile gametes must be made. This depends fundamentally on the health of the prospective...
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- Summary of Section 4 Resource
- Gametes are special cells because they contain only one set of chromosomes instead of the more usual two sets.
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- 5.1 How fertilization happens Resource
- Now that we have dealt with the basic biology, we can resume and give more detail to our story, and return to where we left it: fully mature, strongly swimming sperm have been deposited in the vagina,...
- 5.2 Why fertilization may not happen Resource
- It is estimated by most practitioners that more than 50% of all conceptions are genetically abnormal, and it has been suggested that this results in part from the fertilizing of old eggs. Of course, good...
- Summary of Section 5 Resource
- After ejaculation some sperm penetrate the cervical mucus, and on arriving in the uterus become capacitated.
| | | | | 6 Small beginnings – the first two weeks
- 6.1 Pre-implantation and assymetric division Resource
- Let us now return to the Fallopian tube, where a fertilized egg is assembling its chromosomes prior to commencing a series of mitotic divisions which will eventually give rise to the millions of cells...
- 6.2 Compaction and adhesion Resource
- 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...
- Summary of Section 6 Resource
- For the first week after fertilization, the conceptus (early embryo) foats freely in the female reproductive tract, obtaining some of its nutrients from the fuid in which it is bathed.
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- 7 A new life Resource
- There is a common belief that life begins at the moment of conception, i.e. when a sperm fuses with an egg. This is a step forward from past years, when life was alleged to start at the time of ‘quickening’,...
| | | | | 8 How does a woman know she's pregnant?
- 8.1 Identifying the pregnacy Resource
- Our description of the developing embryo has, so to speak, detached it from its mother. But we should remember that on the other end of the placenta is a woman whose reaction to her pregnancy may lie almost...
- 8.2 Experiencing the pregnancy Resource
- 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...
| | | | | 9 Selecting the sex of a child
- 9 Selecting the sex of a child Resource
- Once a pregnancy has been established, many couples are anxious to know the sex of their unborn baby. The reasons for this are many, ranging from the prosaic (will the baby be able to use its brother's...
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- 10 Review Resource
- In this unit we have looked at some of the factors which infuence a couple's decision to have a child. For people who choose not to do so, at least for some part of their lives, a range of contraceptive...
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- Questions for Unit Resource
- Figure 19 is a graph showing how the viscosity (thickness and stickiness) of a woman's cervical mucus changes with time. Day 0 is the start of her menstrual period.
| | | | | References and Acknowledgements | | |
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