The Reproductive System, Third Edition

By Randolph Krohmer

Organisms reproduce to ensure the continued survival of their respective species. For humans, our ability to produce offspring and contribute to genetic variability in the world is made possible by our body's reproductive system. In The Reproductive System, Third Edition, learn how the development of the reproductive systems in both males and females depends on the delicate and coordinated balance of genetic makeup, hormones, and the nervous system. Also examined are the reproductive systems of males and females, and how the body develops from conception through puberty and into maturity. Packed with full-color photographs and illustrations, this absorbing book provides students with sufficient background information through references, websites, and a bibliography.

• Language: English
• Publisher: Chelsea House
• Release date: Oct 1, 2021
• ISBN: 9781646937233

Book preview

The Reproductive System, Third Edition

The Reproductive System, Third Edition

Copyright © 2021 by Infobase

All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For more information, contact:

Chelsea House

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New York NY 10001

ISBN 978-1-64693-723-3

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Contents

Cover

Copyright

Chapters

Reproduction: A Characteristic of Life

Early Embryonic Development

Development of the Reproductive System

Developmental Differences in Brain and Behavior

Adolescent Puberty

Puberty in the Male

Puberty in the Female

Concerns and Complications

Support Materials

Glossary

Bibliography

Further Resources

About the Author

Index

Chapters

Reproduction: A Characteristic of Life

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The fact that this book is not a living organism should not be much of a surprise to anyone over the age of five. But how do we know that it is an inanimate (not living) object? The scientific community has developed a list of characteristics that can be used to determine if an object is truly alive. One of those characteristics is its ability to reproduce, thus ensuring the continued existence of the organism's species. Although this text has been reproduced many times for many different readers, it has no self-regulating mechanism for reproducing. However, all living organisms, from a single-celled amoeba to a 72 trillion-celled human, have an innate drive—not simply a desire—to reproduce.

There are two kinds of reproduction: asexual and sexual. Many biochemical events must occur before an organism can reproduce either way. Asexual reproduction, the simplest form of reproduction, literally means without sex. In organisms that reproduce asexually, reproduction occurs without partners coming together. Asexual, single-celled organisms grow to a certain stage or size and then divide into two identical organisms. This division, which is a complex process, is called mitosis. It requires the organized division of the genetic material (see figure below). This division must be coordinated with the division of the cytoplasm, a process called cytokinesis. The end result of asexual reproduction is two identical daughter cells.

Mitosis and cytokinesis result in the equal division of the nucleus and cytoplasm, respectively, producing two identical daughter cells. During interphase, the cell grows and the genetic material in the nucleus is duplicated. The cell then enters prophase in which the nuclear envelope breaks down, and the paired centrioles migrate to opposite sides of the cell while sending out fibers to form the mitotic spindle. During metaphase, the chromosomes line up in the middle of the cell and fibers from both centrioles attach to each pair of chromosomes. Prometaphase is the stage during which the nuclear membrane begins to disintegrate. During anaphase, the daughter chromosomes are pulled by the spindle fibers to opposite sides of the cell. By late anaphase, as the daughter chromosomes near their destination, a cleavage furrow begins to form in the cell membrane indicating the beginning of cytokinesis. In the final stage, telophase, the cell membrane continues to constrict and eventually divides into daughter cells. As this is occurring, the nucleus is reestablished, and the daughter cells are once again in prophase.

Multicellular organisms that reproduce asexually have developed several unique reproductive strategies. For example, the jellyfish reproduces by budding, a process in which a new individual begins to grow, or bud, from the original organism and is eventually released as a small, free-swimming organism. Starfish have a similar method of reproduction. More than 100 years ago, men working the oyster beds wanted to eradicate starfish because starfish eat oysters. When workers brought up a starfish with their catch, they would cut it into pieces and throw it back into the water thinking they had put an end to that starfish. Little did the workers know that an entire starfish could be regenerated from each piece. Obviously, this put the oyster farmers at an even greater disadvantage as they caused an increase in the starfish population rather than eliminating it. Asexual plants, such as strawberries, propagate new individuals by sending out shoots that will develop into new plants. This reproductive process is also how new plants can be generated from cuttings of existing plants. All of these reproductive methods produce offspring that are clones (genetically identical) to the parent organism.

The benefits of asexual reproduction include the fact that an organism can reproduce independently. That is, no individual is dependent on another to reproduce. Organisms that reproduce by asexual means are capable of creating a large population in a relatively short time. Because the organisms are genetically identical, they will all be equally successful in the same constant environment. The genetic similarities, however, confer some disadvantages to asexual organisms. For example, if a population of clones is perfectly suited for an environment that has a pH of 7.0 and a temperature range of 77°F-86°F (25°C-30°C), what happens if the environment changes? If the temperature increases and the pH of the environment becomes more acidic, the population has no genetic variability and, therefore, no way to compensate for changes in this new environment. The entire population will likely disappear under these altered conditions because it could not tolerate or live in the new environment.

Although sexual reproduction is much more complex than asexual reproduction, it offers the benefit of genetic variability. While sexual reproduction may waste some nutrients on males who cannot add to the population number directly, these males offer a different set of chromosomes with different characteristics, thus generating genetic variability and allowing sexually reproducing species to evolve and occupy essentially every corner of the Earth. As described previously, a cell copies its genetic blueprint during mitosis before it divides into two identical daughter cells. Unlike mitosis, sexual reproduction is accomplished by the fusion of an egg nucleus with a sperm nucleus, or fertilization. However, the resulting cell, a fertilized egg (or zygote) must not contain more genetic material than is present in the somatic (nonsex) cells of that species. This is critical because too many chromosomes may result in a genetic burden that can result in problems by providing too much genetic information. One universal example is trisomy 21.  Trisomy 21, or Down Syndrome, results when a fertilized egg has three copies of chromosome 21 instead of the normal two copies. Down Syndrome usually causes varying degrees of intellectual and physical disability and associated medical issues.¹ In sexually reproducing animals, all of