This chapter builds on the principles of reproduction intro-

duced in Chapter 16, including how hormones influence the

menstrual cycle (16.1, 16.2).

You will learn how organ systems (4.8) start to develop in

an embryo and about special features of the cardiovascular

system in a developing fetus (7.1).

We will also see how hormones from the hypothalamus and

pituitary set the stage for birth (15.3).

Key ConCepts

LinKs to earLier ConCepts

Development Begins

A new individual begins to develop

in steps that produce a multicellular

embryo in which tissues and organs

form. Each step is guided by genes

and builds on body structures that

are formed in the preceding stage.

S e c t i o n s 17.1 –17. 4

Prenatal Development

As an embryo develops, so do

vital support structures such as the

placenta. In the fetal phase, organs

and other structures grow and

mature. S e c t i o n s 17. 5 –17. 8

Birth to Adulthood

Birth launches life outside the

womb. Body structures and their

functioning change from infancy

onward. S e c t i o n s 17. 9 –17.12

Later Life

Over time, age-related changes

begin to affect virtually all body

organs and tissues. S e c t i o n 17.13

© iStockphoto.com/ManoAfrica

329

Under age 30? You’re in your biological prime.

If you’ve passed 30, you’ve probably noticed the beginnings of

wrinkles, and possibly the hint of a bit less spring in your step.

Change is the hallmark of biological development. The process

starts as soon as fertilization of an egg by a sperm forms a zygote.

Immediately, genes begin guiding the growth of an embryo and the

formation of tissues and organ systems. From birth onward, more

gene-guided growth and development transforms the body of a

newborn into that of a mature adult. This remarkable journey is our

topic in this chapter.

Top: © Cengage Learning; Second from top: Lennart Nilsson from

A Child Is Born, © 1966, 1977 Dell Publishing;. Second from bottom:

© MitarArt/Shutterstock.com; Bottom: Jose Carillo/Photo Edit

DeVeLopment anD aging

17

Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).