Download Chapter 27 Human Development and Heredity

Chapter 27
Human Development and Heredity
Elsevier items and derived items © 2007, 2003, 2000 by Saunders, an imprint of Elsevier Inc.
Slide 1
Introduction
• The purpose of the reproductive system is to
produce offspring whose genetic information
is faithfully transmitted from generation to
generation.
Slide 2
Fertilization to Birth
• Fertilization
– Fertilization (conception); refers to the union of an
egg and a sperm.
– Fertilization takes place around the time of
ovulation.
– Fertilization normally occurs within the fallopian
tube.
– The fertilized egg is called a zygote.
Slide 3
Fertilization to Birth - cont’d
• Human Development
– Development is a process that begins with
fertilization and ends with death.
– The two phases are prenatal development and
postnatal development.
Slide 4
Fertilization to Birth - cont’d
• Prenatal Development
– Prenatal development includes four processes:
cleavage, growth, morphogenesis, and
differentiation.
– The prenatal period consists of the early embryonic,
embryonic, and fetal periods.
• The early embryonic period lasts for 2 weeks after
fertilization. The zygote develops and implants into the
uterine endometrial lining; its trophoblastic cells secrete
hCG (maintains the corpus luteum).
Slide 5
Fertilization to Birth - cont’d
• Prenatal Development—cont’d
– The prenatal period—cont’d
• The two types of twins: monozygotic (identical) twins
and dizygotic or fraternal (nonidentical) twins.
• The embryonic period lasts for 6 weeks and involves
the formation of the extraembryonic membranes, the
placenta, and all of the organ systems.
• The four extraembryonic membranes are the amnion,
the chorion, the yolk sac, and the allantois.
Slide 6
Fertilization to Birth - cont’d
• Prenatal Development—cont’d
– The prenatal period—cont’d
• The placenta develops as the chorionic villi of the
embryo burrow into the endometrial lining of the uterus.
The mother and embryo form two separate circulations.
• The placenta has two functions: a. the site of “exchange”
of nutrients and waste, and b. glandular function
(estrogen and progesterone) throughout the pregnancy.
• The embryo is hooked up to the placenta by the
umbilical cord.
Slide 7
Fertilization to Birth - cont’d
• Prenatal Development—cont’d
– The prenatal period—cont’d
• The embryonic period is a period of organogenesis.
The organs arise from the primary germ layers:
the ectoderm, the mesoderm, and the endoderm.
• The fetal period extends from week 9 to birth; it is a time
of growth and maturation.
• Hormonal changes during pregnancy are summarized in
Table 27-1.
Slide 8
Fertilization to Birth - cont’d
• Birth (Parturition)
– Labor consists of the forceful contractions that
expel the fetus from the uterus.
– Labor is caused by hormones.
– The three stages of labor are the dilation stage,
the expulsion stage, and the placental stage.
Slide 9
Fertilization to Birth - cont’d
• Breasts and Lactation
– The breasts contain mammary (milk-secreting)
glands and adipose tissue.
– The mammary glands and surrounding structures
are affected by two hormones, prolactin and
oxytocin. Prolactin stimulates the mammary
glands to increase the production of milk.
Oxytocin stimulates the smooth muscle in the
breast to release the milk (part of the milk letdown reflex).
Slide 10
Postnatal Development
• Immediate Postnatal Changes
– The baby takes a first breath and the
cardiovascular system makes some major
adjustments.
– The baby’s transition to “life on the outside” is
monitored by the Apgar scale.
• Developmental Periods: Neonatal Period,
Infancy, Childhood, Adolescence, Adulthood,
and Senescence
Slide 11
Heredity
• DNA, Genes, and Chromosomes
– Genetic information is stored in the DNA of genes,
which are arranged into chromosomes.
– Chromosomes exist in pairs. With the exception of
sex cells, most human cells have 23 pairs of
chromosomes, or 46 chromosomes.
– Genes are dominant, recessive, or codominant.
– A genetic mutation is due to a change in the
genetic code.
Slide 12
Heredity - cont’d
• DNA, Genes, and Chromosomes—cont’d
– The sex chromosomes are designated X and Y.
A female has two X chromosomes, and a male has
one X chromosome and one Y chromosome.
Because only the male has the Y chromosome, the
father determines the sex of the child.
– Sex-linked traits are carried on the sex
chromosomes. Most are carried on the X
chromosome and are therefore also called
X-linked traits.
Slide 13
Heredity - cont’d
• Congenital and Hereditary Diseases
– A congenital disorder is a condition present
at birth.
– Congenital disorders include inherited and
noninherited birth defects and diseases. A
hereditary disease is transmitted genetically
from parent to child.
Slide 14