Fetal-Placental Disorders

Nicholas S. Assali

• Publisher: Academic Press
• Year: 2013
• Print ISBN: 9780120655021
• eBook ISBN: 9781483262697
• Topic: Medizin
• Subtopic: Gynäkologie, Geburtshilfe & Hebammen

Pathophysiology of Gestation, Volume II: Fetal-Placental Disorders covers important areas of reproduction such as maternal-fetal interrelationship, biochemistry and physiology of the fetoplacental unit, and use of amniotic fluid constituents as diagnostic tools for fetal well-being. This book is divided into five chapters. Chapter 1 deals with the disorders of placental transfer, clearly illustrating the physical and biochemical processes involved in placental exchanges between mother and fetus. The second chapter is devoted to disorders of placental endocrine functions. The various methods used for studying placental hormone production and the errors in analysis and interpretation of the results are also elaborated. The pathophysiology of amniotic fluid disorders is discussed in Chapter 3, while the genetic factors affecting growth and development from the gamete stage through fertilization and organ formation are described in Chapter 4. The last chapter considers the teratologic impact of the environmental factors on fetal growth and development. This volume is valuable to medical students and individuals concerned with the disorders of the maternal-fetal interrelationship.

1

Disorders of Placental Transfer

Lawrence D. Longo

Publisher Summary

This chapter discusses the factors adversely affecting placental transfer and their possible implications on fetal metabolism and development. A distinguishing feature of mammalian development is the provision of nutrients from the maternal organism. Adequate exchange across the placenta between the maternal and fetal circulations is essential for normal fetal metabolism and growth. The placenta is unique in its function from several points of view. Its lifetime is short relative to the fetus, and its size and function change continually during the course of gestation. For the fetus, the placenta serves as lung, gastrointestinal tract, kidneys, liver, and even endocrine organ. Its morphology changes during gestation in ways that could only be termed pathological in any other organ. Innumerable substances are transferred from the maternal to fetal circulations. The exchange rates and transfer mechanisms vary for different substances. Either physiological limitations or pathological changes may affect the rate of exchange or the metabolism of various substances by placental cells. Alterations in placental transfer may be either acute or chronic and associated with pathological changes of the maternal or fetal placental circulations or in the chorion or amnion of the placenta per se. The term placental insufficiency is used often in a clinical sense to imply abnormal placental function or some specific alteration in fetal heart rate pattern. Maternal factors include decreases in blood constituents and decreases in uteroplacental blood flow. Placental factors include abnormalities of trophoblast or vascular tissues, which may be primary or secondary to maternal or fetal abnormalities. Fetal factors include alterations in the rate of umbilical blood flow.

I. Introduction

II. Physiological Transfer Mechanisms

A. Simple Diffusion

B. Facilitated Diffusion

C. Active Transport

D. Pinocytosis

E. Bulk Flow or Ultrafiltration

F. Breaks in Placental Villi

III. Normal Transfer of Specific Substances

A. Gases

B. Carbohydrates

C. Amino Acids, Polypeptides, and Proteins

D. Lipids and Steroids

E. Nucleic Acids

F. Vitamins

G. Electrolytes

H. Water Transfer

IV. Relation between Normal Placental Structure and Function

A. Gross Morphology

B. Microscopic Morphology

C. Cellular Changes

D. Relation of Placental Weight to Fetal Weight

E. Physiological Changes during the Course of Gestation

V. Alterations in Placental Transfer Mechanisms

A. Maternal Blood Nutrients

B. Maternal Oxygen Supply

C. Circulatory Disturbances

D. Parenchymal Alterations Affecting Placental Transfer

E. Abnormal Gross Placental Development

VI. The Placenta and the Small-for-Gestational-Age Infant

A. Definitions and Incidence

B. Association with Various Conditions

C. Role of Placenta in Abnormal Fetal Growth and Development

VII. Diagnostic Tests of Altered Placental Transfer

A. Atropine Transfer

B. Isoxsuprine Infusion

C. Fetal Response to Maternal Exercise

D. Fetal Response to Induced Fetal Contractions

E. Selenomethionine Uptake

F. Placental Transfer of Dye

VIII. Sequelae of Altered Placental Function

IX. Possible Therapy for Altered Placental Transfer

X. Summary

References

I Introduction

A distinguishing feature of mammalian development is the provision of nutrients from the maternal organism. Adequate exchange across the placenta between the maternal and fetal circulations is essential for normal fetal metabolism and growth. The placenta is unique in its function from several points of view. Its lifetime is short relative to the fetus and its size and function change continually during the course of gestation. For the fetus the placenta serves as lung, gastrointestinal tract, kidneys, liver, and even endocrine organ. Its morphology changes during gestation in ways which could only be termed pathological in any other organ. Finally, contrary to the belief of early investigators that the placenta is simply a passive, semipermeable sieve, there is probably no organ of the body in which as many mechanisms of transfer operate simultaneously. For example, respiratory gases diffuse between the maternal and fetal circulations; carbohydrates exchange by facilitated diffusion; amino acids and some vitamins are actively transported; macromolecules such as immunoglobulins are probably transported by pinocytosis and water is probably exchanged by bulk flow in response to small hydrostatic or osmotic pressure gradients (see Sections II,E and III,H).

The transfer between the human maternal intervillous space and the fetal placental capillaries is mainly through the chorion frondosum of the discoidal hemochorial placenta. While the role of the yolk sac is important in some rodents and other mammals, its role in the human during early gestation is not clear. The role of the chorion laeve and amnion in the transfer of nutrients whose exchange is limited by blood flow (such as oxygen) is probably not great, since it has been shown that these membranes receive only a small fraction of the total placental flow. On the other hand, these structures may have a role in the transfer of water.

Innumerable substances are transferred from the maternal to fetal circulations. The exchange rates and transfer mechanisms vary for the different substances. Either physiological limitations or pathological changes may affect the rate of exchange or the metabolism of various substances by placental cells. These alterations may be secondary to maternal factors, to fetal factors, or to changes in the placental cells per se, and may act to limit the availability of various substances for normal fetal growth and development.

The purpose of this review is to discuss normal placental transfer mechanisms; the factors adversely affecting placental transfer and their possible implications on fetal metabolism and development; and the diagnosis of abnormal placental function and possible means of treatment of this condition.

II Physiological Transfer Mechanisms

The transfer of substances acros...

Table of contents

• Cover image
• Title page
• Table of Contents
• Contributors
• Copyright
• Dedication
• List of Contributors
• Preface
• Contents of Other Volumes
• Chapter 1: Disorders of Placental Transfer
• Chapter 2: Disorders of Placental Endocrine Functions
• Chapter 3: Disorders of Amniotic Fluid
• Chapter 4: Genetic Disorders Affecting Growth and Development
• Chapter 5: Environmental Effects on Development—Teratology
• Author Index
• Subject Index