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Boundless Anatomy and Physiology
Physiology Textbooks Boundless Anatomy and Physiology
Physiology Textbooks
Physiology

Chapter 27

Human Development and Pregnancy

Book Version 29
By Boundless
Boundless Anatomy and Physiology
Physiology
by Boundless
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Section 1
Overview of Pregnancy and Human Development
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Introduction to Pregnancy and Human Development

Pregnancy is the period of gestation from the fertilization of an egg, through development of a fetus, and ending at birth.

Section 2
First Week of Development
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Fertilization

Fertilization occurs when a sperm and an egg have fused together to form a zygote, which begins to divide as it moves towards the uterus.

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Cleavage of the Zygote

The process of cleavage is the step of embryogenesis where the zygote divides to produce a cluster of cells known as the morula.

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Blastocyst Formation

The blastocyst forms early in embryonic development and has two layers that form the embryo and placenta.

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Implantation

Implantation is the very early stage of pregnancy at which the embryo adheres to the wall of the uterus and begins to form the placenta.

Section 3
Second Week of Development
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Trophoblast Development

Trophoblasts are the outer layer of cells that provide nutrients to the embryo and form part of the placenta.

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Bilaminar Embryonic Disc Development

The floor of the amniotic cavity is formed by the embryonic disc.

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Amnion Development

The amnion contains the fluid that cushions and protects the fetus.

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Yolk Sac Development

The yolk sac is vascularized and contributes nutrients to the embryo.

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Sinusoid Development

The sinusoids are capillaries that develop after implantation to allow the exchange of gas and nutrients with the mother.

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Development of the Extraembryonic Coelom

The extra-embryonic coelom is a cavity that contains the chorion. It is located between Heuser's membrane and the trophoblast.

Section 4
Third Week of Development
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Gastrulation

During gastrulation, the embryo develops three germ layers (endoderm, mesoderm, and ectoderm) that differentiate into distinct tissues.

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Neurulation

Following gastrulation, the neurulation process develops the neural tube in the ectoderm, above the notochord of the mesoderm.

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Somite Development

Somites develop from the paraxial mesoderm and participate in the facilitation of multiple developmental processes.

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Development of the Cardiovascular System

The circulatory system develops initially via vasculogenesis, with the arterial and venous systems developing from distinct embryonic areas.

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Chorionic Villi and Placental Development

In the placenta, chorionic villi develop to maximize surface-area contact with the maternal blood for nutrient and gas exchange.

Section 5
Fourth Week of Development
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Fourth Week of Development

The fourth week of gestation is characterized by the flexion of the superior portion of the neural tube to create the mesencephalon.

Section 6
Fifth Through Eighth Weeks of Development
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Fifth Through Eighth Weeks of Development

Weeks five to eight of gestation develops the major organs, including the circulatory, nervous, and gastrointestinal systems.

Section 7
Birth (Parturition)
Onset of Labor

Prodromal labor, which includes the latent phase of labor, marks the initial stages of parturition.

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Stages of Labor

Vaginal delivery childbirth has three distinct phases: dilation of the cervix, delivery of the infant, and delivery of the placenta.

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Adjustments of the Infant at Birth

Post birth, an infant's physiology must adapt to breathing independently, changes in blood flow and energy access, and a cold environment.

Section 8
Lactation
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Physiology of Lactation

Lactation is the secretion of milk from specialized glands (mammary glands) to provide nourishment to offspring.

Section 9
The Fetal Period
Fetal Development

At the end of the 10th week of gestation, the fetal period begins.

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Teratogens

A teratogen is a compound that permanently deforms the function or structure of a developing embryo or fetus.

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Prenatal Diagnostic Tests

Prenatal diagnosis is a way to screen a fetus for diseases and/or conditions that may increase its morbidity and/or mortality.

Section 10
Changes to the Mother's Body During Pregnancy
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Anatomical Changes

Women undergo many physical changes during pregnancy due to hormonal fluctuations and the need to accommodate a growing fetus.

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Metabolic Changes

Protein and carbohydrate metabolism are affected during pregnancy and maternal insulin resistance can lead to gestational diabetes.

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Physiological Changes

Maternal physiological changes in pregnancy are entirely normal and serve as adaptations to better accommodate embryonic/fetal development.

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Exercise and Pregnancy

In the absence of complications, pregnant women should continue aerobic and strength training exercise for the duration of gestation.

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The Reproductive System
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Human Development and Pregnancy
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Reproduction, Chromosomes, and Meiosis
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