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Figure

The neonatal period extends from birth to the end of the fourth week after birth.

this reason, the newborn may become dehydrated and develop a water and electrolyte imbalance. Also, certain homeostatic control mechanisms may not function adequately. For example, during the first few days of life body temperature may respond to slight stimuli by fluctuating above or below the normal level.

When the placenta ceases to function and breathing begins, changes occur in the newborn's circulatory system. Following birth, the umbilical vessels constrict. The arteries close first, and if the umbilical cord is not clamped or severed for a minute or so, blood continues to flow from the placenta to the newborn through the umbilical vein, adding to the newborn's blood volume.

The proximal portions of the umbilical arteries persist in the adult as the superior vesical arteries that supply blood to the urinary bladder. The more distal portions become solid cords (lateral umbilical ligaments). The umbilical vein becomes the cordlike liga-mentum teres that extends from the umbilicus to the liver in an adult. The ductus venosus constricts shortly after birth and appears in the adult as a fibrous cord (lig-amentum venosum) superficially embedded in the wall of the liver.

The foramen ovale closes as a result of blood pressure changes in the right and left atria as the fetal vessels constrict. As blood ceases to flow from the umbilical vein into the inferior vena cava, the blood pressure in the right atrium falls. Also, as the lungs expand with the first breathing movements, resistance to blood flow through the pulmonary circuit decreases, more blood enters the left atrium through the pulmonary veins, and blood pressure in the left atrium increases.

As the pressure in the left atrium rises and that in the right atrium falls, the valve (septum primum) on the left side of the atrial septum closes the foramen ovale. In most individuals, this valve gradually fuses with the tissues along the margin of the foramen. In an adult, a depression called the fossa ovalis marks the site of the previous opening.

The ductus arteriosus, like other fetal vessels, constricts after birth. After this, blood can no longer bypass the lungs by moving from the pulmonary trunk directly into the aorta. In an adult, a cord called the ligamentum arteriosum represents the ductus arteriosus.

In patent ductus arteriosus (PDA), the ductus arteriosus fails to close completely. This condition is common in newborns whose mothers were infected with rubella virus (German measles) during the first three months of pregnancy.

After birth, the metabolic rate and oxygen consumption in neonatal tissues increase, in large part to maintain body temperature. If the ductus arteriosus remains open, the neonate's blood oxygen concentration may be too low to adequately supply body tissues, including the myocardium. If PDA is not corrected surgically, the heart may fail, even though the myocardium is normal.

Changes in the newborn's circulatory system are gradual. Although constriction of the ductus arteriosus may be functionally complete within fifteen minutes, the permanent closure of the foramen ovale may take up to a year. These circulatory changes are illustrated in figure 23.24 and summarized in table 23.3.

O Define neonatal period of development.

^9 What factors stimulate the first breath?

^9 How do the kidneys of a newborn differ from those of an adult?

□ What is the fate of the foramen ovale? Of the ductus arteriosus?

Infancy

The period of continual development extending from the end of the first four weeks to one year is called infancy. During this time, the infant grows rapidly and may triple its birth weight. Its teeth begin to erupt through the gums, and its muscular and nervous systems mature so that coordinated muscular activities become possible. The infant is soon able to follow objects visually; reach for and grasp objects; and sit, creep, and stand.

Infancy also brings the beginning of the ability to communicate. The infant learns to smile, laugh, and respond to some sounds. By the end of the first year, the infant may be able to say two or three words. Often one of a child's first words is the name of a beloved pet.

Aorta

Foramen ovale closes and becomes fossa ovalis

Ductus venosus constricts and becomes solid ligamentum venosum

Ductus arteriosus constricts and becomes solid ligamentum arteriosum

Blood high in oxygen Blood low in oxygen

Liver

Aorta

Foramen ovale closes and becomes fossa ovalis

Ductus venosus constricts and becomes solid ligamentum venosum

Liver

Ligamentum Venosum

Ductus arteriosus constricts and becomes solid ligamentum arteriosum

Blood high in oxygen Blood low in oxygen

Umbilical arteries constrict

Proximal portions of umbilical arteries persist

Figure 23.24

Umbilical arteries constrict

Proximal portions of umbilical arteries persist

Figure 23.24

Major changes that occur in the newborn's circulatory system.

Because infancy (as well as childhood) is a period of rapid growth, the infant has particular nutritional requirements. In addition to an energy source, the body requires proteins to provide the amino acids necessary to form new tissues; calcium and vitamin D to promote the development and ossification of skeletal structures; iron to support blood cell formation; and vitamin C for production of structural tissues such as cartilage and bone. By the time an infant is four months old, most of the circulating hemoglobin is the adult type.

Childhood

Childhood begins at the end of the first year and ends at puberty. During this period, growth continues at a high rate. The primary teeth appear, and then secondary teeth replace them. The child develops a high degree of voluntary muscular control and learns to walk, run, and climb. Bladder and bowel controls are established. The child learns to communicate effectively by speaking, and later, usually learns to read, write, and reason objectively. At the same time, the child is maturing emotionally.

99 Define infancy.

^9 What developmental changes characterize infancy?

^9 Define childhood.

□ What developmental changes characterize childhood?

Adolescence

Adolescence is the period of development between puberty and adulthood. It is a time of anatomical and physiological changes that result in reproductively functional individuals. Most of these changes are hormonally controlled, and they include the appearance of secondary sex characteristics as well as growth spurts in the muscular and skeletal systems.

Females usually experience these changes somewhat earlier than males, so that early in adolescence, females may be taller and stronger than their male peers.

Pregnancy Diet Plan

Pregnancy Diet Plan

The first trimester is very important for the mother and the baby. For most women it is common to find out about their pregnancy after they have missed their menstrual cycle. Since, not all women note their menstrual cycle and dates of intercourse, it may cause slight confusion about the exact date of conception. That is why most women find out that they are pregnant only after one month of pregnancy.

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