The Neonatal Period: Changes During the First Month of Life

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  • 0:06 The Neonatal Period
  • 1:58 Lungs and Heart
  • 4:28 Digestive and…
  • 6:41 Temperature Regulation
  • 7:39 Lesson Summary
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Lesson Transcript
Instructor: Heather Adewale

Heather has taught reproductive biology and has researched neuro, repro and endocrinology. She has a PhD in Zoology/Biology.

Development of our internal systems doesn't stop with birth. Learn about some of the main changes that occur during a newborn infant's first month of life in this lesson on the neonatal period.

The Neonatal Period: Definition

The human body goes through amazing changes during gestation, which is the time spent in the mother's uterus. It starts out as a tiny, microscopic group of cells that grows and forms all the organs and tissues found in a newborn baby. But, the changes don't stop at birth!

The neonatal period extends from birth through the first month of life. During this time, the newborn undergoes physiological and anatomical changes as it adapts to his or her new environment. Just as a quick refresher, in case you are wondering why the newborn needs to adapt, let's look at the environment before birth.

A baby in the womb is encased in a fluid-filled sac and breathes fluid instead of air.
Fetus Breathes Fluid

Before birth, the newborn was encased in a fluid-filled sac, which means it wasn't breathing air. Instead, it was breathing fluid. Kind of cool, huh? And before you ask, no, newborns don't have gills. All of their nutrients, hormones, antibodies, etc… were all transferred from the mother across the placenta.

But, once born, they are no longer connected to the mother, and their body has to learn to be self-sufficient - to function on its own. Now, that doesn't mean they still don't need help. They can't quite feed themselves yet, or really move around much. All things considered, they're pretty helpless as this stage, but that doesn't mean they don't have potential, right?

During the neonatal period, the newborn's body learns to breathe air, to nurse and digest milk, to excrete waste (yes, those dirty diapers are a sign of a properly developing baby) and learns to control its body temperature.

Neonatal Period: Lungs and Heart

At birth, the lungs are collapsed and filled with fluid.
Newborn Lungs

Let's take a look at some of the key characteristics of that first month - first up: the lungs and the heart. At birth, the lungs of a newborn are collapsed and filled with fluid instead of air. Learning to breath is the first thing a newborn does as it comes out of the birth canal, and it's no easy feat!

In order to inflate the lungs and fill them with air, the newborn needs a massive inhalation of air. Not only does this inhalation of air expand the lungs, but it also changes the respiratory rate and blood pressure - which is higher in newborns than in adults - as well as blood circulation.

You see, when first born, the heart of the baby hasn't fully formed; it has two places where the pulmonary and systemic circuits are not fully separated. The pulmonary circuit is the blood that runs from the heart to the lungs and back to the heart, while the systemic circuit goes from the heart to the rest of the body and back.

The pulmonary and systemic circuits separate when the lungs inflate.
Pulmonary and Systemic Circuits

Under normal circumstances, these two circuits are separated, but in newborns, there are two connections. The first is the ductus arteriosis, which is a connection from the pulmonary artery to the aorta, and the foramen ovale, which is a hole between the left and right atria. During gestation, these connections served to speed up fetal circulation. You see, when in the mother's womb, the fetus relied on the mother for oxygen-rich blood. However, once born, the newborn must now rely on its own pulmonary circulation and lungs to produce oxygen-rich blood. For this circuit to operate properly, the connections between the pulmonary and systemic circuits must close.

Closure of both the ductus arteriosis and the foramen ovale completes the separation of the pulmonary and systemic circuits. This closure occurs because the increased blood pressure produced when the lungs inflate forces the connections to close. In some patients, closure fails to occur; this is considered to be a congenital heart defect, meaning something the baby is born with, rather than a disease.

Neonatal Period: Digestive and Excretory Systems

Just as the respiratory system needs a little bit of a jumpstart, so do the digestive and excretory systems. Before birth, all nutrition and waste was taken care of by the placenta. Just as nutrition passed from the mother to the fetus via the placenta, waste products passed from the fetus to the placenta and were filtered out. Once born, however, these systems need to learn to function on their own.

To begin, the excretory system gets rid of a substance called meconium over the first few days of life. Meconium is a mixture of bile, mucus and epithelial cells that has accumulated in the digestive system. If this substance is excreted prior to - or during - the birthing process, instead of after, it can pose a threat of infection to the fetus.

As other waste products begin to build up in the newborn's system, they are filtered from the blood by the kidneys as the excretory system begins to function. However, because this system isn't fully mature yet, filtration often yields a high amount of water loss as the kidneys learn to concentrate the urine. This is why it's important to keep newborns hydrated.

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