What is Dilation? - Definition & Meaning

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  • 0:01 Definition of Dilation
  • 0:54 Dilation in Labor & Delivery
  • 1:45 Dilation of Bronchi
  • 2:35 More Examples
  • 2:55 Lesson Summary
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Lesson Transcript
Instructor: John Williams
Dilation is a key factor in regulating body processes. In this lesson, you will learn the definition of dilation, the purpose of it, and examples of its use in the body.

Definition of Dilation

The word dilation, in terms of human physiology, means to relax, open, or widen. This is usually used in structures where materials are allowed to pass. Dilation is an autonomic process, which means it cannot be consciously controlled. It is used as a method of regulating, or controlling, the passage of materials, fluids, and solids within the body.

So how does it work?

Two words: smooth muscle. Smooth muscle is one of three muscle types in the body and is often found in internal organs, such as the stomach, bronchi, and bladder. Smooth muscle is also found in several other structures, such as in blood vessels and muscle sphincters. When smooth muscle relaxes, it allows for dilation to occur in these organs and structures and usually happens when an increase of bodily materials is needed.

Dilation in Labor and Delivery

Picture a pregnant mother who is going into labor. She arrives at the hospital in order to prepare for delivery. Doctors examine her, and they make note of several key parts of her body. One doctor announces that her cervix has dilated. What does this mean?

The cervix is the 'neck' region of the uterus that connects it to the birth canal. Once a child is developed and ready to be birthed, it has to pass through the cervix in order to enter the birth canal. Under normal circumstances, the smooth muscle in the cervix is contracted, which closes the cervix and keeps the baby in the uterus for development. But when it is time for birth, the smooth muscle of the cervix relaxes, causing the cervix to dilate, or open wider. In this example, dilation is used by the smooth muscle of the cervix to allow the passage of a newborn child from the uterus to the birth canal.

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