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Hormones initiating labor

A graph hormone concentration versus week of pregnancy shows how three hormones vary throughout pregnancy.
A positive feedback loop of hormones works to initiate labor.

A common sign that labor will be short is the so-called “bloody show.” During pregnancy, a plug of mucus accumulates in the cervical canal, blocking the entrance to the uterus. Approximately 1–2 days prior to the onset of true labor, this plug loosens and is expelled, along with a small amount of blood.

Meanwhile, the posterior pituitary has been boosting its secretion of oxytocin, a hormone that stimulates the contractions of labor. At the same time, the myometrium increases its sensitivity to oxytocin by expressing more receptors for this hormone. As labor nears, oxytocin begins to stimulate stronger, more painful uterine contractions, which—in a positive feedback loop—stimulate the secretion of prostaglandins from fetal membranes. Like oxytocin, prostaglandins also enhance uterine contractile strength. The fetal pituitary also secretes oxytocin, which increases prostaglandins even further. Given the importance of oxytocin and prostaglandins to the initiation and maintenance of labor, it is not surprising that, when a pregnancy is not progressing to labor and needs to be induced, a pharmaceutical version of these compounds (called pitocin) is administered by intravenous drip.

Finally, stretching of the myometrium and cervix by a full-term fetus in the vertex (head-down) position is regarded as a stimulant to uterine contractions. The sum of these changes initiates the regular contractions known as true labor    , which become more powerful and more frequent with time. The pain of labor is attributed to myometrial hypoxia during uterine contractions.

Stages of childbirth

The process of childbirth can be divided into three stages: cervical dilation, expulsion of the newborn, and afterbirth ( [link] ).

Cervical dilation

For vaginal birth to occur, the cervix must dilate fully to 10 cm in diameter—wide enough to deliver the newborn’s head. The dilation    stage is the longest stage of labor and typically takes 6–12 hours. However, it varies widely and may take minutes, hours, or days, depending in part on whether the mother has given birth before; in each subsequent labor, this stage tends to be shorter.

Stages of childbirth

This multi-part figure shows the different stages of childbirth. The top panel shows dilation, the middle panel shows birth and the bottom panel shows afterbirth delivery.
The stages of childbirth include Stage 1, early cervical dilation; Stage 2, full dilation and expulsion of the newborn; and Stage 3, delivery of the placenta and associated fetal membranes. (The position of the newborn’s shoulder is described relative to the mother.)

True labor progresses in a positive feedback loop in which uterine contractions stretch the cervix, causing it to dilate and efface, or become thinner. Cervical stretching induces reflexive uterine contractions that dilate and efface the cervix further. In addition, cervical dilation boosts oxytocin secretion from the pituitary, which in turn triggers more powerful uterine contractions. When labor begins, uterine contractions may occur only every 3–30 minutes and last only 20–40 seconds; however, by the end of this stage, contractions may occur as frequently as every 1.5–2 minutes and last for a full minute.

Questions & Answers

what is the difference between basal laminal and basal membrane
Nartey Reply
If one is missing the opsin which detects wavelengths of approximately 560 nm what color would they be unable to see?
Alicia Reply
how do I explain into details the epithelial tissue
Sir Reply
Epithelial tissues line the outer surfaces of organs and blood vessels throughout the body, as well as the inner surfaces of cavities in many internal organs. An example is the epidermis, the outermost layer of the skin. There are three principal shapes of epithelialcell: squamous, columnar, and cub
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explain how the intestinal irritation results in diarrhoea
what is cerebrospinal fluid
nitesha Reply
Cerebrospinal fluid is a clear, colorless body fluid found in the brain and spinal cord. It is produced by the specialised ependymal cells in the choroid plexuses of the ventricles of the brain, and absorbed in the arachnoid granulations.
cerebrospinal fluid is the fluid present in the brain and spinal cord
it is whitish in colour
what are the function of the blood
Hannah Reply
to transport oxygen in hemoglobin and nutrients
describe the pulmonary circulation
Which of the following structures contains membranes with mucus glands and blood vessels to help humidify and warm air?
Sheika Reply
thoracic pump for blood, and lymphatic flow for mucus membranes .
explanation shortly about organizaton of human body
Maulidi Reply
the human body is the entire structure of a human being.it is composed of many different types of cells that together create tissues and subsequently organ systems.they ensure homeostasis and viability of the human body
which is the largest body organ?
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hello everyone what is blood carcinoma?
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smallest basic unit of life
Adna Reply
how does the cell work
cells in our body together with similar cells and form tissues in our body
different kinds of sutures and their functions...
its cell
what is Gross anatomy
gross anatomy is the study of what you can observe of the human body without a microscope.
what is smallest bone
excuse me if you are questing us or testing our knowledge?
susana ...gross anatomy this are body structures tht we can see with our naked eyes
How to work heart
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five vital organ hote hain beta koi mushkil pocho bacho wale question m ni dhekta
beta cell is the basic setrecture and function unit of the body
define the cns Dr. Shahid plz
reema... cns .. central nervous system is the one of the two major division of the nervosu system
what are the types of vein
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what is a bone ?
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give examples of short bones
how is a bone formed under the endochondral process
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what is forced breathing
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when oxygen supply was slow to lungs to beathe it is difficult to breathe and heart pumping also slow so it is known as forced breathing
im one word its rescusitation...
in my thinking
when we take breathing very quick during doing any work

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Source:  OpenStax, Anatomy & Physiology. OpenStax CNX. Feb 04, 2016 Download for free at http://legacy.cnx.org/content/col11496/1.8
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