Parturition

Question 1

__________ a.k.a. bringing forth of young Phases

Answer 1

Parturition

Question 2

WHat is the first phase of parturition?

Answer 2

: - a prelude to—first phase

Question 3

What is the second phase of parturition?

Answer 3

• the preparation for—second phase

Question 4

What is the thrid phase of parturition?

Answer 4

• the process of—third phase -

Question 5

What is the fourth phase of parturiotion

Answer 5

recovery from—fourth phase

Question 6

____________

• uterus must initiate extensive changes in its size and vascularity to accommodate the pregnancy and prepare for uterine contractions in phase 3 of parturition

Answer 6

Uterine Quiescence

Question 7

• some myometrial contractions are noted during the quiescent phase, they do not normally cause cervical dilatation . What type of contraction is this?

Answer 7

o unpredictability

o low intensity

o brief duration

Question 8

____________contraction is a discomfort that they produce usually is confined to the lower abdomen and groin

Answer 8

• Braxton Hicks

Question 9

Is there a contraction in the first phase of parturition?

Answer 9

yes there is but it doesnt lead to dilation

Question 10

What are the function of cervix in pregnancy?

Answer 10

Cervix has multiple function in pregnancy

1. maintenance of barrier function to protect the reproductive tract from infection,
2. maintenance of cervical competence despite the increasing gravitational forces imposed by the expanding uterus
3. orchestrating extracellular matrix changes that allow progressive increases in tissue compliance in preparation for birth.

Question 11

What happens at the- End of pregnanc with our cervix? -

Answer 11

cervix is easily distensible, and its consistency is similar to the lips of the oral cavity

Question 12

o ____________ - is characterized by an increase in tissue compliance, yet the cervix remains firm and unyielding

Answer 12

Softening

Question 13

Structural Changes with Softening

Answer 13

• Cervical softening results from

o increased vascularity

o stromal hypertrophy

o glandular hypertrophy and hyperplasia

o compositional or structural changes of the extracellular matrix -

Phase 1 of parturition o cervix begins a slow, progressive increase in turnover of matrix components

o change in collagen processing or a change in the number or type of covalent cross-links between collagen triple helices which are normally required for stable collagen fibril formation

Question 14

Describe phase 1

Answer 14

Phase 1

Quiescent

Contraction Unresponsive

Cervical softening

Question 15

Describe phase 2

Answer 15

ACtivation

Preparation for labor

Cervical Ripening

Question 16

______________ - process constitutes phase 2 and represents a progression of uterine changes during the last 6 to 8 weeks of pregnancy

Answer 16

Uterine awakening or activation

Question 17

The last few hours of human pregnancy are characterized by forceful and painful uterine contractions that effect cervical dilatation and cause the fetus to descend through the birth canal.

There are extensive preparations in both the_________________ long before this.

Answer 17

uterus and cervix

Question 18

During the first ____________- of normal gestation, the myometrium is in a preparatory yet unresponsive state.

Answer 18

36 to 38 weeks

Question 19

Concurrently, the cervix begins an early stage of remodeling— termed_____________—yet maintains structural integrity.

Answer 19

softening

Question 20

Following this prolonged uterine quiescence, there is a transitional phase during which myometrial unresponsiveness is suspended, and the cervix undergoes ___________, _____________ and ______________

Answer 20

ripening, effacement, and loss of structural integrity.

Question 21

It is clear, however, that labor onset represents the culmination of a series of biochemical changes in the uterus and cervix. These result from _________________________
Their relative contributions vary between species, and it is these differences that complicate elucidation of the exact factorsthat regulate human parturition.

Answer 21

endocrine and paracrine signals emanating from both mother and fetus.

Question 22

When parturition is abnormal,then_________, ____________ and ____________ may result.

Answer 22

preterm labor, dystocia, or postterm pregnancy

Question 23

Of these results when partuition is abnormal ,_____________remains the major contributorn to neonatal mortality and morbidity in developed countries.

Answer 23

preterm labo

Question 24

The bringing forth of young—_____________—requires wellorchestrated transformations in both uterine and cervical function. As shown in Figure 21-1,

Answer 24

parturition

Question 25

parturition can be arbitrarily divided into four overlapping phases that correspond to the major physiological transitions of the myometrium and cervix during pregnancy (Casey, 1993, 1997; Challis, 2000; Word, 2007). These phases of parturition include:

Answer 25

(1) a prelude to it,
(2) the preparation for it,
(3) the process itself, and (
4) recovery.

Note: Importantly, the phases of parturition should not be confused with the clinical stages of labor, that is, the first, second, and third stages—which comprise the third phase of parturition

Question 26

Beginning even before implantation, a remarkably effective period of myometrial ________________ is imposed. This phase normally comprises 95 percent of pregnancy and is characterized by uterine smooth muscle tranquility with maintenance of cervical structural integrity.

The inherent propensity of the myometrium to contract is held in abeyance, and uterine muscle is rendered unresponsive to natural stimuli.

Concurrently, the uterus must initiate extensive changes in its size and vascularity to accommodate the pregnancy and the pregnancy and prepare for uterine contractions
in phase 3 of parturition. The myometrial unresponsiveness
of phase 1 continues until near the end of pregnancy.

Answer 26

Uterine Quiescence

Question 27

Although some myometrial contractions are noted during the quiescent phase, they do not normally cause cervical dilatation. They are characterized by their unpredictability, low intensity, and brief duration. Any discomfort that they produce usually is confined to the lower abdomen and groin. Near the end of pregnancy,contractions of this type become more common, especially in multipaous women. They are sometimes referred to as__________________

Answer 27

Braxton Hicks contractions or false labor

Question 28

The cervix has multiple functions during pregnancy that include: _____________________________

In nonpregnant women, the cervix is closed and firm, and its consistency is similar to nasal cartilage.

Answer 28

(1) maintenance of barrier function to protect the reproductive tract from infection

, (2) maintenance of cervical competence despite the increasing gravitational forces imposed by the expanding uterus, and

(3) orchestrating extracellular matrix changes that allow progressive increases in tissue compliance in preparation for birth.

Question 29

By the end of pregnancy, the cervix is easily distensible, and its consistency is similar to the lips of the oral cavity. Thus, the first stage of this remodeling— termed______________—is characterized by an increase in tissue compliance, yet the cervix remains firm and unyielding. Hegar (1895) first described palpable softening of the lower uterine segment at 4 to 6 weeks’ gestation, and this sign was once used to diagnose pregnancy.

Answer 29

softening

Question 30

Clinically, the maintenance of cervical anatomical and structural integrity is essential for continuation of pregnancy to term. Preterm cervical dilatation, structural incompetence, or both may forecast an unfavorable pregnancy outcome that ends most often in preterm delivery (see Chap. 36, p. 814). Indeed, **cervical shortening between ____________ **has been associated with an increased risk of preterm delivery (Hibbard and associates, 2000; Iams and colleagues, 1996).

Answer 30

16 and 24 weeks

Question 31

Structural Changes with Softening.

Cervical softening results from _________________(Danforth and colleagues, 1974; Leppert, 1995; Liggins, 1978 ; Word and associates, 2007). Specifically, during phase 1 of parturition, the cervix begins a slow, progressive increase in turnover of matrix components. For example, in mouse models with deficiency of the extracellular matrix protein, thrombospondin 2, collagen fibril morphology is altered and there is premature cervical softening (Kokenyesi and co-workers, 2004).

Answer 31

increased vascularity, stromal hypertrophy, glandular hypertrophy and hyperplasia, and compositional or structural changes of the extracellular matrix

Note: Another change found in animal models is that physiological
softeningispreceded by an increase in collagen solubility (Read
and associates, 2007). This reflects a change in collagen processing
or a change in the number or type of covalent cross-links between
collagen triple helices which are normally required for
stable collagen fibril formation (Fig. 6-3) (Canty and Kadler,
2005). A reduction in cross-linking of newly synthesized collagen
may aid cervical softening because decreased transcripts and
activity of the cross-linking enzyme, lysyl oxidase, have been reported
in the mouse cervix during pregnancy (Drewes and associates,
2007; Ozasa and colleagues, 1981).

Question 32

In humans, the clinical importance of these matrix changes is shown by the greater prevalence of cervical incompetence in women with inherited defects in collagen and elastin synthesis or assembly—for example,__________________ and _____________

Answer 32

Ehlers-Danlos and Marfan syndromes

Question 33

To prepare for labor, the myometrial tranquility of phase 1 of parturition must be suspended through what has been called ____________________. This process constitutes phase 2 and represents a progression of uterine changes during the last 6 to 8 weeks of pregnancy. Importantly, shifting events associated with phase 2 can cause either preterm or delayed labor. Thus, understanding myometrial and cervical modifications during phase 2 provides a better understanding of events leading to normal and abnormal labor..

Answer 33

Phase 2 of Parturition: Preparation for Labor

uterine awakening or activation

Question 34

Myometrial Changes During Phase 2

Most myometrial changes during phase 2 prepare it for labor contractions. This shift probably results from alterations in the expression of key proteins that control contractility. These contraction- associated proteins (CAPs) include the ____________ (Smith, 2007).

Answer 34

oxytocin receptor, prostaglandin F receptor, and connexin 43

Note: Thus, myometrial oxytocin receptors markedly increase along with increased numbers and surface areas of gap junction proteins such as connexin 43. Together these lead to increased uterine irritability and responsiveness to uterotonins—agents that stimulate contractions.

Question 35

Another critical change in phase 2 is

formation of the lower uterine segment from the isthmus. With this development, the fetal head often descends to or even through the pelvic inlet— so-called___________ The abdomen commonly undergoes a change in shape, sometimes described as “the baby dropped.” It is also likely that the lower segment myometrium is unique from that in the upper uterine segment, resulting in distinct roles for each during labor.

Note:This is supported by baboon studies that demonstrate differential expression of prostaglandin receptors within myometrial regions. There are also human studies that report an expression gradient of oxytocin receptors, with higher expression in fundal myometrial cells (Fuchs, 1984; Havelock, 2005; Smith, 2001, and all their colleagues).

Answer 35

lightening.

Question 36

Cervical Ripening During Phase 2

Prior to the initiation of contractions, the cervix must undergo more extensive remodeling. This eventually results in cervical yielding and dilatation upon initiation of forceful uterine contractions in the third phase of parturition. Cervical modifications during this second phase principally involve connective tissue changes—so-called____________.

Answer 36

cervical ripening.

Question 37

The transition from the softening to the ripening phase begins ___________ before onset of contractions. During this transformation, the total amount and composition of proteoglycans and glycosaminoglycans within the matrix are altered.

Many of the processes that aid cervical remodeling are controlled by the same hormones regulating uterine function. That said, the molecular events of each are varied because of differences in cellular composition and physiological requirements.

Answer 37

weeks or days

Question 38

The uterine corpus is predominantly _____________, whereas the cervix is primarily ____________. Cellular components of the cervix include smooth muscle, fibroblasts, and epithelia.

Answer 38

smooth muscle

connective tissue.

Note: Because from the uterine, mucles will contract to push the baby and the cervix needs to dilate thats why it is primarily composed of collagen”

Question 39

. During pregnancy, ___________cells proliferate such that endocervical glands occupy a significant percentage of cervical mass by the end of pregnancy.

Answer 39

Endocervical Epithelia

Question 40

The endocervical canal is lined with _____________and _____________, which protect against microbial invasion.

Answer 40

mucus-secreting columnar and stratified squamous epithelia

Question 41

____________ function as sentinels that recognize antigens, respond in ways that lead to bacterial and viral killing, and signal to underlying immune cells when pathogenic challenge exceeds their protective capacity (Wira and co-workers, 2005).

Recent studies in mice suggest that cervical epithelia may also aid cervical remodeling by regulating tissue hydration and maintenance of barrier function. Hydration may be regulated by expression of aquaporins—water channel proteins, whereas paracellular transport of ion and solutes and maintenance of barrier function is regulated by tight junction proteins, such as claudins 1 and 2 (Anderson and colleagues, 2006; Timmons and Mahendroo, 2007).

Answer 41

Mucosal epithelia

Question 42

Cervical Connective Tissue. The cervix is made up of only ___________ percent smooth muscle with the remaining tissue comprised **primarily of extracellular connective tissue. **

Answer 42

10 to 15

Question 43

Cervical Connective Tissue. The cervix is made up of only 10 to 15 % percent smooth muscle with the remaining tissue comprised primarily of extracellular connective tissue. Constituents of the latter include_____________.

Answer 43

type I, III, and IV collagen,

NMEM: 143 ILY

glycosaminoglycans, proteoglycans, and elastin

Question 44

. This material is the major component of the cervix and it is largely responsible for its structural disposition.

Answer 44

Collagen

Collagen is the most abundant mammalian protein, and it has a complex biosynthesis pathway including at least six enzymes and chaperones to accomplish maturation (see Fig. 6-3). Each collagen molecule is composed of three alpha chains, which wind around each other to form procollagen. Multiple collagen triple-helical molecules are cross-linked to one another by the actions of lysyl oxidase to form long fibrils.

Question 45

Collagen fibrils interact with small proteoglycans such as _________________. These interactions determine fibril size, packing, and organization so collagen fibrils are of uniform diameter and are packed together in a regular and highly organized pattern (Canty and associates, 2005).

Answer 45

decorin or biglycan, as well as matricellular proteins such as thrombospondin 2

Question 46

During cervical ripening, collagen fibrils are________________

These changesmay result in part from accumulation of poorly cross-linked
collagenandreduced expression of matricellular proteins.

Dispersion of collagen fibrils leads to a **loss of tissue integrity **and increased tissue compliance.

Answer 46

disorganized, and there is increased spacing between fibrils.

Question 47

________________ are proteases capable of degrading extracellular matrix proteins. Of thes :e, collagenase members of the** thse family degrade collagen**.

NoteSome studies support a role of this in cervical ripening. But, others suggest that the biomechanical changes are not consistent solely with collagenase activation and loss of collagen. For example, Buhmschi and colleagues (2004)
performed tissue biomechanical studies in the rat and suggest
that ripening correlates with changes in the three-dimensional
structure of collagen rather than its degradation by collagenases.
Moreover, mouse and human studies document no changes in
collagen content between nonpregnancy and term pregnancy
(Akins, 2011; Myers, 2008; Read, 2007).
Thus, it is likely that dynamic changes in collagen structure
rather than collagen content may regulate remodeling.
This point is well illustrated in specialized microscopy images
of mouse and human cervical collagen (Zhang, 2012). In further
support, polymorphisms or mutations in genes required
for collagen assembly are associated with an increased incidence
of cervical insufficiency (Anum, 2009; Paternoster, 1998;
Rahman, 2003; Warren, 2007).

Answer 47

Matrix metalloproteases (MMPs

Question 48

. These are high-molecularweight polysaccharides that complex with proteins to form proteoglycans. One glycosaminoglycan is ___________, a carbohydrate polymer whose synthesis is carried out by hyaluronan synthase isoenzymes. Expression of these enzymes is increased in the cervix during ripening (Akgul, 2012; Osmers, 1993; Straach, 2005).

Answer 48

Glycosaminoglycans (GAGs)

hyaluronan (HA)

Question 49

The functions of hyaluronans are dependent on size, and the breakdown of large- to small-molecularweight molecules is carried out by a family of hyaluronidase enzymes.

Hyaluronidase genes are expressed in both the mouse and human cervix, and increased hyaluronidase activity is reported in the mouse cervix at term (Akgul, 2012).

__________ predominates in the mouse cervix during ripening and has a dynamic role to increase viscoelasticity and matrix disorganization.

__________ has proinflammatory properties, and studies in mice and women reveal increased concentrations during labor and in the puerperium

Answer 49

Largemolecular- weight HA

Low-molecular-weight HA

Question 50

The importance of regulated changes in HA size during cervical ripening and dilatation is supported by a study reporting hyaluronidase administration to the cervix for ripening in term pregnant women (Spallicci, 2007). Activation of intracellular signaling cascades and other biological functions requires interactions with cell-associated HA-binding proteins such as ____________ (Ruscheinsky, 2008).

Answer 50

versican

Question 51

Expression of these enzymes is increased in the cervix during ripening (Akgul, 2012; Osmers, 1993; Straach, 2005).

The functions of hyaluronans are dependent on size, and the breakdown of large- to small-molecularweight molecules is carried out by a family of hyaluronidase enzymes.

Answer 51

Glycosaminoglycans

Question 52

Hyaluronidase genes are expressed in both the mouse and human cervix, and increased hyaluronidase activity is reported in the mouse cervix at term (Akgul, 2012). ____________ predominates in the mouse cervix during ripening and has a dynamic role to increase viscoelasticity and matrix disorganization.

Answer 52

Largemolecular- weight HA

Question 53

___________ has proinflammatory properties, and studies in mice and women reveal increased concentrations during labor and in the puerperium

Answer 53

Low-molecular-weight HA

Question 54

These glycoproteins are composed of a protein core and GAG chains.

Changes in the amount of core protein or in the number, length, or degree of sulfation of GAG chains can influence proteoglycan function. Although not well-defined, changes in proteoglycan composition are thought to accompany cervical ripening. At least three small leucine-rich proteoglycans are expressed in the cervix—–_______________

Answer 54

—decorin, biglycan, and fibromodulin

Question 55

In addition to the cervix, these proteoglycans are expressed in the ______ and ___________ Changes in expression levels may regulate fetal membrane tensile strength and uterine function (Meiner, 2007; Wu, 2012).

Answer 55

fetal membranes and uterus.

Question 56

The marked changes within the extracellular matrix during cervical ripening in phase 2 are accompanied by stromal invasion with inflammatory cells. This has led to a model in which ____________ is considered an inflammatory process. As such, cervical chemoattractants attract inflammatory cells, which in turn release proteases that may aid degradation of collagen and other matrix components.

In phase 3 or 4 of parturition, there is increased cervical expression of chemokines and collagenase/ protease activity. It was assumed that processes regulating phases 3 and 4 of dilation and postpartum recovery of the cervix were similar to those in phase 2 of cervical ripening (Bokström, 1997; Osman, 2003; Sennström, 2000; Young, 2002).

NOTE :

This has been challenged by observations from both human and animal studies. Sakamoto and associates (2004, 2005) found no correlation between the degree of clinical cervical ripening and the tissue concentrations of cervical neutrophil-chemoattractant interleukin 8 (IL-8). Microarray studies comparing gene expression patterns at term before and after cervical ripening report little increase in expression of proinflammatory genes. In contrast, there is a robust increase in proinflammatory and immunosuppressive genes in the cervix after delivery compared with during cervical ripening (Bollapragada, 2009; Hassan, 2006, 2009).

Answer 56

cervical ripening

Question 57

Induction and Prevention of Cervical Ripening

Answer 57

There are no therapies to prevent premature cervical ripening.

Question 58

_____________ is used to circumvent cervical insufficiency, although success appears limited.

Answer 58

​Cervical cerclage

Question 59

en, 2012). In contrast, treatment to promote cervical ripening for labor induction includes direct application of _________________

Answer 59

prostaglandins E2 (PGE2) and F2α (PGF2α).

Note : Prostaglandins likely modify extracellular matrix structure to aid ripening. Although the role of prostaglandins in the normal physiology of cervical ripening remains unclear, this property is useful clinically to assist labor induction (Chap. 26, p. 526). In some nonhuman species, the cascades of events that allow cervical ripening are induced by decreasing serum progesterone concentrations. And in humans, administration of progesterone antagonists causes cervical ripening. As discussed later, humans may have developed unique mechanisms to localize decreases in progesterone action in the cervix and myometrium.

Question 60

This phase is synonymous with active labor, which is customarily divided into three stages. These compose the commonly used labor graph shown in Figure 21-2.

Answer 60

Phase 3 of Parturition: Labor

Question 61

The clinical stages of labor may be summarized as follows.

Answer 61

The first stage is the stage of cervical effacement and dilatation.

The second stage is the
stage of fetal expulsion.

third stage of labor is the stage of placental
separation and expulsion.

Question 62

The first stage begins when spaced uterine contractions of sufficient frequency, intensity, and duration are attained to bring about cervical thinning, or effacement.

This labor stage ends when the cervix is fully dilated—about 10 cm—to allow passage of the term-sized fetus. The first stage of labor, therefore, is the stage of_____________.

Answer 62

cervical effacement and dilatation.

Question 64

The first stage begins when spaced uterine contractions of sufficient frequency, intensity, and duration are attained to bring about cervical thinning, or effacement.

. The first stage of labor, therefore, is the stage of cervical effacement and dilatation his labor ends Nextwhen________________

Answer 64

the cervix is fully dilated—about 10 cm—to allow passage of the term-sized fetus

Question 65

The second stage begins when cervical dilatation is complete and ends with delivery. Thus, the second stage of labor is the stage of ___________.

Answer 65

fetal expulsion

Question 66

The second stage begins when cervical dilatation is _________ and ___________. Thus, the second stage of labor is the stage fetal expulsion.

Answer 66

complete and ends with delivery

Question 67

. Last, the third stage begins_____________ Thus, the third stage of labor is the stage of placental separation and expulsion.

Answer 67

immediately after delivery of the fetus and ends with the delivery of the placenta.

Question 68

. Last, the third stage begins immediately after delivery of the fetus and ends with the delivery of the placenta. Thus, the third stage of labor is the stage of________________

Answer 68

placental separation and expulsion.

Question 69

First Stage of Labor: Clinical Onset of Labor

In some women, forceful uterine contractions that effect delivery begin suddenly

. In others, labor initiation is heralded by spontaneous release of a small amount of blood-tinged mucus from the vagina. This extrusion of the mucus plug that had previously filled the cervical canal during pregnancy is referred to as______________

Answer 69

“show” or “bloody show.”

Question 70

There is very little blood with the ___________, and its passage indicates that labor is already in progress or likely will ensue in hours to days.

Answer 70

mucous plug

Question 71

Uterine Labor Contractions

Unique among physiological muscular contractions, those of uterine smooth muscle during labor are _________.

Answer 71

painful

Question 72

Uterine Labor Contractions Unique among physiological muscular contractions, those of uterine smooth muscle during labor are pain.

The cause of this is not known definitely, but several possibilities have been suggested:

Answer 72

(1) hypoxia of the contracted myometrium— such as that with angina pectoris;
(2) compression of nerve ganglia in the cervix and lower uterus by contracted interlocking muscle bundles

; (3) cervical stretching during dilatation; and

(4) stretching of the peritoneum overlying the fundus.

Question 73

Of these, compression of nerve ganglia in the cervix and lower uterine segment by the contracting myometrium is an especially attractive hypothesis.

Paracervical infiltration with local anesthetic usually produces appreciable pain relief with contractions (Chap. 25, p. 509).

Uterine contractions are ________ and, for the most part, ___________.

Answer 73

involuntary

independent of extrauterine control

Question 74

Neural blockade from epidural analgesia does not diminish their frequency or intensity. In other examples, myometrial contractions in paraplegic women and in women after bilateral lumbar sympathectomy are normal but painless.

Answer 74

:)

” KHIT Sa PARALYZE NORMAL ANG CONTRACTION PERO PAINLESS

Question 75

Mechanical stretching of the cervix enhances uterine activity
in several species, including humans. This phenomenon
has been referred to as the ___________ (Ferguson, 1941).
Its exact mechanism is not clear, and release of oxytocin has
been suggested but not proven.

Manipulation of the cervix and
“stripping” the fetal membranes is associated with an increase
in blood levels of prostaglandin F2α metabolite (PGFM).

Answer 75

Ferguson refleX

Question 76

The interval between contractions diminishes gradually from approximately ____________ at the onset of first-stage labor to as little as__________ in the second stage.

Answer 76

10 minutes

1 minute or less

Question 77

Periods of relaxation between contractions, however, are essential for fetal welfare.

Unremitting contractions compromise uteroplacental blood flow sufficiently to cause _____________

Answer 77

fetal hypoxemia.

Question 78

​ In _____________, the duration of each contraction ranges from 30 to 90 seconds, averaging about 1 minute.

Answer 78

activephase laboR

Question 79

There is appreciable variability in contraction intensity during normal labor. Specifically, amnionic fluid pressures generated by contractions during spontaneous labor average _________, but vary from ___________

Answer 79

40 mm Hg

20 to 60 mm Hg

Question 80

Distinct Lower and Upper Uterine Segments.

During active labor, the anatomical uterine divisions that were initiated in phase 2 of parturition become increasingly evident (Figs. 21-4 and 21-5). By abdominal palpation, even before membrane rupture, the two segments can sometimes be differentiated.

The ___________ is firm during contractions, whereas the ______________ is softer, distended, and more passive.

Answer 80

upper segment

Lower segment

Question 81

This mechanism is imperative because if the entire myometrium, including the lower uterine segment and cervix, were to contract simultaneously and with equal intensity, the net expulsive force would be markedly decreased

. Thus, the upper segment ___________ the fetus. In response to these contractions, the____________________

Answer 81

contracts, retracts, and expels** **

softened lower uterine segment and cervix dilate and thereby form a greatly expanded, thinned-out tube through which the fetus can pass.

Question 82

The myometrium of the___________ does not relax to its original length after contractions. Instead, it becomes relatively fixed at a shorter length. The upper active uterine segment contracts down on its diminishing contents, but myometrial tension remains constant. The net effect is to take up slack, thus **maintaining the advantage gained in expulsion of the fetus. **

Concurrently, the uterine musculature is kept in firm contact
with the uterine contents. As the consequence of retraction,
each successive contraction commences where its predecessor Left off.

Thus, the upper part of the uterine cavity becomes slightly smaller with each successive contraction. Because of the** successive shortening** of the muscular fibers, the upper active segment becomes progressively thickened throughout first- and second-stage labor (see Fig. 21-4). This process continues and** results in a tremendously thickened upper uterine segment immediately after delivery.**

Answer 82

upper segment