Labor and Lactation

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Ermin's doc/block life cycle/2010 1

PHYSIOLOGY

OF LABOR

AND

LACTATION

Ermin Rachmawati, MD




LABOR

Process by which the fetus is expelled

from uterus through vagina

D e f i n i t i o n




Mechanism of LABOR

Determined by complex interaction of several

placental and fetal hormones

Dilatation of the cervix and uterine

contraction

Progressive hormonal changes and progressive

mechanical changes




Female hormonal system

Consists of three hierarchies of hormones, as follows:

1. A hypothalamic releasing hormone, gonadotropin-releasing hormone(GnRH)

2. The anterior pituitary sex hormones, follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which are secreted in response to the release of GnRHfrom the hypothalamus

3. The ovarian hormones, estrogen and progesterone, whichare secreted by the ovaries in response to the two femalesex hormones from the anterior pituitary gland




GLANDS AND HORMONS

• Ovaries• Estrogens Promotes growth and development of female Steroid,

reproductive system, female breasts, and female secondary sexualcharacteristics

• Progesterone Stimulates secretion of “uterine milk” by the uterine

Steroid endometrial glands and promotes development of secretoryapparatus of breasts

• Placenta• Human chorionic gonadotropin (HCG) Promotes growth of corpus

luteum and secretion of Peptide

estrogens and progesterone by corpus luteum• Human somatomammotropin Probably helps promote development

of some Peptidefetal tissues as well as the mother’s breasts




HORMONAL CHANGES

•RATIO OF ESTROGEN TO PROGESTERON INCREASE

• FETAL HORMONS

• EFFECT OF OXYTOCIN

• EFFECT OF PROSTAGLANDIN

• EFFECT OF RELAXIN




The primary hormones produced by the placentaare human chorionic gonadotropin (hCG),corticotropin-releasing hormone (CRH),estrogens, progesterone, human placental lactogen (hPL), and proopiomelanocortin

(POMC)• Maternal conc. of hPL and CRH-controlled

estrogens rise sharply during the third trimester • Placental hormones are distributed to mother

and fetus. Because of the close connectionbetween maternal, fetal and placental hormonesynthesis, they are jointly referred to as thefetoplacental unit




LEVEL OF ESTROGEN IN THE

MOTHER’S BLOOD RISE

SHARPLY

INCREASING SECRETION BY

THE PLACENTA OF CRH

STIMULATES THE FETAL

ANTERIOR PITUITARY TO

SECRETE ACTH

ACTH STIMULATES THE FETAL

ADRENAL GLAND TO SECRETE

CORTISOL AND DHEA

PLACENTA CONVERTS DHEA

INTO ESTROGEN




Toward the end of pregnancy, the daily production of placental estrogens increases to about 30 times themother’s normal level of production. However, thesecretion of estrogens by the placenta is quite differentfrom secretion by the ovaries. Most important, the

estrogens secreted by the placenta are not synthesizedde novo from basic substrates in the placenta. Instead,they are formed almost entirely from androgenic steroidcompounds, dehydroepiandroster one and 16-hydroxydehydroepiandrosterone, which are formed both

in the mother’s adrenal glands and in the adrenal glandsof the fetus. These weak androgens are transported bythe blood to the placenta and converted by the trophoblastcells into estradiol, estrone, and estriol




Placental CRH stimulates the release of

ACTH by the fetal pituitary, resulting in

increased

cortisol production in the adult zone

of FAC; this again stimulates the release of CRH

(positive feedback). CRH also stimulates

lung

development and the production of DHEA

and

DHEA-S in the fetal zone of FAC




HIGH LEVEL OF ESTROGEN

cause uterine muscle fiber to display receptor

for oxytocin

Increase the number of gap junction between the

adjacent cells of smooth muscle

stimulate the placenta to release prostaglandin

HIGH LEVEL OF ESTROGEN




O X Y T O C I N and P G

• Release by posterior pituitary stimulates

uterine contraction

• Prostaglandin induce production of

enzymes that digest collagen fibers in the

cervix causing it soften

Function IN labor




Mechanical

• Stretch of uterine

muscle

• Irritation of the cervix




Cervical changes

During most of the pregnancy, The cervix

must remain unyielding and reasonably rigid.

With initiation of parturition, the cervix mustsoften, yield and more readily dilatable.




• The process by which the cervix becomessoft, compliant and partially dilated istermed ‘cervical ripening’ .

• Cervical ripening is due to a combinationof biochemical, endocrine, mechanical and

possibly inflammatory events. It is believedthat the increasing myometrial contractility,in the form of Braxton Hicks contractions,seen with advancing gestation plays a vital

role in the effacement of the cervix, prior to the actual commencement of labour.




• Structurally, the cervix is mainly composed of collagen, predominantly type I and III.

• In the cervix, the main glycosaminoglycans aredermatan sulphate and chondroitin sulphate whichare hydrophobic and are responsible for thefirmness of the cervix. Towards term, the

glycosaminoglycan concentration of the cervixalters and the dermatan and chondroitin sulphatesare replaced by hyaluronic acid, which ishydrophilic and imbibes water, destablishing thecollagen fibrils contributing to cervical ripening.Collagenase produced by fibroblasts andleucocytes is an enzyme which breaks downcollagen types I, II, III.




• Leukocyte elastase produced by macrophages, neutrophils

and eosinophils is an enzyme that breaks down elastin,collagen and proteoglycans. The level of both these enzymes

are found to increase with advancing gestation and are

associated with progressive decline in concentration of

cervical collagen.

• Prostaglandins has a direct effect on the production of

procollagenase, which is a precursor of collagenase. This

explains why the administration of intracervical

prostaglandins both PGE2 and PGF2a produces cervical

changes in women without inducing uterine contractions.




• Process of cervical remodeling takes place with

advancing gestation. The mature collagen is replaced

by immature collagen with few cross links which isweaker and is easily broken down during labour. Sex

steroids, estrogen and progesterone play opposing

roles with regard to cervix during labour.

Progesterone prevents cervical ripening during

pregnancy . Progesterone antagonist, mifepristone

has been found to cause cervical ripening in women

undergoing termination of pregnancy. Estrogen promotes cervical ripening . Concentration of relaxin

increases towards late pregnancy and induces

cervical ripening. It increases production and

secretion of collagenases from the aminon.




Myometrial changes.

• The myometrium undergoes a series of changes phase I toprepare it for labour. There is transition from a contractile statecharacterized predominantly by occasional painless contractionsto one in which more frequent contractions develop. This is dueto alteration in the expression of contraction associated proteins

(CAPs). There is increase in myometrial oxytocin receptors.There are increased numbers and surface areas of myometrialcell gap junction proteins such as connexin-43. these changesresult in increased uterine irritability and responsiveness touterotonins.

• Another change that occurs in phase I is formation of lower uterine segment with the development of well formed lower segment, the fetal head descends to or even through the pelvicinlet- an event referred to as lightening.




POSITIVE FEED BACK




Estrogen

Mendorong janin

menekan serviks

Ketanggapan uterus thdp

oksitosin dlm darah

Kontraksi uterus

Reseptor oksitosin di miometrium

Melalui refleks neuroendokrin

Sekresi oksitosin

Berperan dlm

kemajuan

persalinan

Memicu awitan

atau persalinan

(teori utama)

Pembentukanprostaglandin

++

++

UMPAN BALIK HORMONAL POSITIF SELAMA PERSALINAN




1. STAGE OF DILATATION

2. STAGE OF EXPULSION

3. PLACENTAL STAGE

a period of progressive cervical dilatio




CRITICAL FACTORS IN LABOR

Primary forces of labor – The frequency, duration, and intensity of uterine contractions as

the fetus moves through the firth passage – The effectiveness of maternal pushing effort – The duration of labor

The birth passage – size of pelvis – type of pelvis – Ability of cervix to dilate and efface and vaginal canal to distend

The fetus – Fetal head, Fetal attitude, Fetal lie, Fetal presentation, Fetal

position, Size of fetus, Placenta implantation site




LACTATION

Breast feeding




D e f I n I t I o n

The secretion and ejection of milk from themammary gland




During pregnancy

• high estrogen level causes the extensivedevelopment of ductus

• high progesteron level stimulate formation of alveoli lobule

• Prolactin, secreted from pituitary anterior stimulated by the increase level of estrogen,have an important role in the development of mammary glands by secretion of enzymes thatis already needed to milk formation




P R O L AC T I N

• This hormone is secreted by the mother’s

anterior pituitary gland, and itsconcentration in her blood rises steadily

from the fifth week of pregnancy until birth

of the baby, at which time it has risen to10 to 20 times the normal nonpregnant

level

P R O L AC T I N




Immediately after the baby is born,

the sudden loss of both estrogenand progesterone secretion fromthe placenta allows the lactogeniceffect of prolactin from the mother’spituitary gland to assume its naturalmilkpromoting role, and over thenext 1 to 7 days, the breasts begin

to secrete copious quantities of milk instead of colostrum.




• This secretion of milk requires adequatebackground secretion of most of themother’s other hormones as well, but most

important are growth hormone, cortisol , parathyroid hormone, and insulin.

• These hormones are necessary to providethe amino acids, fatty acids, glucose, andcalcium required for milk formation.




• After birth of the baby, the basal level of prolactin secretion returns to the nonpregnantlevel over the next few weeks

• each time the mother nurses her baby,nervous signals from the nipples to thehypothalamus cause a 10- to 20-fold surge inprolactin secretion that lasts for about 1 hour This prolactin acts on the mother’s breasts to

keep the mammary glands secreting milk intothe alveoli for the subsequent nursingperiods.




• The hypothalamus mainly stimulates production of all the other hormones, but it mainly inhibits prolactin production.

• anterior pituitary secretion• of prolactin is controlled either entirely or almost• entirely by an inhibitory factor formed in the hypothalamus

• and transported through the hypothalamichypophysial• portal system to the anterior pituitary• gland. This factor is called prolactin inhibitory • hormone. It is almost certainly the same as the catecholamine• dopamine, which is known to be secreted

• by the arcuate nuclei of the hypothalamus and can• decrease prolactin secretion as much as 10-fold.




• Milk is secreted continuously into thealveoli of the breasts, but milk does not

flow easily from the alveoli into the ductal

system and, therefore, does notcontinually leak from the breast nipples.

Instead, the milk must be ejected from the

alveoli into the ducts before the baby can

obtain it.




Suckling on one breast causes milk flow not only inthat breast but also in the opposite breast. It is especially

interesting that fondling of the baby by the

mother or hearing the baby crying often gives enough

of an emotional signal to the hypothalamus to cause

milk ejection.

When the baby suckles, it receives virtually no milkfor the first half minute or so. Sensory impulses must

first be transmitted through somatic nerves from the

nipples to the mother’s spinal cord and then to her

hypothalamus, where they cause nerve signals that

promote oxytocin secretion at the same time that they

cause prolactin secretion.The oxytocin is carried in theblood to the breasts, where it causes myoepithelial cells

(which surround the outer walls of the alveoli) to contract,

thereby expressing the milk from the alveoli into

the ducts at a pressure of +10 to 20 mm Hg

THE MILK EJECTION REFLEX, A




Suckling of baby on nipple causes

Effectors

Contraction of myoepithelial cells in mammary glands

Receptors

Touch sensitive sensory neurons in nipple

Control centresHypothalamus and posterior pituitary

Touch sensation

Milk injection

Interruption of cycleBaby ceases to suckle, thus breaking the positive feedback cycle

Positive feedback : milk availability

encourages continued suckling,

so touch sensaitions on nippleand oxytosin release continue

Increasing

Nerve pulseOutput

Increase oxytocin in bloodinput

,

POSITIVE FEEDBACK CYCLE




• Grabowski., Tortora. (2003). “Principles of Anatomy and

Physiology”.10th edition.USA. John Wiley&Sons, Inc. ISBN 0-471-

22934-2.

• Hall, Guyton.(1997). “Buku Ajar Fisiologi Kedokteran”.Edisi :9.

Jakarta. EGC. ISBN 979-448-357-5

• Sherwood. (2005). “Physiology from Cellular to Cell”.10th

edition.USA. John Wiley&Sons,Inc. ISBN 0-471-29301-2

Labor and Lactation

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