physiology of parturition & lactation 5042012
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Female Reproductivesystem
Adaptations to pregnancy,Physiology of Parturition and
Lactation
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Learning objectives
To discuss ~ Physiological adaptations of Cardiovascular,
respiratory, renal and gastrointestinal during thecourse of normal pregnancy
Uterine changes during pregnancy
Physiology of Parturition
Physiology of lactation including Role ofhormones in functioning of mammary glands
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Learning Outcomes
At the end of the lecture student should beable to;
Describe physiological adaptations during the course ofnormal pregnancy
Describe the cardiovascular, respiratory, renal andgastrointestinal changes during normal pregnancy
Describe the uterine changes during pregnancy
Describe the physiology of Parturition Describe the role of hormones in functioning of
mammary glands
Describe the physiology of lactation
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MATERNAL CHANGES IN
PREGNANCY
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MATERNAL CHANGES DURINGPREGNANCY
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Weight Gain
About 24 lb increase in weight especially duringlast two trimesters
Weight gain attributes to
7 pounds is fetus
4 pounds is amniotic fluid, placenta, and fetalmembranes.
2 pounds due to increase in the uterus
2 pounds due to increase in breasts
6 pounds of this is extra fluid in the blood andextracellular fluid
3 pounds is generally fat accumulation.
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Increased desire for food during pregnancy
partly as a result ofremoval of food
substratesfrom the mothers blood by the
fetus.
partly because ofhormonal factors
Mothers weight gain can be as great as 75
pounds instead of the usual 24 pounds
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Increase Basal Metabolic Rate
During the latter halfof pregnancy.
15 per cent Increase in BMR consequent to:
Increased secretion of many hormones such as
thyroxine, adrenocortical hormones, and the sexhormones,
Frequent sensation of becoming over-heated,
owing expenditure of more energy for muscle activityfor carrying extra load that she is carrying, greater
amounts of energy than normal.
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Increased absorption of Nutrients
Mother stores sufficient protein, calcium, phosphates, and iron fromher diet in advance in placenta as well as in normal store depots tomeet the anticipated extra requirement of these nutrients forgreatest growth of the fetus occurs during the last trimester ofpregnancy.
Maternal deficiencies of calcium, phosphates, iron, and the vitaminscan occur during pregnancy if appropriate care to provide additionalnutritional elements are not present in a pregnant womans diet.
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Iron requirement during pregnancy is about 975 mg against
normal store of 100 mg, maximum reaches upto 700 mg.
Iron requirement is met by :
by the fetus (375 mg) by the mother (600 mg) form her own extra blood.
Hence iron supplements must during pregnancy.
Increase demand for vitamin D, for calcium absorption
(normally poorly absorbed by the mothers gastrointestinaltract without vitamin D).
Supplementation with vitamin K to the mothers diet to
provide sufficient prothrombin to prevent hemorrhage,
particularly brain hemorrhage, caused by the birth process.
Increased absorption of Nutrients
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Mammary Glands
Breasts grow larger,
Skin appears thinner,
Diameter of the areola increases,
Veins become more prominent.
As the nipples become more erect, Pigmentation of the areola increases and the
mammary glands enlarge.
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Cardiovascular Adaptations
30 to 40 per cent increase in cardiac outputabove normal at end of II Trimester andbeginning of third trimester, falls to little above
normal during the last 8 weeks of pregnancy. Blood Pressure also varies.
Systolic remains same
There is fall in diastolic pressureVasodilation (Kinin,Nitric oxide,EDF)
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Blood Volume During Pregnancy
1 to 2 liters of extra blood in circulatory system of
mother at the time of birth of the baby .
30 per cent increase in Maternal blood volume
shortly before term, Partly due to Increased in aldosterone and estrogens during
pregnancy,
Increased fluid retention by the kidneys.
Increase activity ofbone marrow to produce extra
red blood cells to go with the excess fluid volume.
Only about one fourth of this amount is normally lost
through bleeding during delivery of the baby,
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Respiration During Pregnancy
Consumption of oxygen increases Because of Increased basal metabolic rate of a pregnant woman
greater size ,
the total amount of oxygen used by the mother is about 20 per cent
above normal, and a commensurate amount of carbon dioxide is
formed.
Increase minute ventilation of mother ~ believed that the high
levels of progesterone increases the respiratory centers
sensitivity to carbon dioxide
Respiratory rate increased to maintain the extra ventilationdue to pressure exerted by the growing uterus against the
abdominal contents, press upward against the diaphragm.
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Maternal Urinary System
About 6 pounds of extra water and salt accumulates during
pregnancy
Rate of urine formation increased because of increased fluid
intake and increased load or excretory products.
Increased reabsorptive capacity of renal tubules for sodium,
chloride, and water 50 per cent consequent of increased
production of steroid hormones by the placenta and adrenal
cortex.
Increased GFR as much as 50 per cent
Increase the rate of water and electrolyte excretion in the
urine due to increase GFR.
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Amniotic Fluid
It is the fluid inside fluid present in uterus in
which the fetus floats
Normal volume is between 0.5 -1 L, increased few
ml to several L Increased turnover of the amniotic fluid due to
additional formation and absorption through the
amniotic membranes
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Changes in the gastrointestinal system
Increases absorption of nutrients and water Increase chances for constipation due to decrease intestinal
mobility.
Decrease Peristalsis together with tone and mobility becauseof the production of the progesterone
Slows the rate of secretion of hydrochloric acid and pepsin.
Increase nausea and heartburn (pyrosis) due to reducedgastric emptying.
Relaxation of the cardiac sphincter may increase
regurgitation and chance for heartburn. Growth of uterus pushes the abdominal Organs such as
Stomach , intestines, and other adjacent organs
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Changes in endocrine system activity
Increases secretion of Parathyroid Gland to meetsthe increased requirements for calcium needed for
fetal growth.
Large amounts of estrogen and progesterone secretion
by placenta by 10 to 12 weeks of pregnancy. It serves
to
Maintain the growth of the uterus,
helps to control uterine activity, Cause many of the maternal changes in the body.
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Changes of the skeletal system
Realignment of the spinal curvatures duringpregnancy to maintain balance
due to the increase in size of the uterus andpressure on the abdominal wall
Slight relaxation and increased mobility of thepelvic joints, which allows stretching at the time ofdelivery of the infant.
"waddling" gait ; walks with head and shouldersthrust backward and chest protruding outward tocompensate.
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Uterine Changes
Uterus gains weight from 50g to 1000g
Increases in width and length approximately
five times its normal size.
Uterus rises above the symphysis pubis by the
12th week, reach the xiphoid process by the 36th
week of pregnancy
Abdominal Changes corresponding to changes
that occur in the uterus.
Increase in connective tissue and elastic tissue.
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Physiology of Parturition
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Parturition:
Duration of pregnancy is 280 days or 40 weeks
from the first day of last menstrual period.
Defined as act or process of giving birth;
Physiologic process~ refers to expulsion of
products of conception (i.e. the fetus,membranes, umbilical cord, and placenta)
by the uterus.
Labor
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Sudden change of slow, weak rhythmicity of
uterus transform in to strong tonic contraction~
positive feedback theory
Labor contractions follow principles of
positive feedback
Two types of positive feedback:
Stretching of cervix
Release of Oxytocin
Parturition
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Parturition
Progressive
hormonal
changes
UterineExcitability
Uterine
Contractions
Mechanical
changes
Highly excited and contractile Uterus
with progress in pregnancy at term
Expulsion of Child giving birth
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Hormonal Factors of
Parturition
Increased Secretion
of Oxytocin
Hormonal
Secretions from
fetal glandsE/P Ratioincreases
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Stretch of uterine
musculature
Gradual increase and
frequent fetal
movement in uterus
Stretch & irritation
of cervix ~ rupture
of membrane
Myogenic transmission of
signals from cervix touterine wall
Mechanical Factors of
Parturition
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Uterine contractions
Stretch of cervix and distention of vagina
Afferents from cervix and vagina
positive feedback to the hypothalmus
Oxytocin from posterior pituitary
Formation of Prostaglandins in the decidua
Positive feedback theory
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Parturition
STAGES:
1. DIALATATION OF CERVIX
2. EXPULSION OF FETUS
3.EXPULSION OF PLACENTA
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Parturition has not yet begun
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Dilatation of Cervix; 1st Stage
10-12 hrs in primigravidas, 6-8 hrs inmultigravidas
Retraction of lower uterus & cervix, so acontinuous birth canal formed
Head of fetus pressing cervix initiation ofneuroendocrine reflex
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The cervix is dilating
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Expulsion: 2nd stage
Last for 40 min in primi and 15-30min in multi
Once full dilatation achieved
Fetal membrane ruptures
Fetus head move suddenly to birthcanal and move continuously tilldelivery effected.
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The cervix is completely dilated, and the fetusshead is entering the cervical canal; the amniotic sac has
ruptured and the amniotic fluid escapes.
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The fetus is moving through the vagina.
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Separation & Expulsion of placenta
15-30 Min
Further continued uterine contractions~
size decreases gradually.
Separation of placenta from uterine layer
associated.
Uterus involutes after 4 to 5 wks
weight decreases and attain normal size.
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The placenta is coming loose from theuterine wall preparatory to its expulsion.
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1.PRESSURE ON CERVIX BY FETAL HEAD
2. DIALATATION OF CERVIX & STRECHINGOF NERVE ENDINGS
3. OXYTOCIN & PROSTAGLANDINS
4.STRONG CONTRACTIONS OF UTERUS
5. FURTHER INCREASE IN WIDTH OFCERVIX & SHORTENING OF
ENDOCERVICAL CANAL 6. HEAD GOES FURTHER DOWN
7. POSITIVE FEED BACK SET IN
MECHANISM
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Two types ofpositive feedbackmechanisms
increase uterine contractions during labor:
1. Stretching of the cervix causes the entire
body of the uterus to contract
2. Cervical stretching also causes the pituitary
gland to secrete oxytocin
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Physiology of
Lactation
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Physiology of Lactation
Divided into three phases
Mammogenesis (the growth of the mammary
glands)
Lactogenesis (the initiation of milk
production),
Galactopoiesis (the maintenance of the milk
supply).
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Mammogenesis
Mammary gland development during childhood is limitedto general growth.
Mammary gland development begins during the 7-8 week of gestation when primary and secondary ductsdevelop.
At puberty, estrogen exertsmajor influence onbreastgrowth in a girl, when primary and secondaryducts grow.
Complete development of mammary functionoccurs only in pregnancy.
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Hormonal Effects
Breast growth continue to occur during each menstrual cyclein response to the changes in hormones.
Several hormones control breast development duringpregnancy; estrogen, progesterone, Adrenocorticotropic hormone (ACTH),
prolactin, and growth hormone.
Estrogen causes the ductal system to proliferate anddifferentiate,
Progesterone promotes an increase in the size of the lobes,lobules, and alveoli.
ACTH and growth hormone combine with prolactin andprogesterone to promote mammary growth.
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Lactogenesis Lactogenesis is the onset of milk secretion.
During the second half of pregnancy, secretory activityaccelerates and colostrum is produced.
Comprises oftwo phase:
StageI: capacity of the breast to secrete milk during laterpregnancy
Stage II; onset of copious milk secretion occurs after birth(days two or three to eight postpartum)
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Lactogenesis is triggered by a fall in progesterone andestrogen levels and continued presence of prolactin.
Decrease progesterone and estrogen levels Causes~Releases very large amounts of prolactin.
Prolactin levels rise and fall in proportion to the
frequency, intensity, and duration of nipple stimulation
and the suckling stimulus.
Hormonal control
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Milk Ejection Reflex The milk ejection reflex (MER), causes the alveoli to release the
milk.
Suckling of the nipple of breast ~ stimulates the nipple~signals sent up the nerve pathways to the paraventricular andsupraoptic nuclei in the hypothalamus causing the production ofoxytocin.
Oxytocin released from the posterior pituitary gland. and causesthe muscles around the alveoli (myoepithelia) to contract andpush the stored milk down the ducts through the collectingsinuses and out the nipple pores.
The MER has a strong psychological base.
Emotional upsets, stress, embarrassment, severe cold, certaindrugs, anxiety, pain, discomfort, excessive nicotine, caffeine, oralcohol intake, or inadequate rest may inhibit the MER.
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Ejection of Milk: Oxytocin
Milk let down reflex or Suckling reflex
Neuroendocrine reflex
Suckling of breast Afferent conduction of APs spinal cord
hypothalamus
Prolactin
secretion
Oxytocinsecretion
Increase [milk] in the alveoli of the breast
Contraction of the myoepithelial cells
Ejection of milk
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Galactopoiesis
Galactopoiesis, or the maintenance of a milk supply,requires removal of milk from the breast.
It is the quantity and quality of infant suckling or milkremovals that controls breast milk synthesis.
Milk production reflects the infants appetite rather thanthe womans ability to produce milk.
As long as milk is regularly removed, the alveolar cellswill continue to secrete milk.
This phenomenon, called the supply-demand response,is a feedback control that regulates the production ofmilk to match the infant of the infant.
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Effect of Estrogen on the Breast
Causes: Development of stromal tissue
Growth of an extensive ductal system
Deposition of fat in the breasts
Inhibits the actual secretion of milkDevelopment of alveoli and lobules brought about by
estrogens is slight. Progesterone and prolactin causesthe determinative growth and function of thesestructures.
Therefore, estrogens initiate growth and is responsiblefor the characteristic external appearance of themature female breast, but they do not complete thejob of converting the breasts into milk producingorgans.
Eff t f P t th
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Effect of Progesterone on theBreast
Promotes development of lobules and alveoli
Causes alveolar cells to proliferate, enlarge andbecome secretory in nature
Does not cause alveoli to secrete milk (actuallyinhibits the secretion of milk), milk is secretedonly after the prepared breast is furtherstimulated by prolactin.
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Effect of Prolactin
1. Major function of prolactin is milkproductionoxytocin stimulates ejection
2.Release is inhibited by PIH (dopamine)
3.Suckling response inhibits PIH release