Physiology of Parturition & Lactation 5042012

8/2/2019 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

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Physiology of Parturition & Lactation 5042012

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