Parturition, Lactation and Neonatal Physiology Flashcards
What does parturition involve?
- myometrium becomes highly contractile
- remodeling of cervix–> softens and dilates
- rupture of fetal membranes
- expulsion of urterine contents
- return of uterus to prepregnant state
What categories of effects lead up to intense contractions during childbirth?
- progressive hormonal changes
*relaxin, oxytocin,
prostaglandins,
progesterone,
estrogens - progressive mechanical changes
*cervical remodeling,
uterine size
Describe Braxton Hicks contractions
toward end of pregnancy
not powerful enough to induce labor
–>thought to prepare uterus for childbirth
Describe uterus during most of pregnancy
Relaxed, quiescent, insensitive to contraction hormones (prostaglandins, oxytocin)
Hypertrophy of myometrial cells as uterus expands to fit fetus
What is necessary for onset of labor?
Reciprocal changes in uterine progesterone and estrogen receptors
What hormone blocks contractions of labor and promotes myometrial relaxation during pregnancy?
progesterone
Injection of what antagonist can induce labor at any stage of pregnancy?
nuclear progesterone antagonist
What hormone increases myometrial contractility and cervical dilation?
estrogen
What happens to uterine cells in terms of progesterone and induction of childbirth?
desensitization of cells to progesterone allows increase in estrogen receptor expression–> childbirth
What hormone is necessary to increase responsiveness to progstaglandins and oxytocin to kickstart childbirth?
estrogen
–> stimulate gap jxn formation
–>increase # oxytocin receptors in myometrium and decidual tissue
What stimulates expression of proteolytic enzymes in the cervix?
estrogen
What hormone increases production of prostaglandins in the fetal membrane?
estrogen
What initiates labor via stimulation of strong myometrial contractions?
prostaglandins
Large doses of what during pregnancy can induce labor at any gestation?
prostaglandins
PGF2a and PGE2
What potentiates oxytocin induced contractions by promoting formation of gap jxns?
PGF2a
What stimulates synthesis of prostaglandins?
- estrogen in fetal membranes
- oxytocin in uterine cells
- uterine stretch
What stimulates effacement of cervix early in labor?
prostaglandins
Uterus is insensitive to what until 20 weeks?
oxytocin
What increases the number of oxytocin receptors in myometrium and decidual tissue?
estrogen
What does oxytocin do in uterine myometrium?
smooth muscle contraction to sustain labor
What does oxytocin do to decidual tissue?
stimulates prostaglandin (PGF2a) production
Describe the frequency of oxytocin release during labor
Released in bursts that increase in frequency as labor progresses
What is the primary release for oxytocin?
distention of cervix
Ferguson reflex, + feedback
What is the Ferguson reflex?
oxytocin is released as the cervix is distended
–>positive feedback loop to enhance labor
What is the role of relaxin in childbirth?
keeps uterus in quiet states during pregnancy
- ->help soften and dilate cervix
- ->max concentration at 38-42 weeks
What is elevated relaxin at 30 weeks associated with?
premature birth
What secretes relaxin?
corpus luteum
placenta
decidua
What is relaxin structurally related to?
insulin
What does uterine stretch cause?
Ferguson reflex–> positive feedback
Prostaglandin production
Why do twins average 19 day shorter gestation?
increased uterine stretch activates pathways faster
What is necessary for expulsion of the fetus?
cervical remodeling
Describe the initiation of labor
Placenta produces CRH
- -> maternal levels rise during late preg and labor
- -> promotes myometrial contractions
- -> stimulates fetal ACTH secretion
What does fetal ACTH do during labor?
increases cortisol production to stimulate further placental CRH release
increases fetoplacental estrogen to enhance myometrial contractility
Where does the cervix move during pregnancy?
up to just below the pelvic inlet
How long does it take to fully dilate the cervix and draw it up just below the pelvic inlet?
occupies most of labor time
How long does it take to push the fetus downward and through the pelvis?
less than 1 hour
What constricts uterine blood vessels as the placenta is expelling from the uterus?
oxytocin
What induces oxytocin release?
nipple stimulation
What trimester does surfactant begin to be produced?
last trimester
What are stimuli to start breathing at birth?
- asphyxiation during birth
- sudden drop in temp of skin
Why can there be delayed breathing upon birth?
- use of general anesthesia during delivery
- prolonged labor
- head trauma (depressed resp center)
Describe alveoli at birth
collapsed, filled with amniotic fluid
Describe the physiology of breathing at birth
need 25mmHg negative inspiratory pressure to overcome surface tension and open alveoli
- ->1st inspiration (-60(
- ->1st insp movements (40mL air)
Deflation requires strong positive pressure to overcome viscous resistance of fluid in broncioles
When does breathing become normal after birth?
40 minutes
- -> RR 40
- ->6-10 tidal volume
What do the “legs” of the umbilical arteries connect to?
IVC
Where does blood enter via the umbilical V?
ductus venosus
How does the fetus bypass the liver?
umbilical V to IVC
How does the fetus bypass the R ventricle?
foramen ovale (27%)
Blood enters IVC to the left ventricle to supply what?
carotid and brain
How does the fetus bypass the lungs?
ductus arteriosus
–>SM dilated by prostaglandins
Describe closure of foramen ovale upon birth
reversal of pressure gradient across atria pushes it shut
–>eventually seals
**increased venous return to L atrium and elevated L atrial pressure
***Decreased right atrial pressure
Describe closure of ductus arteriosus upon birth
Aortic pressure rises above pulmonary
- -> blood flows wrong way, oxygenated aortic blood flows through ductus
- –>causes vasoconstriction (PCO2) along with falling progesterone levels that eventually close ductus
When is the ductus arteriosus closure sufficient?
1-8 days
When is the ductus arteriosus anatomically closed?
1-4 months
Describe patent foramen ovale
20% by 2 years
–>increased R atrial pressure can push flap open
HTN or transient increases
Describe patent ductus arteriosus (PDA)
heart problems soon after birth (murmur)
mixing of ox and deox blood puts strain on heart–> increases pulmonary BP
Describe closure of ductus venosus
Immediately after birth, portal blood flows through ductus venosus
–>1-3 hours, muscle wall contracts and closes
–> portal venous pressure rises, forcing through liver sinusoids
**rarely fails to close
When does nephrogenesis begin?
8 weeks–> 36 weeks
When does urine production begin?
as early as 10 weeks–>20 weeks
What accounts for 70-80% of amniotic fluid?
fetal urine
When does renal function mature rapidly?
3rd trimester
–> acid base balance, body fluid balance, electrolyte balance
When is functional development of the kidneys complete?
1 month
Due to poor fxn of liver when born, how does the infant cope?
stores fats and proteins for metabolism until it can get mother’s milk
When are normal adult hemoglobin levels achieved?
12 weeks
–> Hb A (a2b2)
What is the major hemoglobin in fetus?
Hb F (a2y2)
What are the main neonatal nutritional needs?
Ca++ and vitamin D
–> via milk
Iron
–> enough stored for 6 months
Vitamin C
–> not stored in fetus, needed from milk
Does the fetus form its own antibodies?
NO, inherits immunity from mother
–> protects for 6 months against major diseases
When does infant’s own immune system form?
12-20 months
Describe breast development from birth to puberty
Mammary gland entirely lactiferous ducts with few alveoli at birth
–> remains until puberty
Estrogens–> lactiferous ducts to sprout and branch, ends develop into alveoli
Whatisre the fxn of alveolar epithelium in breasts?
milk synthesis and secretion
What is the fxn of myoepithelial cells in breasts?
b/t epithelial cells and basement membrane
moves milk from alveoli into ducts on contraction
Describe breast formation once menstrual cycle begins
exposed to estrogen and progesterone
–> induces additional alveolar growth
breast tissue increases
–>CT and adipose
cyclical changes
- -> increase in volume
- -> breast tenderness
- -> may have some secretory activity
- -> involution
What are the 5 major pathways of milk secretion by alveolar cells?
1: secretory pathway
2: transcellular endocytosis and exocytosis
3: lipid pathway
4: transcellular salt and water transport
5: paracellular pathway
What are the 4 effects of suckling on hormone release?
1: suckling stimuli or sight of child
- –> afferent neural pathway from breast to spinal cord and hypothalamus
2: Dopamine release inhibited, prolactin released to stimulate milk production
3: Stimulation of production of oxytocin from posterior pituitary
- -> activates myoepithelial cells (let down)
4: Inhibition of GnRH production
- -> inhibits ovarian cycle via decrease in LH and FSH
Describe cessation of lactation
Milk accumulates when suckling stimulus discontinued
- -> cell and debris phagocytosed
- -> lobar acinar structures smaller
- -> ductal system predominates
How long can full involution of breast take after lactation cessation occurs?
3 months
