Lecture 37: Parturition, Lactation and Neonatal Physiology Flashcards
What events are hallmarks of parturition?
- Myometrium becomes highly contractile
- Fetal membranes rupture
- Uterine cervix dilation
Characteristics of gravid uterus
- relaxed, insensitive to hormones that stimulate contractions
- uterine myometrium cells hypertrophy
- only does weak contractions that don’t stimulate labor
What is the role of progesterone in inducing labor?
Progesterone is a pro-pregnancy hormone
decreased progesterone receptors > uterine cells become desensitized to effects of progesterone > increase estrogen receptor expression
What is the role of estrogen in inducing labor?
progesterone desensitization of uterine cells > increase in estrogen receptors
Effects of estrogen:
- increase myometrium contractions and cervical dilation
- increase responsiveness to oxytocin and prostaglandins by increasing the receptors
- release of prostaglandins from fetal membranes
- increased expression of proteolytic enzymes in cervix
What are the effects of prostaglandins (PGF/PGE)?
What stimulates its synthesis?
- stimulates the strong myometrial contraction that induces labor
- estrogen from fetal membranes, oxytocin in uterine cells, uterine stretch
What are the effects of oxytocin in inducing labor?
- stimulates uterine contractions that sustain the labor
- stimulates PGF2a production by placenta which is released in bursts
- stimulates cervical dilation (Ferguon reflex - positive feedback loop)
What is the significance of relaxin?
How does it relate to premature birth?
- maintains quiet uterus during pregnancy, but increases towards end of pregnancy and induces cervix dilation at labor
- if female has elevated relaxin at 30 weeks, may be a sign of premature birth
What are the mechanical stimuli for labor induction?
- increased uterine stretch (thus size) induces the Ferguson reflex
- cervix is remodeled to accommodate expulsion of fetus
Be able to draw the pathway of labor induction by the placenta
Ok
Describe the uterine contractions during and at the end of pregnancy
During: weak (braxton hicks)
End: become exceptionally strong > stretching and dilating the cervix
How do uterine contractions expel the fetus?
1st stage: fully dilated cervix is drawn upward past the pelvic inlet (takes most of labor time)
2nd stage: pulsatile uterine contractions push the fetus down
How is the placenta expelled?
oxytocin > more uterine contractions after the fetus is out detaches the placenta from uterus = clotting occurs afterwards
What factors stimulate the first breath?
- asphyxiation (due to umbilical cord being compressed during birth)
- sudden drop in temperature/skin cooling (from inside body to outside environment)
What factors can delay breathing after birth?
-general anesthesia, prolonged labor, head trauma (which depresses the respiratory center)
Physiology of the first breath
Inspiration: -25 mmHg needed to expand the alveoli > infant capable of -60
Expiration: infant overcomes viscous resistance of fluid in bronchioles for to achieve + pressure to deflate the alveoli
Be able to draw the pathway of fetal circulation
Ok
Significance of these fetal structures
Ductus venosus
Ductus arteriosus and foramen ovale
- allows fetal blood to bypass the liver
- allows fetal blood to bypass the lungs
What stimulates closure of the foramen ovale?
-increased pressure in the left atrium and decreased pressure in the right atrium
What stimulates the closure of the ductus arteriosus?
Aortic pressure now higher than pulmonary artery pressure, causing oxygenated blood to flow through the ductus arteriosus > high PO2 flowing through triggers vasoconstriction of the arteriosus and eventual closure
How does high oxygenation close the ductus arteriosus?
High PO2 > vasoconstriction hours after birth (repressed prostaglandins) = fully constricted/closed at 4 months
Pathophysiology of Patent Foramen Ovale
Pathophysiology of Patent Ductus Arteriosus
- Increased RA pressure pushes the flap open (in cases of pulmonary HTN or transient increases)
- oxygenated and deoxygenated blood mix at the pulmonary artery > strains the heart and increases pulmonary BP (can be heard as murmur in neonate)
How does the ductus venosus close?
muscle wall of the ductus venosus contracts and closes,
-blood shunted from venosus to portal vein
Characteristics of the fetal kidneys
Characteristics of the fetal liver
- rapid maturation of renal function at 3rd trimester, functional at 1 month of age
- does not become fully functional until age 2 (poor conjugation of bilirubin, deficient gluconeogenesis)
Neonatal Hemoglobin
HbF degenerates to bilirubin and HbA is formed at birth. Infant does reach normal HbA levels until around 12 weeks of age
Neonatal Physiological Anemia
in-utero there is no hypoxic stimulus (dependent on maternal blood) so not much RBCs are synthesized.
Once born, there’s an increase in this stimulus that induces RBC production in infant
What are the important neonatal nutritional needs?
Ca2+ and vitamin D = bone growth
Iron
Vitamin C
*infant needs this since body does not make enough, acquired from nutrition
Neonatal immunity
Antibodies passed by mom to fetus. Good for 6 months.
Baby forms own antibodies at 12-20 months
Describe the process of breast development through these stages:
Birth
Puberty
Menstrual age
- Birth: mammary gland mostly lactiferous ducts with few alveoli
- Puberty: estrogen > lactiferous ducts branch out and form masses of cells (alveoli)
- Menstrual age: breasts grow due to exposure to hormones from menstrual cycle. estrogen and progesterone > additional alveolar growth, adipose and connective tissue deposition
Breast alveolar epithelium vs myoepithelial cells
Epithelium: surrounds the lumen of the alveoli > synthesizes and secretes milk
Myoepithelial cells: between the epithelium and basement membrane > contractile muscles that move milk from alveoli to ducts
Mammogenic hormones
Lactogenic hormones
Galactokinetic hormones
Galactopoietic hormones
- promotes proliferation of alveolar and duct cells
- promotes initiation of milk production
- promotes myoepithelial cell contraction to eject milk
- maintain milk production
Briefly describe these pathways of milk production by alveolar epithelial cells:
- Secretory pathway
- Transcellular endocytosis and exocytosis
- Lipid pathway
- Transcellular salt and water transport
- Paracellular pathway
- milk proteins secreted from Golgi via vesicles
- proteins endocytosed into cell and released by epithelial cell into milk
- main method of transporting lipids between milk and cell
- main method of transporting electrolytes between milk and cell
- salts and water squeeze through junctions into milk
What are the 4 effects of suckling on hormone release?
- activation of afferent neutral pathway from breast to hypothalamus
- Dopamine/lactotroph inhibition > prolactin release
- Oxytocin released from posterior pituitary
- inhibition of GnRH, LH and FSH production > inhibits the ovarian cycle
What happens when suckling stimulation is gone?
Milk accumulates in the ducts > ducts distend > capillaries compressed leading hypoxia of alveoli > lobular-acinar structures will hypotrophy and leaves ductal cells
