Lecture 37: Parturition, Lactation and Neonatal Physiology

Question 1

What events are hallmarks of parturition?

Answer 1

1. Myometrium becomes highly contractile
2. Fetal membranes rupture
3. Uterine cervix dilation

Question 2

Characteristics of gravid uterus

Answer 2

• relaxed, insensitive to hormones that stimulate contractions
• uterine myometrium cells hypertrophy
• only does weak contractions that don’t stimulate labor

Question 3

What is the role of progesterone in inducing labor?

Answer 3

Progesterone is a pro-pregnancy hormone

decreased progesterone receptors > uterine cells become desensitized to effects of progesterone > increase estrogen receptor expression

Question 4

What is the role of estrogen in inducing labor?

Answer 4

progesterone desensitization of uterine cells > increase in estrogen receptors

Effects of estrogen:

1. increase myometrium contractions and cervical dilation
2. increase responsiveness to oxytocin and prostaglandins by increasing the receptors
3. release of prostaglandins from fetal membranes
4. increased expression of proteolytic enzymes in cervix

Question 5

What are the effects of prostaglandins (PGF/PGE)?

What stimulates its synthesis?

Answer 5

• stimulates the strong myometrial contraction that induces labor
• estrogen from fetal membranes, oxytocin in uterine cells, uterine stretch

Question 6

What are the effects of oxytocin in inducing labor?

Answer 6

1. stimulates uterine contractions that sustain the labor
2. stimulates PGF2a production by placenta which is released in bursts
3. stimulates cervical dilation (Ferguon reflex - positive feedback loop)

Question 7

What is the significance of relaxin?

How does it relate to premature birth?

Answer 7

• 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

Question 8

What are the mechanical stimuli for labor induction?

Answer 8

• increased uterine stretch (thus size) induces the Ferguson reflex
• cervix is remodeled to accommodate expulsion of fetus

Question 9

Be able to draw the pathway of labor induction by the placenta

Answer 9

Ok

Question 10

Describe the uterine contractions during and at the end of pregnancy

Answer 10

During: weak (braxton hicks)

End: become exceptionally strong > stretching and dilating the cervix

Question 11

How do uterine contractions expel the fetus?

Answer 11

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

Question 12

How is the placenta expelled?

Answer 12

oxytocin > more uterine contractions after the fetus is out detaches the placenta from uterus = clotting occurs afterwards

Question 13

What factors stimulate the first breath?

Answer 13

• asphyxiation (due to umbilical cord being compressed during birth)
• sudden drop in temperature/skin cooling (from inside body to outside environment)

Question 14

What factors can delay breathing after birth?

Answer 14

-general anesthesia, prolonged labor, head trauma (which depresses the respiratory center)

Question 15

Physiology of the first breath

Answer 15

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

Question 16

Be able to draw the pathway of fetal circulation

Answer 16

Ok

Question 17

Significance of these fetal structures
Ductus venosus
Ductus arteriosus and foramen ovale

Answer 17

• allows fetal blood to bypass the liver

- allows fetal blood to bypass the lungs

Question 18

What stimulates closure of the foramen ovale?

Answer 18

-increased pressure in the left atrium and decreased pressure in the right atrium

Question 19

What stimulates the closure of the ductus arteriosus?

Answer 19

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

Question 20

How does high oxygenation close the ductus arteriosus?

Answer 20

High PO2 > vasoconstriction hours after birth (repressed prostaglandins) = fully constricted/closed at 4 months

Question 21

Pathophysiology of Patent Foramen Ovale

Pathophysiology of Patent Ductus Arteriosus

Answer 21

• 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)

Question 22

How does the ductus venosus close?

Answer 22

muscle wall of the ductus venosus contracts and closes,

-blood shunted from venosus to portal vein

Question 23

Characteristics of the fetal kidneys

Characteristics of the fetal liver

Answer 23

• 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)

Question 24

Neonatal Hemoglobin

Answer 24

HbF degenerates to bilirubin and HbA is formed at birth. Infant does reach normal HbA levels until around 12 weeks of age

Question 25

Neonatal Physiological Anemia

Answer 25

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

Question 26

What are the important neonatal nutritional needs?

Answer 26

Ca2+ and vitamin D = bone growth
Iron
Vitamin C

*infant needs this since body does not make enough, acquired from nutrition

Question 27

Neonatal immunity

Answer 27

Antibodies passed by mom to fetus. Good for 6 months.

Baby forms own antibodies at 12-20 months

Question 28

Describe the process of breast development through these stages:
Birth
Puberty
Menstrual age

Answer 28

1. Birth: mammary gland mostly lactiferous ducts with few alveoli
2. Puberty: estrogen > lactiferous ducts branch out and form masses of cells (alveoli)
3. Menstrual age: breasts grow due to exposure to hormones from menstrual cycle. estrogen and progesterone > additional alveolar growth, adipose and connective tissue deposition

Question 29

Breast alveolar epithelium vs myoepithelial cells

Answer 29

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

Question 30

Mammogenic hormones
Lactogenic hormones
Galactokinetic hormones
Galactopoietic hormones

Answer 30

• promotes proliferation of alveolar and duct cells
• promotes initiation of milk production
• promotes myoepithelial cell contraction to eject milk
• maintain milk production

Question 31

Briefly describe these pathways of milk production by alveolar epithelial cells:

1. Secretory pathway
2. Transcellular endocytosis and exocytosis
3. Lipid pathway
4. Transcellular salt and water transport
5. Paracellular pathway

Answer 31

1. milk proteins secreted from Golgi via vesicles
2. proteins endocytosed into cell and released by epithelial cell into milk
3. main method of transporting lipids between milk and cell
4. main method of transporting electrolytes between milk and cell
5. salts and water squeeze through junctions into milk

Question 32

What are the 4 effects of suckling on hormone release?

Answer 32

1. activation of afferent neutral pathway from breast to hypothalamus
2. Dopamine/lactotroph inhibition > prolactin release
3. Oxytocin released from posterior pituitary
4. inhibition of GnRH, LH and FSH production > inhibits the ovarian cycle

Question 33

What happens when suckling stimulation is gone?

Answer 33

Milk accumulates in the ducts > ducts distend > capillaries compressed leading hypoxia of alveoli > lobular-acinar structures will hypotrophy and leaves ductal cells