Lectures 9 & 10 - Birth and Lactation Jan 27 & 29, 2025

Question 1

What are prostaglandins produced from?

Answer 1

Arachidonic acid

Prostaglandins are derived from arachidonic acid, which is a fatty acid present in cell membranes.

Question 2

What is the role of phospholipase A2 (PLA2) in the direct pathway of arachidonic acid signaling?

Answer 2

Releases arachidonic acid from membrane phospholipids

PLA2 is activated by agonists binding to receptors.

Question 3

Name the three indirect pathways through which arachidonic acid can be released.

Answer 3

• Activation of PLC leading to DAG and IP3 formation
• IP3 releasing Ca2+ from internal stores
• MAPK stimulating PLA2

These pathways facilitate the release of arachidonic acid from different sources.

Question 4

What eicosanoids are produced by the cyclooxygenase pathway?

Answer 4

• Thromboxanes
• Prostacyclins
• Prostaglandins

These eicosanoids play various roles in inflammation and other physiological processes.

Question 5

What initiates labor according to the document?

Answer 5

Signals from the placenta or fetus

The factors leading to labor initiation include endocrine, paracrine, and mechanical stretching of the uterus.

Question 6

What role does progesterone play in pregnancy?

Answer 6

Maintaining the length of gestation

Although not conclusively proven in humans, progesterone appears to have an important role in gestation duration.

Question 7

List the three major effects of prostaglandins during labor.

Answer 7

• Stimulate uterine smooth muscle contraction
• Induce softening and effacement of the cervix
• Promote formation of gap junctions between uterine smooth muscle cells

These effects are crucial for the progression of labor.

Question 8

What physiological changes occur in prostaglandin levels before and during labor?

Answer 8

Levels increase in blood and amniotic fluid

This increase is associated with the initiation of labor.

Question 9

True or False: Oxytocin is synthesized in the posterior pituitary gland.

Answer 9

False

Oxytocin is synthesized in the hypothalamus and then transported to the posterior pituitary gland.

Question 10

What triggers the release of maternal oxytocin during labor?

Answer 10

Distention of the cervix

This response is known as the Ferguson reflex.

Question 11

What is the effect of estrogen on oxytocin receptors during pregnancy?

Answer 11

Increases the number of oxytocin receptors

This increase enhances the uterus’s sensitivity to oxytocin as pregnancy progresses.

Question 12

What is the primary role of relaxin during pregnancy?

Answer 12

Keeps the uterus in a quiet state

Relaxin is produced by the corpus luteum, placenta, and decidua.

Question 13

Fill in the blank: The _______ reflex is an example of positive feedback involving oxytocin.

Answer 13

Ferguson

This reflex enhances uterine contractions as pressure is applied to the cervix.

Question 14

What is the relationship between fetal and maternal oxytocin levels after delivery?

Answer 14

Fetal oxytocin levels are higher after vaginal delivery than after cesarean section

This is likely due to maternal oxytocin crossing the placenta.

Question 15

What hormone stimulates uterine contractions during labor?

Answer 15

Oxytocin

Oxytocin production increases during labor, leading to greater uterine contractions.

Question 16

What is the role of relaxin during pregnancy?

Answer 16

Keeps the uterus in a quiet state

Relaxin is produced by the corpus luteum, placenta, and decidua, and increases during labor to help dilate the cervix.

Question 17

What mechanical factor can stimulate uterine contractions?

Answer 17

Mechanical stretch

Stretching of the uterine muscle may lead to rhythmic contractions of labor.

Question 18

What feedback mechanism sustains labor once it is initiated?

Answer 18

Positive feedback loops

These loops involve prostaglandins and oxytocin which enhance uterine contractions.

Question 19

What effect do uterine contractions have on prostaglandins?

Answer 19

Stimulate their release

Prostaglandins increase the intensity of uterine contractions.

Question 20

What reflex is involved in the release of oxytocin during labor?

Answer 20

Ferguson reflex

Stretching of the cervix during uterine activity stimulates oxytocin release.

Question 21

Which hormones are primarily responsible for breast development at puberty?

Answer 21

Estrogens and progesterone

These hormones lead to the development of breast tissue.

Question 22

What hormones lead to full development of the breasts during pregnancy?

Answer 22

Prolactin, hCS, estrogens, and progesterone

Gradual increases in these hormones are necessary for breast development.

Question 23

What are the four types of hormones affecting the breast?

Answer 23

• Mammogenic
• Lactogenic
• Galactokinetic
• Galactopoietic

Each type has a specific role in breast development and milk production.

Question 24

What is the composition of milk?

Answer 24

• Fats
• Sugar (lactose)
• Proteins (lactalbumin and casein)
• Cations (K+, Ca2+, Na+)
• Anions (Cl- and phosphate)

The composition varies between human milk, human colostrum, and cow’s milk.

Question 25

How does the composition of cow's milk differ from human milk?

Answer 25

Higher protein and electrolyte content ## Footnote Cow's milk has nearly three times more protein than human milk, primarily due to higher casein concentration.

Question 26

What is the primary mammogenic hormone?

Answer 26

Prolactin ## Footnote Prolactin promotes the proliferation of alveolar and duct cells in the breast.

Question 27

What hormone is responsible for milk ejection?

Answer 27

Oxytocin ## Footnote Oxytocin promotes the contraction of myoepithelial cells, leading to milk ejection.

Question 28

What is the effect of suckling on prolactin release?

Answer 28

Stimulates increased release ## Footnote Suckling inhibits dopamine release, allowing prolactin to increase.

Question 29

What is the role of dopamine in lactation?

Answer 29

Inhibits prolactin release ## Footnote Dopamine travels to the anterior pituitary and inhibits lactotrophs.

Question 30

How does suckling affect GnRH release?

Answer 30

Inhibits GnRH release ## Footnote This inhibition prevents the ovarian cycle during breastfeeding.

Question 31

What are the key peptides released by the hypothalamus affecting the anterior pituitary?

Answer 31

* GHRH * CRH * TRH * GnRH * AVP ## Footnote These peptides regulate various hormonal activities in the body.

Question 32

How does dopamine inhibit adenylyl cyclase in lactotrophs?

Answer 32

Through G-proteins ## Footnote Dopamine activates the Gαi protein to inhibit cAMP production.

Question 33

What happens when a ligand binds to a receptor coupled to the αs subunit?

Answer 33

Adenylyl cyclase is activated ## Footnote This leads to an increase in cAMP production.

Question 34

What effect does the binding of dopamine to the αi subunit have?

Answer 34

* Decreases intracellular cAMP * Increases potassium influx * Decreases [Ca2+]i ## Footnote This results in inhibition of prolactin release.