Physiology of the parturition and lactation

Female Reproductive System – Physiology: Parturition & Lactation

Lecturer: Dr Faiza
MBBS (Best Graduate, AIMC Lahore)
FCPS (Physiology), ICMT, CHPE, DHPE (STMU)
MHPE (Riphah International University)
MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)

This lecture describes the physiological control of childbirth and milk secretion in the female reproductive system.
It explains the hormonal, mechanical, and neural mechanisms that initiate labor, sustain uterine contractions, and establish lactation after delivery.
The content connects basic physiology with obstetric and clinical applications for medical learners.

Learning Objectives

At the end of this session, learners will be able to:

Explain hormonal and mechanical triggers of labor.

Describe the stages and feedback mechanisms of parturition.

Understand uterine involution after delivery.

Outline the physiology of milk production and ejection.

Identify hormonal regulation of prolactin and oxytocin.

Recognize maternal and neonatal benefits of breast-feeding.

Clinical Significance

Understanding parturition and lactation physiology aids in:

Managing preterm labor and postpartum hemorrhage.

Supporting safe induction of labor and monitoring oxytocin use.

Counseling mothers on lactation, nutrition, and neonatal health.

Educational Value

This lecture integrates endocrine, neural, and mechanical control systems governing childbirth and milk secretion.
Illustrations, flowcharts, and hormone-timing diagrams help learners visualize feedback loops and clinical correlations.

Ideal for MBBS students, postgraduate physiology trainees, and obstetric residents.

References

Guyton & Hall. Textbook of Medical Physiology, 14th ed., Ch. 83: Pregnancy and Lactation.

Barrett KE et al. Ganong’s Review of Medical Physiology, 26th ed., Ch. 22.

Sherwood L. Human Physiology: From Cells to Systems, 9th ed., Ch. 20.

Tags

parturition, labor physiology, childbirth, uterine contractions, oxytocin, estrogen progesterone ratio, fetal hormones, prostaglandins, stages of labor, uterine involution, lactation, prolactin, milk ejection reflex, colostrum, oxytocin release, lactational amenorrhea, breast-feeding benefits, maternal physiology, neonatal immunity, reproductive physiology, Dr Faiza, FCPS Physiology, MBBS lecture, Guyton and Hall, Ganong, Sherwood, physiology of reproduction

1. a
$
So
S
a
a
by
à
a
a
Ss

Female Reproductive System Physiology
Parturition & Lactation

Dr Faiza

MBBS (Best Graduate, AIMC Lahore)
FCPS Physiology,

ICMT, CHPE, DHPE (STMU)

MHPE (Riphah Int. University)

MPH (GC University, Faisalabad)
MBA (Virtual University of Pakistan)

2. a
$
So
S
a
a
IR
à
a
a
Ss

Learning Objectives

At the end of this lecture, you will be able to understand;

+ Fertilization and implantation

+ Anatomy and function of placenta

+ Pregnancy Hormones

+» Feto-placental unit

+ Maternal body response to pregnancy
+ Parturition

+ Lactation

3. a
$
So
S
a
a
IR
à
a
a
Ss

we

www.nucleusinc.com

4. 0310-7990649

1. Baby's hoad strotchos corvix

2. Cervical stretch excites fundic contraction

3. Fundic contraction pushes baby down and stretches.
Corvix some moro

4. Cyclo repeats over and over again

[email protected]

5. Parturition (birth of baby)

0310-7990649

¢ Positive feedback to increase excitability of uterine musculature

6. a
$
So
S
a
a
IR
à
a
a
Ss

Hormonal factors that increase uterine
contractility

1) Increased Ratio of Estrogens to Progesterone
2) Oxytocin

3) Effect of Fetal Hormones on the Uterus

7. a
$
So
S
a
a
IR
à
a
a
Ss

Increased Ratio of Estrogens To Progesteror M)

Se ac

* Progesterone inhibits uterine contractility

« Estrogens increase the degree of uterine
contractility.....?

(Estrogens increase the number of gap junctions between the adjacent
uterine smooth muscle cells)

8. Increased Ratio of Estrogens To Progesteror M)

Se ac

a
$
So
S
a
a
IR
à
a
a
Ss

* From the seventh month gestation onward,

estrogen secretion continues to increase
progesterone secretion remains constant or perhaps decrease

9. 2. Oxytocin

a
$
So
S
a
a
IR
à
a
a
Ss

+ Specifically causes uterine contraction increasingly near term

1. Uterine muscle increases its oxytocin receptors
2. The rate of oxytocin secretion is considerably increased at labor

10. 0310-7990649

[email protected]

2. Oxytocin

Increase in oxytocin receptors

Y

Prostaglandins

pn? Uterine contractions

|

Dilation of cervix and
distention of vagina

k 2

Stimu from cervix
and vagina

|

Increased secretion
of oxytocin

11. Oxytocin Increases Uterine Contractions {|
Two Ways ge

2

a
$
So
S
a
a
IR
à
a
a
Ss

* It acts directly on uterine smooth muscle cells to make them contract

« It stimulates the formation of prostaglandins in the decidua

(prostaglandins enhance the oxytocin-induced contractions)

+ Is delivery of baby possible without oxytocin....?

12. 3. Effect of fetal hormones on the uterus

a
$
So
S
a
a
IR
à
a
a
Ss

1. Fetus’s pituitary gland secretes increasing quantities of oxytocin
2. Fetus’s adrenal glands secrete large quantities of cortisol

3. Fetal membranes release prostaglandins in high concentration at

the time of labor

13. ee PLACENTA

4

679066/-0TEO

14. a
$
So
S
a
a
IR
à
a
a
Ss

|

Increase in Circulating Estrogens Produced
Increased Circulating DHEAS "net

Placenta Fetal Adrenal
Cholesterol
Pregnenolone —————=> DHEAS
16-OHDHEAS

Cortisol,

Progesterone > _
corticosterone

Estradiol <—— DHEAS

Estriol «—————— 16-OHDHEAS

15. 2 Role of Inflammation z £
El 9:
3 Inflammatory response ae

Stretching of the uterine muscle
Pulmonary surfactant protein in amniotic fluid

Activation of nuclear factor kB (NF-kB) in the uterus
Production of inflammatory cytokines IL-8, PG’s
* Bacterial infections

« Allergic reactions
* Multiple fetus pregnancies

16. Se ac?

+ Pregnancy duration and delivery timing are determined largely by
the placenta’s rate of CRH production

0310-7990649

17. Stages of labor

1. Cervical dilation

Cervix dilates to accommodate the diameter of the baby’s head, to a
maximum of 10 cm.

Lasts several hours to as 24 hours ina first pregnancy

a
$
So
S
a
a
IR
à
a
a
Ss

2. Delivery of the baby

Stretch receptors in the vagina activate a neural reflex that triggers
contractions of the abdominal wall in synchrony

Lasts 30 to 90 minutes

3. Delivery of the placenta
completed within 15 to 30 minutes after the baby is born

18. 0310-7990649

+ How bleeding is stopped after separation of placenta.....?

19. 0310-7990649

Uterine involution

» After delivery,
uterus shrinks to its pre-gestational size
endometrium is restored to its non-pregnant state

+ Endometrial tissue not expelled with the placenta gradually disintegrates
and sloughs off, producing a vaginal discharge called lochia

+ Involution occurs because of decreased estrogen and progesterone

20. a
$
So
S
a
a
IR
à
a
a
Ss

Uterine Involution

* Breast Feeding Mothers
* Oxytocin (in response to suckling)

promotes myometrial contractions
enhancing involution

Involution is usually complete in
4 weeks in nursing mothers
6 weeks in those who do not breast-feed

21. 0310-7990649

Myoopithelial colls

Milk

Milk
secroting
opitholial

colls

Cc

[email protected]

22. 679066/-0TEO

Hypothalamus

23. a
$
So
S
a
a
IR
à
a
a
Ss

hr

ln
Hpotiaans OS
== ==
= Be
Le de
4
J |,
Feen

|
BE]

24. 0310-7990649

[email protected]

Nervous | Prolactin-inhibiting hormone or
pathway | Prolactin-releasing peptide
| * Y+
U Posterior pituitary Anterior pituitary
| «
*
1 Oxytocin | Prolactin
| + ma 5.3
Contraction of Secretion by
myoepithelial cells alveolar epithelial
surrounding alveoli cells

| |
=

Ejection à ¿2 Coriracion >.
Dun Se causes) Secretion
Se “)— Alveolus
Myoepithelial cell (Lumen) amis

epithelial cell

25. Lactation

a
$
So
S
a
a
IR
à
a
a
Ss

1. Development of the breasts

» Estrogens

+ Progesterone

Fat accumulation in stroma of beast
Stimulate Growth of the Ductal System of the Breasts

Full Development of the Lobule-Alveolar System
Secretory changes in alveolar system

26. 2. Production Of Milk

Prolactin

©

0310-7990649

Secreted by the mother’s anterior pituitary gland

Concentration starts rising from the 5!" week of pregnancy until
birth of the baby

Human chorionic somatomammotropin

| Colostrum
The fluid secreted during the last few days before and the first few days after parturition

Same concentrations of proteins and lactose as milk
Almost no fat

27. 3. Ejection Process In Milk Secretion

a
$
So
S
a
a
IR
à
a
a
Ss

+ Oxytocin
* Causes myoepithelial cells to contract

+ Within 30 seconds to 1 minute after a baby begins to suckle, milk
begins to flow

« Fondling of the baby by the mother

+ Hearing the baby crying

« Psychogenic factors

* Generalized sympathetic nervous system discharge

28. a
$
So
S
a
a
IR
à
a
a
Ss

Prolactin z
Loss of inhibitory action of estrogen and progesterone after delivery «€ me

Intermittent reflexive release of Prolactin

Growth hormone
Cortisol

Parathyroid hormone
Insulin

If no lactation for 1 week...?

29. Regulation of Prolactin

0310-7990649

+ Action of prolactin antagonized by;
Pregnant Female Estrogen and progesterone at receptor level
Non-Pregnant Female Prolactin Inhibitory Hormone

¿+ Role of Hypothalamus

+ Role of dopamine

30. Lactational Amenorrhea

0310-7990649

+ Nervous signals
+ Increased prolactin

31. a =
E %
a
2
Ss

Constituent Human Milk (%) Cow’s Milk (%)

Water 88.5 87.0

Fat 3.3 3.5

Lactose 6.8 4.8

Casein 0.9 27

Lactalbumin and 0.4 0.7

other proteins
Ash 0.2 0.7

32. a
$
So
S
a
a
IR
à
a
a
Ss

Advantages of Breast-feeding for the Infant ©

bb une

uu

Y,
®mics

Se ac?

. Antibodies

. Immune cells (B and T lymphocytes, macrophages, neutrophils)

. Secretory IgA

. Mucus (adhere to potentially harmful microorganisms, preventing

them from attaching to and crossing the intestinal mucosa)

. Lactoferrin (decreases the availability of iron)
. Bifidus factor (promotes multiplication of the nonpathogenic

microorganism Lactobacillus bifidus in the infant’s digestive tract)

33. Advantages of breast-feeding for the mothe! @®

Se ac?

0310-7990649

* Oxytocin release hastens uterine involution
* Lactation, decreases the likelihood of another pregnancy

34. 0310-7990649

[email protected]

1e es
4 | into fotl circulation Proton in
m
Fetal anterior fluid
pituitary
fi y
| Macrophages.

TACTH

aa 2
1 Cortisot TDHEA = —
Le

++ ++

Fotal lungs: Placenta

y y A
| Pulmona Conversion ot
rs DHEA o estrogen ine
y | Retain rom
the corpus
Bi] Es —
I

Tri
par

35. 0310-7990649

[email protected]

y Rolaxin trom
the corpus.
Lung maturation lutoum and
in roadinoss for placonta
breathing air

1 Gap ul
betwoen
‘myometrial colis

y

| Utorus ablo to
J) contract as a

co"

à

KEY
> Soquonco of ovants loading to

the onset of parturition

—> Positivo-toodback cyclo
responsible for the progression
of parturition

= Oxytocin

| Prostaglandin
receptors in
‘myometrium on
| Uterine
responsiveness to Corvical
low levels of sohoning
oxytocin
| Uterine be
contractions
Push lotus
against corvix
(through
nouroendocrine
rotlox)
+)
1 Oxytocin * | Prostaglandin
secretion production

Responsible for
progression of
parturition

36. a
$
So
S
a
a
IR
à
a
a
Ss

Thank You

References:

* Guyton, A. C, & Hall, J. E. (2021). Textbook of Medical Physiology (14th ed, Chapter 83: Pregnancy and Lactation).
Philadelphia, PA: Elsevier. Y

+ Barrett, K. E., Barman, S. M., Brooks, H. L., & Yuan, J. X.-J. (2019). Ganong's Review of Medical Physiology (26th ed., Chapter
22: Reproductive Development & Function of the Female Reproductive System). New York, NY: McGraw-Hill Education.

+ Sherwood, L. (2015). Human Physiology: From Cells to Systems (9th ed., Chapter 20: The Reproductive System
). Boston, MA: Cengage Learning.