Repro physiology 9 – Parturition and puerperium

Which animals CL keeps going (not placenta)

• alpaca

• bitch

• camel

• goat

• llama

• quen

• rabbit

• sow

Which animals placenta takes over LATE?

cow

Which animals placenta takes over EARLY?

• EWE

• Mare

• Woman

Variation between species in gestation length for a Queen

63

Variation between species in gestation length for a Bitch

62-64

Variation between species in gestation length for a Sow

114

Variation between species in gestation length for a Ewe

146-147

Variation between species in gestation length for a mare

330

Birth is initiated by the

foetus by increased pressure inside

uterus (uterine crowding)

Foetal brain produces

corticotrophin releasing hormone

(CRH)

CRH causes

pituitary gland to release adrenocorticotropic

hormone hormone (ACTH)

ACTH stimulates

adrenal glands to secrete cortisol

PGF2α is produced by

endometrium

Cortisol (not PGF2α)

causes the changes in

E2

and P4

Cortisol travels in

blood to placenta and uterus

Cortisol Causes placenta to

• to stop producing P4

• to convert P4 to E2

PGF2a transferred to

ovary by counter-current exchange

PGF2a causes

luteolysis

E2 causes

production of oxytocin receptors on the

myometrium

Oxytocin stimulates

contractions

PGF2a and oxytocin amplify

contractions

Amplification of contractions is

caused by

the feed-forward actions

of PGF and oxytocin on each other.

If birth is to be prevented (e.g.,

premature) this cycle must be

blocked.

If anti-inflammatory drugs

(cyclooxygenase inhibitors like

aspirin) are given, what occurs

parturition may

be delayed.

Cyclooxygenase or COX2 is the

enzyme that makes

PGF

Expulsion of fetus requires strong

myometrial and abdominal muscle

contractions

What are the key hormones?

• Cortisol

• Oxytocin

• Progesterone removal

• PGF

• Estrogens (estriol in human placenta)

• Relaxin

Fetal hypothalamas produces

produces corticotrophin releasing hormone (CRH).

CRH causes pituitary gland to release adrenocorticotropic hormone

hormone (ACTH), which stimulates fetal adrenal glands to secrete cortisol

In human pregnancy, P4 binds to

progesterone receptor (PR) →

↑ZEB1, which inhibits the expression of genes coding for

contractile proteins essential for the uterine contractions

P4 levels do not decline rapidly at the end of

pregnancy – rather

the myometrial P4 receptors become less sensitive to P4 a

phenomenon called “functional progesterone withdrawal”

So ZEB1 ↓ and contractility

increases

What is the first stage of parturition

dilation of the cervix

What is the second stage of parturition

expulsion delivery of the infant

What is the third stage of parturition

delivery of the placenta

Myometrial contractions

continue after

parturition (but

weaker)

Stage I – colostrum.

• Production starts days before parturition

• High in protein, especially immunoglobulins

• IgG- passive immunity

• IgA- protects digestive tract

Stage II – initiation of copious milk secretion

• Declining P4 removes inhibition

• Rising E2 stimulates prolactin (PRL) secretion

• PRL initiates lactogenesis II

E2 and P4 promote

mammogenesis and inhibit lactogenesis

Placental lactogen (PL) and growth hormone (GH) promote

mammogenesis

P4 inhibits production of

lactose synthetase (inhibits

prolactin action)

Removal of P4 initiates

lactogenesis

Corticosteroids (mainly cortisol) stimulate

differentiation of

secretory cells (they make more mitochondria and Golgi)

• E2 peak stimulates

prolactin (PRL) release

PRL stimulates production of

lactose synthetase

UDP-galactose + glucose →

UDP + lactose

Lactose draws in water so

copious volume of milk is

produced

Endocrine control of

lactogenesis

Sensory neural input from

birth canal (and mammary gland if stimulated) stimulates hypothalamus to increase prolactin releasing hormone and decreases

Prolactin stimulates

lactogenesis

The mammary gland undergoes continoues change from prenatal life through ?

subsquesent lactation.

During pubertal onset the ductal and seretory tissue of the mmarry gland increases or decreases

increases

During the first pregnancy these tissues continue to

increase but at a faster rate

At the time of parturition, the serectory tissue mass is

high and continues to increase until it peaks shortly after parturition during the first lactation. At the conclusion of the first lactation (either weaning or drying off in the dairy cow), the secretory tissue mass decreases siginicatly.

During the second pregnancy and lactation secretory tissues what happens

the secretory tissues and ductal tissue increase significantly, following lacataion a second involution takes place

Uterine involution

• Involution is reduction in

uterine size and

remodelling of the

endometrium

• Uterus can then sustain

another pregnancy

Lochia is the normal vaginal

discharge consisting of

blood,

mucus, and uterine tissue that

occurs for 2-3 weeks post-

parturition as the uterus heals

and returns to its pre-pregnancy

size

Changes occurring at birth in newborn

• Umbilical arteries completely constrict and atrophy to become

the medial umbilical ligaments; umbilical vein constricts shut

and becomes the round ligament of the liver

• Ductus venosus (liver bypass) constricts

• Foramen ovale closes

• Ductus arteriosus (lung bypass) constricts

• Lungs begin to function

In late pregnancy glucocorticoids stimulate

surfactant secretion

by lung epithelium

Surfactant is a mixture of

phospholipids and lipoproteins

Surfactant lowers what

surface tension of alveolar fluid enabling

easier inflation

In humans, the first breath occurs within

10 seconds of birth

Pulmonary expansion at birth

(with the first breath) means

previously compressed lung blood

vessels can expand, hence,

pulmonary vascular resistance

decreases dramatically

Closure of the placental

circulation approximately

doubles

systemic vascular resistance at

birth with consequent increase in

left heart and aortic blood

pressures