Onset and management of parturition

Question 1

What are the stages of labour? (4)

Answer 1

Latent
1 - regular contractions, effacement, dilation
2- full dilation, birth
3 - placenta

Question 2

What do Braxton Hicks contractions do?

Answer 2

Prepare uterine muscle for labour and assist in effacement

Question 3

Give 3 factors that make labour happen

Answer 3

Activation of myometrium
Placental steroids
PGs 
Oxytocin
Inflammatory processes
\+ve biofeedback mechanisms

Question 4

Describe/draw the oxytocin +ve feedback loop

Answer 4

Baby pushes against cervix stretching it
Nerve impulses to brain
Posterior pituitary stimulated to release oxytocin
Oxytocin causes uterine contractions
Etc

Question 5

What is happens in myometrial quiescence? (2)

Answer 5

Significant proliferation and hypertrophy of smooth muscle

Capacity for contractility decreased

Question 6

Give 3 factors that decrease the capacity for contractility

Answer 6

HCG (stops MGJ formation)
Progesterone (stops oestrogen)
CRH
Relaxin
Oxytocin (increases relaxatory PGs)
Melatonin (suppresses myometrial oxytocin receptors)

Question 7

What causes activation of the myometrium? (3)

Answer 7

Uterine stretch
Increased oxytocin receptors in endometrium and myometrium
Foetal-hypothalamic-pituitary adrenal axis and increased cortisol

Question 8

What are MGJs?

Answer 8

Symmetrical portions of plasma membrane from adjacent cells that form intracellular channels for the rapid propagation of action potentials between cells

Question 9

What is the formation of MGJs stimulated by? (3)

Answer 9

Oestrogen
Prostaglandin
Melatonin

Question 10

What is the formation of MGJs inhibited by? (3)

Answer 10

Progesterone
hCG
Relaxin

Question 11

What is fundal dominance?

Answer 11

Increased number of MGJs in fundus

Progressive conductance of electrical activity to cervix

Question 12

Give 2 possible purposes of CRH

Answer 12

Direct effects on myometrium
Indirect effects by stimulating PG production
Augmenting contractile response to PGE2 and oxytocin

Question 13

How does the foetus trigger the onset of parturition? (3)

Answer 13

Increased cortisol from foetal adrenal gland
Cortisol acts on placenta to cause decreased progesterone and increased oestrogen
Increased stimulatory PGs from uterus

Question 14

What do cytokines do in labour? (3)

Answer 14

Stimulate the synthesis of PGs
Interleukins increase collagenolytic activity in cervix
NO stimulates release of PGE2

Question 15

Where is oxytocin produced?

Answer 15

Hypothalamus

Question 16

Where is oxytocin released from?

Answer 16

Posterior pituitary

Question 17

What are the actions of oxytocin?

Answer 17

Indirectly inhibits release of adrenocorticotrophic releasing hormone and cortisol
Direct action on myometrium
Indirect action on PG production
Uterotonic
Emotional well-being and bonding

Question 18

What is oxytocin regulated by?

Answer 18

Oxytocinase

Enzyme that rapidly degrades oxytocin to prevent receptor desensitisation during prolonged oxytocin release

Question 19

What is the action of oxytocin on foetal neurons?

Answer 19

GABA from excitatory to inhibitory

Silences foetal brain for delivery and reduces vulnerability to hypoxic damage

Question 20

What is the general maximum duration for the second stage of labour?

Answer 20

Primi - 2 hours

Multi - 1 hour

Question 21

What occurs in cervical effacement? (3)

Answer 21

Shortening of cervix
Solubility of collagen changes
Forms lower uterine segment

Question 22

What happens to the uterine muscle fibres in labour?

Answer 22

Contract and retract, gradually shortening

Question 23

What are the 3 aspects of the second stage of labour?

Answer 23

Power
Passage
Passenger

Question 24

What is the valsalva manoeuvre?

Answer 24

Closed glottis and holding breath

Question 25

Why is the valsalva manoeuvre not recommended?

Answer 25

Increased intrathoracic pressure
Decreased venous return to heart
Decreased CO, BP, utero-placental blood flow