Topic 95 - The endocrinology of parturition; birth

Question 1

Words to include in birth

Answer 1

Phases of parturition

• Before parturition (initial phase)
  
  • Edema of vulva
  • Mucous hanging out of vagina
  • Edematous udder
  • Dripping of colostrum
  • Loosening of lig. sacroiliaca (effect of relaxin)
• Preparatory phase
  
  • Opeining of cerix
  • 0.5-1.0 ˚C decrease in body temperature
  • Uterus reaches tonic status
  • No labor pains
  • Opening
    
    • Tonicity of uterus is replaced with rhytmical contraction
      
      • Labor pains
    • Fetal and maternal placenta connection loosens
    • Preparsatory pains (dolores preparantes)
• Phase of contraction
  
  • ​Rhytmical uterine contractions increased by oxytocin
  • Most severe pain (dolores ad partum)
• After phase
  
  • ​After-pains
    
    • Expelling membranes
  • Morphological recovery of uterus (puerperium)
    
    • Reach pre-gravid status (involution)
• End of parurion
  
  • ​Contraction of uterine muscles
    
    • Separation of allantochorion from endometrium
  • Allantochorion
    
    • Inside out transferred to environment

Normal birth positions of a fetus

• Presentation
  
  • Position of fetus in birth canal
  • Longitudinal
  • Head/bottom first
    
    • Head first: normal in large animals
• Position
  
  • Location of fetal vertebral column
  • Abdominal position
    
    • Abdomen up: eq
    • Abdomen down: ru
• Deportment
  
  • Position of fetal limbs and head
  • Stretched limbs

Question 2

Words to include in the endocrinology of parturition

Answer 2

• End of pregnancy:
  
  • ​P4 high
  • E2 low
  • Uterus is insensitive to contracting effect of
    
    • E2
    • Oxytocin
• Intiator of changes
  
  • Fetal stress
    
    • Mechanical stress
    • Chemical stress
    • High environmental temperature
    • Maturation of hypothalamus
    • Maturation of fetal adrenal cortex
• Fetal hypoth-hypophysis (ACTH)-adrenocortex axis
  
  • Synthesized:
    
    • Glucocorticoids
    • C19 steroids (androgens)
  • Glucocorticoid inhibits P4 syntheis in placenta and ovary
  • P4 → E2
    
    • ​Due to activity of 17-α-hidroxylase
  • Andorgens → E2
    
    • Phosphorylase A2 activated
      
      • Prostaglandin synthesis stimulated in uterus and placenta
  • ↑ Prostaglandin stimulate:
    
    • Luteolysis
    • Oxytocin secretion
  • Myometrium sensitive to oxytocin
    
    • Contraction phase: fetus puts pressure on birth canal
      
      • Ferguson reflex
        
        • Relasing oxytocin from posterior pituitary
        • Abdominal pressure

Regulators of parurition

• Labor onset
• Strectch stimulus
• Oxytocin
• Prostaglandins
• Positive feedback
  
  • Cervical stretch →
  • Oxytocin ↑
  • Parutition
• Positive feedback loop of parturition
  
  • Fetus drops lower in uterus
  • Cervical stretch
  • Uterine contractions
  • Oxytocin from posterior pituitary
  • Prostaglandins from uterine wall

Endocrionlogical changes in hors

• Parturition → prostaglandin & oxytocin ↑
  
  • Uterine contractions ↑

Role of hormones

• AC steroids
• Activation of 17-α-hydroxylase
• Progesterone
• Estrogens
• Level of estrogens high +
• Levels of progesterone low ÷
• Contractions of uterus
• Cervix is pushed (and stretched) by the head of the foetus
• Ferguson reflex
• Oxytocin secretion
• PGF_2α, PGI₂
• Luteolysis
• Development of gap junctions in myometrium

Can include:

• Sexual period and breeding maturity
• Pregnancy duration
• Size of litter

Question 3

Parturition

Give the phases of parturition

Answer 3

• 0. Initial phase: Before parutition
• 1. phase: Preparatory phase
• 2. phase: Phase of contraction
• 3. phase: After-phase

0. Initial phase: Before parutition

• ​Signals of coming parurition:
  
  • Edema of vulva
  • Mucus is hanging out of vagina
  • Edematous udder
  • Dripping of colostrum
  • Relaxin effects:
    
    • Uneasiness
    • Bending of back
    • Loosening of lig. sacroiliaca

1. phase: Preparatory phase​:

• Opening of cervix
• Infiltration and swelling of birth canal
• Cervical plud is dissolved and appears in vagina
• Pelvic ligament relaxed
• Abdominal wall lowered
• 0.5-1.0 ˚C decrease in body temperature
• Uterus reaches tonic status
• Opening (dilation):
  
  • Rhytmical contractions of uterus
    
    • Labor pains
  • Connection between fetal and maternal parts of placenta gets looser
  • Preparatory pains begin
  • Upper limbs of foetus may already be out

2. phase: Phase of contraction

• The rhytmic uterine contractions increased by:
  
  • Oxytocin
  • Increased abdominal pressure
• Head is pushed out
• Most intensive stage with the most severe pain (dolores ad partum)
• Following is a short break for gathering of strength

3. phase: After-phase

• After-pains
• Expelling the fetal membranes to the environment
• Morphological recovery of uterus (purperium), in order to rach pre-gravid status (involution)
• Ovary is reactivated, new cycle

End of parurition

• Contraction of the uterine muscles result in the separation of the allantochorion from the endometrium
• Allantochorion is inside out transferred to the environment

Question 4

Parturition

Normal birth positions of a fetus

Answer 4

• Presentation
  
  • Position of fetus in birth canal
  • Longitudinal
    
    • Head or bottom first
      
      • Head first: normal in large animals
• Position
  
  • Location of fetal vertebral column and birth canal
  • Abdominal position
    
    • Abdomen up: horse
    • Abdomen down: cow
• Deportment
  
  • Position of fetal limbs and head in relation to the birth canal
  • Stretched limbs

Question 5

The endocrinology of paturition

Answer 5

• End of pregnancy:
  
  • High P4
  • Low E2
  • Uterus is insensitive to contracting effects of E2 and oxytocin
• Intiator of changes:
  
  • Fetal stress
    
    • ​Mechanical stess
    • Chemical stress
    • High environmental temperature
    • Maturation of hypothalamus
    • Maturation of fetal adrenal cortex
• Activaiton of fetal hypthalamus-hypophysis (ACTH)-adrenocortex axis
  
  • ​Synthesized:
    
    • Glucocorticoids
    • C18 steroids (androgens)
  • Glucocorticoids inhibits P4 synthesis in the placenta and ovary
  • P4 is converted to E2
    
    • ​Due to activity of 17-α-hidroxylase
  • Androgens are converted to E2
    
    • ​Activate phsphorylase A2, which stimulates prostaglandin synthesis in the uterus and placenta
• Increasing prostaglandin stimulate:
  
  • Luteolysis
  • Oxytocin secretion
• Myometrium is getting sensitive to oxytoxin
  
  • During contraction phase, the fetus puts pressure on the birth canal → Ferguson reflex
  • Ferguson reflex leads to
    
    • Oxytocin secretion from posterior pituitary
      
      • ​Intensive uterinal contractions
      • Depolarization
      • AP ↑
    • Abdominal pressure

Question 6

The endocrinology of parturation

Give the graph of hormonal changes during parturation

Answer 6

Except the horse pregnancy, where P4 increase and E decrease (unlike in others)

Question 7

The endocrinology of paturition

Regulators of parurition

Answer 7

• Labor onset
• Strectch stimulus
• Oxytocin
• Prostaglandins
• Positive feedback
  
  • Cervical stretch →
  • Oxytocin ↑
  • Parutition

Figure: the positive feedback loop of paturition

Question 8

The endocrinology of parturition

Endocrinological changes in horse

Answer 8

• Parturition is leads to large increases in prostaglandin and oxytocin concentrations
  
  • Induce uterine contractions and delivery of the foal