Labour And Birth Flashcards
Estrogen in initiation of labour
- Promote gap junctions formation in myometrium
- increase oxytocin receptors and their sensitivity
- increase prostaglandin synthesis
- softening of Cx
3 mechanisms of initiating labour
Estrogens
Oxytocin
Prostaglandins
Oxytocin in initiation of labour
- Increases myometrial contractivity & frequency of pacemaker APs through fergusons reflex
- lowers AP threshold and mediates prostaglandin synthesis
Prostaglandin role in initiation of labour
Increase gap junction, intracellular Ca++ & frequency of APs
Enhances cervical softening
First stage of labour: definition
Begins: onset of regular contractions
Ends: full dilation of Cx
First stage of labour: uttering contractions
Coordinated by pacemaker cells
Fundal dominance
Myometrial cells exhibit retraction (greatest in fundus)
Contractions decrease uterine cavity, pushing presenting part to Cx
First stage of labour: Cx
Effacement: thinning and merging of upper Cx with lower uterine segment
Dilation: opening of the external Cx so to width of presenting part, aprox 10cm
Second stage of labour
Begins: full dilation
Ends: birth of baby
Mechanism of labour:
Descent Flexion Internal rotation Crowining and Extension Restitution External rotation of head/ internal rotation of shoulders Lateral flexion
Third stage of labour:
Begins: birth of baby
Ends: birth of placenta and membranes
Third stage: placental separation
- delivering contraction reduces placental site causing placenta to buckle
- intervillous blood forced back in to decidua causing congestion in chorionic capillaries
- chorionic vessels begin to rupture and pull on decidua causing separation within decidua
Third stage: physiological control of blood loss
- living ligatures
- uterine walls pressure
- hypercoagulability, clot formation begins during separation
Labour physiology: CV system
- CO & BP progressively rise, significant increases during contractions
- increased erythropoises and coagulability
Labour physiology: respiratory
RR, tidal volume and ventilation all increase to accommodate increased O2 demand
Labour physiology: renal, body fluid and temperature
Increases renin-angiotensin activity, blood volume, osmolarity and body temperature
Labour physiology: GI and metabolism
- overall decreased GI activity
- increased metabolic needs met by increased glucose use and lipolysis
Types of nociceptors in the body
Mechanical
Thermal
Chemical
Polymodal
Location of nociceptors in the body
Cutaneous
Viscera
Somatic
Pathway for pain:
Primary sensory neuron > secondary sensory neuron > tertiary sensory neuron
Primary sensory neurons are
- Connected to nociceptors
- run to dorsal horn of spinal cord
- 2 types:
- alpha-delta fibres (myelinated)
- c fibres (unmeylinated)
Secondary sensory neurons are…
Decussates (crosses over) immediately
Ascends within spinothalamic tract to thalamus
Tertiary sensory neurons…
Thalamus > primary somatosensory cortex (conscious perception of pain) AND lambic system (emotional response to pain)
Referred pain
Visceral pain sensed in somatic areas:
Visceral sensory pain pathways run within the same tract as somatic sensory pathways and the brain cannot distinguish between the two.
Pain perception occurs when:
Action potentials are received by the primary somatosensory cortex
What does the primary somatosensory cortex determine:
Location and Intensity of pain
Prefrontal cortex and lambic system
PFC: behavioural response
Limbic: emotional response
Paint tolerance v. Pain threshold
Tolerance: subjective perception of pain
Threshold: intensity of stimuli to generate AP in nociceptive neuron
Physiological mechanisms for pain regulation
Afferent
Descending
Endorphins
How does Afferent pain regulation work?
Simultaneous activity of lower threshold stimulate non-nociceptors mechanoreceptors of alpha-beta primary sensory neurons > also synapse with secondary sensory neurons in pain pathway causing hyperpolarisation > reduces the pain signals received by the thalamus
Descending regulation
- Ability of brain to diminish/suppress the pain sensation
- periaqueductal grey matter (PAG) is a group of neurons in the midbrain:
Receives pain signals from brain regions > sends AP to dorsal horn of spinal cord to depress activity of nociceptors as it enters the spinal cord
Endorphins
Endorphins are peptides (small proteins) that bind to opioid receptors
Located in CNS to process/modulate nociceptor information
Suppress release of neurotransmitters
Hyperpolarise the cell membrane of neurons in pain pathway
Locations of Pain in labour
Viscera : uterus, Cx blood vessels
Somatic: pelvis, vagina, perineum
Cutaneous: skin of perineum
Trauma that can occur during vaginal birth
Bruising Swelling Stretching Tearing Placental separation
Perineal tears
1st: fourchette only
2nd: fourchette, and muscles of perineal body
3rd: fourchette, perineal body and external anal sphincter
4th: 3rd + internal anal sphincter and anal mucosa
Trauma in cesarean section
Laceration of skin, connective tissue and skeletal muscle and smooth muscle
Placental separation
