Parturition Definition Uterine contractions that lead to expulsion of the fetus to extra uterine environment Towards the end of pregnancy the uterus become progressively more excitable and develops strong rhythmic contractions that lead to expulsion of the fetus.

Parturition Uterus is spontaneously active. Spontaneous depolarization of pacemaker cells. Gap junctions spread depolarization Exact trigger is unknown Hormonal changes Mechanical changes

Hormonal changes Estrogen & Progesterone From 7th month till term Progesterone inhibit uterine contractility Estrogen stimulate uterine contractility From 7th month till term Progesterone secretion continuously secreted Estrogen secretion continuously increase Increase estrogen/progesterone ratio

Hormonal changes Progesterone Estrogen ▼ GAP junctions ▼ Oxytocin receptor ▼prostaglandins. ▲ resting membrane potential Estrogen ▲ GAP junctions with onset of labour. ▲ Oxytocin receptors. ▲ Prostaglandins E P

Hormonal changes Oxytocin Dramatic ▲of oxytocin receptors (200 folds) gradual transition from passive relaxed to active excitatory muscle (↑responsiveness). Increase in oxytocin secretion at labor Oxytocin increase uterine contractions by Directly on its receptors Indirectly by stimulating prostaglandin production

Hormonal changes Prostaglandins Central role in initiation & progression of human labor Locally produced (intrauterine) Oxytocin and cytokines stimulate its production Prostaglandin stimulate uterine contractions by: Direct effect: Through their own receptors Upregulation of myometrial gap junctions Indirect effect: upregulation of oxytocin receptors

Effect of fetal hormones on uterus 1-Fetal pituitary secrete oxytocin which might play a role in uterine excitation 2-fetal adrenal glands secrete cortisol also can stimulate uterus 3- Fetal membrane secrete prostaglandins

Mechanical changes Stretch of the uterine muscle Stretch of the cervix Increases contractility Fetal movements Multiple pregnancy Stretch of the cervix Increases contractility (reflex) Membrane sweeping & rupture (induction contraction) Fetal head Positive feedback mechanism

Positive feedback mechanism

Initiation of Labor Figure 16.19, step 1 Baby moves deeper into mother’s birth canal Figure 16.19, step 1

Initiation of Labor Figure 16.19, step 2 Pressoreceptors in cervix of uterus excited Baby moves deeper into mother’s birth canal Figure 16.19, step 2

Initiation of Labor Figure 16.19, step 3 Afferent impulses to hypothalamus Pressoreceptors in cervix of uterus excited Baby moves deeper into mother’s birth canal Figure 16.19, step 3

Initiation of Labor Figure 16.19, step 4 Hypothalamus sends efferent impulses to posterior pituitary, where oxytocin is stored Afferent impulses to hypothalamus Pressoreceptors in cervix of uterus excited Baby moves deeper into mother’s birth canal Figure 16.19, step 4

Initiation of Labor Figure 16.19, step 5 Hypothalamus sends efferent impulses to posterior pituitary, where oxytocin is stored Posterior pituitary releases oxytocin to blood; oxytocin targets mother’s uterine muscle Afferent impulses to hypothalamus Pressoreceptors in cervix of uterus excited Baby moves deeper into mother’s birth canal Figure 16.19, step 5

Initiation of Labor Figure 16.19, step 6 Hypothalamus sends efferent impulses to posterior pituitary, where oxytocin is stored Posterior pituitary releases oxytocin to blood; oxytocin targets mother’s uterine muscle Uterus responds by contracting more vigorously Afferent impulses to hypothalamus Pressoreceptors in cervix of uterus excited Baby moves deeper into mother’s birth canal Positive feedback mechanism continues to cycle until interrupted by birth of baby Figure 16.19, step 6

Phases of parturition Phase 0 Phase 1 Phase 2 From conception to beginning of labor; uterus is relaxed (quiescent) Phase 1 Activation: expression of contraction proteins Phase 2 Stimulation: stage 1& stage 2 of labor cervical dilatation & expulsion of fetus Phase 3 = stage 3 of labor Delivery of the placenta and uterine involution

Uterine Activity During Pregnancy Inhibitors Progesterone Prostacycline Relaxin Nitric Oxide Parathyroid hormone-related peptide CRH HPL Quiescence Uterotrophins Estrogen Progesterone Prostaglandins CRH Activation Uterotonins Prostaglandins Oxytocin Stimulation Involution Oxytocin Thrombin 8/23/2019

Phases of parturition Phase 0: quiescent uterus: associated with Increased cAMP, due to progesterone, relaxin, prostacyclin, PTH-related peptide, NO Adapted from Smith, 2007

Phases of parturition Phase 1 (activation) Occurs in third trimester Promote a switch from quiescent to active uterus Increase excitability & responsiveness to stimulators by Increase expression of gap junctions Increase G protein-coupled receptors Oxytocin receptors

Phases of parturition Phase 1: activation of uterus 50X increase myometrial oxytocin receptors uterus responsive to uterotonins dilation and effacement of cervix, cervical softening due to rearrangement of collagen fibers,

Phases of parturition Phase 2 (stimulation) Occurs in last 2-3 gestational weeks Increase in synthesis of Cytokines Prostaglandins Oxytocin Includes 2 stages: Stage 1 Stage 2

Phases of parturition Phase 3 (uterine involution) Pulsatile release of oxytocin Delivery of the placenta Involution of the uterus Occurs in 4-5 weeks after delivery Lactation helps in complete involution

Braxton-Hicks contractions -- irritability of uterine muscle --- weak, slow contractions -- begins about 1 month before labor In contrast: stronger contractions stretch cervix and force baby through birth canal True labor has circadian rhythm, peaks between 12 midnight and 5 am. “labor pains” -- due to ischemia of uterine muscle in early stage, then stretch of cervix, perineum, vagina

Mechanics of Parturition Contractions start at the fundus and spreads to the lower segment The intensity of contractions is strong at the fundus but weak at the lower segment In early stages 1 contraction/ 30 minuets As labor progress 1 contraction/ 1-3 minutes Abdominal wall muscles contract Rhythmical contractions allows blood flow

Labor and Parturition Parturition: Denotes the whole process by which the baby is born. Labor: Strong uterine contractions, cervical dilatation, forcing the fetus through the birth canal

Onset of labor During pregnancy Periodic episodes of weak and slow rhythmical uterine contractions (Braxton Hicks) 3rd trimester Towards end of pregnancy Uterine contractions become progressively stronger & regular Suddenly uterine contractions become very strong leading to: cervical effacement and dilatation

Mechanisms of labor Effacement Dilatation Three “P’s” Powers Passage Uterine activity Passage Passenger 8/23/2019

Cervical effacement Effacement is the process by which the cervix prepares for delivery. After the baby has engaged in the pelvis, it gradually drops closer to the cervix; the cervix gradually softens, shortens and becomes thinner. You may hear phrases like "ripens," or "cervical thinning" which refers to effacement.

Stages of labor Stage 1: Stage2: stage 3: Commences with the onset of labor and terminates when the cervix has reached full dilatation and membranes ruptured (lasts 8-24 hours). Stage2: Stage of expulsion begins at full cervical dilatation and ends with expulsion of the fetus (lasts 1-30 minutes). stage 3: Begins with the delivery of the child and ends with the expulsion of the placenta. (for 10-45 minutes after birth of the baby).

SEPARATION OF THE PLACENTA 1 SEPARATION OF THE PLACENTA 1.The uterine muscle fibers arranged in fig 8 around the BV so the contraction after delivery constrict the vessels that had supply the placenta and 2.vasoconstrictors prostaglandin formed at the placenta separation site cause additional vessel spasm.

INVOLUTION OF UTERUS 1.Develop during 4-5 weeks after labor and if the mother lactate uterus may become as small as before pregnancy. 2.Some vaginal discharge during early involution from the site of placenta on endometrium called lochia bloody for 10 days. Then the endometrial surface become re-epithelialized and ready for normal sex life

Stages of labor 1 2 3

Stages of Labor Dilation Uterine contractions begin and increase Cervix softens and effaces (thins) Cervix becomes dilated Full dilation is 10 cm The amnion ruptures (“breaking the water”) Longest stage at 6–12 hours

Stages of Labor Figure 16.20 (1 of 3)

Stages of Labor Expulsion Infant passes through the cervix and vagina Can last as long as 2 hours, but typically is 50 minutes in the first birth and 20 minutes in subsequent births Normal delivery is head first (vertex position) Breech presentation is buttocks-first

Stages of Labor Figure 16.20 (2 of 3)

Stages of Labor Placental stage Delivery of the placenta Usually accomplished within 15 minutes after birth of infant Afterbirth—placenta and attached fetal membranes All placental fragments should be removed to avoid postpartum bleeding

Stages of Labor Figure 16.20 (3 of 3)

New arrival