Pregnancy and Parturition Flashcards

Question

Decreased Hematocrit

Answer 1

↓ Hematocrit during pregnancy (“physiological anemia”) ~ 36% vs. 38% ↑ RBC production rate doesn’t match ↑ plasma expansion ↓ Viscosity: ↓ TPR Helps minimizes maternal cardiac work as CO increases

Answer 2

↑ 30 – 50% by end of pregnancy (~ 35% ↑ in 1st trimester) CO = HR x SV ↑ HR (15-20 bpm) ↑ SV

Answer 3

Very late stages of pregnancy: SV may periodically decrease due to compression of the IVC ↓ VR leads to ↓ EDV leads to ↓ SV Positional changes

Answer 4

``` Increased distribution of blood flow: Uterus: 15% of CO (~ 1% normally) Renal: ↑ by 40% Elimination of additional wastes Skin: temperature regulation Heart: support increased CO Breasts: mammary development ``` No change: brain, gut, skeleton

Answer 5

Low-resistance circuit added in parallel: utero/placental circulation Vasculogenesis and angiogenesis Vasodilation Estrogen & progesterone: proposed antagonists to vasopressive action (ANGII) Progesterone may promote vasodilation as a smooth m. relaxant

Answer 6

MAP = CO x TPR ↑ CO and ↓ TPR Result: MAP is same or lower vs. pre-pregnancy MAP Benefit: ↓ afterload and cardiac work

Answer 7

↑ capillary hydrostatic pressure ↑ venous pressure in L.E. due to: Compression of IVC by growing uterus Increased venodilation under hormonal influence 2. ↓ capillary colloid osmotic pressure Maternal synthesis of plasma proteins does not keep pace with increase in plasma volume

Answer 8

Mechanical & hormonal changes lead to Increased alveolar ventilation 1. Elevation of diaphragm Increased intra-abdominal pressure with fetal growth Progesterone effect: relaxing m. and fascia ↓ RV and ↓ FRC 2. ↑ O2 demand and CO2 production Support of fetal metabolism and pregnancy ↑ O2 consumption (~20%) ``` 3. ↑ Sensitivity to CO2 Progesterone effect (estrogen) ↓ Medullary respiratory center set-point for respiratory response to central chemoreceptor detection of CO2 ↑ TV and Alveolar Ventilation ↓ Pco2 (From ~ 40 to 32 mmHg) ```

Answer 9

``` ↓ Functional residual capacity (FRC) ↓ Residual volume (RV) ↑ Tidal volume (TV) Respiratory rate ~ unchanged (RR) ↑ minute ventilation, ↑ Alveolar ventilation (VA) ↓ Pco2 ``` Net Result: ↑ ventilation leads to ↓ Pco2 Respiratory alkalosis* Renal compensation: ↑ HCO3- excretion

Answer 10

↑ Fetal O2 – carrying capacity with ↑ [Hb] late in pregnancy (50% > adult level) ↑ Fetal Hb O2 binding affinity (> maternal) ↓ CO2 affinity, favoring pick-up by maternal blood

Answer 11

↑ RBF and ↑ GFR (~ 50%+) Due to ↑ blood volume and CO 2. ↑ Plasma renin, angiotensin II, and aldosterone Estrogens stimulate increased production 3. ↑ Na+ retention ↑ Aldosterone 4. ↑ H2O retention and intake ↓ threshold for ADH/AVP & thirst during pregnancy Increased sensitivity of osmoreceptors (Net: ↓ osmolality despite ↑ Na+ retention) 5. ↓ Serum Na+ (~ 5 mEq/L decrease) Change in set-point for ADH/AVP and osmoreceptor sensitivity

Answer 12

``` Factors causing reflux: ↓ Gastric emptying rate (progesterone) ↓ LES tone (progesterone) ↑ Intra-abdominal pressure ``` decreased intestinal motility causing constipation

Answer 13

↑ protein, iron, and folic acid demand Protein Supports fetus, placenta, uterus, breasts, blood volume Additional 30 g protein/day Iron Supports increased maternal Hb, placenta, fetus 7 mg/day absorbed iron requirement (vs. 1.5 mg/day nonpregnant) 60 mg/day supplement recommended Folate Supports increased RBC production; protects against neural tube defects 400-800 mg/day folic acid supplementation recommended

Answer 14

Myometrial quiescence during pregnancy Progesterone Relaxin Onset of Labor 38 wks. following fertilization (fetal age) 40 wks. after last menstrual period (gestational age) Initiated by hormonal (endocrine, paracrine) and mechanical factors Process not completely understood Additional proposed involvement of inflammatory signals Positive feedback mechanisms sustain

Answer 15

Braxton Hicks Contractions Periodic episodes of weak, slow rhythmic contractions during pregnancy Become very strong during the last hours of pregnancy Eventually become labor contractions Stretching the cervix Push baby through the birth canal False Labor: contractions initially become stronger but then fade away Failure to re-excite uterus with subsequent positive-feedback mechanism Afferent pain signals from uterine contractions reflexively result in abdominal m. contraction

Answer 16

Cervical Dilation and Effacement Initiation of labor Contractions go from ~ 30 min to

Answer 17

Descent and Expulsion Active Labor Cervix fully dilated (10 cm) Contractions push fetus downward; delivery Average 20-50 min. (Longer for 1st pregnancy vs. after many)

Answer 18

Expulsion of the Placenta Uterus contracts reducing area of attachment Separation of placenta results in bleeding and clotting Bleeding limited by uterine contractions that compress vessels supplying placenta Average 15 min. (Range 10 - 45 mins.)

Answer 19

PGF2 alpha and PGE2 Believed to initiate labor ↑ before onset of labor Uterus, placenta, & fetal membranes synthesize ↑ uterine smooth m. contractility Uterine responsiveness to prostaglandins can occur throughout pregnancy ↑ synthesis is stimulated by: Estrogens (promote conversion of arachidonic acid) Oxytocin in uterine cells Uterine stretch

Answer 20

3 prostaglandin actions: 1. Stimulate myometrial smooth m. contraction 2. Promotes gap junction formation between uterine smooth m. cells Estradiol also promotes gap junctions 3. Softening, dilatation, and thinning (effacement) of the cervix Can be used to induce labor in large doses Aspirin: inhibits labor and prolongs gestation Reduces PGF2α and PGE2 formation

Answer 21

Required for parturition ↑ placental secretion throughout pregnancy Ratio of estrogen:progesterone shifts during the last several months of pregnancy and there is a functional withdrawal of progesterone effects ``` Estrogen actions to promote increased uterine contractility for parturition: ↑ Gap junctions ↑ Oxytocin receptor expression ↑ Myometrial sensitivity to oxytocin ↑ Prostaglandin production ```

Answer 22

Considered to maintain labor (vs. initiate) Uterine sensitivity to oxytocin only at end of pregnancy 1° stimulus for oxytocin release: Distention of cervix Released from posterior pituitary Neurogenic reflex (Ferguson) Response to stretching of the cervix Bursts of oxytocin are released during Labor Stage 1; frequency increases with progression of labor Estrogen increases number of oxytocin receptors ↑ 80x receptor expression by 36 wks. ↑ 200x receptor expression during early labor

Answer 23

Receptor activation promotes uterine smooth m. contraction PLC --> IP3 --> ↑ [Ca2+ ]i --> activate calmodulin --> MLC kinase --> phosphorylation of regulatory light chain --> smooth m. contraction Stage 3 Labor: uterine contractions important for constricting blood vessels after placental delivery Promotes hemostasis Stimulates uterine PGF2α production

Answer 24

Production and maternal serum levels rise quickly late in pregnancy/labor ↓↓ CRH-binding protein ↑ Free bioactive CRH CRH promotes myometrial contractions Sensitizes uterus to prostaglandin & oxytocin Placental CRH stimulates fetal ACTH ↑ fetal adrenal cortisol (positive feedback for CRH) Cortisol stimulates placental CRH production (in contrast to inhibitory effect of cortisol on hypothalamic CRH production) ↑ fetoplacental estrogens

Answer 25

Produced by corpus luteum and placenta Thought to promote myometrial quiescence during pregnancy Production increases during labor May soften cervix during labor

Answer 26

Fetal Hypothalamic-Pituitary-Adrenal Axis Fetal & placental signals preparing for/initiating labor: CRH production by the placenta ↑ fetal pituitary production of ACTH ↑ fetal adrenal production of cortisol, DHEA, DHEA-S ↑ fetoplacental estrogen production Cortisol: positive feedback to ↑ placental CRH production CRH promotes contractions by sensitizing uterus to prostaglandins and oxytocin Estrogens also stimulate contractions

Answer 27

Fetal pituitary : Oxytocin Fetal placental membranes : Prostaglandins Fetal adrenals: Cortisol (+ placental CRH) -Fetal cortisol induces surfactant production in the lungs at about 32 weeks (range 24-35 weeks)

Answer 28

Stretch of smooth m. --> Increases smooth m. contraction Fetal movement can elicit smooth muscle contraction Twins are typically born earlier than a single child (~ 19 days) Indicates significance of mechanical stretch in promoting uterine contractions Contractions stimulate uterine prostaglandin production Positive feedback Ferguson Reflex: Uterine contractions push baby against cervix --> stretching cervix --> stimulating more oxytocin Positive feedback

Pregnancy and Parturition Flashcards

(52 cards)