BSNC 5000 OB Questions with Correct
Answers
Uteroplacental circulation
- uterine arterial blood supply shown at right
- both the ovarian and uterine arteries supply the myometrium
- spiral arteries elongate as the endometrium cyclically thickens to accommodate the
possibility of implantation of a blastocyst
Intervillous space
- the space in the placenta in which maternal blood bathes chorionic villi, allowing the
exchange of materials between the fetal and maternal circulations.
Divided into 3 parts:
- arterial circulation
- circulation in the intervillous space
- venous drainage
Hemodynamics of uteroplacental circulation
Volume of placental blood flow - 600-700mL/min
Pressure in supplying uterine artery - 80-100 mmHg
Pressure in spiral arteries - 70mmHg
Pressure in draining uterine vein - 10mmHg
, Maternal intravascular volume changes
- plasma volume increases by up to 1L
- rise in #rbc/blood volume but to lesser extent (placental lactogen stimulates production of
erythropoietin)
- dilutional gap causes physiological anemia
Blood pressure change in normal pregnancy
- progesterone relaxes smooth muscle in the wall of blood vessels
- relaxin increases systemic arterial compliance (vasodilation) to reduce peripheral resistance
- decreases the effective circulating volume (same volume but larger space to fill)
- effects of vasodilation:
•non-osmotic release of vasopressin/ADH
•activation of SNS and RAAS increases plasma volume for adequate organ perfusion
Maternal cardiovascular changes
- increasing volume -> increase in preload -> increased contractility.
- decrease in vascular resistance reduces afterload which increases cardiac output by nearly
50% thereby increasing the efficiency of the heart.
Risk of thrombosis during pregnancy
Answers
Uteroplacental circulation
- uterine arterial blood supply shown at right
- both the ovarian and uterine arteries supply the myometrium
- spiral arteries elongate as the endometrium cyclically thickens to accommodate the
possibility of implantation of a blastocyst
Intervillous space
- the space in the placenta in which maternal blood bathes chorionic villi, allowing the
exchange of materials between the fetal and maternal circulations.
Divided into 3 parts:
- arterial circulation
- circulation in the intervillous space
- venous drainage
Hemodynamics of uteroplacental circulation
Volume of placental blood flow - 600-700mL/min
Pressure in supplying uterine artery - 80-100 mmHg
Pressure in spiral arteries - 70mmHg
Pressure in draining uterine vein - 10mmHg
, Maternal intravascular volume changes
- plasma volume increases by up to 1L
- rise in #rbc/blood volume but to lesser extent (placental lactogen stimulates production of
erythropoietin)
- dilutional gap causes physiological anemia
Blood pressure change in normal pregnancy
- progesterone relaxes smooth muscle in the wall of blood vessels
- relaxin increases systemic arterial compliance (vasodilation) to reduce peripheral resistance
- decreases the effective circulating volume (same volume but larger space to fill)
- effects of vasodilation:
•non-osmotic release of vasopressin/ADH
•activation of SNS and RAAS increases plasma volume for adequate organ perfusion
Maternal cardiovascular changes
- increasing volume -> increase in preload -> increased contractility.
- decrease in vascular resistance reduces afterload which increases cardiac output by nearly
50% thereby increasing the efficiency of the heart.
Risk of thrombosis during pregnancy
