Physiology of Pregnancy and the Fetus Flashcards
what are the main functions of the placenta? and the features that help allow this
Fetal gut and supplies the nutrients
Fetal lung that exchanges the O2 and the CO2
Fetal kidney that regulates the fluid volumes and disposing the waste metabolites
Endocrine gland: synthesizes steroids and proteins that affect both maternal and fetal metabolism
Large surface area for exchange
Highly developed vascularity of both fetal and maternal components
what are the 3 major physical features of the placenta and what are its characteristics
Chorionic Villi
Intervillious space
Decidua basalis
Chorionic villi represent functional unit of theplacenta
- extensive branching
- increased surface area for exchange
Spiral arteries from maternal side empty into the intervillious space which is drained by maternal veins
Regulation of blood flow for the placenta: Maternal blood flow
Maternal blood flow:
- arterial blood discharged from spiral arteries
- enters into the intervillous space
- intervillious space dissapates the force and reduces blood velocity
- slowing allows for adequate time to exchange nutrients
- blood drains through venous orifices and enter placental veins
- no capillaries present
Regulation of blood flow: Fetal blood flow
Originates from two umbilical arteries:
- carry deoxygenated blood
- umbilical arteries branch and penetrate the chorionic plate to form the chorionic capillary network
- obtain O2 and nutrients and returns the fetus from single umbilical vein
terminal dilations in capillary network
- slower blood flow
- exchange nutrients
Characteristics of the gas exchange between mother and fetal blood
Maternal blood entering intervillous space
- Po2 100mmHg
- PCO2 40mmHg
- pH of 7.4
Diffusion of O2 into the chorionic villi causes the Po2 in intervillious space to fall to 30-35 mmHg and lower in umbilical vein of the fetus
Differences in hemoglobin structure allows for sufficient Hb saturation in fetus because it more readily grabs O2 and releases CO2
CO2 transfer between mother and fetus
Driven by a concentration gradient
Near term:
-Pco2 is 48 mmHg in umbilical arteries
-Pco2 43 mmHg in intervillous space
Fetal blood has a slightly lower affinity for CO2 than maternal blood
-all factors factors favor transfer of CO2 from fetus to mother
Solute transfer mechanisms between mother and fetus
Passive exchange:
- non protein nitrogen wastes (urea/creatine) from fetus to mother
- lipid soluble hormones transfer between mother, placenta, fetus
Facilitated diffusion of glucose to fetus
Primary and secondary active transport to fetus to support growth of:
- Amino acids
- Vitamins
- Minerals
Receptor mediated endocytosis:
- large molecule exchange
- LDL, hormones (insulin), antibodies IgG
Endocrine function of the placenta, what does it produce, and how can it regulate?
Placenta plays a key role in manufacture of
- steroid hormones
- amines
- polypeptides (hormones and neuropeptides)
- proteins/glycoproteins
Placenta can regulate in a paracrine fashion
- release of local placental hormones
- release of hormones into fetal or maternal circulations
what are the general functions of placental hormones in pregnancy
Maintaining the pregnant state of the uterus
stimulating lobuloalveolar growth and function of maternal breasts
Adapting aspects of maternal metabolism and physiology to support a growing fetus
Regulation aspects of fetal development
regulating timing and progression of parturition
hCG function and what produces it?
Produced by the syncytiotrophoblasts
Structurally similar to LH
- binds with high affinity LH receptors
- glycosylation increases half life
- rapidly accumulates in maternal circulation
Surum levels double daily up to 10 weeks
Primary function is to stimulate LH receptors in the corpus luteum
- prevents luteolysis
- maintains high levels of luteal derived progesterone
thought to be responsible for nausea associated with morning sickness
stimulate fetal leydig cells to produce testosterone
function of Chorionic somatomammotropin hormone (hCS) and what is is its role
same as Human placental lactogen (hPL):
- structurally related to growth hormone and prolactin
- produced by syncytiotrophoblast
- detected at day 10 in syncytiotrophoblasts and in maternal serum at 3 weeks
Role in corrdinating fuel economy of fetoplacental unit
- conversion of glucose to fatty acids and ketones
- can have antagonistic action to maternal insulin contributing to diabetogenicity of pregnancy
Lipolytic actions help mother shift to free fatty acid use for energy
promote development of maternal mammary glands during pregnancy
Function of progesterone during pregnancy
High levels of progesterone required throughout pregnancy:
required for implantation and early maintenance of pregnancy
- derived from corpus luteum
- provides a window of receptivity (increased adhesion proteins in endometrium)
- stimulates endometrial gland secretions for early nutrient transfer
- Reduces uterine motility
- inhibits propagation of uterine contractions
- induces mammary growth and differentiation
function of estrogen throughout pregnancy
induces endometrial growth, progesterone receptor expression and LH surge just prior to ovulation
increases uteroplacental blood flow
increases LDL receptor expression in syncytiotrophoblasts
induces prostaglandins and oxytocin receptors which are necessary for parturition
increase growth and development of mammary glands
what is the Maternal-Placental-Fetal-Unit and what is it critical for?
During pregnancy maternal levels of progesterones and estrogens (estradiol, estrone, estriol) rise to levels substantially higher during a normal menstrual cycle
the placenta is an imperfect endocrine organ and cannot produce these alone
Coordination between the maternal, placental, and fetal tissues are required
- Mother supplies the cholesterol
- Fetal adrenal gland and liver supply enzymes the placenta lacks
how does the M-P-F affect the progesterone levels?
increases progesterone
Luteal-placental shift occurs around week 8
progesterone production is largely unregulated
- syncytiotrophoblasts important for importing the cholesterol from the maternal blood
- express CYP11A1 and 3B-HDS1 to increase the production of the needed progesterone
Released primarily into maternal compartment
maternal progesterone serum levels rise throughout pregnancy
