Phsyiology Of Pregnancy And The Fetus Flashcards
What are the main functions of the placenta?
Fetal gut supplying nutrients
Fetal lung exchanging O2 and CO2
Fetal kidney regulating fluid volumes and disposing of waste metabolites
Endocrine gland: synthesizes steroids and proteins that affect both maternal and fetal metabolism
Describe maternal and fetal blood flow across the placenta
Transport from atmosphere to alveoli -> diffusion across alveolar membrane -> transport from lungs to placenta -> diffusion across the placenta -> transport from placenta to fetus -> diffusion into fetal tissues
The placental interface is organized to facilitate what?
Exchange between maternal and fetal circulations
Large SA for exchange
Highly developed vascularity of both fetal and maternal components
Intimately juxtaposed but physically separate
What are the 3 major features of the maternal-fetal circulation?
Chorionic villi, intervillous space, decidua basalis
What represents the functional unit of the placenta?
Chorionic villi
Has extensive branching which increases SA for exchange
Spiral arteries from maternal side empty into intervillous space which is drained by maternal veins
Describe maternal blood flow
Arterial blood discharged from 120 spiral A
Supply blood in spurts into intervillous
Filling of intervillous spaces dissipates the force and reduces blood velocity
Slowing of blood flow allows adequate time for exchange of nutrients
Blood drains through venous orifaces and enter placental vein - no capillaries are present
Describe fetal blood flow
Originates from two umbilical A
Carry deoxygenated blood*
Umbilical A branch and penetrate the chorionic plate to form the chorionic villi capillary network
Obtain oxygen and nutrients and returns to the fetus from single umbilical vein
Terminal dilations in capillary network (slower blood flow and exchange of nutrients)
Describe gas and solute exchange
Maternal blood entering intervillous space
Diffusion of O2 into the chorionic villi causes the PO2 of the blood in intervillous space to fall to 3-35mmHg (lower than what it was in the uterine A) and lower in the umbilical vein of the fetus
Differences in hemoglobin structure allows for sufficient Hb saturation
Fetus has higher oxygen affinity
Describe CO2 transfer
Driven by a concentration gradient difference
Near term PCO2 in umbilical arteries is slightly higher than in intervillous space
Fetal blood has a slightly lower affinity for CO2 than maternal blood
All factors factor transfer of CO2 from fetus to mother
What structures undergo passive exchange across the placenta?
Non-protein nitrogen wastes (urea/creatine) from fetus to mother
Lipid soluble hormone transfer between mother, placenta and fetus
What substance undergoes facilitated diffusion from the mother to the fetus?
Glucose
Which structures undergo primary and secondary active transport to the fetus?
Amino acids, vitamins, minerals
Support growth of fetus
Which structures undergo receptor mediated endocytosis?
Large molecule exchange like LDL, hormones (insulin), Abs
What is the endocrine function of the placenta
Plays a key role in the manufacture of steroid hormones, amines, polypeptides (hormones and neuropeptides), proteins/glycoproteins
Placenta can regulate in a paracrine fashion (release of local placental hormones and release of hormones into fetal or maternal circulations)
What are the general functions of placental hormones during pregnancy?
Maintains 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
Regulating aspects of fetal development
Regulating timing and progression of parturition
Describe hCG
Produced by syncytiotrophoblasts
Structurally related to LH
-binds with high affinity to LH receptors
-glycosylation increases half life
-rapidly accumulates in maternal circulation
Serum levels double daily up to 10 weeks
What is the primary function of hCG?
To stimulate LH receptors in the CL which prevents luteoloysis and maintains high levels of luteal derived progesterone
Thought to be responsible for nausea associated with morning sickness
Small amounts enter fetal circulation (stimulate fetal Leydig cells to produce testosterone)
Describe human placental lactogen (hPL)
Aka human somatomammotropin (hCS)
Structurally related to growth hormone and prolactin
Produced by syncytiotrophoblast
Detected at day 10 in syncytiotrophoblast and in maternal serum at 3 weeks
What are the functions of hPL?
Role in coordinating fuel economy of fetoplacental unit
-conversion of glucose to FAs and ketones
-can have antagonistic action to maternal insulin, contributing to diabetogenicity of pregnancy
Lipolytic actions help mother shift to free FA use for energy
Promote development of maternal mammary glands during pregnancy
Describe why high levels of progesterone are required throughout pregnancy
Required for implantation and early maintenance of pregnancy
Derived from CL and provides 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
Describe the role of estrogen
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 necessary for parturition
Increase the growth and development of mammary glands
What is the maternal placental fetal unit?
During pregnancy maternal levels of progesterone and estrogens (estradiol, estrone and estriol) rise to levels substantially higher than 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 (MPF unit, mother supplies cholesterol, fetal adrenal gland and liver supply enzymes the placenta lacks)
Describe progesterone in the maternal placental fetal unit
Luteal phase shift occurs around week 8
Progesterone production is largely unregulated
Syncytiotrophoblasts import cholesterol from maternal blood and express CYP11A1 and 3-beta-HSD1
Released primarily into maternal compartment
Maternal serum levels rise throughout pregnancy
Describe estrogen in the MPF unit
Placenta cannot produce cholesterol and lacks 17 alpha hydroxylase as well as 17,20 desmolase needed for estrone and estradiol
Lacks 16 alpha hydroxylase needed for estriol
MPF unit overcomes this
-mother supplies cholesterol
-production of DHEAS and 16 OH DHEAS produced by fetal adrenal gland (weak androgens)
