Placenta Physiology and Development Flashcards
Functions of the Placenta
Metabolic- metabolizes glycogen, cholesterol, and fatty acids for energy
Endocrine- uses precursor molecules such as cholesterol, estrogen, or protein to synthesize both peptide and steroid hormones
Peptide hormones produced by placenta
hCG human placental lactogen (HPL) ACTH corticotrophin releasing hormone relaxin inhibin
Steroid hormones produced by placenta
estrogen
progesterone
What does relaxin do?
quiets the myometrium facilitates decidual reaction remodels collagen helps soften cervix affect cartilage of maternal skeletal system
What does DHEA-S do?
essential precursor to placental synthesis of estrogen
What role does estrogen play in gestation?
- Prepares the endometrium for pregnancy
- stimulates phospholipid synthesis
- enhances prostaglandin production
- promotes uterine vasodilation
- prepares breasts for breastfeeding
- increases fetal lung surfactant production
What role does progesterone play in gestation?
- Essential for preparation of the endometrium for implantation
- maintains quiescent uterus
- inhibits prostaglandin development
- inhibits maternal cell-mediated immune system
- reduces CO2 sensitivity in maternal resp. center
- Inhibits prolactin secretion
- relaxes maternal smooth muscle
- causes increase in maternal temp
- increases cervical mucus and formation of mucus plug
role of hCG
maintain corpus luteum
promotes vasodilation and relaxation of uterus
stimulates the male testicle to secrete testosterone
stimulates maternal thyroid
promotes secretion of relaxin
role of hPL
maternal lipolysis
increases maternal insulin resistance
angiogenesis
increases synthesis of lipids
role of Human Chorionic Adrenocorticotropin (ACTH)
promotes fetal lung maturation
plays role in timing of labor
role of corticotrophin-releasing hormone
- Acts to increase ACTH secretion from trophoblast
- causes smooth muscle relaxation in blood -vessels and uterus
- facilitates maternal immunosuppression
- near term contributes to genesis of labor
role of inhibin
acts with other hormones to decrease release of FSH, which stops ovulation
role of syncitiotrophoblast
the outer layer of blastocyst. sends out fingerlike extensions that take in uterine cells as it invades the endometrium
The syncytiotrophoblast cells secrete both peptide and steroid hormones important to the maintenance of pregnancy
role of cytotrophoblast
inner layer, secretes peptide hormones need for the pregnancy;
In early development, contains the embryo, amnion, and yolk sac
After the end of the 2nd wk, small projections of the cytotrophoblast extend into the syncytiotrophoblast to form primary chorionic villi
what are villous trophoblasts?
they give rise to the chorionic villi, which primarily transport oxygen, nutrients, and other compounds between the fetus and mother
what are extravillous trophoblasts?
migrate into the decidua and myometrium and also penetrate maternal vasculature, thus coming into contact with various maternal cell types
Four main modes of transport for substances across the placental membrane
simple diffusion
facilitated diffusion
active transport
pinocytosis
simple diffusion
movement from higher to lower concentration
- gases
- drugs
- steroids
- electrolytes
facilitated diffusion
movement that needs a transporter but no energy
- glucose
- cholesterol
active transport
movement against a concentration gradient that requires energy
- amino acids
- vitamins
- transferrin
- calcium
- iodine
pinocytosis
carrier molecule is required to engulf the molecule and move it across the placental barrier
igG
Immunological status of placenta
Fetal semi-allograft survival may be explained by immunological neutrality
immunologically inert and therefore unable to create a maternal immune response
Villous trophoblast cells lack MHC class I and II antigens
utero-placental circulation
two arteries and a vein
umbilical cord goes from fetus umbilicus to placenta
Deoxygenated venous-like fetal blood flows to the placenta through two umbilical arteries
Umbilical vein brings oxygenated blood, nutrients back to the fetus from the placenta
The umbilical vessels are contained with the cord and surrounded by wharton’s jelly, a gelatinous connective tissue
What is aerobic metabolism?
energy production in the presence of oxygen
fetus uses glucose to convert to ATP
What are the end products of aerobic metabolism?
CO2 and H2O
They rapidly diffuse across the placenta
What is anaerobic metabolism?
energy production in the absence of oxygen or with insufficient oxygen
fetus converts glucose to ATP
What is the end product of anaerobic metabolism?
lactic acid
slow to cross the placenta –> acidosis –> brain damage and damage to other organs in fetus
Where does amniotic fluid come from?
Early gestation- secretions from the surface of the body of the embryo through intramembranous and transmembranous flow
Mid gestation- fetal urine begins to enter the amniotic sac and fetus begins to swallow AF. The fetal lungs also begin to secrete liquid into the AF
Late gestation- AF production from fetal urine and fetal lung liquid. Clearance comes from fetal swallowing and intramembranous pathway (pathway where water and solute exchange occurs directly between AF and fetal blood)
What is normal amniotic fluid index (AFI)?
5-24 cm
Volume of amniotic fluid throughout pregnancy
30ml at 10wks 200ml by 16 wks 400ml between 22-30wks Reaches 800 ml by the mid-third trimester Decline by 8% per week after 40 wks
maintenance of amniotic fluid
Fetal Urine production
Fetal lung liquid secretion
(Approximately 50 percent of this fluid (170 mL/day) is swallowed and the remainder enters the AF compartment, which is the basis for fetal lung maturity testing)
Fetal swallowing
Intramembranous flow
Oral-nasal secretions
Transmembranous flow
Functions of amniotic fluid
Protects the embryo/fetus from trauma to the maternal abdomen
Is a barrier to most bacteria; has some antibacterial properties
Provides the necessary fluid, space, and growth factors to permit normal development of the fetal lungs and musculoskeletal and GI systems
Allows for fetal movement and growth
Reflects fetal kidney function
Provides thermoregulation
It serves as a reservoir of fluid and nutrients for the fetus
Cushions the umbilical cord from compression between the fetus and uterus
