placenta

Question 1

structure of placenta

Answer 1

humans have a villous hemochorial placenta- maternal blood comes in direct contact with fetal trophoblasts (but not fetal blood). It is discoid in shape and has chorioallantoic vasculature. Placental structure is not highly conserved among species

Question 2

· Explain the different functions of the placenta.

Answer 2

Support the growth and development of the fetus, Transport Nutrients, O2, Waste, CO2, Endocrine- Steroid and peptide hormones

Question 3

describ prelacunar stage

Answer 3

Days 6-8. Outer layer of trophoectoderm forms non-miotic multinucleated syncytiotrophoblast. Inner layer remains as single cells called cytotrophoblasts. The cytotrophoblast cells proliferate providing for the developing syncytium that invades the adjacent maternal tissue

Question 4

Lacunar stage

Answer 4

aka trabecular stage. Days 9-12. Vacuoles appear within the syncytiotrophoblasts and fuse to form lacunae (lakes). syncytiotrophoblasts form pillars called trabeculae. The lacunae make contact with the endometrial capillaries and some maternal erythrocytes may be observed within the lacunae. This is the region that will develop into the intervillous space. Implantation is complete at this point.

Question 5

Villous stage

Answer 5

Days 13-18. development (in three stages) of chorionic villi. The cytotrophoblasts proliferate and begin to invade up the trabeculae.

Question 6

Describe a primary, secondary and tertiary villous

Answer 6

Primary: consists of a cytotrophoblast core surrounded by synctytiotrophoblast. Secondary: extraembryonic mesoderm grows into the cytotrophoblast. Tertiary: Eventually, the mesenchymal cells differentiate into blood vessels resulting in the formation of an arteriocapillary network within the villous

Question 7

floating villi/ anchoring villi

Answer 7

anchoring: attachment to uterus. Site for invasive cytotrophoblast deployment. Floating: majority of placental mass. Site of nutrient and waste exchange

Question 8

types of trophoblast invasion

Answer 8

Interstitial invasion: cytotrophoblasts invade the entire endometrium and the first third of the myometrium. Endovascular invasion: cytotrophoblasts invade the uterine spiral arterioles through their superficial myometrial segments. Only the termini of veins are breached

Question 9

maternal fetal blood separation

Answer 9

No direct mixing. Fetal blood in the capillaries of the tertiary villi are separated from maternal blood surrounding the villous by a “placental membrane” composed of the capillary endothelium, mesenchyme, cytotrophoblast, and syncytrophoblast.

Question 10

Maternal fetal circulation

Answer 10

the two umbilical arteries carry deoxygenated blood from the fetus to the placenta, branching into arterioles following the course of the villous tree forming a capillary network within the chorionic villi. Maternal blood in the intervillous space provides oxygen to the fetal blood in the villi. The chorionic villi capillaries then form venules that ultimately connect to the umbilical vein, which carries oxygenated blood back to the fetus

Question 11

Third trimester placenta divisions

Answer 11

The maternal surface is divided by septa into cotyledons. Each cotyledon contains several main stem villi with many branching villi.

Question 12

Placental terminal villi

Answer 12

Grape-like structures located on tertiary villi that have many capillaries and highly dilated sinusoids. Terminal villi are the locations where most of the villous growth and transplacental transport takes place. This arrangement minimizes the transit distance between the fetal and maternal circulations

Question 13

amniotic fluid function

Answer 13

vital factor for fetal growth and development and provides mechanical protection for the fetus. Amniotic fluid volume ranges from 250 ml at 18 weeks to 1,000 ml at 34 weeks, with decreasing volume thereafter

Question 14

Amniotic fluid production

Answer 14

Early in pregnancy, amniotic fluid is simply an ultrafiltrate of maternal plasma. Once the fetal kidneys start working (12 weeks), fetal urine becomes the major source; and in late pregnancy amniotic fluid is primarily fetal urine, with a small contribution from fetal lung secretions

Question 15

Oligohydramnios

Answer 15

a subnormal volume of amniotic fluid. Can be caused by rupture of membranes, poor placental perfusion due to pre-gestational diabetes, hypertension, preeclampsia, or twin-twin transfusion. Also nephrotoxic drugs like prostaglandin synthase inhibitors and ACEI interfere with normal fetal renal function

Question 16

Polyhydramnios

Answer 16

supernormal volume of amniotic fluid. Common in congenital anomalies that interfere with fetal swallowing of amniotic fluid (neural tube defect, esophageal atresia). Hydrops (fetal fluid excess secondary to hemolysis, congenital heart defect or infection) and gestational diabetes also cause this.

Question 17

types of placental transport

Answer 17

diffusion, facilitated diffusion (glucose) and active transport (amino acids)

Question 18

Rate limiting step in diffusion across placenta

Answer 18

The rate-limiting step is the rate of movement across the syncytiotrophoblast membranes between the intervillous space and the fetal capillaries. Therefore, the rate of transport is primarily influenced by the characteristics of the syncytiotrophoblast cell membrane. direct damage to the syncytiotrophoblast will affect oxygen transport to the fetus.

Question 19

flow limited transport

Answer 19

For substances that cross the placenta more rapidly, transport is dependent on plasma concentration and the rate of blood flow. This flow-limited transport can be affected by several factors, including changes in uterine blood flow and therefore placental perfusion. Pregnant women with aortic stenosis have reduced cardiac output, which often leads to growth restricted fetuses

Question 20

Placental respiratory function

Answer 20

Fetal hemoglobin has different beta like chains than adult Hb. HbF has greater affinity for oxygen that adult HbA. Fetal erythrocytes have a lower concentration of 2, 3 diphosphoglycerate than maternal erythrocytes

Question 21

Placental hepatic function

Answer 21

The placenta is the primary barrier preventing fetal exposure to drugs in the maternal circulation; it has functional capacity for drug metabolism (with enzymes for oxidation, glucuronidation, and sulfation). Produces glycogen, cholesterol and fatty acids. excretion of wastes.

Question 22

Placental temp regulation

Answer 22

placenta acts as a heat exchanger to maintain fetal temperature. Heat produced by fetal metabolic processes is removed by the maternal circulation (women report feeling warmer during pregnancy.)

Question 23

Placental endocrine function

Answer 23

Syncytiotrophoblast produces hCG and human placental lactogen (hPL). hCG maintains the corpus luteum. hPL is an anti-insulin hormone that contributes to increased insulin resistance. Also produces estrogens and progesterone

Question 24

How long is corpus luteum maintained

Answer 24

8 weeks, until placenta makes enough progesterone

Question 25

· Diagram the steroid production process by the maternal-placental-fetal unit.

Answer 25

The fetal liver produces 16-OH DHEA-S which is taken to placenta and converted to estriol. The fetal adrenals produce pregnenolone which is taken to placenta and converted to progesterone. Progesterone is then taken back to the adrenals and converted to aldosterone or cortisol

Question 26

fetal antibodies

Answer 26

IgG is transferred across placenta. If antigenic stimulus, the dominant fetal response is IgM. IgM does not cross the placenta so any IgM in fetus was produced by the fetus.

Question 27

monozygotic vs dizygotic twins

Answer 27

mono: arise from a single fertilized oocyte that later divides. Genetically identical. Time of division determines extent to which placenta or amniotic sac is shared. Di: two independently fertilized oocytes. Each zygote has its own placenta and amniotic sac.

Question 28

classify the types of monozygotic twins

Answer 28

1. division at day 0-5, dichorionic, diamniotic, low mortality. 2. division at day 5-8 (trophoblast differentiated), monochorionic, diamniotic, 25% mortality. 3. division at day 8-13 (amnion formed), monochorionic, monoamniotic, 50% mortality. 4. division at 13-15 days same as #3 but higher mortality