Sherpath: Auxiliary structures & fetal circulation (N.332)

Which shunt allows for the delivery of blood from the right to the left atrium in the fetus?

foramen ovale

During late pregnancy, the ______ receives 75% to 80% of the oxygenated venous blood.

liver

The placenta depends upon the _________________ to maintain circulation

maternal blood pressure

the placenta secretes hormones that regulate _____________

metabolic function

What are the 3 auxiliary structures?

placenta umbilical cord fetal membranes

what makes up the fetal membranes?

the amnion and chorion

what are oxygen, nutrients, and waste products exchanged thru?

the chorionic villi

what parts of the fetus receive most of the oxygenated blood?

the head and upper body

maternal side of placenta

the maternal side is rough where it attaches to the uterus

what is the purpose of the 3 shunts?

they divert most circulating blood away from the lungs and liver. Why: because the fetus does not breathe air or metabolize substances in the liver.

what are some transfer functions of the placenta

transfers oxygen, nutrients, and waste products between the mother and fetus.

where does blood exchange between the mother and the fetus occur?

within the intervillous space of the placenta

maternal circulation

- About 150 mL of maternal blood is contained within the intervillous space. - This blood is changed about three or four times per minute. - Maternal blood enters the intervillous spaces through 80 to 100 spiral arteries in the decidua. - The oxygenated and nutrient-bearing maternal blood washes over the chorionic villi containing fetal capillaries. - The blood then returns to the maternal circulation through the endometrial veins for elimination of fetal waste products.

Which placental variations present a risk for fetal hemorrhage?

- Battledore - Vasa previia - Velamentous

fetal circulation

- Blood is circulated to and from the fetal side of the placenta by the fetal heart. - The chorionic villi are bathed in oxygen-rich and nutrient-rich maternal blood in the maternal intervillous spaces. - Fetal capillaries in the chorionic villi are separated from direct contact with the mother's blood by the membranes of each villus. - Separation allows contact close enough for exchange but avoids mixing of fetal and maternal blood, which may not be compatible.

transfer function: waste removal

- Carbon dioxide, urea, uric acid, and bilirubin are readily transferred for disposal by the mother.

transfer function: nutrient transfer

- Glucose, fatty acids, electrolytes, and vitamins pass readily across the placenta to the growing fetus.

endocrine functions of the placenta

- In the embryo, human chorionic gonadotropin (hCG) causes the corpus luteum to persist and secrete estrogen and progesterone for the first 6 to 8 weeks. - In the mother, human chorionic somatomammotropin (hCS) is produced, and this acts as a growth hormone, contributes to breast development, and affects the woman's metabolism. - the presence of the Y chromosome causes the fetal testes to secrete testosterone necessary for normal development of male reproductive structures. - Estrogen and progesterone are steroid hormones also secreted by the placenta. - Estrogen causes enlargement of the mother's uterus, breasts, and external genitalia and growth of the ductal system of the breasts. Estrogen also enhances uterine activity. - Progesterone causes the endometrium to change into the decidua, which provides nourishment for the early conceptus. Progesterone reduces uterine contractions and suppresses maternal reactions to fetal antigens.

Which characteristics allow the fetus to thrive despite a lower-than-average blood partial pressure of oxygen (PO2)?

- Low partial pressure of carbon dioxide (PCO2) causes the fetal hemoglobin to carry more oxygen. - Blood entering the placenta from the fetus has a high partial pressure of carbon dioxide (PCO2). - Fetal hemoglobin can carry more oxygen than adult hemoglobin can.

transfer function: transfer of maternal hormones

- Most maternal protein hormones do not reach the fetus in amounts sufficient to cause fetal abnormalities.

transfer function: gas exchange

- Oxygen and carbon dioxide pass through the placental membrane by simple diffusion. - Carbon dioxide quickly diffuses to the mother's blood, where the PCO2 is lower, reversing the levels of carbon dioxide in maternal and fetal blood supplies. - Fetal blood becomes more alkaline, and maternal blood becomes more acidic. This difference allows the mother's blood to give up oxygen and the fetal blood to readily combine with oxygen.

Which cardiovascular changes that occur in fetal circulation occur after birth?

- Pressure decreases in the right atrium. - The three fetal shunts constrict or close. - Blood flow from the pulmonary artery to the aorta reverses.

Which factors allow for the exchange of nutrients and waste products between maternal and fetal blood without the physical mixing of their blood?

- The intervillous space of the placenta - The lack of direct contact between fetal capillaries in chorionic villi and mother's blood SUBMIT

chorion

- The outer membrane - blends with placenta - houses the amniotic fluid

metabolic functions of the placenta

- The placenta produces some nutrients needed for the fetus and for its own functions. - Glycogen, cholesterol, and fatty acids are synthesized.

umbilical arteries

- The umbilical cord has two arteries that carry blood with high carbon dioxide content and other waste products away from the fetus to the placenta. - These substances are transferred to the mother's circulation for elimination.

umbilical vein

- The umbilical vein carries freshly oxygenated and nutrient-rich blood from the placenta back to the fetus.

transfer function: antibody transfer

- Transfer of immunoglobulin G antibodies to the fetus may provide temporary (passive) immunity against diseases such as rubella or tetanus (if the mother is immune). - ABO Incompatibility - Passage of antibodies from mother to fetus also may be harmful if maternal and fetal ABO blood types or Rh factors are not compatible. If this is the case, the mother may have already produced antibodies against fetal erythrocytes. The mother's antibodies may then destroy the fetal erythrocytes, causing fetal anemia or even fetal death.

name placental variations

- battledore placenta - velamentous placenta - vasa previa

structures in the order that fetal blood flows through them from the inferior vena cava.

- ductus venosus - right atrium - foramen ovale - left atrium - left ventricle - aorta

Which physiologic change in fetal circulation is triggered by clamping of the umbilical cord after birth?

Ductus venosus constriction

amnion

- inner membrane - blends with the umbilical cord

Which auxiliary structures play a role in the elimination of fetal waste?

- placenta - umbilical arteries

What are the 3 shunts in fetal circulation?

1. ductus venosus 2. foramen ovale 3. ductus arteriosus

circulation after birth

1.) As the infant breathes, blood flow to the lungs increases, pressure in the right atrium falls, and pressure in the left atrium increases, causing the foramen ovale to close. 2.) Pressure in the aorta rises as pressure in the pulmonary artery falls, causing the direction of blood flow through the ductus arteriosus to reverse, from the aorta into the pulmonary artery. 3.) The ductus arteriosus constricts as the arterial oxygen level rises. 4.) The ductus venosus constricts when blood flow from the umbilical cord stops.

The fetus can thrive in this low-oxygen environment for three reasons

1.) Fetal hemoglobin can carry 20% to 30% more oxygen than can maternal hemoglobin. 2.) The fetus has a higher oxygen-carrying capacity because of higher average hemoglobin (15 to 24 g/dL) and hematocrit (44% to 70%) values. 3.) Hemoglobin can carry more oxygen at a low partial pressure of carbon dioxide (PCO2) compared with a high one (Bohr effect); blood entering the placenta from the fetus has a high PCO2.

fetal circulation process

1.) Oxygenated blood from the placenta enters the fetal body through the umbilical vein. 2.) About half the oxygenated venous blood goes through the liver during early pregnancy, and the rest bypasses the liver and enters the inferior vena cava through the first shunt, the ductus venosus. 3.) The blood then enters the right atrium. 4.) Most of the blood passes directly into the left atrium through the second shunt, the foramen ovale, where it mixes with the small amount of blood returning from the lungs. 5.) Blood flows from the left atrium into the left ventricle. 6.) Blood is pumped from the left ventricle into the aorta to nourish the body. 7.) A small amount of blood from the right ventricle is circulated to the lungs to nourish the lung tissue. 8.) The rest of the blood from the right ventricle joins oxygenated blood in the aorta through the third shunt, the ductus arteriosus.

In which direction does neonate blood flow from the inferior vena cava? Place the structures in the order of blood flow from the inferior vena cava in the neonate.

1.) right atrium 2.) right ventricle 3.) pulmonary artery 4.) lungs

At term, ______% of maternal cardiac output goes to the uterus to support the fetus

10%

how many arteries and veins are in the umbilical cord?

2 arteries 1 vein

This describes the fetal circulation circuit process

Oxygenated blood from the placenta enters the fetal body through the umbilical vein. About half the oxygenated venous blood goes through the liver during early pregnancy and the rest bypasses the liver and enters the inferior vena cava through the first shunt, the ductus venosus. The blood then enters the right atrium. Most of the blood passes directly into the left atrium through the second shunt, the foramen ovale, where it mixes with the small amount of blood returning from the lungs. Blood travels from the left atrium to the left ventricle and is then pumped from the left ventricle into the aorta to nourish the body. A small amount of blood from the right ventricle is circulated to the lungs to nourish the lung tissue. The rest of the blood from the right ventricle joins oxygenated blood in the aorta through the third shunt, the ductus arteriosus.

fetal side of placenta

The fetal side is smooth, with branching vessels covering the membrane-covered surface

placental functions in relation to organ systems after birth?

The placenta's functions for the fetus are similar to the role of the lungs, gastrointestinal system, liver, kidneys, and endocrine organs after birth.

at the end of week 8.....

all organ systems & external structures are present, & the embryo's appearance is human.

A woman is at 36 weeks gestation when her toddler hits her in the abdomen with a Wiffle-ball bat. Which auxiliary component protects the fetus from this impact?

amniotic fluid

Which placental function has the potential to cause harm to the fetus?

antibody transfer Why: The passage of antibodies from mother to fetus is most often protective, although it may be harmful in the case of blood incompatibility. In this case, the mother's antibodies may then destroy fetal erythrocytes, causing fetal anemia or even fetal death.

The placenta has a vital function first as an _________________ to support and maintain the pregnancy.

endocrine gland