Fetal circulation

Fetal circulation

Q. 1 The primitive uteroplacental circulation is functionally established during  which  period  of embryonic/fetal development?
 A First week
 B Second week
 C Third week
 D End of first month
Q. 1 The primitive uteroplacental circulation is functionally established during  which  period  of embryonic/fetal development?
 A First week
 B Second week
 C Third week
 D End of first month
Ans. D

Explanation:

End of first month.

During the second week of fetal development, lacunar spaces develop between cells of the syncytiotrophoblast,

particularly in the region of the embryonic pole as the conceptus invades the endometrium. Endometrial capillaries in this region become dilated and engorged with blood to form sinusoids. The syncytial cells direct erosion of the endothelium of the maternal capillaries, allowing maternal blood to enter the lacunae and bathe the syncytial cells. During the second week, core will then differentiate to form capillaries and blood cells by the end of the third week (tertiary villus). primary villi consist of projections of syncytial cells surrounding a core of cytotrophoblast cells (answer b). During the third week (answer c), the villus core is invaded by mesodermal cells to form a secondary villus. Cells of the mesodermal Those vessels become connected to the fetal circulation early in the fourth week establishing the functional uteroplacental circulation.


Q. 2 Fetal blood is returned to the umbilical arteries and the placenta through the
 A Hypogastric arteries
 B Ductus venosus
 C Portal vein
 D Inferior vena cava
Q. 2 Fetal blood is returned to the umbilical arteries and the placenta through the
 A Hypogastric arteries
 B Ductus venosus
 C Portal vein
 D Inferior vena cava
Ans. A

Explanation:

(Reece, 2/e, pp 54, 119–121.) Fetal blood is returned directly to the placenta through the two hypogastric arteries. The distal portions  of  the  hypogastric  arteries  atrophy and obliterate within 3 to 4 days after birth; remnants are called umbilical ligaments. Fetal oxygenation is aided by the presence of three vascular shunts: the ductus venosus, foramen ovale, and ductus arteriosus. The ductus venosus shunts oxygenated blood from the umbilical vein into the inferior vena cava. The foramen ovale deflects the more oxygenated blood from the right atrium into the left atrium, thereby bypassing pulmonary circulation. Approximately two-  thirds  of  the  blood  ejected from the right ventricle is shunted pulmonary circulation through the ductus arteriosus.


Q. 3

The immunoglobulin which passes the placental barrier in humans is:

 A

IgM

 B

IgD

 C

IgE

 D

IgG

Q. 3

The immunoglobulin which passes the placental barrier in humans is:

 A

IgM

 B

IgD

 C

IgE

 D

IgG

Ans. D

Explanation:

There are five known classes of amino globulins: IgG, IgA, IgM IgD and IgE. IgG is the major middle globulin that is found in human serum and the one that has been shown to pass the placental barrier in humans.
IgM possesses higher agglutinating and complement-fixing capacity than IgG.
IgM has a molecular weight of 900,000. Carbohydrates constitute 7 to 11 percent of the total weight of IgM.
IgD constitutes a minor portion of serum immunoglobulins (1 percent).

It contains higher amounts of carbohydrate (13 percent) than the other immunoglobulins, but it has an important B-cell receptor.

No other biological functions have been described for IgD. IgE is the immunoglobulin that has been associated with anaphylactic hypersensitivity.
IgE has a molecular weight of 190,000 to 200,000, contains 11 to 12 percent carbohydrate and constitutes .002 percent of the total serum immunoglobulin.
IgA is the major immunoglobulin of extracellular secretions.
It has a molecular weight of 160,000 to 440,000, had modest agglutinating capacity and its carbohydrate content is two to three times higher (7.5%) than that of IgG.
 
Ref: Levinson W. (2012). Chapter 59. Antibodies. In W. Levinson (Ed), Review of Medical Microbiology & Immunology, 12e.

Q. 4

All of the following are components of placental barrier, EXCEPT:

 A

Trophoblast

 B

Fetal capillary endothelium

 C

Mesoderm

 D

Amnion

Q. 4

All of the following are components of placental barrier, EXCEPT:

 A

Trophoblast

 B

Fetal capillary endothelium

 C

Mesoderm

 D

Amnion

Ans. D

Explanation:

The fetal and maternal blood is never in contact.

They are separated by the placental barrier or placental membrane, which consists of:

  • Syncytiotrophoblast
  • Cytotrophoblast
  • Basement membrane
  • Mesoderm
  • Endothelium of the fetal capillaries

This thins out as term approaches due to attenuation of the syncytiotrophoblast.

These thinned out areas, offer better exchange between the mother and fetus.

Ref: Textbook of Obstetrics Sheila Balakrishnan, 1st Ed, page 75


Q. 5

Which of the following statements regarding fetal circulation is correct?

 A

The liver and heart of the fetus receive blood with very high oxygen saturation

 B

PO2 of fetal blood leaving the placenta is slightly greater than maternal mixed venous PO2

 C

The presence of fetal hemoglobin shifts the oxyhemoglobin dissociation to the right

 D

The foramen ovale closes during the third trimester unless the fetus has an atrial septal defect

Q. 5

Which of the following statements regarding fetal circulation is correct?

 A

The liver and heart of the fetus receive blood with very high oxygen saturation

 B

PO2 of fetal blood leaving the placenta is slightly greater than maternal mixed venous PO2

 C

The presence of fetal hemoglobin shifts the oxyhemoglobin dissociation to the right

 D

The foramen ovale closes during the third trimester unless the fetus has an atrial septal defect

Ans. A

Explanation:

Since the liver is supplied by umbilical venous blood from the placenta, and the heart and head receive blood before it has mixed with significant amounts of desaturated blood, these important organs receive blood that is relatively high in saturated oxyhemoglobin.

The high rate of blood flow at the placenta and the significant resistance of the placenta to diffusion of oxygen result in blood in the umbilical vein that has a lower PO2 (30 mm Hg) than the maternal mixed venous blood.

However, the left shift in fetal oxyhemoglobin concentration and the Bohr effect both act to increase the transport of oxygen to fetal tissues.


A number of significant differences in circulating patterns are present in the fetus.

The foramen ovale remains open until after birth and a significant portion of inferior vena cava flow is shunted through it to the left.

The major portion of right ventricular output is shunted through the ductus arteriosus to the aorta, not the lungs.


The net effect of these shunts in the presence of high fetal pulmonary vascular resistance is very low fetal pulmonary blood flow.

At birth, these patterns normally are quickly changed to ex-utero patterns with high pulmonary perfusion.
 
Ref: Barrett K.E., Barman S.M., Boitano S., Brooks H.L. (2012). Chapter 33. Circulation through Special Regions. In K.E. Barrett, S.M. Barman, S. Boitano, H.L. Brooks (Eds), Ganong’s Review of Medical Physiology, 24e.

Q. 6

Maximum level of alpha feto protein is seen in :

 A

Fetal serum

 B

Placenta

 C

Amniotic fluid

 D

Maternal serum

Q. 6

Maximum level of alpha feto protein is seen in :

 A

Fetal serum

 B

Placenta

 C

Amniotic fluid

 D

Maternal serum

Ans. A

Explanation:

Ans. is a i.e. Fetal serum

  • Alpha feto protein is the most abundant protein in the fetal serum throughout fetal development.
  • It is transferred from fetus to amniotic fluid when fetus passes urine.
  • The concentration of AFP in amniotic fluid is approximately 100 folds less than in fetal serum, peaks at 13-14 weeks and then decreases in the second trimester (by 10% per week).
  • AFP reaches the maternal serum by diffusion across the amniotic membranes and via the placenta.
  • The level of AFP in maternal serum is less than fetal serum as is suggested by :

“Fetal serum contains AFP in a concentration 150 times that of maternal serum”.

“Ordinarily high level of fetoprotein are found in developing fetus and low levels exist in maternal serum and amniotic fluid”.


Q. 7

True about fetal circulation-

 A

Blood in SVC has more oxygen saturation

 B

Pressure in left ventricle is more

 C

Brain receives blood with low oxygen saturation

 D

Heart receives blood with high oxygen saturation

Q. 7

True about fetal circulation-

 A

Blood in SVC has more oxygen saturation

 B

Pressure in left ventricle is more

 C

Brain receives blood with low oxygen saturation

 D

Heart receives blood with high oxygen saturation

Ans. D

Explanation:

Ans. is ‘d’ i.e., Heart receives blood with high oxygen saturation

o Blood in IVC has more saturation than blood in SVC as IVC carries the oxygenated blood of umblical vein.

o The left ventricular blood has more oxygen saturation that right ventricular blood because it carries the blood of IVC,

while blood in right ventricle is a mixture of blood from IVC and SVC.

o So, the brain and coronary circulation receive blood with higher saturation (through ascending aorta) than the lower half of body.

o The left ventricular output is approximately half of right ventricular output because volume of blood reaching in left atrium is considerably lower than volume of blood reaching in right atrium. Infact right atrium is the major source of blood to left atrium.

o Aorta and pulmonary trunk are connected by ductus arteriosis, and pulmonary trunk has pressure slightly higher or equal to that of arota –> So, blood flows from pulmonary trunk to aorta.

o The pressure in right and left ventricles are equal.


Q. 8

Fetal Hb shows high pO2 saturation compared to adult Hb because ‑

 A

Affinity to binding to DPG is different in fetal Hb

 B

Right shift to Oxygen dissociation curve

 C

Acidic environment

 D

Cooperative binding

Q. 8

Fetal Hb shows high pO2 saturation compared to adult Hb because ‑

 A

Affinity to binding to DPG is different in fetal Hb

 B

Right shift to Oxygen dissociation curve

 C

Acidic environment

 D

Cooperative binding

Ans. A

Explanation:

Ans. is ‘a’ i.e., Affinity to binding to DPG is different in fetal Hb



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