downs syndrome is caused by

HESI LPN

HESI Maternal Newborn

1. What causes Down's syndrome?

A. Alcohol abuse by the mother at the time of conception.
B. Sex-linked chromosomal abnormalities.
C. An extra chromosome on the 21st pair.
D. Drug abuse by the mother during pregnancy.

Correct answer: C

Rationale: Down's syndrome, also known as trisomy 21, is caused by the presence of an extra chromosome on the 21st pair. Choice A is incorrect as alcohol abuse is not the cause of Down's syndrome. Choice B is incorrect because Down's syndrome is not related to sex-linked chromosomal abnormalities. Choice D is also incorrect as drug abuse by the mother during pregnancy is not the cause of Down's syndrome.

2. Twins that derive from a single zygote that has split into two are called:

A. monozygotic (MZ) twins.
B. fraternal twins.
C. non-identical twins.
D. dizygotic (DZ) twins.

Correct answer: A

Rationale: The correct answer is A: monozygotic (MZ) twins. Monozygotic twins, also known as identical twins, occur when a single zygote splits into two embryos, leading to two genetically identical individuals. Choice B, fraternal twins, are twins that develop from two separate eggs fertilized by two different sperm cells, resulting in non-identical siblings. Choice C, non-identical twins, is not a common term used to describe this type of twinning. Choice D, dizygotic (DZ) twins, refer to twins that develop from two separate eggs fertilized by two different sperm cells, leading to non-identical twins.

3. According to a survey by Adhikari and Liu in the year 2013, at birth, women have:

A. close to 100,000 ova.
B. around 300,000 to 400,000 ova.
C. around 100 to 200 ova.
D. only 500 ova.

Correct answer: B

Rationale: Women are born with approximately 300,000 to 400,000 ova, which gradually decrease in number as they age. Choice A ('close to 100,000 ova.') is incorrect as the actual number is much higher. Choice C ('around 100 to 200 ova.') is incorrect as it underestimates the quantity significantly. Choice D ('only 500 ova.') is incorrect as it greatly underestimates the number of ova present at birth.

4. A healthcare provider is assessing a newborn upon admission to the nursery. Which of the following should the provider expect?

A. Bulging Fontanels
B. Nasal Flaring
C. Length from head to heel of 40 cm (15.7 in)
D. Chest circumference 2 cm (0.8 in) smaller than the head circumference

Correct answer: D

Rationale: Upon admission to the nursery, a healthcare provider should expect the newborn's chest circumference to be slightly smaller than the head circumference. This is a normal finding in newborns due to their physiological development. Bulging fontanels (Choice A) can indicate increased intracranial pressure, which is abnormal. Nasal flaring (Choice B) is a sign of respiratory distress and is also an abnormal finding. While a length from head to heel of 40 cm (15.7 in) (Choice C) falls within the normal range for newborns, it is not a specific expectation upon admission to the nursery. Therefore, the correct expectation for a newborn upon admission is for the chest circumference to be slightly smaller than the head circumference.

5. According to a study in the year 2013 by Fellman, if a woman is a twin, if her mother was a twin, or if she has previously borne twins, then:

A. she will bear only monozygotic (MZ) twins.
B. the chances of her becoming pregnant decrease.
C. she is likely to be a healthy mother.
D. the chances rise that she will bear twins.

Correct answer: D

Rationale: According to the study, the chances of a woman bearing twins increase if she is a twin herself, if her mother was a twin, or if she has previously borne twins. Therefore, the correct answer is D. Choice A is incorrect because the study does not specify that she will bear only monozygotic twins. Choice B is incorrect as the study does not mention any decrease in the chances of becoming pregnant. Choice C is incorrect because the study does not provide information about the woman's health status, focusing instead on the likelihood of bearing twins.