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Real Doctors (Life Makers)  |  Basic Science  |  Anatomy , applied anatomy and embryology  |  CASES « previous next »
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cleo_md
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CASES
« on: /October/ 07, 2005, 05:50:12 PM »

 History

A 20-year-old woman comes to your office worried that she is abnormal because she has never menstruated. The patient has a history of coarctation of the aorta, which was repaired when she was 6 months old because of its severity. Otherwise the patient has no significant past medical history. She takes no regular medications. Family history is unremarkable. The patient has never been sexually active.

Physical Exam

The patient is <5 feet tall and has some webbing of her neck. You also note a low posterior hairline and broad chest with widely spaced nipples. No abnormal heart sounds are appreciated, and the lungs are clear to auscultation. She has prepubescent development of secondary sex characteristics. On pelvic exam, the uterus is small. No neurologic deficits are appreciated.

Tests

Hemoglobin: normal
Liver function tests: normal
Follicle-stimulating hormone (FSH): elevated
Thyroid-stimulating hormone: normal
Pelvic ultrasound: small "streak" ovaries noted bilaterally
Buccal smear: no Barr bodies identified

Questions
What condition does this patient have?
What is a Barr body?
 
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Turner syndrome (TS)

Discussion

TS is a chromosomal disorder affecting females. It is classically due to a missing X chromosome (45, XO karyotype), although mosaicism and isochromosomes, deletions, and ring forms of one X chromosome also can cause TS. The lack of critical X chromosome genes results in a lack of adult sexual development. Associated developmental abnormalities are frequent : aortic coarctation, short stature (<5 feet tall), low posterior hairline, webbing of the neck, broad chest with widely spaced nipples, and cubitus valgus (a wide carrying angle at the elbow).

The most common causes for aneuploidy (wrong number of chromosomes) are nondisjunction, which is when a chromosomal or chromatid pair fails to separate during the first or second meiotic division, and anaphase lag. In the latter, one chromosome (meiosis) or chromatid (mitosis) moves too slow for the group and is excluded from the nucleus of a cell.

Findings

Classic TS patient presentations are for primary amenorrhea (patients who have not menstruated by age 16) or infertility, although many are diagnosed prenatally or shortly after birth. Classic physical exam findings include perinatal swelling in the neck from a cystic hygroma (benign cystic growth, classically in the neck) and lack of adult sexual development, including sparse pubic hair, lack of breast development, small uterus, and " streak" ovaries (i.e., small, nonfunctional ovaries). Elevated gonadotropin (e.g., FSH) levels occur and stem from attempts by the hypothalamus and pituitary gland to stimulate the ovaries (a form of premature menopause).

Treatment

Treatment may be needed for embryologic defects (e.g., coarctation, cystic hygroma). Intelligence is usually normal, but the risk of mental retardation is increased.


A Barr body is a condensed mass of chromatin representing an inactivated X-chromosome. Males (XY) and TS patients (XO) have no Barr bodies, but normal women (XX) have Barr bodies, as only those with more than one X chromosome (including males with Klinefelter syndrome [XXY]) can "afford" to have one X chromosome inactivated. Only roughly half of cells have Barr bodies in those with more than one X chromosome.
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eman
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Re: CASES
« Reply #1 on: /October/ 13, 2005, 09:31:55 PM »

DR-cleo -md? ? ? ?thank you for this good case? ? ?we need more &more ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?Rules? ? ? ? ? ?Wink
« Last Edit: /October/ 15, 2005, 12:08:32 AM by eman » Logged
 
cleo_md
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Re: CASES
« Reply #2 on: /October/ 20, 2005, 07:08:59 PM »

History
A pregnant 25-year-old woman comes to the hospital while in labor. The woman, who is 36 weeks pregnant, has had no prior complaints and had a normal pregnancy. This is her first pregnancy. She has no significant past medical history, takes no medications, and does not smoke or drink alcohol.

Physical Exam
The exam is normal, and you can hear a normal fetal heartbeat with your stethoscope. The infant delivers vaginally without difficulty, and the umbilical cord is clamped. The infant appears healthy at birth.

Questions

Describe the fetal circulation by naming the blood vessels, in order, that a fetal red blood cell (RBC) would travel through beginning at the point where the RBC picks up maternal oxygen at the placenta and ending at the point where the RBC returns to the placenta to release CO2 and wastes.
What are the three main fetal "shunts" in utero that facilitate getting oxygenated maternal blood to the fetus' systemic circulation?
What happens to the fetal circulation after birth?
Name the vessels (arteries or veins) that contain the blood with the highest oxygen saturation in the fetal circulation. How about after birth?



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Topic

Fetal circulation

Discussion
The fetal circulation is significantly different from that of the adult because the fetus gets oxygen from its mother, via the placenta, instead of through the lungs (i.e., the placenta provides respiratory function). Three primary shunts are designed to get the most oxygenated blood to the developing tissues: the ductus venosus, foramen ovale, and ductus arteriosus.

Anatomy

In utero, oxygen is released from maternal RBCs and picked up by fetal RBCs, which contain large amounts of fetal hemoglobin (e.g., hemoglobin F) and have an oxygen dissociation curve that is shifted up and to the left (i.e., greater oxygen affinity). This occurs in the left umbilical vein, the location of the blood with the highest oxygen saturation. Blood flows through the umbilical vein up to the liver, where most of it is shunted through the ductus venosus, bypassing the liver, to enter the inferior vena cava. From the inferior vena cava, blood flows into the right atrium, mixing with deoxygenated blood returning to the heart from the superior vena cava. Then the blood is largely shunted across the foramen ovale and into the left atrium, left ventricle, aorta, and systemic arteries to supply oxygen and nutrients to the developing organs.
When blood flows through the capillaries and returns to the heart by systemic veins, it goes into the right atrium and right ventricle and out into the main pulmonary artery. The pulmonary artery pressures are high because the lungs are not inflated, however, and most blood is preferentially shunted through the ductus arteriosus into the descending thoracic aorta. Blood returns to the placenta via the aorta and iliac arteries, then through the umbilical arteries to reach the placenta.

More High-Yield Facts
The left umbilical vein becomes the ligamentum teres (round ligament), and the umbilical arteries become the medial umbilical folds; the ductus venosum and arteriosum become their respective ligamenta.
After birth, the infant begins to breathe, decreasing pulmonary artery pressures, and the umbilical cord is clamped, stopping flow in the umbilical arteries and vein. Functional closure of the foramen ovale occurs as a result of decreased pulmonary resistance and increased left-sided heart pressures, and flow ceases through the ductus venosus. The ductus arteriosus also normally begins to close shortly after birth. When these changes have occurred, an adult circulation pattern is established, and the highest blood oxygenation levels are in the pulmonary veins, followed by the systemic arteries.

 
« Last Edit: /October/ 20, 2005, 07:10:57 PM by cleo_md » Logged
 
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