DANIL HAMMOUDI.MD

SINOE MEDICAL ASSOCIATION

 

USMLE REVIEW FOR STEP1

 

 

Initiation of the action potential (phase 0) in ventricular myocytes is due to activation of the rapid Na+ channels

The diagram depicts a typical ventricular myocyte action potential. The stable resting membrane potential (phase 4) is approximately -90 mV. This highly polarized state indicates that the membrane has a high conductance (permeability) to K+. The rapid reversal of the membrane potential in ventricular myocytes (phase 0) is due to the opening of the rapid Na+ channels and the approach of the membrane to the equilibrium potential for Na+ (+60 mV). During phase 1, the membrane potential begins to repolarize. This is caused by the transient opening of K+ channels, as well as the inactivation of the Na+ current. Phase 2 (the plateau phase) results from the opening of the slow Ca++ channels. The influx of Ca++ is balanced by the efflux of K+, so a stable plateau potential is maintained. During phase 3, the membranes' conductance to K+ increases and the membrane repolarizes. Myocytes do not possess automaticity and depend on the spread of electrical activity for activation.

 

A patient with eczema, thrombocytopenia, and recurrent infections is best characterized by which disorder?

Deficiency of adenosine deaminase

The Wiskott-Aldrich syndrome is a sex-linked recessive disease with a characteristic triad of thrombocytopenia, eczema, and recurrent infections.

Additional clinical findings include bloody diarrhea, cerebral hemorrhage, septicemia, severe infections by encapsulated bacteria, and an increased propensity for malignant lymphomas.

Laboratory findings include low lymphocyte counts as the T cells decrease with subsequent impairment in cellular immunity, low immunoglobulin M levels, and increased levels of immunoglobulin G, immunoglobulin A, and particularly immunoglobulin E.

 

The triad of Howell-Jolly bodies, target cells, and reticulocytosis is most compatible with which clinical finding? Splenectomy

 

The finding of Howell-Jolly bodies, target cells, and reticulocytosis is most compatible with splenectomy.

 

The spleen has many functions, including the removal of defective and aged blood cells, hematopoiesis (in times of severe stress when the marrow is unable to meet the needs of the organism), iron conservation, blood cell storage, and host defense in the form of humoral immunity.

 

Therefore, splenectomy can result in a number of hematologic abnormalities.

 

 Following splenectomy, Howell-Jolly bodies (leftover nuclear remnants) are not removed from the cytoplasm of erythrocytes, resulting in increased numbers of nucleated erythrocytes and erythrocytes containing Howell-Jolly bodies.

 

The spleen plays an important role in the maturation of reticulocytes into erythrocytes; therefore, splenectomy can result in a reticulocytosis.

 

Target cells are erythrocytes with too much membrane; normally, the spleen would remove the excess membrane.

 

Thrombocytosis also occurs because normally, the spleen is a reservoir for one-third of the platelets in the body. Thrombotic thrombocytopenic purpura (TTP) is associated with increased numbers of reticulocytes (as a result of intravascular damage to erythrocytes); however, Howell-Jolly bodies and target cells are not normally seen in patients with TTP. Disseminated intravascular coagulation (DIC) is associated with an increase in reticulocytes due to destruction of erythrocytes by fibrin in the microvasculature, but again, target cells and Howell-Jolly bodies are not normally present. Sickle cell trait is not associated with any hematologic abnormalities. Autoimmune hemolytic anemias are associated with a pronounced reticulocytosis that is often accompanied by nucleated erythrocytes because the markedly stressed bone marrow is barely able to keep pace with the extravascular removal of erythrocytes. However, target cells are not usually present.

 

A 48-year-old woman has a large, fungating tumor involving her right breast. A simple mastectomy is performed without axillary dissection. Grossly, the tumor has a bulging surface with numerous cystic spaces on cut section. Histologic sections show a densely cellular stroma with normal ductal epithelium. Cystosarcoma phyllodes

 

 

A 65-year-old woman has an erythematous, scaly rash involving her left nipple. The nipple is retracted. Painless lymphadenopathy is noted in the left lower axillary chain. PAGET DISEASE

 

A 48-year-old woman has a nonpalpable, 1.3-cm mass in the left upper outer quadrant that was detected by mammography. The right breast was reported as normal. On the mammogram, the left breast mass was described as having an irregular border and a tightly clustered grouping of punctate microcalcifications. The mass is locally excised after needle localization. Histologic sections reveal terminal lobules distended by intermediate-size cells with scant mitotic activity. Calcifications are noted in the acini. Neoplastic cells infiltrate the stroma in an Indian-file pattern. Lobular carcinoma

 

A 57-year-old woman has a 1.5-cm mass located in the right upper outer quadrant. She has three palpable lymph nodes present in the right lower axillary chain. A tru-cut needle biopsy specimen exhibits ducts lined by malignant cells. Some of the ducts have a central area of necrosis. There is no evidence of invasion of the surrounding stroma. Comedocarcinoma

 

 

A 63-year-old woman has dimpling of her skin medial to her left nipple when she raises her left arm over her head. A 2-cm, fixed, indurated, and nontender mass is palpated underneath the area of dimpling. A tru-cut needle biopsy of the mass shows malignant cells streaming through a desmoplastic stroma. One duct is filled with malignant cells exhibiting a cribriform pattern. Infiltrating ductal carcinoma

A 28-year-old woman presents with a bloody nipple discharge. Palpation around the nipple reveals blood coming from one of the duct openings. No masses are identified. A cytology specimen of the bloody material reveals blood intermixed with foamy macrophages and clumps of benign ductal epithelium with a fibrovascular core. Intraductal papilloma