human males). When centrifuged with anticoagulants, blood separates into
three layers. The uppermost layer is the plasma; the buffy coat is a thin
white layer consisting of leukocytes found beneath the plasma; and the
packed erythrocyte layer at the bottom of the tube.
159.The answer is c.(Junqueira, p 250. Kierszenbaum, p 156. Kasper,
pp 674–676.)Idiopathic thrombocytopenic purpura (ITP) is primarily a
disease of increased peripheral platelet destruction and/or reduction in
platelet production by the bone marrow. The main symptom is bleeding,
which can include bruising (“ecchymosis”) and tiny red dots on the skin or
mucous membranes (“petechiae”). In some instances bleeding from the
nose, periodontal ligament (“gums”), urinary or gastrointestinal tracts may
occur. Cerebral hemorrhage occurs rarely in ITP. Red and white cell counts
are normal, but platelet counts range from 10,000 to 30,000/mL^3 (answer b)
with 150,000 mL^3 as normal and higher than 100,000 mL^3 is safe.
The reduction in platelets increases clotting time (answer a),
decreases coagulation (answer d),and would result in heavier menstrual
bleeding(answer e).ITP appears to be an autoimmune disease since most
patients have autoantibodies to specific platelet membrane glycoproteins.
ITP patients often show diminished platelet production by the bone mar-
row. Acute ITP often follows an acute infection or in response to pharma-
ceutical administration. It can also occur during pregnancy and in chronic
diseases such as hepatitis C, HIV, and lupus.
160.The answer is c.(Ross and Pawlina, p 395. Junqueira, pp 208,
211–212, 214.)The photomicrograph shows several types of blood or lym-
phatic vessels. Frequently, peripheral nerves are found in association with
blood vessels (neurovascular bundle). In this section, a small peripheral
nerve is labeled A.It is characterized by an outer covering of perineurium.
The dark nuclei visible within the cross section belong mostly to Schwann
cells. Neuronal cell bodies (perikarya) are not found within peripheral
nerves. The structure labeled Bis a small lymphatic vessel. Small lymphatic
vessels are characterized by a wall consisting only of an exceedingly thin,
single layer of endothelium. The lumen is usually larger than that of com-
parable venules. As observed in the photomicrograph, valves are also
present in lymphatic vessels. A small muscular artery (C)and comparable
vein(D)are also present in the field. The patient is diabetic with neuropathy.
Cardiovascular System, Blood, and Bone Marrow Answers 265