163.The answer is d.(Kumar, pp 65–68, 513–514. Kierszenbaum, pp
334–335. Junqueira, pp 75, 206. Kasper, p 337.)Endothelial cells synthesize
a number of antithrombogenic factors including plasminogen activator and
prostacyclin. Prostacyclin functions through cyclic AMP to inhibit throm-
boxane production by platelets (answer e).Endothelial cells synthesize the
basal lamina including type IV collagen. Fibroblasts synthesize type III col-
lagen(answer c).Serotonin is released from platelets and enteroendocrine
cells(answer b).Other endothelial cell functions include: secretion of
endothelin [the most potent vasoconstrictor (answer a)], plasminogen
inhibitor (a coagulant), and nitric oxide [NO, also known as endothelium-
derived relaxing factor (EDRF)]. Angiotensin-converting enzyme (ACE) on
the endothelial cell surface converts angiotensin I to angiotensin II (a potent
vasoconstrictor), but also serves as an inactivation enzyme (bradykininase)
for bradykinin, a vasodilator. Von Willebrand factor (factor VIII) is found in
Weibel-Palade granules localized in the endothelial cells of vessels larger
than capillaries. A deficiency of factor VIII leads to decreased platelet aggre-
gation and hemophilia.
164.The answer is d.(Kierszenbaum, p 323. Kumar, p 8. Junqueira, pp
198, 201, 217. Kasper, pp 213, 2131.)Atrial natriuretic peptide (ANP) is an
important diuretic and natriuretic molecule that is released from the atria
in response to atrial stretch and/or endothelin-1 stimulation. In the
absence of ANP, peripheral vasoconstriction increases due to the absence of
the ANP-induced relaxation of vascular smooth muscle and the increase in
aldosterone levels. Aldosterone increases Na+permeability of the luminal
membrane in the distal renal tubule and the activity of Na+pumps. The
increased salt causes water retention, expanded blood volume, and ele-
vated blood pressure. ANP would not be expressed in ANP knockout mice
(answer a).Excretion of urine [diuresis (answer b)] and sodium [natri-
uresis (answer c)], and capillary permeability (answer e)all decrease in
the absence of ANP. The main targets of ANP are the kidneys and vascular
smooth muscle. ANP decreases blood pressure due to a direct relaxation of
vascular smooth muscle. In addition, it increases salt and water excretion,
enhances capillary permeability, and inhibits the release or action of sev-
eral hormones, in addition to aldosterone, such as angiotensin II,
endothelin, renin, and vasopressin. The natriuretic effect results from a
Cardiovascular System, Blood, and Bone Marrow Answers 267