Webster's New World Medical Dictionary

Ventricular septal defect (VSD)
A
hole between the two bottom chambers,
the ventricles, of the heart that permits
oxygen-poor blood from the right ventri-
cle to mix with oxygen-rich blood from
the left ventricle.
•
Pulmonary stenosis
Narrowing of the
outlet to the pulmonary artery area with
an abnormal pulmonary valve impeding
blood flow from the right ventricle to the
lungs.
•
Right ventricular hypertrophy (RVH)
Thickening and enlargement of the mus-
cle of the right ventricle.
•
Overriding aorta
A case in which the
aorta overrides or straddles the wall (the
septum) between the ventricles, permit-
ting oxygen-poor blood to flow through
the VSD into the aorta.
Open-heart surgery is done on patients with tetral-
ogy of Fallot in infancy or early childhood.
Untreated tetralogy of Fallot is usually fatal before
age 20. With open-heart surgery, the patient has an
excellent chance of survival.
tetraphocomelia–thrombocytopenia syn-
drome
See 
TAR syndrome.
testicle
418
21_189283 ch20.qxp 4/18/08 10:19 PM Page 418
http://www.rashidislamiccenter.com
http://www.allofislam.com/

---

tetraploid
Having four full sets of chromosomes: 4
copies of each autosomal chromosome plus 4 sex
chromosomes. In humans, tetraploid is equal to 92
chromosomes.
T-4 cell
A T cell that expresses the CD4 trans-
membrane glycoprotein (CD4+ T cell). T-4 cells are
active in the body’s immune response, helping to
turn on this system when it is challenged by an
infection or by foreign matter in the body. HIV
attacks T-4 cells, knocking out the body’s ability to
defend itself against infections. T-helper cells fall
into two main classes: those that activate other T
cells to achieve cellular inflammatory responses;
and those that drive B cells to produce antibodies in
the humoral immune response. These two classes of
response are generally incompatible with one
another and require coordination by substances
called cytokines to promote one response while
dampening the other. Also known as T-helper cell
and TH cell. See also 
CD4; T cell.