tissue and surgery to remove the plaque. A key
risk of either procedure is ERECTILE DYSFUNCTION
(inability to obtain erections). Generally these
treatments are most appropriate when the con-
tracture completely prevents sexual intercourse.
See also CHORDEE; PARAPHIMOSIS; PHIMOSIS; PRI-
APISM.
phimosis A condition in which the foreskin
becomes fused to the glans of an uncircumcised
PENISand will not retract. Phimosis occasionally
occurs as a congenital condition (present at birth)
though more often develops later in life, typically
as a consequence of poor PERSONAL HYGIENE. Phi-
mosis is the leading cause of BALANITIS, a fungal
INFECTIONof the inner surface of the foreskin, and
can interfere with URINATIONand cause PAINwith
ERECTION. Recurrent phimosis increases a man’s
risk for CANCER OF THE PENIS.
The doctor is sometimes able to gently free the
adhered foreskin after anesthetizing the penis.
Frequent retraction of the foreskin and diligent
cleansing are necessary to prevent phimosis from
recurring. When this is not effective or phimosis
becomes chronic, the recommended treatment is
CIRCUMCISION, an OPERATION to surgically remove
the foreskin. Though in some men an unusually
tight foreskin (congenital phimosis) is the primary
cause of phimosis, diligent personal hygiene can
prevent most phimosis. It is important for uncir-
cumcised boys and men to clean beneath the fore-
skin every day by retracting the foreskin, washing
the glans gently but thoroughly to remove any
accumulated secretions, and allowing the foreskin
to return to its natural position.
See also CHORDEE; CONGENITAL DISORDERS; PARAPHI-
MOSIS; PEYRONIE’S DISEASE.
placenta An organ of PREGNANCYthat nourishes
and sustains the FETUS. The placenta also secretes a
number of hormones that maintain the biochemi-
cal environment within the woman’s body to sup-
port the pregnancy. The placenta develops within
the first two weeks after the blastocyst implants
into the endometrium of the UTERUS, arising from
the outer layer of the blastocyst’s cells, the tro-
phoblast. The amniotic sac, which encloses the
developing fetus, and the UMBILICAL CORDalso arise
from the trophoblast.
PLACENTAL HORMONES
activin chorionic adrenocorticotropin
CHORIONIC GONADOTROPIN chorionic somatomammotropin
CORTICOTROPIN-RELEASING CORTISOL
HORMONE(CRH) ESTROGENS
GONADOTROPIN-RELEASING GROWTH HORMONE–RELEASING
HORMONE(GNRH) HORMONE(GHRH)
INHIBIN placental actinogen
PROGESTERONE PROLACTIN
RELAXIN THYROTROPIN-RELEASING HORMONE
(TRH)The placenta uniquely belongs to both the
mother and the fetus. Though the maternal BLOOD
circulation delivers NUTRIENTSand oxygen to the
fetal blood circulation and carries away fetal
wastes, the two circulations do not normally mix
with each other. The side of the placenta that faces
the fetus is the chorion. Fringelike extensions
called the chorionic villi permeate the tissue of the
maternal portion of the placenta. Fetal blood cir-
culates through the chorionic villi. Arterioles (tiny
arteries) and venules (tiny veins) extend from the
myometrium (muscular wall of the uterus) into
the spaces between the chorionic villi. The arteri-
oles carry maternal blood into the spaces where it
circulates around the chorionic villi. Nutrients,
oxygen, and wastes pass across the thin mem-
branes that enclose the chorionic villi.
Problems that can arise with the placenta dur-
ing pregnancy include- placenta abruptio (also called placental abrup-
tion), in which the placenta partially or com-
pletely separates from the uterus; partial
separation reduces nutrition to the fetus and
complete separation is fatal to the fetus - placenta accreta, in which the tissues that
anchor the placenta to the wall of the uterus
penetrate the myometrium too deeply, making
it difficult for the placenta to separate after
birth - placenta previa, in which the placenta grows
partially or completely across the CERVIX, neces-
sitating CESAREAN SECTION to prevent hemor-
rhage during labor
After the fetus is born a second round of con-
tractions separate the placenta from the uterineplacenta 319