Biomedical Engineering Reference
In-Depth Information
Urinary System and Adrenal Glands
The urinary system includes two bean-shaped unlobulated
kidneys, their ureters, the bladder, and the urethra (
Line-
back, 1933a
). The urinary system of nonhuman primates
generally resembles that of humans in development,
morphology, and function, although the left kidney is
generally caudal (inferior) to the right kidney
(
Figure 4.12C
) which is the reverse of humans. An addi-
tional difference from humans is seen in the kidneys
themselves, which are unipapillary in all nonhuman higher
primates except Ateles (
Straus, 1936
). This probably results
from displacement by the larger left lobe of the liver in
nonhuman primates. Details of the urethral openings are
included in the description of the perineum (see the section
“Perineal morphology” below).
The adrenal (suprarenal) glands (
Miller and Leonard,
1933
) are not part of the urinary system but are contiguous
with the superior poles of the kidneys and tucked caudal to
the diaphragm against the dorsal abdominal wall as in
humans. They are surrounded by fat of the renal fascia
which also surrounds the kidney. Their extensive associated
vascular and nerve supply is quite similar to that of humans.
(posterior) portion of the vagina to produce a deeper
posterior fornix (
Wislocki, 1933
). The blood supply to the
uterus includes extensive anastomoses between uterine and
ovarian arteries which follow courses similar to those of
humans.
The ovaries are oval or fusiform and lie on the posterior
layer of the broad ligament. Both ovulation and luteiniza-
tion are spontaneous. Many nonhuman primates are
seasonal breeders and thus the cycles of ovarian follicular
development are not year around as in humans.
As a general rule pregnancy in primate species results in
a single infant, although twinning is common in some New
World species. All primates have relatively long gestation
periods and well-developed, precocious neonates. Birth
occurs through ruptured membranes. The placenta and long
umbilical cord remain functionally intact until the neonate
begins to breathe. Fetuses which die before term are usually
aborted, although occasional cases of “mummified” fetuses
have been reported (
Mossman, 1977
). The fetal membranes
of anthropoids differ from those of other mammals
(including other primates) and include a hemochorial
villous placenta, a rudimentary yolk sac, and only a rudi-
mentary allantoic vesicle if it is present at all (
Luckett,
1974
).
Female Genital System
The female genital system includes paired ovaries and
uterine (fallopian) tubes (oviducts) whose medial ends
enter into a midline simplex uterus (
Figure 4.13
). (The
mammary gland is described above in the external
morphology of the thorax (see the section “External
morphology and position of organs” above).) The female
genital systems of all primates, both human and nonhuman,
are very similar but different morphologically from most
other mammals. In primates the female genital organs
(
Wislocki, 1932; Mossman, 1977
) undergo considerable
migration during development. In the nongravid adult they
are positioned caudally in the pelvis where they lie caudal
(inferior) to the peritoneal sac. The major ligaments of the
viscera are formed by reflections or folds of the perito-
neum. The degree of convolution of the uterine tubes varies
among species. The single midline uterus can be sub-
divided into a fundus, body, and cervix and although the
cranial aspect of the fundus may be indented by a midsag-
ittal groove, this is an external feature only (
Wislocki,
1933
). The uterus is not anteverted as in humans, but the
cervical canal itself contains a 90
angle between its cranial
one third and caudal two thirds (
Wislocki, 1933
). The
endometrium of the simplex uterus undergoes cyclic
changes in response to changes in hormonal levels associ-
ated with follicular development in the ovary. Some species
have visible menstrual cycle blood loss. The uterus has
a more vertical attitude relative to the vagina than in
humans, and the cervix protrudes further into the dorsal
Male Genital System
The male genital system includes a pair of testes, ductus
deferens, seminal vesicles, and bulbourethral (Cowper's)
glands as well as two single midline structures, the prostate
and urethra. The overall morphology of the spermatic cord
and male genital system in nonhuman primates is similar to
humans and most other mammals.
In the adult the testes are located in a scrotum outside
the body cavity. In all primates the testes descend into the
scrotum before birth or shortly thereafter (
Martin, 1990
).
Following this initial descent of the testes, there is
considerable variation between primate species as to
whether or not they stay in the scrotum prior to puberty. For
example, in young rhesus macaques the immature testes
actually ascend out of the scrotum and reenter the inguinal
canal to redescend nearer puberty (
Wislocki, 1933
). Once
puberty is passed the testes do not reenter the body cavity
and the inguinal canal collapses. In species with well-
defined nonbreeding seasons the testes of nonsexually
active adult males may ascend to the external inguinal ring
and the scrotum may contract. Conversely during the
breeding season testes volume may increase (
Sade, 1964;
Conaway and Sade, 1965
). Although spermatogenic
features are similar among all primates, the male repro-
ductive endocrinology of New World monkeys appears to
differ from that of other primates (
Luetjens et al., 2005
).
Ductus deferens enter the abdomen from each testis via
the inguinal canals and course medially caudal (inferior) to
