Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

304 CHAPTER 7
are carried by the seminal fluid. Inside each of the testes is a number of convoluted
seminiferous tubules whose inner surfaces are lined with a basement membrane consisting
of the germinal cells from which the sperm eventually develop. The germinal
cells give rise to the spermatogonia, which develop into primary spermatocytes. The
primary spermatocytes undergo a meiotic division that decreases their chromosomes
from the diploid number of 46 to the haploid number of 23 to become secondary
spermatocytes. These secondary spermatocytes undergo a second meiotic division
to become spermatids, which then develop into mature male gametes called spermatozoa.
Thus, four spermatozoa evolve from a single spermatocyte, and every one
of these spermatozoa is capable of fertilizing the female egg. The sole purpose of
the male reproductive system is to produce the male gametes, which are designed to
fertilize the female gametes. The germinal tissue in the seminiferous tubules forms
the most radiosensitive tissue in the male reproductive system. Sterility can result
from a dose of about 6 Gy (600 rads) to the basement membrane in the convoluted
seminiferous tubules. Male potency, however, is related to the testosterone levels in
the blood. A dose to the testes of about 30 Gy (3000 rads) or more is required in
order to shut down testosterone production in the testes.
The reproductive system in the female consists of two ovaries; the uterus, where
the fertilized egg develops into an embryo and then into a fetus; two fallopian tubes,
which lead from each ovary to the uterus; and the vagina. The ovaries contain several
thousand immature eggs, called oocytes, which are all present at the time of a female
infant’s birth. However, only several hundred will develop into mature eggs. The
oocytes undergo two meiotic divisions, as in the case of spermatogenesis. However,
in the case of oogenesis, only one mature ovum, the female gamete, is produced. In
contrast to the production of male gametes, which is a continuously ongoing process,
oogenesis is a cyclical process that is repeated about every 28 days. Whereas the male
reproductive system has finished its task with the production and ejaculation of
sperm, the female reproductive system is also designed to nurture and protect the
developing conceptus until it is ready to be born. The hormone progesterone is
secreted by the corpus luteum, which is formed in the ovary during the menstrual
cycle.
Sensory Organs and Tissues
The sensory organs and tissues include the eyes, ears, olfactory nerve endings in
the nose, the taste buds in the tongue, and the sensory nerve endings in the skin
for tactile sensations and for monitoring temperature. The eyes, skin, and ears are
of great interest in the practice of health physics and industrial hygiene because of
ionizing and nonionizing radiation, and noise-regulatory requirements.
Eye. The structure of the eye is shown in Figure 7-11. The optical system of the eye
includes those tissues that act together to focus a real image of the object on the
retina. The system includes the following:
1. The cornea—A transparent layer about 0.5 mm thick with a mean index of
refraction of 1.376. The anterior surface has a radius of curvature of about
7.7 mm, while the radius of curvature of the posterior surface is about 6.8 mm.
2. The aqueous humor—A clear, transparent, dilute solution (>99% water) of albumin,
globulin, and sugar; its index of refraction is 1.336.