b. Testes (Male). The testes, located in the scrotum, secrete testosterone. The
testes of a fetus secrete testosterone to stimulate the development of the male
anatomy. After birth, the testes become dormant and remain so until puberty when
testosterone is secreted once again and stimulates the development of secondary male
sex characteristics, including enlargement of the male sex organs; growth of facial,
pubic, and chest hair; growth of the larynx to deepen the voice; and disposition of
protein to increase muscularity and general body size.
The islet cells of the pancreas produce the hormone insulin, which is essential for
the transfer of sugar from extracellular fluids into cells.
3-52. INTESTINAL GLANDS
The duodenum supplies a hormone called "secretin," which causes the intestinal
juices to flow whenever food reaches the intestines. The liver and spleen are also
believed to supply hormones to the blood.
3-53. PINEAL GLAND
The pineal gland is a small gland posterior to the third ventricle of the brain. It
exerts an influence on the rate of growth and the commencement of puberty.
The thymus is a temporary organ located partly in the neck and thorax. It is large
in infancy and shrinks as the individual matures. The thymus plays an important role in
the development of the lymphatic system and production of lymphocytes in the fetus
and infant. It secretes hormones that activate lymphatic tissue.
Section VII. THE SPECIAL SENSES
The specific adaptation of certain structures in the body permits reception of
stimuli and their subsequent transformation into sensation. In the designated areas of
the cerebral cortex, these stimuli are converted into conscious processes. The skin and
underlying connective tissue contain receptors for pain, temperature, and touch. Other
receptors are located in muscles, tendons, the tongue (taste buds), the nose (olfactory),
the retinas of the eyes (visual), the cochleae of the ears (hearing), and the labyrinths of
the ears (equilibrium). The parts of the sensory mechanism are the sense organ
receptors, the pathways by which the messages are conducted into the central nervous
system, and the sensory centers in the central cortex. The special senses include
smell, taste, sight, and hearing.