The details of the secretions and functions of the pineal gland are still not fully
understood. Apparently, they are associated with sexual drive and reproduction. At
least in lower animals, the pineal gland is influenced by the cumulative number of hours
of light passing into the eyes each day.
Section IV. THE THYROID AND PARATHYROID GLANDS
THE THYROID GLAND
a. Location and Structure. The thyroid gland is located around the trachea,
just below the larynx. It consists of two lobes, left and right. They are connected across
the front of the trachea by an isthmus.
(1) Thyroxin. The most important hormone produced by the thyroid gland is
thyroxin. Thyroxin affects the basal metabolic rate (BMR), the level of activity of the
body. Since iodine is an important element in the structure of thyroxin, the dietary
intake of iodine is very important. When the gland is not functioning properly, it may
become enlarged (goiter). Insufficient or excess thyroxin has serious effects on the
(2) Calcitonin. A second hormone of the thyroid gland is calcitonin. It is
involved with calcium metabolism in the body.
11-10. THE PARATHYROID GLANDS
On the posterior side of each thyroid lobe is a pair (2 + 2 = 4) of tiny bodies
called the parathyroid glands. The hormone of the parathyroid glands is
parathoromone. It is important in maintaining the calcium levels of the body. When
excess thyroid tissue is removed in surgery, the surgeon takes care not to remove the
Section V. THE PANCREATIC ISLETS (ISLANDS OF LANGERHANS)
11-11. LOCATION AND STRUCTURE
There are small groups of cells, known as islets, distributed through the
substance of the pancreas. These cells function independently of the pancreas and
produce their own hormones.