Section VI. THE ENDOCRINE SYSTEM
Within the body, in various localities are the glands of internal secretion
("ductless glands"). The substances secreted by these endocrine glands into the blood
are named hormones. Hormones are secreted in minute quantities since only a trace is
necessary to produce an effect. They reach different parts of the body in the
bloodstream and influence the activity of one or another organ or tissue. The glands
which produce hormones are: thyroid, parathyroid, adrenal, pituitary, sex glands,
pancreas (islet cells), intestinal glands, pineal gland, and thymus.
3-46. THYROID GLAND
The thyroid gland lies in the anterior region of the neck below the lower border of
the larynx. It consists of two lobes connected by a strip of tissues called the "isthmus."
The hormone secreted by the thyroid is thyroxin; its main function is to regulate
metabolism of the body.
3-47. PARATHYROID GLAND
The parathyroids are small round bodies, usually four in number, located in the
posterior border of the lobes of the thyroid gland. The hormone of the parathyroid gland
is parathormone. It regulates the calcium content of the blood and is related to the
general metabolic state of calcium in the body. This is of particular importance since it
influences the amount of calcium in certain tissues, bone formation, coagulation of
blood, maintenance of normal muscular excitability, and milk production.
3-48. ADRENAL GLANDS
The adrenal glands ("suprarenal glands") are two small bodies shaped like a
cocked hat on top of each kidney. They consist of an outer portion, the cortex, and an
inner portion, the medulla. The hormone secreted by the medulla is epinephrine
(adrenalin). It causes an increase in heart rate and blood pressure and a rise in the
sugar content of the blood. It enables the individual to mobilize the resources of the
body during emergency periods.
3-49. PITUITARY GLAND
a. Frequently this gland is called the hypophysis. It is a small oval mass, about
the size of a pea, situated in a bony depression of the middle cranial fossa known as the
sella turcica. It is composed of an anterior and a posterior lobe.