Notice: This material is the copyrighted property of the author
and should not be reproduced without the author's permission.
The material on this page supplements that found in Chapter 5 of The Anatomy of Medical Terminology.
These notes are to be used cautiously, as they represent only the best understanding of a classicist with no training in medicine proper.Further medical information is given in the Etymological Notes under some individual entries.
The circulatory system (1-21) involves the movement of BLOOD (1-7), as pumped by the HEART (8-13), through a complex system of VESSELS (14-21); some important components of blood are provided by the LYMPHATIC SYSTEM (22-26), and one function of the blood system is to deliver the products of various GLANDS (27-40). In addition, blood circulation is vital to, and linked in complex ways with, the functioning of the respiratory, digestive and urinary systems (Chapters 6, 9 and 10 respectively).
I Cardiovascular System (1-21)
BLOOD (1-2) is a complex substance, carrying oxygen and nutrients to body tissues, and waste materials away from them; among the "carrying" components of blood are HEMOGLOBIN (3) and PLASMA (4). The blood cells which cause it to form CLOTS (5) are called thrombocytes or PLATELETS (6). The movement of blood is accompanied by a PULSE (7), or rhythmic contraction and expansion of certain vessels caused by the pumping action of the HEART (8); it is felt in those vessels which stem from the AORTA (9), one of the vessels by which blood leaves the heart, and the one by means of which it is circulated through most of the body's tissues.
Blood circulation (in which the blood moves in a kind of "figure-eight" pattern: from the heart to the lungs, back to the heart, from the heart to the rest of the body, back to the heart, and so on) depends upon the blood always moving in one direction only through each section of the heart and the vessels attached to it; this is accomplished by means of VALVES (10), which open when pressured from one side but close when the pressure comes from the other side.
The heart itself has two distinct parts, each functioning as a double-chambered pump. The two upper chambers receive blood, while the two lower ones, or VENTRICLES (11), pump it back out. More specifically, on the left side, oxygen-rich blood comes in from the lungs and is pumped out by the ventricle (through the aorta) to the rest of the body, while the right side receives the "used," de-oxygenated blood and pumps it to the lungs, where the carbon dioxide it has picked up during circulation is exchanged for oxygen. A thin, tough membranous sac, the PERICARDIUM (12) surrounds and protects the heart, the walls of which consist of muscle called the MYOCARDIUM (13).
Blood circulates through a complex, branching system of VESSELS (14-15) of three main types. The ARTERIES (16), stemming from the aorta, carry blood away from the heart, while the VEINS (17-18) carry it back. At their extremities, arteries and veins are very small, and these extremities are connected by means of systems of CAPILLARIES (19), tiny "hair-like" vessels through whose thin walls oxygen and nutrients are diffused out of the blood and into the cells of the body, while waste materials are diffused out of body cells and into the blood. Vessels are subject to various problems, one common one being when a vein becomes an abnormally twisted and swollen VARIX (20-21).
A secondary, quasi-circulatory, system is that which moves the LYMPH
(22), a colorless fluid which contains a type of white blood cells, through
LYMPH VESSELS (23) between body tissues and the blood stream. Numerous
LYMPH NODES (24), the largest of which is the SPLEEN (25-26), filter wastes
from the lymph and manufacture both white blood cells and antibodies.
The endocrine, or glandular SECRETION (27), system depends upon the circulation of blood for the delivery of the complex chemicals, or HORMONES (28), which are produced by various ductless GLANDS (29-30) and secreted directly into the blood. While the products of specific glands (31-40; presented in AMT roughly in order from the head down) are various and multipurposed, in each case the hormone causes specific effects in a particular "target organ," to which it is carried by the blood.
Thus the PAROTID GLANDS (33; located in front of and slightly below each ear), which have ducts through which they secrete saliva directly into the mouth, are not endocrine glands at all; they are by contrast exocrine glands, erroneously included at this point in AMT. Of the true endocrine glands, the functions of the PINEAL GLAND (31), within the brain, are ill-understood; an over-view of the functions of the other endocrine glands follows.
IV Functions of Specific Endocrine Glands
Called by some the "master gland," or "master switch," the peanut-sized PITUITARY GLAND (32), or HYPOPHYSIS, located under the brain, produces hormones which affect the production of at least three other glands (the gonads, the thyroid gland and the adrenal glands). In addition, it secretes other hormones which stimulate the growth of body tissues and the production of both milk and the pigment melanin, several hormones involved in regulation of urine production, one which stimulates uterine contractions during childbirth, and one which regulates blood pressure.
When stimulated by a hormone from the pituitary gland, the THYROID GLAND (34), located at the top of the windpipe and just behind the larynx (for which, see Chapter 6 below), itself produces an iodine-containing hormone which controls the rates of bodily chemical reactions and the rate of growth of sexual characteristics. Another hormone secreted by this gland acts in conjunction with vitamin D and a hormone produced by the PARATHYROIDS (35), four pearl-sized glands located in or near the corners of the thyroid, to regulate the body's use of calcium and phosphorus.
The THYMUS (36), near the heart in the centre of the upper chest, becomes vestigial or disappears after puberty. Before and during puberty, however, it affects certain lymphocytes (called "T cells" [from the first letter of "thymus"]) involved in the production of antibodies and the rejection of foreign tissue.
The grape-sized ADRENAL GLANDS (37-38), or SUPRARENAL GLANDS, located on top of the kidneys (for which, see Chapter 10 below), produce hormones (including adrenaline) which help to regulate the heart beat, the blood pressure and the working of muscles, as well as a number of steroid hormones which control certain bodily chemicals and their reactions; under stimulation from the pituitary gland, the adrenal glands also produce several sex hormones, estrogen and progesterone in women and androgens in men. Other sex hormones are produced by the GONADS (40), the ovaries in women, and the testes in men (for which, see Chapter 10 below).
Finally, insulin, a hormone which is required for the conversion of blood sugar into energy, is produced by the ISLETS OF LANGERHANS (39), small clusters of cells located in various parts of the pancreas (for which, see Chapter 10 below).
To top of page
To Chapter 5 of The Anatomy of Medical
Terminology