secretion which is absorbed by the blood and lymph streams. This material, derived from the circulation, is changed within the gland by some unknown phenomena and secreted by the cells of the ductless glands to be taken into the blood and lymph direct, and thus aid in promoting the metabolism of the body. They possess no ducts. The Thyroid Gland. — This is a very vascular organ, situated at the front of the neck, overhanging the upper rings of the trachea and laterally extending as high as the oblique line on the alse of the thyroid cartilage, and as low as 1 inch above the upper border of the sternum, when the head is extended. It weighs about 1 ounce; slightly heavier in the female. It has three lobes — two lateral connected by an isthmus ; and one third or middle lobe. It is firmly attached to the cricoid cartilage and posterior fascia of the trachea by two lateral or suspensory ligaments and its lobes and isthmus are enclosed within a fibrous capsule derived from the pretracheal portion of the deep fascia of the neck. The isthmus lies on the second and third ring of the trachea, and measures about J inch in breadth and depth. The functions of the thyroid are not thoroughly understood. It is an established fact, however, that when the gland is secreting more or less than the normal quantity, changes in development arise as a result of some physiologic disturbance interfering with the general metabolism of the body; as cretinism, a condition occurring in infants and children as a result of a congenital absence or arrested development of the gland; myxedema, a condition (occurring in adults) of the skin in which it becomes thickened, giving rise to a change in the patient's expression, due to the face becoming broader, swollen, and flattened. The mind is dull, the subject is almost idiotic as regards the mental condition. Myxedema is due to atrophy or some pathologic change taking place in the gland which interfered with its normal secretion; removal of the gland by operation gives rise to a similar condition, called cachexia strumipriva; an increase in the secretion from the thyroid gland causes a condition characterized by protrusion of the eye-balls — the patient's expression is staring and frightened — palpitation of the heart and enlargement of the gland, termed exophthalmic goitre or Graves' disease. An enlargement of the thyroid gland, which is gradually progressive, can be seen in the necks of people living in or coming from certain localities where the diseased condition is due to the drinking water containing lime; this is termed ordinary goitre. The Parathyroid Glands. — These are small, reddish-brown bodies, composed of masses of cells, arranged in a more or less reticular manner with numerous intervening bloodvessels. They are usually found one on either side (the superior) at the level of the lower border of the cricoid cartilage, behind the junction of the pharynx and esophagus, and in front of the prevertebral fascia. The lower are just below the lower edge of the lateral lobe one on either side. There are usually four, but may be only three, or again, as many as six or eight. Their location is variable. The functions of the parathyroids have not been sufficiently established to warrant a description within these pages. However, their removal from animals has given rise to tetany, characterized by spasmodic contractions and paralyses of certain groups of muscles, convulsive seizures, and death. Spleen. — The spleen is the largest of the ductless glands. It is found in the left hypochondrium, entirely surrounded by peritoneum, except around the hilum, which attaches it to the fundus of the stomach (the gastrosplenic omentum). It is purplish in color, oblong, flattened, tetrahedral form, soft, of a very friable consistency, and highly vascular. It measures 5 inches in length, 2 to 3 inches in width, and 1 to IJ inches in thickness at the centre. It weighs 6| ounces, 20 The spleen is attached to the stomach by the gastrosplenic omentum. The lienorenal ligament is a peritoneal fold, which attaches it to the upper pole of the left kidney, and the phrenocolic assists to support it by its attachment to the diaphragm. The spleen when seen under the microscope shows a capsule of fibrous tissue which sends off slips or trabeculae from its under surface; these spread out and form a connective-tissue supporting frame-work for the contents of the organ, which consists of a dark red semifluid mass called the splenic pulp, filling the spaces between the fibrous tissue. Microscopically the splenic pulp is seen to consist of adenoid tissue, rich in leukocytes or white-blood cells, arranged in small groups throughout the pulp, called Malpighian corpuscles; red corpuscles are also present in the pulp. The Functions of the Spleen. — Owing to the numbers of red cells seen in the splenic pulp undergoing all stages of disintegration, it has been concluded that the spleen aids in the destruction of red cells; another theory is based on the presence of the large quantity of white cells within the Malpighian corpuscles, that the spleen is the chief centre for the production of white cells, and thus contributes to the formation of the blood. The spleen is larger in childhood than old age; it is enlarged during and after digestion. In typhoid fever and malaria a marked increase can be noted; I . . . also in various blood diseases. Thymus Gland. — The thymus gland is a temporary organ, attaining its full size at the end of the second year and gradually shrinking until puberty, when it entirely disappears. Consists of two lateral lobes placed in close contact along the median line. It is found in the superior mediastinum, covered by the sternum and the origins of the sternohyoid and sterno- thyroid muscles; below, it rests upon the pericardium, niul separated from the arch of the aorta and great vessels by fascia. In the neck it lies on the front and sides of the trachea beneath the sternohyoid sternothyroid muscles. Suprarenal Glands. — The suprarenal glands are two flattened bodies, of a yellowish color, found in the epigastrium, lying behind the peritoneum, and above and in front of the upper extremity of each kidney. They are triangular in shape, H to nearly 2 inches in length, less in width, and J of an inch in thickness. The Functions of the Suprarenal Glands. — They secrete a substance, termed adrenalin (takamine, Aldrich) or epinephrin (Abel), which is absorbed by the blood, and stimulates to increased activity the muscle fibers of the heart and arteries, and thus aids in maintaining the normal blood-pressure. Disease of the suprarenal glands causes a bronzing of the skin and mucous membranes with disturbances of nutrition, muscular weakness, and anemia. Gradu- ally the heart becomes weak; the pulse is soft and feeble, indicating a general reduction in blood-pressure from interference with the secretion of the active physiologic material from the cells of the gland. Addison's disease is the name applied to this condition, as he first described the disease. The Pituitary Body (Hypophysis). — The pituitary body is a small glandular body situated at the base of the brain, lodged in the sella turcica of the sphenoid bone. It is divided into an anterior and posterior lobe; the former is reddish in color, is larger than the posterior lobe, and is derived from an invagination of the epiblast of the mouth cavity, and shows micro- scopically gland tissue; the posterior lobe is yellowish gray in color, and represents an outgrowth from the brain. It is connected by a thin slip to the infundibulum. The functions of the pituitary are still under inves- tigation; however, it has been proved by experiment that an injection of the extract made from the internal secretion of this gland will cause an increase in the force of the heart-beat and a rise in blood-pressure by stimulating the arterioles. According to Howell, the extract given intravenously from the posterior lobe will cause a rise in blood-pressure and slow the heartbeat, the extract from the anterior lobe being negative as to its effect on the circulatory and respiratory organs. Disease of the pituitary body will give rise to the condition of acromegalia, in which there is a marked enlargement of the bones of the face and extremities. When diseased in early life it is respon- sible for the progressive changes, characterized by extreme growth of the body, termed gigantism; also a marked increase of fatty tissue. Carotid Glands. — The carotid glands or bodies are small reddish-brown bodies, oval in shape, their long diameter measuring i of an inch. They are found in the cervical region, at the bifurcation of the common carotid artery into the internal and external carotid trunks. Coccygeal Gland. — The coccygeal gland or body, or Luschka's gland, is as large as a millet-seed, found at the tip of the coccyx. It is connected with middle sacral artery. QUESTIONS 1. Give the difference between an external and internal secretion. 2. Name some of the external secretions. 3. How are secretions utilized by the tissues of the body? 4. Name the secreting membranes of the body. 5. Name the organs of internal secretion. 6. Give the general arrangement of the structures seen in a secretory gland. 7. By what structure does a secreting gland communicate with a membrane upon which its secretion is poured out? 8. What part does the nerve system play in regard to gland secretion? 9. What is excretion? 10. Describe the structure of a mammary gland. 11. Is human milk alkaline or acid in reaction? 12. Does milk contain oil globules? QUESTIONS 309 13. How much milk is secreted every day by the mammary glands in a healthy woman? 14. Give the chemical composition of milk. 15. How does woman's milk differ from cows' milk? 16. What is colostrum? Give its function. 17. Which is the largest gland of the body? 18. How much does the liver weigh? 19. How many lobes has it? 20. What structures pass out of and enter the transverse fissure of the liver? 21. Give the location of the liver in the abdominal cavity. 22. What is the serous membrane surrounding the liver called? The fibrous capsule? 23. What microscopic structures are seen in the liver lobules? 24. Name the functions of the liver. 25. How is glycogen formed? Where is it stored in the body chiefly? 26. Is urea a waste product resulting from metabolism? Which organs excrete it? 27. What is the function of the gall-bladder? Name its duct. 28. Where is it located? 29. What ducts form the common bile duct? 30. Where does the common bile duct drain? 31. How long is the cystic duct? The common bile duct? 32. To which variety of glands does the pancreas belong? 33. Give the dimensions of the pancreas. 34. Name the duct of the pancreas. Which portion of the duodenum does it open into? 35. What is the opening in the duodenum for the common bile and pancreatic duct called? 36. How does the pancreatic secretion leave the pancreas? 37. Name the organs of internal secretion. 38. Which one of the ductless glands is the largest? 39. Give its dimensions and weight. 40 How is the spleen attached to the stomach? The left kidney? The diaphragm? 41. Where are the suprarenal glands located in the abdominal cavity? 42. Name their functions?
Key Takeaways
- The thyroid gland's role in metabolism and its effects on development, such as cretinism and myxedema.
- The functions of the spleen include destruction of red blood cells and production of white blood cells.
- Suprarenal glands secrete adrenalin (epinephrin) which affects heart activity and blood pressure.
Practical Tips
- Understand the importance of maintaining proper thyroid function to avoid conditions like cretinism or myxedema.
- Recognize signs of spleen enlargement, such as in typhoid fever, and seek medical attention if necessary.
- Be aware that adrenal gland dysfunction can lead to serious health issues including Addison's disease.
Warnings & Risks
- Do not attempt to self-diagnose or treat thyroid conditions without professional medical advice.
- Avoid ignoring symptoms of spleen enlargement as they may indicate underlying diseases like typhoid fever.
- Recognize the critical role of adrenal glands in maintaining blood pressure and seek immediate care if experiencing related symptoms.
Modern Application
While many of the specific glandular functions described in this chapter are still relevant today, modern medicine has advanced our understanding of these processes. For instance, the thyroid's role in metabolism is well-established, but new treatments for conditions like hyperthyroidism and hypothyroidism have been developed. The knowledge of the spleen's function in blood cell destruction and production remains crucial for diagnosing and treating various diseases. However, modern diagnostic tools and treatment methods provide more precise and effective care.
Frequently Asked Questions
Q: What are the functions of the thyroid gland?
The thyroid gland is very vascular and situated at the front of the neck. It has three lobes: two lateral connected by an isthmus, one middle lobe. The gland's function is not fully understood, but it can cause conditions like cretinism in infants or myxedema in adults when its secretion is abnormal.
Q: What are the symptoms of a diseased spleen?
A diseased spleen may be enlarged due to various reasons such as typhoid fever. Symptoms include a broader, swollen face and changes in mental condition. If you notice these signs, it's important to seek medical attention.
Q: What is the function of the suprarenal glands?
The suprarenal glands secrete adrenalin (epinephrin), which helps maintain normal blood pressure by stimulating muscle fibers in the heart and arteries. Their dysfunction can lead to conditions like Addison's disease, characterized by a bronzing of the skin and anemia.