Endocrine glands

The pituitary gland, or hypophysis, is known to secrete some major hormones (e. g. antidiuretic hormone, growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, lipotropins, prolactin) that directly regulate numerous body functions and the secretory activity of several other endocrine glands. The hypothalamus of the brain regulates the secretory activity of the pituitary gland, and, in turn, the activity of the hypothalamus is influenced by the central nervous system, and by the emotional state of the individual. The hypothalamus and pituitary gland are the major sites in which the two regulatory systems of the body (the nervous and endocrine systems) interact. Indeed, a major portion of the pituitary gland (the posterior pituitary) is an extension of the hypothalamus. As for pituitary gland, it is roughly 1 cm in diameter and weighs 0.5 to 1 g. The pituitary gland is located inferior to the hypothalamus. It is divided functionally into two parts (posterior pituitary gland and anterior pituitary gland).

The thyroid gland is composed of two lobes connected by a narrow band of thyroid tissue. The lobes are lateral to the upper portion of the trachea just inferior to the larynx. The thyroid gland is one of the largest endocrine glands with a weight of approximately 20 g. It is highly vascular and appears redder than its surrounding tissues. The thyroid hormones include both triiodothyronine (T3) and tetraiodothyronine (T4); T4 is also called thyroxine. These substances constitute the major secretory products of the thyroid gland, with 10% T3 and 90% T4. Thyroid hormones bind with intracellular receptor molecules and initiate new protein synthesis.

The adrenal glands are near the top of each kidney. Like kidneys, they lie posterior to the parietal peritoneum and are surrounded by adipose tissue. They are enclosed by a connective tissue capsule and receive a well-developed blood supply. The adrenal glands are composed of an inner medulla and an outer cortex, which are derived from two separate embryonic tissues. Unlike most glands of the body, which develop from epithelial tissue, the adrenal cortex is derived from mesoderm. The adrenal medulla is a component of the autonomic nervous system and secretes two types of hormones: epinephrine (adrenaline), 80%, and norepinephrine (noradrenaline), 20%. The adrenal cortex secretes three hormone types: mineralocorticosteroids, glucocorticoids, and sex hormones. All are similar in structure in that they are steroids, highly specialized lipids that are derived from cholesterol.

The pancreas lies behind the peritoneum between stomach and the duodenum. It is elongated structure approximately 15 cm long. It weighs 85 to 100 g. The head of the pancreas lies near the duodenum, and its body and tail extend toward the spleen. The pancreas plays a key part in the digestive process, producing enzymes essential to the digestion of food. The pancreas is both an exocrine gland and endocrine gland. The endocrine portion, consisting of pancreatic islets (islets of Langerhans), produces hormones that enter the circulatory system. Each islet is composed of alpha cells (20%), which secrete glucagons, beta cells (75%), which secrete insulin, and other cell types (5%). The remaining cells are either immature cells of questionable function or delta cells, which secrete somatostatin.

Ex. 27. Insert the missing words from the box:

1. The _ secretes at least nine hormones that regulate numerous body functions and other endocrine glands. 2. The hypothalamus _ pituitary gland activity through neurohormones. 3. The _ is just inferior to the larynx. 4. Thyroid hormones increase the rate of glucose, fat, and protein metabolism in many tissues, thus increasing body _. 5. Normal growth of many tissues is dependent on _ hormones. 6. The adrenal glands are near the superior pole of each_. 7. The adrenal cortex is derived from _. 8. Norepinephrine stimulates cardiac muscle and causes constriction of most peripheral _ vessels. 9. The adrenal _ hormones prepare the body for physical activity. 10. The pancreas is located along the small _ and the stomach. 11. It is both an _ and endocrine gland. 12. The endocrine portion of pancreas _ the pancreatic islets.

thyroid gland; exocrine; regulates; consists of; thyroid; mesoderm; blood; medulla; temperature; pituitary gland; kidney; intestine.

Ex. 28. Answer the following questions:

1. What hormones of the pituitary gland do you know? 2. What is the major function of the pituitary gland? 3. Where is the pituitary gland located? 4. What is the thyroid gland composed of? 5. What thyroid hormones do you know? 6. What do thyroid hormones initiate? 7. Where are the adrenal glands located? 8. What are the adrenal glands composed of? 9. What hormones does the adrenal cortex secrete? 10. What does the pancreas consist of? 11. What is the major function of the pancreas?

Ex. 29.Pick up correct statements (true or false choice):

1. As a group, endocrine glands are concerned with the regulation of metabolic processes. 2. Exocrine glands secrete hormones. 3. Hormone is carried to its target cells by body fluid. 4. Endocrine glands do not secrete hormones that affect target cells possessing specific receptors.

Ex. 30. Retell the text “Endocrine Glands”.

Ex. 31. Pronounce and translate the following terms to the theme studied:

Minute [maI'nju:t] amount; interstitial ["Intq:'stISql] space; fuel [fjuql]; starchy ['sta:CI] food; potassium [pq'txsIqm]; sodium ['squdjqm]; the rate of chemical activity; distinct [dIs'tINkt] hormones; prompt [prOmpt]; urine output ['autput].

Ex. 32. Read the following text, make up a plan, and speak on the functions of hormones: