1. What kinds of molecules are hormones and how are they made?

• Hormones include proteins (insulin), and small peptides, steroids (progesterone, testosterone), eicosenoids (prostaglandins), and amines (epinephrine). (Eckert, Fig. 9-11-1), (Eckert, Fig. 9-11-2), (Eckert, Fig. 9-11-3), (Eckert, Fig. 9-11-4).
• Hormones are released from the cells they are made in by the process of exocytosis. (Eckert, Fig. 9-4a). This is a very complicated process, much more so than implied by the Fig. 9-4 in your textbook., involving docking of transport vesicles and fusion of the membrane of the vesicle and the external cell membrane.

2. What kinds of organs secrete hormones?

• Exocrine glands secrete fluids through a duct onto the body surface. These include sweat glands and the gall bladder. (Eckert, Fig. 9-9a)
• Endocrine glands secrete hormones into the circulatory system. (Eckert, Fig. 9-9b). Since the system producing these hormones is so important, the field of endocrinology became an important discipline in its own right. We offer a course in behavioral endocrinology in the Department of Biology.

3. The pituitary - the master gland.

• Neuroendocrine systems - Some neurons can manufacture and release hormones, which travel throught the bloodstream to some non-neuronal endocrine tissue, where another hormone is released into the bloodstream. This second hormone travels to the target tissue and causes some effect. (Eckert, Fig. 9-14)
• There are two important parts of the pituitary - the anterior and posterior pituitary.
• The anterior pituitary is a non neuronal tissue. Hormones (RH's and RIH's) are released from the hypothalamus, travel through blood vessels to a capillary bed in the anterior pituitary and diffuse out to the surrounding tissue. (Eckert, Fig. 9-15). The hormones from the hypothalamus either stimulate (RH's) release of hormones from the anterior pituitary or inhibit release (RIH's). (Eckert, Fig. 9-16)
• Some of the hormones released from the anterior pituitary have a tropic action - they travel through the bloodstream and have their action on other endocrine tissues. Examples are follicle stimulating hormone (FSH) and lutenizing hormone (LH), that act on the gonads. Other hormones, like growth hormone (GH) act directly on somatic non-endocrine tissues.

• The posterior pituitary is an extension of the brain and consists of neuronal tissue. (Eckert, Fig. 9-15) We will look at antidiuretic hormone (ADH, also called vasopressin because of its vasoconstrictive effect on blood vessels) and oxytocin as examples of hormones produced in cell bodies in the hypothalamus, and then travel down nerve axons, through the infundibulum, to be secreted into the bloodstream by the posterior pituitary.

  CASE STUDY: A human patient complains of urinating a lot. He wakes up frequently during the night to urinate. He complains of feeling thirsty a lot. As the physician, you ask a lot of questions. One question is if the patient has had any recent head trauma . You also ask if the patient is seeing a psychiatrist. You most carefully inquire if this person is spending a lot of time in bars. Finally, you order a blood glucose test . In class, we will investigate why we might be asking these questions. But, to arrive as some of the answers, let's look at ADH secretion by the hypothalamus. (Eckert, Fig. 9-17) Look carefully at this figure for important details that may be on an examination. Let's take care of the first three questions right now:

  • Head trauma can damage the hypothalamus and prevent ADH manufacture and thus its subsequent release.
  • Ethanol inhibits ADH release by the pituitary. ADH affects water reabsorption by the kidney. (We will discuss the mechanism briefly in class now, and then again later when we discuss the kidney.)
  • Lithium salts are often given as treatment for bipolar disorder (manic-depressive). Lithium blocks action of ADH on kidney tubules.

  Suppose our patient doesn't drink alcohol and doesn't take Lithium. It is possible that the person has neurogenic diabetes insipidus, in which ADH production has failed because of a head injury, an invasive tumor damaging the hypothalamus, or autoimmune distruction of the ADH-secreting neuron. Diabetes insipidus can give rise to polyuria, excessive urination, with as much as 20 l of urine per day! Of course, the cause of the increased urination might be due to some other disease process, including type I or type II diabetes mellitus, which we shall discuss shortly.

All text and images, not attributed to others, including course examinations and sample questions, are Copyright, 2008, Thomas J. Herbert and may not be used for any commercial purpose without the express written permission of Thomas J. Herbert.