Mader/Inquiry into Life, 9/e

Lecture Enrichment Ideas - Chapter 19

20.1. How Hormones Work

Quantity and duration are important considerations with hormones. An observant student may inquire if a person gets a dosage of hormones in a blood transfusion. A male who receives a blood transfusion from a female donor does get some additional estrogen in the plasma but the quantity of blood is a small proportion of his total blood volume, and this diluted hormone level is not sustained.

Blood-borne hormones wash throughout the body and are recognized by target tissues only as they "pass by." Stress that there is no intent or "purposefulness" in the movement of chemicals by physical properties. However, the close placement of endocrine organs to target tissues can speed the process.

20.2. Hypothalamus and Pituitary Gland

Classes generally covered organ systems organ-by-organ as if they were distinct operators on an assembly line. However, many organs must coordinate with others and hormones are a major part of this coordination. Query students what would happen if the gall bladder didn't "know" when fat was moving onward from the stomach, or the production of breast milk was not in some way associated with the contractions of the uterus in childbirth.

Why is the hypothalamus and pituitary buried so deep and protected at the base of the brain? Why have so many critical functions controlled from this one center?

20.3. Thyroid and Parathyroid Glands

Students may have seen huge laboratory rats with growth hormone irregularities. There are a growing number of U.S. students and professors who are heavier than average, but otherwise "normal." What symptoms would be expected if this obesity was hormonal?

A network newscaster reporting immediately after the Chernobyl nuclear plant disaster reported that citizens in northern Europe were taking iodine tablets "...to prevent radioactive iodine fallout from entering their body." The newscaster got the reason wrong; students who understand the use of iodine by the thyroid for synthesis of hormones, and the limited number of receptor sites, and the excretion of surplus substances by the kidney, should be able to identify this error.

20.4. Adrenal Glands

Embryologically, the adrenal medulla is differentiated from tissues similar to nerves. Query students on whether this makes sense, considering the function of the adrenal medulla hormones.

Cortisone has anti-inflammatory action and is useful for reducing deep inflammation, as in Bell palsy, etc. Yet the dosage is given rapidly and for only a brief time. Why would a physician not want to boost cortisone levels over a long time?

20.5. Pancreas Is Both Endocrine and Exocrine Gland

Students sometimes deduce wrongly that eating lots of sugar makes a normal person diabetic. You may wish to lead students through a review of the compensating mechanisms involved while cavalierly eating several candy bars. It is also possible to carry in a urine sample and test for sugar in urine, although test results are visual but not easily projected on a screen, and must be reported by eyesight. Adding sugar to a normal sample can convert the test. Query why the medical lab wants a patient to abstain from eating eight or more hours before a blood sample is taken.

20.6. Other Endocrine Glands

Many secondary sex characteristics can be explained in terms of the beef industry for students in the Plains and Midwestern regions. Steers (castrated before they matured into bulls) lack the heavy shoulder musculature, have meat that has more fat marbling, and are much more manageable.

Estrogen is also produced in fat tissue that provides a base level that the ovaries add onto to reach a critical level to trigger a uterine cycle. Students will be aware of this from female Olympic athletes who reduce fat tissue and turn off their menstrual cycles. However, this also occurs during famine when a pregnancy would put the mother at risk of losing nutrients to the developing fetus. Query students on the evolutionary advantage of such a mechanism of placing hormonal control in these two tissues.

20.7. Environmental Signals

"Tales of the Limberlost" by Gene Stratton Porter relates the authentic story of a pioneer girl who captured a newly emerged female moth and placed it inside a cage in her log cabin, only to awake to find the cabin full of male moths who could not reach the female.

It is possible to suggest to students that they can also "play" with a trail of ants to experimentally determine the direction of their nest, food source, etc., and determine the nature of the communication by placing a paper on the trail, then twisting it after a trail has been laid across, etc. No less than the great physicist Richard Feynman played such pheromone games with ants in his college room; see "Surely You're Joking, Mr. Feynman" for a potential class reading.

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