fter drinking all that water, soft drinks, and other beverages, the volleyball players needed to take periodic “potty breaks.” Their kidneys filtered any excess water from their blood streams and sent it to their bladders to await release. Because ethanol (the alcohol in alcoholic beverages) interferes with secretion of a hormone called antidiuretic hormone (ADH), the kidneys of anyone who consumed beer to quench his/her thirst removed more water than they normally would have.

Excretory (Urinary) System

The excretory system consists of the kidneys, ureters, bladder, and urethra. The excretory system removes excess water (liquid waste) and nitrogenous waste left over from metabolism of amino acids. Please note that the excretory (urinary) system is not involved in elimination of solid waste – that is part of the job of the digestive system.

As amino acids are broken apart, the amino group is converted to ammonia (NH₃). In aquatic animals such as fish, that ammonia can be directly eliminated from their skin into the water. In most terrestrial animals where water loss is a major concern, the ammonia is converted to uric acid, which is not water-soluble, and eliminated in that form (that’s the white “goo” in bird droppings). In humans and other animals where water loss is not as big of a concern, the ammonia is converted to water-soluble urea, and eliminated in that form.

Any substance which promotes/stimulates the production and elimination of urine is called a diuretic. A variety of synthetic diuretics are prescribed for people with high blood pressure, with the thought that elimination of water will decrease blood volume, and therefore blood pressure. Our bodies produce a hormone called antidiuretic hormone, which has exactly the opposite effect. Antidiuretic hormone (ADH) is secreted by the pituitary gland (located just under the brain) and travels, via the blood, to the kidneys. ADH is part of a negative feedback loop which helps to maintain homeostasis of blood volume/concentration. Typically, ADH is secreted in response to low blood volume (high concentration) to tell the kidneys to not filter and excrete water. Secretion of ADH is inhibited by ethanol, and thus, consumption of alcoholic beverages will increase the amount of water a person’s kidneys eliminate. The more alcohol that is consumed, the more water is eliminated, to the point where a person who consumes a large quantity of alcohol can become dehydrated, possibly even to the point of needing to be hospitalized or of dying.

There are several other molecules that are filtered and removed by the excretory system, including various salts. Since another part of the kidneys is able to reabsorb many of the salts, etc. that were, initially, filtered out, what actually ends up in the urine is, again, a matter of homeostasis, and only what is actually “excess” will be eliminated. Because our bodies burn sugar for fuel, that is a “good” molecule that the kidneys, typically, do not filter out, even if the blood sugar level is a little bit high, and there should never be sugar in a person’s urine. However, if the blood sugar level rises “dangerously” high, the kidneys will begin to filter sugar, too, and put that into the urine. Thus, in the “old days” before all the convenient medical tests and analyses we have now, doctors used to diagnose diabetes by tasting(!) urine – if it tasted sweet, that indicated the presence of sugar in it, thus the person had “diabetes mellitus” (dia = across, through; bainein, badis = to go, walk, step; thus diabetes = a siphon + mel = honey; thus mellitus = honey, honeysweet). The “diabetes” part of the name refers to the fact that a diabetic is often very thirsty (the body’s attempt to dilute all the excess sugar in the blood by adding water), yet the kidneys typically filter and remove all that excess volume of water, so the person typically voids a larger-than-normal amount of urine. The “mellitus” part of the name refers to the sweet taste of the urine.

Background Information

Links to Related Information on Our Web Server

The following Web pages contain information related to the excretory system.

Bio Lecture Excretory System

Information on the functioning of the kidneys and elimination of nitrogenous wastes – not to be confused with the digestive system’s function of eliminating solid wastes

Your Assignment
Research a Disease or Disorder

There will be only one, combined assignment for this week’s topics (skeletal, immune, and excretory systems). Thus even though this will appear on each of those three pages to remind you, you only need to do it once. Pick a disease or disorder that affects humans, and do library and/or Web research to find out more about that disease (see below). Suggestion: get in touch with your classmates via e-mail (addresses available from the Check Grades (and Class E-Mail List) Web page) to find out what each other are doing so everybody doesn't do the same thing. As a suggestion, it seems like AIDS is almost “overdone,” these days – it might be more interesting to pick something a bit more “unusual.” If you’re looking for ideas for “different” sorts of things, a few things that come to mind include Hansen’s disease, androgen insensitivity syndrome, scurvy, kuru, beriberi, hemophilia, malaria, sickle-cell anemia, syphilus, bubonic plague, mononucleosis, human papilloma virus, etc., etc. Malaria has recently become a “hot topic.” A couple of Web sites which may be of use include The Merck Manual Online and OMIM Home Page (OMIM deals specifically with genetic conditions). The grading criteria for this assignment are given below, and you should also refer to those as you work on the assignment. A total of 30 points is possible.

For the disease or disorder you have chosen:
1. As you research this condition, if you find any other good Web sites with general information, please record their URLs so we can share them with other students
2. What causes that disease/disorder? Is it caused by a disease organism (virus? bacterium?) or is it genetic or accidental or . . . ?
3. How/when was this disease/disorder “discovered” or categorized/described? By whom?
4. What is the primary/main body system that it affects, and how does it affect that system – what “problems” does it cause?
5. What other systems of the body are affected, and how? How does it all “fit together?” (For example, given what you’ve learned about diet/nutrition, how might having a broken bone affect the functioning of your immune system?)
6. What are the signs and symptoms of that condition (Hint: do you know the “official” difference between “signs” and “symptoms”?)
7. How is this condition diagnosed? Is it “obvious” or are any tests run to determine if someone has it (if so, what kind of tests)?
8. How is this condition treated/managed? Does eating a good diet or some kind of special diet help? If a person is given drugs for this condition, can you find out anything about those drugs – are they addictive, are there any side-effects, are there any major drug interactions with other drugs the person may be taking? If surgery is involved, how complicated is the surgery and what is the “success rate” of that surgery?
9. Is this something permanent that requires ongoing treatment, or is this something from which a person will recover? (For example, while a person usually recovers from mono or chicken pox or cold sores, all of these stay permanently in the person’s body.)
10. Is there any interaction between this disease/disorder and any other conditions present in a person’s body? (For example, sickle-cell decreases susceptibility to malaria and hypertension increases chances of stroke.)
11. Is it contagious? If so, how is it spread? How likely is it that a person could get this from someone else? Can it cross the placenta and affect an unborn baby? (For example, both rabies and German measles can do that.)
12. We’re a bit ahead of ourselves here, because we haven’t discussed genetics, yet, but if it’s a genetic disorder, what is its “pattern of inheritance”? Find out if it’s a dominant or a recessive gene – what are the chances that a parent who carries that allele will pass it on to a child? Is it a “sex-linked” allele (is it on the X or Y chromosome), or is it “autosomal” (on the “regular” chromosomes)?
13. Can any other species of organism besides humans get this? Can it be transferred back and forth between that species and humans?
14. What is the incidence of this disease/disorder? How many/what percentage of the population have it? What are the chances that you or someone from your family could have/get this?
15. Is it more prevalent among certain ethnic groups or populations of people or parts of the world, or is it equally present everywhere?
16. Are people of all ages, both sexes affected or does it affect some more than others?
17. What are some of the “urban legends,” misconceptions, “old wives’ tales,” and other false “information” about this condition, and what are the true facts in opposition to the false beliefs?
18. Did this condition ever play an important role in human history? (For example, both hemophilia and bubonic plague have done so in very different ways.)
19. At this point, if you are a registered student, you should submit your work.

Grading Criteria

1.   Cause of Disease/Disorder:
2	—	The cause of the disease/disorder was thoroughly researched and accurately and clearly presented
1	—	The cause of the disease/disorder was adequately researched and presented
0	—	Information on the cause of the disease/disorder was sketchy and/or mostly incorrect
2	—	Thorough discussion of pre-existing conditions that increase chances of getting or exacerbate the condition was also included
1	—	At least some mention was made of pre-existing conditions that increase chances of getting or aggravate the condition
0	—	Either no or incorrect information on effects of pre-existing conditions was included
2.   Discovery of Disease/Disorder:
2	—	The history of the discovery/description of this condition was thoroughly researched and accurately and clearly presented
1	—	The history of the discovery/description of this condition was adequately researched and presented
0	—	Information on the discovery of this condition was sketchy and/or mostly incorrect
2	—	This information was presented in a manner that was entertaining and fun to read
1	—	This information was adequately presented
0	—	Presentation of this information was monotonous and lacked interest
3.   Signs, Symptoms, etc.:
2	—	The signs, symptoms, and effects on the body systems were thoroughly researched and accurately and clearly presented
1	—	The signs, symptoms, and effects on the body systems were adequately researched and presented
0	—	Information on the effects of this disease/disorder was sketchy and/or mostly incorrect
2	—	The student clearly demonstrated that (s)he knows the difference between “signs” and “symptoms”
1	—	The delineation between “signs” and “symptoms” was included and was at least partially correct
0	—	“Signs” and “symptoms” were not delineated or were incorrectly distinguished from each other or most manifestations of the condition were assigned to the wrong category
4.   Diagnosis & Treatment:
2	—	The diagnosis and treatment of this condition were thoroughly researched and accurately and clearly presented
1	—	The diagnosis and treatment of this condition were adequately researched and presented
0	—	Information on the diagnosis and treatment of this condition was sketchy and/or mostly incorrect
2	—	Thorough discussion of role and usefulness of diet and/or “alternative” therapies was also included
1	—	Effectiveness of diet and/or “alternative” therapies was at least mentioned and partially discussed
0	—	No mention made of effects/influence of diet and/or “alternative” therapies
5.   Spread & Distribution:
2	—	The prevalence, distribution, and means of acquisition were thoroughly researched and accurately and clearly presented
1	—	The prevalence, distribution, and means of acquisition were adequately researched and presented
0	—	Information on the prevalence, distribution, and means of acquisition was sketchy and/or mostly incorrect
2	—	Discussion of likelihood of contracting and means of prevention was thoroughly presented
1	—	Likelihood of getting and means of prevention were at least mentioned
0	—	No mention made of how to keep from getting this disease/disorder or information presented was incorrect
6.   Misconceptions & Role in History:
2	—	Information on misconceptions associated with this condition and its role in history was thoroughly researched and accurately and clearly presented
1	—	Information on misconceptions associated with this condition and its role in history was adequately researched and presented
0	—	Information on misconceptions and/or the role in history was sketchy and/or mostly incorrect
2	—	This information was presented in a manner that was entertaining and fun to read
1	—	This information was adequately presented
0	—	Presentation of this information was monotonous and lacked interest
7.   Overall:
2	—	The grammar, English usage, punctuation, and spelling were very good
1	—	The grammar, etc. were OK
0	—	The grammar, etc. were poor
2	—	The student, obviously, went beyond the minimum requirements of the assignment
1	—	The student adequately completed the assignment
0	—	The student completed considerably less of the assignment than what was required
2	—	It is evident that the student used much insight, thoughtfulness, and critical thinking when completing this assignment
1	—	The student adequately thought about the assignment – there was, perhaps, a bit of “fuzzy thinking” in a couple places
0	—	The assignment gives the appearance of being “slapped together” just to get it done, with little evidence of thoughtfulness
Total Possible:
30	—	total points