Download Smith_Janice_Yoder_project_version 2

Janice Yoder Smith
Renal Biology Final Project
HAPS-I 2008
June 24, 2008
What’s Wrong with Viele?
A Case Study About Diabetes Insipidus
Teacher’s Guide
Introduction:
This case study is designed as a semester long study. Students who have completed study of
the nervous and endocrine systems will be most successful on section I. To perform well on
section II, students should understand the roles of the cardiovascular system. Those who
have studied the urinary system and mechanisms of fluid balance will do best on stage III.
The scenario presents a fictional situation in which a foreign exchange student begins having
excessive urination and thirst shortly after a skateboarding accident. The case study is
divided into three sections. Each section has an informative story followed by several
questions to be answered by students.
The names chosen for the story are purposely linked to the overall case study. Orina is the
Spanish word for urine. Viele is the German word for much or many, urin is the German word
for urine, and reparatur is the German word for repair. Also note two historical names, Barton
and Nightingale, used for the nurses. Erik Von Willebrand was a physician that documented
an unusual bleeding disorder. Some of the names are puns based on the physicians’
specialties. Telling students that the names are clues and that Babel Fish website
(http://yahoo.babelfish.com) will help them translate those names. Use of that site may be
helpful to students as they deal with patients who speak other languages when there is no
available translator. (As for Clara Barton and Florence Nightingale being referenced,
shouldn’t future nurses learn a bit about the history of their career choice?)
Individual or Group Activity
As either an individual student effort or a group project, this case study should help the
students link the structures of the brain to the endocrine system and the endocrine system to
the urinary system. It should also help students integrate those systems with the
cardiovascular system.
If the project is assigned to groups, the instructor must decide whether students will choose
their own groups or if the instructor will choose members of each group. The value of student
chosen groups is that the group members may already work well together. There are several
values of instructor assigned groups. Students in such groups must learn to work with people
they don’t know as well, perhaps even people from a different culture or economic class.
Assigning groups would also negate the possibility of a student being left out of a group
because no one chose them.
Notes re: Web Searches and Plagiarism
Students who use “ADH” as a search term will discover many articles about alcohol
dehydrogenase. Instructors may wish to provide guidance to students about how to
successfully search for relevant information.
Many students know that simply copying and pasting from a website is an act plagiarism.
Few of them realize that merely changing a preposition or reversing the order of a sentence
does not undo plagiarism. A good way to teach students to paraphrase is to take a sentence
from a textbook and have the students work to put the sentence in their own words. If there is
a specific citation style that an instructor wants a student to use, presenting some samples
after doing the paraphrasing examples will help the students be more successful.
Grading Suggestions
If students work in groups, a rubric judging peer participation may be useful. Using a five point
system, perhaps the following rubric could be helpful. The instructor could use the average of
the peer evaluations to determine the points and individual student earned. If the groups
contained five or more students, it might be possible to discard the lowest (and /or highest)
peer evaluations. An instructor grading the three sections of the project separately might wish
to have 3 separate group grades. An instructor grading the total case study at the end of a
term might wish to increase the point values in the rubric.
Points Earned Criteria
5
Student involved in every group meeting (online or in person).
Student cited references for answers and could explain reasoning behind
answers.
4
Student involved in most group meetings, usually well-prepared for meeting,
could explain suggested answers
3
Student missed some group meetings, but caught up with other students, just
as prepared as others in group
2
Student missed most meetings, contributed accurate but insufficient
information to the group
1
Student missed most meetings, contributed insufficient and inaccurate
information to the group
0
Student did not participate in group activities and made no contributions.
When grading the individual questions associated with the case study, a rubric may be also
prove helpful. If each question had a value of five points, the following rubric could be used:
Points Earned Criteria
5
fully developed answer, provides accurate information, shows insight into
physiological processes
4
somewhat developed answer, most information accurate
3
provides minimal but accurate information, a few minor errors
2
organized but with some major errors
1
unorganized, many major errors
0
does not address questions asked
The instructor certainly had the discretion to state that some points might also be derived from
the ability to follow directions, the use of correct grammar and spelling, etc.
Objectives: (Stated here for instructor convenience. Also stated in sections of the study.)
Students completing this case study will be able to:
1. Identify the structures in and near the sella turcica. Describe their basic functions.
2. State which of these structures are involved in the synthesis and release of ADH.
3. Describe ADH. (List other names, state its action mechanism, and state its general
function)
4. List two disorders associated with ADH. Which seems to be the problem with the patient?
5. Research the prescription drug DDVAP. What is it? What does it do? How is it relevant?
6. List and describe the uses of clinical laboratory tests relevant to diagnosis of this patient.
7. Explain the general roles of each of the medical specialist involved in diagnosis and care
of this patient.
8. What is von Willebrand’s disease? How is that disorder result relevant to this case?
9. Relate the functions of ADH to the cardiovascular system.
10. Distinguish between central and nephrogenic diabetes insipidus. How do the doctors
decide which condition the patient has?
11. Describe in detail the functions and interactions of these body systems as related to
diabetes insipidus:
urinary
endocrine
nervous
cardiovascular
Webliography: (Listed before the bibliography because many use the internet first.)
http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/adh.html
Colorado State University Pathophysiology Course Website
http://www.diabetesinsipidus.org/whatisdi.htm
Diabetes insipidus Foundation
http://www.emedicine.com/med/TOPIC543.HTM
Diabetes Insipidus by Michael D. Cooperman, M.D.
http://kidney.niddk.nih.gov/kudiseases/pubs/kdictionary/
National Institute of Diabetes, Digestive and Kidney Diseases
Searchable dictionary of medical terms
http://kidney.niddk.nih.gov/kudiseases/pubs/insipidus/
National Institute of Diabetes, Digestive and Kidney Diseases
Diabetes insipidus, patient information
http://www.labtestsonline.org/
Lab Tests Online
Describes lab tests including: normal values, reasons for tests, preparation
http://www.merck.com/mmhe/sec13/ch162/ch162d.html
Merck Patient Website
http://www.nlm.nih.gov/medlineplus/diabetesinsipidus.html
National Library of Medicine
Diabetes insipidus, patient information plus links to additional information
http://www.rxlist.com
Rx List; Excellent site providing clinical pharmacology and other info re: Rx meds
http://fitsweb.uchc.edu/student/selectives/mMeyer/new_page_11.htm
University of Connecticut Medical School; description of Von Willebrand’s disease
Bibliography:
Eaton, Douglas C. and Pooler, John P.; Vander’s Renal Physiology; pp. 122-125; © 2004;
Lange Medical Books/McGraw Hill.
Kasper, Dennis L, Braunwald, E.; Fauci, Anthony S; Hauser, Stephen L.; Longo, Dan L; and
Jamesons, J. Larry. Harrison’s Principles of Internal Medicine, vol. 2, pp. 2098-211, © 2005;
McGraw Hill Medical Publishing Division.
(Note that this is a standard text for internal medicine in many medical schools.)
Tortora, Gerard J. and Derrickson, Bryan; Principles of Anatomy and Physiology, 12th ed.
pp. 657-658; pp. 1029-1049; ©2009; John Wiley and Sons.
What’s Wrong with Viele?
A Case Study for Anatomy and Physiology Students.
I. Objectives
Students completing this case study will be able to:
1. Identify the structures in and near the sella turcica and describe their basic functions in the
maintenance of homeostasis.
2. State which of these structures are involved in the synthesis and release of ADH.
3. Describe ADH. List other names for this substance. Which action mechanism does this
substance use to change the activities of other cells?
4. List two disorders associated with ADH. Which disorder seems to be the problem with the
patient in this study?
I. Background
Viele Urin, a seventeen year old German foreign exchange student has just been brought to
the emergency department by his host parents. They tell the clerk that Viele may have a
head injury. The clerk is skeptical because she doesn’t see any obvious head wounds, but
she gives the parents some forms to complete and notifies the triage nurse, Ms. Barton. The
emergency department is not terribly busy on this day, and before long Ms. Barton is calling
the group back to an examination room.
“The initial notes from the clerk say you may have a head injury and that you are from
Germany. What happened? Oh-- sprechen Sie Englisch?” asked the nurse, Ms. Clara
Barton.
Viele answered, “Ja, Ja. Ich spreche Englisch. I have a small bump on my head and some
headaches. I have been in the US about a week. My host brother and I were outside, riding
skate boards. He said there was a park nearby with skateboard ramps. We went there, and I
was showing him skills I mastered at home in Germany. I made a mistake on one, though,
and landed on my head. I didn’t think it was any problem. I was not bleeding; I only had a
headache. I did not have a big lump.”
The nurse moved closer to Viele and looked at his head. She asked, “Your English is
excellent. Thank goodness. My German vocabulary is very limited. Were you wearing a
helmet when you fell?”
“Nein. I mean no. Brother offered one, but I told him we don’t wear them at home. I would be
ok.”
“Well, I don’t see any tears in the scalp. I can palpate a bump. I do see some bruising there
and elsewhere on your arms. I don’t like the location of what I see on your head. You said
that you weren’t initially concerned. Some of these bruises on your extremities look older.
Why are you here now?” asked the nurse.
The host mother replied, “Viele doesn’t see the connection. He thinks maybe we have bad
water in our neighborhood. However, he wasn’t having this problem before he bumped is
head.”
“What problem?”
“It is nothing really,” said Viele. It’s just that the water here doesn’t seem to stop my thirst. It
only makes me go to the toilet often. I have to go 9, 10 times a day and 3 or 4 times at night.
I will have my parents send me some bottle water from home. I am so thirsty all of the time.
I’ll be ok. I agreed to come to the hospital to satisfy my host family and my parents that I am
not hurt. Will you tell them that I am ok so I may go back to my host home?”
“I cannot promise that, Viele. Tell me more about all of those bruises.”
“Oh, I’ve bruised a little easily all of my life. My parents documented that in my exchange
papers. I always stop bleeding and the bruises always heal. I’m no different from other
skateboarders. We all get bruises.
“I will have the doctor come in to examine you as soon as possible.” Ms. Barton then looked
at the host parents. “Have you notified his family? Do you have the forms authorizing you to
seek treatment for Viele?”
“Here are our copies of the documents from the exchange agency. We have called Viele’s
parents. They are naturally worried about their son. They have access to a fax machine and
can send any other documents you need. There is about a seven hour time difference, but
they said to call at any time.”
The emergency physician came into the room about 15 minutes later. “Hi, I’m Dr. George
Reparatur. What seems to be the problem today?”
Viele smiled and asked, “Sind sie Deutsch? Ihren namen ist Deutsch. Looking to his host
parents, he said “The doctor’s name means repair in German.”
The doctor acknowledged some German heritage and a limited knowledge of the German
language and repeated his request for information. After listening carefully, he examined
Viele’s head again. He didn’t like the locations of the bruise and lump on his head either. He
didn’t seem as concerned about the bruises elsewhere as the nurse had been.
“Have you had any nausea or vomiting since the accident? Any weakness? Any other
differences?”
“No, no, no – just this incredible need to go to the toilet. I’ve drunk several cups of water and
gone to the toilet 5 times in the hour we have been here. It is probably nothing, though, just
getting used to American water. It leaves me thirsty,” said Viele.
“Hmmm...did you have that problem the first days you were here or only after the fall?” asked
the doctor.
“No -- only after the fall.”
“Ok. I’m not exactly sure what is going on, but I’m going to get some blood work and a
urinalysis. I’m going to order an MRI to make sure you don’t have a closed head injury, and
I’m going to call the nephrologist on duty today and have him come in. Are you
claustrophobic?”
“Nein”, said Viele.
Dr. Reparatur left the exam room and went to his office to call Dr. Orina, the on call
nephrologist.
“Dr. Orina, how may I help you?”
“Hey, Felipe, this is John Reparatur from Metroplex General ER. I have a 17 year old German
boy in here. Says he got a bad bump from a skateboard accident. There’s no obvious trauma
but there is a lump and a bruise at the junction of the coronal and sagittal sutures. The weird
thing is, since the accident he has to urinate 8-10 times a day and 3-4 times at night. He’s
blaming American water, but I think we may have a closed head injury and a nephrology issue
here. I’ve already ordered an MRI. I think we need a look at the hypothalamus and pituitary
gland, so I’m checking on which neurologist is on call. I’ve ordered a UA, a CMP, and a CBC
w/ differential, too. What do you think? Do we need more tests right now? How soon can
you get here?”
“George, that case does sound a bit odd. You’d think if the kid had a closed head injury he
would have had other problems by now. You have the basic tests covered. It will take me at
least an hour with traffic to get from the Suburban Regional Hospital where I am now to your
location. Here’s another test I want you to do. First, as soon as that kid pees again, weigh
him. Record the start time. Figure out 5% of his body mass. Don’t let him have anything to
drink. Have him pee into a urinal and measure the volume each time. Weigh him after every
void. Get the specific gravity and osmolality of the urine after every void. Keep that up until I
get there or he has lost 5% of his weight. Oh...and tell the pharmacy to send up some
DDVAP, 10 micrograms per puff inhaler. If I’m right, that will fix the kid up within hours. One
more thing—see if you can get Cere Brum to look at that MRI with you and the radiologist.
She’s a great neurologist.”
“Ok, Felipe. Will do. I’ll tell the family and we’ll see you in an hour. Cere Brum is on call, too.
Hey, I’m a little worried re: the bruising pattern on this kid. It’s probably just because he’s a
reckless skateboarder, but I’m going to call in Erik von Willebrand, the hematologist, too. The
nurses are changing shifts, but I’ll see if I can get one of the more experienced nurses to look
after this kid. I don’t want him going downhill suddenly.”
I.
Questions
1.
Where is the sella turcica in relation to the intersection of the coronal and sagittal
sutures?
The sella turcica forms part of the floor of the cranium. It is deep to the junction of the
coronal and sagittal sutures.
2.
What lies in the sella turcica? Which structure is immediately superior to that one?
The pituitary gland lies in the sella turcica. Immediately superior to the pituitary gland is
the hypothalamus.
3.
What are the general functions of the structures above?
The pituitary gland has two parts. The anterior pituitary or adenohypophysis releases
hormones that stimulate activities of many other endocrine glands. The posterior pituitary
or neurohypophysis releases 2 hormones (ADH and OT). The hypothalamus is a link
between the nervous and endocrine systems. It is the seat of autonomic control. It
secretes hormones that regulate the pituitary gland. It controls thirst, hunger and body
temperature.
4.
Specifically, which structure synthesizes ADH and which structure releases ADH?
Nerve cell bodies in the hypothalamus synthesize ADH, but the axon endings in the
neurohypophysis release it.
5.
What is the full name of ADH? What are its other names?
ADH stands for antidiuretic hormone. It is also called arginine vasopressin or just
vasopressin.
6.
Describe the nature of ADH. What is its general role in the body?
ADH is a peptide hormone. It helps the body retain water.
7.
Which action mechanism use to control cells? What is its target organ?
ADH uses the 2nd messenger system to control cells in the kidney.
8.
Which two disorders are associated with decreased ADH production?
Diabetes insipidus, nocturnal enuresis (bed-wetting)
9.
Which disorder seems to be the problem in this case study? Explain.
Diabetes insipidus. Viele’s problem occurs all day and night; it is not limited to when he
sleeps.
II. Objectives (Numbering continues from part I.)
5. Research the prescription drug DDVAP. What is it? What does it do? How is it relevant?
6. List and describe the uses of clinical laboratory tests relevant to diagnosis of this patient.
7. Explain the general roles of each of the medical specialist involved in diagnosis and care
of this patient.
8. What is von Willebrand’s disease? How is that disorder result relevant to this case?
9. Relate the functions of ADH to the cardiovascular system.
II. More doctors see Viele.
Dr. Orina found himself stuck on the freeway with no exit nearby and a multivehicle accident
in front of him. It actually took over two hours to get to the hospital where Viele was. He kept
in touch with the ER doctor by phone. He was reassured when he found out a nurse he knew
had excellent technical and interpersonal skills, Ms. Florence Nightingale, was assigned to
Viele. Dr. Reparatur let him know that Dr. von Willebrend had examined Viele and ordered
tests for vWF. He said that since Viele wasn’t prone to nosebleeds, he didn’t think that Viele
had the disorder named after his distant relative. He was only ordering the vWF test as a
precaution. Dr. Orina was also relieved to find out that two other excellent doctors would
meet him at the MRI interpretation room.
The radiologist on duty, Dr. Xavier Ray, called in Dr. Brum, the neurologist, and Dr. Reparatur
into the room while he interpreted the scan. Simultaneously, Dr. Brum and Dr. Ray pointed to
a dark area where the neurohypophysis should be. Dr. Brum said that she had seen that type
of image when the neurohypophysis was damaged – sometimes from closed head injuries,
sometimes from open head wounds. Dr. Ray agreed with her. They both said that area should
have given a very bright signal instead of a dark spot. After Dr. Reparatur reviewed the
results obtained so far, the three doctors agreed that Viele’s condition) was probably pituitary
diabetes insipidus. Dr. Orina, who had just rushed into the room, caught up on the
conversation. He and Dr. Reparatur reviewed the case as they walked back to the emergency
department. Dr. Orina was pleased to see that the DDVAP had arrived from the pharmacy
and was being stored properly. He went to read Ms. Nightingales notes re: Viele’s response to
the fluid restriction test he ordered.
II. Questions (Numbering continues from section I.)
10. What is DDVAP? When is it prescribed? What does it do?
DDVAP is also known as desmopressin. It is a synthetic analog of vasopressin,
otherwise known as antidiuretic hormone or ADH. DDVAP acts on the kidneys causing
them to reabsorb more water.
11. The tests the doctors ordered and the reasons for them follow.
MRI
Viele has a history of a head injury. The hypothalamus and pituitary
glands are essential to normal body functions including the production of
urine. Damage to one or both of those structures could result in the loss
of ADH production. Since ADH acts on the collecting tubules of the
kidneys and adjusts the rate/amount of water reabsorption, an
abnormality found in this area might explain Viele’s illness.
urinalysis (UA): Urinalysis is a low cost, effective way to determine if the urine
contents are normal. Among the factors measured in UA are:
pH
should be within the pH 4.5-8 range, most urine around pH 6; values
outside the normal limits may represent metabolic disruption, kidney
disease or respiratory problems; (Note that no respiratory concerns
have been raised in this case.)
glucose should not be present; presence usually indicates diabetes mellitus
protein should not be present; presence usually indicates kidney damage
infection should not be present, follow up with urine culture may be needed if
UA is +, UTIs are know to increase frequency of urination but are
usually accompanied by discomfort, which Viele doesn’t report
specific gravity should be 1.002 to 1.028; values below the normal limit
indicate excessive dilution of urine; values above the normal
limit indicate excessive concentration of urine; either result
may indicate damage to mechanisms regulating the kidneys
comprehensive metabolic panel (CMP):
allows determination of pH, glucose, CO2 (bicarbonate) and
concentrations of key electrolytes (Na+, K+, Ca2+, Cl-); changes in
these levels may indicate issues with renal secretion or reabsorption
creatinine, blood urea nitrogen (BUN), albumin,
total protein, and enzymes reflecting liver function (ALP, ALT,
AST) and bilirubin; these tests allow the physicians to quickly assess
whether a patient’s problem is from the liver or the kidney; BUN levels
may also indicate dehyrdration
complete blood count with differential:
reveals the amount of red blood cells, reticulocytes, white blood cells,
and platelets in the blood; also reveals the percentages of each type
of white blood cell; since the kidney secretes a hormone that controls
red blood cell production, this information may help diagnose a kidney
problem
vWF = von Willebrand’s factor
essential in helping platelets aggregate and stick to damaged
epithelial; needed for platelet interactions with coagulation factors VII
and VII
12. There were several clinical specialists involved in Viele’s case.
ER doctor
Dr. Reparatur: made the initial assessment, decided whom else to call in
to treat patient
Hematologist
Dr. von Willebrand; studies blood and clotting factors, able to decide
whether Viele’s bruises were an additional concern
Nephrologist
Dr. Orina: specializes in diseases of the kidneys; excessive urination
often linked to renal issues.
Neurologist
Dr. Cere Brum: specializes in illnesses and disorders of the brain;
the brain and pituitary gland regulate functions of the kidney and other
organs; able to interpret MRIs of brain and recommend or prescribe
neurological treatments if needed
Radiologist
Dr. Ray: able to interpret MRI; deliver information re: structural changes
which may be the cause of Viele’s illness
13. What is von Willebrand’s disease? How is it treated?
Von Willebrand’s disease is a rare genetic disorder. Patients with the disorder have
difficulty stopping bleeding because their platelets don’t stick together well and their
coagulation factors VII and VIII may not react properly. The patients bruise easily without
feeling the injury causing the bruise. They also have frequent nosebleeds. It is treated
with desmopressin (DDVAP). That is an analog of vasopressin or ADH. Researchers
think that vasopressin helps make some clotting factors more stable and causes platelet
to release more vWF (von Willebrand’s factor), which causes the person to have less
bleeding.
14. How is ADH related to the cardiovascular system?
ADH (vasopressin) helps blood clot. It also causes arterioles to constrict, which can help
elevate blood pressure if fluid depletion occurs. Finally, ADH helps the kidneys reabsorb more
water into the blood. More blood volume  more blood pressure  more resistance for the
heart to overcome. If Viele had lost too much volume too fast, he could have gone into
hypovolemic shock and possibly died. That’s why Dr. Orina set a weight loss limit.
III. Objectives (Numbering continues from part II.)
10. Distinguish between central and nephrogenic diabetes insipidus. How do the doctors
decide which condition the patient has?
11. Describe in detail the functions and interactions of these body systems as related to
diabetes insipidus:
urinary
endocrine
nervous
cardiovascular
III. Diagnosis and Treatment
Before visiting Viele and his family again, Dr. Orina reads Ms. Nightingale’s nursing notes
carefully.
Viele weighed 150 pounds at the start of the fluid restriction. Ms. Nightingale calculated 5% of
his weight to be 7.5 pounds. Viele’s first need to urinate was 10 minutes later; he voided 500
ml of urine — specific gravity 1.0005 and osmolality 150 mosmol/L. Viele lost a pound in that
short period. He continued needing to void about every 10 minutes. After an hour, no change
had been seen in his urine osmolality or specific gravity and he had already lost six pounds.
Radiology had called about that time to say that the MRI was available. Dr. Reparatur looked
at Viele’s weight loss and thought it best to stop the fluid restriction and get Viele rehydrated.
They also agreed it best to provide Uri with a disposable diaper since he would not be able to
go to the toilet for at least 45 minutes while the scan was occurring.
While he was greatly relieved to be able to drink fluids again, Viele was unhappy about the
need to wear a diaper. He reluctantly agreed when given the choice of a condom catheter or a
Foley catheter.
Dr. Orina examined Viele and went over his test results with his host family. His urine was too
dilute, and some of his electrolyte levels were elevated. His von Willebrand factor levels were
normal, so that ruled out that bleeding disorder. His blood counts were ok. Dr. Orina told the
family about the MRI and the conclusion that the doctors had drawn that Viele probably had
diabetes insipidus. He made clear to the family that insipidus and mellitus were two very
different problems that had in common excessive urination and thirst.
“So, family, I think we need to see which form of diabetes insipidus Viele has. With your
permission, he will receive an inhalation treatment with DDVAP. That’s a medicine that acts
like a hormone that Viele seems to be missing. There is another kind of diabetes insipidus,
but I think the MRI shows that he has a kind that will respond to this treatment. Do you want
to try it?” Dr. Orina asked.
The host family used their cell phone to consult Viele’s parents in Germany. Dr. Orina, who
happened to be fluent in German, spoke to them as well. The parents spoke to Viele after
that. All agreed that it was best to try the DDAVP.
Dr. Orina demonstrated the use of the inhaler containing the dDVAP. He asked Viele to take
one puff in each nostril. Then he told Ms. Nightingale to document the time and volume of
each time Viele had to urinate. He also ordered specific gravity and osmolality tests on each
urine sample obtained. He asked Viele to keep a chart re: his thirst level ever 15 minutes,
using 0 for no thirst or 10 for extreme thirst. He watched Viele inhale the medicine and record
his thirst level, and then he excused himself to examine some other patients in the hospital.
Viele’s nurse, Ms. Nightingale, had been very busy with him all day. Now she actually had
some time to help with other patients. She noticed after 30 minutes, though, that neither Viele
nor his host family had summoned her to pick up urine. She went to his room to check on
him.
“Is everything ok in here? Do I have some urine samples to send out?” she asked.
Viele smiled. “I haven’t had to go to the toilet in half an hour. I’m not thirsty. I hope this effect
lasts a long while.”
“Ok, Viele. That is good news. I still have my pager on, so if you need me, call. The doctor
should be back to check on your progress in about 30 minutes.”
It was actually almost two hours before Dr. Orina returned to the room. He looked at the
cumulative time since Viele took the DDAVP. In that time, he had urinated once, not because
he felt a tremendous urgency but because it just seemed odd to go so long without relieving
himself. The specific gravity of the urine sample was 1.01 and the osmolality was 300
mosmol/L. Dr. Orina smiled.
“I think we have figured out the problem, folks. I will write a prescription for this medication.
Take it only as directed. Call me if there is any sudden change, especially if Viele gets a
severe headache, stomach cramps or has a seizure. Call my office Monday morning to set
up a follow up appointment; tell the receptionist that I want to seem him next week and to
work him in. You need to let your family physician and Viele’s doctor in Germany know about
this episode. If you give me your PCPs name, I’ll send notes to him or her. The neurologist,
Dr. Brum, will need to follow up, too. Closed head injuries can have unanticipated
consequences, sometimes. Do we need to call Germany again?”
The host family got Viele’s parents on the phone again. Dr. Orina spoke to them in German
and reassured them that there was a good plan for Viele’s care and that he would take good
care of there son. The parents asked Viele if he wanted to end his exchange stay and come
home to German doctors. He said that he felt that he was in good hands and would like to
stay. His parents said that he could stay if he wanted, but they wanted him to check in at least
weekly with them.
III. Questions (Numbering continues from part II.)
15. What are the two forms of diabetes insipidus? How do they differ?
The two forms of diabetes insipidus are central and nephrogenic. The central form is
related to inadequate production and/or release of ADH. The nephrogenic form results
when defective receptors do not allow ADH to bind to the cell or do not respond correctly
to it binding.
16. If the DDVAP had not worked for Viele, which type of diabetes insipidus would he have
had?
Individuals with diabetes insipidus that don’t respond to DDAVP have the nephrogenic
form of the disease. ADH is still made in those individuals, but the receptors on the
collecting tubules to not react to it. Some forms of nephrogenic DI are hereditary, and
others are caused by some medications including tetracycline derivatives and lithium.
In the latter case, discontinuation of the offending medication may help the patient regain
some control. There are no effective cures for nephrogenic DI at this point. Treatment for
such patients involves regulation of diet and fluid intake. Although it seems counterintuitive, administration of hydrochlorothiazide, a diuretic, seems to reset the sodium ion
balance and thus cause reabsorption of more water in these patients.
17. Why would that form not respond to the DDVAP when the form Viele did?
If Viele had the nephrogenic form, the DDVAP would not have been able to bind to the
receptors or to activate changes in the cell. Nephrogenic DDVAP results when renal cells
are damaged by certain drugs or when there is a genetic defect.
18. What is the effect of DDVAP or ADH on water reabsorption by the nephron? Be specific
this time – down to the cellular levels and specific locations within the kidney.
ADH acts on the cells of the collecting ducts. ADH binds to receptors on the collecting
tubules and ducts. The second messenger response to ADH increases the number and
types of aquaporins by the principal cells the collecting tubules and ducts. Those
aquaporins are differentially permeable to water. The more of them present, the more
water is reabsorbed from the lumens of the ducts and tubules, across the principal cells
and eventually back into the interstitial fluid and blood.
19. Why were the doctors sure that Viele had the central form of the disease even before he
received the DDVAP?
The doctors had seen the dark spot on the MRI where the neurohypophysis should have
been. That spot indicated damage to the neurohypophysis, which releases ADH.
20. Describe in detail the functions and interactions of these body systems as related to
diabetes insipidus: urinary
endocrine
nervous
cardiovascular
Both the nervous and endocrine systems are involved in diabetes insipidus. The
hypothalamus, part of the nervous system, has osmoreceptors that detect whether blood
plasma is too concentrated or too dilute. When the plasma is excessively concentrated
(e.g. dehydration), the hypothalamus responds by secreting more of the hormone ADH.
That hormone production reflects the endocrine nature of the hypothalamus. Another
endocrine organ, the neurohypophysis releases the ADH into circulation. ADH has two effects
on the circulatory. It can stimulate vasoconstriction of arterioles, thus increasing filtration
pressure and rate in the kidneys. It can also create a rise in systemic blood pressure. That
increase systemic pressure may affect the heart. The increase in pressure due to resistance
from the vasoconstriction with an increase of pressure due to increased water volume may
strain the heart if allowed to rise too high.