Download Negative Feedback Regulation of Hypothalamus and

HAPS –I Advanced Neuroendocrine Biology 2009
Paula Curbo
Hill College
112 Lamar Drive
Hillsboro, TX 76645
[email protected]
(254) 659-7866
Learning Module on Hypothyroidism
This is a two part learning module to be used during lecture, during lab, or to be assigned as homework.
It is intended for students that are taking the first year of human anatomy and physiology. Most
students should be able to complete the module within 30 minutes if they have had prior exposure to
the material.
Part One is a learning activity intended to check student understanding of the negative feedback
regulation of the hypothalamus and pituitary gland.
Part Two is an interrupted case study relating to hypothyroidism. Part A is to be given to the student
first. Part B is to be given after the completion of Part A.
Part One and Part two may be used together or independently. They have been designed to
complement each other, aiding in student understanding.
Part One
Negative Feedback Regulation of Hypothalamus and Pituitary Gland
by Serum Levels of T4, T3
The hypothalamus and pituitary gland are regulated by a negative feedback mechanism resulting in the
fluctuation of serum levels of thyroid hormone (T4 and T3) around a set point. Fill in the boxes on the
following page with the terms in Table 1 to illustrate this negative feedback control of the hypothalamus
and anterior lobe of the pituitary gland. Fill in the circles with a + or – sign to show whether a
stimulatory or inhibitory effect is taking place.
Table 1
Anterior Pituitary
Most body cells; metabolism stimulated by T4, T3
Hypothalamus
Increased T4, T3
Serum levels of T4, T3 lowered as cells use T4, T3
Thyroid gland
+
-
Negative Feedback Regulation of Hypothalamus and
Pituitary Gland by Serum Levels of T4, T3
↓Serum T4, T3, ↑Exercise, Stress
Malnutrition, ↓Serum Glucose, Sleep
Releases TRH;
TRH Targets
Releases TSH;
TSH Targets
Releases T4, T3
T4, T3 Target
Answer Key
Negative Feedback Regulation of Hypothalamus and
Pituitary Gland by Serum Levels of T4, T3
↓Serum T4, T3, ↑Exercise, Stress
Malnutrition, ↓ Serum Glucose, Sleep
+
-
+
Hypothalamus
Releases TRH;
TRH Targets
-
Anterior Pituitary
Releases TSH;
TSH Targets
Thyroid Gland
Increased
T4, T3
Most
Releases T4, T3
T4, T3 Target
Most body cells; metabolism
stimulated by T4, T3
Serum Levels of T4, T3
lowered as cells use
T4, T3
Part Two
Case Study
Onset of Hypothyroidism in Young Adult Female
Part A
Sasha, a 22 year old college graduate, spent her summer following graduation filling out job applications
and going to interviews. She had not felt particularly well the last year of college and had trouble
concentrating on completing her courses, but she attributed her symptoms to the stress of graduation
and the transition into the work force. She was hoping to feel better after graduation but her symptoms
continued and some even worsened throughout the summer. Sasha noticed she felt tired all the time
and she sometimes had pain in her muscles and joints. Her hair began to fall out and her skin began to
feel dry. She felt cold and slightly depressed all the time. It also occurred to her that constipation was
becoming common. Her menstrual cycles were abnormally heavy and long. When her symptoms
continued, Sasha finally decided to go to the doctor. At the clinic, her heart rate and blood pressure
were both below average. The doctor thought of several possible problems and suspected a hormone
disorder.
1.
Based upon Sasha’s symptoms, what systems in the body were affected?
2. What potential hormones might be causing the problems?
Part B
The doctor suspects a problem with TSH and/or TH and orders a battery of blood tests.
Sasha’s blood work indicated abnormal readings for the following tests:
Shasha
T4 3.1 µg/dl
T3 uptake 16%
T3 90 ng/dL
TSH 41.1 mIU/L
RBC count 3.38 mil/µL
Hemoglobin 11.5 g/dL
Hematocrit 32.2 %
Normal Range
5 - 12.5 µg/dL
22 - 35% (This is an indirect measure of T4.)
for 15 - 23 years 100 - 220 ng/dL
0.3 – 5 mIU/L
3.9 - 5.20 mil/µL
12.0 - 15.6 g/dL
35.0 - 46.0%
All other blood tests showed normal readings.
3. What are the effects of thyroid stimulating hormone?
4. What are the effects of thyroid hormone on the body?
5. Sasha’s blood work indicated abnormally low levels of T3 and T4 and abnormally high levels of
TSH. Do the results indicate a problem with the hypothalamus, the pituitary gland, or the
thyroid gland? Why?
6. Why were TSH levels high while T4 and T3 were low?
7. Why were the RBC count, hemoglobin values, and hematocrit so low?
Sasha was diagnosed with primary hypothyroidism and was placed on a thyroid replacement treatment
consisting of levothyroxine.
Answer Key
Case Study
Onset of Hypothyroidism in Young Adult Female
Part A
1. Based upon Sasha’s symptoms, what systems in the body were affected? Nervous—lack of
concentration, depression, fatigue; integumentary—brittle hair, dry skin; cardiovascular—
bradycardia (slow heart rate); musculoskeletal—pain in muscles and joints; digestive—
constipation due to slow peristalsis; reproductive—abnormal menstrual cycles.
2. What potential hormones might be causing the problems? Thyroid stimulating hormone (TSH)
and/or thyroid hormone (TH)
Part B
3. What are the effects of thyroid stimulating hormone? TSH promotes an increase in the size,
number, and activity of the cells in the thyroid gland and stimulates the release of thyroid
hormone (T3 and T4).
4. What are the effects of thyroid hormone on the body? Thyroid hormone (T3 and T4) increases
the basal metabolic rate of cells, increases metabolism of proteins, carbohydrates and lipids,
and affects the normal development and functioning of systems in the body. TH raises the heart
rate, respiratory rate, and strength of muscle contraction. TH affects renal function by
influencing the glomerular filtration rate. In females, the menstrual cycle is frequently affected.
TH promotes alertness and the ability to think quickly. TH also has a calorigenic (heat
production) effect on the body. Since almost all cells are affected by thyroid hormone,
insufficient levels result in wide spread complications.
5. Sasha’s blood work indicated abnormally low levels of T3 and T4 and abnormally high levels of
TSH. Do the results indicate a problem with the hypothalamus, the pituitary gland, or the
thyroid gland? Why? Since T3 and T4 were low while TSH levels were high, the problem is with
the insufficiency of the thyroid gland to secrete thyroxine (T4) and triiodothyronine (T3). Had T3,
T4 and TSH levels all been below the normal range, the disorder would be attributed to the
insufficiency of the hypothalamus to secrete thyrotropin-releasing hormone (TRH).
6. Why were TSH levels high while T4 and T3 were low? TSH stimulates the thyroid gland to secrete
mainly thyroxine, some of which is converted to triiodothyronine. In an underactive thyroid
gland, the hypothalamus releases thyrotropin-releasing hormone which stimulates the anterior
pituitary to release more and more TSH.
7. Why were the RBC count, hemoglobin values, and hematocrit so low? Besides the lowered
metabolism in the red bone marrow, Sasha’s loss of blood from her heavy menstrual cycles
would lower these readings.
References
Andrews, Marcia, Peter H. Johnson, Vijay S. Kothare, Doris Weinstock (1999) Handbook of
Diagnostic Tests. 2nd edition. Springhouse Corporation, Springhouse Pennsylvania.
Carson, Maggie (2009) Assessment and management of patients with hypothyroidism. Nursing
Standard. 23, 28, 48-56.
Marieb, Elaine, N. and Katja Hoehn (2010) Human Anatomy & Physiology. 8th edition.
Benjamin Cummings, San Francisco.
Saladin, Kenneth S. (2010) Anatomy & Physiology The Unity of Form and Function. 5th edition.
McGraw Hill, Boston.
Tierney, Jr., Lawrence M., Stephen J. McPhee, Maxine A Papadakis (2000) Current Medical
Diagnosis & Treatment. 39th edition. Lange Medical Books/McGraw-Hill, New York.
Weinstock, Doris, Marcia Andrews, Jane V. Cray (1998) Professional Guide to Diseases. 6th
edition. Springhouse Corporation, Springhouse, Pennsylvania.