Lab 13 Neuroendocrine System

Activity 1: Organs and Tissues

The neuroendocrine system utilizes chemical messengers for various functions.  These chemical messengers serve as a means for cells to communicate between each other using chemical signals, regulate a number of metabolic processes throughout the body, and attempt to induce precise responses only affecting specific target cells. Because every cell will release chemicals base on metabolic activities, any cell and tissue of the body can have an impact as a part of the neuroendocrine system.  In order to have a precise impact, these messengers will only interact where a specific receptor (membrane protein) is present for that specific chemical.  The tissues and structures are divided into two classifications, the glandular tissues and non-glandular tissues.  The glandular organs will utilize the endocrine and exocrine glandular functions to perform the majority of its functions. These glandular tissues and organs include the hypothalamus, pituitary gland, pineal gland, thyroid gland, parathyroid glands, pancreas, adrenal glands, and gonads (testes and ovaries). All of the glandular organs, except the parathyroid and pancreas, are directly regulated by tropic hormones released from the hypophysis (the combined structure of the hypothalamus and pituitary gland). Along with the glandular tissues that are regulated by tropic and trophic signals, there are tissues that possess neuroendocrine functions independent of the hypophyseal signals. These tissues release hormone messengers not based on tropic regulation, but due to metabolic activity of the tissues of the body. Based metabolic activity, almost all tissues can produce a chemical signal that can serve as a hormone, but the review here will focus on the major tissues (and cells) that produce hormones that have a wide-ranging effect.

Procedures:

1.      Obtain torso models, stickers, felt pens
2.      Write names of tissues, organs and structures that will produce hormones on the stickers
3.      Select a “team leader” and use the colored images and reference materials to take turns labeling the torso model

a.       As structures are labeled, indicate a hormone that will be produced by the tissue. If more than 1 hormone is produced, take turns identifying the various hormones

4.      Have your instructor check your progress and finish activity two.

Activity 2: Glucose Tolerance Tests

This activity needs to be started prior to the beginning of activity 1.  Select 1 participant in your group to be the test subject. Test subjects must come to lab in a fasted state (no food, alcohol or caffeine within 8-hours of lab) and should be selected during the previous lab.

Test subject must agree to participate and sign the agreement to be the test subject and willingness to follow all rules for testing their own blood glucose levels for lab purposes.

Background

Glucose tolerance is the ability for the person to withstand a large ingestion of glucose without having prolonged episodes of excessive blood glucose, hyperglycemia. Normal, metabolically healthy, individuals will have a fasting glucose level between 80 and 100 mg glucose/dL plasma that is maintained by tissues of the body (e.g., skeletal muscle, liver and adipose cells) having normal sensitivity to the hormone insulin. Through normal insulin action at these tissues, any increase in blood glucose will be met with a compensatory rise of insulin that will be able to move glucose into these tissues to lead to a reduction in glucose and thus reduction in insulin, through normal feedback regulation.

We are able to test this normal feedback regulation in the laboratory and clinic through glucose tolerance tests. The glucose tolerance test determines how the body responds to ingesting a large amount of glucose (sugar) in a very short period time. The process involves comparing the levels of glucose in the blood before and after drinking a sugary drink. Typically, the test is performed in a laboratory setting to determine the level of insulin sensitivity that the individual has, and allows medical professionals to detect susceptibility to having diabetes, i.e. showing an impaired glucose tolerance. In healthy people, glucose levels in the blood always rise after a meal but they soon return to normal over the next hour during a challenge and 2-3 hours during an actual oral glucose tolerance test (OGTT).

To ensure that the individual is at a fasting level of glucose in the blood, the test subject is asked not to eat for at least 5-8 hours prior to taking the test. Following consumption of the glucose sample there will normally elicit a spike in insulin. That spike ensures that glucose is rapidly cleared from the blood, moving into the insulin sensitive cells (e.g., skeletal muscle, liver and adipose cells). As a result, the amount of glucose found in blood samples taken over the length of the test will slowly return to normal levels (table 1). However, if there is a problem with either producing insulin (from the β-cells of the pancreas) or cells responding to insulin, there will be a continued elevated reading of glucose in the bloodstream.

Table 1. Sample readings of blood glucose and categorization of distress and dysfunction.

Graphing the time response of glucose readings in the plasma over the length of the test will provide a means to diagnosis metabolic issues for the person, i.e. exhibiting metabolic syndrome or having diabetes. The result of which will be the glucose tolerance curve for the individual. This curve can be tracked over the period of weeks, months and years to examine how a person suspected of having impaired glucose metabolism (or impaired insulin response) behaves to ingesting glucose. While the glucose tolerance challenge can be used as a diagnostic tool, a single testing outcome cannot be used a differentially diagnosis a person to being a diabetic. That is where the OGTT, or the more complex intravenous glucose tolerance test (IGTT) will be used; as it compares not only the ability to clear glucose from the blood, but also examines the response of insulin (insulin tolerance test) over the length of the 2-3 hours for the tolerance test.

Materials and Methods
Materials

• Glucose solutions
• Alcohol Swabs
• Lancets
• Blood Glucose Monitors and Test Strips Biohazard Bag
• Sharps Container
• Bandage

Methods
Ensure that your test subject has not eaten, drank anything beyond water, or exercised within the last 5-hours prior to testing of blood glucose.

1.      Make glucose solution by dissolving 50g glucose into 250mL of chilled water
2.      Have test subject test their blood glucose levels

a.       Obtain a lancet, alcohol swab, paper towel, glucose test strip and glucose monitor
b.      Place the test strip into the monitor and turn monitor on so that it will read the test-strip
c.       Have your test subject swab clean the distal edge of the ring finger on their non-dominant hand
d.      Following which perform a lance of their non-dominant ring finger with a lancet
e.       Immediately after lancing finger, place lancet into sharps container
f.       Milk the finger by squeezing and rolling fingers from the proximal end of the digit to the area of the lancing until a large drop of blood is visible
g.      Place the drop of blood on the test strip and allow Blood Glucose Monitor to analyze
h.      Record reading in Table 2.

3. Have your test subject seated for the remainder of the test. Once seated, have them consume the entirety of the glucose solution in a 5-minute period of time
4. Upon consuming all of the solution, wait 2-minutes

a.       Obtain Blood Glucose Reading

i.     Have the test subject “milk” the ring finger to see if able to draw blood droplet prior to repeating the lancing of the digit.
ii.     Record data in Table 2 (this is your 0-min reading)

b.       Set timer for 20-minutes
c.       Repeat step 4a every 20-minutes for 1-hour following consumption of glucose solution. i. Record the data in table 1 in corresponding time (20-min, 40-min, 60-min).

Analysis

1. Determine the initial change in glucose (Δ glu) based on initial concentration of glucose [glu] relative to post-consumption

a.       Δ glu=[glu]post-consumption-[glu]pre-test

2. Calculate glucose clearance at each time point over the length of test relative to the initial reading following consumption

a.       Clearance (C)= ([glu]_{at time point}-[glu]_{at 0-min})/[glu]_{at 0-min} x 100%
b.      Graph C to time
c.       Graph [glu] to time

Results
Table 2. Readings of blood glucose concentrations (mg/dL) throughout the glucose tolerance challenge.

Discussion

In examining the results think about:

How do responses correlate to the concept of feedback regulation and homeostatic balance? What hormones are involved in the response and what do the results indicate about the individual’s ability to tolerate consuming glucose? How would you use this test to determine metabolic issues for a person?