Endocrine and Homeostasis Lab

LAB EXERCISE: Endocrine, Hyperglycemia, Hypoglycemia, Diabetes

The body uses two systems to communicate with the body:

the endocrine system
the nervous system.

The endocrine system is a communication system that utilizes hormones to send information from one part of the body to another.

Hormones are chemical signals that are synthesized and secreted by endocrine cells/glands

Target cells contain specific receptors for the hormone. Receptors may be located on the cell surface, cytoplasm, or in the nucleus of those target cells.

Receptors on the cell surface will use second messenger systems to cause a rapid, non-genomic effect.
Receptors in the cytoplasm and nucleus will influence transcription/translation causing a slower genomic effect.
If a cell does not contain the receptor that is specific for that hormone, then it will not respond to the hormone .

HORMONE CLASSIFICATIONS

The classification of a hormone can help us understand how they affect the target cell.
Hormones can be classified in three different classes:

Steroid Hormones
Non-Steroidal Hormones
- Peptide Hormones
- Amino Acid Derived Hormones

Steroid hormones
Steroid hormones include corticosteroids and sex hormones. Steroid hormones are derived from cholesterol.

PROPERTIES OF STEROID HORMONES
1) Steroid hormones are hydrophobic so they are able to cross the cell membrane
2) Steroid hormones require a carrier protein to travel through the blood stream
3) Steroid hormones have receptors that are located in the cell's cytoplasm or nucleas causing SLOW ACTIONS.
4) Steroid hormones have a long half-life.

Non-Steroidal Hormones
Non-steroidal hormones include
1) peptide hormones
2) amino acid-derived hormones

PROPERTIES OF NON-STEROIDAL HORMONES
1) Non-Steroidal hormones are hydrophillic so they are soluble in bodily fluids
2) Non-Steroidal hormone receptors are located on the cell's surface so they cause a rapid non-genomic effect
3) Non-Steroidal hormones have a short half-life.

Peptide hormones
Peptide hormones are synthesized through transcription and translation and are stored by the cell in storage vesicles until the cell receives a signal to secrete the hormone. Most hormones are considered peptide hormones.

Amino acid-derived hormones
Amino acid-derived hormones are formed from amino acid precursors. For example, the amino acid tryptopohan is used by the body to make a dopamine, norepinephrine, epinephrine, melatonin and serotonin. The amino acid tyrosine is used to make the thyroid hormones triiodothyronine (T3) and thyroxine (T4) which regulate the metabolism and energy levels of the body. The amino acid glutamic acid is used to make histamines which function as part of the body's immune system.

These experiments relate to the body's endocrine pathways and demonstrate how hormones help our body maintain homeostasis.

Regulation of Blood Glucose

Insulin is a hormone released by the body in response to high blood glucose levels. When insulin is introduced into the bloodstream, blood glucose levels fall as a response.
When glucose is ingested, blood glucose levels increase. This increase triggers the release of insulin from eyelet cells of the pancreas. When this insulin reaches the bloodstream, blood glucose levels decrease back to normal.

Diabetes Mellitus (Type 1 or Type 2)

Diabetes Mellitus is a condition in which a person's body cannot regulate blood plasma glucose levels.

NORMAL - Normal blood glucose levels in an adult following an 8-hour fast should fall between 70 and 100mg/dL.
HYPOGLYCEMIC - Blood glucose below 70 mg/dL is a sign of HYPOGLYCEMIA (low blood sugar).
Additionally, blood glucose levels should not exceed 200 mg/dL after a meal.

PRE-DIABETES - A diagnosis of pre-diabetes is given when the fasting blood glucose level is between 100 and 125 mg/dL.
DIABETES - A diagnosis of diabetes can be diagnosed by a patient having their fasting blood glucose levels greater than >125mg/dL.
People with a diagnosis of diabetes suffer from abnormally high blood sugar levels (also known as hyperglycemia). Hyperglycemia is when blood plasma glucose levels increase above normal.

Diabetes mellitus can result when plasma glucose levels are not regulated properly and the body cannot maintain homeostasis. Diabetes mellitus type 1 results when the beta cells of the pancreas fail to produce enough insulin therefore resulting in high plasma glucose levels.
Diabetes mellitus type 2 results when the cells of the body do not respond to insulin properly (insulin resistance) therefore resulting in high plasma glucose levels.

Effects of Insulin

Following a meal, the body's blood glucose levels are raised. The beta cells of the pancreas sense the increased blood glucose levels and in response they secrete insulin (a protein hormone).

Insulin affects...

the cells of the body by increasing the number of glucose transporters on the cell membrane thus increasing facilitated diffusion of glucose into the cell
increasing the rate of glycogenesis (synthesis of glycogen) in the liver,
increasing the uptake of amino acids and increasing the rate of protein synthesis,
increasing lipogenesis (synthesis of fatty acids)
slowing the rate of glycogenolysis (breakdown of glycogen into glucose)
slowing the rate of gluconeogenesis (forming glucose from lactic acid and amino acids).

The secretion of insulin ultimately results in a decrease in plasma glucose levels.

Hypoglycemia

Hypoglycemia is the condition of having blood plasma glucose levels that are below normal.

After several hours of fasting, the body's blood glucose levels decrease below the setpoint. The alpha cells of the pancreas sense the decreased blood glucose levels and they secrete glucagon (a protein hormone). Glucagon affects hepatocytes (cells of the liver) and causes an

1) increase in the rate glycogenolysis (breakdown of glycogen into glucose)
2) increase in the rate of gluconeogenesis (synthesizing glucose from lactic acid, glycerol and amino acids)
3) slowing the rate of glycogenesis (synthesis of glycogen) in the liver, and 4) slowing the rate of lipogenesis (synthesis of fatty acids). The secretion of glucagon ultimately results in an increase of plasma glucose levels.

Students will use a goldfish to study hypoglycemia and 2 student volunteers to study hyperglycemia.

Lab Exercise A: Blood glucose regulation- Insulin Shock

EQUIPMENT:
• Fishnet
• An active goldfish (you may take them home after lab)
• Beaker holding freshwater.
• Beaker holding human insulin solution.
• Beaker holding 5% glucose solution
• Stopwatch (cellphone)

Protocol:

Take the beaker holding freshwater to the provided fish tank.
Using your fish net, choose an active goldfish and place it in the beaker holding freshwater.
Transfer the goldfish to your table and begin timing.
For every minute (<5min), observe how the goldfish behaves and determine the metabolic rate by counting the number of opercula beats per minute (beats/min).
Place your goldfish into the beaker holding human insulin solution and begin timing.
For every minute (<5min), observe how the goldfish behaves and determine the metabolic rate by counting the number of opercula beats per minute (beats/min) every minute.
Place your goldfish into the beaker holding 5% glucose solution and begin timing.
For every minute (<5min), observe how the goldfish behaves and determine the metabolic rate by counting the number of opercula beats per minute (beats/min) every minute.
CLEAN-UP: Place your goldfish back in the fish tank. You may take your fish home (ask your instructor for details). Place all the materials back where you found them. Wipe up any water on the tables.

The operculum is a series of bones found in bonyfish that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding.

NOTE:

If your goldfish becomes lethargic, turns to its side, and begins to float, then IMMEDIATELY put it into the 5% glucose solution.
FOOD-SEEKING BEHAVIOR: Your goldfish may increase its metabolic rate and begin to actively look for food. However, this behavior does not persist for very long and the goldfish soon decreases its metabolic rate and becomes lethargic.

Lab Exercise B: Blood glucose regulation- Consuming glucose tablets increases glucose levels
Equipment

Two student volunteers who are non-diabetic and willing to run the glucose tests on themselves

20g of glucose (form of glucose tablets)
200mL bottled water
Glucose-meter and test-strips
Lancets
Alcohol swabs
Band-Aids
Stopwatch (cellphone)

Protocol

Turn on the glucose-meter.
Place the empty test-strip into the glucose-meter.
Clean your finger with an alcohol swab and wait to dry.
Lance your finger using the lancet.
Place a drop of blood into the test-strip.
Clean the site and put on a Band-Aid.
Allow the glucose-meter to read the initial blood glucose level.
Clean the glucose-meter with an alcohol swab.
The student should now consume 20 grams of glucose and 200mL of bottled water. Begin timing.
Determine their blood glucose levels after 15, 30, 45, and 60 minutes by repeating steps 1-8 at each time interval. Take a reading at 120 minutes if time allows.
Share your results with the class in real-time.
CLEAN-UP

BIOHAZARDS

The lancets and test-strips should go in the Sharps Biohazard waste container. The alcohol swabs with blood, tissue paper with blood, and Band-Aids with blood should go in the Soft Biohazard waste containers. Water cups should go in the regular trash.

Negative feedback mechanism used when plasma glucose levels are high.

Stimulus - Blood Glucose Levels Rise
- Sensory/Receptors - Beta cells in the pancreas detect the rise (change) in blood glucose levels
- Controller - Control centers (integrators) compare the changed plasma glucose level with the set point and signal the effectors to generate a response. Control centers sometimes consider information other than just the level of the variable in their decision-making, such as time of day, age, external conditions, etc -
Efferent Pathway
- Effector(s) - Beta cells in the pancreas respond by releasing insulin
- Response(s) - insulin causes the liver and cells of the body to take up glucose. The liver takes the glucose and stores it as glycogen.

Negative feedback mechanism used when plasma glucose levels are low.

Stimulus - Change in plasma glucose level - Plasma Glucose becomes LOW
- Sensory - Receptors (sensors) detect changes in the plasma glucose level
- Controller - Control centers (integrators) compare the changed plasma glucose level with the set point and signal the effectors to generate a response. Control centers sometimes consider information other than just the level of the variable in their decision-making, such as time of day, age, external conditions, etc
Efferent Pathway - Effectors execute the necessary changes to adjust the blood glucose level.
- Effector(s) - Alpha cells of the pancreas
- Response(s) - Alpha cells release glucagon / Glucagon causes liver to break down glycogen into glucose / Liver releases glucose into blood stream