Link to the  Student learning guide for Feedback/Homeostasis

1. Introduction: Regulating Blood Glucose

Glucose is essential to life, because it’s the primary fuel that cells use to make ATP. For animals like us, the cells in our bodies acquire glucose from capillaries (tiny blood vessels) that supply the tissues of the body with blood. Glucose in the blood, in turn, comes from the food we eat, which gets absorbed into the blood through our intestines.

Unlike body temperature, which we mammals keep confined to a narrow range, blood glucose levels can fluctuate by almost 50% over the course of the day. Nevertheless, blood glucose levels are tightly regulated.  Too little glucose, especially in our glucose-hungry brains, can send us into shock. Too much is associated with diabetes, an increasingly common disease that affects about 30% of our population.

Blood glucose is measured in milligrams/deciliter (mg/dL). To put what follows in context, you can think of 100 mg/dL as just a few grains of sugar in a half a cup of water. Assuming that you’re not a diabetic or prediabetic (much more about those conditions below), your set point for blood glucose is probably about 90 mg/dL (indicated by the dotted line at “E”). When you eat, particularly if it’s a meal with starch or sugar, then your blood glucose will rise to a higher level: up to about 140 mg/dL (point “B”). At that point, homeostatic mechanisms will kick in, lowering your blood glucose back to its set point. If you go a few more hours without eating, then your glucose level will continue to fall. At a certain point (“C”) other homeostatic mechanisms will kick in to raise your blood sugar back to the set point. Your blood sugar will continue to oscillate around a set point until you eat again.

2. Glucose Regulation: Setting the Context

To understand how our bodies regulate blood glucose concentration, you need to know a few organs, tissues, and cell types. The pancreas (shown at right) mostly consists of tissues that create digestive enzymes and other digestive secretions (these are the exocrine cells in the callout at right). These secretions are released into ducts that empty into the intestine. In addition, the pancreas also consists of groups of cells called the Islets of Langerhans. These Islets consist of two types of cells that release hormones that help control blood glucose levels.

Beta cells secrete the hormone insulin, the function of which is to lower blood glucose by inducing a variety of cells to absorb glucose from the blood and to convert it into the polysaccharide glycogen, or into fat. Alpha cells secrete glucagon, which induces cells to break glycogen into glucose, which diffuses into the bloodstream, raising blood glucose levels.

3. Insulin

Insulin is a complex, quaternary protein. At its most basic level, it consists of two polypeptide chains linked by disulfide bridges.

Secondary and tertiary interactions lead insulin to fold into a complex shape, and these molecules will interact with one another to form dimers (two units bonded together by hydrogen bonds) and hexamers (six units bonded together). The hexamer is used for storage, waiting to be released when the body needs to reduce blood glucose levels. The monomer is the most biologically active form.

Insulin Dimer: Notice the alpha helices and the hairpin turns caused by side chain interactions

Insulin Hexamer

3a. Control of Insulin Release

How do the beta cells in the pancreas “know” when to release insulin?

After a carbohydrate-rich meal, glucose will diffuse into the blood from the small intestine. As a polar, water soluble molecule, glucose needs a channel to pass from the extracellular fluid (“A”) through the membrane (“B”) and into the cytoplasm (“C”). That channel is called GLUT2 (see “1”) and it allows glucose to enter the cytoplasm of the pancreatic Beta cells by facilitated diffusion. Once in the cytoplasm, glucose becomes the initial substrate for cellular respiration (“2”), resulting in increased ATP (“3”). This ATP  binds with a potassium channel (“4”), causing it to close. With these positively charged potassium ions no longer diffusing out of the cell, the membrane becomes partially depolarized (“5”).

Depending on where you are in your curriculum, what happens next might remind of of how neurotransmitters are released from axonal bulbs, or about how muscle contraction occurs.  Depolarization causes voltage dependent calcium channels (VDCCs, at “6”) to open. This allows calcium ions to diffuse into the cytoplasm. where they interact with insulin containing vesicles in such a way that induces exocytosis (“8”) releasing insulin into the bloodstream (“9”).

3b. Insulin’s Effect in Liver, Fat, and Muscle Tissue

Once released from the pancreas, insulin will circulate throughout the body in the bloodstream. In the diagram to the right, insulin is indicated by letter “a.” Insulin will bind receptors  (“b”) on cells in your liver, muscles and fatty tissues. Binding with the insulin receptor causes a signal transduction cascade (“f”) that has various effects in insulin’s target cells, one of the most important of which is to bind with glucose transport channels (“c”). In response, these channels open, allowing for glucose (“d”) to enter the cells via facilitated diffusion (“e”).

Once inside the cytoplasm, glucose might be converted into the polysaccharide glycogen (at “g”). Alternatively, glucose might undergo glycolysis (“h”), breaking it down into the 3-carbon molecule pyruvic acid (“i”). In fat cells, pyruvate might be converted into fatty acids (“j”), which can then be stored away as triglycerides.

4. Insulin: Checking Understanding

[qwiz qrecord_id=”sciencemusicvideosMeister1961-M26, Insulin”]

[h]Insulin: Checking Understanding

[i]

 

[q]In the diagram below, the effect of insulin can first be seen at

[textentry single_char=”true”]

[c*] B

[f] Excellent. “B” shows blood glucose dropping after a meal, an effect that would be brought about by insulin.

[c] Enter word

[c] *

[f] No. Here’s a hint. Insulin lowers blood sugar levels. Where do you see that happening?

[q]In the diagram below, at what point would you predict that glucagon would be released?

[textentry single_char=”true”]

[c*] C

[f] Nice. “C” shows the lowest point of blood glucose, followed by a rise. That rise would be brought about by glucagon.

[c] Enter word

[c] *

[f] No. Here’s a hint. Glucagon increases blood glucose levels. Where do you see that starting to happen?

[q]In the diagram below, at what point would glucose first start to be converted into glycogen and fat?

[textentry single_char=”true”]

[c*] B

[f] Nice. “B” shows blood glucose levels dropping. That drop occurs as insulin induces liver (and other tissues) to absorb glucose from the blood and to convert it into glycogen.

[c] Enter word

[c] *

[f] No. Here’s a hint. As glucose is converted into glycogen and fat, blood glucose levels would start dropping. Where do you see that happening?

[q]In the diagram below, which number refers to processes like cellular respiration?

[textentry single_char=”true”]

[c*] 2

[f] Excellent. “2” increases the relative amount of ATP in the cell, which can only come about through cellular respiration?

[c] Enter word

[c] *

[f] No. Here’s a hint. Think about what cellular respiration creates. Now find a process on the diagram that’s creating it.

[q]In the diagram below, three channels are shown. Which one is connected with causing a partial depolarization of the membrane?

[textentry single_char=”true”]

[c*] 4

[f] Nice.  When “4” closes, potassium ions can no longer diffuse out of the cell. Keeping a positive charge locked inside the membrane depolarizes the membrane.

[c] Enter word

[c] *

[f] No. Here’s a hint. One of the channels shown is keeping  positive potassium ions inside the membrane, causing the membrane to depolarize. Look at what each channel does, and you should see the answer. If that doesn’t help, then remember back to nerve cells. What’s the positive ion that’s in high concentration inside a neuron. What would happen to the membrane’s potential if that ion were trapped inside the neuron?

[q]In the diagram below, three channels are shown. Which one allows in the ion that induces exocytosis?

[textentry single_char=”true”]

[c*] 6

[f] Nice.  When “6” opens, calcium ions diffuse into the cell, inducing exocytosis of insulin vesicles.

[c] Enter word

[c] *

[f] No. Here’s a hint. Think back to nerve cells. This is the same ion that causes vesicles with neurotransmitters to release their neurotransmitter into the synapse. Now find the channel that’s allowing that ion in. Or, if that doesn’t help, just work backwards from “8.”

[q]In the diagram below, insulin is being released at

[textentry single_char=”true”]

[c*] 9

[f] Awesome.  Number “9” is showing release of insulin.

[c] Enter word

[c] *

[f] No. Here’s a hint. Insulin is released by vesicles through exocytosis. Where is that happening?

[q]In the diagram below, insulin is at

[textentry single_char=”true”]

[c*] a

[f] Awesome.  Letter “a” is insulin.

[c] Enter word

[c] *

[f] No. Here’s a hint. Insulin is the ligand. When it binds with its receptor, it allows glucose to diffuse into the cell.

[q]In the diagram below, the insulin receptor is at

[textentry single_char=”true”]

[c*] b

[f] Nice.  Letter “b” is the insulin receptor.

[c] Enter word

[c] *

[f] No. Here’s a hint. Insulin is the ligand. What is the ligand binding with.

[q]In the diagram below, facilitated diffusion is indicated by

[textentry single_char=”true”]

[c*] e

[f] Nice.  Letter “e” shows glucose entering into cells through a protein channel, which is what facilitated diffusion is all about.

[c] Enter word

[c] *

[f] No. Here’s a hint. Look for a molecule that’s diffusing into the cell through a protein channel. That’s facilitated diffusion.

[q]In the diagram below, a signal transduction cascade is indicated by

[textentry single_char=”true”]

[c*] f

[f] Nice.  Letter “f” shows a second signal that’s going to the cytoplasm and other parts of the membrane. These signals are transmitted in cells through signal transduction cascades.

[c] Enter word

[c] *

[f] No. Here’s a hint. When insulin (a) binds with its receptor (b), that’s the first message. What arrow inside the cytoplasm shows transmission of a second signal.

[q]In the diagram below, glycogen formation is shown at

[textentry single_char=”true”]

[c*] g

[f] Nice.  Letter “g” shows glucose molecules that have been chained together to form glycogen.

[c] Enter word

[c] *

[f] No. Here’s a hint. Letter “d” is glucose. Glycogen is a polymer of glucose.

[q]In the diagram below, glycolysis is shown at

[textentry single_char=”true”]

[c*] h

[f] Nice.  Letter “h” shows glucose molecules (which have six carbons) being broken down into a 3 carbon molecule. That molecule would be pyruvic acid, and it’s the product of glycolysis.

[c] Enter word

[c] *

[f] No. Here’s a hint. Glycolysis produces pyruvic acid, which is a 3 carbon molecule. What process is producing a 3 carbon molecule.

[/qwiz]

5. Glucagon

Glucagon is a peptide hormone. It consists of 29 amino acids that curl into an alpha helix, as shown below

Glucagon is a peptide hormone

Glucagon works as insulin’s antagonist, inducing physiological responses in its target cells that raise blood glucose levels toward the body’s set point. You can see this happening in a general way in the diagram at right. Glucagon (1) is taken up by cells in the liver (2). In liver cells, a phosphorylation cascade activates enzymes (not shown) to break down the polysaccharide glycogen (3), which is a polymer of glucose. Once broken down, the glucose (4) can diffuse from the liver into the surrounding blood vessels (5).

Note that If you’ve already done my tutorial about how epinephrine (also known as adrenaline) can mobilize tissue in the liver to break down the polysaccharide glycogen into glucose, then everything that follows is going to feel like review (which is a good thing to be doing at this point in the course).

Like epinephrine, glucagon binds with a G-linked membrane receptor. Binding unleashes a chain of events at the membrane that result in the release of the second messenger, cyclic AMP (cAMP). Cyclic AMP, in turn, unleashes a phosphorylation cascade that results in activation of the enzyme phosphorylase, which catalyzes the breakdown of glycogen to glucose.

Here are the details.

Glucagon (“a”) binds with a G-coupled protein receptor (“b”). Binding induces a conformational change in the G protein (“c”), with substitutes a GDP for GTP (remember that these are analogues of ADP and ATP). GTP activates the G protein, which now diffuses through the phospholipid bilayer (“2”) until it encounters the membrane bound enzyme adenylyl cyclase (“e”). Adenylyl cyclase converts (“f”) ATP into the second messenger, cyclic AMP (also known as cAMP).

cAMP is the second messenger because it can continue to transmit information into the cytoplasm (“3”), whereas the first messenger (glucagon) could only bring its signal to the membrane. cAMP unleashes a phosphorylation cascade (“g”) in which enzymes called kinases activate other enzymes by adding phosphate groups to them. At the end of the chain, the target enzyme, phosphorylase a, is activated, and then converts glycogen (at “i”) to glucose (“j”), which can then diffuse out of the cell (indicated by the arrow at “k.”)

Got it? You’ll get a chance to show what you know in the quiz below.

6. Insulin and Glucagon: Checking Understanding

[qwiz qrecord_id=”sciencemusicvideosMeister1961-M26, Insulin and Glucagon”] [h]

Insulin and Glucagon: Checking Understanding

[i]Biohaiku

Blood Glucose Levels

Insulin and Glucagon

Homeostasis

[q labels = “top”]

 

[l]Alpha cells release glucagon

[f*] Great!

[fx] No. Please try again.

[l]Beta cells release insulin

[f*] Excellent!

[fx] No. Please try again.

[l]Blood glucose falls

[f*] Good!

[fx] No. Please try again.

[l]Blood glucose rises

[f*] Great!

[fx] No. Please try again.

[l]Body cells take up glucose

[f*] Correct!

[fx] No, that’s not correct. Please try again.

[l]Liver breaks down glycogen, releases glucose

[f*] Correct!

[fx] No, that’s not correct. Please try again.

[l]Liver takes up glucose; makes glycogen

[f*] Good!

[fx] No, that’s not correct. Please try again.

[l]insulin

[f*] Great!

[fx] No, that’s not correct. Please try again.

[l]glucagon

[f*] Great!

[fx] No, that’s not correct. Please try again.

[q] In the diagram below, which letter shows where Beta cells would be releasing insulin?

[textentry single_char=”true”]

[c*] C

[f] Excellent. “C” shows the pancreas releasing insulin in response to a rise in blood glucose.

[c] Enter word

[c] *

[f] No. Here’s a hint: insulin is released by cells in the pancreas in response to a rise in blood glucose levels.

[q] In the diagram below, where would glucose be converted into glycogen?

[textentry single_char=”true”]

[c*] F

[f] Excellent. “F” is where the liver would convert glucose to glycogen.

[c] Enter word

[c] *

[f] No. Here’s a hint: this is one of the two organs shown above that are responding to insulin, and this occurs when blood sugar levels are rising.

[q] In the diagram below, what letter indicates insulin?

[textentry single_char=”true”]

[c*]D

[f] Nice job. “D” has to be insulin: the hormone that’s released in response to rising blood levels.

[c] Enter word

[c] *

[f] No. Here’s a hint: find where blood glucose is rising above the set point. Insulin is the hormone released in response.

[q] In the diagram below, what letter indicates falling blood glucose levels?

[textentry single_char=”true”]

[c*]G

[f] Awesome. “G” indicates the body’s response to insulin release: falling blood glucose levels.

[c] Enter word

[c] *

[f] No. Here’s a hint: blood glucose levels will fall in response to release of insulin, which is released in response to rising blood glucose levels.

[q] In the diagram below, what letter indicates glucagon?

[textentry single_char=”true”]

[c*]J

[f] Awesome. “J” indicates glucagon

[c] Enter word

[c] *

[f] No. Here’s a hint: glucagon is released in response to rising blood glucose levels.

[q] In the diagram below, what letter indicates where glycogen is being broken down to glucose?

[textentry single_char=”true”]

[c*]K

[f] Nice. “K” indicates where the liver would be breaking down glycogen to glucose.

[c] Enter word

[c] *

[f] No. Here’s a hint: this is going to occur in response to the release of glucagon, which is going to be released by the pancreas in response to falling blood glucose levels. So, the question (and answer) is where is it going to occur?

[q] In the diagram below, what letter indicates where Beta cells are releasing insulin?

[textentry single_char=”true”]

[c*]C

[f] Nice work. “C” indicates where beta cells in the pancreas would be releasing insulin.

[c] Enter word

[c] *

[f] No. Here’s a hint: Beta cells release insulin. Think about what organ releases insulin, and under what conditions insulin is released.

[q] In the diagram below, what letter indicates where alpha cells are releasing glucagon?

[textentry single_char=”true”]

[c*]I

[f] Way to go. “I” indicates where alpha cells in the pancreas would be releasing glucagon.

[c] Enter word

[c] *

[f] No. Here’s a hint: Alpha cells in the pancreas release glucagon, which is released when blood glucose falls below the set point. Put those two together, and you’ll have the answer.

[q] In the diagram below, what letter indicates a G-protein coupled receptor?

[textentry single_char=”true”]

[c*]b

[f] Way to go. Letter “b” indicates the G-protein coupled receptor.

[c] Enter word

[c] *

[f] No. Here’s a hint: Find the membrane embedded receptor that can bind with a ligand, which in this case is glucagon.

[q] In the diagram below, what letter indicates the inactive form of the G-protein?

[textentry single_char=”true”]

[c*]c

[f] Way to go. Letter “c” indicates the inactive form of the G-protein.

[c] Enter word

[c] *

[f] No. Here’s a hint: The G-protein, when inactive,  is linked to the receptor, which is embedded in the membrane.

[q] In the diagram below, what letter indicates adenylyl cyclase?

[textentry single_char=”true”]

[c*]e

[f] Nice. Letter “e” indicates adenylyl cyclase.

[c] Enter word

[c] *

[f] No. Here’s a hint: Adenylyl cyclase responds to a signal from the G protein, and converts ATP to cyclic AMP.

[q] In the diagram below, what letter shows production of the second messenger?

[textentry single_char=”true”]

[c*]f

[f] Nice. Letter “f” shows adenylyl cyclase making ATP into cAMP, which is the second messenger.

[c] Enter word

[c] *

[f] No. Here’s a hint: The enzyme that’s producing the second messenger is Adenylyl cyclase, and it’s converting ATP into the second messenger, cAMP.

[q] In the diagram below, what letter shows a phosphorylation cascade?

[textentry single_char=”true”]

[c*]g

[f] Nice. Letter “g” shows a phosphorylation cascade.

[c] Enter word

[c] *

[f] No. Here’s a hint. During a phosphorylation cascade, a series of enzymes called kinases activate enzymes by adding phosphate groups onto them. Where in the diagram do you see the word “kinase?”

[q] In the diagram below, where do you see production of the enzyme that converts starch into glucose?

[textentry single_char=”true”]

[c*]h

[f] Excellent. Letter “h” shows conversion of phosphorylase a into phosphorylase b, and phosphorylase b is the enzyme that converts glycogen into glucose.

[c] Enter word

[c] *

[f] No. Here’s a hint. In the bottom of the diagram, you see glycogen being converted into glucose. What enzyme is catalyzing that conversion?

[x][restart]

[/qwiz]

7. Understanding Diabetes

Diabetes is a disease in which people can’t regulate their blood sugar levels. Immediate symptoms are frequent urination, thirst, and hunger. Untreated, diabetes can be fatal: before it kills you, diabetes can lead to cardiovascular disease, stroke, kidney disease, ulcers of the feet, and damage to the eyes

There are two forms, Type 1 (which generally occurs in children) and Type 2 (which generally occurs in adults).

7a. Type 1 Diabetes

Type 1 diabetes is an autoimmune disorder that usually sets in during childhood, but can happen later in life, too. Because of its early onset, Type 1 diabetes is also referred to as juvenile diabetes.

In children with type 1 diabetes, beta cells (1) and their secretions (insulin, vesicles, shown at “2”) are seen as antigen by the cells of the immune system (the dendritic cells and cytotoxic T cells shown at “3” and “4”). In response, the cytotoxic T cells unleash the weapons of the cell mediated immune response, releasing granzymes and perforins that attach and destroy the pancreatic Beta cells (“5”). 

Type 1 diabetes only accounts for 5 to 10% of diabetes, and it affects about 1.25 million Americans (source: healthline.com). It can be treated by injection of insulin, attention to diet, and careful monitoring of blood glucose levels. For a tutorial about how insulin can be synthesized through genetic engineering, click here.

7b. Type 2 Diabetes

Far more common is type 2 diabetes. In type 2 diabetes, insulin levels are normal, but cells don’t respond to insulin, a condition known as insulin resistance.

Normal insulin response v. type II diabetes. © sciencemusicvideos, LLC. Made with Biorender.com

 

The diagram above contrasts normal insulin-induced glucose regulation (“A”) with the insulin resistance (“B”) that happens in type 2 diabetes.

In normal glucose regulation, insulin (1) binds with an insulin receptor (3) in liver and muscle cells. This induces a signalling cascade that mobilizes  glucose channels (4) to move to the cell membranes of these cells. These channels allow glucose (2) to enter the cells by facilitated diffusion (5). Notice the high level of glucose inside the cell, and the low level of glucose in the bloodstream (7) .

In type 2 diabetes, cells don’t respond to the insulin signal. This is represented at 6 (malfunctioning of the signaling cascade) and 8 (glucose not diffusing through the absent glucose transport channel). As a result of glucose not being taken up by the cells, glucose builds up in the bloodstream (9).

Because blood levels of glucose remain high in type 2 diabetes, Beta cells continue to receive the signal that they need to produce insulin. This continual stimulation can lead Beta cells to fail. As a result, some type 2 diabetics may require insulin injections as part of their treatment.

Because of lifestyle factors — increasing levels of obesity and decreasing levels of physical activity — Up to 30 million americans (10% of the population) has type 2 diabetes. Up to 100 million American adults have a condition called prediabetes (source: (healthline.com).  Prediabetes involves elevated blood sugar levels, but not at a level high enough to be classified as diabetes. However, some of the organ/tissue damage associated with diabetes may have already begun. Type 2 diabetes has risen to become the 7th most common cause of death in the U.S.

7c. Diabetes: Why sweet urine, excessive thirst.  and urination?

One of the first diagnostic signs of both type 1 and type 2 diabetes is excessive thirst and frequent urination. Let’s look at the underlying biology behind why that is. Note that you can scroll the text below the diagram as you read.

Source: remixed from various sources

The kidneys (one of which is shown in cross-section at “A”) is the main organ responsible for controlling the osmolarity of your body fluids. It does that by filtering your blood through millions of tubules called nephrons (B), then processing the filtrate, reabsorbing needed substances (like glucose and salts), and excreting harmful wastes (like urea).Blood enters your kidneys through a major blood vessel called the renal artery (not shown). This artery divides again and again until it has millions of branches, each of which ends in a bed of thin walled capillaries that form a structure called the glomerulus (shown in a simplified form at “C”). The glomerulus is the filter in the system. It’s evolved to hold back the large components of the blood (red and white blood cells, platelets, and large proteins) within the blood vessels. But smaller components of blood — solutes like sugar and salt,  other small molecules, and waste) — pass through the glomerulus and enter a capsule (at “D”). You can think of this as being similar to pouring water through a coffee filter. The filter holds in the coffee grounds, and lets the dissolved coffee and most of the water through. What passes through the glomerulus is, in fact, called filtrate. To continue the analogy, when you’re drinking coffee, you’re drinking filtrate.

After the capsule, the filtrate winds its way through the nephron tubule (at “E”) Specialized cells in the walls of the nephron tubule attempt to reabsorb valuable materials, such as glucose, and return them to the blood. In this diagram, reabsorption is represented by the upward arrows at letter “G”. Whatever isn’t reabsorbed from the filtrate in the tubule winds up being excreted, with waste products, in the urine (“H”).

In non-diabetics, all of the glucose in the filtrate will be reabsorbed from the tubule, and the urine will be free of glucose. However, in diabetics, the level of blood glucose is so high that high levels of glucose also wind up being in the filtrate in the tubule. The level of glucose in the tubule, in fact, exceeds the capacity of the tubule to reabsorb that glucose into the blood. As a result, glucose stays in the filtrate in the tubule, and diabetics wind up with sweet urine (which is actually the source of the name diabetes mellitus: the mellitus part refers to “honey.”). The sugar concentration in the tubule also creates a filtrate that is hypertonic to the fluid outside the tubule. Because of that, water outside the tubule flows into the tubule (shown by the arrows at “F”). The flow of water into the tubule makes for an abnormally high urine volume. And because of so much water loss, untreated suffer from thirst.

8. Diabetes (and related topics): Checking Understanding

[qwiz qrecord_id=”sciencemusicvideosMeister1961-M26, Diabetes”] [h]

Diabetes and Blood Glucose Regulation: Cumulative Quiz

[i]

[q] The hormone that’s causing the drop in blood glucose between points “B” and “C” is  [hangman].

[c] insulin

[f] Good!

[q] The hormone that’s causing the rise in blood glucose levels between points “C” and “D” is [hangman].

[c] glucagon

[f] Correct!

[q] The pancreatic cells that release insulin are the [hangman]cells. The cells that release glucagon are the [hangman].

[c] Beta

[f] Great!

[c] alpha

[f] Correct!

[q] Glucagon induces cells in the liver and muscle to take the polysaccharide   [hangman] and to convert it into the monosaccharide [hangman], which can then diffuse out of these cells and enter the [hangman]. 

[c] glycogen

[f] Good!

[c] glucose

[f] Correct!

[c] blood

[f] Great!

[q] The diagram below shows how the release of the hormone [hangman] is induced by uptake of[hangman]

into Beta cells. The ATP creating metabolic reaction shown at number 2 is [hangman]  [hangman]. The ATP creates changes in the membrane that allow [hangman]  ions to flow into these cells, causing[hangman] (shown at “9”), releasing this hormone into the bloodstream.

[c] insulin

[f] Good!

[c] glucose

[f] Correct!

[c] cellular

[f] Correct!

[c] respiration

[f] Correct!

[c] calcium

[f] Good!

[c] exocytosis

[f] Good!

[q] The diagram below shows how when [hangman] (at “a”) binds with its receptor, a signal  [hangman] cascade results. One effect of this cascade is to allow [hangman] to enter cells by [hangman] diffusion. Once inside the cells, some of the glucose is converted to [hangman], shown at “g.” Other glucose molecules enter [hangman] (indicated by the arrow at “h”), the products of which can get converted to [hangman] acids (at “j”).

[c] insulin

[f] Good!

[c] transduction

[f] Good!

[c] glucose

[f] Great!

[c] facilitated

[f] Correct!

[c] glycogen

[f] Great!

[c] glycolysis

[f] Excellent!

[c] fatty

[f] Great!

[q] The diagram below shows how [hangman] at “a,” by binding with a G-coupled protein [hangman] can result in release of the [hangman] [hangman] cAMP. cAMP, in turn, can unleash a [hangman] cascade (shown at “g”). Finally, the activation of the enzyme phosphorylase a can result in the conversion of [hangman] to [hangman], which then [hangman] out ot the cell and into the bloodstream.
x

[c] glucagon

[f] Correct!

[c] receptor

[f] Good!

[c] second

[f] Excellent!

[c] messenger

[f] Excellent!

[c] phosphorylation

[f] Great!

[c] glycogen

[f] Good!

[c] glucose

[f] Correct!

[c] diffuses

[f] Excellent!

[q] The diagram below shows how [hangman] (at “D”)  released by the [hangman] cells of the pancreas, acts to [hangman] blood glucose concentration, returning it to the homeostatic [hangman] points. By contrast, the role of [hangman]  (at “J”) is to [hangman] blood glucose levels by getting the liver to convert [hangman] to glucose.
x

[c] insulin

[f] Great!

[c] beta

[f] Good!

[c] lower

[f] Great!

[c] set

[f] Good!

[c] glucagon

[f] Good!

[c] increase

[f] Good!

[c] glycogen

[f] Great!

[q] The diagram below is showing the origin of type ___ diabetes.

[textentry single_char=”true”]

[c*] 1

[f] Good! The diagram above is showing the origin of type 1 diabetes.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No, but here’s a hint: which type of diabetes is caused by an autoimmune reaction that results in the destruction of Beta cells in the pancreas?

[q] In the diagram below, an antigen presenting cell (examples of which are dendritic cells and macrophages) is shown at

[textentry single_char=”true”]

[c*] C

[f] Nice job! In the diagram above, an antigen presenting cell is shown at “C.”

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No, but here’s a hint. Which letter shows a cell that has ingested antigen, and is now showing it to a killer T cell (shown at “E.”)

[q] In the diagram below, a cytotoxic or killer T cell is shown at

[textentry single_char=”true”]

[c*] E

[f] Excellent! In the diagram above, letter “E” indicates a cytotoxic or killer T cell.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No, but here’s a hint. The cytotoxic or killer T cells release chemical weapons that destroy the beta cells in the pancreas. Which cells (based on the flow of arrows) seem to be on the attack?

[q] The diagram below shows how type 1 diabetes is an [hangman] disease, caused when the immune system comes to recognize insulin as an [hangman].
x

[c] autoimmune

[f] Good!

[c] antigen

[f] Good!

[q] The diagram below shows how in type 2 diabetes, cells stop responding to [hangman]. As a result, [hangman] (at “2”) won’t [hangman] through membrane channels (shown at “4”). As a result, concentration of glucose in the [hangman] rises to high levels.

x

[c] insulin

[f] Great!

[c] glucose

[f] Correct!

[c] diffuse

[f] Excellent!

[c] blood

[f] Great!

[q] In the diagram below, which patient is most likely a diabetic?

[textentry single_char=”true”]

[c*] C

[f] Nice job! Patient C’s blood glucose level is way above the healthy set point to begin with, and then stays high even hours after eating.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Here’s a hint. Diabetes is an inability to control blood sugar levels. Of the three patients, who’s blood sugar seems to be the most out of control?

[q] In the diagram below, which patient is most likely a prediabetic?

[textentry single_char=”true”]

[c*] B

[f] Excellent! Patient B’s blood glucose levels are above the healthy levels, but not yet as out of control as the diabetic patient (C).

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Here’s a hint. Prediabetes involves an inability to regulate blood sugar, but not quite to the extent as is found in diabetics.

[q] In the diagram below, which hormone is glucagon?

[textentry single_char=”true”]

[c*] A

[f] Nice job! Hormone A goes up when blood glucose levels go down; exactly what you’d expect for glucagon.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Here’s a hint. Glucagon raises blood glucose levels. Look for the hormone that goes up in concentration when glucose levels go down.

[q] In the diagram below, which hormone is insulin?

[textentry single_char=”true”]

[c*] B

[f] Excellent! Hormone B goes up when blood glucose levels go up; exactly what you’d expect for insulin.

[c] Enter word

[f] Sorry, that’s not correct.

[c] *

[f] No. Here’s a hint. Insulin lowers blood glucose levels. Look for the hormone that goes up in concentration when glucose levels go up.

[q] The diagram below is showing how excess[hangman] in the blood (at “C”) results in [hangman] being excreted into the nephron tubule at levels that can’t be reabsorbed. As a result, [hangman] flows by [hangman] into the nephron tubule, resulting in the high level of[hangman] (letter “H”) production that’s a characteristic sign of [hangman]

[c] glucose

[f] Excellent!

[c] glucose

[f] Good!

[c] water

[f] Excellent!

[c] osmosis

[f] Good!

[c] urine

[f] Correct!

[c] diabetes

[f] Correct!

[q] In the diagram below, a capillary is indicated by letter

[textentry single_char=”true”]
[c*] C

[f] Nice! “C” is a capillary bringing blood to a nephron tubule.

[c] Enter word

[c] *

[f] No. Here’s a hint. The capillaries bring fluid to the tubule. What seems to be bringing fluid into this system?

[q] In the diagram below, reabsorption of glucose (a process that happens poorly in diabetics) is indicated by letter

[textentry single_char=”true”]
[c*] G

[f] Correct! “G” shows where the tubule is reabsorbing glucose. The problem that diabetics have is that so much glucose gets into the tubule that it exceeds that capacity of the tubule to reabsorb it, creating the sugary urine for which diabetes mellitus is named.

[c] Enter word

[c] *

[f] No. Here’s a hint. Reabsorption involves taking solutes out of the tubule, and returning them to the blood. Find the tubule, then find an arrow indicating substances leaving the tubule.

[q] In the diagram below, the filtrate leaving the tubule is indicated by letter

[textentry single_char=”true”]
[c*] H

[f] Great job! “H” indicates the fluid that’s leaving the tubule, which we refer to as urine.

[c] Enter word

[c] *

[f] No. Here’s a hint. Think about the liquid that your kidneys make. What color is that liquid?

[x][restart]

[/qwiz]

Links

  1. Feedback/homeostasis 3: ADH and Osmoregulation (the next tutorial in this module)
  2. Feedback/Homeostasis Main Menu