Download Selected Answers to Unit 4 Homeostasis Review Sheet

Selected Answers to Unit 4 Homeostasis Review Sheet
Homeostasis and Feedback Systems
2. Negative feedback is when a stimulus produces a reaction that reduces the stimulus and its effects. An example
of this is when a person consumes carbohydrates and its blood sugar levels rises above the normal level which is
dangerous. To reduce this effect, the hormone insulin is released by the beta cells of Islets of Langerhans in the
pancreas. The hormone causes the cells of surrounding muscles and organs to become more permeable to glucose,
allowing it to be taken up from the blood, thereby reducing the levels of blood sugar. Insulin also inhibits the
breakdown of glycogen into glucose, fats into fatty acids and proteins into amino acids. The outcome is a decrease
in blood sugar. Positive feedback is when a stimulus produces a reaction that increases the stimulus and its
effects. It is less common than negative feedback. Positive feedback control can be harmful to the body because
continual promotion of the stimulus can put the body into overdrive. For example, promotion of increasing blood
sugar level is very dangerous and can render a person unconscious.
Endrocrine System
6. A marathon runner took a performance-enhancing drug. You would expect him to have an injection of
eythropoeitin (EPO) because marathon runners need plentiful supplies of oxygen if they are to run long distances.
Extreme muscle mass is not seen in marathon runners as it can limit the flexibility of their body (if they used
anabolic steroids). By having injections of EPO, there are MORE red blood cells available in the runner’s body,
enabling them to bind to oxygen and transport them throughout the body to maintain the runner’s performance.
9.
Person
Ms. Y
Correct Curve
A
Ms. X
B
Ms. Z
C
Reasons
If Ms. Y is in good health then she does not have issues with insulin supply and
insulin receptors. The curve shows that upon injection of glucose, there is a rise in
glycemia (blood sugar levels), as expected. People in good health and no issues with
insulin supply/function would have the hormone released in response to the increase
in blood sugar levels. Within an hour of this increase, there is already a decrease in
blood sugar levels going back down to the normal levels (the levels seen before the
injection of glucose).
If Ms. X suffers from high blood sugar (hyperglycemia), then she has issues with the
insulin receptors in her body. She produces insulin but the receptors just do not work
as effectively as a person in normal health. Curve B shows that upon injection of
glucose, there is a rise in glycemia (blood sugar levels) but this rise has a sharper
slope than Curve A. It takes longer for her blood sugar levels to decrease (there is
some insulin released) and the blood sugar levels do not decrease as much (they do
not go back to normal). This shows that the insulin receptors are not working
correctly and not enough insulin has been made/released in her body.
Upon injection of glucose, there is an increase in glycemia (blood sugar levels) as
seen in the curve. Insulin is released by the beta cells, as expected, which
corresponds to the decrease in blood sugar levels after an hour but Ms. Z has
cancerous beta cells, meaning that the release of insulin is not normal and too much
insulin is released (cancerous cells multiply quickly and have aggressive activity).
This can be seen in the graph where too much insulin has been released, making the
blood sugar go below normal range (due to the aggressive activities of the cancerous
cells). This triggers glucagon to be released to try to restore the blood sugar levels
back to normal.
Nervous System
3. In multiple sclerosis, myelin is progressively lost from axons and replaced by hardened scar tissue. Myelin is
the protective coating on axons and it prevents loss of charged ions and therefore, helps with the overall
transmission of the nerve impulse. When myelin is lost, the nerve impulse cannot be transmitted effectively and
quickly along the axon (and onto the next neuron). So the “message” (the nerve impulse itself) cannot be sent
from one neuron to the next neuron with continued myelin loss. This in turn affects the coordination, balance,
memory and speech of an individual.