1. 6.5 Notes
Homeostasis

2. What is homeostasis?
the process of maintaining the internal conditions of an organism between acceptable limits

3. Homeostasis in Humans
What are some conditions need to be kept in homeostasis in humans?
body temperature
blood glucose concentration
blood pH
carbon dioxide concentration
water availability

4. How does the human body react to low temperatures?
thermoreceptors in hypothalamus activates warming mechanisms
nerve impulses from hypothalamus trigger shivering which generates heat
nerve impulses from hypothalamus trigger vasoconstriction of skin arterioles;
this reduces blood flow to extremities –thereby minimizing heat loss through skin

5. How does the human body react to high temperatures?
thermoreceptors in hypothalamus activates cooling mechanisms
nerve impulses from hypothalamus trigger sweat glands and promotes evaporation/cooling
nerve impulses from hypothalamus trigger vasodilation of skin arterioles;
this increases blood flow to extremities thereby heat loss is increased through skin

6. How does the human body react to low blood sugar levels?
pancreatic cells monitor blood glucose
low glucose level induces production of glucagon
glucagon stimulates the liver to break glycogen into glucose
therefore blood glucose increases

7. How does the human body react to high blood sugar levels?
pancreatic cells monitor blood glucose
high level of blood glucose induces production of insulin
insulin stimulates uptake of glucose into cells (muscles)
insulin stimulates uptake of glucose into liver where it is stored as glycogen
insulin leads to decrease in blood glucose
blood glucose regulation is an example of negative feedback

8. Diabetes Type I diabetes Type 2 diabetes insulin-dependent diabetes
people do not have the ability to produce insulin
they must take insulin externally
Type 2 diabetes
non-insulin-dependent diabetes
people can produce insulin but not in proper amounts
can usually be controlled by diet or exercise
much more common than Type I

9. IB Exam Question
1. Which process decreases when the human body temperature decreases? (1 mark)
A. Blood flow to the internal organs
B. Secretion of sweat
C. Secretion of insulin
D. Shivering
Correct answer: B

10. IB Exam Question
2. Describe the response of the human body to low external temperatures. (4 marks)
thermoreceptors in hypothalamus activates warming mechanisms
nerve impulses from hypothalamus trigger shivering which generates heat
nerve impulses from hypothalamus trigger vasoconstriction of skin arterioles;
this reduces blood flow to extremities –thereby minimizing heat loss through skin

11. IB Exam Question
3. Describe the response of the human body to high external temperatures. (4 marks)
thermoreceptors in hypothalamus activates cooling mechanisms
nerve impulses from hypothalamus trigger sweat glands and promotes evaporation/cooling
nerve impulses from hypothalamus trigger vasodilation of skin arterioles;
this increases blood flow to extremities thereby heat loss is increased through skin

12. IB Exam Question
4. Explain how blood glucose concentration is controlled in humans (8 marks)
pancreatic cells monitor blood glucose;
low glucose level induces production of glucagon;
glucagon stimulates the liver to break glycogen into glucose;
therefore blood glucose increases;
high level of blood glucose induces production of insulin;
insulin stimulates uptake of glucose into cells (muscles);
insulin stimulates uptake of glucose into liver where it is stored as storage glycogen;
insulin leads to decrease in blood glucose;
blood glucose regulation is an example of negative feedback;