6. Homeostasis

Question 1

1. Choose one answer below that completes the sentence so that it makes a true statement. Positive feedback:
   A. Is the way the body maintains homeostasis
   B. Is a response that opposes a stimulus
   C. Is a response that maintains a dynamic state of equilibrium
   D. Is a response that enhances a stimulus

Answer 1

Answer is D: “Positive” feedback will reinforce the stimulus, making it greater or more insistent.

Question 2

2. The hypothalamus and core thermoreceptors notice if body temp is too low. The hypothalamus signals the smooth muscle in blood vessels to vasoconstrict and the skeletal muscle to shiver. This activity causes body temp to rise, which is again noticed by the hypothalamus and core thermoreceptors, so the hypothalamus turns off these heat gain mechanisms. In this scenario, which of the following statements is correct?

A. The scenario describes positive feedback in action.
B. The core thermoreceptors are the effector organs.
C. The hypothalamus is the control centre.
D. The skeletal muscle is the efferent pathway to the effector organ.

Answer 2

Answer is C: The hypothalamus interprets the sensory input and determines the response. Choice A is wrong as this is negative feedback. The effector organs are the skeletal muscles (which are not a “pathway”).

Question 3

3. The human body’s ability to maintain a relatively constant internal temperature is an example of what?
   A. Respiratory heat loss
   B. Homeostasis
   C. Vasodilation and evaporative heat loss
   D. Positive feedback

Answer 3

Answer is B: Homeostasis is derived from words that mean remaining similar and standing still and refers to physiological conditions remaining more or less the same.

Question 4

4. Some of the body’s homeostatic responses rely on “negative feedback”. Which of the following happens in negative feedback?
   A. The body ignores changes in a physiological variable that are directed towards the set point for that variable.
   B. The body ignores changes in a physiological variable that are directed away from the set point for that variable.
   C. The body’s response acts to oppose the change in the physiological variable.
   D. The body’s response acts to enhance the change in the physiological variable

Answer 4

Answer is C: “Negative” refers to the response being in the opposite direction to the stimulus. Thus if a variable is increasing, then the body’s response is to produce a change that causes the variable to decrease. The body does not “ignore” stimuli.

Question 5

5. In homeostasis, what is it that produces the response that moves the physiological variable back towards the middle of its healthy range?
   A. The effector
   B. The receptor
   C. The integrating centre
   D. The efferent pathway

Answer 5

Answer is A: The effector produces the effect that it is directed to by the integrating centre. That direction is passed along the efferent (or outgoing) pathway.

Question 6

6. The “afferent pathway”, in the description of a feedback loop in homeostasis, refers to the:
   A. Circulating blood
   B. Pathway from the integrating centre to the effector
   C. Outgoing signal
   D. Path taken by the signal produced by a stimulus

Answer 6

Answer is D: The afferent signal is incoming from the receptor to the integrating centre. It may be via the blood but may be via a nerve.

Question 7

7. Homeostasis usually returns the body to a healthy state after stressful stimuli by:
   A. Negative feedback
   B. Positive feedback
   C. Means of the immune system
   D. Means of the nervous system

Answer 7

Answer is A: Negative feedback is far more common in maintaining homeostasis than is positive feedback.

Question 8

8. What does the word “homeostasis” refer to?
   A. The steps leading to repair of a blood vessel and the coagulation of blood
   B. The maintenance of internal body conditions within narrow limits
   C. The controlled response that opposes the influence that caused it
   D. The production of blood cells in active bone marrow

Answer 8

Answer is B: This is the best definition. Choice C refers to negative feedback only.

Question 9

9. How does homeostasis return the body to a healthy state after stressful stimuli? By producing a:
   A. Responses that oppose the stress B. Learned behaviour
   C. Reflex action
   D. Buffering mechanism

Answer 9

Answer is A: It refers to negative feedback. Positive feedback is also possible (but rare); nevertheless, choice A is the best answer.

Question 10

10. What causes the body to maintain a relatively constant internal environment?
    A. Positive feedback
    B. Homeostasis
    C. Reflexes
    D. pH buffers

Answer 10

Answer is B: Homeostasis matches the definition in the question.

Question 11

11. Homeostasis relies on feedback to achieve its aims. “Negative” feedback refers to which situation below? The body’s response:
    A. Travels from the effector to the integrating centre via the afferent pathway
    B. Opposes the stressful stimulus
    C. Is to decrease the set point
    D. Enhances the stressful stimulus

Answer 11

Answer is B: “Negative” refers to the opposing nature of the response.

Question 12

12. The term “homeostasis” is described by which one of the following statements? The body’s ability to:
    A. Respond to a stimulus or stress in such a way as to enhance the stress B. Maintain a relatively constant internal temperature
    C. Respond to a stimulus or stress in such a way as to reduce the stress
    D. Maintain a relatively constant internal environment

Answer 12

Answer is D: Choice A refers to positive feedback. Choice C refers to negative feedback. Choice B is an example of homeostasis.

Question 13

13. Synthesis and release of most hormones is regulated by negative feedback. Negative feedback means:
    A. A rise in hormone levels affects the target organ which acts to inhibit further hormone release.
    B. A rise in hormone levels affects the target organ which acts to stimulate further hormone release.
    C. The effect of hormones on target cells does not control further release of hormone.
    D. Neural stimuli result in the release of oxytocin and antidiuretic hormone from the hypothalamus.

Answer 13

Answer is A: When the response opposes a change, it is negative feedback.

Question 14

14. Which of the following is a correct definition of “positive feedback”?
    A. The process by which the body maintains homeostasis
    B. A mechanism in which the body’s response to a stimulus opposes the
    stimulus
    C. A mechanism whereby the body responds to a stimulus by acting to enhance
    the stimulus
    D. The dynamic equilibrium maintained by an integrating centre which causes an effector to respond to the stimulus received by the receptor

Answer 14

Answer is C: When the stimulus is enhanced, the feedback is termed “positive”.

Question 15

15. Which of the following is a correct definition of “negative feedback”?
    A. The process by which the body maintains homeostasis
    B. A mechanism in which the body’s response opposes the stimulus
    C. A mechanism whereby the body responds to a stimulus by acting to enhance the stimulus
    D. The dynamic equilibrium maintained by an integrating centre which causes an effector to respond to the stimulus received by the receptor

Answer 15

Answer is B: When an action is taken to cause the stimulus to be reduced, the feed- back is termed “negative”.

Question 16

16. Homeostasis refers to maintaining:
    A. A constant internal body environment through negative feedback
    B. Body conditions relatively constant within a narrow range through negative
    and positive feedback
    C. Adequate concentrations of respiratory gases
    D. Blood glucose level within the healthy range

Answer 16

Answer is B: The maintenance of body conditions through feedback which is usually negative but is positive in some rare situations.

Question 17

17. What does the term “homeostasis” refer to?
    A. The chemical processes that take place in the organelles of the cells
    B. The body’s tendency to maintain a relatively constant internal environment
    C. The body’s use of energy to produce chemical substances and parts for
    growth
    D. Any body response that opposes the stimulus that initiated the response

Answer 17

Answer is B: This is the best definition of homeostasis. Choice D refers to negative feedback.

Question 18

18. The body returns to a healthy state after stressful stimuli, thanks to which of the following?
    A. Positive feedback
    B. Metabolism
    C. Anabolism
    D. Negative feedback

Answer 18

Answer is D: Negative feedback is more common than positive feedback.

Question 19

19. Which of the following would be a negative feedback response by the body to hyperthermia?
    A. Shivering
    B. Sweating
    C. Vasoconstriction of blood vessels in the dermis
    D. An increase in metabolic rate

Answer 19

Answer is B: Hyperthermia is an increase on body temperature above 38 °C. Negative feedback would be a response that opposed the temperature rise. Allowing perspiration to evaporate from the skin would cool the skin and lead to a decrease in body temperature. The effect of the other choices would be to increase body temperature.

Question 20

20. How would the hypothalamus respond if its osmoreceptors noticed an increase in plasma osmotic pressure? It would send a message to:
    A. The posterior pituitary to release more ADH
    B. The posterior pituitary to release less ADH
    C. The adrenal cortex to release less aldosterone
    D. The atria to release more ANP

Answer 20

Answer is A: The hypothalamus would respond in a way that opposed the rise in osmotic pressure. Releasing more ADH would make the distal convoluted tubules of the nephrons to become more permeable to water. This would allow more water to be reclaimed from the filtrate which would act against the osmotic pressure of the plasma from rising further. It would also stimulate thirst.

Question 21

21. During the delivery of a baby, the baby’s head is pushing against the cervix causing the cervix wall to stretch. This stretching causes nerve impulses to be sent to the hypothalamus which directs the posterior pituitary to release oxyto- cin in the blood. Oxytocin stimulates the uterus to contract which pushes the baby’s head deeper into the cervix, stretching it further. This situation is a description of which of the following?
    A. Negative feedback
    B. Positive feedback
    C. Homeostasis
    D. An afferent pathway to an integrating centre

Answer 21

Answer is B: The stimulus (cervical stretching) causes the integrating centre (the hypothalamus) to respond by enhancing the stimulus – releasing oxytocin so that the uterus contracts. Enhancing the stimulus is an example of positive feedback. The feedback stops when the cervix is no longer being stretched, that is, when the baby is delivered.

Question 22

22. Which of the following statements about positive feedback and homeostasis is correct?
    A. They are regulation mechanisms that control most fluctuations in the inter- nal environment of the body.
    B. The response to the stimulus serves to exaggerate the feedback effect.
    C. This type of feedback response only involves an effector not a specific stimulus receptor site.
    D. This feedback mechanism involves adjustments at the organ level but not at
    the cellular level.

Answer 22

Answer is B: Positive feedback causes the stimulus to increase in magnitude which in turn elicits a more exaggerated response.

Question 23

23. Which of the following is an example of negative feedback?
    A. The uterine contractions during childbirth push the baby’s head against the cervix which stimulates the uterus to contract.
    B. The release by platelets that aggregate at the site of a blood vessel injury, of compounds that promote platelet aggregation.
    C. As resting membrane potential rises, voltage-gated ion channels open which allow ions to enter the axon which causes further rise in the membrane potential and more ion channels to open.
    D. As blood sugar level rises, insulin is released which promotes the absorption of glucose from the blood by liver, muscle and fat cells.

Answer 23

Answer is D: In this choice the response to rising glucose is the release of insulin, which promotes a decrease in blood glucose by causing it to be absorbed from the blood. That is, the response is to oppose the change that initiated the response. This is termed “negative” feedback. The other three choices are examples of positive feedback.

Question 24

24. Which of the following is the efferent pathway for the control of body temperature?
    A. The bloodstream
    B. The hypothalamus
    C. The nerve(s) that connect the brain to the adrenal glands
    D. The core body temperature receptors

Answer 24

Answer is C: Only the bloodstream and nerves are “pathways”. Efferent refers to a signal that is leaving the brain and travelling towards an effector. The signalling by the brain to the adrenal glands to alter the release of epinephrine is one way that body temperature is maintained.

Question 25

25. As blood glucose concentration rises, what homeostatic response would the body produce?
    A. Insulin would be released to cause blood glucose to fall.
    B. Glucagon would be released to cause blood glucose to fall.
    C. Insulin would be released to cause blood glucose to rise.
    D. Insulin and glucagon would be released to cause blood glucose to rise.

Answer 25

Answer is A: Homeostasis tends to result in a response that opposes the detected change. So something would be done to arrest the rise in glucose concentration. Insulin is the hormone that causes cells to absorb glucose from the blood.

Question 26

26. As the osmotic concentration of blood increases, what homeostatic response would the body produce?
    A. The glomerular filtration rate would increase.
    B. The feeling of thirst would increase so that a liquid with low osmolarity is
    ingested.
    C. The rate of release of ADH would decrease.
    D. The feeling of satiety would increase so that a low osmolarity liquid is less
    likely to be ingested.

Answer 26

Answer is B: Homeostasis tends to result in a response that opposes the detected change. So something would be done to reverse the rise in osmotic concentration of blood. Drinking water would do this. The other three choices would not oppose the rise in osmotic concentration.

Question 27

27. As body temperature increases, what homeostatic response would the body produce?
    A. Thyroxine would be released to increase the metabolic rate.
    B. Vasoconstriction would occur so that blood is withdrawn from close to the
    skin.
    C. Skeletal muscles may shiver to increase muscular heat production.
    D. Sweating would increase so that evaporation would transfer heat to the air.

Answer 27

Answer is D: Homeostasis tends to result in a response that opposes the detected change. So something would happen to promote the loss of heat from the body. The evaporation of sweat from the skin will produce a cooling effect on the superficial tissues. The other choices would generate more heat or decrease heat loss.

Question 28

28. As acidic chyme enters the duodenum from the stomach, what homeostatic response would the digestive system produce?
    A. Intestinal gastrin would be released to stimulate gastric secretion and move more chyme into the duodenum.
    B. The pancreas would decrease its secretion of alkaline pancreatic juice into the duodenum.
    C. The enterogastric reflex would tighten the pyloric sphincter and decrease gastric secretion.
    D. The duodenal brush border would secrete digestive enzymes that function in an acidic environment.

Answer 28

Answer is C: Homeostasis tends to respond to a detected change with “negative feedback”. The duodenum requires an alkaline environment, so the arrival of acidic chyme would result in a response that causes duodenal pH to rise. By closing the pyloric sphincter, the alkaline pancreatic juice and alkaline brush border secretions will have time to restore duodenal pH to the required level of about 7.4.

Question 29

29. When blood sodium ion concentration moves close to the lower limit of normal (137 mmol/L), what would the body do to maintain homeostasis?
    A. More aldosterone would be released to cause more reabsorption of Na+ from the filtrate.
    B. Additional aquaporins would be inserted in the nephron tubule to allow more water to pass into the filtrate.
    C. More aldosterone would be released to cause more reabsorption of K+ from the filtrate.
    D. Water would move into the intracellular compartment to increase the osmotic concentration of blood.

Answer 29

Answer is A: Homeostasis almost always results in a response that opposes the detected change. Aldosterone promotes the reabsorption of Na+ from the filtrate; this would slow the decline in the blood’s sodium concentration. The other three choices are wrong.

Question 30

30. If blood pressure is detected to be lower than required to optimally perfuse the tissues, what homeostatic response would occur?
    A. The vasomotor centre would be inhibited and so the heart rate would decrease.
    B. Vasoconstriction would occur; hence, total peripheral resistance would increase.
    C. The strength of myocardial contraction would increase and so stroke vol- ume would decrease
    D. Smooth muscle in the walls of veins would relax resulting in vasodilation.

Answer 30

Answer is B: The homeostatic response to decreased blood pressure is to undertake action to increase blood pressure. Vasoconstriction would achieve this by increasing the peripheral resistance. Choices A and D are the opposite of what would happen.

Question 31

31. When peripheral chemoreceptors detect an increase in the concentration of dis- solved carbon dioxide in arterial blood above 45 mmHg (the upper limit of normal), which of the following homeostatic responses would occur?
    A. Respiratory rate increases so that more carbon dioxide may be exhaled.
    B. Respiratory rate decreases so that less carbon dioxide may be exhaled.
    C. Respiratory rate increases so that less carbon dioxide may be exhaled.
    D. Respiratory rate decreases so that more carbon dioxide may be exhaled.

Answer 31

Answers is A: The homeostatic response opposes the stimulus, so if blood pCO2 is rising, the response must produce a decrease in pCO2. If respiratory rate increases, the increase in lung ventilation will blow off more CO2 (not less). This will lead to a decrease in the gas dissolved in arterial blood and a restoration of the healthy dissolved carbon dioxide concentration.

Question 32

32. At the start of each ovarian cycle, FSH and LH are released. These hormones stimulate the granulosa and thecal cells (respectively) of the follicle that sur- rounds the ovum. Consequently a few ovarian follicles are stimulated to mature. Which of the listed subsequent developments is an example of positive feedback?
    A. The developing follicle produces estrogens at a low level which act on the anterior pituitary to inhibit the release of FSH and LH.
    B. Granulosa cells secrete inhibin which inhibits the release of FSH.
    C. Rapidly increasing plasma concentration of estrogens stimulates a surge in LH release which stimulates ovulation.
    D. High plasma concentrations of progesterone and estrogen act on the hypothalamus to inhibit the release of GnRH.

Answer 32

Answer is C: The rapidly increasing production of estrogens by the developing follicle stimulates a surge in the release of LH by the anterior pituitary (rather than a decrease). In turn the follicle is stimulated to ovulate which means that the granulosa and thecal cells cease to secrete estrogens. Instead they become the corpus luteum and secrete progesterone.

Question 33

33. Select the example below that describes an example of positive feedback.
    A. The hypothalamus, noticing that body temperature is falling, initiates the muscular contractions we know as shivering.
    B. The macula densa of the nephron notices an increase in the sodium ion concentration in the filtrate and signals the afferent arteriole to constrict.
    C. The contractions of the uterus force the head of the foetus against the cervix
    which causes the uterus to contract more forcefully.
    D. The stretch receptors of the carotid sinus notice that the wall of the carotid
    artery is more stretched. This information is sent to the brain which then causes the heart rate to decrease.

Answer 33

Answer is C: Examples of positive feedback in human physiology are rare. The contractions of childbirth is one. The other three describe negative feedback.

Question 34

34. What is meant by acid-base balance?
    A. The ability to maintain body solutions as neither acidic nor basic.
    B. The body’s ability to maintain the solutions in the three main compartments
    at pH 7.4.
    C. The situation where the concentration of hydronium ions equals the concentration of hydroxide ions.
    D. Any excess acid entering or being produced by the body is removed by buffer systems.

Answer 34

Answer is B: The buffers in the body operate to maintain the pH of its aqueous solu- tions at close to 7.4 (not pH 7.0 as implied by choices A and C). Excess acid is excreted via the lungs and kidneys.

Question 35

35. What is meant by electrolyte balance?
    A. The maintenance of the dissolved ion concentrations in solution within their narrow healthy ranges
    B. Ensuring that the solution concentrations of sodium and chloride ions are appropriate
    C. The function of the kidneys in reabsorbing required electrolytes from the urine filtrate
    D. Matching electrolyte excretion in sweat and faeces with intake via foodstuffs

Answer 35

Answer is A: Electrolytes such as sodium, potassium, chloride, bicarbonate, cal- cium, phosphate and magnesium ions have an upper and lower limit to their healthy concentrations in the body’s solutions. Electrolyte balance is the metabolic process that ensures that these ions are within their range. Electrolyte balance involves more than just the two ions in choice B, more than just preventing their loss in urine as in choice C, but does include urinary losses, which are missing from choice D.

Question 36

36. What is meant by fluid balance in the body?
    A. Avoiding dehydration
    B. Avoiding overhydration
    C. Replacing the losses via sweating during exercise with balanced electrolyte
    drinks
    D. Ensuring that water inputs are equal to water losses

Answer 36

Answer is D: Unless water intake via food, drink, metabolic production and intravenous infusion exactly matches losses via sweat, respiration, faeces and urine, etc., the body will either dehydrate or “swell up” with water retention.