homeostasis

Question 1

conformers

Answer 1

more ‘primitive’ organisms that are restricted to more constant environments

Question 1

homeostasis

Answer 1

the control or stabilisation of the internal environment

Question 2

regulators

Answer 2

able to control internal environment and therefore able to exploit physiologically hostile and variable environments

Question 3

internal environment

Answer 3

the environment surrounding cells inside the body (extracellular fluid)

Question 4

body water

Answer 4

about 60% of total body weight (for a 70kg man: ~42 lites)

Question 5

extracellular fluid

Answer 5

~33%, represents internal environment, (interstitial fluid, plasma + transcellular fluid)

Question 6

interstitial fluid

Answer 6

fluid surrounding cells (~24%)

Question 7

plasma

Answer 7

fluid component of blood (~8%)

Question 8

intracellular fluid

Answer 8

~67%, fluid within cells (cytosol)

Question 9

transcellular fluid

Answer 9

‘other’ fluid (e.g. CSF, joints, ocular) (~1%)

Question 10

O2 levels

Answer 10

normal: 40 mmHg
range: 34-45 mmHg
non-lethal limit: 10-1000 mmHg

Question 11

CO2 levels

Answer 11

normal: 40 mmHg
range: 35-45 mmHg
non-lethal limit: 5-80 mmHg

Question 12

Na+ levels

Answer 12

normal: 142 mmol/l
range: 138-146 mmol/l
non-lethal limit: 115-175 mmol/l

Question 13

K+ levels

Answer 13

normal: 4.2 mmol/l
range: 3.8-5.0 mmol/l
non-lethal limit: 1.5-9.0 mmol/l

Question 14

Ca2+ levels

Answer 14

normal: 1.2 mmol/l
range: 1.0-1.4 mmol/l
non-lethal limit: 0.5-2.0 mmol/l

Question 15

glucose levels

Answer 15

normal: 6 mmol/l
range: 4-7 mmol/l
non-lethal limit: 0.11-80 mmol/l

Question 16

blood pH levels

Answer 16

normal: 7.4 pH
range: 7.35-7.45 pH
non-lethal limit: 6.9-8.0 pH

Question 17

temperature levels

Answer 17

normal: 37 °C
range: 36.5-37.5 °C
non-lethal limit: 18-43 °C

Question 18

O2 buffering function of haemoglobin

Answer 18

Hb has a high affinity for O2 and only releases O2 when the local concentration is low

Question 19

respiratory control of CO2

Answer 19

end product of aerobic respiration:
C6H12O6 + 6O2 -> H2O + 6CO2
ΔHc 2880 KJ
HYPERventilation DEcreases plasma [CO2]
HYPOventilation INcreases plasma [CO2]

Question 20

temperature regulation

Answer 20

hypothalamus (body’s thermostat) receives afferent inputs from peripheral and central thermoreceptors which initiate thermoregulatory responses (e.g. shivering, sweating, vascular changes)

Question 21

negative feedback

Answer 21

effector system opposes the initiating stimuli
(e.g. an increase in blood pressure causes a compensatory decrease in blood pressure)

Question 22

positive feedback

Answer 22

effector system reinforces or amplifies the initiating stimuli
(e.g. formation of a blood clot stimulates further clotting)

Question 23

characteristics of negative feedback

Answer 23

-a SETPOINT for the physiological parameter being regulated
-a SENSOR to monitor the regulated variable
-the ability to detect any error between the sensor and the setpoint by a COMPARATOR
-an EFFECTOR to bring about a compensatory change

Question 24

(-VE) blood pressure regulation (stimulus)

Answer 24

change in BP away from setpoint

Question 25

(-VE) blood pressure regulation (sensor)

Answer 25

baroreceptors in aortic arch and carotid sinus

Question 26

(-VE) blood pressure regulation (comparator)

Answer 26

vasomotor centres in the medulla

Question 27

(-VE) blood pressure regulation (effector)

Answer 27

change in sympathetic and parasympathetic nervous system activity

Question 28

(-VE) blood pressure regulation (response)

Answer 28

change in heart rate/vaso-response to return to setpoint

Question 29

(+VE) oxytocin stimulation of uterine contraction during labour (stimulus)

Answer 29

as baby moves deeper into birth canal the cervix is stretched

Question 30

(+VE) oxytocin stimulation of uterine contraction during labour (sensor)

Answer 30

stretch receptors send nerve impulses to hypothalamus

Question 31

(+VE) oxytocin stimulation of uterine contraction during labour (effector)

Answer 31

hypothalamus sends impulses to posterior pituitary which releases oxytocin to blood (travels to uterine muscle)

Question 32

(+VE) oxytocin stimulation of uterine contraction during labour (response)

Answer 32

uterus contracts more vigorously until baby is born; at birth, stretching of cervix lessens and the +ve feedback loop is broken

Question 33

why do most physiological systems use -ve feedback ?

Answer 33

+ve feedback provides an unstable, increasing stimulus-response cycle, if not stopped, it can be dangerous and sometimes lethal