homeostasis

Question 1

what is homeostasis

Answer 1

physiological control systems maintain a constant and relatively stable internal environment in a fluctuating environment

Question 2

name the three types of control systems

Answer 2

1. open loop
   - no feedback mechanism so it can lead to a runaway reaction
   - controller -> controlled component -> output
2. closed loop
   - output of system feedbacks and influences controller activity
   - controller -> controlled component -> output -> sensor -> feedback -> controller
   - 2 types:
3. negative feedback
   - returns to setpoint
   - output inhibits controller activity
4. positive feedback
   - moves away from setpoint
   - output induces controller activity
5. feedforward
   - the response generated in anticipation of a change
   - the precision of control depends on power and speed of response of controller and sensitivity of sensor

Question 3

what is the distribution of fluid in body

Answer 3

70% ICF

30% ECF

Question 4

what is the range of normal temperature

Answer 4

orally : 36.7 to 37
rectally : 37.2 to 37.5
hypothalamic set point : 37.1

Question 5

what is hunting

Answer 5

it is when the lag in arrival of corrective response can result in overcorrection causing output to oscillate/ hunt

Question 6

what can cause hunting

Answer 6

when set point changes 
setpoint can change due to metabolic/physiological stress
- fever
-exercise
-high altitude

Question 7

describe the control of arterial blood pressure

Answer 7

1. sensor: baroreceptors in carotid arteries and aortic arch detect stretch when BP is high
2. Control center: solitary nucleus in medulla oblongata references set point and identifies change in BP, then sends signal to effector
3. Effector: heart and blood vessels respond by decreasing heart rate and dilating blood vessels to decrease BP
4. controlled variable: BP is controlled variable. negative feedback returns it to variable safe limits

Question 8

what is gain

Answer 8

the degree of effectiveness of negative feedback control system

• calculated by : correction/error
• varies in diff systems but in thermoregulation (27) so very effective

Question 9

describe positive feedback control

Answer 9

output continuously enhanced and moved further away from setpoint

• requires termination mechanism
• eg:
  1. initial response in AP
  2. childbirth (release of oxytocin)
  3. blood clotting

Question 10

describe oxytocin inducing uterine contraction

Answer 10

-positive feedback loop
fetus pushing against cervix causes the release of oxytocin secretion from pituitary through neuroendocrine relfex which causes uterine contraction
-termination mechanism is the removal of fetus as pushing of fetus against cervix is the stimulus

Question 11

describe blood clotting as a positive feedback control

Answer 11

break in blood vessel cause bleeding

• damaged cells release chemicals and clotting begins
• clotting release more clotting factors which increase/ accelerates clotting
• termination mechanism is formation of clot plug and clot plug breaks in vessel wall and bleeding stops

Question 12

describe feedforward control and provide an example

Answer 12

response generated from anticipation of a change

• digestive system
• sight/smell/thought of food induces response in GI tract
• GI tract prepared to mechanically and chemically digest/absorb

local result

• ingesta broken down
• nutrients absorbed and ready for immediate use/storage

overall result:
- blood-nutrient levels are controlled during and after meal, homeostasis maintained

Question 13

what is adaptive control

Answer 13

it is when a feedforward response can be changed over time and iterations