Control Systems & Homeostasis

Question 1

What is a regulated variable?

Answer 1

The thing that compares the variable with the set point

Question 2

What is an effector?

Answer 2

The thing that restores the variable to the set point

Question 3

What are the three types of sensors?

Answer 3

stretch receptors, temperature receptors, chemical concentration

Question 4

What are the three things that stretch receptors can measure?

Answer 4

pressure, volume, osmolarity

Question 5

What are the two ways that effectors can communicate with variables?

Answer 5

Chemical (hormones) or electrical (nerve endings)

Question 6

What are the different types of effectors?

Answer 6

• heart and blood vessels - for blood pressure
  
  • muscles, sweat glands and cutaneous circulation - for temperature
  • respiratory muscles - for carbon dioxide and oxygen
  • renal collecting ducts - for sodium, potassium, osmolarity and pH
  • liver, muscle and adipose tissue - for glucose

Question 7

When will a set point change?

Answer 7

Set points may change depending on time of day, point of life course and may also change with persistent changes in ambient levels. For example, if blood pressure is constantly higher, the baroreceptor reflex will readjust so that the set point is higher to prevent the baroreceptor from firing too much

Question 8

What is an example of a homeostatic clash?

Answer 8

A homeostatic clash occurs when there are the same effector for two different regulated variables. For example, in exercise, the body wants to increase TPR to keep BP and cardiac output up, however because the body is hot it wants to increase peripheral cutaneous circulation.

Question 9

What factors can be controlled to change blood pressure?

Answer 9

cardiac output, stroke volume, total peripheral resistance

Question 10

What factors can be controlled to change glomerular filtration rate?

Answer 10

pre and post glomerular arteriole tone, mesangial cell contraction

Question 11

Where is the control centre for thermoregulation?

Answer 11

In the hypothalamus - there are separate nerves for cooling, heating and for integration of central and peripheral temperature sensors

Question 12

Where are the temperature sensors?

Answer 12

Central temperature sensors are in the hypothalamus and spinal cord and only detect hot. Peripheral temperature sensors are in the skin and detect hot and cold

Question 13

What is the normal temperature variation?

Answer 13

36-37.5 degrees

Question 14

What are the four ways that the body can loose heat?

Answer 14

Conduction (touch), convection (air), radiation (all down a temperature gradient) and evaporation

Question 15

How does the body cool down at 45 degrees?

Answer 15

evaporation, anorexia, lethargy, shallow breathing, cutaneous vasodilation

Question 16

How does the body heat up at 10 degrees?

Answer 16

vasoconstrict, shiver, curl up, activity, hyperphagia, turn on brown fat, piloerection

Question 17

What happens in a fever?

Answer 17

In a fever, the temperature set point is elevated by pyrogens - either exogenous (from bacteria) or endogenous (cytokines)