Homeostasis

Question 0

Is homeostasis usually achieved via negative or positive feedback?

Answer 0

Negative

Question 1

What is ‘a tendency towards stability of the internal environment of a healthy organism’?

Answer 1

Homeostasis

Question 2

What is mainly achieved by control measures through mainly negative feedback, involving the CONTINUOUS ACTIVITY of sensory receptors?

Answer 2

Homeostasis

Question 3

When trying to maintain homeostasis, is it the external or internal environment that is likely to have large fluctuations?

Answer 3

External is large (e.g. temp and light)

Internal is small (e.g. temp, pH, glucose, BP)

Question 4

Name 5 internal variables that require homeostatic control

Answer 4

Temp, blood glucose, blood volume, blood pressure, calcium, salt, potassium, bicarbonate, osmolarity of blood, oxygen, carbon dioxide etc.

Question 5

Name the following steps in homeostasis:

S……. - I……… C……….. - E………… - correction of the variable: Change in variable

Answer 5

SENSOR - INTEGRATING CENTRE - EFFECTOR - correction of the variable - CHANGE IN VARIABLE

Question 6

What type of pathway connects the sensor to the integrating centre in homeostasis?

Answer 6

Afferent Pathway

Question 7

What type of pathway connects the integrating centre to the effector in homeostasis?

Answer 7

Efferent Pathway

Question 8

In homeostasis, the sensor is sensory receptor cells, where is the integrating centre and the effector?

Answer 8

Parts of the CNS like the hypothalamus

Muscle/secretory cells like blood vessels/sweat glands

Question 9

Outline the negative feedback process if the external temperature was to become really cold

Answer 9

The receptors in the skin would pick up the change
The hypothalamus would detect this and send signals to the effectors
Blood vessels contract, skeletal muscle twitches, muscle around hair follicles contract
Body temp increases and tells sensor to stop the effects

Question 10

Body temperature and blood pressure are examples of what type of feedback in homeostasis?

Answer 10

Negative Feedback

Question 11

Blood clotting and contractions in child birth are examples of what type of feedback in homeostasis?

Answer 11

Positive Feedback

Question 12

How does positive feedback work in blood clotting?

Answer 12

Damage to blood vessel activates clotting factors
Clotting factors activate thrombin
Thrombin keeps activating clotting factors (as well as forming blood clot)

Question 13

How does positive feedback work in childbirth?

Answer 13

Head of fetus on cervix sends nerve impulses to brain
Brain stimulates pituitary gland to secrete oxytocin
Oxytocin goes to uterus to stimulate contractions and also pushes fetus against cervix again

Question 14

What type of feedback decreases the effect of the original stimulus in homeostasis?

Answer 14

Negative

Question 15

What type of feedback increases the effect of the original stimulus in homeostasis?

Answer 15

Positive feedback

Question 16

What is the key integrative centre in homeostasis that converts synaptic signals to humoral/hormonal signals?

Answer 16

Hypothalamus/Pituitary Axis

Question 17

What does the hypothalamus respond to in homeostasis?

Answer 17

The feedback from the system it controls

Question 18

What area of the brain controls hormone secretion from the pituitary gland? (which acts on many systems)

Answer 18

Hypothalamus

Question 19

Can the hypothalamus affect the feeling of stress?

Answer 19

Yes - as it can get the pituitary gland to secrete cortisol in stressful situations - this affects the heart, muscles, GI tract and blood vessels

But cortisol also has negative feedback as inhibits corticotrophin to stop constant stress