Homeostasis

Question 1

Draw or describe the overall homeostatic control of circulating cortisol?

Answer 1

Question 2

Why does the value of a controlled variable always oscillate around a set point?

Answer 2

There is a time delay in sensing a change and its
correction
- Never a flat line basically

Question 3

Draw or describe the overall homeostatic control of blood pressure?

Answer 3

Changes to heart (CO) and peripheral resistance

• > Occurs via symp. nerves (Increases, when BP falls)
• > Leads to changes to CO (CO increases with activation of symp.
• >Leads to changes to HR and TPR -> affecting BP

Due to HR= CO x SV and BP= TPR x HR

Question 4

What is the effect of a pyrogen on the homeostatic control of body temp.

Answer 4

Pyrogen (Bacterial or viral infection)

Infection will cause set point to a higher level
resulting in fever
-> Core body temp. rises

Question 5

Outline principle of negative feedback and +ve feedback

Answer 5

Question 6

What is the benefits of a higher body temperature in defence of pyrogens?

Answer 6

Inhibits bacterial growth
Speeds up metabolic reactions
Increases delivery of white blood cells to infection sites

Pyrogens (viral or bacterial infection)

Question 7

State 2 examples of regulated physical entities?

Answer 7

Blood pressure
Core temperature

Question 8

State 2 examples of Circulating concentrations of chemical substances?

Answer 8

Ions e.g. Na+, Ca2+
Nutrients e.g. blood glucose concentration
Hormones

Question 9

What is the role of the detector/sensor in the homeostatic feedback system?

Answer 9

Detects when controlled variable moves away from set point
-> Known as afferent pathway (goes towards control centre)

Question 10

Describe how BP is restored after a haemorrhage

Answer 10

After a haemorrhage blood volume and hence blood pressure are reduced
To help restore blood pressure several homeostatic control systems are activated:
1. Baroreceptor reflex to increase cardiac output and total peripheral resistance
2. stimulation of vasopressin (ADH) secretion to increase blood volume

Question 11

Role of effector in the homeostatic feedback system?

Answer 11

Effector use processes formulated via control centre to
return variable to set point via efferent pathway
- Induces response

Question 12

Describe the process of control of uterine contractions in labour and how it shows
positive feedback?

Answer 12

1. In labour oxytocin stimulates contraction of uterine muscles
2. Cervix dilates and activate stretch receptors
3. Action potentials signal to hypothalamus
4. Stimulates further release of oxytocin

Question 13

State the 5 components of the feedback system in homeostasis in order?

Answer 13

1. Regulated factor/controlled variables
   - Set point, operating range, error signal
2. Detector/sensor (afferent pathway)
3. Comparator/control centre (intrinsic or extrinsic)
4. Effector (efferent pathway)
5. Response

Question 14

Draw or describe the overall homeostatic control of the core body temp.?

Answer 14

At last stage, Body temps change is measured by receptors and send back to hyp. creating a feedback loop until set point is reached

Question 15

How is the body temperature increased during an infection?

Answer 15

Blood flow shifted to core to conserve heat
Increased muscle activity (shivering)
Chills stop when high temp reached

Question 16

State the components of the controlled variables in the homeostatic feedback
system and define?

Answer 16

1. Set point= Pre-defined normal value
2. Operating range= Normal range that variable can oscillate around set point
3. Error signal= value of the controlled variable minus the set point
   - > When value is out of operating range or moving away from set point
   - > Signals to control centre

Question 17

What does the integrated feedback loops within the body ultimately control?

Answer 17

Sodium balance
Blood pressure
Fluid volume

Question 18

Which events would induce an increase in body tempature during its regulation?

Answer 18

Shivering
Vasoconstriction
Increased metabolism

FC:
Reduces heat loss to the enviroment

Question 19

What stimulates the release of cortisol?

Answer 19

In hypo.CRH (corticotropin-releasing hormone) stimulates ACTH secretion
From PG., ACTH (adrenocorticotropic hormone) stimulates cortisol secretion via adrenal gland

Question 20

What is the effect of long-term hypertension on the homeostaic control pathway of BP?

Answer 20

Hypertension= Increases BP long term
-> Causes the sensitivity of baroreceptors to reset

Baroreceptors adapt to sustained changes in arterial BP

Question 21

Role of comparator/control centre in the homeostatic feedback system?

Answer 21

Determines set point of variable, compares and maintains variable at set point

Occurs via

• Intrinsic: local – cell or tissue autoregulates
• Extrinsic: endocrine system, nervous system

Question 22

What is the homeostatic control cycle of blood pressure known as?

Answer 22

Baroreceptor reflex

Question 23

State the receptors and control centre involved in the homeostatic pathway of
blood pressure?

Answer 23

Baroreceptors- strecth receptors
Stretch receptors found in wall of arteries which detect BP

Control centre= Medulla

Question 24

What is the set point for cortisol affected by?

Answer 24

Stress (increases)
Circadian rhythm (body clock)

Question 25

Which events would induce a decrease in body tempature during its regulation?

Answer 25

Vasodilation Sweating

Question 26

Describe how the body temp. in terms of its time course differs during an infection?

Answer 26

Infection leads to a rapid shift in set point - But actual temp. lags behind for many hours until reaching it - Even when reached, regulation is maintained during fever but is less precise

Question 27

State the role of vasopressin in the control of BP?

Answer 27

ADH leads to vasoconstriction and renal fluid reabsorption -\> Renal fluid reabsorption leads to increased blood volume Both vasoconstriction and increased blood volume increases arterial pressure

Question 28

How does haemostasis display positive feedback?

Answer 28

The response of the effector output reinforces the stimulus e.g. blood clotting, ovulation, childbirth - Clotting occurs where platelets come once break in wall occurs, which then attract more platelets via released chemicals Less common physiologically as it is like a “runaway train” (less control)

Question 29

Define homeostasis?

Answer 29

Ability or tendency of an organim or cell to maintain internal equilibrium by adjusting its physiological process

Question 30

State the receptors and control centre involved in the homeostatic pathway of core body temp?

Answer 30

Cutaneous temp. receptors Hypothalamic temp. receptors Control centre= Hypothalamus

Question 31

What causes the release of ADH from the pituitary glands?

Answer 31

Angiotensin II Hyperosmolarity Decreased atiral receptor firing Sympathetic stimulation

Question 32

How is 'challenge' and 'physiology' involved in homeostasis?

Answer 32

``` Challenge'= Produces change in body status 'Physiology'= Responds to maintain homestasis ```