Homeostasis Flashcards
Draw or describe the overall homeostatic control of circulating cortisol?
Why does the value of a controlled variable always oscillate around a set point?
There is a time delay in sensing a change and its
correction
- Never a flat line basically
Draw or describe the overall homeostatic control of blood pressure?
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
What is the effect of a pyrogen on the homeostatic control of body temp.
Pyrogen (Bacterial or viral infection)
Infection will cause set point to a higher level
resulting in fever
-> Core body temp. rises
Outline principle of negative feedback and +ve feedback
What is the benefits of a higher body temperature in defence of pyrogens?
Inhibits bacterial growth
Speeds up metabolic reactions
Increases delivery of white blood cells to infection sites
Pyrogens (viral or bacterial infection)
State 2 examples of regulated physical entities?
Blood pressure
Core temperature
State 2 examples of Circulating concentrations of chemical substances?
Ions e.g. Na+, Ca2+
Nutrients e.g. blood glucose concentration
Hormones
What is the role of the detector/sensor in the homeostatic feedback system?
Detects when controlled variable moves away from set point
-> Known as afferent pathway (goes towards control centre)
Describe how BP is restored after a haemorrhage
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
Role of effector in the homeostatic feedback system?
Effector use processes formulated via control centre to
return variable to set point via efferent pathway
- Induces response
Describe the process of control of uterine contractions in labour and how it shows
positive feedback?
- In labour oxytocin stimulates contraction of uterine muscles
- Cervix dilates and activate stretch receptors
- Action potentials signal to hypothalamus
- Stimulates further release of oxytocin
State the 5 components of the feedback system in homeostasis in order?
- Regulated factor/controlled variables
- Set point, operating range, error signal - Detector/sensor (afferent pathway)
- Comparator/control centre (intrinsic or extrinsic)
- Effector (efferent pathway)
- Response
Draw or describe the overall homeostatic control of the core body temp.?
At last stage, Body temps change is measured by receptors and send back to hyp. creating a feedback loop until set point is reached
How is the body temperature increased during an infection?
Blood flow shifted to core to conserve heat
Increased muscle activity (shivering)
Chills stop when high temp reached
State the components of the controlled variables in the homeostatic feedback
system and define?
- Set point= Pre-defined normal value
- Operating range= Normal range that variable can oscillate around set point
- 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
What does the integrated feedback loops within the body ultimately control?
Sodium balance
Blood pressure
Fluid volume
Which events would induce an increase in body tempature during its regulation?
Shivering
Vasoconstriction
Increased metabolism
FC:
Reduces heat loss to the enviroment
What stimulates the release of cortisol?
In hypo.CRH (corticotropin-releasing hormone) stimulates ACTH secretion
From PG., ACTH (adrenocorticotropic hormone) stimulates cortisol secretion via adrenal gland
What is the effect of long-term hypertension on the homeostaic control pathway of BP?
Hypertension= Increases BP long term
-> Causes the sensitivity of baroreceptors to reset
Baroreceptors adapt to sustained changes in arterial BP
Role of comparator/control centre in the homeostatic feedback system?
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
What is the homeostatic control cycle of blood pressure known as?
Baroreceptor reflex
State the receptors and control centre involved in the homeostatic pathway of
blood pressure?
Baroreceptors- strecth receptors
Stretch receptors found in wall of arteries which detect BP
Control centre= Medulla
What is the set point for cortisol affected by?
Stress (increases) Circadian rhythm (body clock)
Which events would induce a decrease in body tempature during its regulation?
Vasodilation
Sweating
Describe how the body temp. in terms of its time course differs during an infection?
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
State the role of vasopressin in the control of BP?
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
How does haemostasis display positive feedback?
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)
Define homeostasis?
Ability or tendency of an organim or cell to maintain internal equilibrium
by adjusting its physiological process
State the receptors and control centre involved in the homeostatic pathway of
core body temp?
Cutaneous temp. receptors
Hypothalamic temp. receptors
Control centre= Hypothalamus
What causes the release of ADH from the pituitary glands?
Angiotensin II
Hyperosmolarity
Decreased atiral receptor firing
Sympathetic stimulation
How is ‘challenge’ and ‘physiology’ involved in homeostasis?
Challenge'= Produces change in body status 'Physiology'= Responds to maintain homestasis
