Homeostasis Flashcards
Define homeostasis
Maintenance of a steady state/internal environment
What responds to the challenge produced in a change of body status?
Physiology responds to maintain homeostasis
What are the 5 components of a feedback system?
Regulated factor (set point, operating range, error signal)
Detector/sensor (afferent path)
Comparator/control centre – determines set point of variable, compares and maintains variable at set point
Intrinsic: local – cell or tissue autoregulates
Extrinsic: endocrine system, nervous system
Effector – returns variable to set point (efferent path)
Response
Describe the negative feedback loop
What is the error signal?
- controlled variable - if low you get negative feedback to a sensor then to a comparator or control centre which increases the aspect being regulated
- Setpoint
- Comparator/ control centre
- Effector
Error signal - value of the controlled variable minus the set point
What physical entities can be controlled?
What circulating chemical substances can be regulated?
Blood pressure
Core temperature
Concentrations of:
Ions e.g. Na+, Ca2+
Nutrients e.g. blood glucose concentration
Hormones
What does the body do when we are cold/ hot?
shivering, vasoconstriction and increased metabolism (increased)
vasodilatation, sweating (increases)
Describe the flow diagram of the regulation of body temperature
- Core body temperature is being regulated
- It is being sensed by the Hypothalamic temperature receptors or cutaneous temperature receptors
- This links to the hypothalamus which has its set point - core body temperature
- We then get heat loss/ sweating/ vasodilation
or
Heat gain - shivering, vasoconstriction and metabolism
Define pyrogen
Pyrogens (bacterial or viral infections) change the set point to a higher level resulting in fever
What are the benefits of a higher temperature?
Benefits of a higher temperature:
inhibits bacterial growth
speeds up metabolic reactions
Increases delivery of white blood cells to infection sites
How is temperature increased?
Blood flow shifted to core to conserve heat
Increased muscle activity (shivering)
Chills stop when high temp reached
Describe the flow diagram of the regulation of blood pressure
- Blood pressure is regulated by baroreceptors.
- It is sensed by the medulla via negative feedback
- Changes heart activity and peripheral resistance
How do we respond to an increased blood pressure?
We get an increased parasympathetic input leading to a decreased cardiac output
or decreased sympathetic input leading to a decrease in TPR
What does hypertension cause?
Resetting the baroreceptors
What is activated in response to a decrease in blood volume and BP?
the baroreceptor reflex to increase cardiac output and total peripheral resistance
stimulation of vasopressin (ADH) secretion to increase blood volume
What does the secretion of CRH from the anterior pituitary gland cause?
CRH (corticotropin-releasing hormone) stimulates ACTH secretion
ACTH (adrenocorticotropic hormone) stimulates cortisol secretion
