1: Homeostasis Flashcards
Define homeostasis.
The maintenance of a relatively constant, stable internal environment
Self-regulatory process by which biological systems adjust to environmental changes
Dynamic process
Give examples of certain physiological variables that are regulated to maintain a constant internal environment and what problems can be caused if there are disruptions to regulation.
Body temperature - hypothermia
Weight - obesity/anorexia
Glucose levels - diabetes
Blood gases - hypoxia
Ion concentration - electrolyte imbalances
Blood pressure - hypertension
Blood pH - acidosis
Give examples of environmental changes that can change internal conditions.
Extreme temperatures
Differing oxygen levels
Infectious agents
Dietary iron deficiency
Blood loss
What are active regulatory mechanisms?
Processes by which biological systems maintain homeostasis by responding to changes in internal or external conditions
What are the five components of a homeostatic regluatory (control) system?
1) Sensor
2) Set point
3) Control centre
4) Effector
5) Response
Describe the sensor component of a regulatory system.
Measures the value of the physiological variable
Specific to the variable
E.g. receptor
Describe the set point component of a regulatory system.
The normal range of values for the physiological variable
Not a fixed value - can vary
Reset either physiologically or as a result of a pathological change (e.g. in order to fight infection)
Describe the control centre component of a regulatory system.
Compares measured value of the value to the set point
E.g. in the brain
Describe the effector component of a regulatory system.
The component that can change the variable
E.g. muscles as effectors in response to low temperature (i.e. shivering)
Describe the response component of a regulatory system.
The response of the effector to change the variable
(i.e. muscle would be the effector, shivering would be the response)
Define negative feedback.
A response to a change that decreases the effect of the change
E.g. response of insulin to high blood glucose concentration - causes glucose concentration to decrease
Give each component of the regulatory system using the example of thermoregulation.
1) Variable: body temperature
2) Sensor: temperature receptors in skin and hypothalamus
3) Set point: 36.1℃ - 37.4℃
4) Control centre: hypothalamus
5) Effector: muscles, blood vessels
6) Response: shivering, vasoconstriction
Do homeostatic regulatory systems act in a continuous or discontinuous process?
Continuous
Does not operate like an ON/OFF switch
Homeostasis must be continuously regulated
What is the consequence of the effector’s response in a homeostatic regulatory system?
The effector’s response is NOT the change in the physiological variable, the change is the CONSEQUENCE of the response
Describe the path of a stimulus-response feedback loop in homostasis.
Stimulus –> Receptor –> Integrating Centre –> Effector –> Stimulus
How is sensory information transferred from the receptor to the integrating centre in a feedback loop?
Via afferent pathways
(sensory neurones)
How is sensory information transferred from the integrating centre to the effector in a feedback loop?
Via efferent pathways
(motor neurones)
Compare the characteristics of neuronal control systems to hormonal control systems.
Neuronal control systems:
- Brain neurones activate effectors directly
- Effectors are fast-onset (in seconds0 and short-lasting (minutes)
- Examples: breathing control, blood pressure, body temperature, etc.
Hormonal control systems:
- Hormones released into bloodstream
- Act as distant sites or all over the body
- Effects are slow-onset (minutes, hours) and long-lasting (hours, days, weeks)
- Examples: control of body calcium, blood glucose
How do muscle and liver cells store glucose?
As glycogen
But only in small reserves
How can liver cells and adipose tissue make glucose?
From breaking down fat stores or proteins
Which cell type especially requires a constant supply of glucose from the blood?
Neurones in the brain
Glucose is their primary and preferred energy source
What is the normal blood glucose level range?
3.9-7.1mMol/L
What condition is characterised by high blood glucose levels?
Hyperglycaemia
Glucose must be taken up by liver to be stored
What condition is characterised by low blood glucose levels?
Hypoglycaemia
Glucose must be broken down from glycogen
