Homeostasis Flashcards
What is homeostasis?
It is the maintenance of a steady state/ internal environment.
Describe the different 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
What are some examples of controlled variables?
CIRCULATING CONCENTRATIONS OF CHEMICAL SUBSTANCES:
- ions, eg. Na+ and Ca2+
- nutrients, eg. blood glucose concentration
- hormones
PHYSICAL ENTITY:
- blood pressure
- core temperature
What are some ways in which our bodies regulate body temperature?
- shivering
- vasoconstriction
- increased metabolism
- vasodilation
- sweating
How does an infection affect the elements of the temperature homeostatic negative feedback loop?
Pyrogens (bacterial or viral infections) change the setpoint to a higher level, resulting in a fever.
When you have an infection, what are the benefits of a fever?
- it inhibits bacterial growth
- it speeds up metabolic reactions
- it increases delivery of WBCs to infection sites
During a fever, how is the temperature increased?
- blood flow is shifted to the core to conserve heat
- there is increased muscle activity (shivering)
The chills stop when the high temperature is reached.
Describe the temperature-time course of a typical febrile attack.
The actual body temperature lags behind the rapid shift in set point, and though the regulation is maintained during the fever, it is less precise.
How would the blood pressure negative feedback loop react to increased blood pressure?
If you have an increased blood pressure, your baroreceptors will sense that through the stretching of your blood vessels, and feedback into the cardiovascular control centre within the brain.
It will cause decreased sympathetic activity (and increased parasympathetic activity), which will, in turn, decrease cardiac output and peripheral resistance, both of which will decrease the blood pressure.
What is the role of vasopressin (ADH) in control of blood pressure?
It is released from the pituitary gland.
It causes vasoconstriction, which directly increases blood pressure.
It also increases renal fluid absorption, which increases blood volume. This will, in turn, also increase blood pressure.
Give an example of two control systems activated after a haemorrhage to help restore blood pressure.
- the baroreceptor reflex to increase the cardiac output and total peripheral resistance
- stimulation of vasopressin (ADH) secretion to increase blood volume
Describe the hormonal regulation of cortisol secretion.
Neurosecretory cells in the hypothalamus release a hormone called Corticotropin-releasing Hormone (CRH), which travels down the portal vessels into the anterior pituitary, where it stimulates ACTH secretion.
AdrenoCorticoTropic Hormone (ACTH) will act on the adrenals to stimulate cortisol secretion.
What is the difference between negative feedback control and positive feedback control?
With negative feedback, if there is an increase in a controlled variable, the body will put in motion processes that will eventually decrease that variable. This happens for the majority of cases in our body.
However, some cases involve positive feedback control. Here, if there is an increase in a controlled variable, the body will instead amplify that to further increase that variable. Essentially, the response of the effector output reinforces the stimulus.
Describe the positive feedback control of uterine contractions in labour by oxytocin.
1) In labour, oxytocin stimulates contraction of the uterine muscles.
2) The cervix dilates and activates stretch receptors.
3) Action potentials send signals to the hypothalamus.
4) This stimulates a further release of oxytocin.
