S1: Homeostasis Flashcards
List the components of a feedback system
Regulated factors: have set point, operating range, ‘error signals’
Detector/sensor: Afferent path
Comparator/control centre: Determines the set point of variable. Intrinsic (local cell or tissue) and extrinsic (endocrine, NS, hypothalamus)
Effector: Returns variable to set point
What are error signals in homeostasis?
The value of a controlled variable will oscillate around the set point -> Because of time delay between sensing a change and correction.
The deviation is the error signals.
What increases body temperature?
Shivering
Vasoconstriction
Increased metabolism
What decreases body temperature?
Vasodilation
Sweating
Explain the feedback mechanism for temperature
Variable = core body temp
The temperature is detected by cutaneous temperature receptors or hypothalamic temperature receptors which will relay back to the hypothalamus which can then use effectors to increase or decrease body temeperature
What are pyrogens?
Bacterial or viral infections that change to set point to a higher level resulting in fever
What are the benefits of a higher temperature?
- Inhibits bacterial growth
- Speed of metabolic reactions
- Increases delivery of white blood cells to infection sites
What does pyrexia mean?
Fever
Describe the baroreceptor reflex
BP= TPR x CO
so if CO or TPR increases, BP will increase
If blood pressure is increased, baroreceptors will detect this and relay it to the medulla. Heart rate will decrease and peripheral resistance will decrease.
Increased paraympathetic input and decreased sympathetic input decrease CO
Decreased SI decreses TPR
What structures does the baroreceptor reflex include?
Vagus nerve
Aortic arch receptors
They help increase CO and TPR.
What NS will be activated if blood pressure falls?
Activation of sympathetic output increases CO and TPR which increases BP.
What is hypertension?
High BP
There can be resetting of the sensitivity of baroreceptors which will ultimately alter BP
Explain ADH origin in the hypothalamic pituitary axis and anterior pituitary gland
- Neurones in the hypothalamus synthesise and release hormones into the posterior pituitary e.g.ADH through neurosecretory cells
- There is also anterior pituitary (glandular tissue), other neurosecretory cells in the hypothalamus release their hormones into the portal capillaries in which they are transported directly to endocrine cells of the anterior pituitary gland.
What is another name for ADH?
Vasopressin
Explain the control of extracellular fluid
- When osmolarity increases (due to increased Na+), osmoreceptor cells detect this in the hypothalamus by shrinking
- AP generated which signals posterior pituitary gland to release ADH
- ADH is transported to the kidneys which increases water permeability of distal and collecting tubules resulting in more water reabsorption into the blood and more concentrated urine
Explain the role of ADH in the control of blood pressure
ADH has an effect on the vasoconstriction of vessels which causes an increase in arterial pressure
This increases blood volume
What reflexes would our body use after haemorrhage?
After a haemorrhagebloodvolumeand hencebloodpressureare reduced. To help restore blood pressure several homeostatic control systems are activated, these include:
Thebaroreceptorreflexto increasecardiacoutputandtotalperipheralresistance
Stimulation ofADHsecretionto increasebloodvolume
How is cortisol released?
CRH (corticotrophin-releasing hormone) is released by hypothalamus
This stimulates ACTH (adrenocorticotrophic hormone) to be released from the anterior pituitary gland
This stimulates cortisol secretion from the adrenal cortex
Explain negative feedback on cortisol release
If there is too much cortisol, there will be–ve feedback on the anterior pituitary and hypothalamus. If cortisol is too low, there will be an inhibition of–ve feedback, so these hormones will increase.
Cortisol is released according to ourbodyclock, cortisol is high in themorningand gradually drops down.Stresscan affect this cycle by keeping cortisol levels high.
What do thyroid hormones control?
Rate of metabolism
Explain negative feedback of Thyroid hormones
When T3and T4levels are low, there is a lack of negative feedback causing TRH secretion from hypothalamus.
TSH acts on the thyroid gland to release T3(tri-iodothyronine) and T4(thyroxine)
How are thyroid hormones released?
TRH (thyroid releasing hormone) is released from the hypothalamus]
This acts on the anterior pituitary to release TSH (thyroid stimulating hormone)
TSH acts on the thyroid gland to release thyroid hormone
What is negative feedback?
An increase in a controlled variable results in a decrease in a controlled variable
What is positive feedback?
An increase in a controlled variable results in a increase in a controlled variable
Explain the control of uterine contractions in labour by oxytoxin
- In labour oxytocin stimulates contraction of uterine muscles
- Cervix dilates and activates stretch receptors
- Action potentials signal to hypothalamus
- Stimulates further release of oxytocin
- This stops once birth has occurred
Give an example of positive feedback with nerves
Another example is the generation of action potentials, through the influx of Na+, as a few voltage gated Na+channels opening triggers the opening of many others.
The voltage and time dependent Na+channels then quickly inactive which stops the +ve loop.
