Homeostasis Flashcards
What is a set point?
A value at which a variable must be maintained to maintain homeostasis
What is the set point for temperature?
37 degrees
What is the set point for pH?
7.4
What is the set point for plasma glucose?
5.5mM
What is the set point for blood pressure?
120/80mmHg
What is the set point for plasma osmolality?
300osmoles/kg
What are the set points for PO2 and PCO2?
PO2 = 100mmHg PCO2 = 40mmHg
What happens when a variable deviates from the set point?
There is an error signal that activates a homeostatic mechanism to apply compensation
What is a closed loop system?
When the change from the set point causes an error signal which activates a homeostatic mechanism which applies compensation and makes the variable back to set point and the changing of the variable back to set point then causes a negative feedback mechanism on the error signal and homeostatic mechanism
What part of the brain is known as the homeostatic centre?
The hypothalamus
What 4 things does the hypothalamus control?
- Body temperature
- Plasma osmolality
- Appetite/thirst
- Hormone release
How does the ANS control homeostasis?
Through autonomic reflexes and hormones
What two hormones are involved in regulating plasma glucose levels?
Insulin and glucagon
What happens when plasma glucose exceeds 5.5mM?
Increased insulin secretion leads to an increased uptake of glucose into the tissue particullary by the liver in order to lower it back down to 5.5mM
What happens when plasma glucose drops below 5.5mM?
Increase glucagon secretion leads to an increased release of glucose from the tissues espiecally the liver to raise plasma glucose back to 5.5mM
What is low plasma glucose called?
Hypoglycemia
What is high plasma glucose called?
Hyperglycemia
Where are insulin and glucagon secreted from?
The pancreas
What is absent in people with type one diabetes?
No insulin
What does the absense of insulin mean for people with type 1 diabetes?
Means insulin is not causing the uptake of glucose into the tissues so in the fasted state there is no glucose to be release by glucagon so they need an injection of insulin
How many spinal segments of the spinal chord are there and what regions are they in?
8 Cerivial 12 Thoracic 5 Lumbar 5 Sacral 30 in total
What are baroreceptors?
Arterial stretch receptors in the walls of blood vessels
What do baroreceptor detected?
Changes in arterial blood pressure
What happens if arterial blood pressure falls?
Inhibition of the parasympathetic nervous system to stop the vagus never from inhibiting the heart and activation of the sympathetic nervous system which accelerates the heart beat and also causes vasoconstriction in order to raise the blood pressure back to normal
What happens if arterial blood pressure rises?
Inhibition of the sympathetic nervous system to stop it accerlating the heart and to stop vasocontriction leading to vasodilitation as well are activation of the parasympathetic nervous system leads to increased firing of the vagus nerve to cause slowing of the heart to lower BP back to normal
What is slowing of the heart otherwise known as?
Bradycardia
How do the baroreceptor/arterial stretch receptors detect changes in blood pressure?
If blood pressure falls then the walls of the blood vessels containing the baroreceptor are stretched less and if blood pressure rises they are stretched more
What cranial nucleus does the vagus nerve arises from?
The 10th cranial nucleus
What is released by the pre-ganglionic fibres of the parasympathetic nervous system?
Acetylcholine
Is the preganglionic fibre in the parasympathic nervous system long or short?
Long
What is released by the post ganglionic fibres in the PNS?
Acetylcholine, nitric oxide and VIP
Is the postganglionc fibre of the parasympathic nervous system long or short?
Short
Where do the preganglionic and postganglionc fibres of the PNS meet?
A ganglion
What is a ganglion?
A collection of nerve cells
What is the action of the vagus nerve in the PNS?
- Slow heart rate
- Constrict bronchii
- Increase secretions
What are the actions of the pelvic nerve in the PNS?
- Spinchter relaxation
- Colon and urinary contraction
What do the preganglionic fibres of the sympathetic nervous system release?
Acetylcholine
Are the preganglionic fibres of the sympathetic nervous system long or short?
Short
Where do the preganglion fibres and the postganglion fibres synapse in the sympathetic nervous system?
The paravertebral ganglion/sympathetic chain ganglion
Do all the preanglionic fibres go on to synapse at the ganglia?
No some extended to the adrenal medulla where they innverate it to produce adrenaline and noradrenaline
What is the effect of adrenaline on skeletal muscle vasculature?
Vasodilitation
What is the effect of noradrenaline on smooth muscle vasculature?
Vasoconstriction
What are the actions of the sympathetic nervous system?
- Increase heart rate
- Relax bronchial smooth muscle
- Inhibit secretions
- Inhibit bladder and colon contraction
- Inhibit sphincter relaxation
- Sweating
