Monday, January 2, 2017

Nervous regulation of blood pressure

Hello awesomites ! Some days back I revised my concepts on regulation of blood pressure  so would like to share with you ,so lets start it .This is short -term regulation of blood pressure.

Changes in blood pressure is normally detected by 9th cranial nerve from carotid sinus and by 10th cranial nerve from aortic arch both of them carries signal to NTS (nucleus of tractus solitarius) present in medulla oblongata which in turn co-ordinate 3 centres  present in medulla oblongata.
- Cardio inhibitory centre .
- Cardio stimulatory centre.
- Vasomotor centre.

Now suppose there is increase in blood pressure ,let's see microscopically what changes we are gonna seen in nerve endings of 9th and 10th nerve.
An increase in blood pressure will stretch carotid sinus and aortic arch ,which in turn will cause stretching or spreading of nerve endings ,which will increase influx of the sodium ions . Ultimately increase in depolarisation wave will cause stimulation of NTS (Even decrease in depolarisation wave  will stimulate NTS ,which happens during decrease in blood pressure).Now as we know there is increase in blood pressure , NTS-our main character in this process  will control these 3 centres to control blood pressure. Let's see what it do to these  three  centres  present in medulla oblongata.
1)Cardio-inhibitory centre : This centre will be   stimulated  which in turn send fibers to SA node and AV node via right and left vagus nerve respectively.Leading to decrease in heart rate ,obviously cardiac output will decrease so will be blood pressure!.
2)Cardio-stimulatory centre: This centre will be inhibited which causes decrease in heart rate and cardiac output via it's fibers (post-ganglionic) which passes to lateral horn of spinal cord and then post-ganglionic fibers goes to sympathetic ganglion from where post-ganglionic sympathetic fibers  acts on heart causing decrease in heart rate and cardiac output.
3)Vasomotor centre:This centre do's more work compared to above two mentioned centres .It acts on three areas ,
Arteries
Veins
Adrenal medulla
Let's see how it reacts when there is increase in blood pressure.
a) On arteries :It causes vasodilation leading to decrease in Total peripheral resistance which is directly proportional to diastolic pressure hence causes decrease in diastolic blood pressure.
b )On veins :It causes vasodilation leading to decrease in venous return which is directly proportional to EDV and which in turn causes decrease in Cardiac output and hence decrease in systolic blood pressure.
c )On adrenal medulla: Decreases release of epinephrine and nor-epinephrine which is responsible for decrease in HR,so decrease in blood pressure.

Woahh! Was such a long blog!
I think it's not necessary to mention occlusion of carotid artery causes false phenomenon of decrease in blood pressure so opposite effects will be seen:)

~Ojas.

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