Short term control of blood pressure Flashcards
State the equation for MAP
MAP = CO x TPR
What is the driving force pushing blood through circulation?
MAP
Describe the mechanism of arterial baroreceptors
Stretch reflex
Sensory neurone fire APs when stretched
Have tone and are fired all through the cardiac cycle
State the two types of arterial baroreceptors
Carotid sinus baroreceptors
Aortic arch baroreceptors
What nerve are sensory fibres of carotid sinus baroreceptors carried in?
Sensory fibres travel in GLOSSOPHARYNGEAL NERVE
What nerve are sensory fibres of aortic arch baroreceptors carried in?
Sensory fibres travel in VAGUS NERVE
What arterial baroreceptors have sensory fibres in the vagus nerve?
Aortic arch baroreceptors
What arterial baroreceptors have sensory fibres in the glossopharyngeal nerve?
Carotid sinus baroreceptors
Where do arterial baroreceptors signal to?
Medullary cardiovascular centres
Describe the effect of increased stretch on arterial baroreceptors
More APs fired
Activates parasympathetic (vagus nerve) system
Ach acts on muscarinic receptors
Reduced sinoatrial node activity -> reduced HR ->
reduced CO; since MAP = CO x TPR, MAP is also reduced
Describe the effect of reduced stretch on arterial baroreceptors
Less APs fired
Activates sympathetic (thoracolumbar) system
Noradrenaline and adrenaline act on Beta 1 receptors in the sinoatrial node -> increased HR
Beta 1 receptors in myocytes -> increased contractility and SV, therefore increased CO
Alpha 1 receptors - arteriolar constriction leads to increased TPR and increased MAP and venoconstriction leads to increased EDV
List the other inputs into short term control of BP
Cardiopulmonary baroreceptors Chemoreceptors in muscle Joint receptors Higher centres Posture
Describe the input of cardiopulmonary baroreceptors into short term BP control
Low pressure receptors in atrial walls and lung vessels
Respond to increased blood volume and tell medullary receptors that BP is high
Describe the input of chemoreceptors in muscle into short term BP control
Detect increased K+ or reduced pH
Describe the input of central chemoreceptors into short term BP control
Detect CO2 and O2 and determine rate and depth of breathing - contribute to respiratory drive
Describe the input of joint receptors into short term BP control
Detect movement and send blood back to that area
Describe the input of higher centres into short term BP control
Hypothalamus tells heart going to have to work hard
Describe the input of posture into short term BP
Standing increases hydrostatic pressure leading to the pooling of blood in veins and venules of the feet and legs.
This leads to reduced venous return, reduced EDV, reduced preload, reduced SV, reduced CO and reduced MAP
Describe how there is a reflex response to standing posture to control short term BP
Reduced vagal tone increases HR
Increased sympathetic tone -> increased HR and CO
Increased contractility -> increased SV and CO
Increased venoconstriction -> increased VR, increased EDV, increased SV and increased CO
Increased arteriolar constriction -> increased TPR
Define the valsalva manoeuvre
Forced expiration against a forced glottis, resulting in an increase in thoracic pressure
Describe changes in blood pressure during the valsalva manoeuvre
Increased thoracic pressure transmitted to aorta
Increased thoracic pressure -> reduced venous return -> reduced EDV -> reduced SV -> reduced CO and reduced MAP
Reduced MAP detected by baroreceptors which reflexly increase CO and TPR those increasing MAP
Decreased thoracic pressure transmitted to aorta but reflex doesn’t wear off that quickly
Back to normal - pressure added is subtracted as aortic compression is removed when a person starts to breathe again
What is different about long term BP control?
Cardiopulmonary receptors only
Mostly hormonal
