Short term control of blood pressure Flashcards
What is MAP (mean arterial pressure
MAP is the driving force pushing blood through the circulation
- MAP has to be regulated
What occurs if MAP is too low?
Fainting (syncope)
What occurs if MAP is too high?
Hypertension
What is the arterial baroreflex?
The baroreflex is one of the body’s homeostatic mechanisms that helps to maintain blood pressure at nearly constant levels.
What are baroreceptors?
Baroreceptors are stretch receptors and respond to the pressure induced stretching of the blood vessel in which they are found.
Mechanism of the baroreflex
The baroreflex provides a rapid negative feedback loop in which an elevated blood pressure reflexively causes the heart rate to decrease and also causes blood pressure to decrease.
- Decreased blood pressure decreases baroreflex activation and causes heart rate to increase and to restore blood pressure levels.
What structures is the arterial baroreflex composed of?
- Glossopharyngeal nerve
- Carotid sinus baroreceptors
- Vagus nerve
- Aortic arch baroreceptors
- Medullary cardiovascular centres
- Parasympathetic (vagus)
- Sympathetic nerves
- Adrenal medulla
Where are baroreceptors mainly located?
Aortic arch and Carotid sinuses but they can also be found elsewhere
What are other outputs to the medullary cardiovascular centres?
- Cardiopulmonary baroreceptors
- Central chemoreceptors
- Chemoreceptors in muscle
- Joint receptors
- Higher centres
Features of cardiopulmonary baroreceptors
- They are low pressure receptors/volumoreceptors: right atrium, left atrium, cardiac ventriculi and pulmonary vessels
- They respond to distention, provoke changes in the sympathetic vaso-constrictor outflow and act in the regulation of volume of body fluids
- They exert a greater control over skin and muscle resistance and smaller control over splanchnic vasculature
- Low pressure receptors contribute an important role to minimise arterial pressure changes in response to changes in blood volume
Features of central chemoreceptors
Central chemoreceptors are sensitive to the pH of their environment
- These act to detect the changes in pH of nearby cerebrospinal fluid (CSF) that are indicative of altered oxygen or carbon dioxide concentrations available to brain tissues.
- An increase in carbon dioxide causes tension of the arteries, often resulting from decreased CO2 output (hypercapnia), indirectly causes the blood to become more acidic
Where are higher centres locate?
In the hypothalamus
Features of regulation of blood pressure in the long term
- Cannot be by the arterial baroreceptors
- Revolves around blood volume
- Main sensors are the cardio-pulmonary baroreceptors
- Effects tend to be hormonal
- Act on blood vessels and kidneys
Mechanisms for the regulation of blood pressure in the long term
- Renin-Angiotensin-Aldosterone system
- Vasopressin (=antidiuretic hormone)
- Atrial natriuretic pepetide & brain na
Basic function of renin-angiotensin-aldosterone system
- Angiotensin II causes arteriolar constriction, and therefore increases TPR.
- Increases water permeabillity of collecting duct, and increases plasma volume.
Basic function of Vasopressin
- Causes arteriolar constriction, and therefore increases TPR.
- Increases water permeability of collecting duct, and therefore increases plasma volume.
Basic function of Atrial natriuretic peptide & Brain natriuretic peptide
- Causes arteriolar dilation, therefore decreases TPR.
- Increases Na+ excretion (natriuresis)
Effect of standing on MAP
- Increased hydrostatic pressure causes pooling of blood in veins/venules of feet/legs.
- This causes decreased: VR, EDV, preload, SV, CO, MAP, baroreceptor firing rate.
How does the reflex response affect vagal tone?
Decreased vagal tone causes increased heart rate and increased cardiac output
How does the reflex response affect sympathetic tone
- Increases sympathetic tone by:
- increasing SV and CO
- Increased contractility- due to increased SV & CO
- Increased Venoconstriction- due to increased VR, EDV, SV ,CO
- Increased arteriolar constriction- due to increased TPr
What part of the heart does the vagus nerve innervate?
The sinoatrial node
What receptors does the heart mainly contain?
Beta 1 receptors in the SA node and Ventricular muscle
Beta 2 receptors in coronary arteries
What occurs to pacemaker cells when heart rate is increased?
Pacemaker cells depolarise faster allowing for an increase in heart rate.
What receptors are used for contraction?
Alpha 1 receptors
- However one does not follow this rule
