reflex control of the circulation Flashcards
what is the effect of increased BP(loading) on the baroreflex ?
- pulse pressure falls - decreased stroke volume
- vasodilation decreases TPR and BP
- decreased sympathetic nerve activity
- increased vagus nerve activity
what is the effect of decreased BP(unloading) on the baroreflex ?
- Increased sympathetic activity & decreased Vagus activity.
- Increased HR and force of contraction so increased cardiac output.
- Arteriole constriction gives increased TPR.
- Venous constriction increases central venous pressure and so by Starlings law increases stroke volume & cardiac output.
- This all maintains blood pressure therefore blood flow to vital organs.
describe veno-atrial mechanoreceptors
- Stimulated by increase in
cardiac filling/CVP. - Reduces sympathetic activity to renal arteries increasing glomerular filtration, also secretes atrial natriuretic peptide increasing Na+ excretion all of which lowers blood volume reducing ADH & RAAS.
describe Nociceptive sympathetic afferent nerves
- Stimulated by K+, H+ (lactate), during ischaemia.
- Mediate pain of angina & myocardial infarction. Reflex increased sympathetic activity – pale, sweaty, tachycardia of angina/MI symptoms.
describe ventricular mechanoreceptors
Stimulated by over distension of ventricles – depressor response. Weak reflex – mild vasodilatation, lower blood pressure and preload, protective.
describe arterial chemoreceptors
sensors in blood vessels that detect changes in oxygen (O₂), carbon dioxide (CO₂), and pH levels in the blood. They are mainly found in the carotid bodies (near the carotid arteries) and aortic bodies (near the heart).
When oxygen levels drop, or CO₂ and acidity increase, these receptors send signals to the brain to adjust breathing rate and blood pressure to restore balance.
describe muscle metaboreceptors
sensory receptors in muscles that detect changes in chemical conditions during exercise, such as:
Low oxygen (O₂) levels
High carbon dioxide (CO₂) levels
Increased acidity (low pH)
Buildup of metabolic byproducts like lactate
When activated, they send signals to the brain to increase heart rate, breathing rate, and blood pressure, helping the body meet the muscles’ higher demand for oxygen and nutrients. This is part of the exercise pressor reflex.
what is the role of the NTS ?
Signal from stretched baroreceptor sent via afferent fibres enter Nucleus Tractus Solitarius (NTS).
This then sends information out to the Caudal Ventrolateral Medulla (CVLM).
The CVLM sends information to the rostral ventrolateral medulla (RVLM).
This results in INHIBITION of sympathetic efferent nerves to heart and vessels.
Less sympathetic efferent signals result in reduction in HR, less vasoconstriction, lower BP etc.
describe the vagus parasympathetic impulses to the heart
Loading of the baroreceptors also stimulates the vagus nerve which again activates the NTS.
The signal from the NTS stimulates the nucleus ambiguous (vagal nuclei).
Vagal parasympathetic impulses are sent to the heart and these have a depressor effect.
describe sinus tachycardia
Inhibitory input from inspiratory centre.
Each inhalation switches OFF nucleus ambiguus.
The inhibitory parasympathetic signal to the Vagus decreases and heart rate increases slightly.
Your heart rate is slightly quicker when you inhale compared to exhaling.
what is vasovagal syncope ?
Limbic system (emotional centre) stimulates NTS which in turn stimulates the nucleus ambiguus causing increased activity of the vagal nerve and depressor effect on the AV and SA nodes.
Can lead to fainting (syncope) - vasovagal attack
Syncope caused by decreased cerebral blood flow due to sudden drop in arterial cardiac output & blood pressure.
