Ganong 24e chapter 32 - Cardiovascular Regulatory Mechanisms (1) Flashcards
What is the innervation to the majority of blood vessels? What are the exceptions?
Most blood vessels’ smooth muscle is innervated exclusively by the sympathetic nervous system. The exceptions include the vessels of erectile tissue and reproductive organs, which are innervated by the parasympathetic nervous system.
What is the relationship of the vagus nerve to the heart and cardiac function?
The vagus nerve is the parasympathetic innervation to the heart. Vagal stimulation results in release of acetylcholine, which binds to the M2 muscarinic receptors in the heart, mostly at the SA-node, AV-node and atrial muscle, triggering a decrease in heart rate and contractility.
What is the major nerve conducting baroreceptor afferent signals from the carotid sinus? Where does it terminate? Which neurotransmitter does it release?
Cranial nerve IX (glossopharyngeal), terminating in the Nucleus of the Tractus Solitarius, releasing Glutamate.
The RVLM is one of the major sources of excitatory input to sympathetic nerves controlling the vasculature. What does RVLM stand for?
Rostral Ventro-lateral Medulla.
Of the following factors affecting the RVLM and hence affecting blood pressure, which are excitatory inputs to the RVLM and which are inhibitory?
- Carotid and aortic chemoreceptors
- Pain pathways
- Carotid sinus baroreceptors
The first two are excitatory (activating sympathetics, increasing PVR), whilst baroreceptor inputs are inhibitory.
Where are all the baroreceptors located?
Baroreceptors are in the walls of the carotid sinus and aortic arch, and these regulate arterial circulation. The cardiopulmonary baroreceptors regulate the low-pressure part of the circulation, and are found in the walls of the RA + LA at the entrance points of the SVC + IVC + Pulmonary veins.
What would happen to the BP initially if you perform a bilateral resection of the baroreceptor nerves?
Initially there would be a dramatic rise in BP, because this situations mimics the decrease in baroreceptor discharge that occurs in a sharp fall in BP. The baroreceptors have an inhibitory effect on sympathetic control of peripheral vascular resistance.
Where are the peripheral chemoreceptors? What is the primary stimulus that activates them?
Peripheral chemoreceptors are in the carotid and aortic bodies, and they primarily respond to a reduction in PaO2.
Where are the central chemoreceptors? What do they respond to?
Central chemoreceptors are in the RVLM (rostral ventrolateral medulla). During raised intracranial pressure, the blood supply to the RVLM is compromised, and the neurons discharge in response to the hypoxia and hypercapnoea. This causes a rise in BP, and a bradycardia due the baroreceptor reflex.
Name a vasoactive substance produced by the endothelial cells, whose actions antagonize those of thromboxane A2. Explain its antagonistic relationship with thromboxane A2.
Prostacyclin (also called prostaglandin-I2). Whilst thromboxane A2 promotes platelet aggregation and vasoconstriction, prostacyclin promotes vasodilation and inhibits platelet aggregation. This prostacyclin-TXA2 balance is important in keeping clot formation localized and not excessive.
If aspirin is given, what is the response from endothelial cells, and how is this different from platelets?
Aspirin is an irreversible cyclooxygenase inhibitor. If given, endothelial cells will simply produce more cyclooxygenase, within hours. However, platelets cannot manufacture COX. Platelets have a half-life of about 4 days, so the circulating platelets will contain COX a few days after giving aspirin.
What is the electrolyte change that triggers endothelial NO-synthase to produce NO?
Increased intracellular calcium concentration.
Does bradykinin cause vasodilation or vasoconstriction?
Vasodilation.
What are the effects of bradykinin in tissues?
Vasodilation, increased capillary permeability, leukocyte attraction, pain, contraction of visceral smooth muscle.
Give a basic overview of how blood pressure affects baroreceptors, how baroreceptors affect the brainstem, and how the brainstem affects blood pressure.
An increase in neural output from the brainstem to the sympathetic nerves causes vasoconstriction and increased HR. An increase in BP causes the baroreceptors to increase their activity, causing neural output along the glossopharyngeal nerve, which inhibits the brainstem’s sympathetic output.
