Blood pressure control is based on negative feedback . Negative feedback requires a: Detector

1. In the power company they keep the voltage in your house constant (110 V) and you vary the resistance of what you plug in to determine how much power you want to use.

2. B C A The body works the same way. 100 mmHg is maintained in the aorta and autoregulation controls blood flow in each organ in the periphery. Overall aim of the system is to keep aortic pressure constant and let the organs regulate their own flow through autoregulation.

3. Blood pressure control is based on negative feedback. • Negative feedback requires a: • Detector • Integrator • set point • effector Your furnace

4. Set Point Integrator Detector Effector

5. Arterial baroreceptors are located in the carotid sinus and arch of aorta The sensor

6. Stretch receptors in the carotid sinuses are innervated by the Herring’s nerve (sinus nerve). It is a branch of the glossopharyngeal.

7. The aortic arch has similar receptors that are innervated by the aortic nerve, a branch of the cervical vagus. AKA “depressor branch of the vagus“.

8. Increased blood pressure stretches the walls and increases their frequency of action potentials. A fall in pressure would decrease the frequency.

9. Like most mechanoreceptors they are rate-sensitive and respond to pulsatile pressures better than a steady pressure

10. The carotid sinus receptors have a wider dynamic range than the aortic

11. The integrator

12. Activity in the NTS activates neurons in the dorsal motor nucleus of the vagus (DMV). That inhibits the heart via the vagus The first synapse for all afferent signals is in the Nucleus tractus solitarius (NTS)

13. Those fibers also activate vagal efferent neurons to the heart. That inhibits the heart via the vagus Activity in the NTS also activates neurons in the nucleus ambiguous.

14. That inhibits sympathetic nerves to the heart and blood vessels. Activity in the NTS inhibits neurons in the C1 region.

15. The sympathetic nervous system acts to increase pressure by increasing heart rate, contractility and constricting the arteries and veins Parasympathetic nervous system acts to decrease pressure by slowing heart rate only. Acetylcholine acts to inhibit cAMP in the heart and lowers contractility. However, very few vagal fibers go to the human ventricle. To decrease the heart’s contractility or dilate blood vessels the CNS can only decrease sympathetic tone.

16. The sympathetic and parasympathetic nerves to the heart and blood vessels have resting tone and act reciprocally during reflex activity. AOP + CO x TPR

17. Cutting sympathetics in the spinal cord causes a precipitous drop in blood pressure due to loss of peripheral vascular tone (spinal shock).

18. Parasympathetic nerves do not innervate most of the peripheral vessels. Parasymapthetic nerves in salivary glands and intestine cause dilation that is secondary to increased metabolism (active hyperemia). They also dilate erectile tissue None of the parasympathetic nerves to blood vessels are stimulated in the baroreflex.

19. So what vessels do the sympathetic nerves constrict? Vessels in the resting skeletal muscles, intestine or kidney If the organ becomes active it undergoes an active hyperemia that will over-ride any signal from the sympathetic nerves to constrict (such the skeletal muscle dilation seen in exercise).

20. The baroreflex acts primarily to control minute-to-minute blood pressure. • Blood pressure changes due to: • Active hyperemia • Hydrostatic columns Note that mean pressure is not changed by denervation. That is controlled by blood volume

21. The sequence of events with exercise will be: • An active hyperemia in the exercising muscles, • A drop in peripheral resistance and thus blood pressure. • Detected by the baroreceptors • Initiate a reflex to move pressure back toward the set point In heavy exercise blood pressure will actually increase. That is because the CNS increases the set point during heavy exercise.

22. Cardiopulmonary mechanoreceptors

23. B A B A and B type stretch receptors are found in the left atrium. A-fibers respond to atrial systole and report heart rate while B-fibers respond during ventricular systole and report atrial volume.

24. B A B • Atrial stretch activates B-fibers which will: • Increase the heart rate (Bainbridge reflex) • Decrease sympathetic tone to the kidney causing increased filtration and urine formation. • Decrease production of vasopressin (anti-diuretic hormone)

25. B A B Atrial stretch also causes the atria to make atrial natriuretic peptide (ANP) All of these effects act to lower blood volume

26. mean arterial pressure = cardiac output x peripheral resistance cardiac output ~ filling pressure of the heart ~ blood volume Thus blood pressure can be controlled by controlling blood volume.

27. The blood pressure then adjusts to maintain a balance between salt intake and loss NORMAL INTAKE HIGH INTAKE Because the curve is very steep a large increase in salt intake causes only a small increase in arterial pressure The rate at which the kidney loses sodium is determined by the blood pressure Loss curve

28. It is an integrating controller (blood volume is the integral of the rate of gain/loss) There is no error signal and thus control is perfect. NORMAL INTAKE HIGH INTAKE The kidney is the ultimate controller of blood pressure.

29. A defect in the kidney’s ability to control fluid balance leads to hypertension. Just raising peripheral resistance does not cause hypertension. Otherwise all amputees would suffer from hypertension. Restricting salt and giving diuretics is an effective way to treat hypertension.

30. Peripheral chemoreceptors Primarily control pulmonary function but their effects spill over into the CV system Carotid and Aortic Bodies

31. Carotid and aortic bodies are stimulated by: • 1. Low PO2 • 2. High PCO2 • 3. Low pH • 4. Low aortic pressure

32. Stimulation of the chemoreceptors directly decreases heart rate and constricts the peripheral blood vessels.

33. Systemic hypoxia actually causes a tachycardia due to the increased respiratory activity. The overall effect is to raise the blood pressure.

34. Head injury or a ruptured aneurysm can cause an intracranial bleed. Bleeding inside the cranial vault raises CSF pressure and collapses the brain’s blood vessels.

35. Ischemia in the CNS causes intense stimulation of both the sympathetic and parasympathetic outflow The patient will present with bradycardia and a very high blood pressure. The vagus is dominant over the sympathetics at the SA node

36. A summary of the known controllers of blood pressure.