A summary of the known controllers of blood pressure.

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. A summary of the known controllers of blood pressure.

4. Your furnace • Blood pressure control is largely based on negative feedback. • Negative feedback requires a: • Detector • Integrator • set point • effector Analog systems have an error signal

5. Set Point Integrator The body only senses pressure. There are no flow sensors. Detector Effector

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

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

8. 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“.

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

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

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

12. Sympathetic Nerves go to the heart and blood vessels. Parasympathetic nerves only go to the heart. The adrenal medula secretes epinephrine and norepinephrine: Stimulates heart and constricts blood vessels.

13. 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.

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

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

16. 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.

17. 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).

18. 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

19. 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.

21. 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.

22. 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

23. Only activated in emergency: not part of normal control.

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

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

27. Activation of the chemoreceptors increases respiratory activity and also increases blood pressure. Only very low pressure will activate them: not part of normal blood pressure control.

29. AOP= CO x TPR CO ~ filling pressure of the heart ~ blood volume Thus blood pressure can be controlled by controlling blood volume.

30. 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

31. An integrating control system Water level = integral of inflow rate

32. 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.

33. 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.

35. Lowering arterial pressure lowers capillary pressure Low capillary pressure absorbs fluid from the tissues Absorbed fluid increases blood volume and raises blood pressure.

36. Cardiopulmonary mechanoreceptors detect volume

37. 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.

38. 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)

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