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Blood pressure 1. Regulation of blood flow Local regulation –Adjustment of blood flow by the tissue Nervous system –Global implication Redistribution.

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Presentation on theme: "Blood pressure 1. Regulation of blood flow Local regulation –Adjustment of blood flow by the tissue Nervous system –Global implication Redistribution."— Presentation transcript:

1 Blood pressure 1

2 Regulation of blood flow Local regulation –Adjustment of blood flow by the tissue Nervous system –Global implication Redistribution of blood flow Increase/decrease in heart activity (pumping) Rapid control of arterial pressure

3 Autonomic system Sympathetic system –More important –Components Vasomotor fibers –Thoracic spinal nerves –Lumbar spinal nerves Sympathetic nerves –Innervation of internal viscera and the heart –Peripheral vessels

4 Innervation of blood vessels –Most tissues Not capillaries, precapillary sphincters, or metarterioles –Increased resistance for blood flow Decreased blood flow through the tissue –Decreased volume of vessels Veins Increased heart pumping

5 Innervation of heart –Sympathetic Increased heart rate Increased strength Increased volume of pumping –Parasympathetic (vagus) Decreased heart rate

6 Vasoconstriction Sympathetic nerve fibers –Vasoconstrictor nerve fibers Very small number of vasodilators Wide distribution –Tissue-dependent More powerful in some organs –Kidney, GI tract, spleen, and skin

7 Vasomotor center –Reticular substance of medulla and lower third of pons –Transmission of parasympathetic impulses Vagus nerves –Transmission of sympathetic impulses Spinal cord Peripheral sympathetic nerves

8 Area of vasomotor center –Vasoconstrictor area Signals to all levels of spinal cord –Excitation of preganglionic vasoconstrictive neurons –Vasodilator area Inhibition of vasoconstrictor area –Sensory area Receives sensory inputs from vagus and glossopharyngeal nerves Reflex control of many circulatory functions –Activity of both vasoconstrictor and vasodilator

9 Continuous signals from vasoconstrictor area –Sympathetic vasoconstrictor nerve fibers Continuous firing at 1.5 – 2 impulses per second –Sympathetic vasoconstrictor tone Maintenance of partial constriction of blood vessels –Vasomotor tone

10 Control of heart rate by vasomotor center –Excitatory impulses (sympathetic) Lateral portion Increased heart contraction and heart rate –Parasympathetic impulses Medial portion Sent via dorsal motor nuclei of the vagus nerves Decreased heart rate

11 Control of vasomotor center The CNS –Reticular substances of the pons, mesencephalon, and diencephalon –Hypothalamus Posteriolateral – excitation Anterior – mild excitation/inhibition –Cerebral cortex Motor cortex Basal areas of brain

12 Role of neurotransmitter Norepinephrine –Sympathetic neurotransmitter Vasoconstriction –Alpha receptors Adrenal medulla –Secretion of epinephrine and norepinephrine in response to sympathetic impulses Vasoconstriction Vasodilation via beta receptors (epinephrine)

13 Role of the nervous system in rapid control of arterial blood pressure Stimulation of sympathetic nervous system and cardioaccelerator –Rapid increase in arterial pressure 2 X within 5-10 sec During exercise or stress Reciprocal inhibition of parasympathetic vagal inhibitory signals

14 Arterial Pressure = Cardiac Output x Total Peripheral Resistance Arterial Pressure can be increased by: Constricting almost all arterioles of the body which increases total peripheral resistance. Constricting large vessels of the circulation thereby increasing venous return and cardiac output. Directly increasing cardiac output by increasing heart rate and contractility. Figure 14-1; Guyton and Hall

15 Maintenance of normal arterial pressure Negative feedback reflex mechanism –Majority Baroreceptor reflexes –Reflex initiated by stretching of arterial walls Increased flow of blood and pressure Detected by baroreceptors/pressoreceptors Generation of inhibitory signals

16 Baroreceptor –Spray-type nerve endings –Stretch receptor Carotid sinus –Hering’s nerve to glossopharyngeal nerves Aortic arch –Vagus nerve –Signals enter medulla Tractus solitarius

17 Response to pressure –Very rapid –Respond more rapidly to changing pressure compared to stationary pressure –Inhibition of vasoconstrictor center Vasodilation –Excitation of vagus nerves Decreased heart rate Net effect –Decreased arterial pressure

18 Constrict Common Carotids Constrictors Pressure at Carotid Sinuses Arterial Pressure Figure 18-5; Guyton and Hall Figure 18-7; Guyton and Hall

19 Functions of the Baroreceptors Maintains relatively constant pressure despite changes in body posture. Decrease Cardiac Output Sensed By Baroreceptors SupineStanding Decrease Central Blood Volume Vasomotor Center Sympathetic Nervous Activity Decrease Arterial Pressure

20 Pressure buffer system –Maintenance of constant pressure Reduction of variability in blood pressure Maintenance of pressure within the narrow range –Baroreceptors may not be important in long-term maintenance of blood pressure Adaptation of receptors

21 Other mechanisms Chemoreceptors –Calotid arteries and aorta Detection of oxygen concentrations Detection of carbon dioxide concentrations Detection of pH –Detect changes in chemical concentrations Decreased blood pressure –Excitation of vasomotor center

22 Activation of low-pressure receptors –Atria and pulmonary arteries Detection of increase in pressure caused by increased blood flow Volume reflex –Increase in glomerular pressure Increased fluid loss Decrease blood volume –Secretion of atrial natriaretic peptide Maintenance of blood volume

23 Bainbridge reflex –Increased atrial pressure Increased heart rate Caused by increased volume and stretching of sinus node Triggers increased heart rate –Prevents damming of blood

24 CNS inschemic response Loss of blood flow to brain –Cerebral ischemia Loss of nutrient Accumulation of carbon dioxide –Activation of vasomotor center Excitation of vasoconstrictor and cardioaccelerator Increase in arterial blood pressure

25 Cerebral ischemia –Occlusion of blood flow to the peripheral tissues if severe CNS ischemia response –Emergency pressure control system Maintenance of blood flow to the brain Cushing reaction –Special type of CNS ischemia response Increased CSF pressure around the brain

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