UNIT 3 Blood Vessels Part 2 of 2

1. UNIT 3 Blood Vessels Part 2 of 2 Measuring Blood Pressure Blood Pressure Regulation Autoregulation and Capillary Dynamics (8th edition)

2. Measuring Blood Pressure to help increase your understanding of the material, the following sections are presented in a different way than the textbook; I highly recommend that you view the Interactive Physiology tutorial called “Measuring Blood Pressure” as you read through the following information; it contains helpful audio and animations; information on how to access the tutorial can be found on the BIO 202 course website, Unit 3, Step 4. (8th edition)

3. Measuring Blood Pressure BLOOD PRESSURE - the force that blood exerts against blood vessel walls pumping of the heart generates blood flow blood pressure results when blood flow is met by resistance from blood vessel walls laminar flow - blood in the center of a blood vessel flows faster than blood along the wall; this is due to friction between the blood and the blood vessel wall turbulent flow - blood flow around corners or through restricted arteries PULSE (fig. 19.12) - pressure wave which travels from the heart throughout the arteries (8th edition)

4. Measuring Blood Pressure SYSTOLIC PRESSURE - greatest pressure exerted by blood against artery walls the result of systole (contraction of the ventricles) in a normal, healthy individual (at rest) = about 120 mm Hg   DIASTOLIC PRESSURE - lowest pressure in arteries the result of diastole (relaxation of the ventricles) in a normal, healthy individual (at rest) = about 80 mm Hg Normal blood pressure = 120/80 mm Hg; 120 mm Hg is the systolic pressure and 80 mm Hg is the diastolic pressure PULSE PRESSURE - difference between systolic pressure and diastolic pressure; for a normal, healthy individual (120/80 mm Hg) it would = 40 mm Hg (8th edition)

5. Measuring Blood Pressure MEAN ARTERIAL PRESSURE (MAP) = calculated average pressure MAP = diastolic pressure + 1/3 of the pulse pressure (systolic pressure - diastolic pressure) for a normal, healthy individual (120/80 mm Hg): 80 mm Hg + 1/3 (40 mm Hg) = 93 mm Hg it is not just the average of systolic and diastolic pressures because diastole lasts longer than systole; thus, MAP is closer to diastolic pressure than systolic pressure (8th edition)

6. Measuring Blood Pressure Measuring Blood Pressure using a SPHYGMOMANOMETER (BLOOD PRESSURE CUFF); you will perform the following steps in your lab exercise in order to measure blood pressure a cuff is inflated to constrict the BRACHIAL ARTERY when the pressure in the cuff is greater than the blood pressure in the artery, the blood flow stops as the cuff is gradually released, the artery will partially open and turbulent blood flow will occur through the vessel; the turbulent flow can be heard by using a stethoscope; these sounds are called Korotkoff sounds; this indicates that the systolic pressure has been found as the cuff is slowly deflated further, the sounds of blood flow will eventually stop; this means that there is again laminar flow through the blood vessel; when the sounds stop the diastolic pressure has been found (8th edition)

7. Blood Pressure Regulation to help increase your understanding of the material, the following sections are presented in a different way than the textbook; I highly recommend that you view the Interactive Physiology tutorial called “Blood Pressure Regulation” as you read through the following information; it contains helpful audio and animations; information on how to access the tutorial can be found on the BIO 202 course website, Unit 3, Step 4. (8th edition)

8. Blood Pressure Regulation Short term mechanisms regulate: 1. vessel diameter 2. heart rate (HR) 3. heart contractility (stroke volume or SV) Long term mechanisms regulate blood volume (8th edition)

9. Blood Pressure Regulation - Short Term Mechanisms: BARORECEPTORS (fig. 19.9) - stretch receptors that monitor blood pressure rising blood pressure: when blood pressure rises there is an increased stretch in the elastic arteries in the thoracic cavity baroreceptors in the wall of the aortic arch and carotid sinus are stretched (stimulated) when the baroreceptors are stretched they send more action potentials to the cardiac center in the medulla oblongata of the brain more action potentials to the cardiac center from the baroreceptors results in increased parasympathetic activity and decreased sympathetic activity decreased sympathetic activity results in: - decreased rate of vasomotor impulses - increased arterial vessel diameter (vasodilation) - reduced peripheral resistance (R) - lower blood pressure increased parasympathetic activity via the vagus nerve to the heart results in: - reduced HR (heart rate) - reduced SV (reduced heart contractility) - reduced CO - lower blood pressure (8th edition)

10. Blood Pressure Regulation - Short Term Mechanisms: BARORECEPTORS (fig. 19.9) - stretch receptors that monitor blood pressure falling blood pressure: when blood pressure drops there is less stretch in the elastic arteries in the thoracic cavity baroreceptors in the wall of the aortic arch and carotid sinus are inhibited when the baroreceptors are stretched less they send less action potentials to the cardiac center in the medulla oblongata less action potentials to the cardiac center from the baroreceptors results in decreased parasympathetic activity and increased sympathetic activity increased sympathetic activity results in: - increased rate of vasomotor impulses - decreased arterial vessel diameter (vasoconstriction) - increased peripheral resistance (R) - higher blood pressure * Increased sympathetic activity also triggers release of epinephrine and norepinephrine from the adrenal medulla; these hormones increase HR, SV, CO, and blood pressure decreased parasympathetic activity via the vagus nerve to the heart results in: - increased HR - increased SV (increased heart contractility) - increased CO - higher blood pressure (8th edition)

11. Blood Pressure Regulation - Long Term Mechanisms (fig. 19.10): long term regulation of blood pressure is primarily accomplished by altering blood volume normal blood volume is maintained by conserving water in the kidneys and stimulating uptake of water intake juxtaglomerular cells - these cells in the kidneys monitor changes in blood pressure decreased blood pressure triggers the juxtaglomerular cells to release RENIN renin in the blood binds to the plasma protein angiotensinogen activating it into ANGIOTENSIN I angiotensin I is converted to ANGIOTENSIN II by an enzyme in the lungs angiotensin II triggers the release of ALDOSTERONE from the adrenal cortex aldosterone promotes the increased reabsorption of sodium (Na+) from the kidney tubules as Na+ moves into the bloodstream water follows; the reabsorbed water increases the blood volume increased blood volume increases the blood pressure (8th edition)

12. Blood Pressure Regulation - Long Term Mechanisms (fig. 19.10): angiotensin II is also a vasoconstrictor which raises the blood pressure in the arterioles angiotensin II stimulates the thirst center in the hypothalamus, causing an individual to drink; increased intake of fluids can lead to increase blood volume and blood pressure dehydration - will cause an increase in blood osmolarity (concentration) dehydration can come from excessive sweating without a replacement of fluids, diarrhea, or excessive urine flow dehydration also causes decreased blood volume and blood pressure osmoreceptors in the hypothalamus respond to high osmolarity by secreting ADH (vasopressin) from the posterior pituitary gland; ADH increases the reabsorption of water in the kidneys this conservation of water results in increased blood volume and blood pressure and decreased osmolarity increased osmolarity also stimulates the thirst center in the hypothalamus; the intake of more fluids (rehydrating) results in returning the blood volume to normal, and therefore the blood pressure to normal (8th edition)

13. Autoregulation and Capillary Dynamics to help increase your understanding of the material, the following sections are presented in a different way than the textbook; I highly recommend that you view the Interactive Physiology tutorial called “Autoregulation and Capillary Dynamics” as you read through the following information; it contains helpful audio and animations; information on how to access the tutorial can be found on the BIO 202 course website, Unit 3, Step 4. (8th edition)

14. Autoregulation and Capillary Dynamics AUTOREGULATION - blood flow through individual organs is controlled intrinsically in response to local tissue requirements As long as MAP is normal, tissues can regulate the amount of blood that passes through them according to their needs FEEDER ARTERIOLES (=terminal arterioles) (fig. 19.4) - bring blood to the capillary bed; they constrict or dilate according to tissue needs; precapillary sphincters (at the beginning of each capillary) regulate blood flow through the capillary bed: certain chemicals dilate feeder arterioles and relax precapillary sphincters chemicals and conditions that open the precapillary sphincters include: low O2, high CO2, low pH, lack of nutrients, and fever Active tissues that need more nutrients need more O2 to generate energy in cellular respiration, and have a build up of acidic metabolic wastes and CO2 which need to be removed; blood brings to the tissue what it needs and removes what it needs to get rid of (8th edition)

15. Autoregulation and Capillary Dynamics Capillary exchange (fig. 19.16) - capillaries are where there is an exchange between blood and tissues O2 is exchanged for CO2 and nutrients are exchanged for wastes FENESTRATIONS - pores that may be opened CLEFTS - spaces between cells (smaller than pores) most solutes move across the capillary wall by diffusion lipid soluble molecules diffuse through phospholipids of the membrane non-lipid soluble (water-soluble) molecules can move across the membrane by exocytosis larger, water-soluble solutes diffuse through fennestrations or clefts (8th edition)

16. Autoregulation and Capillary Dynamics BULK FLUID FLOW - movement of fluid into and out of the capillary there is net fluid flow out of the capillary at the arteriole end via hydrostatic pressure there is net fluid flow into the capillary at the venule end via osmotic pressure (osmosis draws it in) fluid not returned to the capillary enters a lymphatic capillary (fig. 19.2); of all the fluid that leaves the capillary at the arteriole end 90% of the fluid re-enters the capillary at the venule end by osmosis; the other 10% enters lymphatic capillaries (8th edition)

17. Autoregulation and Capillary Dynamics Hydrostatic Pressure - the pressure exerted by a fluid on the walls of its container blood in capillaries exerts a (hydrostatic) pressure in the capillary wall called filtration pressure; this pressure forces fluid out of the capillaries filtration pressure is greatest at the arteriole end of the capillary and less at the venule end Osmotic Pressure - the higher the solute concentration of a solution the more that solution pulls or holds water capillary blood has a relatively high osmotic pressure which is due to plasma proteins like albumin (which don't leave the blood) this high osmotic pressure of capillary blood draw fluid into the capillary net osmotic pressure pulls fluids into the capillary EDEMA - excess fluid remains in the interstitial fluid (8th edition)

18. This concludes the current lecture topic (close the current window to exit the PowerPoint and return to the Unit 3 Startpage) (8th edition)