Chapter 10

Pressure gradient

- the difference in pressure between the beginning and the end of a vessel -blood flows from an area of higher pressure to an area of lower pressure down a pressure gradient -the greater the pressure gradient the greater the flow rate through the vessel

Anti-hypertensive Drugs

-angiotensin converting enzyme inhibitors (ACE inhibitors, more later) -beta-blockers reduce heart rate and strength of contraction. (blocking norepinephrine on heart) -diuretics rid the body of excess fluids and salt -calcium channel blockers-decrease heart activity and cause vasodilation -alpha-blockers cause the dilation of arterioles

Arteries

-because of their large radius arteries have low resistance so are rapid-transit passageways -due to elastic properties they act as pressure reservoir to provide driving force for blood when ventricle is in diastole

Vascular Tree

-blood flows in a closed loop between the heart and the organs -the arteries transport blood from the heart throughout the body -arterioles control the amount of blood that flows through each organ by dilating and constricting -the capillaries are the vessels where materials are exchanged between blood and surrounding tissue ells -the veins return blood from the tissue back to the heart

Systemic Blood Flow

-blood is transported to all parts of the body through a system of vessels -reconditioning organs (digestive organs, kidneys, skin) receive a disproportionally high blood flow -this allows them replenish nutrient supplies and remove metabolic wastes to help maintain homeostasis -blood flow to other organs can be adjusted according to metabolic needs -brain function requires constant blood flow -maintaining adequate flow to the brain is a priority of the circulatory system

Long-term adjustments

-blood pressure adjustment made by controlling total blood volume by adjusting urine output and thirst (requiring minutes to days)

Short-term adjustments

-blood pressure adjustment made by neural control of cardiac output and total peripheral resistance (within seconds)

Mean Arterial Pressure

-blood pressure that is monitored and regulated in the body -regulated by controlling cardiac output (CO), total peripheral resistance (TPR), blood volume -control of CO depends on regulation of heart rate and stoke volume -TPR is determined by the degree of arteriolar vasoconstriction -blood volume is controlled by kidneys

Primary Hypertension

-defects in salt management by the kidneys -excessive salt intake -diets low in K+ and Ca2+ -plasma membrane abnormalities (Na+-K+ pump) -genetics -abnormalities in local vasoactive chemicals -excess vasopressin, NE -lifestyle-diet, exercise, smoking, etc.

Hypertension

-defined as blood pressure above 140/90 mm Hg -two classes: 1. primary: unknown cause, accounts for 90% of cases 2. secondary: occurs secondary to another known primary problem, accounts for 10% of cases

Hypotension

-defined as blood pressure below 100/60 mm Hg

Bulk Flow

-determines the distribution of the ECF volume between the vascular and the interstitial fluid compartments -occurs when protein-free plasma filters out of the capillary, mixes with the interstitial fluid and then is reabsorbed -is important in regulating the distribution of ECF between the plasma and the interstitial fluid to help maintain arterial blood pressure Depends on two processes: 1. ultrafiltration 2. reabsorption

Hypovolemic shock

-due to extensive loss of blood

Cardiogenic shock

-due to failure of heart to pump blood adequately

Neurogenic shock

-due to neurally defective vasoconstrictor tone

Vasogenic shock

-due to widespread arteriolar vasodilation

Capillary Exchange

-exchanges between blood and tissues across the capillary are accomplished in two ways: 1. passive diffusion 2.bulk flow

Extrinsic Control

-extrinsic sympathetic control of arteriolar radius is important in regulating blood pressure -these changes in arteriolar resistance bring about changes in mean arterial pressure -NE released from sympathetic nerve bring about vasoconstriction -Skeletal and cardiac muscles have local control mechanisms to override sympathetic vasoconstriction during exercise -The cardiovascular control center in the medulla adjusts sympathetic output to arterioles

Systemic Blood Pressure

-force exerted by blood against a vessel wall pressure depends on: 1. the volume of blood contained within the vessel 2. compliance of vessel walls; vessels with high compliance show lower pressures compared to vessels with lower compliance of the same size

Bulk Flow Forces

-Bulk flow occurs because of difference in the hydrostatic and the colloid osmotic pressures between plasma and interstitial fluid -capillary hydrostatic pressure pushes fluid out of the capillary bed (blood pressure) -plasma colloid osmotic pressure draws fluid back into the capillary bed (plasma proteins that stay behind) -slightly more fluid is filtered out of the capillaries into the interstitial fluid then is reabsorbed from the interstitial fluid back into the plasma -excess fluid is picked up by the lymphatic system and returned to general circulation

Intrinsic control

-local chemical changes associated with changes in the level of metabolic activity affect arteriole resistance -increased blood flow in response to enhanced tissue activity is called active hyperemia -changes blood flow to specific tissue, does not affect overall circulatory activity

Arterioles

-major resistance vessels -high resistance produces a large drop in mean pressure between the arteries and capillaries -this decline enhances blood flow by contributing to the pressure gradient between the heart and organs -have a thick layer of circular smooth muscle -the radius of arterioles can be adjusted to accomplish two functions: 1. to variably distribute cardiac output among the organs depending on body needs 2. to help regulate arterial blood pressure

Diastolic pressure

-minimum pressure in arteries when blood is draining off into vessels downstream -average 80 mm Hg

Circulatory shock

-occurs when blood pressure falls so low that adequate blood flow to the tissues can no longer be maintained -Four types: 1. hypovolemic 2. cardiogenic shock 3. vasogenic shock 4. neurogenic shock

Reabsorption

-occurs when inward-driving pressures exceed outward pressures and net movement of fluid back into plasma

Ultrafiltration

-occurs when pressure inside the capillary exceeds pressure outside and fluid is pushed into ECF (goes into interstitial space)

Systolic Pressure

-peak pressure exerted by ejected blood against vessel walls during cardiac systole -average 120 mm Hg

baroreceptors

-pressure sensors that constantly monitor blood pressure in the circulatory system

Passive diffusion

-primary mechanism for exchanging solutes -individual solutes are exchanged primarily by diffusion down concentration gradients -lipid-soluble substances pass directly through endothelial cells lining a capillary -water-soluble substances pass through water-filled pores between the endothelial cells -plasma proteins generally do not escape

Causes of edema

-reduced concentration of plasma proteins (liver or kidney issues) -increased permeability of capillary wall (disease, allergies, drugs) -increased venous pressure (CHF, pregnancy) -blockage of lymph vessels

Orthostatic hypotension

-results from insufficient sympathetic compensation when a person moves from a horizontal to a vertical position (sitting up too fast)

Baroreceptor reflex

-short-term mechanism for regulating blood pressure -acts on heart and blood vessels to regulate CO and TPR -Baroreceptors in carotid sinus and aortic arch detect blood pressure changes -send signals into cardiovascular control center in the medulla -the cardiovascular control center alters the activity of the sympathetic and parasympathetic systems to return MAP to normal

Edema

-swelling of tissues, occurs when too much interstitial fluid accumulates

Pulse Pressure

-the difference between systolic and diastolic pressures

Resistance

-the hindrance to blood flow through a vessel -based on frictional forces during blood flow -factors affecting resistance include: blood viscosity, vessel length, vessel radius -normally viscosity and length do not play a major role in determining resistance -major determinant of resistance to flow is vessel radius -small change in radius produces significant change in blood flow -doubling the radius reduces the resistance to 1/16th its original value and increases flow 16-fold

Vascular Tone

-the state of partial constriction that establishes a baseline of arteriolar resistance -arteriolar vasodilation decreases resistance and increases blood flow through the vessel -arteriole vasoconstriction increases resistance and decreases flow -arteriolar tone is controlled by local (intrinsic) controls and extrinsic controls

Capillaries

-thin-walled, small-radius, extensively branched vessels -surface area for exchange is maximized -diffusion distance is minimized -large cross-sectional area results in slow blood velocity to maximize time for exchange

Venous return

-veins return blood back to the heart -veins serve as a blood reservoir containing 60% of blood volume -Venous return is enhanced by: 1.venous vasoconstriction by sympathetic system 2.external compression of the veins from contraction of surrounding skeletal muscles 3. one-way venous valves -these actions help counter the effects of gravity on the venous system

Flow rate

-volume of blood passing through per unit of time -directly proportional to the pressure gradient -inversely proportional to vascular resistance F =ΔP R F = flow rate of blood through a vessel ΔP = pressure gradient R = resistance of blood vessels

Mean Arterial Pressure (MAP)

the average driving pressure throughout the cardiac cycle= diastolic pressure + 1/3 (pulse pressure) -monitored and regulated by blood pressure reflexes -with BP 120/80, MAP= 93 mm Hg