Flashcards in Ch 13/14 Cardiovascular Physiology (Day 6) Deck (17):
Affected by blood volume, stroke volume, total peripheral resistance, and HR
-Increase in any of these will increase blood pressure.
-Vasoconstriction of arterioles raises blood pressure upstream in the arteries.
BP(arterial) = CO X TPR
CO = SV x HR
TPR = vasoconstriction
The blood pressure of blood vessels is related to the total cross- sectional area
-Capillary blood pressure is low because of large total cross-sectional area.
-Artery blood pressure is high because of small total cross-sectional area
Blood Pressure Regulation
-Kidneys can control blood volume and thus stroke volume.
-Sympathoadrenal system stimulates vasoconstriction of arterioles (raising TPR) and increased CO.
-Activated by changes in blood pressure detected by baroreceptors (stretch receptors) in the aortic arch and carotid sinuses
-Increased blood pressure stretches these receptors, increasing action potentials to the vasomotor and cardiac control centers in the medulla.
-Most sensitive to drops in blood pressure
-The vasomotor center controls vasodilation and constriction.
-The cardiac center controls heart rate.
-Fall in blood pressure = Increased sympathetic and decreased parasympathetic activity, resulting in increased heart rate and total peripheral resistance
-Rise in BP has the opposite effects.
-Good for quick beat-by-beat regulation— (e.g. going from lying down to standing)
Structures of the Baroreceptor Reflex
1. Baroreceptors (sensors)
2. Vasomotor & cardiac control centers in medulla (integrating centers)
3. Symp/parasymp axons to heart & blood vessels (effectors)
Atrial Stretch Reflexes
Activated by increased venous return to:
-Stimulate reflex tachycardia (sympathetic)—physiologic significance unknown
-Inhibit ADH release; results in excretion of more urine
-Stimulate secretion of atrial natriuretic peptide; results in excretion of more salts and water in urine
-Measured in mmHg using sphygmomanometer.
-Blood pressure cuff produces turbulent flow of blood in the brachial artery—detected as Korotkoff sounds via stethoscope.
1) Cuff inflated to beyond systolic blood pressure to occlude artery;
2) Pressure gradually released, the first (tapping) sound is heard at systole; 3) second “sound” is the last “tap” before sounds disappear—when pressure in cuff = diastolic pressure.
-Average BP is 120/80 (systolic/diastolic).
“Taking the pulse” is a measure of heart rate.
Each “pulse” = increased blood pressure in that artery at systole.
--> P(systolic) – P(diastolic) = pulse pressure.
--> e.g. if BP = 120/80, pulse pressure = 120 – 80 = 40 mmHg.
Pulse pressure is a reflection of stroke volume
How is pulse pressure a reflection of stroke volume?
Mean Arterial Pressure
MAP = average pressure in the arteries in one cardiac cycle.
Significance: MAP – venous pressure = driving force for blood flow into capillaries.
Not a simple arithmetic average, since diastole is longer than systole.
Approximated as: diastolic pressure + 1/3 pulse pressure
--> e.g. for BP = 120/80, pulse pressure = 40, and MAP = 80 + 1/3* 40 = 93 mm Hg.
High Blood Pressure
-Incidence increases with age
-Increases risk of cardiac diseases, kidney diseases, and stroke.
-Classified as “essential” or “secondary.”
-Essential or primary hypertension—Most people fall in this category. Causes not clearly defined in all cases; may include:
a) ↑salt intake coupled with decreased kidney filtering ability
b) ↑ sympathetic nerve activity ↑’s HR
c) altered responses to paracrine regulators from the endothelium
d) ↑ TPR
Secondary hypertension is a symptom of another disease, such as kidney disease.
Dangers of Hypertension
-Vascular damage within organs, especially dangerous in the cerebral vessels and leading to stroke
-Ventricular overload to eject blood due to abnormal hypertrophy, leading to arrhythmias and cardiac arrest
-Contributes to the development of atherosclerosis
Treatments for Hypertension
-Lifestyle modification: ↓ salt intake; ↓ smoking and drinking; ↓ weight; ↑ exercise
-K+ (and possibly calcium) supplements
-Diuretics to increase urine formation
-Beta blockers to decrease cardiac rate
-ACE inhibitors to block angiotensin II production
What is circulatory shock?
Inadequate blood flow to match oxygen usage in tissues
What is hypovolemic shock?
-Due to low blood volume from an injury, dehydration, or burns
-↓ CO and BP
-Blood is diverted to the heart and brain at the expense of other organs.
-Compensation includes baroreceptor reflex, which in response to lower pressure, raises heart rate, raises peripheral resistance, and produces cold, clammy skin and low urine output.
What is septic shock?
-Dangerously low blood pressure (hypotension) due to an infection (sepsis)
-Bacterial toxins (endotoxins) induce NO production, causing widespread vasodilation.
-Mortality rate is high (50−70%).
What are other causes of circulatory shock?
1. Severe allergic reactions --> anaphylactic shock due to production of histamine and resulting vasodilation.
2. Spinal cord injury or anesthesia --> neurogenic shock due to loss of sympathetic stimulation.
3. Cardiac failure --> cardiogenic shock due to significant loss of myocardial function.
congestive heart failure
CO insufficient to maintain blood flow required by the body
a. Caused by myocardial infarction, congenital defects, hypertension, aortic valve stenosis, or disturbances in electrolyte levels (K+ and Ca2+)
b. Similar to hypovolemic shock in symptoms and response