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Goal of the Cardiovascular System: deliver blood to all parts of the body
• Does so by using different types of tubing, attached to a pulsatile pump
• Elastic arteries• Muscular arteries• Arterioles• Capillaries• Venuoles• Veins
• Distribution system broken up into areas called vascular beds
• Skin• Digestive (splanchnic)• Muscle
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Structure of vasculature changes in response to different needs
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Why does blood flow through this closed circuit?
• Blood flows down a pressure gradient
• The absolute value of the pressure is not important to flow, but the difference in pressure (DP or gradient) is important to determining flow.
What happens to pressure if we decrease the volume of a fluid filled compartment (i.e. ventricles during systole)?
P directly proportional to F
The resulting pressure is called the driving pressure in the vascular system
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How does the flow differ in these two vessels?
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Vascular system possesses different mechanisms for promoting continuous flow of blood to the capillaries:
Elastic recoil smooth m. regulation of diameter sphincters valves
Muscular arteries
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Chemical Physiologic role Source Type
NE ( ) Baroreceptor reflex Sympathetic neurons Neural
Endothelin Paracrine Vascular endothelium Local
Serotonin Platelet aggregation, smooth muscle contraction
Neurons, digestive tract, platelets
Local, neural
Substance P Pain, increased capillary permeability
Neurons, digestive tract
Local, neural
Vasopressin Increase blood pressure during hemorrhage
Posterior pituitary Hormonal
Angiotensin II Increase blood pressure Plasma hormone Hormonal
Prostacyclin Minimize blood loss from damaged vessels before coagulation
endothelium local
Substances causing contraction in vascular smooth muscle
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Chemical Physiologic role Source Type
Nitric oxide Paracrine mediator Endothelium Local
Atrial natriuretic peptide
Reduce blood pressure Atrial myocardium, brain
Hormonal
Vasoactive intestinal peptide
Digestive secretion, relax smooth muscle
Neurons Neural, hormonal
Histamine Increase blood flow Mast cells Local, systemic
Epinephrine (2) Enhance local blood flow to skeletal muscle, heart, liver
Adrenal medulla Hormonal
Acetylcholine (muscarinic)
Erection of clitoris, penis Parasympathetic neurons
neural
Bradykinin Increase blood flow via nitric oxide
Multiple tissues Local
Adenosine Enhance blood flow to match metabolism
Hypoxic cells local
Substances that mediate vascular smooth muscle relaxation
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Even though there are many mechanisms for altering the radius of the vascular system, pressure still drops as blood moves further away from the heart. Why?
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Resistance = tendency of the vascular system to oppose flow; Flow =
• Influenced by: length of the tube (L), radius of the tube (r), and viscosity of the blood ()
Poiseuille’s Law R = Lr4
• In a normal human, length of the system is fixed, so blood viscosity and radius of the blood vessels have the largest effects on resistance
1
R
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All four tubes have the same driving pressure. Which tube has the greatest flow? The least flow? Why?
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Even with a decrease in overall pressure, the pressure in the vessels is not constant. The pressure in the vessels mirrors the pressures generated in the heart – systolic and diastolic pressures. Systolic = ventricles contracting Diastolic = ventricles filling
Why does the diastolic pressure rise between the left ventricle and the arteries?
Normal blood pressure = 120/80
High blood pressure = 140/90
What could be happening to increase both the diastolic and systolic blood pressure?
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Blood Pressure
• Reflects the driving pressures produced by the ventricles
• Because arterial pressure is pulsatile, a single value is used to represent the overall driving pressure. This is called the mean arterial pressure.
MAP = diastolic P + 1/3(systolic P-diastolic P)Why does diastolic pressure account for a greater proportion of the overall value?
SVR = systemic vascular resistance
CO = cardiac output
SV = stroke volume
MAP = Q x Rarterioles
Explain how these two equations are equivalent
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What factors influence blood pressure?
• Blood volume
• Vascular resistance
• Autoregulation
• Autonomic influences
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Regulation of Blood Pressure
• Main coordinating center is in the medulla oblongata of the brain; medullary cardiovascular control center
• Reflex control of blood pressure
•Baroreceptor reflex
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