Questions and Answers
What is the primary requirement for the circulatory system to function properly?
What are the two circulations in series in the cardiovascular system?
What is the primary function of the pulmonary circulation?
What are the factors that determine the exact amount of flow around the circulatory circuit?
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What is the term for the part of the cardiovascular system that carries oxygenated blood away from the heart to the body and returns deoxygenated blood back to the heart?
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What is the primary function of the ventricles in the circulatory system?
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Where does the exchange of oxygen and carbon dioxide occur in the circulatory system?
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What is the function of the collecting system in the circulatory system?
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Which of the following is NOT part of the distribution system?
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What is the term for the part of the circulatory system that includes venules, veins, and atria?
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What is a characteristic feature of the walls of arteries?
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What type of blood flow occurs in arteries?
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What type of volume do arteries carry?
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What is the primary function of arteries?
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Which artery is the largest in the systemic circulation?
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What is the primary function of elastic arteries?
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What is the significance of compliance in the circulatory system?
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What is the primary feature of muscular arteries?
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What is the formula to calculate compliance?
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What is the primary difference between elastic and muscular arteries?
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Which of the following is a characteristic of arterioles?
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What is the primary function of arterioles?
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Where is the highest resistance to blood flow encountered?
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What is the purpose of vasoconstriction and vasodilation in arterioles?
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Which receptor subtype is predominantly expressed in the arterioles of most visceral organs and couples to Gq?
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What is the primary endogenous agonist that binds to alpha 1 and alpha 2 receptors in arterioles?
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What is the effect of alpha 1 receptor activation on smooth muscle in arterioles?
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In which location are alpha 2 receptors also present, in addition to arterioles?
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What is the primary function of alpha 1 receptor-mediated vasoconstriction in arterioles?
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What type of receptor does beta 2 adrenergic receptors couple to?
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What is the primary endogenous agonist that binds to beta 2 adrenergic receptors?
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Where are beta 2 adrenergic receptors primarily expressed?
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What is the effect of beta 2 adrenergic receptor activation on smooth muscle?
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What is the significance of beta 2 adrenergic receptors in the body?
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What type of receptor do M3 receptors on coronaries couple to?
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What is the primary endogenous agonist that binds to M3 receptors?
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What is the effect of M3 receptor activation on vascular smooth muscle?
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Where are M3 receptors typically found?
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What is the downstream effect of M3 receptor activation on eNOS?
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What is unique about arterioles in the vasculature?
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What can change the resistance in arterioles?
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Where is the highest resistance to blood flow encountered?
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What type of substances can change the resistance in arterioles?
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What is the significance of arterioles in the vasculature?
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What is the primary function of capillaries in the circulatory system?
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How do lipid-soluble substances cross the capillary wall?
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What type of capillaries have large pores in their walls?
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Why are not all capillaries always perfused with blood?
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What is the structure that surrounds the endothelial cells in capillaries?
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What is the main function of venules in the circulatory system?
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What is a characteristic of veins in the circulatory system?
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What type of volume do veins carry?
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What is the characteristic of veins compared to arteries?
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What determines the volume of blood a vessel can hold?
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Why do arteries hold lower volumes of blood?
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What is the significance of compliance in the circulatory system?
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What is the relationship between compliance and distensibility?
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What happens when the veins constrict?
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What type of nerve fibers innervate the smooth muscle in the walls of veins?
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What is the effect of alpha-1 adrenergic activation on the veins?
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What is the result of changes in compliance of the veins?
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What is the significance of compliance in the veins?
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What is the rate of displacement of blood per unit of time?
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Which blood vessels have larger cross-sectional areas?
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What is the significance of the large cross-sectional area of veins?
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What is the formula to calculate the cross-sectional area of a blood vessel?
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What is the result of a larger cross-sectional area in blood vessels?
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What happens to the total cross-sectional area of blood vessels as systemic arteries branch to form small arteries, arterioles, and capillaries?
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What is the relationship between the velocity of blood flow and the total cross-sectional area of blood vessels?
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What happens to the velocity of blood flow when it enters venules and veins?
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Why does the velocity of blood flow decrease in small arteries, arterioles, and capillaries?
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What is the primary reason for the change in velocity of blood flow in different parts of the circulatory system?
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Study Notes
The Circulatory System
- The circulatory system is a closed circuit, meaning that the flow of blood returning to the heart must equal the flow of blood pumped by the left ventricle into the aorta.
Factors Affecting Blood Flow
- The exact amount of flow around the circuit depends on three key factors: • The number and strength of heart contractions • The total volume of blood • The characteristics of the vessels
The Cardiovascular System
- The cardiovascular system has two circulations in series:
Pulmonary Circulation
- Carries deoxygenated blood away from the heart to the lungs
- Returns oxygenated blood back to the heart
Systemic Circulation (Peripheral or Greater)
- Carries oxygenated blood away from the heart to the body
- Returns deoxygenated blood back to the heart
Circulatory System Divisions
- Each circulation (systemic and pulmonary) has 3 major divisions.
Distribution System
- Composed of ventricles, arteries, and arterioles.
Perfusion/Exchange System
- Composed of capillaries where exchange of oxygen and nutrients with cells occurs.
Collecting System
- Composed of venules, veins, and atria.
- Responsible for collecting and returning blood to the heart.
Characteristics of Arteries
- Aorta is the largest artery of the systemic circulation, receiving blood directly from the heart
- Arteries have strong vascular walls to withstand the high velocity of blood flow
- The walls of arteries are composed of extensive elastic tissue, smooth muscle, and connective tissue
- Arteries transport blood under high pressure to the tissues
Function of Arteries
- Deliver oxygen and other nutrients to the organs
- Carry the stressed volume of blood
Artery Types
- There are two main types of arteries: Elastic Arteries and Muscular Arteries
- Elastic Arteries are high-compliance arteries, meaning they can hold large volumes of blood
- They contain more elastin, which increases their distensibility
- Examples of Elastic Arteries include the Aorta and Carotid Artery
Characteristics of Elastic Arteries
- Have more elastin, allowing for increased distensibility
- Capable of holding large volumes of blood
- Can stretch to accommodate increased blood pressure
Characteristics of Muscular Arteries
- Contain more smooth muscle, enabling vasoconstriction and dilation
- Are high-resistance arteries, distributing blood according to tissue needs
- Examples of Muscular Arteries include the Femoral and Mesenteric Arteries
Compliance and Capacitance
- Compliance (C) is the volume of blood a vessel can hold at a given pressure, measured in mL/mm Hg
- C = V/P, where V is the volume in mL and P is the pressure in mm Hg
- Compliance describes the ability of a vessel to expand and accommodate changes in blood pressure
Vascular Resistance
- Vascular Resistance is the opposition to blood flow in the circulatory system
- Must be overcome to create blood flow and maintain blood pressure
Arterioles
- Are the last smallest branches of the arterial system
- Act as control conduits that regulate blood flow into capillaries
- Characterized by strong muscular walls that enable vasoconstriction and vasodilation
- Heavily innervated by sympathetic adrenergic nerve fibers
- Allow alteration of blood flow in each tissue in response to its specific needs
- Site of the highest resistance to blood flow
Receptor Distribution and Function
- Alpha 1 and 2 receptors are found in the arterioles of most visceral organs.
- Alpha 1 receptors are predominant in these organs and couple to Gq protein.
- Alpha 2 receptors, on the other hand, couple to Gi protein.
Receptor Location and Feedback Mechanism
- Alpha 2 receptors are also present in nerve terminals, where they inhibit norepinephrine (NE) release through a feedback mechanism.
Norepinephrine and Vasoconstriction
- Norepinephrine is the primary endogenous agonist for these receptors.
- It is released from postganglionic neurons and acts on vascular smooth muscle.
- Activation of these receptors leads to smooth muscle contraction, resulting in vasoconstriction.
Beta 2 Adrenergic Receptors
- Expressed in arterioles of coronaries, skeletal muscle, and liver
- G protein-coupled receptor that couples to Gs, a stimulatory G protein
- Activates the cAMP pathway
Agonist and Release
- Epinephrine is the primary endogenous agonist for beta 2 adrenergic receptors
- Released from the adrenal gland
Physiological Effects
- Found in vascular smooth muscle
- Cause vasodilation in areas that will need increased blood flow in "fight or flight" situations
Parasympathetic Innervation and Vasodilation
- Parasympathetic innervation is minimal or absent in most blood vessels of the body
M3 Receptors and Vasodilation
- M3 receptors are present on coronary vessels and respond to vagal tone
- M3 receptors are G protein-coupled receptors that couple to Gq
- Activation of M3 receptors stimulates phospholipase C, leading to the production of DAG and IP3
- DAG and IP3 trigger calcium release, which activates eNOS
- Activated eNOS produces nitric oxide (NO), a potent vasodilator
- Acetylcholine is the primary endogenous agonist that activates M3 receptors
- Acetylcholine is released from postganglionic neurons and acts on vascular smooth muscle
- Vasodilation occurs through the activation of the cAMP pathway, leading to smooth muscle relaxation
Arterioles Function
- Arterioles are the site of highest resistance in the vasculature
- They are the site where resistance can be changed by: • Sympathetic activity • Circulating catecholamines • Other vasoactive substances
Capillaries
- Exchange various substances, including fluids, nutrients, electrolytes, hormones, and others, between blood and interstitial fluid
- Thin-walled structures with a single layer of endothelial cells surrounded by a basal lamina
- Lipid-soluble substances cross the capillary wall by dissolving in and diffusing across the endothelial membrane
- Water-soluble substances, such as ions, cross the capillary wall through:
- Water-filled clefts (spaces) between endothelial cells
- Large pores in the walls of some capillaries (e.g., fenestrated capillaries)
Blood Perfusion in Capillaries
- Not all capillaries are always perfused with blood
- Blood perfusion in capillaries depends on metabolic needs
Venules
- Collect blood from capillaries and merge into larger veins
- Thin-walled structures composed of endothelial layer, elastic tissue, smooth muscle, and connective tissue
Veins
- Function as conduits to transport blood from venules back to the heart
- Characterized by low pressure and thin walls
- Carry unstressed volume, meaning they can expand or contract to meet changing blood volume needs
- Serve as a major controllable reservoir for extra blood depending on the body's requirements
Vascular Compliance
- Compliance of veins is higher than that of arteries
- Compliance is directly related to distensibility
- Higher compliance vessels can hold more volume at a given pressure
- Veins can hold larger volumes of blood at lower pressures
- Arteries have lower compliance compared to veins
- Arteries hold lower volumes of blood, but at higher pressures
Compliance of Veins
- Changes in compliance of the veins lead to redistribution of blood between the veins and arteries
- Constriction of the veins results in a decrease in the volume they can hold
- This causes blood to shift from the veins to the arteries
Regulation of Vein Constriction
- Smooth muscle in the walls of veins is innervated by sympathetic nerve fibers
- Alpha-1 adrenergic activation leads to constriction of the veins
- Constriction of the veins reduces capacitance and unstressed volume
Blood Flow and Vessel Characteristics
- The velocity of blood flow is defined as the rate of displacement of blood per unit of time.
- Blood vessels vary in terms of diameter and cross-sectional area.
- Veins have much larger cross-sectional areas compared to arteries.
- The large cross-sectional area of veins explains their high blood storage capacity.
- The cross-sectional area of a blood vessel is equal to the area of a circle.
Blood Flow Velocity and Cross-Sectional Area
- As systemic arteries branch to form smaller vessels (arterioles and capillaries), the total cross-sectional area of these vessels increases.
- This increase in cross-sectional area leads to a decrease in the forward velocity of blood flow.
- The reverse happens when blood is collected into venules and veins: the total cross-sectional area decreases, and the velocity of blood flow increases again.
- There is an inverse relationship between the velocity of blood flow and the total cross-sectional area of blood vessels.
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Description
This quiz covers the basics of the circulatory system, including the flow of blood, heart contractions, and the characteristics of blood vessels.