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Questions and Answers
What is the primary function of arterioles in the circulatory system?
What is the primary function of arterioles in the circulatory system?
Which blood vessels are primarily involved in the exchange of gases and nutrients?
Which blood vessels are primarily involved in the exchange of gases and nutrients?
What structure regulates blood flow into the capillaries?
What structure regulates blood flow into the capillaries?
What characterizes the structure of capillaries?
What characterizes the structure of capillaries?
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What occurs if all precapillary sphincters contract?
What occurs if all precapillary sphincters contract?
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What is the primary composition of arterioles?
What is the primary composition of arterioles?
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Which vessels serve as collecting and storage vessels in the circulatory system?
Which vessels serve as collecting and storage vessels in the circulatory system?
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What determines the delivery of blood to a particular tissue in the microcirculation?
What determines the delivery of blood to a particular tissue in the microcirculation?
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What happens to the shape of veins at high transmural pressures?
What happens to the shape of veins at high transmural pressures?
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Which of the following factors does NOT affect venous return to the heart?
Which of the following factors does NOT affect venous return to the heart?
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What is the relationship between venous return and cardiac output?
What is the relationship between venous return and cardiac output?
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Which mechanism is described as the reflex increase in heart rate with increased venous return?
Which mechanism is described as the reflex increase in heart rate with increased venous return?
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What occurs to venous compliance at low pressures?
What occurs to venous compliance at low pressures?
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Which factor acts as a backward force on veins and impedes blood flow into the right atrium?
Which factor acts as a backward force on veins and impedes blood flow into the right atrium?
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If smooth muscle contraction in the great veins is activated, what happens to venous return?
If smooth muscle contraction in the great veins is activated, what happens to venous return?
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Which of the following is a key factor in the peripheral circulation that affects venous return?
Which of the following is a key factor in the peripheral circulation that affects venous return?
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What happens to plasma volume without the continuous return of filtered proteins and fluid?
What happens to plasma volume without the continuous return of filtered proteins and fluid?
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How does interstitial fluid enter lymphatic vessels?
How does interstitial fluid enter lymphatic vessels?
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Which factor can increase lymph flow?
Which factor can increase lymph flow?
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What role do the one-way valves in lymphatic vessels serve?
What role do the one-way valves in lymphatic vessels serve?
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What is the primary factor affecting venous flow in the upright position?
What is the primary factor affecting venous flow in the upright position?
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Veins are known to have which of the following properties?
Veins are known to have which of the following properties?
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Which measurement most accurately represents the pressure at the venous end of the capillary bed?
Which measurement most accurately represents the pressure at the venous end of the capillary bed?
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Which mechanism does not contribute to venous return?
Which mechanism does not contribute to venous return?
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What is capacitance in the venous system primarily influenced by?
What is capacitance in the venous system primarily influenced by?
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What is a potential consequence of lymphatic vessel blockage?
What is a potential consequence of lymphatic vessel blockage?
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What indicates a dysfunction of venous valves?
What indicates a dysfunction of venous valves?
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What primarily influences the volume of blood returning to the heart?
What primarily influences the volume of blood returning to the heart?
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How does the shape of a vein change with an increase in venous transmural pressure?
How does the shape of a vein change with an increase in venous transmural pressure?
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Which statement about dynamic pressure is correct?
Which statement about dynamic pressure is correct?
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What is a major contributor to maintaining cardiovascular stability?
What is a major contributor to maintaining cardiovascular stability?
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Which factor plays a minor role in venous flow compared to hydrostatic pressure in the upright position?
Which factor plays a minor role in venous flow compared to hydrostatic pressure in the upright position?
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What happens to precapillary vessels during increased metabolic activity in tissues?
What happens to precapillary vessels during increased metabolic activity in tissues?
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Which of the following organs typically has a high capillary density?
Which of the following organs typically has a high capillary density?
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What type of blood flow bypasses the capillaries and is known as nonnutritional flow?
What type of blood flow bypasses the capillaries and is known as nonnutritional flow?
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Which chemical is a known vasodilator, stimulating cGMP production?
Which chemical is a known vasodilator, stimulating cGMP production?
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What is the primary mechanism for transcapillary exchange?
What is the primary mechanism for transcapillary exchange?
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What fluid do lymphatic vessels collect for recirculation into blood?
What fluid do lymphatic vessels collect for recirculation into blood?
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Which of the following is NOT a component of the lymphatic system?
Which of the following is NOT a component of the lymphatic system?
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Which tissue type lacks lymphatic vessels?
Which tissue type lacks lymphatic vessels?
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Study Notes
Hemodynamics II
- Lecture topic: Microcirculation, veins, lymphatics, and venous return
- Lecturer: Ian Dixon
- Location: Molecular Cardiology Lab, R3010, St. Boniface Hospital Research Centre, Institute of Cardiovascular Sciences
- Note: Overlap with other lectures exists.
The Circulatory System
- Function: Supplies blood and nutrients to tissues
- Arterioles: Regulate regional blood flow (resistance vessels)
- Capillaries: Exchange gases, water, and solutes with interstitial fluid
- Venules and veins: Collect and store blood
Blood Vessels
- Aorta: Predominantly elastic, large diameter
- Peripheral arteries: Become thinner and more muscular as branches narrow
- Arterioles: Primarily muscular (small diameter)
- Capillaries: Single layer of endothelium, crucial for exchange
- Dimensions: Various vessel sizes given (e.g., Aorta diameter, artery diameter etc.)
Microcirculation
- Circulation through the smallest vessels (arterioles, capillaries, and venules)
- Arterioles: Thin adventitial layer, thick smooth muscle layer, endothelial lining (5-100 µm diameter)
- Metarterioles/Capillaries: 5-10 µm (or 10-20 µm) in diameter
- Precapillary sphincters: Smooth muscle cells that regulate blood flow into capillaries
- Thoroughfare channels: Direct flow from metarteriole to venule if precapillary sphincters close
- Metabolic activity influences capillary perfusion
Capillary Exchange
- High density found in metabolically active tissues (heart, muscle, glands)
- Diffusion: Main method for exchange of fluids, gases, nutrients, waste products between capillaries and tissues. Capillaries have water filled channels/pores. Fluid moves across capillary wall at a rate of 300 mL per minute per 100g of tissue.
- Lipid-insoluble molecules restricted to water filled channels in capillaries
Vasoactive Role of Capillary Endothelium
- Chemicals that cause vasodilation (relaxation of smooth muscle):
- Prostacyclin (PGI2): from arachidonic acid (AA) through cyclooxygenase and prostacyclin synthase; increase in cAMP
- Nitric oxide (NO): Stimulates guanylyl cyclase (G Cyc) to increase cyclic GMP (cGMP)
- Nitroprusside (NP): Acts directly on vascular smooth muscle
- Adenosine: Stimulates cAMP levels to relaxed smooth muscle
The Lymphatic System
- Function: Collects fluid and proteins that have escaped from blood vessels, and return them to circulation
- Components: Lymph vessels, lymph nodes, lymphatic tissue
- Lymphatic capillaries: Intercalate with blood capillaries; One-way valves; Endothelial cells overlapped. Anchoring filaments to surrounding tissue. Interstitial fluid moves into lymphatic capillaries.
- Importance: Returns filtered proteins and fluid to blood; Prevents edema (swelling)
Lymphatic System - Additional Points
- Lymph flow influenced by skeletal muscle activity
- Increased by increased capillary filtration and decreased oncotic pressure
- Blockage can result in edema.
The Venous System
- Function: Returns blood to the heart from tissues
- Capacitance: Ability to hold large volumes of blood with little change in pressure
- Resistance: Blood flow resistance determined by muscle pumps and valves, pressure gradients
- Venous return: Quantity of blood flowing into right atrium each minute.
Pressure-Flow Relationships and Venous Return
- Dynamic pressure: Pressure generated by cardiac contraction
- Dynamic pressure gradients determine blood flow
- Pressure drops from arterial side to venous side, reaching 12-18 mmHg at the venous end of capillaries
- Atrial pressure averages 4-7 mm Hg in normal conditions; this drives blood flow from veins to the right atrium
- Hydrostatic pressure influences venous flow in the upright position.
- Muscle pumps and valves are crucial for venous return, working against hydrostatic pressure
Varicose Veins
- Dysfunction of venous valves, resulting in swollen and misshapen veins
Capacitance and Compliance
- Capacitance: Relationship between pressure and volume at a given smooth muscle tone. Veins have low resistance to big volume changes
- Compliance: Change in blood volume per unit of transmural pressure change; slope of capacitance curve.
Venous Capacitance
- Controlled by the collapsible nature of the venous wall
- Elliptical shape at low blood volume; low pressure
- High increase of volume can occur at minimal pressure increase
- Circular shape at high pressure requiring an increase in pressure to add more volume
Cardiac output = Venous Return (CO=VR)
- Cardiac Output: Amount of blood pumped into aorta each minute
- Venous Return: Amount of blood flowing into right atrium each minute
- CO and VR must equal each other, except for brief periods when blood is temporarily stored in lungs/heart
Control of Cardiac Output by Venous Return – The Frank-Starling Mechanism of the Heart
- Various peripheral circulation factors affect venous return
- Heart has automatic mechanisms for pumping (Frank-Starling law of the heart)
- Bainbridge reflex – increased heart rate with increased venous return
Factors affecting Venous Return
- Right atrial pressure: Backwards force to impede blood flow
- Systemic circulation filling: Volume pushing blood toward the heart
- Resistance between peripheral vessels and right atrium: Reduced volume in arterioles = Reduced blood flow back
(Note: This document does not include the references themselves, which were present in the original pages. The references contain authors, titles, and publication details which are not included in this summary)
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Description
Explore the intricate details of hemodynamics in this quiz focusing on microcirculation, veins, and lymphatics. Learn about the function and structure of blood vessels, including arterioles, capillaries, and the venous return process. This quiz is essential for understanding the circulatory system's role in supplying nutrients and oxygen to tissues.
