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Questions and Answers
What is the primary function of the capillaries in the cardiovascular system?
What is the primary function of the capillaries in the cardiovascular system?
Which of the following factors does NOT affect the rate of diffusion?
Which of the following factors does NOT affect the rate of diffusion?
How do lipophilic substances typically diffuse through capillaries?
How do lipophilic substances typically diffuse through capillaries?
What characteristic of a molecule would increase its diffusion resistance?
What characteristic of a molecule would increase its diffusion resistance?
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What role does the cardiovascular system play in the process of diffusion?
What role does the cardiovascular system play in the process of diffusion?
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What does the rate of diffusion primarily depend on?
What does the rate of diffusion primarily depend on?
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Which tissue requires the highest and constant blood flow?
Which tissue requires the highest and constant blood flow?
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What happens to the concentration gradient when the rate of blood flow is low?
What happens to the concentration gradient when the rate of blood flow is low?
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How does an increase in metabolism affect blood flow?
How does an increase in metabolism affect blood flow?
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What determines the concentration gradient driving O2 diffusion into the cells?
What determines the concentration gradient driving O2 diffusion into the cells?
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What is the total blood flow at rest?
What is the total blood flow at rest?
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Which vessels are primarily responsible for regulating blood flow through resistance?
Which vessels are primarily responsible for regulating blood flow through resistance?
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What role do veins play in the circulatory system?
What role do veins play in the circulatory system?
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Which heart chamber is responsible for pumping blood to the systemic circulation?
Which heart chamber is responsible for pumping blood to the systemic circulation?
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During exercise, what can the total blood flow rise to?
During exercise, what can the total blood flow rise to?
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Why is the brain more difficult to perfuse during blood flow regulation?
Why is the brain more difficult to perfuse during blood flow regulation?
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What percentage of total blood volume is located within the veins?
What percentage of total blood volume is located within the veins?
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What happens to blood flow if resistance is added to the system?
What happens to blood flow if resistance is added to the system?
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Study Notes
Introduction to Cardiovascular system
- The cardiovascular system is made up of the heart, blood vessels and blood.
- Its primary function is to facilitate exchange of oxygen, metabolic substrates, carbon dioxide, and waste products between the blood and cells throughout the body.
- The cardiovascular system is involved in distributing blood to different tissues based on their metabolic needs.
Function of Blood
- Blood transports oxygen, metabolic substrates, carbon dioxide and waste products
- The exchange of these substances between the blood and cells of the body occurs primarily by diffusion (98%)
- The cardiovascular system provides the conditions necessary for diffusion to occur in each tissue of the body.
Diffusion
- Diffusion takes place in the capillaries, which are composed of a single layer of endothelial cells and a surrounding basal lamina.
- Lipophilic substances, such as oxygen and carbon dioxide, can diffuse directly through the lipid bilayer of the capillary walls.
- Hydrophilic substances, such as glucose, amino acids, and lactate, diffuse through pores in the capillary walls.
- The maximum molecular weight for substances to diffuse through the pores is 60,000.
- All molecules move down their concentration gradient during diffusion.
Diffusion through Capillaries
- Small, hydrophilic substances diffuse through pores between the endothelial cells of the capillaries.
Factors Affecting Diffusion
- The rate of diffusion is influenced by:
- Area available for exchange
- Diffusion resistance
- Concentration gradient
Area
- The larger the area available for exchange, the faster the rate of diffusion.
- Capillaries provide a large surface area for exchange with surrounding tissues.
- Capillary density is higher in more metabolically active tissues to meet their increased exchange needs.
Diffusion Resistance
- Resistance to diffusion depends on:
- Nature of the molecule (lipophilic or hydrophilic, size)
- Nature of the barrier (pore size and number of pores, especially for hydrophilic substances)
- Path length
- Capillary density is a factor in path length
- The shortest path length exists in the most metabolically active tissues.
- Diffusion resistance is generally low.
Concentration Gradient
- The greater the concentration gradient, the faster the rate of diffusion.
- The concentration gradient between capillary blood and tissues is crucial for exchange.
- To maintain a concentration gradient, the concentration difference between the capillary blood and tissue must be maintained.
Maintaining the Concentration Gradient
- Substances that are used by tissues have lower concentrations in capillary blood than arterial blood.
- The difference in concentrations between arterial and capillary blood depends on:
- The rate at which tissues use the substance
- The rate of blood flow through the capillary bed
- A lower blood flow rate results in lower capillary blood concentration.
- Sufficient blood flow is necessary to maintain a concentration gradient for diffusion.
Supply and Demand
- Blood flow needs to match the metabolic demands of tissues.
- The greater the rate of metabolism, the greater the demand for oxygen and nutrients.
- Increases in metabolism require increases in blood flow.
- The rate of blood flow is known as perfusion rate.
Blood Flow to Different Tissues
- Different tissues have different blood flow requirements:
- Brain: Requires a consistently high blood flow rate, approximately 0.5 ml.min-1.g-1.
- Heart muscle: Requires high blood flow that increases during exercise, reaching 0.9 to 3.6 ml.min-1.g-1.
- Kidneys: Require consistent high blood flow, approximately 1.0 ml.min-1.g-1.
- Skeletal muscle: Can experience very high blood flow during exercise.
- Gut: Blood flow is high after a meal.
Blood Flow to Different Tissues - Table
- The table shows the approximate minimum and maximum blood flow (in liters per minute) to different tissues:
| Tissue | Min. flow (l.min) | Max. flow (l.min) |
|---|---|---|
| Brain | 0.75 | 0.75 |
| Heart | 0.3 | 1.2 |
| Kidneys | 1.2 | 1.2 |
| Gut | 1.4 | 2.4 |
| Muscle | 1 | 16 |
| Skin | 0.2 | 2.5 |
| Others | 0.2 | 0.2 |
| Total | 5 | 24.5 |
Blood Flow Regulation
- Total blood flow in the cardiovascular system can be adjusted to meet the body's requirements.
- At rest, total blood flow is approximately 5 liters per minute, which can increase to 25 liters per minute during exercise.
- To regulate blood flow, resistance needs to be introduced into the system to direct blood flow to different regions.
- Arterioles are the resistance vessels that control blood flow.
The Pump: The Heart
- The heart functions as two pumps in series,
- The left heart pumps blood around the systemic circulation (to the body).
- The right heart pumps blood around the pulmonary circulation (to the lungs for gas exchange).
The Circulation
- The heart pumps blood to the arteries.
- Arteries supply arterioles.
- Arterioles supply capillaries.
- Capillaries drain into venules.
- Venules drain into veins.
- Veins return blood to the heart.
Flexibility in the Circulation
- To handle changes in blood flow, the system requires a temporary store of blood.
- Veins act as a variable reservoir for blood due to their thin walls, which easily distend or collapse.
- This 'capacitance' allows veins to store blood and release it based on the body's needs.
Distribution of Blood in the CVS
- The distribution of blood within the vascular system is as follows:
| Component | Percentage |
|---|---|
| Veins | 67% |
| Capillaries | 5% |
| Heart & Lungs | 11% |
| Arteries & Arterioles | 17% |
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Description
This quiz covers the essential components and functions of the cardiovascular system, focusing on the heart, blood vessels, and blood. Explore how blood facilitates the exchange of gases and metabolic substrates through diffusion. Understand the role of capillaries in this crucial process.
