8.02 Circulatory System
General Structure
Components
A. Heart (Pump)
- Function: Acts as the central pump to circulate blood throughout the body.
- Structure: Typically four-chambered (two atria and two ventricles) in mammals, allowing for efficient separation of oxygenated and deoxygenated blood.
B. Blood Vessels (Tubes)
- Closed Blood System: Blood remains confined within vessels, preventing loss and allowing controlled circulation.
- Types of Blood Vessels:
- Arteries: Carry blood away from the heart.
- Veins: Carry blood towards the heart.
- Capillaries: Microscopic vessels where gas and nutrient exchange occurs.
C. Blood
- Components:
- Red Blood Cells (RBCs)
- (Carry oxygen from the lungs to body tissues and transport carbon dioxide back to the lungs for exhalation.)
- White Blood Cells (WBCs)
- (Defend the body against infections and foreign invaders by identifying and destroying pathogens.)
- Platelets
- (Facilitate blood clotting to prevent excessive bleeding and aid in the repair of damaged blood vessels.)
- Plasma
- (Transport nutrients, hormones, and waste products throughout the body; helps maintain blood pressure and volume; contains proteins essential for blood clotting and immune responses.)
- Red Blood Cells (RBCs)
- Functions: Transport oxygen, nutrients, hormones, and waste products; play roles in immune responses and temperature regulation.
D. Double Circulation
- Definition: Blood passes through the heart twice during each complete circuit around the body.
- Pulmonary Circulation
- Pathway:
- Heart → Lungs → Heart
- Function: Transports deoxygenated blood from the right ventricle to the lungs for oxygenation and returns oxygenated blood to the left atrium.
- Pathway:
- Systemic Circulation
- Pathway:
- Heart → Body (excluding lungs) → Heart
- Function: Distributes oxygenated blood from the left ventricle to body tissues and returns deoxygenated blood to the right atrium.
- Pathway:
Detailed Circulation Pathway
Systemic Circulation
- Left Ventricle → Aorta → Body Tissues (Excludes Lungs)
- Aorta: The largest artery, branching into smaller arteries to supply blood to various body parts.
- Returns to Heart via Vena Cava (to Right Atrium)
- Superior and Inferior Vena Cava: Large veins that collect deoxygenated blood from the upper and lower body, respectively.
Pulmonary Circulation
- Right Ventricle → Pulmonary Arteries → Lungs
- Pulmonary Arteries: Unique as they carry deoxygenated blood from the heart to the lungs.
- Returns to Heart via Pulmonary Veins (to Left Atrium)
- Pulmonary Veins: Unique as they carry oxygenated blood from the lungs to the heart.
Key Characteristics
- Closed System
- Description: Blood circulates within a network of vessels, maintaining pressure and allowing efficient transport of materials.
- Pressure Difference
- Systemic Circulation:
- Higher Pressure: Necessary to propel blood throughout the entire body.
- Pulmonary Circulation:
- Lower Pressure: Prevents damage to delicate lung capillaries during gas exchange.
- Systemic Circulation:
Main Blood Vessels
1.Arteries: Carry Oxygenated Blood (Except Pulmonary Artery)
- Examples:
- Aorta
- (The largest artery in the body, originating from the left ventricle of the heart. It distributes oxygenated blood to all parts of the body through its branches.)
- Carotid Arteries
- (Paired arteries located in the neck that supply oxygenated blood to the brain, neck, and face. They are critical for delivering blood to the brain via the internal carotid arteries.)
- Subclavian Arteries
- (They supply blood to the arms, shoulders, and parts of the thorax and brain through their branches.)
- Hepatic Arteries
- (Branches supply oxygenated blood to the liver, gallbladder, and parts of the stomach and pancreas.
- Renal Arteries
- (Paired arteries branching from the abdominal aorta that supply oxygenated blood to the kidneys. They play a crucial role in filtering blood and regulating blood pressure through the kidneys.)
- Iliac Arteries
- (Divisions of the abdominal aorta that supply blood to the lower limbs, pelvis, and abdominal walls. )
- Aorta
2.Veins: Carry Deoxygenated Blood (Except Pulmonary Vein)
- Examples:
- Vena Cava (Superior and Inferior)
- (The two largest veins in the body. The superior vena cava returns deoxygenated blood from the upper body (head, neck, arms) to the right atrium of the heart. The inferior vena cava carries deoxygenated blood from the lower body (abdomen, pelvis, legs) back to the right atrium.)
- Jugular Veins
- (Veins in the neck that drain blood from the brain, face, and neck. The internal jugular vein drains blood from the brain, while the external jugular vein drains blood from the face and superficial neck tissues.)
- Subclavian Veins
- (They receive blood from the jugular veins and the arms, which eventually merge into the superior vena cava.)
- Hepatic Veins
- (Veins that drain deoxygenated blood from the liver into the inferior vena cava. )
- Renal Veins
- (Paired veins that carry deoxygenated blood away from the kidneys to the inferior vena cava. They run alongside the renal arteries and play a key role in filtering waste from the blood.)
- Iliac Veins
- (Major veins in the lower abdomen that drain blood from the pelvis and lower limbs. )
- Vena Cava (Superior and Inferior)
Comparing Fish and Mammal Circulatory Systems
1.Fish: Single Circulation
- Description: Blood passes through the heart once per circuit.
- Pathway: Heart → Gills → Body → Heart
- Characteristics:
- Lower Metabolic Rate: Suitable for ectothermic (cold-blooded) organisms with lower oxygen demands.
- Less Efficient Oxygen Delivery: Suitable for their environmental and physiological needs.
2.Mammals: Double Circulation
- Description: Blood passes through the heart twice per circuit.
- Pathway: Heart → Lungs → Heart → Body → Heart
- Characteristics:
- Higher Metabolic Rate: Supports endothermic (warm-blooded) organisms with higher oxygen demands.
- Efficient Oxygen Delivery: High-pressure systemic circulation ensures rapid and adequate oxygen supply to tissues.
Reason for Difference
- Mammals:
- Higher Metabolic Rate: Due to endothermy, mammals require a continuous and efficient supply of oxygen to sustain internal heat production and active lifestyles.
- Fish:
- Ectothermic: Fish rely on external sources for body temperature regulation, resulting in lower and more stable oxygen requirements.
Key Terms
- Circulatory System: The system responsible for transporting fluids (primarily blood) throughout the body.
- Closed Blood System: A type of circulatory system where blood is enclosed within vessels, allowing for efficient and controlled distribution.
- Double Circulation: A circulatory pattern where blood passes through the heart twice during one complete circuit (pulmonary and systemic).
- Systemic Circulation: The pathway that carries oxygenated blood from the heart to the body and returns deoxygenated blood back to the heart.
- Pulmonary Circulation: The pathway that carries deoxygenated blood from the heart to the lungs and returns oxygenated blood back to the heart.
Practice Questions
Question 1
Define the circulatory system and explain its primary functions in animals. (5 marks)
Mark Scheme:
- Definition of Circulatory System:
- The circulatory system is the system responsible for transporting fluids (primarily blood) throughout the body. (1 mark)
- Transport of Oxygen:
- It delivers oxygen from the respiratory organs (lungs or gills) to body tissues. (1 mark)
- Nutrient Distribution:
- Transports nutrients from the digestive system to cells for energy production and growth. (1 mark)
- Waste Removal:
- Carries waste products like carbon dioxide and metabolic wastes away from cells to excretory organs. (1 mark)
- Regulation of Body Temperature and Immune Responses:
- Helps in temperature regulation by distributing heat and plays a role in immune responses by transporting white blood cells. (1 mark)
Question 2
Describe the structure and function of the heart in mammals. (5 marks)
Mark Scheme:
- Central Pump Function:
- The heart acts as the central pump to circulate blood throughout the body. (1 mark)
- Four-Chambered Structure:
- Typically four-chambered in mammals, consisting of two atria and two ventricles, allowing for efficient separation of oxygenated and deoxygenated blood. (1 mark)
- Right Atrium and Ventricle:
- The right atrium receives deoxygenated blood from the superior and inferior vena cava and pumps it into the right ventricle. (1 mark)
- Left Atrium and Ventricle:
- The left atrium receives oxygenated blood from the pulmonary veins and pumps it into the left ventricle. (1 mark)
- Efficient Blood Circulation:
- The four-chambered design ensures that oxygenated and deoxygenated blood do not mix, promoting efficient oxygen delivery and waste removal. (1 mark)
Question 3
Compare arteries and veins in terms of structure and function. (6 marks)
Mark Scheme:
- Direction of Blood Flow:
- Arteries carry blood away from the heart. (1 mark)
- Veins carry blood towards the heart. (1 mark)
- Wall Thickness and Elasticity:
- Arteries have thicker, more muscular walls to withstand higher blood pressure. (1 mark)
- Veins have thinner, less muscular walls and often contain valves to prevent backflow. (1 mark)
- Pressure Differences:
- Arteries operate under higher pressure due to the pumping action of the heart. (1 mark)
- Veins operate under lower pressure and rely on muscle contractions and valves to return blood to the heart. (1 mark)
- Location Relative to Heart:
- Arteries are typically located deeper within the body.
- Veins can be found both deep and superficial (close to the skin). (1 mark)
Question 4
Explain the role of capillaries in the circulatory system. (5 marks)
Mark Scheme:
- Microscopic Structure:
- Capillaries are microscopic vessels with thin walls composed of a single layer of endothelial cells. (1 mark)
- Gas and Nutrient Exchange:
- They are the sites of gas exchange, where oxygen and nutrients diffuse from the blood into body tissues, and carbon dioxide and waste products diffuse into the blood. (2 marks)
- Connection Between Arteries and Veins:
- Capillaries connect arteries to veins, forming a network that facilitates efficient exchange of substances. (1 mark)
- Surface Area and Permeability:
- Their extensive network provides a large surface area and high permeability for rapid diffusion of materials. (1 mark)
Question 5
Describe the pathway of blood in systemic circulation, starting from the left ventricle. (6 marks)
Mark Scheme:
- Left Ventricle to Aorta:
- Blood is pumped from the left ventricle into the aorta. (1 mark)
- Aorta Branches:
- The aorta branches into smaller arteries that supply blood to various body parts. (1 mark)
- Arteries to Arterioles:
- Arteries further branch into arterioles, which lead to the capillaries. (1 mark)
- Capillary Exchange:
- In the capillaries, oxygen and nutrients are delivered to tissues, and carbon dioxide and wastes are collected. (1 mark)
- Capillaries to Venules:
- Blood then flows into venules, which collect the deoxygenated blood from the capillaries. (1 mark)
- Venules to Veins:
- Venules merge into veins that carry the deoxygenated blood back to the superior and inferior vena cava, which return it to the right atrium of the heart. (1 mark)
Question 6
Explain the differences between single and double circulatory systems, providing examples of animals with each type. (6 marks)
Mark Scheme:
- Single Circulation Definition:
- In a single circulatory system, blood passes through the heart once per complete circuit. (1 mark)
- Single Circulation Pathway:
- Example Pathway: Heart → Gills → Body → Heart. (1 mark)
- Example of Single Circulation:
- Fish possess a single circulatory system. (1 mark)
- Double Circulation Definition:
- In a double circulatory system, blood passes through the heart twice per complete circuit—once for pulmonary circulation and once for systemic circulation. (1 mark)
- Double Circulation Pathway:
- Example Pathway: Heart → Lungs → Heart → Body → Heart. (1 mark)
- Example of Double Circulation:
- Mammals and birds have a double circulatory system. (1 mark)
Question 7
Discuss the reasons why mammals have a double circulatory system while fish have a single circulatory system. (5 marks)
Mark Scheme:
- Metabolic Rate Differences:
- Mammals have a higher metabolic rate due to endothermy, requiring a continuous and efficient supply of oxygen. (1 mark)
- Oxygen Demand:
- Mammals need rapid oxygen delivery to sustain internal heat production and active lifestyles, necessitating double circulation for efficiency. (1 mark)
- Size and Body Structure:
- Fish are generally smaller and ectothermic, with lower oxygen demands, making a single circulatory system sufficient. (1 mark)
- Efficiency of Gas Exchange:
- Double circulation in mammals allows for separate pathways for oxygenated and deoxygenated blood, enhancing gas exchange efficiency. (1 mark)
- Adaptation to Environmental Needs:
- Mammals adapt to variable and demanding environments with a closed circulatory system, while fish rely on a simpler system suited to their aquatic habitats. (1 mark)
Question 8
Explain the significance of having a four-chambered heart in mammals. (5 marks)
Mark Scheme:
- Separation of Blood Streams:
- A four-chambered heart (two atria and two ventricles) separates oxygenated and deoxygenated blood, preventing mixing. (1 mark)
- Efficient Oxygenation:
- Ensures that oxygen-rich blood from the lungs is delivered directly to the body, enhancing oxygenation efficiency. (1 mark)
- Higher Pressure System:
- Allows for the creation of a higher pressure in the systemic circulation, enabling rapid blood flow to meet the high metabolic demands. (1 mark)
- Enhanced Metabolic Support:
- Supports the endothermic metabolism of mammals by providing a steady and controlled supply of oxygen and nutrients. (1 mark)
- Adaptation to Active Lifestyles:
- Facilitates the high energy needs of active and larger-bodied mammals, enabling sustained muscle activity and physiological functions. (1 mark)
Question 9
Describe the composition of blood and the function of each component. (5 marks)
Mark Scheme:
- Red Blood Cells (Erythrocytes):
- Function: Transport oxygen from the lungs to tissues and carbon dioxide back to the lungs. (1 mark)
- White Blood Cells (Leukocytes):
- Function: Play roles in immune responses, defending the body against infections and foreign invaders. (1 mark)
- Platelets (Thrombocytes):
- Function: Involved in blood clotting, helping to prevent excessive bleeding when injuries occur. (1 mark)
- Plasma:
- Function: The liquid component that carries nutrients, hormones, waste products, proteins, and other solutes throughout the body. (1 mark)
- Other Components:
- May include electrolytes (e.g., sodium, potassium) and proteins (e.g., hemoglobin, albumin) essential for maintaining osmotic balance and transport functions. (1 mark)
Question 10
Explain how the circulatory system supports the high energy demands of muscle contraction and nerve impulse transmission in mammals. (6 marks)
Mark Scheme:
- Oxygen Delivery for Aerobic Respiration:
- The circulatory system delivers oxygen to muscle cells, enabling aerobic respiration to produce ATP required for muscle contraction. (1 mark)
- Nutrient Supply:
- Transports glucose and other nutrients to muscle and nerve cells, providing the necessary substrates for energy production. (1 mark)
- Waste Removal:
- Removes carbon dioxide and lactic acid produced during muscle activity, preventing acidification and fatigue. (1 mark)
- Rapid ATP Supply:
- Ensures a continuous and rapid supply of ATP to support the high-frequency contractions of muscles. (1 mark)
- Ion Transport for Nerve Function:
- Maintains ion gradients (e.g., Na⁺/K⁺) essential for the transmission of nerve impulses through action potentials. (1 mark)
- Heat Distribution:
- Distributes heat generated from muscle contractions, aiding in temperature regulation and maintaining optimal enzyme activity for metabolic processes. (1 mark)
Teaching Resources