CIE AS/A Level Biology -8.1 The circulatory system- Study Notes- New Syllabus
CIE AS/A Level Biology -8.1 The circulatory system- Study Notes- New Syllabus
Ace A level Biology Exam with CIE AS/A Level Biology -8.1 The circulatory system- Study Notes- New Syllabus
Key Concepts:
- state that the mammalian circulatory system is a closed double circulation consisting of a heart, blood and blood vessels including arteries, arterioles, capillaries, venules and veins
- describe the functions of the main blood vessels of the pulmonary and systemic circulations, limited to pulmonary artery, pulmonary vein, aorta and vena cava
- recognise arteries, veins and capillaries from microscope slides, photomicrographs and electron micrographs and make plan diagrams showing the structure of arteries and veins in transverse section (TS) and longitudinal section (LS)
- explain how the structure of muscular arteries, elastic arteries, veins and capillaries are each related to their functions
- recognise and draw red blood cells, monocytes, neutrophils and lymphocytes from microscope slides, photomicrographs and electron micrographs
- state that water is the main component of blood and tissue fluid and relate the properties of water to its role in transport in mammals, limited to solvent action and high specific heat capacity
- state the functions of tissue fluid and describe the formation of tissue fluid in a capillary network
Mammalian Circulatory System
🌱 Definition
- The mammalian circulatory system is a closed double circulation system.
- Closed → Blood is always contained within blood vessels.
- Double circulation → Blood passes through the heart twice during one complete circuit:
- Pulmonary circulation – heart → lungs → heart
- Systemic circulation – heart → body → heart
🔬 Main Components
- Heart
Muscular organ that pumps blood.
Divided into four chambers: two atria and two ventricles. - Blood
Transport medium containing:- Red blood cells (oxygen transport)
- White blood cells (defense)
- Platelets (clotting)
- Plasma (transports nutrients, hormones, wastes)
- Blood Vessels
Tubular structures carrying blood away from and towards the heart.
🫀 Types of Blood Vessels
| Vessel Type | Structure Highlights | Function |
|---|---|---|
| Arteries | Thick, elastic walls; small lumen | Carry blood away from heart under high pressure |
| Arterioles | Smaller branches of arteries | Regulate blood flow to capillaries |
| Capillaries | Single layer of endothelial cells; very thin | Exchange of gases, nutrients, and wastes between blood and tissues |
| Venules | Small vessels collecting blood from capillaries | Carry blood towards veins |
| Veins | Thinner walls than arteries; valves present | Return blood to the heart under low pressure |
📊 Summary: Closed Double Circulation
| Feature | Description |
|---|---|
| Circulation type | Closed, double circulation |
| Pulmonary circulation | Heart → lungs → heart (oxygenation of blood) |
| Systemic circulation | Heart → body → heart (delivery of oxygen and nutrients) |
| Components | Heart, blood, blood vessels (arteries, arterioles, capillaries, venules, veins) |
🧠 Key Points
– Blood never leaves the vessels, ensuring efficient transport.
– Double circulation separates oxygenated and deoxygenated blood, allowing higher metabolic efficiency.
– Arteries carry blood away, veins carry blood towards the heart; capillaries are the site of exchange.
Functions of Main Blood Vessels in Mammalian Circulation
🌱 Overview
- Mammals have a double circulation system:
- Pulmonary circulation – between heart and lungs
- Systemic circulation – between heart and body
- Key vessels transport oxygenated or deoxygenated blood to maintain efficient circulation.
🔬 Pulmonary Circulation Vessels
| Blood Vessel | Function |
|---|---|
| Pulmonary artery | Carries deoxygenated blood from the right ventricle to the lungs for oxygenation. |
| Pulmonary vein | Carries oxygenated blood from the lungs to the left atrium of the heart. |
🫀 Systemic Circulation Vessels
| Blood Vessel | Function |
|---|---|
| Aorta | Carries oxygenated blood from the left ventricle to all parts of the body. |
| Vena cava | Carries deoxygenated blood from the body back to the right atrium of the heart. |
📊 Quick Reference Table: Blood Flow & Oxygen Status
| Vessel | Carries Blood From → To | Oxygen Status |
|---|---|---|
| Pulmonary artery | Heart → Lungs | Deoxygenated |
| Pulmonary vein | Lungs → Heart | Oxygenated |
| Aorta | Heart → Body | Oxygenated |
| Vena cava | Body → Heart | Deoxygenated |
🧠 Key Points:
– Pulmonary artery is unique as it carries deoxygenated blood away from the heart.
– Pulmonary vein is unique as it carries oxygenated blood towards the heart.
– Aorta distributes oxygen-rich blood to the entire body, while vena cava returns oxygen-poor blood to the heart.
– Together, these vessels maintain efficient double circulation, separating oxygenated and deoxygenated blood.
Recognition and Structure of Blood Vessels
🌱 Overview
- Blood vessels carry blood throughout the body in closed circulation.
- Main types: Arteries, Veins, Capillaries
- Can be identified under light microscope, photomicrographs, or electron micrographs.
- Plan diagrams help illustrate their structural differences.
🔬 Recognition of Blood Vessels
| Vessel Type | Features Under Microscope / Photomicrograph | Key Identifying Traits |
|---|---|---|
| Arteries | Thick muscular wall, narrow lumen, round shape in TS, folds in LS | Thick tunica media, withstands high pressure |
| Veins | Thin wall, wide lumen, often collapsed or irregular in TS | Thin tunica media, contains valves, low pressure |
| Capillaries | Very thin wall (single layer of endothelial cells), very small diameter | Allows exchange of gases and nutrients, only one RBC passes at a time |
🫀 Structural Features of Arteries and Veins
1. Artery
- Transverse Section (TS): Circular with thick wall.
- Longitudinal Section (LS): Tube with prominent layers.
- Layers (from inside out):
- Tunica intima – endothelium (single cell layer)
- Tunica media – thick smooth muscle + elastic fibers
- Tunica externa (adventitia) – connective tissue
2. Vein
- Transverse Section (TS): Wider lumen, thin wall, may appear collapsed.
- Longitudinal Section (LS): Tube with thin walls; valves visible.
- Layers (from inside out):
- Tunica intima – endothelium with valves
- Tunica media – thin smooth muscle, few elastic fibers
- Tunica externa – connective tissue, thicker than tunica media
📊 Comparison Table: Artery vs Vein
| Feature | Artery | Vein |
|---|---|---|
| Wall thickness | Thick | Thin |
| Lumen | Narrow | Wide |
| Shape in TS | Circular | Irregular / collapsed |
| Tunica media | Thick, muscular & elastic | Thin, less muscular |
| Valves | Absent | Present (prevent backflow) |
| Pressure | High | Low |
| Function | Carry blood away from heart | Carry blood toward heart |
🧠 Key Points:
– Arteries are adapted for high pressure, veins for low pressure and valves.
– Capillaries are microscopic and allow exchange, identifiable by single layer of endothelial cells.
Structure-Function Relationship of Blood Vessels
🌱 Overview
- Blood vessels have specialised structures adapted to their roles in circulation.
- Key vessel types: Elastic arteries, muscular arteries, veins, capillaries.
- Structure directly influences blood flow, pressure, and exchange.
🔬 1. Elastic Arteries
- Examples: Aorta, pulmonary artery
- Structure:
- Thick tunica media with many elastic fibers
- Wide lumen
- Relatively fewer smooth muscle cells than muscular arteries
- Function:
- Elasticity allows stretching during ventricular systole and recoiling during diastole → maintains continuous blood flow despite high pressure.
🔬 2. Muscular Arteries
- Examples: Radial artery, femoral artery
- Structure:
- Thick tunica media rich in smooth muscle
- Fewer elastic fibers compared to elastic arteries
- Narrow lumen
- Function:
- Smooth muscle allows vasoconstriction and vasodilation → regulates blood distribution to different organs.
🔬 3. Veins
- Examples: Superior and inferior vena cava, jugular vein
- Structure:
- Thin tunica media, less smooth muscle
- Wide lumen
- Valves present to prevent backflow
- Tunica externa relatively thick
- Function:
- Thin walls allow accommodation of large blood volumes at low pressure.
- Valves ensure unidirectional blood flow toward the heart.
- Muscle contraction helps push blood back to the heart.
🔬 4. Capillaries
- Examples: Continuous, fenestrated, sinusoidal capillaries
- Structure:
- Wall is one layer of endothelial cells
- Extremely narrow lumen (one RBC fits at a time)
- No muscle or elastic tissue
- Function:
- Thin walls and narrow lumen allow efficient exchange of gases, nutrients, and waste between blood and tissues.
- Slow blood flow increases time for diffusion.
📊 Summary Table: Structure-Function Relationship
| Vessel Type | Key Structural Features | Functional Significance |
|---|---|---|
| Elastic arteries | Many elastic fibers, thick wall, wide lumen | Stretch & recoil; maintains continuous blood flow |
| Muscular arteries | Thick smooth muscle, fewer elastic fibers, narrow lumen | Vasoconstriction & dilation; controls blood distribution |
| Veins | Thin wall, wide lumen, valves, thick tunica externa | Low pressure blood return; prevents backflow |
| Capillaries | Single endothelial layer, very narrow lumen | Exchange of gases, nutrients, and wastes |
🧠 Key Points:
– Structure of each vessel type is adapted to its function:
– Elasticity for pressure buffering in elastic arteries
– Muscular control for blood distribution in muscular arteries
– Valves and thin walls for volume accommodation in veins
– Single-cell walls for exchange in capillaries
– Structure of each vessel type is adapted to its function:
– Elasticity for pressure buffering in elastic arteries
– Muscular control for blood distribution in muscular arteries
– Valves and thin walls for volume accommodation in veins
– Single-cell walls for exchange in capillaries
Recognition and Drawing of Blood Cells
🌱 Overview
- Blood contains different cell types with specialised functions:
- Red blood cells (RBCs) – oxygen transport
- White blood cells (WBCs) – immune defense
- Monocytes – phagocytosis
- Neutrophils – first line of defense against infections
- Lymphocytes – antibody production and cellular immunity
- Cells can be identified under light microscope, photomicrographs, or electron micrographs.
- Accurate drawings help document cell morphology for study.
🔬 1. Red Blood Cells (Erythrocytes)
- Structure:
- Biconcave disc, no nucleus
- Diameter ~7–8 μm
- Flexible membrane
- Function:
- Transport oxygen and carbon dioxide via hemoglobin
- Recognition:
- Uniform size, central pallor, appear pink with eosin stain
🔬 2. Monocytes
- Structure:
- Largest WBC (12–20 μm)
- Kidney-shaped or horseshoe-shaped nucleus
- Abundant cytoplasm
- Function:
- Develop into macrophages in tissues
- Phagocytose pathogens and debris
- Recognition:
- Large size, pale blue cytoplasm, distinct nucleus
🔬 3. Neutrophils
- Structure:
- 10–12 μm in diameter
- Multi-lobed nucleus (2–5 lobes)
- Granular cytoplasm
- Function:
- First responders to infection
- Phagocytose bacteria and fungi
- Recognition:
- Multi-lobed nucleus, pale pink cytoplasm with fine granules
🔬 4. Lymphocytes
- Structure:
- Small (7–10 μm) or large (10–15 μm) types
- Large round nucleus, occupies most of the cell
- Thin rim of cytoplasm
- Function:
- B cells → produce antibodies
- T cells → cell-mediated immunity
- Recognition:
- Dense round nucleus, scant cytoplasm
📊 Summary Table: Blood Cell Identification
| Cell Type | Size (μm) | Nucleus | Cytoplasm | Function |
|---|---|---|---|---|
| RBC | 7–8 | None | No granules | Transport O₂ & CO₂ |
| Monocyte | 12–20 | Kidney-shaped | Abundant | Phagocytosis, becomes macrophage |
| Neutrophil | 10–12 | Multi-lobed | Granular | Phagocytosis of pathogens |
| Lymphocyte | 7–15 | Large, round | Thin rim | Immune response (B/T cells) |
Role of Water in Transport in Mammals
🌱 Overview
- Water is the main component of blood and tissue fluid.
- Its physical properties make it ideal for transport of substances in mammals.
🔬 Key Properties of Water in Transport
Solvent Action
- Water is a polar molecule and can dissolve many substances (e.g., salts, sugars, gases, proteins).
- Function in transport: Dissolves and carries nutrients, oxygen, carbon dioxide, hormones, and waste products in blood and tissue fluid.
High Specific Heat Capacity
- Water can absorb or release large amounts of heat with little change in temperature.
- Function in transport: Maintains stable internal body temperature, ensuring enzymes and tissues function efficiently while transporting substances.
📊 Summary Table: Water Properties and Transport Roles
| Property | Feature | Role in Transport in Mammals |
|---|---|---|
| Solvent action | Polar molecule dissolves many substances | Carries nutrients, gases, wastes, and hormones in blood/tissue fluid |
| High specific heat capacity | Absorbs/releases heat with minimal temperature change | Maintains stable body temperature for efficient transport and metabolic reactions |
🧠 Key Points:
– Water makes up most of blood plasma (~90%) and tissue fluid, acting as a transport medium.
– Its solvent property enables dissolved substances to move efficiently.
– Its high specific heat buffers temperature changes, ensuring homeostasis during circulation.
– Water makes up most of blood plasma (~90%) and tissue fluid, acting as a transport medium.
– Its solvent property enables dissolved substances to move efficiently.
– Its high specific heat buffers temperature changes, ensuring homeostasis during circulation.
Tissue Fluid – Formation and Function
🌱 Overview
- Tissue fluid is a watery fluid surrounding body cells, derived from blood plasma.
- It enables exchange of substances between blood and cells.
🔬 Functions of Tissue Fluid
| Function | Description |
|---|---|
| Transport of nutrients | Supplies oxygen, glucose, amino acids, and other nutrients from blood to cells. |
| Removal of waste | Collects carbon dioxide and other metabolic wastes from cells to return to blood. |
| Medium for diffusion | Provides an aqueous environment for substances to diffuse between blood and cells. |
| Homeostasis | Helps maintain stable conditions around cells. |
🔬 Formation of Tissue Fluid
- Arterial End of Capillaries:
- Blood pressure (hydrostatic pressure) inside capillaries is higher than tissue fluid pressure.
- Plasma (except large proteins) is forced out of capillaries into surrounding tissue.
- Exchange of Substances:
- Oxygen, glucose, and nutrients diffuse into cells from tissue fluid.
- Carbon dioxide and metabolic wastes diffuse from cells into tissue fluid.
- Venous End of Capillaries:
- Osmotic pressure due to plasma proteins draws some fluid back into capillaries.
- Remaining tissue fluid drains into lymph vessels.
📊 Summary Table: Tissue Fluid Formation
| Stage | Mechanism/Force | Result |
|---|---|---|
| Arterial end of capillary | High hydrostatic pressure | Plasma forced out → tissue fluid formed |
| Exchange at tissue | Diffusion of nutrients & wastes | Cells receive nutrients, remove wastes |
| Venous end of capillary | Osmotic pressure (from plasma proteins) | Fluid returns to capillaries; excess → lymph |
🧠 Key Points:
– Tissue fluid is essential for cell survival, acting as a transport and exchange medium.
– Formation is driven by hydrostatic pressure (outward) and oncotic/osmotic pressure (inward).
– Excess tissue fluid is returned via the lymphatic system, preventing fluid accumulation.
– Tissue fluid is essential for cell survival, acting as a transport and exchange medium.
– Formation is driven by hydrostatic pressure (outward) and oncotic/osmotic pressure (inward).
– Excess tissue fluid is returned via the lymphatic system, preventing fluid accumulation.