BUNDLE 5: CARDIOVASCULAR SYSTEM
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INTRODUCTION
Cardiovascular system consists of:
• **The heart**: Pumps blood for constant circulation
• **The blood vessels**: In which blood flows
Heart pumps blood in two anatomically separate systems:
1. **Pulmonary circulation**
2. **Systemic circulation**
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BLOOD VESSELS
Vary in size, structure, and function.
Types: Arteries, arterioles, capillaries, venules, and veins.
ARTERIES AND ARTERIOLES
Transport blood away from the heart.
Three layers (tunics):
3. **Tunica adventitia**: Outer layer of fibrous tissue
4. **Tunica media**: Middle layer of smooth muscles and elastic tissue
5. **Tunica intima**: Inner layer of squamous epithelium (endothelium)
• Arteries thicker than veins to withstand high pressure
• **Anastomoses**: Arteries forming links between main arteries; provide collateral
circulation if one artery occluded
• **End-artery**: Sole source of blood to a tissue; if occluded, tissue dies
CAPILLARIES
• Smallest arterioles break into minute vessels
• Single layer of endothelial cells on thin basement membrane
• Water and small molecules pass through; blood cells and large particles do not
• Link between arterioles and venules
• Entry guarded by **precapillary sphincters** (ring of smooth muscle)
• **Sinusoids**: Wider, leakier capillaries (e.g., liver, bone marrow)
VEINS AND VENULES
Return blood at low pressure to the heart.
, • Walls thinner than arteries (less muscle and elastic tissue in tunica media)
• Some possess **valves** preventing backflow
• **Venules**: Smallest veins
• **Capacitance vessels**: Distensible; hold large portion of body's blood
CONTROL OF BLOOD VESSEL DIAMETER
• **Autonomic nervous system** innervates smooth muscles of tunica media
• Nerves arise from **vasomotor centre** in medulla oblongata
Resistance to blood flow determined by:
• Diameter of blood vessels
• Length of blood vessels
• Viscosity of blood
• **Vasoconstriction**: Constriction and narrowing
• **Vasodilation**: Dilation and expansion
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LOCAL REGULATION OF BLOOD FLOW
Autoregulation: Ability of organ to control its own blood flow according to needs.
Mechanisms:
• **Metabolic waste**: Increase → increased blood flow to area
• **Tissue temperature**: High → vasodilation → increased blood flow
• **Tissue hypoxia**: Causes vasodilation → increased blood flow
• **Vasodilator chemicals** (e.g., nitric oxide): Increase blood flow to site
• **Vasoconstrictors** (e.g., adrenaline): Decrease blood flow
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CAPILLARY EXCHANGE
EXCHANGE OF GASES
Internal respiration: Gases exchanged between capillary blood and local body cells.
• Oxygen carried as **oxyhemoglobin**
• Exchange occurs between arterial end of capillaries ↔ tissue fluid ↔ cells
• **Oxygen**: Diffuses from arterial blood into tissue (down concentration gradient)
• **Carbon dioxide**: Diffuses from tissue into blood (down concentration gradient)
CO2 transport to lungs:
• Dissolved in plasma water: **7%**
• As sodium bicarbonate: **70%**
__________________________________________________
INTRODUCTION
Cardiovascular system consists of:
• **The heart**: Pumps blood for constant circulation
• **The blood vessels**: In which blood flows
Heart pumps blood in two anatomically separate systems:
1. **Pulmonary circulation**
2. **Systemic circulation**
__________________________________________________
BLOOD VESSELS
Vary in size, structure, and function.
Types: Arteries, arterioles, capillaries, venules, and veins.
ARTERIES AND ARTERIOLES
Transport blood away from the heart.
Three layers (tunics):
3. **Tunica adventitia**: Outer layer of fibrous tissue
4. **Tunica media**: Middle layer of smooth muscles and elastic tissue
5. **Tunica intima**: Inner layer of squamous epithelium (endothelium)
• Arteries thicker than veins to withstand high pressure
• **Anastomoses**: Arteries forming links between main arteries; provide collateral
circulation if one artery occluded
• **End-artery**: Sole source of blood to a tissue; if occluded, tissue dies
CAPILLARIES
• Smallest arterioles break into minute vessels
• Single layer of endothelial cells on thin basement membrane
• Water and small molecules pass through; blood cells and large particles do not
• Link between arterioles and venules
• Entry guarded by **precapillary sphincters** (ring of smooth muscle)
• **Sinusoids**: Wider, leakier capillaries (e.g., liver, bone marrow)
VEINS AND VENULES
Return blood at low pressure to the heart.
, • Walls thinner than arteries (less muscle and elastic tissue in tunica media)
• Some possess **valves** preventing backflow
• **Venules**: Smallest veins
• **Capacitance vessels**: Distensible; hold large portion of body's blood
CONTROL OF BLOOD VESSEL DIAMETER
• **Autonomic nervous system** innervates smooth muscles of tunica media
• Nerves arise from **vasomotor centre** in medulla oblongata
Resistance to blood flow determined by:
• Diameter of blood vessels
• Length of blood vessels
• Viscosity of blood
• **Vasoconstriction**: Constriction and narrowing
• **Vasodilation**: Dilation and expansion
__________________________________________________
LOCAL REGULATION OF BLOOD FLOW
Autoregulation: Ability of organ to control its own blood flow according to needs.
Mechanisms:
• **Metabolic waste**: Increase → increased blood flow to area
• **Tissue temperature**: High → vasodilation → increased blood flow
• **Tissue hypoxia**: Causes vasodilation → increased blood flow
• **Vasodilator chemicals** (e.g., nitric oxide): Increase blood flow to site
• **Vasoconstrictors** (e.g., adrenaline): Decrease blood flow
__________________________________________________
CAPILLARY EXCHANGE
EXCHANGE OF GASES
Internal respiration: Gases exchanged between capillary blood and local body cells.
• Oxygen carried as **oxyhemoglobin**
• Exchange occurs between arterial end of capillaries ↔ tissue fluid ↔ cells
• **Oxygen**: Diffuses from arterial blood into tissue (down concentration gradient)
• **Carbon dioxide**: Diffuses from tissue into blood (down concentration gradient)
CO2 transport to lungs:
• Dissolved in plasma water: **7%**
• As sodium bicarbonate: **70%**
