7b. Human Transport System: Circulatory System Flashcards
Describe double circulation and its advantage in mammals
- Complete separation of the oxygenated and deoxygenated blood in double circulation: ensures that only oxygenated blood reach the tissue cells, maintaining the efficiency of the transport of oxygenated blood.
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Blood passes through the heart twice in one complete circuit:
- Pulmonary circulation at lower pressure: Blood enters the lungs at a lower pressure compared to blood leaving the heart. This ensures that blood flows more slowly through the lungs, allowing sufficient time for the blood to be well oxygenated before it returns to the heart. It also prevents plasma from leaking into the lungs.
- Systemic circulation at higher pressure: So that oxygenated blood is distributed to the rest of the body tissues more quickly. This helps to maintain the high metabolic rate in mammals.
Artery
Structure, Function & Structural adaptations
Structure:
- Thick, elastic and mucular wall
- Absence of semi-lunar valves (except in pulmonary artery and aorta)
Function:
- Transport blood away from the heart
Structural adaptations:
- Thick arterial wall: can withstand high pressure generated by the contraction of the ventricles during ventricular systole.
- Elastic tissue in the wall: enables it to stretch and recoil under high pressure, to push the blood in spurts along the artery, giving rise to a pulse.
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Muscular tissue in the wall: allows for constriction and dialtion to regulate the volume of blood flowing through.
- When an artery constricts, the lumen becomes narrower and less blood flows through it per unit time.
- When an artery dilates, the lumen becomes wider and more blood flows through it per unit time.
Arteriole
Structure & Function
Structure:
- Elastic and muscular wall
- Arteries branch to form arterioles which branch to form capillaries
Function:
- Transport blood away from the heart
Capillary
Structure, Function & Structural adaptations
Structure:
- One-cell thick wall, with single layer of endothelial cells and intercellular clefts (gaps between cells)
Function:
- Allow for the exchange of nutrients and waste products between blood and tissue fluid.
Structural adaptations:
1. One-cell thick wall: decreases the distance over which diffusion occurs and increases the rate of diffusion of materials.
2. Presence of intercellular clefts: increases the rate of diffusion of materials.
3. Extensive network surrounding cells: enable the efficient exchange of materials with tissue cells.
Venule
Structure & Function
Structure:
- Thin, elastic and muscular wall
- Capillaries join together to form venules which join together to form veins
Function:
- Delivers blood to vein
Vein
Structure, Function & Structural adaptations
Structure:
- Thin elastic and muscular wall (relative to artery)
- Presence of semi-lunar valves (except in the vena cava and pulmonary vein)
Function:
- Transport blood towards the heart
Structural adaptations:
- Large lumen: reduces resistance to blood flow so blood can flow smoothy back to heart
- Semi-lunar valves: prevent the backflow of blood under low blood pressure to ensure the flow of blood in one direction
Comparing Blood Vessels
Size of lumen
Artery:
- Small lumen relative to diameter of blood vessel to maintain high blood pressure
Capillary:
- Very small lumen
Vein:
- Large lumen reduces resistance to blood flow so blood can flow smoothy back to heart
Comparing Blood Vessels
Blood pressure & speed of blood flow
Artery:
- High blood pressure which fluctuates (increases during ventricular systole, decreases during ventricular diastole)
- Blood flows rapidly, in pulses (due to the stretch and recoil of the elastic tissue in artery walls)
Capillary:
- Low blood pressure (blood pressure falls allong the capillaries from the arteriole end to the venule end due to the increase in total cross-sectional area)
- Blood flows slowly (to allow more time for exchange of substances to take place)
Vein:
- Very low blood pressure (semi-lunar valves prevent the backflow of blood under low blood pressure to ensure the flow of blood in one direction)
- Blood flows slowly (skeletal muscles next to the veins assist the flow of blood back to the heart by compressing the veins when the muscles contract)
Describe the transfer of materials between capillaries, tissue fluid, and cells
Oxygen and nutrients diffuse from the blood in capillaries to the tissue fluid, then diffuse into body cells.
Carbon dioxide, urea and other metabolic waste diffuse from body cells to the tissue fluid, then duffuse to blood in capillaries.
Left and Right Ventricles
Difference in Structure & Why?
Left ventricle has thicker muscular walls as it has to generate high pressure required to pump blood around the entire body.
Right ventricle has thinner muscular walls as it does not need to generate as high of a pressure to pump blood to the lungs.
Median Septum
Function
Separates left and right sides of the heart, so oxygenated blood (left) and deoxygenated blood (right) stay separate.
Atrial Systole
Process
Atrial systole:
- Atria contract.
- The remaining blood is forced through the open atrioventricular valves into the ventricles.
Atrial Diastole
Process
Atrial diastole (same time as ventricular systole):
- Atria relax.
- Blood from the pulmonary vein (O2 rich) and the vena cava (CO2 rich) starts filling the left and right atria respectively.
Ventricular Systole
Process
Ventricular systole (same time as atrial diastole):
- Ventricles contract.
- Pressure in the ventricles rises, pushing the atrioventricular valves upwards, forcing them shut. This produces a ‘lub’ sound.
- When the pressure in the ventricles is higher than that in the aorta/pulmonary artery, the semi-lunar valves open. Blood from the left and right ventricles enter the aorta and pulmonary artery respectively.
Ventricular Diastole
Process
Ventricular diastole:
- Ventricles relax.
- Pressure in the ventricles fall, resulting in the backflow of blood from the aorta/pulmonary artery toward the left and right ventricles respectively.
- Blood starts to flow backwards and closes the semi-lunar valves. This produces a ‘dub’ sound.
- When ventricular pressure drops below atrial pressure, the atrioventricular valves open and blood from atria flows into ventricles.
