3.2.6 The Circulation of Blood and The Structure Of The Mammalian Heart Flashcards
What is the function of the circulatory system?
Transports raw materials from specialised exchange organs to body cells
Describe the 2 circuits the circulatory system consists of
- 1 takes blood from heart to lungs, then back to heart
- Other loop takes blood around the rest of the body
What the function of a vein?
Take blood back to heart under low pressure
Describe the structure of a vein 4x
- Large lumen
- Very little elastic or muscle tissue = thin walls
- Contain valves to prevent blood flowing backwards
- Blood flow is helped by contraction of body muscles surrounding veins
What is the function of arteries?
Carry oxygenated blood from heart to rest of body
Describe the structure of arteries 2x
- Walls = thick, smooth muscular & have elastic tissue
- Endothelium (inner lining) is folded
What does the walls of the arteries do and what does this help to do? (3)
- Stretches under high pressure
- Recoils under low pressure
- Helps to maintain blood pressure
Arteries divide into smaller vessels called _____
arterioles
What is the function of arterioles?
Control blood flow from arteries to capillaries
Describe how arterioles control blood flow
- Muscles contracts & arterioles narrow to restrict blood flow to capillaries or relax to allow full blood flow
Arterioles branch into _____
capillaries
What is the function of capillaries?
Exchange substances between blood and body tissues
Name 4 adaptations of capillaries for efficient diffusion
- Found near cells in exchange tissues = short diffusion pathway
- Walls = single layer of endothelium cells = shortens diffusion pathway
- Large no. of capillaries & highly branched = increase SA for exchange
- Narrow lumen so RBCs are squeezed flat against capillary
- Reduces diffusion distance
What are capillary beds?
Network of capillaries in tissue
Capillaries have ___ between lining (endothelial) cells
gaps
Why do capillaries have gaps between lining (endothelial) cells?
- They act as a sieve - controlling which molecules can leave the capillaries
- Allows WBCs to escape
What is tissue fluid?
Fluid that surrounds cells
What is tissue fluid made from?
Small molecules that leave blood plasma (e.g. oxygen, water and nutrients)
Why doesn’t tissue fluid contain RBCs or big proteins?
∵ they’re too large to be pushed out through capillary walls
What do cells do with tissue fluid?
They take in oxygen and nutrients from tissue fluid & release metabolic waste into it
In capillary bed, substances move out of capillaries into tissue fluid, by ____ _____
pressure filtration
Describe how substances move out of capillaries into tissue fluid by pressure filtration
- At start/arterial end of capillary bed: hydrostatic (liquid) pressure inside capillaries > hydrostatic pressure in tissue fluid
- Difference in hydrostatic pressure = pressure forces water/fluid + small molecules out of capillaries & into spaces around cells, forming tissue fluid
- Loss of water/fluid = hydrostatic pressure reduces in capillaries ∴ hydrostatic pressure is lower at venule end
- there’s increasing conc. of plasma proteins ∴ Ψw at venule end is lower than Ψw in tissue fluid
- Some water re-enters capillaries from tissue fluid at venule end by osmosis
If asked about a particular end of the capillary, what do you need to do?
Compare hydrostatic pressure and osmotic pressure
Explain how fluid leaves the capillary at the arterial end
Hydrostatic pressure is greater than osmotic effect which forces molecules/fluid out
What within the bloodstream can affect the water potential?
Proteins
If water moves out of the capillary, what happens to the water potential?
The water potential in the capillary will go down
(Proteins within bloodstream can affect the water potential)
Water potential of blood plasma is more negative at venule end of the capillary than at arteriole end of capillary. Explain why. (2)
- Water has left the capillaries
- Proteins (in blood) are too large to leave capillary
- Increasing conc. of blood proteins & thus water potential ↓
What happens to excess tissue fluid?
It’s drained into lymphatic system
What is swelling essentially?
Swelling → excess tissue fluid
Describe the lymphatic system
- Network of tubes that acts like a drain
- Have a dead end
Why does the lymphatic system tubes have dead end?
So pressure on them can only produce movement in one direction
What does the lymphatic system do with the excess tissue fluid
- It transports excess tissue fluid and dumps it back into circulatory system
- Drain their contents back into bloodstream via 2 ducts that join veins close to heart
How is the content in lymphatic system moved?
By
- Hydrostatic pressure of tissue fluid that has left capillaries
- Contraction of body muscles that squeeze lymph vessels
What do the valves in the lymph vessels ensure?
Fluid inside them moves away from tissues in direction of heart
The heart consists of 2 ______ ____
Muscular Pumps
What does the right side of the heart do?
pumps deoxygenated blood to lungs
What does the left side of the heart do?
pumps oxygenated blood to whole body
What is the functions of the atrioventricular (AV) valves?
Link atria to ventricles + stop blood flowing back into atria when ventricles contract
Name and explain an adaptation of the ventricles
- Thicker walls than atria
- ∵ have to push blood out of heart whereas atria need to push blood a short distance → into ventricles
Name and explain an adaptation of the left ventricle
- Thicker, more muscular walls than right ventricle
- ∵ needs to contact powerfully to pump blood all way round body
- (Whereas lungs are nearby right ventricle)
What is the functions of the semi-lunar (SL) valves?
Link ventricles to pulmonary artery and aorta & stop blood flowing back into heart after ventricles contract
What is the function of cords?
Attach AV valves to ventricles → stop them being forced up into atria when ventricles contact
What does whether valves are closed or open depend on?
The relative pressure of heart chambers
When are valves forced open?
Higher pressure behind valve
When are valves forced shut?
Higher pressure in front of valve
Name 3 stages in the cardiac cycle
- Atrial Systole
- Ventricular Systole
- Diastole
Describe Atrial Systole
- Atria contract
- ↓ volume of atria & ↑ atrial pressure increases
- Blood is forced into the ventricles
- Pressure in ventricles increase slightly as blood from atria is forced in
Describe Ventricular Systole
- Atria relax
- Ventricles contract
- ↓ their volume & ↑ ventricular pressure
- As ventricular pressure rises above atrial pressure = AV valves close
- Atria starts to refill and atrial pressure increases as the blood flows in
- Blood returns to heart & atria fill again due to higher pressure in vena cava and pulmonary vein
- As ventricular pressure is higher than aorta and pulmonary artery = forces open SL valves & blood is forced out into these arteries
Describe Diastole
- Ventricles relax and their pressure decreases
- SL valves close as ventricular pressure drops below pressure in pulmonary artery and aorta
- AV valves open as the ventricular pressures drops below atrial pressure
- Blood starts to refill the ventricles
- Allows blood to flow passively (without being pushed by atrial contraction) into ventricles from atria
- Pressure increases slightly
- Whole process then repeats
When does the blood start flowing into the aorta? Explain why you have chosen that point.
At point A, ventricles are contracting (and AV valves are shut) forcing blood into the aorta
Why is ventricular volume decreasing at point B?
Ventricles are contracting, reducing the volume of the chamber
Are the semi-lunar valves open or closed at point C? Explain why.
Closed. The ventricles are relaxed and refilling, so the pressure is higher in pulmonary artery and aorta, forcing the SL valves closed.
Why is the pressure higher in the left ventricle than the right (and in the aorta compared to the pulmonary artery)?
The left ventricle has a thicker wall than the right ventricle so it contracts more forcefully
How is the cardiac cycle controlled?
By electrical activity
Describe how the cardiac cycle is controlled by electrical activity
- SAN generates waves of electrical activity across atrial walls causing atria to contract
- Non-conducting tissue prevents waves of electrical activity from being passed directly from atria to ventricles
- ∴ Waves of electrical activity go to ventricles via AVN
- Delay at AVN allows atria to completely empty before ventricles contract
- AVN sends waves of electrical activity down the bundles of His (on apex)
- Purkinje tissue carries waves of electrical activity into muscular walls of ventricles
- Ventricles contract from the bottom upwards
State the formula for calculating cardiac output
Cardiac output = heart rate x stroke volume
[(Blood out per minute) = beats per minute x blood pumped in 1 beat]
What does ‘P’ represent on the ECG (electrocardiogram)?
Atrial systole
What letters represent ventricular systole on the ECG (electrocardiogram)?
QRS
What letter represent diastole on the ECG (electrocardiogram)?
T
Name 2 substances which are at a higher concentration in the blood at the arteriole end of the capillary than the venule end (1)
Glucose and oxygen
Explain how fluid may be returned to the blood (3)
- The lymph vessels return the fluid to the blood
- Re-absorbtion by osmosis
- Proteins are retained in the blood capillary
Suggest an explanation for the link between high blood pressure and the accumulation of tissue fluid (3)
- High blood pressure = high hydrostatic pressure in capillaries ∴ forces out more fluid from capillary → accumulation of tissue fluid around cells
- High blood pressure at venule end of capillary may reduce amount of fluid reabsorbed
- Lymph system would not be able to drain all excess tissue fluid rapidly enough
Suggest why tissue fluid accumulates more in the ankles and feet than in other parts of the body (2)
- Gravity would cause tissue fluid to accumulate in the ankles and feet
- Fewer lymph vessels in these areas
Explain why a lack of protein in the diet causes swelling (3)
- Less protein in diet = less protein in blood
- Water potential of blood too high
- Water in tissue not drawn back into capillaries by osmosis
- Tissue fluid = stays in tissues = swelling
Describe how veins being thin/having a large lumen help the blood flow at low blood pressure (2)
- Walls of veins are thin so can be compressed
- Large lumen/smooth lining to provide less resistance to flow
