Circulatory System Flashcards
Mammals have a closed double circulatory system, what does “closed” and “double” mean in this context?
Closed = blood is confined to vessels
Double = blood passes twice through the heart for each complete circuit of the body
What does the blood transport?
• respiratory gases
• products of digestion eg glucose, amino acids, monoglycerides and fatty acids
• metabolic waste products eg urea
• hormones
What does the pulmonary artery do?
Carries blood from the heart to the lungs
What does the pulmonary vein do?
Caddies blood from lungs to the heart
What does the aorta do?
Carries blood from the heart to the body
What does the vena cava do?
Carries blood from the body to the heart
What does the renal artery do?
Carries blood from the aorta/body to the kidneys
What does the renal vein do?
Carries blood from the kidneys to the heart/vena cava
Label the internal structure of the human heart
Why do the ventricles have thicker muscle walls then the atria?
Ventricles need to push blood out of the heart to the rest of the body whereas atria just need to push blood a short distance into the ventricles
Why is the left ventricle muscle much thicker than the right ventricle?
Allows it to contract more powerfully and pump blood all the way around the body. The right side is less muscular so it’s contractions are only powerful enough to pump blood to the nearby lungs
What does the septum do?
Separates the two sides of the heart so oxygenated and deoxygenated blood do not mix. It also enables there to be differnt pressures each side of the heart
• the right side of the heart pumps deoxygenated blood to the lungs
• the left side of the heart pumps oxygenated blood to the whole body
Label the external structure of the heart
What is the hearts blood supply?
Left and right coronary arteries
What do arteries do?
Arteries carry blood from the heart to the rest of the body. They divide into smaller blood vessels called arterioles which form a network throughout the body
What is the structure of arteries?
• lumen is small to maintain blood pressure
• collagen fibres and fibrous proteins mean the thick wall can withstand high pressure
• elastic tissue allows the wall to stretch and then recoil - maintains the diastolic blood pressure
• endothelium is smooth to reduce friction and is also folded so can unfold when the artery stretches
• smooth muscle allows contraction thin and vasoconstriction, narrowing lumen of artery
What is the blood pressure like in the arteries?
Very high pressure due to the contraction of the left ventricle muscle
What does the muscles in arterioles allow?
Enables blood to be directed to different areas of demand in the body - muscle contracts to restrict blood flow and relaxes to allow full blood flow
What do veins do?
Veins carry blood back to the heart. Have valves to prevent the back flow of blood
What is the structure of veins?
• lumen is large to ease the flow of blood
• walls have less collagen, smooth muscle and elastic tissues as they do not need to perform the roles of the artery. The wall is therefore thin but still strong
What is the pressure like in the veins?
Blood is at a lower pressure than the artery, arterioles or capillaries.
There is residual pressure from the contraction of the left ventricle muscle wall
What do capillaries do?
Arterioles branch into capillaries which are the smallest of blood vessels. Molecules are exchanged between capillaries and cells
What is the structure of capillaries?
• walls are made up of a single layer of flattened endothelial cells which reduces the diffusion distance
• narrow lumen which is the same diameter as a RBC ensures that the cells are squeezed as they travel through the capillaries so reduces diffusion distance, it also slows the RBCs so more time for diffusion
• smooth endothelium which reduces friction for blood flow
• gaps between the endothelial cells allows movement of nutrients proteins cannot pass
• has a large total surface area/ cross sectional area allowing for more exchange
What is the blood pressure like in capillaries?
Blood is at high pressure at the arteriole end due to the contraction of the left ventricle wall but the pressure falls as it goes towards the venous end
Describe what happens at each of the 3 stages on this graph in regards to pressure changes in blood vessels
1) high pressure in arteries due to contraction of left ventricles
2) fluctuation is due to stretching and recoiling of elastic fibres
3) pressure decreases through arterioles and capillaries and venues and veins due to moving further from the heart, splitting into more blood vessels
What are the 3 stages of the cardiac cycle?
- Atrial systole - ventricles relax, atria contracts
- Ventricular systole - ventricles contract, atria relax
- Diastole - ventricles and atria relax
What is systole?
Contraction of cardiac muscle
What is diastole?
Relaxation of cardiac muscle
How long does the cardiac cycle last?
Around 0.8 seconds giving a heart rate of 75 beats per minute
Describe atrial systole
• atria fill with blood
• atria contract decreasing the volume of the atria and increasing the pressure inside the chambers
• blood is squeezed into ventricle via atrioventricular valve
• pressure is greater in the atria than the ventricle causing the atrioventricular valve to open
Describe ventricular systole
• ventricles contract decreasing their volume and increasing the pressure inside the chambers
• the pressure inside the ventricle became higher than the pressure inside the atria forcing the atrioventricular valves shut to prevent back flow
• the pressure in the ventricles is also higher than taht of the arteries which forces the semi lunar valves open
Describe ventricular and atrial diastole
• ventricles and atria both relax
• the higher pressure in the arteries then ventricles causing the semi-lunar valves to close to prevent back flow of blood into the ventricles
• atria fill with blood
• cycle starts again
What causes valves to open?
Valves open when the pressure above the valve is greater than below it.
• atrioventricular valves open when the pressure in the atria is greater than the ventricles
• semi-lunar valves open when the pressure in the ventricles is greater than the arteries
What causes valves to close?
Valves close when the pressure beneath the valve is greater than above it. Valves close to prevent the back flow of blood
The lub dub sound the heart makes is due to the closing of the atrioventricular valve followed by the closing of the semilunar valve
Learn:
What is an electrocardiogram? (ECG)
Monitors the electrical activity of the heart. Electrical activity generated by the heart spreads through the tissue nearby. Sensors on the skin pick up the electrical excitation created by the heart and turn it into a trace
P- excitation of the atria
Q,R,S - excitation of the ventricles
T - diastole
What is the equation for cardiac output?
Cardiac output = stroke volume x heart rate
• Cardiac output - volume of blood pumped by the heart per minute
• Heart rate - the number of beats per minute
• stroke volume - volume of blood pumped during each heartbeat
