3.3.4.1 Mass transport in animals

• Circulatory system in humans:

  • Double circulatory system
  • 3 types of blood vessels- arteries, veins, capillaries
  • 4 chambers of the heart- right atrium, right ventricle, left ventricle, left atrium
  • Vena cava- deoxygenated blood from the body to the heart
  • Aorta- oxygenated blood from the heart to the body
  • Pulmonary vein- oxygenated blood from the lungs to the heart
  • Pulmonary artery- deoxygenated blood from heart to the lungs
  • Coronary artery- oxygenated blood to heart muscle
  • Coronary vein- deoxygenated blood away from heart muscle
• Superior vena cava- connected to the right atrium, carries deoxygenated blood from the upper body to the right atrium
• Inferior vena cava- connected to the right atrium, carries deoxygenated blood from the lower body to the right atrium
• Pulmonary artery- connected to the right ventricle, carries deoxygenated blood from the heart to the lungs
• Renal vein- carries deoxygenated blood from the kidneys to the vena cava
• Pulmonary vein- connected to the left atrium, carries oxygenated blood from the lungs to the heart
• Aorta- connected to the left ventricle, carries oxygenated blood from the heart to the rest of the body (excl. the lungs)
• Renal artery- carries oxygenated blood from the aorta to the kidneys for 'cleaning'
• Coronary arteries directly supply the heart muscle with oxygenated blood.
• Coronary veins take away deoxygenated blood from the heart muscle.
• Atrioventricular valves- prevents the backflow of blood between the atria and ventricles, have tendons to help the valves withstand the pressure from the contraction of ventricles
• What causes valves to open?

  A high blood pressure above the valve and a lower blood pressure below the valve establishes a pressure gradient. This forces the valves to open, allowing the flow of blood. When the blood pressure above the valve is lower than the blood pressure below the valve, this causes the valves to close, preventing blood from flowing back into the ventricles.
• Semi-lunar valves- found between the arteries and ventricles, controls the flow of blood and prevents backflow
• The semi-lunar valves are forced open when the blood pressure is higher below the 'pocket' valve, which allows blood to flow through. The valve closes when the blood pressure is lower below the 'pocket' valve, allowing blood to fill the pockets, causing them to bulge downwards and close so no blood can flow though or flow back.
• The left ventricle is the thickest chamber of the heart, meaning it can exert more pumping force and pressure, allowing blood to be pushed out of the heart and around the body.
• 3 stages of the cardiac cycle:

  1. Atrial systole- atria contraction
  2. Ventricular systole- ventricle contraction
  3. Cardiac diastole- whole heart relaxes
• Cardiac diastole:

  • All muscles in the heart are relaxed which allows blood to flow into the heart
  • Blood is able to fill the atria and flow into the ventricles through the open atria-ventricular valves
  • Semi-lunar valves are closed to prevent the backflow of blood
• Atrial Systole:

  • Atrial muscles contract and ventricular muscles relax, forcing blood from the atria into the ventricles because of the pressure difference.
  • Valves of the blood vessels are closed to prevent the backflow of blood and also to stop anymore blood from entering the ventricles.
• Ventricular systole:

  • Atrial muscles relax and ventricular muscles contract.
  • Atrioventricular valves are forced shut from the large pressure of blood which entered the ventricles.
  • Ventricular muscles contract, forcing blood out of the ventricle and into the arteries.
  • Semi-lunar valves are forced open because of the pressure of the blood being forced into the arteries.
• The Cardiac Cycle:

  • Ventricular contraction causes atrioventricular valves to close.
  • Pressure in ventricles increases, causing semi-lunar valves to open.
  • Pressure in ventricles decreases, blood flows back towards the relaxed ventricles, causing semi-lunar valves to close.
  • When the pressure in the ventricles is lower than the pressure in the atria, atrioventricular valves open so blood can flow into the relaxed ventricles.
  • Atria contract, completing the filling of the ventricles.
• Cardiac Cycle Graph:

  1. During atrial systole, pressure in atria is greater than pressure in ventricles.
  2. Start of ventricular systole- ventricular pressure exceeds pressure of atria during atrial systole, causing AV valves to close.
  3. Pressure in ventricles exceeds pressure in aorta (artery), forcing SL valves open.
  4. End of ventricular systole, pressure in ventricle decreases to lower than the pressure in the aorta (artery), SL valves close to prevent backflow.
  5. Diastole- ventricular pressure decreases, atrial pressure exceeds it, AV valves forced open, blood fills heart.

  
• Cardiac Output- the volume of blood pumped by one ventricle of the heart in one minute, measured in 1dm^3 min^-1
• Cardiac Output= Heart Rate X Stroke Volume
• Blood vessels- artery, arteriole, capillary, venule, vein
• Structures in blood vessels:

  • Inner-most layer- endothelium surrounded by a connective tissue membrane with elastic fibres which stretch and recoil.
  • Middle layer- smooth muscle, thickest layer which provides support and changes vessel diameter to regulate blood pressure and flow.
  • Outer layer- attaches the vessel to the surrounding tissue using connective tissue with collagen and elastic fibres.
• Arteries:

  • Smooth endothelium- reduces friction of blood flowing.
  • Thick middle (muscle) layer- prevents bursting due to high blood pressures (straight from the heart) and to maintain a high pressure to send blood around the body.
  • Collagen- provides strength and stability.
  • Narrow lumen- maintains a high blood pressure.
• Veins:

  • Thinner muscle wall- due to lower blood pressures.
  • Thinner middle layer.
  • Large lumen- reduces blood pressure.
  • Collagen- provides strength and stability.
• Capillary:

  • One cell thin- made of endothelium, decreases diffusion distance.
  • Small lumen- only big enough for one blood cell to squeeze through (blood cells are close to the capillary walls, short diffusion distance).
• Veins have valves to maintain blood pressure. Blood flowing towards the heart (via the veins) opens the valves. Blood flowing away from the heart (via the arteries) pushes the valves and closes them. Veins are situated between the muscles- assists the veins by squeezing, which pushes and transports the blood.
• Capillaries are permeable to gases and are involved in the exchange of substances with tissues.
• Direction of blood flow:

  • Artery- away from the heart
  • Capillary- unidirectional, to and from the heart
  • Vein- to the heart
• Thickness of the wall:

  • Artery- thickest blood vessel
  • Capillary- one cell thin
  • Vein- thinner than an artery
• Lumen size:

  • Artery- smaller size than a vein's lumen, but larger than a capillaries
  • Capillary- width of a red blood cell
  • Vein- largest lumen
• Permeability:

  • Artery- not permeable
  • Capillary- permeable to gases
  • Vein- not permeable
• Valves in blood vessel:

  • Artery- no valves
  • Capillary- no valves
  • Vein- pocket valves
• Blood pressures in the blood vessel:

  • Artery- highest pressure
  • Capillary- pressure between an artery and vein
  • Vein- lowest pressure
• Flow rate of blood vessels:

  • Artery- fastest flow
  • Capillary- slowest flow
  • Vein- flow rate in between artery and capillary
• The capillaries have an 'in between' pressure and the slowest flow rate as their function is to help decrease the pressure and flow rate before the blood reaches the veins, to prevent damage.
• Tissue fluid- made from plasma which has leaked from gaps in the capillary walls, contains a small number of proteins but no red blood cells (they're too big to leak through capillary walls)
• The amount of tissue fluid produced depends on the pressure being placed on the plasma.