Transport in Animals

• Animals need transport systems because:

  • metabolic demands are high
  • distances are large
  • SA:V is low
  • substances made in one part of the organisms but are needed elsewhere
  • waste products are excreted
• Circulatory system:

  • mass transport system - when substances are moved in mass of fluid around the body
  • they have a liquid transport medium
  • vessels that carry the medium
  • pumping mechanism to move the fluid around the system
• Open circ. system

  • no distinction between blood and tissue fluid, and general body fluid is called haemolymph
  • the heart extends the length of the body cavity which is known as the haemocoel
  • the haemolymph is under low pressure and comes into direct contact with tissues and cells
  • haemolymph is drawn back into the heart as it relaxes
  • haemolymph carries food, nitrogenous waste and plasmatocytes
• Closed circ. System

  • blood is enclosed in vessels and does not come into direct contact with cells
  • heart pumps blood under pressure and quickly
  • substances enter and leave by diffusion
  • most closed circ systems contain a blood pigment that carries the respiratory gases
  • blood flow can be controlled by widening or narrowing of blood vessels
• Plasma:

  • yellow fluid
  • carries: dissolved glucose, amino acids, mineral ions, hormones, large plasma proteins, fibrinogen, globulins, RBCS, WBCS, platelets, water
• Functions of the blood:

  • transport: oxygen, carbon dioxide, digested food, nitrogenous waste, hormones, food molecules, platelets, antibodies
  • maintains a steady temperature
  • acts as a buffer to reduce the change in pH
• Oncotic pressure - around 3.3kPa, caused by Albumin which lowers the water potential of blood causing blood to move back into blood vessels
• Arteries and arterioles:

  • carry blood away from heart at high pressure
  • carry oxygenated blood except pulmonary artery and umbilical artery
  • artery walls contains elastic fibres, smooth muscle, collagen and endothelium
• Structure of artery/arterioles:

  • elastic fibres: can stretch and recoil to smooth out blood supply to organs (less fluctuation of blood pressure), provides flexibility to vessels
  • smooth muscle: contracts or relaxes to change the size of the lumen to control where blood flows in the body
  • arterioles have more smooth muscle and less elastin
  • collagen: provides structural support
  • endothelium: smooth lining so blood can flow easily
• Capillaries:

  • lumen diameter: 7.5-8 micrometers; red blood cells travel in single file, squashed against the wall to decrease diffusion distance
  • there are many capillaries providing a very large surface area
  • the cross sectional area of the capillaries is greater than the arterioles supplying them so blood flow slows and there is more time for diffusion
  • walls are made of single endothelial cells
• Transfer out of capillaries:

  • gaps where the endothelial cells of the capillary walls are relatively large as this is where exchange of materials occurs
  • the gaps in the capillaries that supply the CNS are smaller and thus less can enter and leave the capillaries, creating the blood - brain barrier to prevent pathogens entering the brain
• Veins and venules:

  • carry deoxygenated blood towards heart except pulmonary and umbilical vein
  • blood flows from capillaries into venules and then veins
  • veins have no pulse and the pressure is low
• Structure of veins:

  • medium sized veins have valves; larger veins such as the jugular, vena cava and pulmonary do not
  • veins contain a lot of collagen and a little elastic fibre
  • veins have a small endothelium and a large lumen which reduce friction in the veins
  • venules have thin walls and a small amount of smooth muscle
• Valves:

  • stop backflow
  • in veins which run between active muscles, prevent blood going the wrong direction when blood vessel is squeezed by muscle contraction
  • pressure changes caused by breathing allow blood to move through the veins
• Tissue fluid:

  • blood arrives from arteries at high pressure (4.6 kPa) which is higher than the oncotic pressure
  • fluid is forced out of the capillaries, which fills the spaces between the cells (tissue fluid)
  • diffusion occurs between cells and tissue fluid
  • at venous end, the hydrostatic pressure in the blood is much lower so tissue fluid returns to the blood vessel
  • around 10% does not drain back in and is called lymph
• Lymph:

  • similar in composition to plasma and tissue fluid but contains less oxygen and fewer nutrients
  • it also contains fatty acids absorbed in the villi
  • lymph contains antibodies
• Lymph vessels:

  • lymph capillaries join up to form larger lymph vessels
  • fluid is transported by the squeezing of body muscles
  • valves prevent backflow
  • the lymph drains back into the circ. system at the right and left subclavian veins
• Lymph nodes:
• Lymph nodes:

  • a collection of lymphoid tissue
  • lymphocytes accumulate here during an infection and produce antibodies which pass into the blood
  • Lymph nodes intercept bacteria in the lymph and phagocytes ingest them
  • lymph nodes swell during an infection
• Erythrocytes:

  • large SA
  • can pass through narrow capillaries
  • formed continually in bone marrow
  • no nuclei to maximise space for haemoglobin
• Haemoglobin:

  • large globular conjugated protein made up of 4 peptide chains with a haem prosthetic group each
  • there are 300 million haemoglobin molecules in each RBC and each haemoglobin can bind to 4 oxygen molecules
  • oxygen binds reversibly to haemoglobin
• Carrying oxygen:

  • when there is a steep conc. gradient oxygen moves into the eryththrocytes
  • the first oxygen takes longer to bind to the haem, but once it has the molecule changes shape making the next 2 easier, although the last one is more difficult again
  • when oxygen is bound to haemoglobin, the free oxygen conc. is low so a steep gradient is maintained, meaning oxygen continues to diffuse into the erythrocyte
• Releasing oxygen:

  • when the blood reaches the respiring tissue, the concentration gradient is reversed as there is little free oxygen available
  • oxygen diffuses out of the erythrocytes into the cells and as the first one is removed, the other three are easier to remove
• • at a low pO2, few haem groups are bound to oxygen
  • at a higher pO2, more haem groups are bound to oxygen, making it easier for more to be picked up
  • the haemoglobin is saturated at a very high pO2
  • in areas where o2 levels are low, haemoglobin has a low affinity for oxygen and will give it up
  • fetal haemoglobin has a higher affinity for blood than adult haemoglobin at all the points along the dissociation curve

  
• Bohr effect:

  • as the partial pressure of carbon dioxide rises, haemoglobin gives up oxygen more readily
  • an increase in CO2 creates a drop in the pH which reduces haemoglobin's affinity for oxygen

  
• Transportation of CO2:

  • 5% in blood plasma
  • 10-20% in amino groups to for carbaminohaemoglobin
  • 75-85% converted into hydrogen carbonate ions in the RBCs and then move out into plasma
• CO2

  Carbon dioxide
• Hydrogen carbonate ions

  Bicarbonate ions
• CO2 transport in blood

  1. Diffuses into blood from cells

  2. Transported to the lungs in the form of hydrogen carbonate ions

  3. Reacts slowly and reversibly with water to form carbonic acid (H2CO3-)

  4. Carbonic acid dissociates to form hydrogen ions and hydrogen carbonate ions

  5. Carbonic anhydrase in the RBCs catalyses this reaction

  6. Hydrogen carbonate ions move into the plasma by diffusion

  7. Negatively charged chloride ions move into the cell to maintain electrical balance (the chloride shift)

  8. Erythrocytes remove CO2 to maintain a steep concentration gradient for CO2 to diffuse into blood from tissue
• Most of the CO2 that diffuses into blood from cells is transported to the lungs in the form of hydrogen carbonate ions
• Haemoglobin acts as a buffer during the chloride shift to prevent changes in the pH by accepting free hydrogen ions in a reversible reaction to form haemoglobinic acid
• Heart:

  • 4 chambers; 2 pumps working together
  • right side receives deoxygenated blood and pumps it to the lungs
  • left side receives oxygenated blood and pumps it to body
  • cardiac muscle contracts and relaxes, and never fatigues
  • coronary arteries supply the cardiac muscle with oxygen
  • the pericardium prevents the heart from overfilling with blood, anchors it to surrounding walls, protects against infection, provides lubrication
• • blood enters atrium at low pressure
  • as the blood flows, there is a build in pressure due to increased volume until the atrioventricular valve opens and blood flows in the ventricle
  • when both atria and ventricle are filled with blood, atria contracts forcing blood into ventricle
  • ventricle contracts and tricuspid valve shuts, semi lunar valve opens
  • heart relaxes

  
• Cardiac cycle:

  • diastole
  • heart is relaxed
  • atria and ventricles fill with blood
  • volume and pressure of heart increases
  • pressure in arteries is at a minimum
  • systole
  • atria and ventricle contract
  • blood is forced out
  • at end, pressure and volume in heart are low and pressure in the arteries is at a maximum as blood has been pumped out of the heart
• Cardiac muscle:

  • myogenic
  • contract spontaneously without impulse from nerve cells
  • intrinsic rhythm of around 60bpm
• Rhythm:

  • sino-atrial node generates an electrical signal that spreads through the atria, making them contract
  • signal reaches non-conducting tissue at bottom of atria and is stopped for 0.1 second to allow ventricles to fill completely with blood
  • atrioventricular node sends an impulse down the bundle of His which branches in two to travel to the apex of the heart
  • at the apex the purkyne fibres spread out through the walls of both ventricles, the impulse travels along these causing the ventricle to contract from the bottom up
• Electrocardiogram

  • measures electrical differences in skin from electrical activity of heart
  • electrodes pick up the signals
  • can diagnose heart problems
  • P- atrial contraction
  • QRS - ventricular contraction
  • T - ventricles repolarising

  
• Tachycardia:

  • very rapid heartbeat, over 100bpm
  • normal after exercise, fever, fright
  • if abnormal, may be cause by problems in the electrical control of the heart
• Bradycardia:

  • slow heart rate, lower than 60bpm
  • normal for healthy individuals
  • abnormal may require an artificial pacemaker
• Ectopic heartbeat:

  • extra heartbeats that are out of rhythm
  • most people have one a day
  • usually normal but can be linked to serious conditions when very frequent