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Mass transport in animals (Tissue fluid (The cells in the tissue have…
Mass transport in animals
Tissue fluid
The cells in the tissue have numerous spaces around them (tissue space) which can be filled b a fluid (tissue fluid) which is formed from blood plasma.
Materials pass from the plasma into the tissue fluid and then into the cells
There are 2 different forces that act on the capillaries they are hydrostatic pressure and difference in water potential.
The blood has a high hydrostatic pressure, at the ateriole end of the capillary
This forces fluid out of the capillaries
This is called tissue fluid- exchange of gases, nutrients e.g. glucose and waste products like urea occurs between the tissue fluid and the cells.
Large plasma proteins remain in the blood as they are too big to leave the capillary.
This lowers the water potential inside the capillary at the venule end of the capillary
Water does not move back into the capillary by osmosis as it does not diffuse across a partially permeable membrane
Excess tissue fluid is absorbed by lymph vessles
The lymphatic system
The net force pushing liquid out at the start of the capillary is greater than the net force pulling back at the end of the capillary
The fact that the pressure is not equal means more liquid leaves the capillary than re-enters. If the fluid stayed in the cells swelling would occur
The fluid drains into open ended tubes known as lymphatic vessles which is like a secondary circulatory system that empties back into the bloodstream in the neck
capillaries
The walls only have an endothelial layer which is a supporting membrane made is fibrous proteins
Involved in exchange of materials between blood and the tissue cells
The diameter is very small as there are a large number of capillaries. This creates considerable friction and the blood pressure created by the heart is lost as the blood flows through the capillaries
Veins
Similar structure to an artery
Muscle layer is very thin
There is no need for vasoconstriction as all the blood is going back to the heart
Elastic layer is run so the pressure is very low and the wall doesn’t need to stretch or recoil
The veins have valves. The residual blood pressure is very low. The blood is moved along the vein by the squeezing action of skeletal muscles when they contract. The valves only allow the blood to pass through in one direction to ensure that the blood goes back to the heart
Transporting oxygen (haemoglobin)
Haemoglobin contains 4 sub units. Alpha chains beta chains and 2 haem molecules which both contain iron atoms
Haemoglobin is a protein with a quaternary structure
All the subunits have the ability to carry 1 molecule of oxygen due to them all containing 1 haem group.
As the haemoglobin loads oxygen with each molecule it gets easier because the oxygen molecules changes the shape of the haemoglobin group.
Haemogflobin binds to red blood cells to transport oxygen around the body.
Haemoglobin has a high affinity for oxygen in the lungs allowing it to almost fully saturate with oxygen. Then when it reaches the respiring tissue it has a much lower affinity for oxygen so the oxygen unloads
Mass flow
Is the bulk movement of liquids (and gases) due to a pressure difference
This is essential for efficient transport of liquids and gases around the body
Closed systems are tubes of liquid and are more efficient than open systems it is easier to generate and maintain a pressure gradient
In most animals the contraction of the heart generates a large pressure. The pressure in the capillaries and veins is much lower, therefore blood moves along the pressure gradient.
Whether or not there is a specialised transport medium and whether or not it is circulated by a pump, depends on 2 factors: The surface area to volume ratio and how active the organism is.
The Lower The surface area to volume ratio and the more active the organism is the greater the need for a more specialised transport system with a pump
Mammals have a double circulatory system which is because the blood passes through the heart twice for each complete circuit of the body
This is because when blood passes through the lungs the pressure is reduced blood is therefore returned to the heart to increase the pressure before being circulated to the rest of the body.
Single and double circulation
The lower the surface area to volume ratio and the more active the organism, the greater the need for a specialised transport system with a pump
Mammals have a double circulatory system which means blood passes through the heart twice for each complete circuit of the body.
This is because when blood passes through the lungs the pressure is reduced
Blood is therefore returned to the heart to boost its pressure before being circulated around the rest of the body.
The heart
The heart is is two separate pumps, side by side, each consisting of an upper chamber (atrium) and a lower chamber (ventricle)
The wall of the heart is made from cardiac muscle fibres
Deoxygenated blood returns from the body in the vena cava (vein) and enters the right atrium
The blood then passes, via an atrio- ventricular valve into the tight ventricle and out, via the semi-lunar valve, into the pulmonary artery
The blood now passes through the lungs and returns to the left atrium via the pulmonary vein.
The blood passes through a second atrio-ventricular valve into the left ventricle and then through the semi-lunar valve into the aorta and then onto the body tissues
Valves
Atrio-ventricular valves
These open when the pressure in the atria increases above that in the ventricles. They close when the pressure in the atria decreases below that in the ventricles.
Semi- lunar valves
These open when the pressure in the ventricle increases above that in the aorta. They close when the pressure int he ventricle decreases below that of the aorta
The atrio-ventricular and semi- lunar valves ensure that the blood flows in one direction only through the heart. These valves only open in one direction. They open and close due to pressure differences on either side of the valve
Graphs
Curve shifts left
Haemoglobin has a higher affinity for oxygen
At the same partial pressure of oxygen there is
Curve shifts left plus altitude
At altitude there is a lower partial pressure of oxygen in the atmosphere
So there will be a lower partial pressure of oxygen in the lungs
Haemoglobin has a
higher affinity
for oxygen
At the same
partial pressure of oxygen
there is a greater percentage saturation of haemoglobin
This means that more oxygen can be transported / carried to respiring tissues
Curve shifts right
There is an increased rate of
respiration
This
produces more CO2
The curve shifts to the
right
(Bohr shift)
This causes haemoglobin to have a
lower affinity
for oxygen
At the same
partial pressure of oxygen
there is a
lower percentage saturation of haemoglobin
with oxygen
So
more
oxygen is unloaded / dissociates
more readily
at respiring tissues
The cardiac cycle
This is the sequence of events that leads to the filling and emptying of the heart i.e the events of 1 complete heart beat
The sequence of events which allows the heart to fill with blood. The blood is then pumped into the arteries
