Mass transport in animals Flashcards
What are the haemoglobin molecules?
A group of chemically similar molecules found in a variety of organisms.
They are protein molecules with a quaternary structure that has evolved to make it efficient at loading oxygen under one set of conditions but unloading it under a different set of conditions.
What is the structure of haemoglobin?
Primary - sequence of amino acids in the four polypeptide chains.
Secondary - each polypeptide chain is coiled into a helix.
Tertiary - each chain is folded into a precise shape, an important factor in its ability to carry oxygen.
What is the quaternary structure of haemoglobin?
All 4 chains are linked together to form an almost spherical molecule.
Each polypeptide is associated with a haem group - which contains a ferrous ion.
Each Fe^2+ ion can combine with a single oxygen molecule, making a total of 4 oxygen molecules that can be carried by a single haemoglobin molecule in humans.
What is loading and unloading?
Or associating, the process by which haemoglobin binds to oxygen. In humans this takes place in the lungs.
Unloading or dissociating is the process by which haemoglobin releases its oxygen. This takes place in the tissues.
Haemoglobins with a high affinity for oxygen take up oxygen more easily, but release it less easily.
What is the role of haemoglobin?
To transport oxygen, to be efficient at this haemoglobin must:
Readily associate with oxygen at the surface where gas exchange takes place.
Readily dissociate with oxygen at those tissues requiring it.
It achieves this because its shape changes in the presence of certain substances, such as carbon dioxide.
In the presence of CO2, the new shape of haemoglobin molecule binds more loosely to oxygen, and releases it.
Why do different haemoglobins have different affinities for oxygen?
Each species produces a haemoglobin with a slightly different amino acid sequence.
Each species one therefore has a slightly different tertiary and quaternary structure and hence different oxygen binding properties.
Ranging from high affinity to low affinity for oxygen.
Why do large organisms have a transport system?
Surface area to volume ratio decreases to a point where the needs of the organism cannot be met by the body surface alone.
Specialist exchange surfaces are therefore required to absorb nutrients and respiratory gases, and remove excretory products.
A transport system is required to take materials from cells to exchange surfaces and vice versa.
As organisms have evolved into larger and more complex structures, tissues have become more specialised and dependent upon one another.
What does the transport system depend on?
The lower the surface area to volume ratio is, and the more active the organism, the greater is the need for a specialised transport system with a pump.
What are the features of transport systems?
A suitable medium in which to carry materials, e.g. blood, this is normally a liquid based on water because it readily dissolves substances and can be moved around easily, but can be a gas.
A form of mass transport in which the transport medium is moved around in bulk over large distances - more rapid than diffusion.
A closed system of tubular vessels that contains the transport medium and forms a branching network to distribute it to all parts of the organism.
A mechanism for moving the transport medium within vessels. This requires a pressure difference between one part and another.
How are the features of the transport systems achieved?
Animals use muscular contraction either of the body muscles or of a specialised pumping organ, e.g. heart.
Plants rely on natural, passive processes such as the evaporation of water.
A mechanism to maintain the mass flow movement in one direction - e.g. valves.
A means of controlling the flow of the medium to suit the changing needs of different parts of the organism.
A mechanism for the mass flow of water or gases, e.g. intercostal muscles and diaphragm during breathing.
What is the circulatory system in mammals?
A closed, double circulatory system in which blood is confined to vessels and passes twice through the heart for each complete circuit of the body.
This is because, when blood passed through the lungs, its pressure is reduced. If it were to pass immediately to the body its low pressure would make circulation very slow.
Blood is therefore returned to the heart to boost its pressure before being circulated to the rest of the tissues.
Substances are delivered quickly, which is necessary as mammals have a high body temperature and hence high rate of metabolism.
What is the arrangement of main arteries and veins in mammals?
Oxygenated blood leaves the lungs, goes into the left atrium then ventricle and out the aorta.
It goes to the liver, the stomach and intestines, which joins to the liver, the kidneys through the renal artery, and the lower/hind limbs.
It then becomes deoxygenated, and leaves through veins, with the renal vein from the kidneys.
From the aorta, oxygenated blood goes to the fore limbs and head and neck, then becomes deoxygenated, and joins the vena cava.
It enters the right atrium through the vena cava and into the right ventricle, then to the lungs where it becomes oxygenated again.
What is the structure of the human heart?
It is two separate pumps, lying side by side.
The pump on the left deals with oxygenated blood from the lungs, while the right deals with deoxygenated blood from the body.
Why does the heart need two separate pumps?
Blood has to pass through tiny capillaries in the lungs in order to present a large surface area for the exchange of gases.
In doing so, there is a very large drop in pressure and so the blood flow to the rest of the body would be very slow.
Mammals therefore have a system in which the blood is returned to the heart to increase its pressure before it is distributed to the rest of the body.
It is essential to keep the oxygenated blood in the pump on the left side separate from the deoxygenated blood in the pump on the right.
What are the atrium and ventricle?
The atrium is thin-walled and elastic and stretches as it collects blood.
It receives blood from the veins.
The ventricle has a much thicker muscular wall as it has to contract strongly to pump blood some distance, either to the lungs or to the rest of the body.
They pump blood away from the heart and into the arteries.
How do the ventricles work together?
The right ventricle pumps blood only to the lungs, and it has a thinner muscular wall than the left ventricle.
The left ventricle has a thick muscular wall, enabling it to contract to create enough pressure to pump blood to the rest of the body.
While they are separate, and after birth, there is no mixing of the blood in each of them, they pump in time with each other.
Both atria contract together and then both ventricles, pumping the same volume of blood.
What are the valves between the ventricles and atrium?
They prevent backflow of blood into the atria when the ventricles contract.
The left atrioventricular (bicuspid) valve.
The right atrioventricular (tricuspid) valve.
What are the pulmonary vessels?
Aorta - connected to the left ventricle and carries oxygenated blood to all parts of the body except the lungs.
The vena cava is connected to the right atrium and brings deoxygenated blood back from the tissues.
The pulmonary artery is connected to the right ventricle and carries deoxygenated blood to the lungs, where its oxygen is replenished and its carbon dioxide removed.
The pulmonary vein is connected to the left atrium and brings oxygenated blood back from the lungs.
What are the coronary arteries?
They supply the heart muscle with blood, which branch off the aorta shortly after it leaves the heart.
Blockage of these arteries, leads to myocardial infarction, or heart attack, because an area of the heart muscle is deprived of blood and therefore oxygen.
The muscle cells in this region are unable to respire and so die.
What is the cardiac cycle?
The heart undergoes a sequence of events that is repeated about 70 times each minute at rest.
There are two phases - contraction (systole) and relaxation (diastole).
What is relaxation of the heart?
Blood returns to the atria through the pulmonary vein and the vena cava.
As the atria fill, the pressure in them rises.
When this pressure exceeds that in the ventricles, the atrioventricular valves open, allowing the blood to pass into the ventricles.
The passage of blood is aided by gravity.
The muscular walls of the atria and ventricles are relaxed, which causes them to recoil and reduces the pressure within the ventricles.
This causes the pressure to be lower than that in the aorta and the pulmonary artery, and so the semi-lunar vales in the aorta and pulmonary artery close.
What is the contraction of the atria (atrial systole)?
The contraction of the atrial walls, along with the recoil of the relaxed ventricle walls, forces the remaining blood into the ventricles from the atria.
Throughout this stage the muscle of the ventricle walls remains relaxed.
The semi lunar valves stay closed and the atrioventricular valves open.
What is the contraction of the ventricles (ventricular systole)?
After a short delay to allow the ventricles to fill with blood, their walls contract simultaneously.
This increases the blood pressure within them, forcing shut the atrioventricular valves and preventing backflow of blood into the atria.
The pressure in the ventricles rises further, once it exceeds that in the aorta and pulmonary artery, blood is forced from the ventricles into these vessels.
What are the atrioventricular valves?
Between the left atrium and ventricle and the right atrium and ventricle.
These prevent backflow of blood when contraction of the ventricle means that ventricular pressure exceeds atrial pressure.
Closure of these valves ensures that, when the ventricles contract, blood within them moves to the aorta and pulmonary artery rather than back to the atria.
What are the semi-lunar valves?
In the aorta and pulmonary artery.
These prevent backflow of blood into the ventricles when the pressure in these vessels exceeds that in the ventricles.
This arises when the elastic walls of the vessels recoil increasing the pressure within them and when the ventricle walls relax reducing the pressure within the ventricles.
What are pocket valves?
In veins that occur throughout the venous system.
These ensure that when the veins are squeezed, e.g. when skeletal muscles contract, blood flows back towards the heart rather than away from it.
