Adaptations For Transport In Animals Flashcards
Transport systems in animals have the following features:
A suitable medium in which to carry materials
A pump, such as the heart, for moving the blood
Valves to maintain the flow in one direction
Explain open circulatory systems
The blood does not move around the body in blood vessels but if bathes the tissues directly while held in a cavity
Explain closed circulatory systems
The blood moves in blood vessels. There are two types:
- in a single circulation, the blood moves through the heart once in its passage around the body
- in a double circulation, the blood passes the heart twice In its circuit around the body.blood is pumped by a muscular heart, organs are not in direct contact with the blood
What are the three types of blood vessels?
Arteries
Veins
Capillaries
Describe structure of arteries and veins?
The innermost layer is the endothelium, which is one cell thick surrounded by the tunica intima. It is smooth lining, reducing friction
The middle layer, the tunica intima, contains elastic fibres and smooth muscle. It is thicker in arteries than in veins. In arteries, the elastic fibres allow stretching to accommodate changes in blood flow and pressure as blood is pumped from the heart. At a certain point, stretched elastic fibres recoil, pushing blood though the artery. This maintains blood pressure, the contraction of the smooth muscle regulates blood flow and maintains blood pressure as the blood is transported further from the heart.
The outer layer, the tunic externa, contains collagen fibres, which resist over stretching.
Explain arteries
They carry blood from the heart
Their thick, muscular walls withstand the bloods high pressure, derived from the heart.
They branch into smaller vessels called arteriolar, that further subdivide into capillaries
Explain capillaries
Form a vast network that penetrates all the tissues and organs of the body.
Blood from the capillaries collects into venules, which take blood into veins, which return it to the heart
Explain veins
They have a larger diameter lumen and thinner walls with less muscle than arteries. Consequently the blood pressure and flow rate are lower.
For veins above the heart, blood returns to the heart by gravity. It moves through other veins by the pressure from surrounding muscles.
Veins have semi-lunar valves along their length ensuring flow in one direction and preventing back flow, these are not present in arteries other than at the base of the aorta and pulmonary artery,
Describe structure of capillaries
Have thin walls which are only one ,Ayer of endothelium in a basement membrane.
Pores between the cells make the capillary walls permeable to water and salutes, such as glucose, so exchange of materials between the blood and the tissues takes place
Capillaries have a small diameter and the rate of blood flow slows down. There are so many capillaries in a capillary bed reducing the rate of blood flow, that there is plenty of time for the exchange of materials with the surrounding tissue fluid
Describe the heart
A pump to circulate blood is essential for a circulatory system
There are two relatively thin walled collection chambers, the atria, which are above two thicker walked pumping chambers, the ventricles, allowing the complete separation of oxygenated and deoxygenated blood.
The heart consists largely of cardiac muscle, a specialised tissue with myogenic contraction. This means it can contract and relax rhythmically, of its own accord, in life the heart rate is modified by nervous and hormonal stimulation
What is the cardiac cycle
It describes the sequence of events of one heartbeat, which lasts about 0.8 seconds.
The action of the heart consists of alternations contractions (systole) and relaxations (diastole)
It has three stages:
Atrial systole
Ventricular systole
Diastole
Explain atrial systole
The atrium walls contract and the blood pressure in the atria increases. This pushes the blood through the tricuspid and bicuspid valves into the ventricles, which are relaxed
Explain ventricular systole
The ventricle walls contract and increase the blood pressure into the ventricles. This forces blood up through the semi-lunar valves, out of the heart, into the pulmonary artery and the aorta. The blood cannot flow back from the ventricles into the atria because the tricuspid and bicuspid valves are closed by the rise in ventricular pressure. The pulmonary artery carries deoxygenated blood to the lungs and the aorta carries oxygenated blood to the rest of the body
Explain diastole
The ventricles relax. The volume of the ventricles increases and so pressure in the ventricles falls. This risks the blood in the PA and aorta flowing backwards into the ventricles, that tendency causes the semi-lunar valves at their bases to shut, preventing blood re-entering the ventricles
The atria also relax during diastole, so blood from e vena Cavae and pulmonary veins enter the atria and the cycle starts again
Flow of blood through left side of heart:
The left atrium relaxes and received oxygenated blood from the pulmonary vein
When full, the pressure forced open the bicuspid valve between the atrium and ventricle
Relaxation of the left ventricle draws blood from the left atrium
The left atrium contracts, pushing the remaining blood into the left ventricle, through the valve
With the left atrium relaxed and with the bicuspid valve closed, the left ventricle contracts. It’s strong muscular wall exerts high pressure
This pressure pushes blood up out of the heart, through the semi-lunar valves into that aorta and closes the bicuspid valve, preventing back flow of blood into the left atrium
Briefly explain the heart and the cardiac cycle
The two sides of the heart work together, the atria contract at the same time, followed milliseconds later by the ventricles contracting together. A complete contraction and relaxation of the whole heart is called a heartbeat
When a chamber of the heart contacts, it is emptied of blood. When it relaxes it fills with blood again
Atria walls have little muscle as the blood only has to go to the ventricles. Ventricle walls contain more muscle and generate more pressure, as they have to send the blood furthermore either to the lungs or rest of the body
The left ventricle has a thicker muscular wall than the right ventricle as it has to pump the blood all round the body, whereas the right ventricle has only to pump the blood a short distance to the lungs
Describe the valves
Prevent back flow of blood
The atrio-ventricular valves (bicuspid and tricuspid), semi-lunar valves at the base of the aorta and PA and semi lunar valves in veins all operate by closing under high pressure, preventing blood flowing backwards
How is the heartbeat controlled
Contraction of cardiac muscle is myogenic. The wall of the right atrium has a cluster of specialised cardiac cells, called the sino-atrial node (SAN) that acts as a pacemaker
A wave of electrical stimulation arises at the SAN and spreads over both atria, so they contract together
The ventricles are insulated from the atria by a thin layer of connective tissue, except at another specialised cluster of cardiac cells, the atrio-ventricular mode (AVN). So the electrical stimulation only spreads to the ventricles at this point, the AVN introduces a delay in the transmission of the electrical impulse, the muscles of the ventricles do not start to contract until the muscles of the atria have finished contracting.
The AVN passes the excitation down the nerves of the bundle of His , the left and right bundle branches and to the apex of the heart. The excitation is transmitted to Purkinje fibres in the ventricle walls, which carry it upwards through the muscles of the ventricle walls
The Impulses cause the cardiac muscle in each ventricle to contract simultaneously, from the apex upwards
This pushes the blood up to the aorta and Pa and empties the ventricles completely
What is an electrocardiogram? (ECG)
A trace of the voltage changed produced by the heart, detected by electrodes on the skin,
What happens at each wave of the ECG.
The P wave is the first part of the trace and shows the voltage change generated by the sino-atrial node, associated with the contraction of the atria. The atria have less muscle than the ventricles so P waves are small
The time between the start of the p wave and the start of the QRS complex is the PR interval. It is the time taken for the excitation to spread from the atria to the ventricles, through atrio-ventricular node
The QRS complex shows the depolarisations d contraction of the ventricles. Ventricles have more muscle than the atria and so the amplitude is bigger than that of the p wave
The t wave shows the depolarisation of the ventricle muscles. The ST segment lasts from the end of the S wave to the beginning of the T wave
The line between the t wave and p wave of the next cycle is the baseline of the trace and is called the isoelectric line.
4 other variations of ECG
A person with atrial fibrillation has a rapid heart rate and may lack a p wave
A person who has had a heart attack may have a wide qrs complex
A person with enlarged ventricle walks may have a qrs complex showing greater voltage change
Changes in the height of the St segment and t wave may be related to insufficient blood being delivered to the Heart muscle, such as happens in patients with blocked coronary arteries and atherosclerosis
Pressure changes in blood vessels
The blood pressure is highest in the aorta and large arteries. It rises and falls rhythmically with ventricular contraction
Friction between the blood and vessel walls and the large total surface area causes a progressive drop in pressure in arterioles, despite their narrow lumen, although their blood pressure also depends on whether they are dilated or constricted
The extensive capillary beds further reduce blood pressure as fluid leaks from the capillaries to the tissues
In arteries and capillaries the higher the blood pressure the faster the blood flows so both pressure and speed fall as the distance from the heart increases
Veins are not subject to pressure changes derived from the contraction of the ventricles do their blood pressure is low
Veins have a large diaper lumen so blood flows faster than in capillaries despite the lower pressure
Blood does not return to the heart rhythmically. It’s return is enhanced by the massaging effect of muscles around the veins
What is blood made up of
Cells 45%
In a solution called plasma 55%
Describe plasma
Pale yellow liquid
90% water containing glucose, amino acids, vitamins, mineral ions, urea, hormones, plasma proteins
Explain the transport of oxygen
To transport it efficiently, haemoglobin must associate readily with oxygen where gas exchange takes place, at the alveoli, and readily dissociate from oxygen at the respiring tissues, the muscles. Haemoglobin does this by changing its affinity for oxygen because it changes its shape
Each haemoglobin molecule contains four haem groups, each haem contains an ion of iron. One oxygen molecule can bind to each iron ion, so four oxygen molecules can bind to each haemoglobin Molecule. The first oxygen molecule that attaches changes the shape of the haemoglobin molecule, making it easier for the second molecule to attach. The second oxygen molecule attaching changes the shape again, making it easier for the third molecule to attach. This is cooperative binding and it allows haemoglobin to pick up oxygen very rapidly in the lungs, the third oxygen molecule does not induce a shape change, so it takes a large increase in oxygen partial pressure to bind the fourth oxygen molecule
The partial pressure of a gas is the pressure it would exert if it were the only one present. Cooperative binding means that haemoglobin exposed to increasing partial pressures of oxygen shows a sigmoid curve, at very low oxygen partial pressure it is difficult for haemoglobin to load oxygen but the steep part of the graph shows oxygen binding increasingly easily. At high partial pressures of oxygen, the percentage saturation of oxygen is high
Oxygen dissociation sigmoid curve shows:
The oxygen affinity of haemoglobin is high at high partial pressure of oxygen and oxyhemoglobin does not release its oxygen
Oxygen affinity reduced as the partial pressure of oxygen decreases and oxygen is readily released, meeting respiratory demands. The graph shows that a very small decrease in the oxygen partial pressure leads to a lot of oxygen dissociating from haemoglobin
Relationship between oxygen partial pressure and % saturation of haemoglobin with oxygen of graph were linear
At higher partial pressure of oxygen, haemoglobins oxygen affinity would be too low. And so oxygen with be readily released and would not reach the respiring tissues
At lower partial pressure of oxygen, haemoglobins oxygen affinity would be too high and oxygen would not be released in respiring tissues, even at low oxygen partial pressures
Analysis of graph or oxygen dissociation curve for adult human haemoglobin
Red blood cells load oxygen in the lungs where the oxygen partial pressure is high and the haemoglobin becomes saturated with oxygen, the cells carry the oxygen, as oxyhemoglobin, to respiring tissues, such as muscle. There, the partial pressure of oxygen is low because oxygen is being used up in respiration. Oxyhemoglobin then unloads its oxygen, that is, it dissociates
The dissociation curve of fatal haemoglobin
The haemoglobin in the blood of a fetus must absorb oxygen from the maternal haemoglobin at the placenta. The fetus has haemoglobin that differs in two of the four polypeptide chains from the haemoglobin of the adult. This gives fetal haemoglobin a higher affinity for oxygen than the mothers, at the same partial pressure of oxygen. Their blood flows very close in the placenta, so oxygen transfers to the fetus’ blood and at any partial pressure of oxygen, the percentage saturation of the fetus’ blood is higher than the mothers
This moves the whole dissociation curve to the left
Transport of oxygen in other animals
Lugworm
Lives under sand, low oxygen environment
Has a low metabolic rate
It’s haemoglobin has a dissociation curve that is to the right of a human meaning it’s haemoglobin loads oxygen readily but only releases it when the partial pressure is very low
Llama
Increase in altitude, oxygen partial pressure Im atmosphere decreases
Dissociation curve to left of humans
It’s haemoglobin has a higher affinity for oxygen at all oxygen partial pressures, so loads oxygen more readily in the lungs and releases oxygen when the oxygen partial pressure is low, in its respiring tissues
Effects of co2
If the co2 concentration increase em haemoglobin releases oxygen more readily. At any oxygen partial pressure, the haemoglobin is less saturated with oxygen, so the data points on the dissociation curve are all lower. This is described by saying the curve moves to the right.
The shift in the graphs position is called the Bohr effect. It accounts for the unloading of oxygen from oxyhemoglobin in respiring tissues, where the partial pressure of carbon dioxide is high and oxygen is needed
Reactions in a red blood cell
Carbon dioxide in the blood diffuses into the red blood cell
Carbonic anhydrase catalysed the combination of carbon dioxide with water, making carbonic acid
Carbonic acid dissociates into H+ and HCO3- ions
HCO3- ions diffuse out of the red blood cell into the plasma.
To balance the outflow of negative ions and maintain electrochemical neutrality, chloride ions diffuse into the red blood cell from the plasma. This movement is called the chloride shift,
H+ ions cause oxyhemoglobin to dissociate into oxygen and haemoglobin, the H+ ions combine with haemoglobin to make haemoglobonic acid, HHb. This removes hydrogen ions and so the pH of the red blood cell does not fall
Oxygen diffuses out of the red blood cell into the tissues
What does the sequence of reactions in the blood cell explain
Why most carbon dioxide is carried in the plasma as HCO3- ions
The Bohr effect: more co2 produces more h+ ions so more oxygen is released from oxyhemoglobin. In other words, the higher the partial pressure of carbon dioxide, the lower the affinity of haemoglobin for oxygen
How carbon dioxide results in the delivery of oxygen to the respiring tissues, more respiration means more carbon dioxide is present so ,ore oxyhemoglobin dissociates and provides oxygen to the respiring cells
How are capillaries well adapted
Thin permeable walls
They provide a large surface area for exchange of materials
Blood flows very slowly through capillaries allowing time for exchange of materials
What is tissue fluid
The solution surrounding cells. It’s composition is similar to plasma but without proteins which stay in the capillaries
What is plasma
The liquid part of the blood. It is 55% blood and 90% water, it is the blood minus the blood corpuscles
What happens at arterial end
Hydrostatic pressure is greater than osmotic forces - fluid forced from the capillaries
Diffusion gradient for solutes (e.g. Oxygen, glucose etc) favours movement into the cells
Diffusion gradient for cell solutes (e.g. Carbon dioxide etc) favours movement from cells to tissue fluid
What happens at the venous end
Hydrostatic pressure is weaker than osmotic forces - fluid drawn back to capillaries
Some fluid also drains back into lymph, eventually draining back into a vein neat the heart via the thoracic duct
What does tissue fluid contain
Water Glucose Amino acids Fatty acids Glycerol Mineral salts Dissolved gases Vitamins
Tissue fluid is constantly…
Being produced at arterial end of capillary bed and re absorbed (some) at the venous end, some drains into lymphatic capillaries.
Excess tissue fluid enters the lymphatic system and is known as lymph
What is lymph
The solution inside lymph vessels, it’s composition is similar to tissue fluid, but with more fats (from digestive system)
