Mass Transport in Animals

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Transport of oxygen by haemoglobin:
blood is a tissue and consists of a fluid called plasma in which red blood cells, white blood cells and platelets are suspended
platelets are small fragments of cells involved in clotting at the site of a wound. They have no nucleus
red blood cells contain haemoglobin, which loads oxygen in the lungs, transports it around the body, and unloads it at respiring tissues. Red blood cells do not live long (120 days)
Structure of a red blood cell:
red blood cells are very small. This means there's a short diffusion pathway for oxygen to reach the haemoglobin inside. They also have a large SA:VOL
red blood cells are shaped like a biconcave disc. This further increases the SA:VOL and provides a shorter diffusion pathway
red blood cells lack a nucleus. This adaptation allows red blood cells to carry as much haemoglobin, and therefore as much oxygen, as possible
Haemoglobin's affinity;
Haemoglobin is the blood pigment found throughout the animal kingdom; this pigment has a high affinity for $O_2$ and readily loads $O_2$ where there is a high partial pressure of $O_2$ (p $O_2$ ), i.e in the lungs, and unloads (or dissociates from) $O_2$ where the p $O_2$ is low. i.e at respiring tissues
Affinity;
the tendency a molecule has to bind with oxygen (condition-dependent)
haemoglobin with a high affinity for oxygen loads oxygen easily but unloads it less easily
haemoglobin with a low affinity for oxygen loads oxygen less easily but unloads it easily
Haemoglobin;
haemoglobin is a quaternary protein; four polypeptides are linked together (2 alpha, 2 beta), with each polypeptide associating with a haem group, which contains a ferrous (Fe $^{2+}$ ) ion. Each Fe $^{2+}$ ion can combine with a single oxygen molecule ( $O_2$ ), making a maximum of 4 $O_2$ molecules per haemoglobin
Haemoglobin;
haemoglobin is a quaternary protein; four polypeptides are linked together (2 alpha, 2 beta), with each polypeptide associating with a haem group, which contains a ferrous (Fe $^{2+}$ ) ion. Each Fe $^{2+}$ ion can combine with a single oxygen molecule ( $O_2$ ), making a maximum of 4 $O_2$ molecules per haemoglobin
Oxyhaemoglobin:
when haemoglobin is bound to oxygen it is known as oxyhaemoglobin
the amount of oxygen carried by haemoglobin can be referred to as a percentage of the maximum that can be carried - this is known as the percentage saturation
Oxygen dissociation curve:
the curve is a sigmoidal (S) shape. The graph starts off with a gradual slope as haemoglobin finds it hard to bind to the first oxygen
once the first $O_2$ binds to the haem group, it changes the tertiary structure of the haemoglobin and increases the affinity of the other haem groups to bind more oxygen, the slope therefore rises sharply
Oxygen dissociation curve:
the situation change after the binding of the third molecule. With most of the binding sites occupied, it is less likely that a single $O_2$ molecule will find an empty site to bind to
the gradient of the curve reduces, and the graph flattens off
Oxygen dissociation curves:
there are different types of haemoglobin molecules in different species. In addition, the shape of any one type of haemoglobin molecule can change under different conditions
therefore, there are many different $O_2$ dissociation curves with a roughly similar shape but differ in their position on the axes
Oxygen dissociation curves:
the many different $O_2$ dissociation curves are better understood if two facts are kept in mind;
the further to the left the curve, the greater the affinity of haemoglobin for $O_2$ (so it loads $O_2$ readily)
the further to the right the curve, the lower the affinity of haemoglobin for $O_2$ (so it unloads $O_2$ more readily)
Process of loading and unloading:
high $O_2$ concentration $\rightarrow$ high partial pressure $\rightarrow$ high affinity $\rightarrow$ oxygen loads (associates)
low $O_2$ concentration $\rightarrow$ low partial pressure $\rightarrow$ low affinity $\rightarrow$ oxygen unloads (dissociates)
The Bohr shift:
haemoglobin has a reduced affinity for $O_2$ in the presence of $CO_2$ . The greater the p $CO_2$ , the more readily the haemoglobin releases it's $O_2$ (the Bohr effect)
at respiring tissues, p $O_2$ is low and p $CO_2$ is high. The affinity of haemoglobin for $O_2$ is reduced so it can be readily unloaded into the muscles cells
The Bohr shift:
the increased p $CO_2$ shifts the oxygen dissociation curve to the right. This is because the dissolved carbon dioxide is acidic in solution (carbonic acid is formed in blood), and the low pH causes haemoglobin to change shape and release its $O_2$ into the respiring tissues
Different forms of haemoglobin (low affinity):
dissociation curves that move to the right, indicates that the affinity of the haemoglobin for $O_2$ has decreased, therefore, unloading or delivery of $O_2$ to the tissues is increased
this is usually seen in animals with high metabolic rates (small SA:VOL or active animals), which therefore have high rates of respiration and require more unloading of oxygen
Different forms of haemoglobin (high affinity):
dissociation curves that move to the left indicate affinity of the haemoglobin for $O_2$ is increased, therefore loading of $O_2$ is increased
this is usually seen in animals living in environments with low $O_2$ (high altitudes or underground) so it can load as much $O_2$ as possible from the environment
it is also seen in foetal haemoglobin, the foetal haemoglobin will have a higher affinity than the mother's haemoglobin, so oxygen unloads from the mother's haemoglobin and loads onto the baby's haemoglobin
High affinity haemoglobin:
usually organisms that live in low $O_2$ environments
haemoglobin loads $O_2$ more readily (in lungs)
curve shifts to the left
haemoglobin is more saturated at any given p $O_2$
Low affinity haemoglobin:
usually organisms that have a high metabolic rare
haemoglobin unloads $O_2$ more readily (at tissues for respiration)
curve shifts to the right
haemoglobin is less saturated at any given p $O_2$
The circulatory system:
mammals have 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 is passed through the lungs, its pressure is reduced. If it were to pass immediately to the rest of 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
The human heart:
the heart is made of cardiac muscle and acts as two separate pumps, one on either side
the one in the right is the pulmonary circulation and pumps deoxygenated blood coming from the body to the lungs
the one on the left is the systemic circulation and pumps oxygenated blood coming from the lungs to the rest of the body
Structure of the heart:
each pump has two chambers (therefore the heart has 4 in total)
the atrium is thin-walled and elastic and stretches as it collects blood
the ventricle has a much thicker muscular wall as it must contract strongly to pump blood some distance, either to the lungs or to the rest of the body
The flow of blood throughout the heart:
blood from the vena cava (bringing deoxygenated blood back from around the body) flows into the right atrium, while blood from the pulmonary veins (brining oxygenated blood back from the lungs) flows into the left atrium
when the atria contract blood passes through atrioventricular valves into thicker walled lower chambers called ventricles. When the ventricles contract, blood passes up through the open semi-lunar valves into major arteries
The flow of blood through the heart:
blood from the right side passes into the pulmonary artery and carries deoxygenated blood onto the lungs
blood from the left side passes into the aorta and carries oxygenated blood to the rest of the body
Contraction of the heart:
both atria contract together and then both ventricles contract together, pumping the same volume of blood
because the right ventricle only pumps blood to the lungs, it has a thinner muscular wall than the left ventricle
the left ventricle, in contrast has a thicker muscular wall, enabling it to contract with more force to create enough pressure to pump blood to the rest of the body
Heart valves:
heart valves only open one way, which prevents the backflow of blood and therefore they ensure blood always flows in one direction. Heart valves only open when the pressure behind them is higher than the pressure in front. If the pressure in front is higher, they will remain shut
increased pressure in the chambers of the heart is either caused by the chambers contracting (making the chamber smaller) or blood filling the chamber
only one set of valves in the heart is open at any one time
Myocardial infarction:
the heart itself needs a blood supply. The coronary arteries branch off the aorta to supply the heart muscle with oxygen and glucose and remove waste products
if they become blocked it is known as myocardial infarction (also known as a heart attack)
this is because an area of the heart is deprived of oxygen, meaning the muscle cannot respire (aerobically) and therefore it dies
The cardiac cycle:
one complete sequence of contraction and relaxation (a heartbeat) is called a cardiac cycle
it consists of;
atrial systole (contraction of the atrial muscle)
ventricular systole (contraction of the ventricular muscle)
cardiac diastole (relaxation of the heart muscle)
Atrial systole:
atria contract, ventricles relax
decreases the volume in the atria, increasing the pressure, pushing blood through into the ventricles
AV valves are open as pressure in the atria is higher than pressure in the ventricle
as ventricles receive the blood from the atria there is a slight increase in pressure in the ventricles
Ventricular systole:
atria relax, ventricles contract
ventricular volume decreases and therefore the pressure increases
pressure is now higher in the ventricles than the atria so AV valves shut to prevent backflow
pressure in the ventricles is higher than the pressure in the aorta and pulmonary artery, forcing the SL valves open
blood moves out into the arteries
Cardiac diastole:
ventricles and atria both relax
pressure is now higher in the pulmonary artery and aorta than in the ventricles so the SL valves shut
atria begin to passively fill with blood due to higher pressure in the pulmonary vein and vena cava, so pressure in the atria starts to increase slightly
pressure in the atria is now higher than pressure in the ventricles so AV valves pen, allowing some blood to passively flow through into ventricles
Control of the heartbeat:
cardiac muscle is myogenic; its contractions arise from within the cardiac muscle itself, and not from nervous stimulation from the brain (although this is required to alter the heart rate)
within the wall of the right atrium is the sinoatrial node (SAN). It is like a pacemaker; it sets the rhythm of the heartbeat by sending out regular waves on electrical activity into the walls of the atria. This causes the left and right atria to contract at the same time
Control of the heartbeat:
the waves of electrical activity do not pass directly down from the atria to the ventricles due to a band of non-conducting collagen separating them
the waves of electrical activity transfer instead to the atrioventricular node (AVN)
the AVN then passes the wave of electrical activity down the septum of the heart to the apex through a collection of fibres called the bundles of His. There is a slight delay before the AVN transfers this, allowing the atria to fully empty before the ventricles begin to contract
the bundle of His then splits into finer fibres called Purkinje fibres, which carry the wave of electrical activity into the ventricular muscle walls, causing them to contract simultaneously from the bottom up
Cardiac output:
when the ventricles of the heart contract, a surge of blood flows into the aorta and the pulmonary arteries under pressure. The surge of blood stretches the arteries, which contain elastic tissue in their walls
the stretch and subsequent recoil of the arteries travels as a wave known as a pulse. The pulse rate is identical to the heart rate. This is measured in beats per minute
stroke volume is the volume of blood pumped out from one ventricle during each contraction
cardiac output is the total volume pumped out from one ventricle per minute
cardiac output (cm $^3$ min $^{-1}$ ) = stroke volume (cm $^3$ ) x heart rate (bpm)
1dm $^3$ = 1000cm $^3$
Cardiac output:
the resting heart rate of an individual can vary greatly, although we all need to produce roughly the same cardiac output
if a person does a lot of aerobic work their resting pulse rate of drops to 60 bpm or lower
therefore, the stroke volume increases
this is because as the heart gets used to regular exercise, it gets bigger and has stronger contractions
Heart disease:
heart disease kills more people in the UK than any other disease. Almost half of heart disease deaths are from coronary heart disease (CHD)
in CHD layers of fatty material (atheroma) build up inside the coronary arteries that supply the heart muscle with blood
this narrows them and reduces the flow of blood through them, resulting in a lack of oxygen for the heart muscle
an atheroma can lead to an aneurysm (a balloon-like swelling of the artery), thrombosis (a blood clot) or myocardial infarction (a heart attack)
Risk factors of heart disease:
a risk factor is any factor that increases the probability of developing a disease. They are correlational with a disease but not necessarily casual. There are several risk factors for heart disease;
inheritance/genetics
gender
increasing age
smoking
diet
high blood pressure
The blood vessels:
a blood vessel is a tube with a space in the centre called the lumen where the blood flow goes. This is surrounded by smooth endothelium which reduced friction to maintain blood pressure
arteries called blood away from the heart and into arterioles
arterioles are smaller arteries that control blood flow from arteries to capillaries
capillaries are tiny vessels that link arterioles to veins
veins carry blood from capillaries back to the heart. Small veins are called venules
arteries, arterioles and veins all have the same basic layered structure (endothelium, elastic and muscle tissue). What different between each blood vessel is relative to the proportions of each layer. Arteries and veins are examples of organs as they are a collection of different tissues which work together
Specific blood vessels:
the heart - vena cava and pulmonary vein enter the heart and aorta and pulmonary artery leave the heart. The heart also has the coronary artery
the lungs - the pulmonary artery enters the lung and the pulmonary vein leaves the lung
the kidneys - the renal artery enters the kidneys and the renal vein leaves the kidneys
Arteries:
these carry blood at high pressure, travelling fast, and pulsing - that is, the pressure fluctuates with the heartbeat
thick muscle layer - smaller arteries can be constricted and dilated to control the volume of the blood passing through them
thick elastic layer - the elastic wall is stretched at each beat of the heart and then can recoil when the heart relaxes. This helps to maintain high pressure and smooth pressure surges created by the contraction of the ventricles
Arteries:
large overall thickness of the wall - withstands high pressure and prevents bursting
there are no valves (except in the arteries leaving the heart) because blood is constant high pressure due to the heart pumping blood unto the arteries
relatively narrow lumen - maintains high pressure
inner endothelium folded - allows artery to stretch to maintain high pressure