Download Unit 1.2.2 - Transport in Animals

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1.2.2. Transport in Animals
1.2.2 – Transport in Animals
So, we have covered a lot of material so far and there’s not thaaaaat much left. 2 pages
worth of syllabus and we are done…..for module 1! Anyhoo, one of the things we’ve looked
at is the way in which humans need a circulatory system to ensure that all cells receive the
oxygen they need for respiration. We did this by looking at surface area:volume ratio.
One of the reasons for us having lungs was to ensure that we could get oxygen to all the
cells (for respiration…). Some organisms don’t use lungs. They just have a single
circulatory system. This keeps a low blood pressure and as a general whole is used in fish.
The “gills” act as the lungs as this is where the oxygen is obtained.
A double circulatory system is when there are two separate systems: one pulmonary
circulation (for the lungs) and one systemic circulation (for the rest of the body).
Another way of distinguishing the circulatory systems is open and closed.
An open circulatory system is one in which the interstitial fluid and the blood are one in the
same (this fluid is known as haemolymph). All the organs are bathed in this liquid which
supplies them with both oxygen and nutrients. The fluid cannot move around much – but
movement is helped with muscle movements. Hemolymph is composed of water, inorganic
salts (mostly Na+, Cl-, K+, Mg2+, and Ca2+), and organic compounds (mostly
carbohydrates, proteins, and lipids). The primary oxygen transporter molecule is
hemocyanin.
A closed circulatory system is one in which the blood always remains within the vessels.
However, substances such as oxygen and nutrients do transfer across the blood vessel layers
and the interstitial fluid.
So let’s talk about the heart! ☺
-
-
The heart lies between the lungs – behind the sternum (the sternum is in the
centre of the chest. You can feel it very easily by lightly pressing the middle of
your chest)
the sternum protects the heart from damage in the thoracic cavity
Pericardium
consists of two membranes which surround the heart:
a) the inner one – attached to the heart
b) the outer one – attached to the surrounding tissue (e.g. diaphragm)
-
the pericardium holds the heart in position
it reduces friction between the heard and the surrounding tissue
it is non-elastic and so prevents the heart from over stretching
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pericarditis – inflamation of
the membrane: the heart no
longer functions properly
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1.2.2. Transport in Animals
Structure of the heart
What is the heart?? (apart from the thing that we give away to those we love:
awwww…)
complex pump
two pumps side by side
the right side pumps to lungs via the pulmonary artery
left side pumps to the head/body via the aorta
-
four chambered structure
made of cardiac muscle
o cardiac just means related to the heart
Atria
thin walled
receive blood from:
a) vena cava (coming back from the head and body: full of CO2)
b) pulmonary vein (coming back from the lungs: full of yummy
oxygen!)
Ventricles
thick walled
pumping chambers
left ventricle has a thicker muscular wall to create higher pressure to pump the
blood all the way round the head/body and back.
As the right side contains blood that has come back from the head and the body, it is
deoxygenated. The blood on the left side has just come back from the lungs. So it is
oxygenated. Therefore, mixing the two would be silly…and inefficient. There is therefore a
septum in between the two sides separating them.
One way flow needs to be ensured:
a) semi-lunar valves: valves in pulmonary artery and aorta
to stop the backflow of blood into the ventricles when they relax
b) atrio-ventricular valves – between the atria and the ventricle (tricuspid / bicuspid)
to prevent the backflow of blood into the atria when the ventricle
contracts
valve do not turn inside out as they are attached by non-elastic tendons
to muscle “bumps” on the inside wall of the ventricles.
c) Ventricles – muscular chambers
contract to create a “force” to pump blood to the lungs or head and body
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1.2.2. Transport in Animals
Differences
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the differences in the thickness between the atria and the ventricle walls
relate to their function.
The walls of the atria are thinner than the walls of the ventricles
The left ventricle is thicker than the right ventricle as the left ventricle
pumps blood to the head and the body whereas the right ventricle only
pumps blood to the lungs.
Coronary artery:
Immediately above the semi-lunar valve in the aorta is the entrance of the coronary artery
this supplies blood to the heart muscle itself
this branches over the surface of the heart muscle
deoxygenated blood is “collected” in the coronary vein which empties
directly into the right atrium (along with the rest of the blood from the
head and body)
Take a blank piece of paper and draw a reasonably big picture of the heart. Show the vessels
going to and away from it and label each part of the heart and each vessel.
Good…that should keep you occupied for a while! Muhahahaha.
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1.2.2. Transport in Animals
Lungs
Head
Pulmonary vein
Pulmonary artery
Right Atrium
Head
Left Atrium
aorta
Body
vena cava
Coronary artery going
back to the heart
Body
Tricuspid atrioventricular valve
Right ventricle
Left ventricle
Bicuspid atrioventricular valve
The heart has four chambers of equal volume.
2 Atria (left and right)
receiving chambers
thin walled
Right Atrium:
receiving vena cava (from
head and body)
blood rich in CO2, low in O2
Left Atrium:
receiving pulmonary vein
(from lungs)
rich in O2
2 Ventricles
pumping chambers
thick muscular walls to create high pressure
Right ventricle:
pumps blood to lungs via pulmonary vein
blood rich in CO2, low in O2
Left Ventricle:
pumps blood to the head and the body via the aorta
blood rich in O2
muscular wall much thicker than right ventricle as it has to pump the
blood around the whole body.
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1.2.2. Transport in Animals
Cardiac Cycle – 1 heart beat
a) deoxygenated blood enters the right atrium (from the vena cava)
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oxygenated blood enters the left atrium (from the pulmonary artery)
b) the resulting pressure forces open the tricuspid and bicuspid (mitral) valves and
blood flows from the atria into the ventricles.
these stages represent the DIASTOLIC phase
this is passive filling of the ventricles: no contraction of atria
c) when the diastolic phase ends, the two atria contract completely filling the ventricles
with blood.
this is the ATRIAL SYSTOLE (A.S.)
d) the ventricles then contract – ventricular systole (V.S.)
the tricuspid valve and mitral valves close to stop backflow into the atria
e) the blood is then forced simultaneously into the pulmonary artery and aorta
the semi-lunar valves prevent the backflow from the aorta and pulmonary
artery into the ventricles – unidirectional flow (valves closed)
f) the atria fill with blood again
the cycles continues
N.B. all the contraction in the cycle STARTS in the right atrium and spreads across the
heart muscle from he Sino-Atrial Node (SAN)
Thus the heart operates in two ways:
a) contraction phase – systole
b) relaxation phase – diastole
The heart muscle is myogenic:
it contracts without nerve stimulation
nerve impulses to the SAN merely modify the speed and the
strength of the contraction
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1.2.2. Transport in Animals
Initiation and propagation of contractions
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the sino atrial node is a natural pacemaker, which provides the basic rhythm
of the heart contractions / initiates / sends out the heart beat
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the heart muscle is myogenic / beats spontaneously / does not require nerve
impulse
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the rate of the beating is influenced / modified by nerve impulses to the SAN
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a wave of nerve impulses / electrical activity / excitation passes over the
atrium
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this triggers the contraction of the atria
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the electrical activity cannot pass to the ventricles because of fibrous tissue
between the atria and the ventricles
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when the electrical activity reaches the AVN (atrio ventricular node) at the
base of the atria, the AVN passes the nerve impulse along “the bundle of
His” to the base of the ventricles
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there is a (time) delay at the AVN (this allows the atria to fully contract and
empty)
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once the impulses have reached the base of the ventricles, the ventricles
contract from the base upwards via “Purkinje fibres”
SAN
AVN
fibrous tissue
bundle of His
Purkinje
fibres
Heartbeat
base
The pattern of the spread of excitory nerves through the heart ensures this.
(a)
the atria contract to force the blood down into the ventricles
(b)
the ventricles contract top force the blood up into the pulmonary artery and
aorta
Detection of excitation through the heart by electrodes attached to the skin of the chest are
displayed as an “electrocardiograph” (ECG trace)
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1.2.2. Transport in Animals
The above table shows the normal ECG tracing. There is:
a P wave
a QRS complex
a T wave
These are the main points and are clearly shown in the table above. In an abnormal ECG,
these waves will be changed in some manner. An ECG is very complicated and you are not
expected to be able to read one. Even doctors have trouble with this.
Blood Vessels
Having looked at the heart, we said that the heart acts as a pump. But in the end, all pumps
have to use piping to transfer the liquid from one place to another (come on…that analogy
must deserve a round of applause…). In the case of the human body, the heart is used to
pump blood to blood vessels. We have already looked at some of these and also why we
need them:
diffusion only is suitable for short distances (approx. 2mm)
so blood needs to flow very close to all tissues
Purely for my own entertainment, let’s have a look at GCSE stuff so we can reminisce to the
good old days. And of course you can enjoy yourselves by filling in the blanks (*awaits
cries of joy”)
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1.2.2. Transport in Animals
Order in which blood flows
Arteriole
(small artery)
Artery
Venule
(small vein)
Capillary
Vein
Heart
Capillary
Vein
Artery
elastic
tissue
elastic
tissue
1 cell thick
nucleus
lumen
lumen
muscle
layer
muscle
layer
. . . ..
..
.
. ..
red blood cell
(approximate scale)
Thick muscular wall
Highly elastic
Not permeable
Small Lumen
Thin muscular wall
Not very elastic
Not permeable
Large lumen
1 cell thick – no muscular wall
No elastic layer
Permeable – leaky
Lumen – 1 cell thick
Blood pressure dissipated – low
blood pressure
High blood pressure
Low blood pressure
Blood moving away from
heart
No valves (except aorta and
pulmonary artery)
High in oxygen – except
pulmonary artery
Blood moving towards
heart
Blood between arteries and veins
Valves present
No valves
Low in oxygen – except
pulmonary vein
Varied: gain in CO2 and loss of
oxygen due to tissues.
Small gaps in cells to allow
Deep in tissue for protection
Can be near surface
white cells out
OK, so those are the basics. If you remember, I have said that the basics of GCSE are the
foundation of a lot of AS level material.
Blood vessels
an organ may be defined as a structure consisting of several tissues forming a
complex function
-
blood vessels are organs whose function is the circulation of blood throughout
the body
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1.2.2. Transport in Animals
Arteries, arterioles and veins
Arteries close to the heart have a large cross sectional area and thick elastic
walls
-
They are stretched by the cardiac output (what the heart gives out…) when
the heart contracts
-
It then recoils as the arterial blood pressure drops when the heart relaxes
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The recoil assists circulation by smoothening the flow between beats
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The stretching and recoiling is felt as the pulse in places where the arteries
come close to the surface (e.g. wrist, neck)
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Further from the heart, the arteries branch into smaller arterioles
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These penetrate all tissues of the body
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They connect to beds of finely branched capillaries
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There are so many capillaries that someone could have about 25 000 – 60 000
miles of capillaries in them (so I’ve been told…)!!!
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But they are so thin that they force red blood cells to go through them one by
one: this increases the surface area for exposure to tissues (O2 and CO2
exchange)
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Plasma (without the proteins) can go through these thin walls to the tissues
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from these beds of vessels, venules join together to form veins
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these then take the blood back to the heart
o the last vessel on the way to the heart is called the vena cava
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the individual veins have a larger cross sectional area compared to arteries
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there are also more veins than arteries
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the walls of veins are thinner and less elastic
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there are many valves in the veins which stop back flow of blood: ensuring
one way flow back to the heart
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veins are compressed by the smallest movements – particularly skeletal
muscle surrounding it
-
these movements help to move the blood as the pressure in the veins is low
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1.2.2. Transport in Animals
Blood and body fluids
Have you ever cut yourself? Have you ever looked at the red stuff pouring our and thought,
“Hmm, I wonder what that is? What makes that up? Why did it stop coming out?” If so,
THIS is the lesson for you! (Oh, and also…next time, try actually doing something about the
fact that you’re bleeding – or better still don’t get suicidal thoughts and start cutting
yourself up in the first place!)
Blood is made up of two main parts: plasma and blood cells. There are many different cells
which are constituent parts of this and we will look into this in more detail soon.
Blood plasma
As we learnt from GCSE (yes yes, I LOVE bringing up GCSE material…that’s what makes
my day…) plasma is a watery solution containing many substances. It is the water that
carries the cells. What else does it do?
transports CO2
transports urea
transports hormones
transports heat
transports clotting factors
transports antibodies
As you can see, the plasma is used for transporting many materials. We will now look at the
blood cells.
Tissue Fluid (umm…no…not fluid that comes from your toilet roll…)
As cells become more differentiated and specialised, the less capable they are of surviving
independently. They are less able to protect themselves from toxic chemicals, pH changes
or extreme temperatures and, if fixed in position within a tissue, cannot seek food, ingest
solid bits of food or move away from their own toxic products. The substance that bathes
cells and performs these vital functions for them is called tissue fluid (or interstitial fluid
or intercellular fluid).
Do not confuse intercellular fluid and extracellular fluid (because that’s jus silly…I mean
they aren’t exactly spelt the same…???). Extracellular fluids are all fluids outside the cells
including blood plasma, tissue fluid, lymph and the aqueous humour of the eye. The term
intercellular fluid (or interstitial fluid) refers to tissue fluid only. Do not confuse either of
these terms with intracellular fluid - the fluid inside cells.
Capillary walls are lined by a very thin epithelium and its basement membrane of fine
connective tissue fibres. In places, called fenestrations, the cells are missing and only the
basement membrane is present. The basement membrane acts as a ‘molecular sieve’ preventing protein loss from blood. This can be seen in the kidney: if you remember, the
blood is filtered into the nephron due to the high blood pressure in the glomerulus…but
proteins should not go through (which of course you remember from last year *cough*).
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1.2.2. Transport in Animals
Basement
membrane
fenestrations
epithelium
Production and drainage
As we’ve mentioned, the pressure at the arterial end of the capillary is very high (also called
hydrostatic pressure). This FORCES water and dissolved substances out of the
fenestrations into the interstitial fluid. This is also happening by osmosis: the water potential
is higher in the capillary than in the interstitial fluid. However, as the fluid moves along the
capillary, it loses water (as it is moving out) and so at the venous end, the water potential is
lower in the capillary: therefore osmosis forces fluid INTO the capillary. This is called
reabsorption. There are also other forces that force fluid into the capillary (e.g. oncotic
pressure).
Lymph is the fluid that is formed as the interstitial fluid enters the lymph vessels by
filtration. The lymph then travels to at least one lymph node before emptying ultimately into
the right or the left subclavian vein, where it mixes back with blood.
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1.2.2. Transport in Animals
Transport of oxygen and carbon dioxide
We already know how blood transports oxygen – we did this not only at GCSE but also
about 4 pages earlier…(3 pages to be exact….but that is about 4). So you WILL remember
and complete the following:
Red blood cells contain haemoglobin, which binds to oxygen so that it can be transported
around the body. Red blood cells are adapted to this function in many ways. I can’t be
bothered to write them all out, so I will refer back to page 4. But for jokes, the equation of
haemoglobin binding is………
Hb + 4O2
HbO8 (oxyhaemoglobin)
Carbon Dioxide
Carbon dioxide is a waste gas from metabolism. *Sighs*. We would ask you for the
equation, but seeing as you may get it wrong (and we don’t want to waste 10 minutes going
over the equation), we’ll just ASSUME you know it.
The carbon dioxide then needs to be taken to the lungs to be exhaled. It can be transported
in different ways. The main way is by converting it into bicarbonate ions:
CO2 + H2O → H2CO3 → H+ + HCO3Another way is to just have it dissolved in the plasma. There is one more way…*drum
roll*: carbon dioxide can bind to haemoglobin. However, carbon dioxide does NOT bind to
the same place as oxygen. But even though this is the case, by binding, it decreases the
amount of oxygen that the haemoglobin can take.
Looking at oxygen concentration at different concentrations of oxygen
-
a dissociation curve shows the percentage saturation of a sample of
haemoglobin in comparison to the partial pressure of oxygen at that point
the partial pressure of oxygen (abbreviated to “p(O2)”) shows the amount of
oxygen present
-
Take two points: A and B:
100
‘A’ shows the partial pressure of oxygen at the lungs
-
80
percentage
saturation
here, the haemoglobin is almost completely
saturated
60
‘B’ shows the partial pressure at a muscle
40
-
the muscle is respiring so it takes up oxygen
-
there will obviously be a lower partial
pressure of oxygen in a respiring tissue than in
the lungs – because a lot of the oxygen has
been given up to the tissue
20
B
A
partial pressure of oxygen
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S-Shape
-
1.2.2. Transport in Animals
you may also see that in the graph above, the shape of the curve is “S-shaped”
this is because each haemoglobin molecule can carry up to four oxygen
molecules:
o the first molecule of oxygen binds with some difficulty, but as it does, it
brings about a change in the shape of haemoglobin
o therefore, other oxygen molecules can bind on easier than the first
o the last oxygen molecule binds on hundreds of times faster than the first
The Bohr Effect
the graph we saw above shows what happens then there is very little carbon
dioxide present (i.e. low partial pressure of carbon dioxide: low p(CO2))
however, as the p(CO2) increases, the p(O2) decreases
so an increase in p(CO2) causes the curve to shift to the right:
o this is called the Bohr effect
If we once again look at the two points A and B:
‘A’ – as before – shows the partial pressure at the lungs
o
as the p(CO2) would be very low here (as it is
being removed), the p(O2) would be very high:
we would be dealing with the top curve
100
80
percentage
saturation
low partial
pressure of
CO2
60
40
high partial
pressure of
CO2
20
B
A
partial pressure of oxygen
-
‘B’ shows the partial pressure in a respiring muscle
tissue
o
the muscle would be using the oxygen (so would
have a low p(O2))
o
but it would also be producing CO2 so would
have a high p(CO2)
o
therefore we would be looking at the lower
curve
the effect of increasing the p(CO2) results in the haemoglobin giving up
more oxygen to the tissues (as is needed in the muscle! Perfect ☺)
Different sorts of haemoglobin
different animals live in different places with different environments
these environments all differ – they even differ in p(O2)
therefore, the animals living there must be adapted to this
-
take the example of a seal
o they have lungs, but are still able to stay under water for long periods
o they are adapted to be able to do this
YAY!! Colouring in!!
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1.2.2. Transport in Animals
They have myoglobin
o myoglobin is similar to haemoglobin except for a difference in the
chemical structure
o myoglobin only has one subunit (not four like in haemoglobin)
o this results in a different dissociation curve:
100
Myoglobin has two properties making it
very useful for its function
o
it picks up oxygen very readily
o
it is saturated at very low partial
pressures of oxygen
o
but this means that the oxygen is
not given up very readily
80
percentage
saturation
60
myoglobin
40
haemoglobin
20
partial pressure of oxygen
Foetal Haemoglobin
A baby (/foetus) does not breathe in the womb. Therefore the amount of oxygen is very
limited. The haemoglobin of the foetus is therefore different to the adult’s.
-
foetal haemoglobin has a higher affinity for oxygen (it picks it up easier)
therefore the curve is shifted to the left
This haemoglobin is replaced by normal haemoglobin (by the baby’s body) when the baby
is born.
100
80
percentage
saturation
60
Foetal haemoglobin
40
Adult haemoglobin
20
B
A
partial pressure of oxygen
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