MODULE THREE NOTES
THE MAMMALIAN HEART
From a general engineering standpoint
Type:
General Description:
Dimensions:
Performance data:
Regulation systems:
Construction material:
Blood pump for human circulation
2 pumps linked in series, self lubricating, self regulating,
operational lifetime ~ 75-86yrs
Inverted cone shape, Base width ~ 100mm, Max. length ~
155mm; Weight ~ 300g
Cardiac output = stroke volume x heart rate (CO= ml
x bpm). At rest = 5-8 lm-1 , At peak = 30 lm-1, Normal
stroke vols. = 80-120 ml. Normal heart rate = 68 bpm
1. Pacemakers (Main SAN, Auxillary AVN)
2. Nervous system: (Heart accelerator = nerve of herring.
Heart decelerator = Vagus depressor)
3. Hormonal system (Adrenaline and Thyroxin)
Cardiac Muscle, special feature no fatigue or oxygen debt
CARDIAC CYCLE REGULATION
MYOGENIC -heartbeat is initiated from within the heart muscle itself
SINO-ATRIAL NODE (SAN) - group of SPECIALISED CARDIAC MUSCLE CELLS in
the wall of the RIGHT ARTIUM near where the vena cava enters. It DETERMINES the
BASIC RATE of the heartbeat ie a PACEMAKER.
An impulse spreads from the SA Node to BOTH atria causing them to contract almost
simultaneously. This impulse also reaches a similar ATRIO VENTRICULAR (AV)
NODE which lies between the two atria.
The impulse is conducted along the PURKINJE FIBRES (collectively making the
BUNDLE OF HIS) through the septum to the APEX of the heart. These cause the
impulse to travel from the APEX of the ventricles UPWARDS, thus forcing the blood
into the arteries.
Within the CARDIAC CENTRE of the MEDULLA in the brain are 2 CENTRES:
CENTRE
CARDIOACCELERATORY
CENTRE
CARDIO-INHIBITORY
CENTRE
NERVE LINKING TO SAN
IN HEART
SYMPATHETIC NERVE
(nerve of Herring)
EFFECT OF
STIMULATION
> CARDIAC OUTPUT
PARASYMPATHETIC
NERVE (vagus depressor)
< CARDIAC OUTPUT
Changes in the following factors in the blood cause stimulation of the appropriate
centre:
pH, [CO2], [O2] and pressure – detected by receptor cells in aortic arch, carotid body
and sinus and the vena cava
HEART RATE
Heart Rate increased by:1.
2.
3.
4.
5.
6.
7.
8.
Increase in blood pressure in the Vena Cava.
Increase in blood [CO2].
Decrease in blood [O2].
Decrease in blood pH.
Increase in body temperature (core temperature).
Increase in hormone adrenaline.
Decrease in hormone thyroxin.
Increase in the nervous input from pain receptors.
Heart Rate decreased by:1.
2.
3.
4.
5.
6.
7.
Increase in blood pressure in Aorta and large arteries
Decrease in blood [CO2].
Increase in blood [O2].
Increase in blood pH.
Decrease in body temperature (core temperature).
Decrease in adrenaline.
Increase in thyroxin.
BLOOD
Blood is classified as a CONNECTIVE TISSUE i.e. Specialised cells in a fluid or a
semi-fluid matrix .
MATRIX
WATER
SALTS
PLASMA PROTEINS
ALBUMINS
45 - 54%
SODIUM
2400mg/l
POTASSIUM
80 mg/l
CALCIUM
80 mg/l
MAGNESIUM
28 mg/l
CHLORIDE
2600mg/l
HYDROGEN CARBONATE 1500mg/l
6.8 - 8.5 G/100cm3 of plasma
53 % of total plasma protein: Responsible for
osmotic pressure of blood
43% of total plasma protein: Involved in the
defence against disease (often called
immunoglobulins.
Involved in the clotting process
GLOBULINS
FIBRINOGEN
All these make plasma about six times more viscous than water and contribute to
regulation of water between plasma & tissue fluids.
The hydrogen carbonate ions are important buffers that keep the pH of blood constant
SUSTANCE TRANSPORTED IN THE BLOOD
1.
2.
3.
4.
5.
6.
7.
SUGARS
AMINO ACIDS
FATTY ACIDS, GLYCEROL
HORMONES
NITROGENOUS WASTSE
CARBON DIOXIDE
OXYGEN
RED BLOOD CELLS (ERYTHROCYTES)
Biconcave discs 7 – 8 micrometres diameter 1 - 2 micrometres thick.
No nucleus when mature (mammalian)
Elastic framework - permits the cell to bend and twist as it passes through blood
vessels smaller than its diameter.
Av. 5.4 Million per mm3
Each R.B.C. contains approx. 265,000,000 molecules of HAEMOGLOBIN.
FUNCTION OF HAEMOGLOBIN
HAEMOGLOBIN + O2
=
OXYHAEMOGLOBIN
The DIRECTION of this reaction depends on:
The Partial Pressure(P) of OXYGEN: i.e. when O2 is at LOW (P) e.g.. in capillaries
reaction occurs to the left and O2 is released . When O2 is at HIGH (P) e.g.. in lungs
the reaction occurs to the right and O2 is taken up by haemoglobin
and to a lesser extent [CO2]
Thus: in the CAPILLARIES OF THE TISSUES the [CO 2] is HIGH and a large amount
of O2 is released from the oxyhaemoglobin by the combined action of these two
effects.
CARBON MONOXIDE (CO) has a greater affininty for Hb than oxygen does, thus when
air is breathed containing only 0.5% CO more than HALF the Hb molecules combine
with it. It is a reversible union taking several hours to clear a persons blood.
The release of O2 from haemoglobin is HELPED/INFLUENCED BY THE PRESENCE
OF CARBON DIOXIDE (CO2) = THE BOHR EFFECT/SHIFT.
where CO2 is HIGH (RESPIRING TISSUE) OXYGEN IS RELEASED READILY
where CO2 is LOW (RESPIRATORY SURFACE) OXYGEN IS TAKEN UP READILY
FOETAL HAEMOGLOBIN
HAS A HIGHER AFFINITY FOR O2 than maternal Hb.
CO2 IS TRANSPORTED IN THE BLOOD IN 3 WAYS
1) in solution
~ 10%
2) bound to haemoglobin
~ 30%
3) as bicarbonate ions
~ 60%
1) The greater solubility of CO2 contributes to the relatively lower PCO2 compared with
O2.
2) Carboxyhaemoglobin. CO2 combines with the globin portion of haemoglobin, when
the affinity of haemoglobin for O2 is at it’s lowest CO2 can bind readily with
haemoglobin.
3) Most CO2 is transported in the blood as bicarbonate which is produced via a 2 step
reaction:
CO2
+
H2O
→
This reaction is catalysed
by the enzyme carbonic
anhydrase which is present
in high concentration inside
red blood cells so this
reaction normally occurs
inside red blood cells.
H2CO3
→
H+
+
HCO3-
this disassociation occurs
immediately. The HCO3diffuses out of the RBC into
the plasma, the H+ are
taken up by the
haemoglobin within red
blood cells (i.e. they are
buffered). Cl- ions diffuse
into RBC’s to equalise the
charge when the HCO3leaves, this is known as the
chloride shift.
% saturation of
haemoglobin
Low
CO2
High
CO2
Tissues
Lungs
Partial pressure of oxygen
TOP END OF CURVE
This area shows Hb's ability to take up O2 FROM THE ENVIRONMENT.
The Oxygen pressure at which Hb reaches saturation is called the LOADING TENSION
(TL) or loading pressure - where curve starts to flatten out.
The UNLOADING TENSION (TU) is arbitrarily defined as the OXYGEN PRESSURE AT
WHICH Hb CARRIES ONLY HALF AS MUCH O2 AS IT CAN HOLD WHEN
SATURATED.
MIDDLE OF CURVE
The steep slope in this area means there is a BIG change in how much O 2 the Hb can
carry over a SMALL RANGE of OXYGEN pressures.
These Oxygen pressures are normally present in the FLUIDS DEEP WITHIN THE
BODY.
The graph can be used to explain the following points:
There is a high concentration of O2 in the lungs and a low concentration of CO2.
The haemoglobin will therefore be virtually saturated with O 2.
In tissues which are respiring actively there will be a low concentration of O 2 and a high
concentration of CO2.
The haemoglobin will therefore give up a lot of the O 2 that it is transporting
Transport
.......in flowering
plants.
Mass Flow
Large or complex organisms which cannot rely on diffusion and active transport alone,
they must have long-distance transport systems.
Materials are generally moved by a mass flow system, mass flow being the bulk
transport of materials from one point to another as a result of a pressure difference
between the two points.
Mass flow
system
Xylem
Phloem
Materials moved
Driving force
mainly water and mineral
salts
mainly organic food e.g.
sucrose
transpiration & root
pressure
mechanism not fully
understood
Study the following notes which relate to xylem and phloem. These both consist of
more than one type of cell.
N.B.
The notes include information on structural features of xylem and phloem
which are related to their mechanical functions. We will only be relating their structure
to their role in transport at this time.
1) Xylem
Conduction of water and mineral salts
Support
Four cell types:- Tracheids, Vessels, Parenchyma, Fibres
Tracheids
 Single cells; elongated and lignified
 Tapering end walls which overlap
 Dead with empty lumens
These are efficient water conductors, but due to their ancestral nature they are not
abundant in angiosperms (flowering plants).
Vessels
 Long, tubular structures
 Formed by fusion of several cells end to end in a row
Just to keep things simple (?!) there are two types of vessel. These are protoxylem
and metaxylem.
Protoxylem
 Formed from vessels found just behind apical meristem
 Growth and cell elongation occurs in this area
 Protoxylem stretches as the surrounding cells elongate
 Stretching possible because lignin is not deposited over entire cellulose wall
 Lignin only deposited as rings or spirals
Early protoxylem stretches and collapses during initial growth from a meristem. More
mature regions form metaxylem.
Metaxylem
 Formed by extensive lignification of protoxylem
 Dead, rigid, fully lignified and cannot stretch
Why does xylem provide an ideal system for translocation of water. Read about it
in your text book and make notes in the space below. N.B. This is important as you are
required to be able to relate structure of both xylem and phloem to their role in
transport.
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2) Phloem
Translocation of solutions of organic solutes
No mechanical function
Similar to xylem in possessing tubular structures modified for translocation. Tubes,
however, are living cells lined with cytoplasm.
Five cell types:- Sieve tube elements, Companion cells, Parenchyma, Fibres, Sclereids
Photosynthetic products must obviously be transported to non-photosynthetic tissues of
the plant.
Movement of these solutes must be bidirectional.
Compare this movement with that of xylem:
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Phloem also carries certain mineral elements in various forms. e.g. potassium ions,
hormones and vitamins. The following are transported as constituents of which organic
solute:Nitrogen and sulphur?.........................................................................
Sieve Tube Elements and Companion Cells
Sieve Tube Elements:
 Living cells which contain obstructions to flow of solution (i.e. sieve plates and, to a
lesser extent, the cytoplasm)
Formation: Nucleus degenerates (comparison to which mammalian
cell?)…………………………………
 Cell walls at each end develop into sieve plates
 Sieve plates formed when plasmodesmata enlarge to form sieve pores. This
forms a tube-like structure with a wide lumen and a narrow, peripheral layer of living
cytoplasm.
Companion Cells:
 Closely associated with each sieve element
 Dense cytoplasm with small vacuoles and usual cell organelles
 Metabolically very active (What evidence is there for this?
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Very close link with sieve tube elements. If companion cell dies, so do some
elements. In leaves they function as transfer cells, absorbing sugars and transferring
them to sieve tube elements
There is still a great deal of controversy over the mechanism of translocation in
phloem. Obviously though, the enlarged plasmodesmata (sieve pores) play an
integral role in movement of solutes along the elements.
The Transpiration Stream
Remember that this can be thought of as the movement of water from a less negative
to more negative water potential. Water moves from less negative  in soil to more
negative  of air surrounding leaves. The  of air with a low humidity is nearly zero.
This provides a very steep gradient from soil to air and is one of the driving forces of
the transpiration stream.
Soil

•
•
•

Root cortex

Xylem

Leaves

Air
Transpiration stream
 Transpiration 
Transpiration stream is movement of water from root to leaf.
Transpiration is the loss of water from plant surfaces.
When water evaporates from a leaf mesophyll cell, this cell’s  will fall. Water from
an adjacent cell will then move into this cell by osmosis as a result of the 
difference between them. This ‘chain’ of  differences continues back to the xylem
sap which obviously has a high . Water moves smoothly and continuously along
this  gradient.
Water loss may occur from:1. Stomata (evaporation from mesophyll cells & diffusion via stomata this way = 90%
water loss)
2. Cuticle (evaporation from epidermal cell walls). 10% depending on cuticle
thickness.
3. Lenticels (minute amount lost this way, but main source of water loss after leaf fall
in deciduous).
The three pathways of water movement through cells are:1. ........................................................................................................
2. ........................................................................................................
3. ........................................................................................................
The Casparian strips are formed when a waterproof substance called suberin is
deposited in the cell walls of endodermal cells.
Which pathway of water movement will be affected by Casparian strips, and what
purpose do you think this serves?
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The Cohesion-Tension Theory






Xylem vessels are full of water.
Tension is set up in water column as water leaves xylem.
Tension transmitted back to root due to cohesion of water molecules.
Water  polar molecule  H-bonding   high cohesion
Adhesion = water molecules tend to ‘stick’ to xylem walls.
Columns of water in xylem have a high tensile strength, a force capable of pulling
water long distances upwards by means of mass flow.
A Mechanism of Stomatal Opening
(THIS IS STARCH SUGAR HYPOTHESIS YOU ALSO NEED TO KNOW POTASSIUM ION HYPOTHESIS)
A vertical section through a stoma would show the asymetrically thickened guard cell
walls. As guard cells inflate with water and become turgid, this uneven thickening
causes the guard cells to assume a semi-circular shape, this opening a hole between
them. Conversely, the cells close the hole as they lose water. The mechanisms which
bring about these changes in turgidity are not yet completely understood.
Guard cells are the only epidermal cells which possess chloroplasts. The ‘starchsugar hypothesis’ suggests that sugar accumulates in guard cells during exposure to
light.
Explain, in terms of WP, how this could bring about stomatal opening:
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It has been shown that this accumulation of sugar is insufficient to bring about stomatal
opening on its own. What else has been shown to accumulate in guard cells during
daylight, and what happens to this at night?
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Mineral Ion Uptake and Transportation
Mineral elements exist in the form of ions in salts. The ions dissociate in solution
(water in soil). Uptake is greatest in region of the root hairs. Uptake occurs by both
diffusion and active tranport in the piliferous region of the root hairs. In
attempting to explain the uptake and movement of mineral ions, the following facts
must be taken into account:-
What happens when ions moving in the apoplast (in solution) reach the Casparian
strips?
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This is how plants monitor and control which types of ions eventually reach the xylem.
The symplast pathway extends from the piliferous region right through to the xylem.
This route allows ions to travel without having to cross further membranes.
Ions moving from root cells into xylem vessels must pass across a cell membrane via
diffusion or active transport.
Remember that minerals are either tranlocated upwards in the xylem, or up and down
the phloem as constituents of organic solutes.
Evidence for Movement in Phloem
1. Radioactive Labelling - 1945 - Plants supplied with 14CO2 and a light source.
Radioactivity later detected in phloem.
2. Aphids - these feed on translocating sugars by penetrating sieve tubes with
modified mouthparts (stylets). Aphid is anaesthatised and body removed leaving
stylets embedded in phloem. Sieve tube contents continue to exude from stylet, can
be collected and analysed.
3. Metabolic poisons - when introduced to phloem, translocation is halted therefore
suggesting active processes involved.
Munch’s Mass Flow (Pressure) Hypothesis
This is the major hypothesis used to explain movement in phloem though it has its
limitations.
Comparison of Xylem and Phloem Sap
SUBSTANCE
Sucrose
Amino Acids
Nitrate
Xylem Sap
g ml-1
0
700
10
Phloem Sap
g ml-1
154,000
13,000
0
ADAPTATION OF PLANTS TO HOT CONDITIONS
 Shiny cuticle ~ reflects light
 Evaporation from stomata causing cooling
 Wilting as a response to reduce leaf S/A in light
ADAPTATIONS OF PLANTS TO DRY CONDITIONS (XEROPHYTIC PLANTS)
 Needle shaped leaves ~ permit max. heat dissipation
 Survive extreme conditions by remaining in seed or spore stage = drought
evaders (4 weeks)
 Drought endurers Xeromorphic - structural adaptations e.g. British Marram
Grass (Ammophylia)