F211
Exchange and Transport
Heart and Circulation
LO: explain the need for transport systems in multicellular
animals in terms of size, activity and surface area to volume
ratio
• All cells need energy, where do they get it from?
• How is the energy released?
• How do the food molecules and oxygen get to the cells in
simple organisms and complex organisms?
• How does the organism’s activity level influence how fast the
food molecules and oxygen have to get to the cells?
• Does the fact that some organisms are ectothermic (cold
blooded) and some are endo thermic (warm blooded) affect
how fast these molecules need to be supplied to cells?
What are the features of an efficient oxygen and
nutrient molecule transport system?
• A fluid medium to carry molecules
• A pump to push the fluid round
• Exchange surfaces for oxygen and nutrients to
enter and leave the blood
• Vessels to carry the fluid medium round the
organism
• Separate circuits to pick up oxygen from the
environment and deliver it to the cells.
Explain the meaning of the terms single and double
circulation with reference to the systems of fish and mammals
Fish have a single circulation
system. Blood flows from the heart
to the gills and then on to the
body before returning to the heart
• What are the disadvantages of
this system?
• Heart cannot pump at high
pressure
• Reduced blood pressure in
capillaries of gills to reduce
chance of damage
• Slow rate of flow in rest of body
• Limited rate of delivery of oxygen
and glucose to tissues
Explain the meaning of the terms single and double
circulation with reference to the systems of fish and mammals
Mammals have double
circulatory systems. One circuit
(pulmonary) takes blood from
the heart to the lungs and back,
the other(systemic) takes blood
from heart to body tissues and
back.
• What are the advantages of the
mammalian system?
• Heart can increase blood pressure
after blood passes through lungs
• Increased speed of delivery
• Increased blood pressure in systemic
system, oxygen and glucose get to
tissues quickly
• Lower blood pressure in pulmonary
system decreases the chance of
damaging capillaries in the lungs
Explain the meaning of the terms single and double
circulation with reference to the systems of fish and mammals
• To see how the heart and
circulatory systems have
evolved go to:
• http://mhhe.com/biosci/ge
nbio/biolink/j_explorations
/jhbch05.htm
Learning outcomes
• Describe the external and internal structure of
the mammalian heart.
• Explain the differences in thickness of the
walls of the different chambers of the heart in
terms of their functions.
Heart diagrams
• Label as much as you can on the diagram
using the labels on the sheet supplied.
External view of Heart
Describe the cardiac cycle with reference to the action of the
valves in the heart.
For animation of the cardiac cycle and explanation of
the changes in pressure that take place
• http://library.med.utah.edu/kw/pharm/hyper
_heart1.html
Be able to link
changes in pressure
and volume shown on
the graph with the
stages of the cardiac
cycle.
Control of the Cardiac cycle
Read text book pages 58-59
Make notes on the meaning of:
Myogenic
Sinoatrial node
Atrioventricular node
Purkyne (Purkinje) tissue
Control of the cardiac cycle
Non –conducting
tissue
Interpret and explain electrocardiogram (ECG) traces
with reference to normal and abnormal heart activity.
ECG interpretation
• P-R interval (usually 0.12 to 0.2 secs) greater than 0.2 secs means a delay
in the transmission of the excitation wave to the ventricles due to damage
to the AV node or Purkine tissue
• QRS complex is usually 0.06 to 0.1 sec in duration, if longer it indicates
problems with the conduction of the excitation wave across the ventricles.
• Small unclear P waves indicate atrial fibrillation due to damage to the SAN,
this means that the ventricles are not filled during atrial systole, so
ventricle contraction doesn’t expel the normal amount of blood.
• No regular PQRS pattern discernible indicates fibrillation of the atria and
ventricles, uncoordinated weak contractions of the chambers so that
blood is not pumped out of the heart effectively.
• Deep S waves indicate an increase in ventricle thickness due to increase in
blood pressure.
Interpret and explain electrocardiogram (ECG) traces with reference to
normal and abnormal heart activity.
•
•
•
•
•
•
•
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P shows atrial excitation just prior to atrial
systole
QRS shows ventricle excitation that causes
ventricular systole
T shows repolarisation of the heart muscle
during diastole
Top ECG normal
Any changes to the shape and length of each
section of the trace can indicate heart
abnormalities
Raised ST section indicates heart attack, no
ion pumps workinging to repolarise cells
Fibrillation is unco-ordinated contraction of
either / or / both atria and ventricles
Hypertrophy: extra muscle growth to
overcome increased blood pressure due to
blockages in blood vessels
Complete the question on ECG traces
Explain the meaning of the terms “open” and “closed”
circulatory systems with reference to insects and fish
•
Closed circulatory system
Vertebrates, and a few invertebrates, have a
closed circulatory system. Closed circulatory
systems have the blood closed at all times
within vessels of different size and wall
thickness. In this type of system, blood is
pumped by a heart through vessels, and
does not normally fill body cavities.
•Open circulatory system
The open circulatory system is common to
molluscs and arthropods. Open circulatory
systems (evolved in crustaceans, insects,
mollusks and other invertebrates) pump blood
into a hemocoel with the blood diffusing back to
the circulatory system between cells. Blood is
pumped by a heart into the body cavities, where
tissues are surrounded by the blood.
Describe the structure of arteries,
veins and capillaries
Describe the structures and functions
of arteries, veins and capillaries
• Cut up the table that
you have been given
and sort it out!
• When completed
collect a correct version
• Learn the sequence of
tissues that make up
the walls of arteries and
veins. ie: endothelium,
elastic fibres, smooth
muscle, collagen fibres
• Make notes on the
functions of:
endothelium, elastic
fibres, smooth muscle
and collagen fibres
• How does skeletal
muscle help blood flow
back to the heart?
• What are valves for in
veins?
Features of arteries, veins and
capillaries
Feature
Wall thickness
Muscle in wall
Elasticity of wall
Arteries
Thicker than veins
Thick muscle layer
Thick layer of elastic
tissue
Inner surface
Smooth endothelium,
often folded, can
unfold when stretched
Shape of cross section Round
Size of lumen
small
Direction of blood flow From heart towards
organs
Pressure of blood
high
valves
No valves apart from
at exit of ventricles
(semi-lunar valves)
Capillaries
Very thin, walls only
one cell thick
NO muscle layer
NO elastic tissue
veins
Thinner than arteries
Only one layer of cells
made of endothelium
Smooth endothelium,
not folded
round
Tiny (only 7 µm across)
From arterioles to
venules
low
No valves
Irregular or flattened
Larger than artery
From organs back to
heart
low
Pocket valves all along
length
Thin muscle layer
Little elastic tissue
Sequence of tissues in arteries, veins
and capillaries
Functions of tissues
• Endothelium –
• provides a smooth lining that offers little friction to slow down the
passage of blood. It may be folded lining arteries to allow it to
expand when blood surges though and the artery stretches
• Elastic fibres• allow vessels to stretch as high pressure blood flows through; and
recoil to maintain pressure in arteries when heart is in diastole.
• Smooth muscle –
• in arteries and arterioles can be contracted to constrict the vessel
and decrease the volume of blood flowing through
• Collagen• forms a strong external layer to withstand high pressure generated
by ventricular systole
Importance of pocket valves in veins
• Because blood pressure
is low in veins there is a
tendency for blood to
“pool” due to the effects
of gravity.
• Valves prevent blood
flowing backwards
• Veins are situated
between skeletal muscle,
when this contracts it
squeezes blood up the
veins and assists in its
return to the heart
Explain the differences between blood, tissue
fluid and lymph.
Feature
Blood
Tissue fluid
Lymph
Cells
Erythrocytes(red) Leucocytes
(white) and platelets
phagocytes
lymphocytes
Proteins
Hormones and plasma
proteins
Hormones and protein
secreted by body cells
Few proteins
Fats
Some transported as
lipoproteins (HDL, LDL)
NONE
More than in blood (absorbed
from lacteals in small intestine)
Glucose
80-120mg per 100cm3
Less than in blood Gets
absorbed by cells
Less than in blood and tissue
fluid
Amino acids
More than in other fluids
Less than in blood Gets
absorbed by cells
Less than in blood and tissue
fluid
Oxygen
More than in other fluids
Less than in blood Gets
absorbed by cells
Less than in blood and tissue
fluid
Carbon dioxide
Little
More than in blood.Gets
absorbed by cells
More
Describe how tissue fluid is formed
from plasma.
• Arteries branch into arterioles and
then into capillaries around the
tissues of organs
• The contractions of the heart
maintain some pressure in the
capillaries (hydrostatic pressure)
• This squeezes fluid out between
the endothelial cells of the
capillaries
• The fluid contains oxygen, amino
acids and glucose; but no cells
apart from a few phagocytes and
no plasma proteins which are too
large to go through the pores
Exchange in the capillary bed
• Tissue fluid bathes the cells
• Nutrients (glucose, mineral ions
and amino acids) and oxygen
are taken into cells by diffusion,
facilitated diffusion and active
transport
• Waste such as CO2 and urea are
removed from cells by similar
processes
• Tissue fluid must now return to
the circulatory system to
maintain blood volume
How does the fluid return to the
blood?
• Plasma proteins which remain in the
blood give blood a lower water
potential than tissue fluid so water
tends to flow back into the
capillaries down a water potential
gradient, solutes diffuse down their
concentration gradients.
• At the arteriole end of the capillary
hydrostatic pressure is greater than
osmotic pressure (solute potential)
so there is net outflow from the
capillary
• At the venule end of the capillary
the hydrostatic pressure has
dropped considerably due to fluid
leaving the blood, it is now lower
than the osmotic pressure(solute
potential);so there is net inflow to
the capillary
Importance of the lymphatic system
• Without the lymphatic system tissue
fluid could accumulate and cause
oedema
• The lymph nodes contain large
numbers of phagocytic lymphocytes
that engulf and kill bacteria. They
are part of the immune system
Describe the role of haemoglobin in
carrying oxygen
• REMEMBER Haemoglobin becomes
oxygenated not oxidised
• It forms Oxyhaemoglobin
• Haemoglobin is an example of a
quaternary protein- it is made up
of 4 polypeptide units each of
which holds an iron
(Fe2+)containing “Haem” group
(NB: More on protein structures
later in the other part of your
course)
• The Haem group has an affinity
(attraction) for oxygen
• Each haem group can hold one
molecule of oxygen, so the
haemoglobin molecule carries 4
molecules of oxygen
Taking up and releasing oxygen
• Oxygen is absorbed in the
alveoli of the lungs
• Oxygen diffuses into
blood plasma and from
there into red blood cells
• The oxygen is taken up by
Haemoglobin and is
removed from solution
• This maintains the
diffusion gradient so
more oxygen diffuses into
the plasma and red blood
cells
Uptake of oxygen by haemoglobin
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Rate of uptake of oxygen depends on
the partial pressure of oxygen
Partial pressure can be thought of as
the amount of a particular gas in a
mixture of gases measured in kPa
At low partial pressures it is difficult for
oxygen molecules to associate with
haemoglobin; it is hard for the first
oxygen molecule to get in to the
complex and reach the haem group.
Once one oxygen molecule is in, the Hb
molecule changes shape and this makes
it easier for more oxygen to get in.
Second and third O2 molecules
associate quite easily
To get the fourth one in and get almost
100% saturation the partial pressure
needs to be very high
Uptake of oxygen by haemoglobin
• This means that in areas
where the partial pressure
of oxygen is high,such as
the lungs, haemoglobin is
almost saturated.
• In areas where the partial
pressure of oxygen is low,
such as respiring tissues,
the oxygen dissociates from
the haemoglobin easily and
then diffuses out of the
blood plasma to the cells
that need it.
Uptake and release of oxygen by
haemoglobin
• Foetal haemoglobin has a
higher affinity for oxygen
than adult haemoglobin
• As the mothers blood
flows through the
placental tissue the PO2 is
low so thefaet
oxygen
dissociates from the
haemoglobin
• The foetal haemoglobin
picks up the released
oxygen.
Oxygen availability at altitude
• The % of oxygen in the air is the same as at sea level but the
atmospheric pressure is much lower
• This means that fewer molecules of oxygen are inhaled per
breath, so % saturation of haemoglobin in the lungs is greatly
reduced
• Lack of oxygen at altitude results in heavy breathing, and
increased heart rate as the body tries to maintain normal
levels of oxygen supplied to tissues.
• Dizziness, headaches, nausea, increasing confusion, inability
to walk straight may follow
• In extreme cases this can turn into HACE (high altitude
cerebral edema) or HAPE (high altitude pulmonary edema)
which are potentially life threatening conditions unless the
person descends to an area where oxygen availabilty is higher