3.3.4.1 Mass Transport in animals Flashcards
Describe the structure of haemoglobin.
Globular, water soluble. Consists of four
polypeptide chains, each carrying a
haem group (quaternary structure).
Describe the role of haemoglobin.
Present in red blood cells. Oxygen
molecules bind to the haem groups and
are carried around the body to where
they are needed in respiring tissues.
Name three factors affecting oxygen-haemoglobin
binding.
- Partial pressure/concentration of oxygen.
- Partial pressure/concentration of carbon
dioxide. - Saturation of haemoglobin with oxygen.
How does partial pressure of oxygen
affect oxygen-haemoglobin binding?
- pressure of oxygen increases, the
affinity of haemoglobin for oxygen also
increases, so oxygen binds tightly to haemoglobin. - When partial pressure is low, oxygen is released from haemoglobin.
How does partial pressure of carbon
dioxide affect oxygen-haemoglobin
binding?
- As partial pressure of carbon dioxide increases, the
conditions become acidic causing haemoglobin to
change shape. The affinity of haemoglobin for
oxygen therefore decreases, so oxygen is released
from haemoglobin.
This is known as the Bohr effect.
How does saturation of haemoglobin
with oxygen affect oxygen-haemoglobin
binding?
It is hard for the first oxygen molecule to bind. Once
it does, it changes the shape to make it easier for
the second and third molecules to bind, known as
positive co-operativity. It is then slightly harder for
the fourth oxygen molecule to bind because there is
a low chance of finding a binding site.
Explain why oxygen binds to haemoglobin in the lungs
● Partial pressure of oxygen is high.
● Low concentration of carbon dioxide in the lungs,
so affinity is high.
● Positive cooperativity (after the first oxygen
molecule binds, binding of subsequent molecules
is easier).
Explain why oxygen is released from haemoglobin in
respiring tissues.
● Partial pressure of oxygen is low
● High concentration of carbon dioxide
in respiring tissues, so affinity
decreases.
What do oxyhaemoglobin dissociation curves show?
Saturation of haemoglobin with oxygen
(in %), plotted against partial pressure of
oxygen (in kPa). Curves further to the left
show the haemoglobin has a higher
affinity for oxygen.
How does carbon dioxide affect the position of an
oxyhaemoglobin dissociation curve?
Curve shifts to the right because
haemoglobin’s affinity for oxygen has
decreased.
Name three common features of a mammalian
circulatory system.
- Suitable medium for transport, water-based to
allow substances to dissolve. - Means of moving the medium and maintaining
pressure throughout the body, such as the heart. - Means of controlling flow so it remains
unidirectional, such as valves.
Structure of atria
thin-walled and elastic, so they can
stretch when filled with blood
structure of ventricles
thick muscular walls pump blood under high pressure. The left ventricle is thicker than the right because it has to pump blood all the way around the body.
Why do arteries have thick, muscular and elastic walls?
to handle high pressure without tearing, and are muscular and elastic to control blood flow.
Why do veins have thin walls and less muscular and elastic?
Veins have thin walls due to lower pressure,
therefore requiring valves to ensure blood doesn’t
flow backwards. Have less muscular and elastic
tissue as they don’t have to control blood flow.
Why is a double circulatory system important for humans?
To maintain blood pressure around the whole body.
When blood passes through the narrow capillaries of
the lungs, the pressure drops sharply and therefore
would not be flowing strongly enough to continue
around the whole body. Therefore it is returned to the
heart to increase the pressure.
Describe what happens during cardiac diastole
- The heart is relaxed.
- Blood enters the atria, increasing the pressure and pushing open the atrioventricular valves.
- This allows blood to flow into the ventricles.
- Pressure in the heart is lower than in the arteries, so semilunar valves remain closed.
Describe what happens during atrial systole.
The atria contract, pushing any remaining blood into the ventricles.
Describe what happens during ventricular systole.
- ventricles contract.
- The pressure increases, closing the atrioventricular
valves to prevent backflow, and opening the semilunar valves.
-Blood flows into the arteries.
Name the nodes involved in heart contraction and
where they are situated.
● Sinoatrial node (SAN)= wall of right
atrium.
● Atrioventricular node (AVN)= in
between the two atria.
What does myogenic mean?
The heart’s contraction is initiated from within the muscle itself, rather than by nerve impulses.
Explain how the heart contracts.
● SAN initiates and spreads impulse across the
atria, so they contract.
● AVN receives, delays, and then conveys the
impulse down the bundle of His.
● Impulse travels into the Purkinje fibres which
branch across the ventricles, so they contract
from the bottom up.
Why does the impulse need to be delayed?
If the impulse spread straight from the
atria into the ventricles, there would not
be enough time for all the blood to pass
through and for the valves to close.
How is the structure of capillaries suited to their
function?
● Walls are only one cell thick; short diffusion pathway.
● Very narrow, so can permeate tissues and red blood
cells can lie flat against the wall, effectively delivering
oxygen to tissues.
● Numerous and highly branched, providing a large
surface area.
