Transcript 12c - Macmillan Academy

The Cardiac cycle
• Can confidently label internal
& external photos of the heart
• Can describe the cardiac cycle
• Can explain how the heart
valves help with the cardiac
cycle
Bell Task
• Label the heart diagram and complete
the questions
Label the gaps
Answer these questions
•
•
•
•
•
•
Which side has the thickest muscular wall and
why.
Where does blood go to from the right side of
the heart?
Where does blood go to from the left side of
the heart?
What is the heart made from?
What is the function of the valves?
What 2 problems would occur with a hole in
the wall between the left and right side?
Where are the Valves in the
heart?
• Atrioventricular valves: these valves
separate an atrium from a ventricle.
• Semilunar valves: found in arteries
leaving the heart (pulmonary arteries
and aorta).
Semilunar
Atrioventricular valves
• Tricuspid – 3 flaps
• Biscuspid – 2 flaps
Valves
Inside the heart and at the base of
the vessels that leave the heart are
valves.
These valves only open one way,
which ensures that there is no
backflow of blood.
The cardiac cycle
• Beats around 70 times a minute.
• If you listen to the heart with a stethoscope
you hear the sounds often described as
“lubb-dupp”.
• The cardiac cycle is sequence of events
that make up one heart beat.
• Continuous
Arterial systole
• The heart fill up with blood and the
muscle in the atrial wall contracts.
• Pressure developed is not very big, as
muscular atrial walls are only thin.
• Forces blood through the atrioventricular valve and into the ventricles.
The blood cannot flow
back into the vena cava or
the pulmonary vein,
As these have semilunar
valves, to prevent
backflow.
Instead it is pushed into
the ventricles
Ventricular systole
• About 0.1 second after atrial
systole the ventricles contract.
• The thick muscular walls of the
ventricles squeeze inwards on the
blood.
• This increases the pressure and
pushes it out of the heart
As soon as the pressure
in the ventricles becomes
greater than in the atria.
The pressure pushes the
atrio-ventricular valves
shut, preventing
backflow. (‘lubb’)
Instead it rushes up into
the aorta and the
pulmonary artery pushing
open the semilunar valves.
Ventricular diastole
• After about 0.3 seconds, the muscle
relaxes and diastole begins.
• As pressure drops the semilunar valves
snap shut as blood fills their cusps.
(‘dubb’)
• Whole heart relaxes and blood flows
into atria again and the cycle is
repeated.
The valves are held open or closed by
tendons (heart strings), which are
attached at the other end to the papillary
muscles in the ventricle walls.
The valves open to let blood through and
then snap shut. This sound of the valves
closing is the ‘lub dub’ sound of the
heartbeat.
• The muscle of the heart is called cardiac
muscle and is made of tightly connecting
cells. This close contact allows rapid ion
transport from cell to cell. This then allows
smooth, efficient waves of depolarisation
to produce contractions (and repolarisation
to bring about relaxation), which pass
through the heart.
• The tissue is said to be myogenic i.e. it does
not need electrical impulses from a nerve to
make it contract. If the cardiac muscle is
supplied with oxygen and nutrients (a task
carried out by the coronary arteries which you
can see running over the surface of the heart) it
will continue to contract at a steady pace.
Nerves supplying the heart, though they are not
needed to start the contractions, can bring about
an increase or decrease in the rate of
contractions when appropriate.
Task…
• Answer question 5 on page
69
–You will need to draw the
graph
Heart Action
• Can explain how the SAN, AVN
& Purkyne tissue coordinate
the heart action
• Interpret & describe ECG
traces in normal & abnormal
heart rhythms
Task: Describe what
is happening at 1,2,3
and 4.
Semilunar valve
in aorta shuts
(aortic valve)
1) Atrio-ventricular
valves close
because the
pressure is higher
in the ventricle than
in the atria.
2) Semilunar valve in
aorta opens due to
pressure from the
ventricles.
3) Semilunar valves
close because the
pressure in aorta is
higher than in
ventricle. (Blood
tries to flow back
and closes the
cups in the valve
4) Atrio-ventricular
valves close
because the
pressure is higher
in the atrium than
in the left ventricle.
The electrical control of the heart
• Cardiac muscle is MYOGENIC
which means it can contract &
relax without receiving signals
from nerves
• It can control it’s own activity
•The heartbeat is initiated
in a specialised area of
muscle in the right atrium
called the sinoatrial node
(SAN) or the pacemaker.
•The SAN starts the waves
of electrical activity, which
results in contraction.
1
•There is an area, however,
which conducts in the
septum, and the waves can
pass from here through the
ventricles.
•This specialised area is
called the atrioventricular
node (AVN) and will pass
on the waves of electrical
activity after about 0.1s.
3
•The waves spread out over
the 2 atrial walls so that they
contract.
•There is a band of fibres
between the atria and
ventricles, which have a high
electrical resistance so the
waves cannot spread from
the atria to the ventricles. 2
The AVN passes the waves on to
the Purkinje (also called
Purkyne) fibres in the interventricular septum. The excitation
is passed to the apex of the heart
and then through the ventricle
walls. This causes the ventricles
to contract from the base upwards
ensuring that the blood is forced
up and out in the vessels leaving
the heart.
4
It would be disastrous if the ventricles
contracted at the same time as the atria so
that is why there is a short period of delay
before the ventricles contract.
Task…
• With the help of diagrams you must
produce a flow chart showing the stages
that are involved in the heart beat
• Pages 70, 71 & 72 will help you
• Use all of the relevant keywords:
Myogenic, SAN, AVN, Purkyne tissue…
Un-Control of Heart Beat!
Put in the correct order
SAN contracts and starts off signal
Passes to the base of the septum and up
through the ventricle wall
 Wave passes to Purkyne fibres in the
septum
Fibres between atria and ventricles do not
contract
Wave spreads to AVN in septum
Ventricles contract
Atria contract
Un-Control of Heart Beat!
Put in the correct order
SAN contracts and starts off signal
Atria contract
Fibres between atria and ventricles do not
contract
Wave passes to Purkyne fibres in the
septum
Wave spreads to AVN in septum
Passes to the base of the septum and up
through the ventricle wall
Ventricles contract
ECG - Electrocardiograph
• Doctors can check heart activity by
using a machine that records the
electrical activity of the heart
• The heart depolarises (looses electrical
charge) when it contracts
• It repolarises (regains charge) when it
relaxes
• An electrocardiogram allows doctors to
assess heart health
ECG
QRS complex = contraction of ventricles
T wave = relaxation
(repolarisation) of ventricles
P wave = contraction
(depolarisation) of atria
Time/s
0
0.2
Atrial systole
0.4
Ventricular systole
0.8
Diastole
Fibrillation = irregular
Tasks
• What is fibrillation?
• Describe an electrocardiogram showing
fibrillation
• How do heart monitors save a patient’s
life?
• What is a defibrillator & when might it
be used?
• Answer SAQ 6
• Past questions
Blood vessels
• Can identify veins, arteries &
capillaries from
diagrams/photos
• Can describe how the
structure of these vessels
relates to their function
Which is the ‘normal?’
Regular rhythm of approx 60 bpm
Irregular rhythm, heart rate too slow
Which is the ‘normal?’
Regular rhythm of approx 60 bpm
Irregular rhythm, heart rate too fast
Which is the ‘normal?’
Regular rhythm of approx 60 bpm
Irregular rhythm, no clear P wave, SA node not initiating beat
Which is the ‘normal?’
Regular rhythm of approx 60 bpm
Irregular rhythm, Atrial fibrulation, no clear SAN, most of atrium generating own
impulses, no clear P wave due to random impulses
Which is the ‘normal?’
Regular rhythm of approx 60 bpm
AV block, impulse not reacing AVN from SAN, long PR interval
Summarising ECG irregularities
Irregularity
AVN block – problems
with the SAN reaching
the AVN
Fibrillation – irregular
heart beat
Heart rate too fast or
slow
How it is shown on ECG
Blood vessels
Veins
Venules
Capillary
Heart
Artery
Arteriole
Tunica
externa
Arteries…
• Transport blood at high pressure to the
tissues
• Inner endothelium made of squamous
epithelium (smooth cells to reduce
friction)
• Tunica media containing smooth muscle,
collagen & elastic fibres
• Tunica externa containing elastic fibres
& collagen
Externa
& collagen
& elastic
fibres
Arterioles…
• Smaller branches of the arteries
• Walls are similar to arteries but have a
greater proportion of smooth muscle
• This allows them to contract & narrow
the lumen so blood flow can be controlled
• For example during exercise they will be
dilated to allow maximum blood flow to
muscles
Capillaries
• Smaller branches of the arterioles & will
serve every cell in the body
• Found in every tissue except the cornea
& cartilage
• Group together to form capillary beds
• The lumen is same size as a RBC to allow
efficient diffusion
• They are 1 cell thick… made up of
endothelial tissue
Venules  Veins
• Capillaries regroup to form venules which them
turn into veins
• Transports blood back to heart at very low
pressure
• Contains semi-lunar valves to prevent backflow
of blood
• The Tunica externa is mostly collagen
• The Tunica media is very thin & contains some
smooth muscle & elastic fibres
• The Tunica intima is the same as the artery
with endothelium tissue
Questions
1.
2.
3.
4.
5.
How do muscles help veins perform their
function?
Arteries carry oxygenated blood away from
the heart, but what is the 1 exception?
Why do you think there are no capillaries in
the cornea of the eye?
What does blood pressure oscillate (go up &
down) in the arteries?
Why does the blood pressure drop in the
arterioles & capillaries?
Vein or artery
Which one?
B
A
Which one?
C
Blood plasma, tissue fluid
& lymph
• Explain the differences
between blood, tissue
fluid & lymph
• Describe how tissue fluid
is formed from plasma
Summarising…
Blood/plasma
Red blood
cells
White blood
cells
Platelets
Proteins
Water
Dissolved
solutes

Tissue Fluid

Lymph

Summarising…
Blood/plasma
Red blood
cells
White blood
cells
Platelets
Proteins
Water
Dissolved
solutes
Tissue Fluid
Lymph





!
Summarising…
Blood/plasma
Red blood
cells
White blood
cells
Platelets
Proteins
Water
Dissolved
solutes
Tissue Fluid
Lymph





!



Summarising…
Blood/plasma
Red blood
cells
White blood
cells
Platelets
Proteins
Water
Dissolved
solutes
Tissue Fluid
Lymph





!






Summarising…
Blood/plasma
Red blood
cells
White blood
cells
Platelets
Proteins
Water
Dissolved
solutes
Tissue Fluid
Lymph





!









Summarising…
Blood/plasma
Red blood
cells
White blood
cells
Platelets
Proteins
Water
Dissolved
solutes
Tissue Fluid
Lymph





!












Blood
Lymph
1.List the components
that make up the
tissue/liquid found in
each box
2. Describe what is
added or lost on each of
the arrows.
3. Include any extra
information you think is
important.
Tissue Fluid
Plasma
Blood plasma, tissue fluid
& lymph
• Explain the differences
between blood, tissue
fluid & lymph
• Describe how tissue fluid
is formed from plasma
The role of haemoglobin
• Describe the role of
haemoglobin in carrying
oxygen & carbon dioxide
Oxygen Fact file
• Oxygen is transported around the body in
combination with haemoglobin (Hb)
• Each molecule of haemoglobin can combine
with 8 atoms (4 molecules) of oxygen
• The resulting compound is named oxyhaemoglobin
• Hb will combine with oxygen when
concentrations of oxygen are higher
• Hb will release it’s oxygen in areas where
oxygen is in low concentration
How much oxygen can be
carried?
• Overall each molecule can combine with
four oxygen molecules
• This means that eight oxygen atoms can
be carried by each haemoglobin molecule
Hb
haemoglobin
+
4O2
HbO8
oxyhaemoglobin
The binding of oxygen is a reversible reaction.
Carbon dioxide fact file
•
•
Carbon dioxide is constantly produced by the
respiring tissues & is transported in the blood to
the lungs
When carbon dioxide diffuses into the plasma 1 of
3 things can happen…
1. Some of it remains as CO2 dissolved in the plasma
(about 5%)
2. Some diffuses into the erythrocytes and is converted
into Carbonic acid (about 85%)
3. Some combines with the Hb forming
carbaminohaemoglobin (about 10%)
•
When blood reaches the lungs all of these
processes are reversed releasing CO2 & leaving
the Hb free to go about it’s business!
2. Conversion to carbonic acid
1.
2.
3.
plasma
Inside the red blood cells are many
molecules of an enzyme called
carbonic anhydrase *.
CO2
It catalyses the reaction between
CO2 and H2O.
CO2
+
carbon
dioxide
4.
Red cell
During respiration, CO2 is produced.
This diffuses into the blood plasma
and into the red blood cells.
H2O

water
The resulting carbonic acid then
dissociates into HCO3- + H+.
(Both reactions are reversible).
H2O
*
H2CO3
HCO3- + H+.
H2CO3
carbonic
acid
HCO3-
Why is this process important?
• The hydrogen ions quickly combine with Hb
forming heamoglobinic acid
• This makes the Hb release the oxygen it is
carrying
• The hydrogencarbonate ions diffuse out of
the erythrocyte & into the plasma
• They remain here in solution
• This helps the blood to remain at pH neutral
Divide your page in to 4…
1. Hb combining with oxygen
2. CO2 dissolving in plasma
3. CO2 diffusing into erythrocyte &
becoming carbonic acid
4. CO2 combining with Hb to
become carbaminohaemoglobin
Define time
1. Haemoglobin
2. Oxyhaemoglobin
3. Carbonic Anhydrase
4. Haemoglobinic acid
5. Carbaminohaemoglobin
CO & O Transport
2
2
• Describe & explain the
significance of the haemoglobin
dissociation curve
• Can use knowledge of Carbon
Dioxide transportation to explain
the Bohr effect
Look at graph 5.26 on page
81…
What do you think it shows?
Haemoglobin
• Oxygen is transported
around the body
inside red blood cells
in combination with
the protein
haemoglobin
• Each haemoglobin is
made up of four
polypeptides each
containing one haem
group
Haem
group
What is partial pressure?
• The pressure that one
component of a mixture
of gases would exert if
it were alone in a
container.
• Note: During this topic
you will come across
the term of partial
pressure. Essentially it
is a measure of the
concentration of
oxygen. It is written in
shorthand as pO2 and
is measured in
kilopascals (kPa).
How much oxygen can be
carried?
• Overall each molecule can combine with
four oxygen molecules
• This means that eight oxygen atoms can
be carried by each haemoglobin molecule
Hb
+
haemoglobin
4O2
HbO8
oxyhaemoglobin
The binding of oxygen is a reversible reaction.
The haemoglobin dissociation
curve
• The balance can be
shown by an oxygen
dissociation curve for
oxyhaemoglobin.
The
amount of oxygen
held by the haemoglobin,
i.e. its saturation level, is
normally expressed as a
percentage.
The haemoglobin dissociation
curve
At
low partial pressures of
oxygen, the percentage
saturation of haemoglobin is
very low, that is the
haemoglobin is combined
with only a very little oxygen.
 E.g. In the muscles!
At
high partial pressures
of oxygen, the percentage
saturation of haemoglobin
is very high. It is combined
with large amounts of
oxygen.
 E.g. In the lungs!
Answer SAQ 13 on page 81!
What determines the loading and
unloading of oxygen by
haemoglobin?
The amount of oxygen that
haemoglobin carries is
affected by:
1)
2)
High
pC02
The partial pressure of
oxygen and
The partial pressure of
carbon dioxide
The presence of a high partial pressure of carbon dioxide
causes haemoglobin to release oxygen.
This is called the Bohr effect
Haemoglobin
releases
oxygen
The Bohr effect
1.
2.
3.
Inside the red blood cells are many
molecules of an enzyme called
carbonic anhydrase *.
It catalyses the reaction between
CO2 and H2O.
CO2
carbon
dioxid
e
4.
Red cell
During respiration, CO2 is produced.
This diffuses into the blood plasma
and into the red blood cells.
+
H2O

water
The resulting carbonic acid then
dissociates into HCO3- + H+.
(Both reactions are reversible).
plasma
H2O
CO2
*
H2CO3
HCO3- + H+.
H2CO3
carbonic
acid
HCO3-
The Bohr effect (continued)
5. Haemoglobin very readily combines with
hydrogen ions forming haemoglobinic
acid.
6. As a consequence haemoglobin releases
some of the oxygen it is carrying.
7. By removing hydrogen ions from the
solution, haemoglobin helps to maintain
the pH of the blood close to neutral. It is
acting as a buffer.
The Bohr effect
Three Oxygen Dissociation
curves illustrating the Bohr
Effect.
Increased carbon dioxide in
the blood causes a right-shift
in the curves, such that the
hemoglobin more easily
unloads the oxygen it is
carrying.
Why is the Bohr effect useful?
• High concentrations of carbon dioxide are
found in actively respiring tissues, which
need oxygen. Due to the Bohr effect,
these high carbon dioxide concentrations
cause haemoglobin to release its oxygen
even more readily than it would do
otherwise.
How is carbon dioxide
transported?
• Carbon dioxide is mostly carried as
hydrogencarbonate ions in blood
plasma, but also in combination with
haemoglobin in red blood cells
(carbamino-haemoglobin) and
dissolved as carbon dioxide
molecules in blood plasma.
Carbon dioxide transport
About 5% of the CO2
produced simply dissolves in
the blood plasma.
About 85% of the CO2 produced by
respiration diffuses into the red blood cells
and forms carbonic acid under the control
of carbonic anhydrase.
The carbonic acid dissociates to produce
hydrogencarbonate ions (HCO3-)
The HCO3- diffuses out of the red blood
cell into the plasma
Some CO2 diffuses into the red
blood cells but instead of forming
carbonic acid, attaches directly onto
the haemoglobin molecules to form
carbaminohaemoglobin.
Since the CO2 doesn’t bind to the
haem groups the Haemoglobin is
still able to pick up O2.
Fetal Haemoglobin
• Explain the significance of the
different affinities of fetal
haemoglobin & adult
haemoglobin for oxygen
How does a developing fetus
obtain it’s oxygen?
• A fetus cannot breath therefore is
reliant upon it’s mother for a supply of
oxygen.
• This does happen in the placenta where
mother’s & fetus’ blood passes very
closely together (without mixing) to
allow oxygen to diffuse.
Fetal Haemoglobin & partial pressure
• Oxygen arrives at the placenta (in
mothers blood) combined with Hb in
the erythrocytes
• The partial pressure of oxygen in the
fetal blood is low due to respiration
• This causes the mothers Hb to
release oxygen which diffuses from
her blood into the fetus’ blood
Fetal Haemoglobin & partial pressure
• The partial pressure of oxygen in the
fetus’ blood is only a little lower than
that of the mothers blood so oxygen
diffusion is slow. However…
• The fetal haemoglobin is different
from the mothers, it has a greater
affinity for oxygen so will bind more
readily with available oxygen
• The dissociation
curve for fetal
haemoglobin is to
the left of adult
haemoglobin. What
does this say about
the affinity of fetal
haemoglobin for
oxygen?
• Fetal Hb has a
higher affinity for
O2 than adult Hb at
all partial pressures
• Why does fetal
haemoglobin need a
higher affinity than
adult?
• So when oxygen
dissociates from
maternal Hb it is
picked up by fetal
Hb