KUFA medical college

1. Introduction to the
Cardiovascular Module
module leader: Dr. ali yahya al-salime
email: aliy.alsalime@uokufa.edu.iq

2. How the module is structured
• First 3 sessions
– introduction to cardiovascular system, the
anatomy & development of the heart
• important physiology of the cardiovascular
system
• final sessions more clinically focussed
• group work throughout
• case studies

3. Formative assessments
• 2 formative assessments
– week 7
– week 8 ECG quiz
– week 14
• Sample summative questions at end of
module

4. Recommended text books

5. Cardiovascular Module
• The broad aim of this module is that you
should understand the structure and
function of the human cardiovascular
system, how its condition is assessed, and
how cardiovascular function is altered in
common diseases

6. Why do we need a cardiovascular
system?
• single-celled or tiny organisms can get O2 and
nutrients directly by diffusion from environment
• larger organisms need a circulatory system
• human body has around 1014
cells
– most cells far away from source of O2 and nutrients
• cells are metabolically active
– use O2 and produce CO2
• a system is required to carry O2 and nutrients to
cells and carry waste products away

7. We need a cardiovascular system
because -
• Distance of cells from the source of O2
and metabolic substrates
THEREFORE
• A mechanism for transporting these
substances to the cells is essential to
allow diffusion to take place

8. Components of the cardiovascular
system
• Distribution system – vessels & blood
• Pump – the heart
• Exchange mechanism - capillaries

9. Blood
• Transports O2, metabolic substrates, CO2
and waste products around the body
• There is exchange of these substances
between the blood and cells of the body

10. Blood
• Exchange occurs by diffusion
• Substances diffuse between the blood and
the surrounding tissue
• The function of the cardiovascular system
is to provide adequate conditions for
diffusion to each tissue of the body

11. Where does diffusion take place?
• Capillaries are the site for diffusion
between blood and the tissues
• Capillaries are composed of a single layer
of endothelial cells surrounded by basal
lamina

12. Diffusion
• Some substances eg O2 and CO2 are
lipophilic and diffuse through the lipid
bilayer
• Others molecules such as glucose, amino
acids and lactate are hydrophilic and
diffuse through small pores in the
capillaries
• All molecules will move down their
concentration gradient

13. O2 CO2
lipid soluble
molecules
small water
soluble
molecules
endothelial cell
capillary lumen
interstitial fluid
Diffusion through capillaries
small hydrophilic (lipid insoluble) substance such as glucose diffuse
through aqueous pores between endothelial cells

14. What factors affect diffusion
• rate of diffusion depends on:
– area
– diffusion ‘resistance’
– concentration gradient

15. Area
• rate of diffusion depends on the area
available for exchange

16. Area
• rate of diffusion depends on the area
available for exchange

17. Area
• area for exchange between capillaries and
tissues is generally very large
– it depends on capillary density
• a tissue which is more metabolically active
will have more capillaries

18. Diffusion resistance
• resistance to diffusion depends on
– nature of the molecule
• eg lipophilic or hydrophilic, size
– nature of the barrier
• eg pore size and number of pores for hydrophilic
substances
– path length
• depends on capillary density
• path is shortest in the most active tissues
• diffusion resistance is mostly low

19. Concentration Gradient
• rate of diffusion is dependent on the concentration gradient
– the greater the concentration gradient the greater the
rate of diffusion
– the concentration which matters is between capillary
blood and tissues
• for exchange to continue the concentration gradient
between the capillary blood and tissues must be
maintained

20. • a substance which is used by the tissues
will have a lower concentration in capillary
blood than arterial blood
• how much lower depends on
– rate tissues use the substance
– rate of blood flow through the capillary bed
Concentration Gradient
arterial end
venous end
blood flow
capillary

21. Maintaining the concentration
gradient
• at any rate of use, the lower the blood flow the
lower the capillary concentration
• rate of blood flow must be high enough to
maintain a sufficient concentration gradient for
diffusion
• i.e. rate of blood flow determines the
concentration gradient driving O2 diffusion into
the cells

22. Supply and Demand
• blood flow must match the tissues’
metabolic needs
– the higher the rate of metabolism the greater
the demand for O2 and nutrients
– increases in metabolism must be met by
increases in blood flow
– the rate of blood flow is known as the
perfusion rate

23. Blood flow to different tissues
• Brain needs high, constant flow
– 0.5 ml.min-1
.g-1
• Heart muscle needs high flow which increases
during exercise
– 0.9 to 3.6 ml.min-1
.g-1
• Kidneys need high, constant flow
– 1.0 ml.min-1
.g-1
• Blood flow to skeletal muscle can be very high
during exercise and gut blood flow is high after a
meal

24. Blood flow to different tissues
Tissue Min. flow l.min-1
Max. flow l.min-1
brain 0.75 0.75
heart 0.3 1.2
kidneys 1.2 1.2
gut 1.4 2.4
muscle 1.0 16.0
skin 0.2 2.5
other 0.2 0.2
TOTAL 5.0 24.5

25. Blood flow must adjust to meet
requirements
• At rest total blood flow is about 5 l.min
• In exercise this can rise to 25 l.min

26. Specification for the CVS
• The cardiovascular system must supply
between 5 and 25 l.min-1 of blood to the
tissues whilst at all times maintaining
perfusion to vital organs such as the brain,
heart and kidneys

27. Regulating blood flow
• If a pump is just connected to a network of
vessels blood will only flow to the parts that are
easiest to perfuse
• The brain is harder to perfuse due to gravity
• To regulate blood flow you need to add
resistance to the system
– Reduce the ease with which some regions are
perfused in order to direct blood flow to the more
difficult to perfuse regions
• Arterioles are the resistance vessels

28. The pump
• Heart is two pumps in
series
• The left heart pumps
blood around the
systemic circulation
• The right heart pumps
blood around the
pulmonary circulation
Right
heart
Left
heart
A
B
C
Lungs
systemic
circulation
pulmonary
circulation

29. The Circulation
• Heart pumps blood to arteries
• Arteries supply arterioles
• Arterioles supply capillaries
• Capillaries drain into venules
• Venules drain into veins
• Veins return blood to the
heart
heart
arteriolesvenules
arteriesveins
capillaries

30. Need for flexibility
• The total flow in the system has to be able
to change. This requires a temporary
store of blood which can be returned to
the heart at a different rate.
• Veins have thin walls which can easily
distend or collapse enabling them to act
as a variable reservoir for blood.
• The capacitance of the veins provides the
temporary store

31. Distribution of blood in the CVS
67%
11%
5%
17%
arteries and arterioles
capillaries
heart and
lungs
veins