LECTURE 4_ The Conducting System of the Heart _ Blood Vessels.ppt

Presentation on conducting systems of the heart, specifically the blood vessels.

1. The Conducting
System of the Heart

2. The Conducting System of the
Heart
•Generates and distributes impulses to
the contractile cells of the heart

3. The Conducting System of the Heart
•Consists of the:
•Sinoatrial Node (SA node)
•Atrioventricular node (AV
node)
•Conducting Cells
•Internodal pathways
•AV Bundle (Bundle
of His)
•Bundle Branches
•Purkinje Fibres
Purkinje
Fibres
Bundle of His

4. Conducting System of the Heart
•Cell membranes of the SA and AV nodes cannot
maintain a stable resting potential (-90 mV)
•Membrane drifts toward threshold (-75mV) after
repolarisation: Pre-potential
•Rates of Spontaneous Depolarisation
•SA node: 80 –100 per minute
•AV node: 40 –60 per minute
•Therefore, SA node sets heart rate

6. Pathway of Impulses through the Heart
1.Generation of action
potential at SA Node
2.Impulse transmitted to
AV node via internodal
pathways (Elapsed time
50 msec)

7. Pathway of Impulses through the Heart
(cont’d)
•100msec delay at the AV
node.
•Cells of the AV node
have a smaller diameter
than SA node cells,
therefore transmit
impulses slower
•Atrial contraction begins

8. Pathway of Impulses through the Heart
(cont’d)
3.Impulse transmitted to
AV bundle (Bundle of His)
(Elapsed time150ms)

9. Pathway of Impulses through the
Heart (cont’d)

10. Impulse passes through ventricular
myocardium; atrial contraction
completed ventricular contraction
begins (Elapsed time 225 msec)

11. The Electrocardiogram (ECG)
•Records the electrical activity of the heart
•10 electrodes placed on the surface of the body
•Used to detect abnormalities in the nodes,
conducting and contractile cells of the heart

12. The Electrocardiogram (ECG)

13. ECG Waveform
•P Wave –Atrial
Depolarization
•QRS Complex –Ventricular
Depolarization
•T Wave –Ventricular
Repolarization

15. The Cardiac Cycle

16. Blood Vessels
Structure and Major Types

17. Types of Blood Vessels
•Arteries–transport blood away from the heart
•Veins–transport blood to the heart
•Capillaries–vessels of exchange between the blood
and tissues

18. Structure of Vessel Walls
•There are threedistinct
layers in the walls of
arteries and veins:
•Tunica Intima
•Tunica Media
•Tunica Externa

19. Structure of Vessel Walls
Tunica Intima (Tunica Interna)
•Innermost layer
•Consists of an endothelial lining and
underlying connective tissue with elastic
fibres
•In arteriesthe outer margin of the tunica
intima contains a thick layer of elastic fibres
called the Internal Elastic Membrane

20. Structure of Vessel Walls
Tunica Intima

21. Structure of Vessel Walls
Tunica Media
•The middle layer
•Consists of concentric sheets of smooth muscle in a
loose connective tissue framework
•This layer is thicker in arteries than in veins
•Collagen fibres bind this layer to the tunica intima
and externa
•External Elastic Membrane surrounds this layer
in arteries
•The Tunica Media changes the diameter of the blood
vessel

22. Structure of Vessel Walls
Tunica Media
Note the location of the External Elastic
Membrane (Lamina)
Artery
Vein

23. Structure of Vessel Walls
Tunica Externa/Tunica Adventitia
•Outermost layer
•Connective tissue sheath
•Stabilizes and anchors vessel to adjacent tissues
•Thicker in veins than in arteries
•In arteriesit consists of collagen fibres with
scattered elastic fibre bands
•In veinsit consists of bundles of elastic fibres and
smooth muscle cells

24. Structure of Vessel Walls
Tunica Externa/Tunica Adventitia

25. Comparison of a Typical Artery and
Vein
•Artery
•Usually rounded, with
relatively thick wall
•Tunica Intima usually
rippled, due to vessel
constriction; internal
elastic membrane
present
•Vein
•Usually flattened or
collapsed, with relatively
thin wall
•Tunica Intima often
smooth; internal elastic
membrane absent

26. Comparison of a Typical Artery and
Vein
•Artery
•Tunica Media is thick,
dominated by smooth
muscle and elastic fibres
•External Elastic
Membrane present
•Tunica Externa of
collagen and elastic fibres
•No Valves
•Vein
•Tunica Media is thin,
dominated by smooth
muscle and collagen
fibres
•External Elastic
Membrane absent
•Tunica Externa of
collagen and elastic fibres
and smooth muscle cells
•Valves line lumen

27. Veins Showing Valves

28. Which of these is the Artery?

29. Types of Arteries
•Elastic
•Muscular
•Arterioles
•Peripheral capillaries

30. Elastic Arteries
•Up to 2.5 cm lumen diameter
•Large vessel
•Close to the heart
•Tunica media of mostly elastic fibres, few
smooth muscle fibres –Elastic Rebound
•Eg. Aorta, Pulmonary trunk, Common
Carotid, Subclavian

32. Muscular Arteries
•Medium sized
•0.4 cm –0.5 mm lumen diameter
•Distributes blood to skeletal muscle and
internal organs
•Thick tunica media, much thicker than in
elastic arteries
•Eg. External carotid, brachial, mesenteric,
femoral

34. Arterioles
•30 µm or less lumen diameter
•Poorly defined tunica externa and tunica
media reduced to 2 layers in larger arterioles
•Small arterioles have scattered smooth muscle
•Diameter changes under sympathetic nervous
stimulation and hormonal control
•Low oxygen levels cause dilation

36. Capillaries
•8 µm average diameter
•Posses an endothelial layer with basal lamina

37. Types of Capillaries
Continuous Capillaries
•The endothelium is a
complete lining
•A cross-section of large
continuous capillaries cuts
through several endothelial
cells
•In small continuous capillaries
a single endothelial cell may
completely encircle the lumen
•Located in all tissues except
epithelia and cartilage

38. Types of Capillaries
Fenestrated Capillaries
•Contain windows or pores
that penetrate the endothelial
lining
•Permit rapid exchange of
water and solutes as large as
small peptides
•Eg. Choroid plexus of the
brain and blood vessels in the
hypothalamus, small intestine
and filtration slits of the
kidneys

39. Venous System
•Venules
•Medium-Sized Veins
•Large Veins

40. Venules
•Average diameter 20 µm
•Collects blood from
capillary beds
•Valves present
•No tunica media in
venules smaller than 50
µm

41. Medium –Sized Veins
•2 –9 mm lumen
diameter
•Thin tunica media
with few smooth
muscle cells
•Thick tunica externa
of longitudinal
bundles of elastic
and collagen fibers
•Valves present

42. Large Veins
•All tunica layers
present
•Tunica externa
very thick; elastic
and collagen
fibres
•Eg. Superior and
inferior vena cava