Describe the structure of the heart Explain the importance of the valves Describe the cardiac cycle List the factors that leads to the heartbeat

1. The heart
Jorge Melo

2. Recap

3. Recap

9. Objectives YSBAT
 Describe the structure of the heart
 Explain the importance of the valves
 Describe the cardiac cycle
 List the factors that leads to the heartbeat

10. Mind Map
 Heart structure
 Chambers
 Valves
 Muscle
 Cardiac cycle
 Heartbeat

11. Some interesting facts
 The heart beats between 80,000 to 100,000 times and
pumps approximately 23,000 liters of blood a day!
 That means it will have beat 2-3 billion times and
pumped 50-65 million gallons of blood over a 70-90
year lifespan.

12. The heart
 Surrounded by a tough sac:
Pericardium
 Outer part: inelastic white
fibrous tissue (prevents heart
from overstretching)
 Inner part: 2 membranes
-inner attached to the heart
-outer attached to the fibrous
tissue
Pericardial fluid: between the two
inner membranes for friction
reduction

13. The heart
 Between the two lungs
 Behind the sternum in the thorax

14. Heart chambers
 4 chambers
 2 upper (thin)
 Atrium
 2 lower (thicker)
 ventricles

15.  The heart contains four hollow chambers
 The top two chambers are called Atria……..(Above)
 The bottom two chambers are called Ventricles
RIGHT LEFT
ATRIUM ATRIUM
LEFT
RIGHT
VENTRICLE
VENTRICLE
MUSCLE

16. AORTA
PULMONARY ARTERY
PULMONARY VEIN
VENA CAVA
SEPTUM
The function of the labelled parts:
SEPTUM – Divides the two sides of the heart preventing oxygenated blood
mixing with deoxygenated blood.
THE PULMONARY VEIN – Transports oxygenated blood to the heart.
THE AORTA – Transports oxygenated blood away from the heart to the body.
THE VENA CAVA – Transports deoxygenated blood from the body back to the heart.
THE PULMONARY ARTERY – Transports deoxygenated blood to the lungs.

17. Simple Plan of our Circulatory System

18. Valves in the Heart
Valves allow blood to travel one way but not the other
SEMI-LUNAR VALVES
Atrioventricular
valves
TRICUSPID VALVE BICUSPID (MITRAL)
VALVE

19. Atrioventricular valves
 Tricuspid valve
 Right
 Bicuspid valve
 Left
 Function: prevent the backflow of blood
Into the atria when the ventricles contract

20. Structure of cardiac muscle
 Heart walls composed by:
 Cardiac muscle fibres
 Connective tissue
 Tiny blood vessels
 Muscle fibre
 1 or 2 nuclei
 Many large mitochondria
 Many myofibrils

21. Cardiac muscle
 Myocardium
 Epicardium
 Endocardium

22. Cardiac muscle
Cardiac muscle
 Intercalated discs: cell Muscle fibres
surface membranes
separating individual
muscle cells Interconnecting
muscle cells
 Structure can change to
allow ions to diffuse
 Allowing a fast spread of
impulses
 When one cell is excited
The action potential
spreads
Quickly to all the others

23. The cardiac cycle
 Series of events which takes place during the
completion of one heartbeat.
 Involves repeated contraction and relaxation of the
heart muscle,
 Note that: Contraction = Systole
Relaxation = Diastole

24. Atrial diastole
 Atria and ventricles both
relaxed
 Blood returning to the
heart under low pressure
 Oxygenated Blood
entering the left atrium
 Deoxygenated blood right
atrium
 Valves closed at the
beginning

25. Atrial diastole
 When the
pressure rises the
bicuspid and
tricuspid valves
open allowing the
blood to enter in
the ventricles

26. Atrial systole
 When atrial diastole ends, the two atria contract
simultaneously to pump the blood into the ventricles

27. Ventricular systole
 0.1/0.2 sec. later
 Contraction
 Pressure rises in the
ventricles making the
semi lunar valves to
open
 Blood enter the vessels
The closing of the atrioventricular valves during this stage produces the first
heart sound (lub)

28. Ventricular diastole
 High pressure
developed in the
aorta and pulmonary
artery tends to force
some blood back
towards the ventricles
and this closes the
semi-lunar valves of
the aorta and
pulmonary artery
 Closing the valves
cause the second
heart sound (dub).

29. How the heart acts as a pump
Click me…. (the heart says)

30. Task
 Write and explain the process that happens in the
heart as blood travels through it.
 Include all the names of the main parts of the heart
covered in the lesson.
 E.g. 1)Deoxygenated blood enters from the body through the Vena
Cava into the right atrium ……………..

31. Quick Quiz
1) What type of muscle is the heart made up of?
2) The top two chambers of the heart are
called………….?
3) The bottom two are called………?
4) What divides the left side of the heart from the
right side?
5) Blood entering the right atrium comes through
what?
6) Blood leaving the left ventricle travels through
what?
7) What is the purpose of the valves?

32. The heart beat
 The heart is made up of cardiac muscle.
 Cardiac muscle is myogenic, which means it naturally
contracts and relaxes.
 Therefore, it receives no impulse from a nerve to make
it contract.

33. The heart beat
 If you remove a heart and place it
in well-oxygenated place salt
solution at 37 ̊C, the heart will
continue to beat for some time
 Myogenic nature of the
stimulation of the heart

34. The heart beat
 The cardiac cycle is initiated by a small patch of
muscle called the Sino atrial node (SAN) or
pacemaker.
 This node sets the rhythm for all the other cardiac
muscle.
 Pacemaker cells have an inbuilt rhythm that is faster
than the other cells in the heart.

35. The heart beat
 Stimulus for contraction: SAN (Sino-atrial node)
 Near the opening of
the Vena cava
 Small numbers of
cardiac muscle fibres
and a few nerves
endings from
autonomic nervous
system

36. The heart beat
 The SA node sends out an excitation wave of electrical
activity over the atrial walls.
 The cardiac muscle responds to this wave by
contracting at the same speed as the SAN.
 Speed rate: 1 m s -1
 This results in both right and left atria contracting
simultaneously.

37. The heart beat
 There is a delay between atrial contraction and ventricular
contraction.
 Fibres between the two chambers that do not conduct the
excitation phase cause this delay.
 Collagen fibres prevent the electrical signals to from passing
through the heart wall from atria to ventricles
 What cause the ventricles to contract then?

39. The heart beat
 A second node
 The AVN (atrio-ventricular node), which picks ups the
impulses that have passed through the atrial muscle and
respond generating its own electrical impulses
 After about a delay of 0.15 seconds the AV node passes the
wave into His bundle (fibres from the right and left that meet
together in the septum)
 They branch to form the right and left bundle
 The wave is sent to another set of conducting fibres that run
down the centre of the septum between the ventricles called
the Purkyne (Purkinje) fibres

41. The heart beat
 The wave is then transmitted (very rapidly) down to
the bottom of the septum, where it spreads through
the ventricles’ walls in an upward direction.
 This movement causes the muscle to contract and the
ventricles squeeze the blood out of the heart.

43. Task
 Describe the series of events that lead to the heartbeat
 Use a diagram to support your explanation

44. ECG
 Detects electrical activity during cardiac cycle.
P
Q
R
S
T
U

46.  Absolute refractory period
 Period in which the heart cannot respond to a second
stimulus – enables full recover without being fatigued
 Relative refractory period

47. Regulation of heart rate
 Demands of the blood system is always changing
 Heart rate needs to be adjusted
 Homeostatic response (nervous and chemical)

48. Regulation of heart rate
 Cardiac Output: amount of blood flowing from the
heart over a period of time and depends on upon the
volume of blood pumped out of the heart at each beat,
the stroke volume, and the heart rate (number of beats
per minute)
 CO= SV x HR
 CO is important variable supplying blood to the blood

49. Nervous control of Heart Rate
 Medulla
 Controls heart rate
 Nerves connecting medulla and the heart
 Nervous system divided in voluntary nervous system
and an autonomic nervous system (acts
automatically)

50. Nervous control of the heart rate
 ANS:
 Sympathetic Nervous System (SNS)
excitation and preparation of the body for action
 Parasympathetic Nervous System (PNS)
relaxing influence
Both involved in the heart rate

51.  Medulla
 Cardiac inhibitor centre (CIC)
 Reduces HR
 Cardiac accelerator centre (CAC)
 Stimulates HR

52. Nervous control of the heart rate
 PN (vagus nerves) leaves CIC to the
heart ( SAN, AVN and bundle of His)
 Impulses reduce HR
 Nerves on the CAC run on the SNS
To the heart (SAN)
 Impulses increase HR

53. Nervous control of the heart rate
 Coordinated activity of the inhibitor and
accelerator centres in the medulla that controls
the heart rate

54. Nervous control of the heart rate
 Sensory nerve fibres from stretch receptors within the walls
of the aortic arch,
 The carotid sinuses and
 the vena cava
 Run to the cardiac inhibitor and accelerator in the medulla
 Impulses fro the aorta and carotids decrease the heart rate
 Impulses from the vena cava stimulated the accelerator
centre which increases the heart rate
 This stimulates the stretch receptors and increases the
number of nerve impulses transmitted to the centres in the
medulla

55. Nervous control of the heart rate
 Intense activity
 Body muscles contract strongly
 More venous blood return to the heart
 Walls of vena cava stretch by large quantities of blood
and heart rate increases

56. Nervous control of the heart rate
 Increased blood flow to the heart
 Increases the pressure of the cardiac muscle
 Cardiac muscle responds automatically contracting
more strongly (systole), pumping more blood
 Stoke volume is increased
 Starling’s Law

57.  Increased stroke volume stretches the aorta and
carotids which in turn, via stretch reflexes, signal the
cardiac inhibitor centre to slow the heart rate.
 This prevents heart from working to fast

58. Hormonal control
 Adrenaline secreted by the medulla of the adrenal
glands (also produces noradrenaline)
 Both Stimulate the heart
 Cardiac output and blood pressure are increased by
increased heart rate

59. Hormonal control
 Thyroxine: produced by thyroid glands
 Raises basal metabolic rate
 Leads to greater metabolic activity, with greater demand
for oxygen and production of more heat
 Result: vasodilation followed by increased blood flow
 Increased cardiac output

60. Other factors controlling heart rate
 Emotions
 Embarrassment
 Anger
 Sounds/ sights