3'10'3,4,5,6

1
3.10.3,4,5,69 Heart and Circulatory System.

• Objectives
• Be able to label a diagram of the heart.
• Be able to explain the difference in artery and
  vein structure
• Be able to describe the stages of the cardiac
  cycle.
• Be able to describe what makes the heart beat and
  how its rate can be varied.
• Revise homeostasis.

2
Structure of the Heart.
3
The table!

• Write out the route that blood takes from the
  lungs to heart to the body and back to the heart.
• Include the details of the heart chambers, valves
  and major vessels passed through.

4
Heart defects

• The two parts of the circulation in the heart are
  separated by the septum.
• In the uterus a foetus has a hole in the septum
  to bypass the pulmonary circulation.
• At birth this hole usually seals over as blood
  starts to flow in the pulmonary artery.
• If the hole does not seal over blood will not
  pass efficiently to the lungs and body. This will
  result in lower blood pressure and less oxygen
  reaching the body.
• Exercise is more difficult and growth may be
  impaired.

5
Contd.

• Similar situations can arise if the heart has not
  grown properly.
• Some adults can suffer from leaky valves. These
  allow blood to leak backwards and reduce the
  circulatory efficiency.

6
The Cardiac Cycle

• The cardiac cycle describes the wave of
  contractions that pumps the blood from veins to
  atria to ventricles to arteries.
• There are two main stages
• Cardiac diastole.
• Cardiac systole itself made up of two stages
  atrial systole and ventricular systole.

7
The Graph.
8
Cardiac diastole

• Heart muscle relaxes 0.5s at rest.
• Bicuspid and tricuspid valves close and the atria
  fill with blood.
• An increase in blood pressure then causes the two
  valves to open

9
Cardiac systole.

• Heart muscle contracts 0.3s at rest.
• Aortic and pulmonary valves stay closed and the
  atria contract forcing blood into the ventricles.
  (Atrial systole)
• The ventricles contract closing the bicuspid and
  tricuspid valves. The ventricles contract forcing
  open the aortic and pulmonary valves, allowing
  the blood to flow into the aorta or pulmonary
  artery. (Ventricular systole).

10
Valves.

• Valves prevent blood from flowing backwards.
• On the previous diagram label when
  atrioventricular valve opens and closes and when
  the aortic valve opens and closes.

11
The heart Beat.
12
What makes the heart beat?

• Heart muscle is said to be myogenic it beats at
  an intrinsic rhythm.
• Nerves connected to the heart have two effects
• Sympathetic nerve causes the heart rate to
  speed up.
• Parasympathetic nerve causes the heart rate to
  decrease.

13
How does the wave of contraction spread across
the heart?

• The contraction is initiated in the sino-atrial
  (SA) node.
• The wave of contraction moves through the atrial
  myocardium (muscle).
• The wave reaches the atrio-ventricular (AV) node.
• The impulse is passed to the bundle of His.
• It travels from the bundle to Purkinje fibres.
• The fibres pass the impulse on to the walls of
  the ventricles which in turn contract from the
  bottom upwards.

14
What happens during exercise?

• Homeostasis is the process where the internal
  environment of the body is kept constant.
• When you exercise the body needs to respond to
  the changes in order to keep temperature, pH, CO2
  , O2 levels at a reasonable level.
• Why is this important?

15
General Homeostasis.

• This should be recognisable from GCSE.
• The same pathway applies to most changes that
  occur in the body.

16
How does the heart respond to exercise?
17
Changes contd.

• Increased exercise leads to the production of
  carbon dioxide which leads to the blood pH
  falling more acidic.
• This is detected by receptors in the aorta and
  carotid sinus.
• These receptors increase their rate of nerve
  impulse transmission to the cardiac centre in the
  brain.

18

• The cardiac centre sends impulses along the
  sympathetic nerve to the SA node, AV node and
  ventricle walls.
• This causes the heart rate to increase and supply
  more oxygen to the tissues and remove the extra
  carbon dioxide.
• In addition, vasoconstriction of the blood
  vessels leads to an increase in blood pressure,
  increasing the efficiency of supply to the
  tissues.

19
Abnormal Rhythm

• If the heart does not beat at a regular rhythm
  this may be due to a damaged or faulty SA node or
  electrical activity in the heart.
• This may lead to inefficient blood movement and
  hence lead to chest pain, tiredness etc.
• A pacemaker can be fitted to regulate the heart
  beat.
• Usually these monitor heart rate and apply
  electrical impulses if the rate sets below a
  predetermined level eg 60 beats per minute.
• See p189 for details.

20
Arteries and Veins
21
Arteries and Veins.
22
Valves.

• Valves ensure that blood flows in one direction
  only.
• List all of the places where valves are found.