1. 4'8+'9

2. SA = Sinoatrial AV= Atrioventricular
The SA node is pacemaker which is stimulated by
two nerves: a sympathetic nerve that accelerates the heart,
and the vagus nerve that slows the heart which restores the
heartbeat to a homeostatic level. It is located towards the
top of the right atrium, so that the atria beat from the top
down. The AV node receives the signal from the SA node and
delays a tenth of a second before firing, to allow the atria t
to
finish contracting before ventricular systole begins. The
impulse from the AV node travels down the common bundle,
then is carried up the walls of the ventricles by fibers. This
ensures that the ventricles contract from the bottom up.

3. Atherosclerosis happens when arteries become
sis
damaged and form scar tissue. Cholesterol and other lipids
build up on the scar tissue, forming a plaque. This plaque can
induce platelets to release chemicals that cause a clot to form
over the plaque, called a thrombus.
Age - older people have greater risk/ less elasticity in arteries
Sex - male at greater risk than female
Genetic - having a family history of CDH
High blood pressure
Obesity - increases in blood pressure/ leads to plaque formation in arteries
Physical inactivity- lack of exercise increase risk due to weakened circulation
Smoking - constricts blood vessels/ increase blood pressure/ heart rate // increases fibrinogen and
platelets in blood lead to more clotting
Diet- increases fat/cholesterol/LDL in blood/leads to plaque formation in arteries

4. References:
- IB Biology/Option H - Further Human Physiology - Wikibooks, Open Books for an
Open World. Wikibooks. Web. 9 Mar. 2011.
http://en.wikibooks.org/wiki/IB_Biology/Option_H_-_Further_Human_Physiology.
- ”Option H: Further Human Physiology | Science Video Resources. Science Video
Resources | IB Biology, Science and More…. Web. 8 Mar. 2011.
http://sciencevideos.wordpress.com/options/further-human-physiology/.
- ”Option H: Further Human Physiology. Transport System Web. 8 Mar. 2011.
http://health.medicbd.com/library/document_play/3834577
-