1. Transport Mechanisms
Chapter 20

2. Cardiac Cycle Pattern of contraction & relaxation in 1 heartbeat
Average = 0.8 secs (75/min)
Atrial Systole (contraction)
– blood sent into ventricles through AV valves
Ventricular Systole
– ventricles contract
- AV valves close
- high pressure opens SL valves
- blood into arteries
Diastole (relaxation)
– Blood from veins enters & fills atria
- pressure differences open AV valve

3. Valves & Heart Sounds AV (mitral) valve closure = heart sound (‘lubb’)
SL (aortic) valve closure
= second heart sound (‘dubb’)
Irregular sounds = heart murmur
Due to valve problems
Measured by phonocardiogram
Heard using a stethoscope

4. Heart Conducting System
Pacemaker (Sino-atrial node – SAN): (1)
Found in the right atrium wall
Exhibits spontaneous excitation
Starts electric impulses
- heart muscle cells contract
Wave of excitation makes atria contract – (2)
Impulse picked up by atrio-ventricular node (AVN) – (3)
Impulse passed to conducting fibres – (4)
Ventricles stimulated
– ventricular systole – (5)

5. Measuring Electrical Activity
Electrocardiogram (ECG) shows electrical activity of the heart
Abnormal ECG’s - caused by rapid electrical excitation
Atrial Flutter:
Co-ordinated, but very rapid contractions
Fibrillation:
Heart muscle contraction irregular & uncoordinated
Ventricular Tachycardia:
Abnormal ventricular cells act like pacemakers
Ventricle contracts independently of the atrium
All 3 can be relieved by artificial pacemakers

6. Blood Pressure Ventricular Systole
– aorta pressure rises to a max (avg.120mmHg)
Ventricular Diastole – pressure is at a min (avg. 80 mm Hg)
Measured using a sphygmomanometer
Aorta elastic walls maintain blood pressure
As blood circulates round the body the pressure gradually decreases
Blood flowing through blood vessels = peripheral resistance

7. High Blood Pressure Increased heart contraction rate/force
= higher blood pressure
Common causes: stress or high salt intake
Dangers:
Ventricles work much harder
Arterial walls more prone to atherosclerosis
Damage to blood vessels - stroke

8. Lymphatic System Lymphatic vessels absorb excess tissue fluid (lymph)
Lymph moved by vessel compression
- body movements
Backflow prevented by valves
Lymph re-enters bloodstream via lymphatic ducts in the arms
Lymph also contains lipids
- absorbed by lacteals in the intestine

9. Lymph Nodes Occur in glands around the body - e.g armpit, neck, groin
Consist of lymph nodules, central medulla, & germinal centre
Fibres in between the nodules lined with macrophage cells
As lymph passes, macrophage remove unwanted material
- by phagocytosis
Lymph drains into medulla & exits by lymphatic vessel
Illness = too many bacteria = nodes swell up

10. Oedema Accumulation of tissue fluid in between cells & capillaries
Causes swelling
Caused by:
High blood pressure
Malnutrition
– low plasma protein in blood
- blood and tissue fluid equal conc.
- fluid doesn’t return osmotically
- causes kwashiorkor
Parasites
– invade lymphatic system & block vessels (e.g legs)
- causes elephantiasis