M3 - CARDIAC CYCLE, HAEMOGLOBIN AND BOHR

Question 1

Atrial systole

Answer 1

Atria contract and ventricles relax
Decreases volume in atria - increases pressure
Causes atrioventricular valves to open and pushes blood into ventricles

Question 2

Ventricular systole

Answer 2

Ventricles contract
Decreases volume - increases pressure
Pressure higher in ventricles compared to atria - atrioventricular valves close
Semi-lunar valves open and blood moves into arteries (aorta and pulmonary artery)

Question 3

Ventricular diastole

Answer 3

Ventricles relax and pressure low in both chambers
Semi-lunar valves close
Blood returns to heart in the atria

Question 4

Myogenic contraction

Answer 4

1. Sino-atrial node sends out electrical activity to atrial walls - left and right atria contract
2. Wave is directed towards atrioventricular node which passes electrical wave towards group of muscle fibres in centre of the heart - bundle of his
3. There is delay to ensure atria have emptied blood
4. Wave passes down Bundle of his in walls of ventricles as purkyne fibres
5. This causes left and right ventricles to contract from the apex of the heart

Question 5

QRS complex

Answer 5

Big spike in middle
Ventricular systole

Question 6

T wave

Answer 6

Bump at end
Ventricular diastole

Question 7

P wave

Answer 7

Small bump at start
Atrial systole

Question 8

Bradycardia

Answer 8

Heartbeat less than 60bpm

Question 9

Trachycardia

Answer 9

Heart rate over 100bpm

Question 10

Fibrillation

Answer 10

Irregular rhythm of heartbeat

Question 11

Ectopic heartbeat

Answer 11

Additional heartbeat not in rhythm

Question 12

How does haemoglobin bind to oxygen

Answer 12

Four polypeptide chains contain a haem group containing iron
Four oxygen molecules can bind to four haem groups - 4 oxygen molecules per haemoglobin
Binds to oxygen to form oxyhemoglobin

Question 13

How does partial pressure affect affinity

Answer 13

In places with high partial pressure (like lungs) affinity for oxygen is high - easy to load o2
In places with low partial pressure (like respiring tissue) affinity is low - difficult to load

Question 14

How does affinity change when more oxygen loads

Answer 14

Cooperative binding
When one oxygen loads onto haemoglobin, the quaternary and tertiary structure change shape, making it easier for more oxygen to load
However, if only one site available, it’s harder to load onto

Question 15

How does carbon dioxide affect affinity for oxygen

Answer 15

At higher partial pressures of carbon dioxide, haemoglobin has lower affinity for oxygen
Useful bc at respiratory tissues, producing a lot of co2, oxygen will need to be unloaded and co2 loaded on

Question 16

Bohr effect

Answer 16

1. Carbon dioxide released from respiring cells move into red blood cells, react with water to form carbonic acid
2. Carbonic acid dissociates to form hydrogen ion and hydrogencarbonate ion
3. Higher acidity causes oxygen to unload from oxyhaemolgobin
4. Hydrogen ions bind to haemoglobin to form haemoglobonic acid
5. Hydrogen carbonate ions diffuse out of blood cell to blood plasma
6. To balance charge, chloride diffuses into blood cell - CHLORIDE SHIFT
7. When blood reaches lungs hydrogen ion recombines w hydrogencarbonate to form co2 and water
8. This is diffused into alveoli and breathed out