The Heart

Question 1

What are the adaptations of erythrocytes (rbc)

Answer 1

-biconcave shape, larger SA than simple disc structure or sphere, more SA for gas diffusion. Also helps them pass through narrow capillaries.

-In adults, erythrocytes are formed continuously in the red bone marrow. Mature erythrocytes lose their nucleus, maximises haemoglobin that fits into cells. Also limits their life-last about 120 days in bloodstream.

Question 2

What is haemoglobin

Answer 2

Red pigment that carries oxygen and gives colour. Very large globular conjugated protein made up of four peptide chains, each with an iron-containing haem prosthetic group. 300 million haemoglobin molecules in each rbc.

Question 3

How does haemoglobin carry oxygen

Answer 3

Steep conc. gradient between rbc and alveoli. Oxygen moves into erythrocytes and binds with haemoglobin.

Question 4

What is positive cooperativity

Answer 4

• As soon as one oxygen molecule binds to haem group, the molecule changes shape, making it easier for the next molecule to bind.

-Because the oxygen is bound to the haemoglobin, the free oxygen concentration in the erythrocyte stays low, so a steep diffusion gradient is maintained until all the haemoglobin is saturated with oxygen.

Question 5

What happens when the blood reaches the body tissue

Answer 5

Situation is reversed. Conc. of oxygen in cytoplasm of body cells is lower than in the erythrocytes. Oxygen moves out. Once the first oxygen molecule is released by the haemoglobin, the molecule again changes shape and it become easier to remove the remaining oxygen molecules.

Question 6

Describe stages of the oxygen dissociation curve

Answer 6

1. At low p02, few haem groups are bound to oxygen, so haemoglobin doesn’t carry much oxygen.
2. At higher p02, more haem groups are bound to oxygen making it easier for more oxygen to be picked up.
3. The haemoglobin becomes very saturated at very high p02 as all the haem groups become bound.

Question 7

What happens to the erythrocytes when you are not very active

Answer 7

Only 25% of oxygen carried is released into body cells. The rest acts as a reservoir for when body demands more.

Question 8

What’s the effect of carbon dioxide on oxygen Bohr effect.

Answer 8

As partial pressure of C02 increases, haemoglobin gives oxygen more easily.-

Question 9

Why is the Bohr effect important

Answer 9

-Active tissues- high partial pressure of C02, haemoglobin gives up its oxygen more readily.

-In the lungs where the proportion of C02 is low, oxygen binds to the haemoglobin molecules easily.

Question 10

What is feral haemoglobin

Answer 10

Has a higher affinity for oxygen. Oxygenated blood from mother runs close to deoxygenated fetal blood in placenta.

Question 11

What are the three ways carbon dioxide is transported to the lungs

Answer 11

-5% carried dissolved in plasma

-10-20% is combined with amino groups in the polypeptide chains of haemoglobin to form a compound called carbaminohaemoglobin.

-75-85% is converted into hydrogen carbonate ions in the cytoplasm of the rbc.

Question 12

How does carbon dioxide form carbonic acid

Answer 12

Carbon dioxide reacts slowly with water to form carbonic acid. The carbonic acid then dissociates to form hydrogen ions and hydrogen carbonate ions.

Question 13

Why are carbonate ions formed quickly in rbc cytoplasm

Answer 13

The cytoplasm contains high levels of the enzyme carbonic anhydrase- catalyses reaction between carbon dioxide and water.

Question 14

What is the chloride shift

Answer 14

Negatively charged hydrogen carbonate ions move out of the erythrocytes into the plasma by diffusion and negatively charged chloride ions move into the erythrocytes, which maintains the electrical balance of the cell.

Question 15

Why does the chloride shift happen

Answer 15

By removing C02 and converting it to hydrogen carbonate ions, the erythrocytes maintain a steep concentration gradient for carbon dioxide to diffuse from the respiring tissues into the erythrocytes.

Question 16

What happens when the blood reaches the lung tissue

Answer 16

Carbonic anhydrase catalyses the reverse reaction, breaking down carbonic acid into carbon dioxide and water. Hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to form more carbonic acid. Chloride ions diffuse out of rbc into plasma.

Question 17

How does haemoglobin play a role in the chloride shift

Answer 17

Acts as a buffer and prevents changes in the pH by accepting free hydrogen ions in a reversible reaction to form haemoglobinic acid.

Question 18

What is the heart made out of

Answer 18

Cardiac muscle- contracts and relaxes in regular rhythm. Doesn’t get fatigued. Coronary arteries supply cardiac muscle with oxygenated blood it needs to keep contracting and relaxing.

Question 19

What are the atrioventricular valves called

Answer 19

Right-tricuspid valve
Left-bicuspid valve

Question 20

What do the tendinitis cords in the heart do

Answer 20

Make sure the valves are not turned inside out by the pressures exerted when the ventricle contracts.

Question 21

What’s the inner dividing wall of the heart called

Answer 21

The septum-prevents mixing of blood

Question 22

What’s diastole

Answer 22

Heart relaxes, atria and ventricles fill with blood. The volume and pressure of the blood in the heart fills, but pressure in arteries is at minimum.

Question 23

What’s systole

Answer 23

Atria contract, then ventricle. Pressure increases dramatically. Volume and pressure low at end, though high in arteries.

Question 24

Where do heart sounds come from

Answer 24

Made by blood pressure closing the heart valves. Two sounds- atrioventricular valves closing and ventricle contract, then semilunar valve closing as ventricle relax.

Question 25

What is cardiac muscle

Answer 25

Myogenic- maintains its own beat of the heart- body doesn’t have to waste resources maintaining it- around 60/70 bpm.

Question 26

Stages of the rhythm of heart

Answer 26

1. Wave of electrical excitation begins in pacemaker area called sino-atrial node, atria contracts. Layer of non-conducting tissue prevents the exitation passing directly into ventricles.
2. The electrical activity is picked up by the atrio-ventricular node. The AVN imposes a slight delay before stimulating the bundle of his, a bundle of conducting tissue made up of purkyne fibres, which penetrate through septum between ventricles.
3. Bundle of his splits into two branches and conducts the wave of excitation to the apex (bottom) of the heart.
4. At the apex the purkyne fibres spread out through the walls of the ventricles on both sides. The spread of excitation triggers the contraction of ventricles, starting at the apex. Contraction starting at the apex allows more efficient emptying of the ventricles..

Question 27

Why is there a delay with the AVN

Answer 27

Makes sure the atria have stopped contracting before the ventricles start.

Question 28

What’s bradycardia

Answer 28

Slow heart rate- beats evenly spaced, rate <60 bpm- may need artificial pacemaker.

Question 29

What’s tachycardia

Answer 29

Fast heart rate- beats evenly spaced, rate >100bpm- treated by medication or surgery.

Question 30

What’s an ectopic heart beat

Answer 30

Altered rhythm, extra beat followed by longer than normal gap before next beat. Normal but can be serious if frequent.

Question 31

What’s atrial fibrillation

Answer 31

Abnormal irregular rhythm from atria, ventricle loses regular rhythm- example of arrhythmia- rapid electrical impulses generated in atria- contract very fast (fibrillate) up to 400 times a minute. However they don’t contract properly and only some of the impulses are passed on to the ventricles, which contract less often. Therefore heart doesn’t pump blood properly.