Circulation + Blood

Question 1

Why is a circulatory system needed?

Answer 1

The circulatory system is needed because cells require a constant supply of oxygen and metabolites to release ATP in respiration. Since organisms are several layers of cells thick, they cannot rely on simple diffusion because the diffusion distances would be too long, leading to low surface area to volume ratio (SA:V) and increased metabolic demand.

Question 2

What are the advantages of a circulatory system?

Answer 2

The advantages of a circulatory system include maintaining blood pressure and controlling the average speed of blood flow through capillaries, which helps maintain a steeper concentration gradient for efficient exchange of gases and nutrients.

Question 3

What is a closed double circulatory system?

Answer 3

A closed double circulatory system is one in which blood is contained in vessels and flows to the lungs to be oxygenated. Oxygenated blood then flows from the lungs to the body tissues. Passes through heart twice.

Question 4

What is the pulmonary circulatory system?

Answer 4

The pulmonary circulatory system involves the right side of the heart pumping deoxygenated blood to the lungs to be oxygenated.

Question 5

What is the systemic circulatory system?

Answer 5

The systemic circulatory system involves the left side of the heart delivering oxygenated blood to the body tissues.

Question 6

What is the pericardium?

Answer 6

The pericardium is a protective, tough fibrous tissue that encloses the heart.

Question 7

What is the cardiac cycle?

Answer 7

The cardiac cycle is a series of contractions (systole) and relaxations (diastole) of the cardiac muscle, and it is a continuous process.

Question 8

What happens during muscle contraction in the cardiac cycle?

Answer 8

During muscle contraction, the volume of the heart chamber decreases, causing the pressure to increase.

Question 9

What happens during atrial systole?

Answer 9

During atrial systole:
- The atrial walls contract, decreasing the volume and increasing the pressure in the atrium.
- The pressure in the atrium becomes greater than the pressure in the ventricles, so the atrioventricular (AV) valves open.
- Blood is forced into the ventricles, which experience a slight increase in pressure and their volume increases as they are in ventricular diastole.

Question 10

What happens during ventricular systole?

Answer 10

During ventricular systole:
- The ventricles contract, decreasing their volume and increasing the pressure.
- The pressure in the ventricles becomes greater than in the atria, causing the AV valves to close to prevent backflow.
- The pressure in the ventricles becomes greater than in the aorta and pulmonary artery (PA), forcing the semilunar valves to open.
- Atrial diastole occurs at the same time, causing the atria to begin filling with blood again.

Question 11

What happens during diastole?

Answer 11

During diastole:
- Both the ventricles and atria relax.
- The pressure in the ventricles drops below that in the aorta and PA, causing the semilunar valves to close.
- The pressure in the atria becomes greater than in the ventricles, so the AV valves open and blood flows into the ventricles.

Question 12

What is cardiac output?

Answer 12

Cardiac output is the volume of blood pumped by the heart per minute, calculated as:
Cardiac output = Heart rate × Stroke volume

Question 13

What is heart rate?

Answer 13

Heart rate is the number of cardiac cycles or beats per minute.

Question 14

What is stroke volume?

Answer 14

Stroke volume is the volume of blood pumped out of the left ventricle in one cardiac cycle.

Question 15

What do ECGs measure? Describe the waves.

Answer 15

ECGs measure the electrical activity of the heart. The key waves include:
- P wave: Depolarisation of the atria, causing atrial systole.
- QRS complex: Depolarisation of the ventricles, causing ventricular systole; it is the largest due to the largest muscle mass.
- T wave: Repolarisation of the ventricles, resulting in ventricular diastole.
- U wave: Potentially caused by the repolarisation of Purkinje fibers.

Question 16

What are the properties of arteries?

Answer 16

Arteries:
- Carry blood away from the heart (except the pulmonary artery).
- Have thick walls with collagen (tunica adventitia) to prevent overstretching, smooth muscle (tunica media) to withstand blood pressure, and elastic fibres to allow expansion when heart contracts and recoil when heart relaxes to maintain blood pressure.
- Have a narrow lumen and a pulse.

Question 17

What are the properties of veins?

Answer 17

Veins:
- Carry blood back to the heart (except the pulmonary vein).
- Have thinner walls with collagen, smooth muscle, and elastic fibres.
- Have a wider lumen to prevent friction with endothelial walls and allow blood to return to the heart at an adequate speed.
- Contain valves to prevent backflow of blood.

Question 18

What are the properties of arterioles?

Answer 18

Arterioles:
- Have a lower proportion of elastic fibres and more muscle cells than arteries.
- Can constrict to limit blood flow to specific organs, such as reducing blood flow to the intestines during exercise.

Question 19

What are the properties of capillaries?

Answer 19

Capillaries:
- Have one-cell-thick endothelial walls with pores that form tissue fluid.
- Are part of capillary beds, which are important exchange surfaces.
- Have a narrow lumen and branch between cells to shorten the diffusion distance.
- White blood cells can squeeze through intercellular junctions.

Question 20

What is tissue fluid?

Answer 20

Tissue fluid has almost the same composition as plasma but with fewer proteins, allowing for the exchange of substances between blood and tissues.

Question 21

What happens at the arteriole end of the capillary?

Answer 21

At the arteriole end of the capillary:
- Oncotic pressure remains constant due to large proteins like albumin (lowers water potential in plasma) in the blood, creating a water potential gradient between capillaries and tissues.
- Hydrostatic pressure from the heartbeat is high.
- The hydrostatic pressure is greater than the osmotic pressure, so fluid is forced out of the capillary into the tissues.
- Hypertension may cause oedema due to fluid buildup.

Question 22

What happens at the venule end of the capillary?

Answer 22

At the venule end of the capillary:
- The oncotic pressure remains the same, but the osmotic pressure is higher as nutrients have been taken up by cells.
- Hydrostatic pressure is lower, causing less fluid to move out of the capillaries.
- Some fluid may move back into the capillaries with waste products like carbon dioxide and urea.

Question 23

What are the risk factors for coronary heart disease (CHD)?

Answer 23

Risk factors for CHD include:
- Genetic factors
- Age (risk increases with age)
- Sex (males are more likely to develop CHD)
- Hypertension (causes atheromas to develop)
- Smoking
- High concentrations of LDL (low-density lipoprotein), which promote the development of atheromas.

Question 24

What is the role of haemoglobin in gas transport?

Answer 24

Haemoglobin improves the solubility of oxygen for efficient exchange and has a prosthetic group that allows reversible binding of oxygen to form oxyhaemoglobin.

Question 25

What is cooperative binding in haemoglobin?

Answer 25

Cooperative binding refers to the process where the binding of the first oxygen molecule causes a conformational change in the haemoglobin molecule, making it easier for subsequent oxygen molecules to bind. The reversal occurs when oxygen dissociates.

Question 26

What is partial pressure?

Answer 26

Partial pressure is the pressure exerted by oxygen in a mixture of gases. It is directly proportional to the oxygen concentration, and haemoglobin is saturated when the molecules of O2 bind.

Question 27

What is the difference between high and low affinity in haemoglobin?

Answer 27

High affinity: Haemoglobin binds oxygen easily and dissociates slowly.
Low affinity: Haemoglobin binds oxygen slowly and dissociates quickly.

Question 28

How does the sigmoid curve relate to haemoglobin’s oxygen binding?

Answer 28

The sigmoid curve occurs due to cooperative binding. As more oxygen molecules bind, the affinity of haemoglobin for oxygen increases, leading to faster binding. However, when haemoglobin reaches full saturation (with four oxygen molecules), binding slows down.

Question 29

How does low pO2 affect oxygen binding to haemoglobin?

Answer 29

At low partial pressure of oxygen (pO2), haemoglobin binds oxygen slowly and has low affinity. It becomes saturated as it passes through tissues with low pO2.

Question 30

How does medium pO2 affect oxygen binding to haemoglobin?

Answer 30

At medium pO2, the saturation of haemoglobin increases quickly, and a small increase in pO2 causes a large increase in oxygen affinity.

Question 31

How does high pO2 affect oxygen binding to haemoglobin?

Answer 31

At high pO2, haemoglobin binds oxygen easily and has high affinity, but small increases in pO2 cause only a small increase in saturation because most binding sites are already occupied.

Question 32

What is the Bohr shift?

Answer 32

The Bohr shift is a change in oxygen dissociation caused by changes in carbon dioxide concentration. High pCO2 decreases oxygen affinity in haemoglobin, which helps release oxygen in respiring tissues. CO2 lowers blood pH by forming carbonic acid when combined with water, which dissociates into HCO3- and H+, and the H+ ions bind to haemoglobin, facilitating oxygen release. Haemoglobin acts as a buffer to prevent H+ from reducing pH.

Question 33

What is foetal haemoglobin?

Answer 33

Foetal haemoglobin has a higher affinity for oxygen than adult haemoglobin, allowing the fetus to obtain oxygen from the mother’s blood in the placenta, even when the mother’s haemoglobin is dissociating from oxygen at low pO2. (shifts left on the graph)

Question 34

How is carbon dioxide transported in the blood?

Answer 34

Carbon dioxide is transported in the blood in three ways:
1. Dissolved in plasma (a small amount)
2. Bound to haemoglobin to form carbaminohaemoglobin
3. As bicarbonate ions (HCO3-), after reacting with water inside red blood cells, catalyzed by carbonic anhydrase.
4 HCO3- ions travel out of RBCs on transport proteins

Question 35

What is the chloride shift?

Answer 35

The chloride shift is the movement of chloride ions (Cl-) into red blood cells when HCO3- ions are formed, to maintain electrical balance as HCO3- ions move out of RBCs via the same transport proteins.

Question 36

Annotate the heart diagram with the depolarisations of the cardiac cycle

Answer 36

Look at annotated diagram