Circulation Of Blood

Question 1

What is the main function of the cardiovascular system?

Answer 1

To maintain an adaptable supply of blood to tissues to supply nutrients and signalling molecules and remove waste products.

This function is achieved through generating pressure differentials across tissues to enable capillary exchange.

Question 2

What two major factors determine the flow of blood from A to B?

Answer 2

• Pressure difference between A and B (ΔP)
• Resistance to flow (R)

F= ΔP
——
R

Where higher pressure = faster flow

Question 3

What is vascular resistance?

Answer 3

The opposition to blood flow due to friction between blood and vessel walls.

Question 4

How does vessel radius affect blood flow?

Answer 4

Flow is proportional to the r^4 where r= vessel radius

small changes in arteriole diameter dramatically affect tissue blood flow.

Question 5

What is the pressure gradient generated by the heart?

Answer 5

The contraction of the heart muscles generates a pressure gradient that moves blood through the circulation from heart → tissues → heart. (High to low pressure)

Elastic arteries (i.e aorta) act as “pressure reservoirs” to maintain blood flow during diastole

Question 6

What are the systolic and diastolic pressures in a typical blood pressure reading?

Answer 6

Systolic Pressure: 120 mmHg

Diastolic Pressure: 70 mmHg (this is the minimum pressure in the artery)

Question 7

What does the cardiac cycle consist of?

Answer 7

Dictates blood flow through the heart

A series of electrical and mechanical events determining blood flow through the heart and into the circulation during one heartbeat.

Question 8

What is the role of the sinoatrial (SA) node in the cardiac conduction system?

Answer 8

It acts as the pacemaker, initiating the electrical impulses that trigger heart contractions.

Question 9

What happens during isovolumic contraction?

Answer 9

Ventricles contract, AV valves close, and LV pressure rises without a change in volume.

Question 10

True or False: The left side of the heart generates more pressure than the right side.

Answer 10

True

Question 11

What is mean arterial pressure (MAP) and how is it calculated?

Answer 11

MAP = DBP + 1/3 Pulse pressure; calculated using diastolic blood pressure and pulse pressure.

Question 12

What occurs during ventricular diastole?

Answer 12

Ventricles relax, aortic valve closes, and blood fills the ventricles.

Question 13

What is the primary purpose of elastic arteries in the cardiovascular system?

Answer 13

To act as pressure reservoirs to maintain blood flow during diastole.

Question 14

List the components of the cardiovascular system.

Answer 14

• Heart
• Blood Vessels
• Brain
• Adrenal Glands
• Kidney

Question 15

What is haemodynamics?

Answer 15

The physics of blood flow: The flow (F) of blood from A to B is determined by 2 major factors

Question 16

What factors affect the rate of blood flow?

Answer 16

1. Pressure
2. Vessel radius
3. Vessel length
4. Viscosity
5. Vascular resistance

Question 17

Name the vessels from the fastest to slowest rate of flow

Answer 17

1. Elastic artery
2. Muscular artery
3. Arteriole
4. Capillary
5. Venule
6. Vein
7. Vena cava

Question 18

How are blood pressure values measured?

Answer 18

Arterial pressure gradient, measured at brachial artery

Mean Arteriole pressure (MAP) = Diastolic blood pressure (DBP) + 1/3 pulse pressure (difference between systolic and diastolic pressure)

Question 19

What is the cardiac conduction system?

Answer 19

A system that rapidly carries electrical impulses across the heart, initiating contraction/relaxation events

Question 20

Describe the electrical events of the cardiac conduction system (7 marks)

Answer 20

1. Sinoatrial (SA) node in the right atrium acts as pacemaker cells
2. Causing spontaneous depolarisation
3. Cell-to-cell conduction across the atria occurs (all depolarise) in 50 msec
4. Impulse reaches Atrioventricular (AV) node where 100 msec delays occurs through the node to allow atrial contraction
5. This slows conduction
6. Impulse reaches Bundle of His where rapid conduction for coordinated ventricular contraction occurs
7. Ventricular myocardium contraction

Question 21

What is an ECG?

Answer 21

Detects electrical activity across the heart

It is an amalgamation of all the action potentials occurring in the heart

Question 22

What is the P wave shown in an ECG?

Answer 22

Atrial systole

Atrial depolarisation = contraction (blood is squeezed into the ventricles)

Question 23

What is the QRS complex shown in an ECG?

Answer 23

Ventricular Systole

Ventricular depolarisation = contraction
Atrial repolarisation = relaxation AT THE SAME TIME

Question 24

What is the T wave shown in an ECG?

Answer 24

Ventricular Diastole

Ventricular repolarisation = relaxation

Question 25

What are the mechanical events in the phases of the cardiac cycle? (6 marks)

Answer 25

1. Atrial systole begins - atrial contraction forces small amount of blood into ventricles
2. Atrial systole ends and atrial diastole begins
3. Ventricular systole (Phase 1) - ventricular contraction pushes AV valves closed but not enough pressure to open semilunar valves
4. Ventricular systole (Phase 2) - as ventricular pressure rises and exceeds arterial pressure, semilunar valves open and blood is ejected
5. Ventricular diastole (early) - ventricles relax and pressure drops, blood flows back against cusps of semilunar valves and forces them closed. Blood flows into the relaxed atria
6. Ventricular diastole (late) - all chambers are relaxed and ventricles fill passively