Basics (Lecture 1)

Question 1

How does diffusion occur? What molecules can diffuse?

Answer 1

Diffusion occurs passively down concentration gradients for small molecules and short distances
Hydrophobic: O2, CO2 can diffuse through the lipid bilayer
Hydrophilic: glucose, amino acids, lactate require small pores to diffuse

Question 2

List what composes the following…

a) Distribution system
b) pump
c) exchange mechanism
d) transporters
e) flow control

Answer 2

a) vessels and blood
b) heart
c) capillaries
d) blood
e) arterioles and pre-capillary sphincters

Question 3

What are the 3 factors affecting diffusion?

Answer 3

1. Area: how much area is available/how capillary dense the ara is (more metabolically active areas will have more capillaries)
2. Diffusion ‘Resistance’: nature of the molecule, nature of barrier, path length (depends on capillary density)
3. Concentration Gradient: a greater CG = a greater rate of diffusion

Question 4

What determines the concentration of substances (that are used up by tissues) in capillary blood?

Answer 4

1. The rate the tissues use the substance

2. The rate of bloodflow through the capillary bed

Question 5

What is the rate of bloodflow at rest vs during strenuous exercise?

Answer 5

Rest: 5L/min
Exercise: can go up to 25L/min

Question 6

How much bloodflow do the following tissues require?

a) Brain
b) Heart
c) kidneys
d) skeletal muscle and the gut

Answer 6

a) Brain: a high, constant flow
b) Heart: High flow that increases during exercise
c) Kidneys: High constant flow
d) skeletal muscle needs a high amount after exercise and the gut a higher amount after a meal

Question 7

What is the perfusion rate?

Answer 7

Rate of bloodflow

Question 8

What are the heart’s “2 pumps”?

Answer 8

The Right heart: pumps around the pulmonary circulation

The Left heart: pumps blood around the systemic circulation

Question 9

How is bloodflow ‘regulated’?

Answer 9

If you reduce perfusion to some areas, it is easier to direct bloodflow to areas that are harder to perfuse and very important, this is aided by arterioles which provide resistance
E.g; the brain is harder to perfuse due to gravity, so an increased resistance may be applied to bloodflow going away from the brain so more blood goes to the brain

Question 10

Why is the heart called a double and a closed circulatory system?

Answer 10

Double as there are 2 pumps, and closed as it isn’t exposed to the outside environment

Question 11

Where is most blood found in the body at any given point?

Answer 11

In the veins, as their capacitance provides a temporary store

Question 12

List the atrioventricular valves and the outflow valves

Answer 12

AV valves: mitral and tricuspid

Outflow valves: pulmonary and aortic (semi-lunar)

Question 13

Give 4 descriptive features for a cardiac myocyte

Answer 13

1. Striations
2. 1-2 centrally positioned nuclei
3. Intercalated discs (electrical and mechanical coupling with adjacent cells)
4. Branching

Question 14

What are the 2 types of myocardial cells?

Answer 14

1. Myocardial contractile cells (99%): conduct impulses and are responsible for contractions
2. Myocardial conducting cells (1%): smaller, fewer myofibrils and filaments as they don’t do contractions. Similar to neurones

Question 15

Describe the process that occurs after a pacemaker generates one AP

Answer 15

1. Pacemakers generate one AP in the SA node (at rest, 1 AP/second)
2. Short atrial systole
3. Excitation reaches AV node: delayed 120 ms
4. Impulses enter the bundle of HIS that conduct rapidly
5. Impulses divide into Purkinje fibres
6. Excitation spreads through the ventricular myocardium from the endocardial - epicardial surface
7. Ventricular systole: 280 ms, contraction is apex up
8. Diastole: 700 ms relaxation as ventricles re-fill

Question 16

What is occurring at the end of diastole?

What is diastasis?

Answer 16

Valves: outflow shut, AV open and ventricles are filling slowly (stop filling when ventricular pressure> atrial pressure)
Diastasis: the passive filling of ventricles have slowed but still before atria have contracted

Question 17

What happens during atrial systole? What heart sound can this generate?
Can the heart work if this is damaged?

Answer 17

Atrial systole forces a small amount of extra blood into the ventricles to limit the loss of atrial regurgitation that may occur when the valves shut - CAN generate an S4

Yes, the heart functions fine without atrial systole

Question 18

What happens during ventricular systole and what heart sound can this generate?

Answer 18

When interventricular pressure > atrial pressure, the AV valves shut, outflow valves are still shut. Generates the LUP

Question 19

What is an isovolumetric contraction?

Answer 19

When the heart contracts but there is no change in volume, occurs at the start of ventricular systole

Question 20

When do outflow valves open and what happens when they do?

Answer 20

Outflow valves open when the ventricular pressure> arterial pressure, this generates the rapid ejection phase

Question 21

What peaks at the end of systole?

Answer 21

Arterial and interventricular pressure, but as the rate of ejection falls outflow eventually ceases

Question 22

What is isovolumetric relaxation and when does it occur? What heart sound is associated with this?

Answer 22

When the aortic valve closes and the ventricles can relax

DUP; signifies the end of systole

Question 23

When do the AV valves open?

Answer 23

During systole the blood has continued to return to the atria, when Atrial pressure > interventricular the AV valves open.

Question 24

What generates S3? (and how long is it?)

Answer 24

Rapid filling phase is the rapid filling of the ventricles when the AV valves open; typically 200-300 ms. This can generate S3

Question 25

What generates a heart murmur? What are the 2 types?

Answer 25

Turbulent blood generates a heart murmur, it can be:

1. Stenosis: Narrowing of the valve
2. Incompetence: valve cannot close properly

Question 26

What kind of murmur is an aortic stenosis? List 2 things that could cause this.

Answer 26

A systolic murmur, LUP WHOOSH DUP

1. Congenital: Having a bicuspid valve instead of a tricuspid valve
2. Age-related calcification

Question 27

What composes CO?

Answer 27

CO = HR X SV