Circulation

Question 1

What is the function of the kidneys?

How are they controlled?

Answer 1

Plasma volume control
Glomerular filteration rate (GFR)- all fluid entering all Bowmans capsules. Increased renal blood flow increases GFR

Endocrine and autonomic NS

Question 2

State 6 function of circulation

How is pulmonary circulation different to systemic circulation?

Answer 2

Infection control
Supply oxygen and glucose to respiring cells
thermal regulation
removing waste
haemostasis of extracellular fluid in kidneys
Distribution of hormones

Pulmonary circulation is in series, systemic circulation is in parallel

Question 3

Whats the equation for BP and how are resistance, pressure and flow related ?

Answer 3

BP=CO x PR
Blood flow rate = pressure difference/ resistance

Blood pressure is the balance between circulatory blood volume and circulatory capacity.

Question 4

State the function of each blood vessel type.

Answer 4

Aorta - stretch and recoil, energy
Arteries- distribute, volume adjust 
Arterioles- regulate capillary pressure, set BP and TPR
Capillary- exchange
Venules- collect blood, some exchange
Veins- blood reservoir, muscle pump

Question 5

How does the right and left heart differ in appearance in the sagittal plane? Any other differences?

Answer 5

Right- Crescent shape

Left - Circular cross section

Question 6

Compare the changes in pressure between

a) LV systole and aortic systole
b) LV systole and arterial pressure
c) Arterial and LV diastole
d) LV systole and RV systole
e) LV diastole and mean LA/RA
f) RV systole and RV diastole
g) mean LA and mean RA

Answer 6

a) Equal
b) Approx. equal
c) Ten times >
d) Five times >
e) LVD approx. equal
f) 5-7x >
g) >

Question 7

Compare the changes in pressure between

a) PA systole and RV systole
b) PA diastole and PA systole
c) PA diastole and RV diastole

Answer 7

a) Equal
b) <
c) >

Question 8

What is the apex beat?

Answer 8

During systole, the apex (most inferior and lateral part of the heart) strikes the chest wall.

Question 9

Describe the differences between atrioventricular valves and semi-lunar valves with examples.

Answer 9

Atrioventricular valves: 
Tricuspid valve and Mitral valve
Papillary fibres
Closed during systole
Responsible for "Lub" sound

Semilunar valves:
Pulmonary valve and Aortic valve
Diastole time > Systolic time so delayed “Dub”

Question 10

Outline the steps involved contraction of the heart.

Answer 10

Cardiomyocyte is stimulated by neighbouring cells or conducting cells

Action potential causes extracellular environment to become more negative and the intracellular environment to become less negative

Increase in cytosolic free calcium ions

Muscle contraction

Calcium ions removed and muscle relaxes

Question 11

Describe the changes in GFR according to the following changes:

a) Increase in size of afferent artery, decrease in efferent artery size
b) Decrease in size of afferent artery

Answer 11

a) increase in pressure, increase in filtration

b) decrease in pressure, decrease in filtration

Question 12

Define a) Hypoxia b) Anoxia c) Hypoxaemia and d) Ischaemia

State a possible cause of Hypoxia and Ischaemia

Answer 12

a) Hypoxia - insufficient O2 supply to an area of the body
b) Anoxia- complete deprivation of O2 supply (low po2)
c) Hypoxaemia- insufficient O2 throughout arterial blood
d) Ischaemia- insufficient perfusion

Hypoxia can be caused by hypoxaemia and/or ischaemia.

Ischaemia can be caused by blockage, constriction of a vessel, decreased BP or insufficient pressure generation by the heart

Question 13

Describe the fast homeostatic response to decreased cardiac output.

Answer 13

Increased sympathetic activity leading to:

Increased heart rate
Increased heart contractility
Vasoconstriction

Question 14

Describe the slow homeostatic response to decreased cardiac output.

Answer 14

Kidneys accumulate fluid which leads to decreased GFR

As a result an increase in central venous pressure

Leads to increased venous return and increased preload

Question 15

Describe the similarities and differences between a low output stage and a low volume state.

Answer 15

Both end in shock

Low output stage more common in patients over 50 and maintains normal blood pressure.

Low volume stage can occur at any age and is due to loss of fluid (i.e. haemorrhage and diuresis)

Question 16

State the equation for cardiac output. Which factors effect it?

Answer 16

CO= HR x SV

Stroke volume is affected by contractility, preload and after load. Preload itself is affected by venous tone and volume. If returning blood vessels high, preload likely to increase

Question 17

What is meant by mean arterial pressure and what is the equation used to calculate it?

Answer 17

MAP, or mean arterial pressure, is defined as the average pressure in a patient’s arteries during one cardiac cycle.

MAP= DBP + 1/3(SBP-DBP)

Question 18

Define stroke volume. Equation?

How does the heart rate and RR interval relate. What is the RR interval?

Answer 18

The volume of blood pumped out of one ventricle per beat. SV= EDV-ESV

Heart rate is 1/RR.

The RR interval refers to the QRST complexion an ECG. It depicts the interval between two successive peaks

Question 19

Define end diastolic volume and end systolic volume.

Answer 19

EDV= The volume of blood in the ventricle after trial systole.

ESV= The volume of blood left in the ventricle after ventricular systole.

Question 20

What is term given to the percentage of ventricular volume pumped out during a heart beat? What is its formula?

How can this be indicative of heart failure ?

Answer 20

Ejection fraction = SV/EDV

Ejection fraction is less than 40% in HF

Question 21

What does Poiseuilles law suggest to us about blood flow.

Answer 21

Viscosity, radius and length of BV change the flow of blood.

An increase in the blood vessel radius will cause the greatest increase in blood flow (i.e. decreased resistance)

Question 22

Describe the physiological changes that occur during exercise and when standing in terms of blood vessels, HR and BP.

Answer 22

Exercise causes peripheral vasodilation and vasoconstriction of inactive skeletal muscles and the gut.
HR increases as does systolic BP. Diastolic pressure decreases

When standing the blood follows gravity and wants to pool in the lower extremities and not the brain. The sympathetic system senses the initial drop in BP and employs compensatory measures.
HR increases as does diastolic BP. Systolic pressure remains the same

Question 23

Describe the three methods by which systemic pressure is controlled

Answer 23

Local- NO from endothelium

Neurological- autonomic sympathetic: noradrenaline

Humoral- kidney secreted hormones as does pituitary and adrenal gland.

Question 24

Describe the two forces that act on blood vessel walls.

Answer 24

Hydrostatic pressure

Shear force: frictional force parallel to the wall
It is atheroprotective and enhanced by laminar flow

Question 25

Describe the location and function of baroreceptors

Answer 25

Carotid sinuses, left and right internal carotid arteries Senses low blood pressure

Question 26

Describe the location and function of chemoreceptors

Answer 26

Carotid bodies and aortic bodies Detect low O2

Question 27

Describe the key principles of the Frank-Starling mechanism

Answer 27

The stroke volume of the heart is directly proportionate to the end diastolic volume, to an extent. The heart pumps a greater volume with greater force.

Question 28

What is the difference between preload and afterload? How does volume overload occur? How does pressure overload occur?

Answer 28

Preload is the initial stretching by cardiac myocytes of the ventricles during diastole. It depends on venous return Afterload the resistance that the chambers of the heart must overcome in order to eject blood out of the heart. It can be increased by back pressure and failure of exit valves to open. Preload too large which causes the heart is overfilling Afterload load to large

Question 29

Which factors can affect preload?

Answer 29

Increased ventricular compliance (increases elasticity Decreased heart rate (increased diastolic time) Increased central venous return Increased aortic pressure because the ventricle doesn't empty enough

Question 30

Describe features of pulmonary circulation

Answer 30

``` High capillary density low vascular resistence acts a blood reservoir Endocrine control of bp (produces ACE) filter ``` When O2 supply to lungs is low or ventilation is low, vasoconstriction occurs and perfusion is low to minimise the blood that is poorly oxygenated.

Question 31

Describe the difference between laminar and turbulent flow. How does tension and vessel size relate?

Answer 31

Laminar flow is slower at edges due to friction. Turbulent flow occurs in high speed, low viscosity and branching vessels. Its caused by junctions, mixing, atherosclerosis and endothelium damage. The greater the vessel, the greater the wall tension

Question 32

Describe functions of the endothelium

Answer 32

1. Maintaining blood vessel tone: local control of perfusion, vasodilation (NO) 2. Fluid filteration: as in blood brain barrier, CSF, glomerulus, GI secretions 3. Haemostasis 4. White cell recruitment 5. Angiogenesis 6. Hormone trafficking: e.g. as in transcytosis (travel through the cytoplasm of a cell)

Question 33

What is meant by contractility?

Answer 33

The intrinsic ability of the myocardium to contract