L19 - Cardiovascular System 2

Question 1

What is the equation for net pressure?

Answer 1

net pressure = hydrostatic pressure - colloid osmotic pressure

Question 2

What do Starling forces describe?

Answer 2

describe whether there is filtration / movement of fluid out of capillaries or absorption / movement into the capillaries

Question 3

Which end of a capillary is involved in filtration / outward movement of fluid? Why?

Answer 3

arterial end

hydrostatic pressure is high

Question 4

Which end of a capillary is involved in absorption / inward movement of fluid? Why?

Answer 4

venous end

hydrostatic pressure is low

Question 5

Which factor results in absorption of fluid into the capillaries?

Answer 5

oncotic pressure which is determined by albumin inside the capillaries

Question 6

What happens when hydrostatic pressure is greater than oncotic pressure?

Answer 6

net filtration / inward movement of fluid occurs

Question 7

What happens when oncotic pressure is greater than hydrostatic pressure?

Answer 7

net absorption / outward movement of fluid occurs

Question 8

How much fluid flows out of the capillaries and is not reabsorbed (per day)? How is this excess fluid dealt with?

Answer 8

3 L/day

lymphatic system recirculates this fluid

Question 9

Will interstitial oncotic pressure favor filtration or absorption?

Answer 9

filtration

Question 10

What does colloid osmotic pressure favour?

Answer 10

water movement into capillary

Question 11

What does hydrostatic pressure favour?

Answer 11

water movement out of capillary

Question 12

What does net movement depend on?

Answer 12

balance of filtration and absorption

balance changes down length of capillaries

Question 13

What is bulk flow?

Answer 13

movement of fluid into and out of the capillaries via Starling forces

Question 14

What is the route via which excess fluid takes after leaving the capillaries?

Answer 14

capillaries -> lymph vessels -> larger lymphatic vessels -> lymph ducts -> venous circulation

Question 15

What is the role of the lymphatic system?

Answer 15

return fluid / proteins filtered out of the capillaries back to the circulatory system
pick up fat absorbed at small intestine and transfer it to circulatory system
serve as filter to help capture and destroy foreign pathogens

Question 16

What does lymph flow depend upon?

Answer 16

smooth muscle contraction of larger lymphatic vessels
one-way valves which stop back-flow
external compression created by skeletal muscle contraction

Question 17

Which one/s of the following conditions is likely to cause oedema? (dehydration / increase in blood protein concentration / severe malnutrition / heart failure which increases venous pressure / obstruction of lymph nodes by parasites or cancerous cells)

Answer 17

obstruction of lymph nodes by parasites or cancerous cells, severe malnutrition and heart failure which increases venous pressure

Question 18

What is ventricular systole?

Answer 18

contraction of the ventricles

Question 19

What is ventricular diastole?

Answer 19

relaxation of the ventricles

Question 20

What is the conduction system of the heart?

Answer 20

SA node which is autorhythmic and has pacemaker cells (~70 bpm)
also AV node (50 bpm) and purkinje fibers (25-40 bpm)

Question 21

What is the role of the AV node?

Answer 21

delays transmission of electrical signal so that ventricles have the chance to fill with blood
electrical signal cannot pass from the atria to the ventricles without passing through the AV node

Question 22

How does an electrical signal pass through the heart?

Answer 22

SA node -> atria -> AV node -> ventricles

Question 23

What is the role of the Purkinje fibres?

Answer 23

allow for rapid conduction and contraction of these fibres starts at apex

Question 24

What are the steps of electrical conduction in the heart?

Answer 24

SA node depolarises -> electrical activity goes rapidly to AV node via internodal pathways -> depolarisation spreads more slowly across atria, conduction slows through AV node -> depolarisation moves rapidly through ventricular conducting system to the apex of the heart -> depolarisation wave spreads upward from the apex

Question 25

What is an electrocardiogram?

Answer 25

body surface recording which measures whole heart average extracellular potential

Question 26

What are the three major waves of an ECG recording?

Answer 26

P wave (small wave - atrial depolarisation) -> QRS complex (main spike - ventricular depolarisation) -> T wave (small wave - ventricular repolarization)

Question 27

When is ECG recording above baseline?

Answer 27

when there is net charge movement towards ‘+ve’ electrode

Question 28

Which direction does a signal move when there is an upward inflection in the ECG?

Answer 28

down into the left

Question 29

Which direction does a signal move when there is an downward inflection in the ECG?

Answer 29

up into the right

Question 30

Where is the positive electrode of an ECG located?

Answer 30

left leg

Question 31

Where is the negative electrode of an ECG located?

Answer 31

right arm

Question 32

What causes the rise and fall of the P wave?

Answer 32

depolarisation of the SA node and spreading of this signal across the atria
movement to the left (+ signal), therefore rise and fall once the signal stops

Question 33

What causes the flat portion between the P wave and the Q wave?

Answer 33

delayed transmission of electrical signal from the AV node

Question 34

What causes the fall of the Q wave?

Answer 34

left bundle of his firing before the right bundle of his resulting in movement to the right (- signal)

Question 35

What causes the rise and fall of the R wave?

Answer 35

majority of movement to the left (+ signal) causes the rise

signal moving back up ventricles towards the negative electrode causes the fall (- signal)

Question 36

Why does the heart overshoot baseline during the fall of the R wave? What happens once the signal stops?

Answer 36

due to the anatomical makeup of the ventricles which results in the signal moving up for longer
when the signal stops the heart returns to baseline

Question 37

What causes the rise and fall of the T wave?

Answer 37

repolarisation of the ventricles from the bottom to the top (however negative electrical signal resulting in a + ECG signal)

Question 38

What is atrial fibrillation caused by?

Answer 38

erratic atrial activity which is caused by cells contracting on their own instead of in unison

Question 39

What is ventricular fibrillation caused by?

Answer 39

ventricle beating on its own from pacemakers in the ventricular muscle, perhaps caused by damaged muscle

Question 40

How is normal rhythm restored during ventricular fibrillation?

Answer 40

defibrillator = high voltage shock to synchronise all muscle