Cardiovascular system

Question 1

Conduction in the heart

Answer 1

1. sinoatrial nerve fires at the top of the RA
2. signal is conducted through myocardium causing atrial contraction
3. impulse enters the atrioventricular node and is paused for blood to enter ventricles
4. AV node fires causing ventricles to contract

Question 2

The left side of the heart has a more developed conduction system because…

Answer 2

It has a thicker muscle layer as it is pumping blood around the whole body, so needs more innervation to fire at the same time as the RV

Question 3

Speed of conduction

Answer 3

10m/sec, compared to 0.8m/sec for other muscle

Question 4

6 stages of an ECG wave from limb lead II

Answer 4

1. P wave - atrial depolarisation
2. Pause at the AV node
3. Q wave - septum depolarisation
4. R wave - ventricular depolarisation
5. Depolarisation at ventrical base (negative dip)
6. S wave - repolarisation

Question 5

Where is the ‘second heart’?

Answer 5

In the leg, veins are sheathed by muscle. Contractions during walking cause blood to flow. Valves prevent backward flow.

Question 6

Blood distribution

Answer 6

27% liver
20% kidney
16% brain
15% muscle (ncreases to 66-70% during exercise)
8% skin
6% bone
4% heart

Question 7

Cardiac cycle

Answer 7

1. Blood flows into RA from vena cavae and flows into RV
2. RA contracts, forcing remaining blood into RV
3. RV contracts, forcing pulmonary artery valve open
4. Blood flows into pulmonary artery into lungs’ arterial tree
5. Blood flows from lung into LA and LV
6. LV contracts, forcing remaining blood into LV
7. LV contracts, forcing aortic valve open
8. Blood flows into aorta, causing aorta to bulge and recoil, snapping the aortic valve shut and pushing blood into the aortic arch

Question 8

The pulse is…

Answer 8

the wave of blood that flows down the artery following ejection from the ventricle

Question 9

Normal pulse rate

Answer 9

60-100bpm

Question 10

Pulse locations (3)

Answer 10

Carotid (neck)
Brachial (elbow)
Radial (wrist)

Question 11

Blood pressure is…

Answer 11

The pressure exerted by the blood on the walls of the blood vessel (mm Hg)
Systolic - during heart contraction
Diastolic - at rest

Question 12

Normal blood pressure range

Answer 12

120-135 / 70-85

Question 13

Stroke volume is…

Answer 13

The volume of blood ejected from the ventricle on each contraction
About 70mls in adults
Depends on preload, afterload, contractility and ventricle shape

Question 14

Preload is…

Answer 14

The fluid in the ventricle just before it contracts

Question 15

Afterload is…

Answer 15

The pressure the ventricle has to generate to open the aortic or pulmonary valve, largely determined by elasticity of arteries and constriction in arterioles

Question 16

Cardiac output =

Answer 16

stroke volume x heart rate

Measured over 1 minute

Question 17

Normal cardiac output

Answer 17

4.5-5 litres per minute

Question 18

Starling’s Law

Answer 18

The larger the volume of the heart, the greater energy it will use

Question 19

Frank’s observation

Answer 19

An increase in diastolic heart volume stimulates the ventricle to contract more rapidly and more forcefully

Question 20

Mean arterial pressure =

Answer 20

cardiac output x systemic vascular resistance

heart rate x stroke volume x systemic vascular resistance

Question 21

SNS control of cardiac function

Answer 21

Stellate nerve from spinal cord innervates cardiac muscle, SA node and AV node via beta 1 receptors

Question 22

PSNS control of cardiac function

Answer 22

Vagal nerve from the brain innervates SA and AV nodes via muscarinic receptors

Question 23

Baroreceptor reflex

Answer 23

1. As heart contracts and blood is pumped, baroreceptors in carotid artery and aortic arch detect stretch
2. Signal sent to medulla
3. Increase in parasympathetic nerve firing which reduces sympathetic nerve firing
4. Blood pressure drops

Question 24

Bainbridge reflex

Answer 24

Similar to baroreceptor reflex but in atria