Control of Heart function

Question 1

How can the main anatomical components of the heart be broadly categorised?

Answer 1

Muscle cells - cardio myocytes : pump blood by electrically stimulated contraction

Specialised electrical cells : spontaneous currents created. To regulate contraction of cardio myocytes

Vessels : transporting blood, coronary vessels for the heart

Question 2

What is the pacemaker of the heart?

Answer 2

Sinoatrial (SA) node
Pacemaker of the heart: 60-100 bpm
Junction of crista terminalis; upper wall of right atrium & opening of superior vena cava

Question 3

What does the Atrioventricular node do?

Answer 3

Atrioventricular (AV) node
Has pacemaker activity: slow calcium mediated action potential
Triangle of Koch at base of right atrium

Question 4

What two tracts are found in the heart?

Answer 4

The bundle of his and branches

purkinye fibres

Question 5

What do the bundle of his do?

Answer 5

Specialised myocytes. AV node: His bundle

branches at intraventricular septum –> apex

Question 6

What do prukinye fibres do?

Answer 6

Specialised conducting fibres

Question 7

How many phases does nodal cell action potential have?

Answer 7

Phase 0 - upstroke
Phase 4 - pre-potential
Phase 3 - repolaristion

• no phases 1 or 2

Question 8

What is the upstroke in nodal cells due to?

Answer 8

Calcium influx

Repolarisation due to k Efflux

• Nodal cells do not have a resting membrane potential - only a pre-potential due to Na+ influx through a ‘funny’ channel

Question 9

Why do different parts of the heart have different action potential graph shapes?

Answer 9

Caused by different ion currents flowing and different ion channel expression in cell membrane

Question 10

Characteristics of cardiac muscle action potential?

Answer 10

Compared to nerves, cardiac AP is long (200-300 ms vs. 2-3 ms)

Duration of AP controls duration of contraction of heart

Long, slow contraction is required to produce an effective pump

AP has 5 phases numbered 0-4
Absolute refractory period (ARP) = time during which no AP can be initiated regardless of stimulus intensity

Relative refractory period (RRP) = period after ARP where an AP can be elicited but only with larger stimulus strength

Question 11

What are the 5 phases of cardiac muscle action potential?

Answer 11

0 - Upstroke
1 - Early repolarisaion
2 - Plateu ( maintains depolarisation
3 - repolarisation
4 - resting membrane potential

*

Question 12

How is the maximum rate the heart can beat at limited?

Answer 12

By refractory periods

• relative and absolute

Question 13

What ion changes take place in a ventricular cell during action potential?

Answer 13

Depolarisation due to sodium influx

Plataeu due to Calcium influx

repolarisation due to potassium efflux

Question 14

Why does the CNS regulate the heart?

Answer 14

can effect immediate changes through nerve activity or slower changes through hormonal activity

Question 15

What components of the cns regulate heart?

Answer 15

autonomic :

• cardio regulatory centre
• vasomotor centres in medulla

Question 16

Wht does the parsympathethic do to heart rate?

Answer 16

‘Rest & digest’

decrease heart rate (HR) – decreases the slope of phase 4

Affects pre-potential of action potential in nodal cell

Question 17

What does the sympathetic do to heart rate?

Answer 17

‘fight or flight’
Increases HR (chronotropy) – increases the slope of phase 4 and decreases the time

Increase force of contraction (inotropy) – increases Ca2+ dynamics

Question 18

What NT do parasympaththic pre ganglionic fibres use

Answer 18

Acetylcholine to Muscarinic receptor

Question 19

What NT do parasympaththic post ganglionic fibres use?

Answer 19

Acetylcholine

Question 20

What NT do sympaththic pre gangalionic?

Answer 20

acetylcholine

Question 21

What NT do sympaththic post ganglionic fibres ause?

Answer 21

Noradrenalie

Question 22

where is the vasomotor centre located?

Answer 22

located bilaterally in reticular substance of medulla & lower third of pons

Question 23

What is the VMC composed of?

Answer 23

Composed of:
Vasoconstrictor (pressor) area
Vasodilator (depressor) area
Cardio-regulatory inhibitory area

Question 24

what does the vasomotor do?

Answer 24

Transmits impulses distally through spinal cord to almost all blood vessels

Lateral portions of Vasomotor controls heart activity by influencing heart rate and contractility

Medial portion of VMC transmits signals via vagus nerve to heart that tend to decrease heart

Question 25

What can effect the VMC?

Answer 25

Many higher centers of the brain such as the hypothalamus can exert powerful excitatory or inhibitory effects on the VMC.

Question 26

what do the sympathetic nerves to the kidneys do?

Answer 26

increase activity

decrease glomerular filtration –> decrease Na+ excretion

Question 27

How is blood volume detected?

Answer 27

Detected by venous volume receptors

Question 28

How is blood pressure controlled by the kidney?

Answer 28

Increased renin secretion –> increase angiotensin-II production: vasoconstriction & increases blood pressure

Blood pressure :
Detected by arterial baroreceptors

Question 29

what do the sypathetic nerves from the cns innervate ( kidneys )

Answer 29

innervate afferent & efferent arterioles of the glomerulus (& nephron tubule cells)

Question 30

What do the afferent aterioles do?

Answer 30

Primary site of sympathetic activity
a1-adrenoceptor –> vasoconstriction
decreasing in glomerular filtration rate –> decrease Na+ filtered
Juxtaglomerular cells are the site of synthesis, storage & release of renin
alpha1-adrenoceptor –> renin secretion

Question 31

What two circuits do the blood vessels split into?

Answer 31

Cardiopulomnary circuit : volume sensors. large pulmonary vessels

Aterial circuit : Pressure sensors . Aortic arch, carotid sinus & afferent arterioles of kidneys

Question 32

Where do the volume sensros in large pulomnary veins send signals to?

Answer 32

Glossopharyngela and vagus

Question 33

What happens when the cardiopulmonary circuit is decreased in filling?

Answer 33

decreased baroreceptor firing –> increase sympathetic nerve (SNS) activity
Distention –> increase baroreceptor firing –> decrease SNS activity

Question 34

Where do the pressure sensors to?

Answer 34

glossopharyngeal & vagus nerves

Question 35

What happens during a decrease in pressure ina rterial circuit?

Answer 35

Decrease in pressure –> decrease baroreceptor firing –> increase SNS activity
Increase in pressure –> increase baroreceptor firing –> decrease SNS activity

Question 36

What is venous volume distrubtuon affected by?

Answer 36

Venous volume distribution affected by peripheral venous tone, gravity, skeletal muscle pump & breathing

Question 37

What is the central venous pressure?

Answer 37

Central venous pressure (mean pressure in the right atrium) determines amount of blood flowing back to heart.

Question 38

In veins, constriction ( increases/decreases ) compliance and ( increases/decreases ) venous return

Answer 38

• reduces

- increases

Question 39

What is smooth muscle for in the terms of blood flow?

Answer 39

Intrinsic to the smooth muscle (or closely associated)

Important for reflex local blood flow regulation within an organ

Question 40

What chemicals in the endothelium affect blood flow? ( 4 )

Answer 40

Nitric oxide (NO): potent vasodilator, which diffuses into vascular smooth muscle cells.
Prostacylin: vasodilator that also has antiplatelet & anticoagulant  effects
Thromboxane A2 (TXA2): vasoconstrictor that is also heavily synthesised in platelets 
Endothelins (ET): vasoconstrictors generated from nucleus of endothelial cells

Question 41

What are non- endothelium derived mediators? affecting blood flow

Answer 41

Kinins: bind to receptors on endothelial cells & stimulate NO synthesis – vasodilator effects
Atrial natriuretic peptide (ANP): secreted from the atria in response to stretch – vasodilator effects to reduce BP
Vasopressin (ADH): secreted from pituitary gland. Binds to V1 receptors on smooth muscle to cause vasoconstriction
Noradrenaline/Adrenaline: secreted from adrenal gland (& SNS); causes vasoconstriction
Angiotensin II: potent vasoconstrictor from the renin-angiotensin-aldosterone axis. Also stimulates ADH secretion.