Control of heart function

Question 1

What are the 3 major tissues that control heart function?

Answer 1

CNS
Blood Vessels
Kidneys

Question 2

Where is the SAN found?

Answer 2

Junction of crista terminalis; upper wall of right atrium & opening of superior vena cava

Question 3

What molecule regulates the AVN?

Answer 3

Ca2+

Question 4

Where is the AVN found?

Answer 4

Triangle of Koch at base of right atrium

Question 5

What kind of cells are in the bundle of His and describe the pathway

Answer 5

Specialised myocytes.

AV node: His bundle > branches at intraventricular septum > apex

Question 6

What are the purkinje fibres made of?

Answer 6

Specialised conducting fibres

Question 7

Answer 7

3 phases: 0, 3, 4
Ca2+ influx
K+ efflux
Na+ influx

Question 8

What kind of channels create the pre-potential present in the SAN?

Answer 8

‘Funny’ channels

Question 9

How do action potentials vary across the heart?

Answer 9

Have different action potential shapes
-Due to different ion currents flowing and different ion channel expression in cell membrane

Question 10

How and why are cardiac muscle APs different to nerve APs?

Answer 10

Compared to nerves, cardiac AP is long (200-300 ms vs. 2-3 ms)
-Duration of AP corresponds to duration of contraction
-Long contractions necessary for effective pumping

Question 11

def Absolute refractory period

Answer 11

Time during which no AP can be initiated regardless of stimulus intensity

Question 12

def Relative refractory period

Answer 12

Period after ARP where an AP can be elicited but only with larger stimulus strength

Question 13

How many phases are in a cardiac muscle AP and what are they?

Answer 13

5

Question 14

What causes the upstroke in a cardiac muscle AP?

Answer 14

Na+ influx

Question 15

What is different about K+ efflux and Na+ influx in cardiac muscle cells and SA node cells?

Answer 15

SA node has K+ efflux only during AP, cardiac muscle AP has K+ efflux continuously, apart from the first influx of Ca2+

SA node has Na+ infux continuously, but cardiac muscle cell has Na+ influx only at the upstroke

Question 16

How does the sympathetic and parasympathetic nervous system innervate the heart?

Answer 16

Sympathetic: Controls SAN, AVN and lower heart fibres

Parasympathetic(Vagus nerve): Controls SAN and AVN only

Question 17

What is the effect of sympathetic innervation of the heart?

Answer 17

‘fight or flight’
↑ HR (chronotropy) – increases the slope of phase 4
↑ force of contraction (inotropy) – increases Ca2+ dynamics

Question 18

What is the effect of parasympathetic innervation of the heart?

Answer 18

‘Rest & digest’
↓ heart rate (HR) – decreases the slope of phase 4

Question 19

What are the neurotransmitters in pre and post ganglionic fibres in the SNS?

Answer 19

Pre-ganglionic fibres use ACh
Post ganglionic fibres use noradrenaline

Question 19

What is the neurotransmitter in pre and post ganglionic fibres in the PNS?

Answer 19

ACh

Question 20

Between the cardiac plexuses and spinal cord where do sympathetic fibres pass through first?

Answer 20

Sympathetic chain(Paravertebral ganglia)

Question 20

What are the SNS and PNS useful for in heart control?

Answer 20

PNS: Heart rate
SNS: Circulation

Question 21

When innervating the heart, where do the parasympathetic and sympathetic fibres arise from?

Answer 21

SNS: Thoracic + Lumbar vertebrae

PNS: Cervical + Sacral vertebrae

Question 22

What is the function of the vasomotor centre and what comprises it?

Answer 22

Transmits impulses distally through spinal cord to almost all blood vessels

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

Question 23

Where is the vasomotor centre located?

Answer 23

VMC(Vasomotor centre) **located bilaterally in reticular substance of medulla & lower third of pons**

Question 24

What different functions do the lateral and medial portions of the vasomotor centre control?

Answer 24

Medial: Transmits signals via vagus nerve to heart that **tend to decrease heart rate.** Lateral: Controls heart activity by influencing **heart rate and contractility**

Question 25

At the SAN, what kind of receptors do Ach(PNS) and NA(SNS) bind to?

Answer 25

G-protein coupled receptors which activate a protein cascade(ATP>cAMP>PKA)

Question 26

How is the vasomotor centre excitatorily/inhibitorily controlled?

Answer 26

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

Question 27

By what 3 means is kidney function controlled?

Answer 27

Sympathetic innervation(No PNS) Blood volume Blood pressure

Question 28

How does decreased blood volume alter kidney function?

Answer 28

↑renin secretion > ↑angiotensin-II production: vasoconstriction & ↑blood pressure(via aldosterone)

Question 29

How does increased sympathetic innervation alter kidney function

Answer 29

α1-adrenoceptor > vasoconstriction > ↓ glomerular filtration > ↓Na+ excretion: increase in blood volume (aldosterone)

Question 30

What are changes in blood **volume** detected by?

Answer 30

Venous volume receptors

Question 31

How are changes in blood pressure detected?

Answer 31

Arterial baroreceptors

Question 31

Where do renal sympathetic fibres innervate on the kidney?

Answer 31

Afferent and efferent arterioles

Question 32

What is the site of storage, synthesis and release of renin?

Answer 32

Juxtaglomerular cells

Question 33

What do kidney B1-adrenoceptors control?

Answer 33

Renin secretion

Question 34

How do baroreceptors control blood pressure in the CP circuit?

Answer 34

(Decrease in filling)/Distension > Less/More baroreceptors firing > More/Less SNS activity

Question 35

Which nerves do volume+pressure sensors (also atria & right ventricle) send signals through?

Answer 35

Glossopharyngeal + Vagus

Question 36

In the arterial circuit, how do pressure sensors control heart rate?

Answer 36

Decrease/Increase in pressure > Less/More baroreceptors firing > More/Less SNS activity

Question 37

What factors are SNS activity based off of in the cardiopulmonary and arterial circuit?

Answer 37

CP: Volumes Arterial: Pressures

Question 38

What are the 2 circulations in the body?

Answer 38

Two circulations: pulmonary and systemic Right heart > lungs > left heart > body

Question 39

What does constriction in veins cause?

Answer 39

-Reduced compliance -**Increased** venous return

Question 40

What is peripheral venous volume affected by?

Answer 40

Peripheral venous tone(SNS) Gravity Skeletal muscle pump Breathing

Question 41

What does central venous pressure dictate?

Answer 41

Amount of blood flowing back to the heart, and thus **preload and stroke volume**

Question 42

What does constriction determine in arteries?

Answer 42

Blood flow to downstream organs Mean arterial blood pressure The pattern of blood flow to organs

Question 43

Top is atrial pressure

Answer 43

Question 44

What is the function of Nitric oxide (NO) and is it a local or systemic factor for blood flow regulation?

Answer 44

Local vasodilator

Question 45

What is the function of Prostacylin and is it a local or systemic factor for blood flow regulation?

Answer 45

Local vasodilator

Question 46

What is the function of Noradrenaline/Adrenaline and is it a local or systemic factor for blood flow regulation?

Answer 46

Systemic vasoconstriction

Question 47

What is the function of Atrial natriuretic peptide (ANP) and is it a local or systemic factor for blood flow regulation?

Answer 47

Systemic vasodilator

Question 47

What is the function of Vasopressin (ADH) and is it a local or systemic factor for blood flow regulation?

Answer 47

Systemic vasoconstriction

Question 48

What is the function of Angiotensin II and is it a local or systemic factor for blood flow regulation?

Answer 48

Systemic vasoconstrictor

Question 49

What is the function of Kinins and is it a local or systemic factor for blood flow regulation?

Answer 49

Systemic vasodilator

Question 50

What is the function of Endothelins (ET) and is it a local or systemic factor for blood flow regulation?

Answer 50

Local vasoconstrictors

Question 51

What is the function of Thromboxane A2 (TXA2) and is it a local or systemic factor for blood flow regulation?

Answer 51

Local vasoconstrictor

Question 52

What is the difference between systemic and local blood flow regulators?

Answer 52

Local: Intrinsic to the smooth muscle (or closely associated) Important for reflex local blood flow regulation within an organ Systemic: Extrinsic to the smooth muscle These include the autonomic nervous system & circulating hormones

Question 53

What is the effect of SNS innervation on the afferent glomerular arterioles?

Answer 53

α1-adrenoceptor > vasoconstriction ↓ in glomerular filtration rate > ↓Na+ filtered > Increased blood volume

Question 54

What is the function of aldosterone

Answer 54

Increase Na+ reabsorption Increase K+ excretion

Question 55

What is renins' effect on aldosterone?

Answer 55

Renin increases aldosterone