Control of Heart function

Question 1

What are the 3 major organs that control heart function

Answer 1

• Brain (CNS)
• Kidneys
• Blood vessels

Question 2

Where is the Center(s) for autonomic control of heart function in the brain

Answer 2

Cardio-regulatory and vasomotor centres in medulla

Question 3

How does parasympathic nervous system affects the heart?

Answer 3

Decreases heart rate (Negative chronotropy) - this decreases the slope of phase 4 in sinoatrial nodal cells during their action potential

Question 4

How does the sympathetic nervous system control the heart?

Answer 4

• Positive chronotropy- by increasing slope of phase 4 in sinoatrial nodal cells
• increases force of contraction (ionotropy) by increasing Ca²⁺ dynamics.

Question 5

Which autonomic nervous system is dominant for control of heart rate

Answer 5

Parasympathetic is CHRONICALLY active

Sympathetic switches on in extreme conditions

Question 6

How does increase in sympathetic activity in kidney increase blood volume

Answer 6

Increased sympathetic activity to renal artery only

this causes decrease in glomerular filtration

less Na⁺ excretion

water follows Na⁺ and this increases blood volume

Question 7

How does increase in sympathetic activity to renal artery increases blood pressure?

Answer 7

Increased sympathetic activity

increased Renin secretion by glomerualr cells

increased angiotensin-II production; this causes vasoconstriction

increased blood pressure

Question 8

What detected blood volume and blood pressure?

How does this affect the heart

Answer 8

1. Blood volume- detected by venous volume receptors in atria and right ventricle
2. Blood pressure- detected by arterial barorecptors

increase in blood volume increases preload and increases in blood pressure increases afterload- hence can increase force of contraction of heart

the kidney is INDIRECTLY affecting the heart via the blood

Question 9

Is there any parasympathetic activity in kidney that control heart functions

Answer 9

No, only sympathetic

Question 10

Describe the cardiopulmonary circuit?

Answer 10

Mainly Large pulmonary vessels

Volume sensors (in atria and right ventricle) send signals via CNIX and CNX to medulla

If there’s less filling, there’d be less baroreceptor firing- hence increased SNS activity

If there’s distension, there’s more baroreceptor firing, this decreases SNS activity

Question 11

Describe the arterial circuit and how it regulate blood pressure

Answer 11

Baroreceptors found in aortic arch, carotid sinus and afferent arterioles of kidneys

Pressure sensors send signals via CN IX and CN X

If there’s a decrease in pressure, there’s less baroreceptor firing, hence theres increased SNS ACTIVITY

Increase in pressure will increase baroreceptor firing and decrease SNS activity

Question 12

What is the difference between volume sensors and baroreceptors (pressure sensors)

Answer 12

Volume sensors are a type of barorecptors- but are located in DIFFERENT LOCATIONS to normal barorecptors (pressure sensors)

Question 13

Contrast sympathetic and parasympathetic in terms of control of the heart and cardiovascular system

Answer 13

Sympathetic important for controlling the circulation

parasympathetic important for controlling heart rate

Question 14

Where is the vasomotor centre located?

Answer 14

It is located bilaterally in reticular substance of medulla and lower third of pons

Question 15

What is the vasomotor centre composed of and where do they send impulses to?

Answer 15

1. Vasoconstrictor (pressor) area
2. Vasodilator (depressor) area
3. Cardio-regulatory inhibitory area

they transmit impulses distally through spinal cord to almost all blood vessels.

the pressor and depressor area has effects on blood vessels

Question 16

What other areas of the brain infleunce the vasomotor area?

Answer 16

Hypothalamus can extert powerful excitatory or inhibitory effects on VMC

There are many factors that influence this area; to become integrated

*learn the diagram as best as you can*

Question 17

What does the lateral portion of the VMC control?

Answer 17

Controls heart activity by influencing heart rate and contractility

it is most associated with sympathetic branch

Question 18

What does the medial portion of the VMC responsible for?

Answer 18

Send signals via vagus nerve to heart that tend to decrease heart rate

more associated with parasympathetic activity

Question 19

Describe the action of parasympathetic activity from brain to the SA nodal cells that leads to reduction heart rate

Answer 19

• Ach binds to M2- receptors on SA nodal cells
• M2 is a inhibitory (G_i) G protein coupled receptor
• Gi binds to adenylate cyclase
• this Decreases cyclic AMP levels
• this Decreases chronotropy and ionotropy

Question 20

Describe how sympathetic activity increases heart rate

Answer 20

Noradrenaline bind to B-1 receptors on SA NODAL CELLS

B1 receptor is Gs Protein coupled receptors

this activates and carries out a cascade of reaction seen on diagram that INCREASES cAMP

This increases SA node activity and increases heart rate

Question 21

What does this graph signify

Answer 21

Parasympathetic activity is more dominant than sympathetic

As parasympathetic nerve and sympathetic nerve being cut causes The heart rate to be above normal

Question 22

compare the effect of sympathetic nerves on afferent and efferent arterioles?

Answer 22

More effect on afferent arterioles than efferent although sympathetic nerve fibres innervate both afferent and efferent arterioles of the glomerulus

Question 23

Describe the mechanism in which sympathetic activity leads to less Na⁺ excretion

Answer 23

A-1 adrenoceptor is activated

this leads to vasoconstriction in afferent arteriole

this leads to less glomerular filtration rate

less Na⁺ filtered

Question 24

Explain the mechanism in which sympathetic activity in afferent arteriole can cause release of renin

Answer 24

Juxtoglomerular cells are site of synthesis, storage and release of renin

B-1 adrenoceptor activate, this causes renin excretion

*learn diagram if possible*

Question 25

What affects venous volume distribution

Answer 25

* Peripheral venous tone * gravity * skeletal muscle pump * breathing

Question 26

In veins what are the effects of constriction

Answer 26

Reduces compliance and venous return hecne less stroke volume as preload is affected

Question 27

In arterioles, what does constriction determine?

Answer 27

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

Question 28

Outline the amount of blood in different organs and circulation of the heart

Answer 28

Question 29

What is the importance of the Local mechanisms of regulating blood flow and where are they located?

Answer 29

Intrinsic to the smooth muscle or closely associated Important for reflex local blood flow regulation within an organ

Question 30

What are the endothelium derived mediators and their features

Answer 30

* Nitric oxide- potent **vasodilator** - diffuses into vascular smooth muscle * Prostacyclin- vasodilator ; has antiplatelet and anticoagulant effects * Thromboxane A2; ***vasoconstrictor*** also synthesised heavily in platelets * **Endothelins-** vasoconstrictor made from **nucleus** of endothelial cells

Question 31

What are features of the systemic mechanisms of regulating bloo flow

Answer 31

Extrinsic to the smooth muscle these include the autonomic nervous system and circulating hormones

Question 32

What are the ***Non-endothelium*** derived mediators and their functions?

Answer 32

* _Kinins_- bind to endothelial cell receptor and stimulate nitric oxide synthesis - **vasodilator** * **Atrial natriuretic peptide (ANP)**- made in atria in response to stretch- **vasodilator** effects to reduce Blood pressure * Vasopressin- bind to V1 receptors on smooth muscle to cause **vasoconstriction** * **NA/adrenaline**- made in adrenal medulla to cause **vasoconstriction** * **Angiotensin II - potent vasoconstrictor ;** also stimulate ADH release

Question 33

What are the factors that can ultimately lead to increased atrial pressure?

Answer 33

* Increased blood volume * increased SNS activity of veins * increased skeletal muscle pump * increased respiratory movements they all lead to other venous return

Question 34

Describe the features and location of the SA Node

Answer 34

* Pacemaker of the heart- 60-100bpm * Located at Junction of Crista terminalis; upper wall of right atrium and opening of SVC

Question 35

Describe the fucntion and location of AVN

Answer 35

Has pacemaker activity; caused by slow calcium mediated action potential located at triangle of Koch at base of right atrium

Question 36

What are the features of the tracts (Bundle of His and purkinje fibres)

Answer 36

Question 37

Compare the cardiac action potential with normal nerve AP in terms of speed explain why there's a difference

Answer 37

Cardiac AP is much slower (**200-300ms**) compared with normal nerve AP (2-3ms) this is because duration of AP controls duration of contraction of heart; Long slow contraction is required to produce an effective pump

Question 38

What are the 5 phases of cardio myocyte action potential

Answer 38

* Phase 0- upstroke * Phe 1- EARLY repolarisation * Phase 2- Plateau - contributes to slow AP * Phase 3- repolarisation * Phase 4- Resting membrane protential

Question 39

How does Sympathetic and parasympathetic activity affect absolute refractory period

Answer 39

Sympathetic decrease ARP parasympathetic increases ARP

Question 40

What is the relative refractory period ?

Answer 40

Question 41

Different parts of the heart have different action potential shapes explain why? And also draw the different AP shapes for different parts of the heart

Answer 41

This is caused by ***different ion currents flowing*** and different ***ion channel expression in cell membrane .*** ***Diffferent plateau levels between bundles and epicardium is due to different amount of VGCa2+ channels .*** Atria depolarisation is AP of sinoatrial node to AVN node ventricular depolarisation is AP of bundle to epicardium

Question 42

What determines the resting membrane potential in cardiac cell

Answer 42

K⁺ efflux

Question 43

What determines the upstroke phase in cardiac cell AP

Answer 43

Large increases in membrane Na+ permeability

Question 44

Describe the role of calcium ions in upstroke of cardiac AP

Answer 44

Ca²⁺ influx needed to trigger Ca²⁺ release from intracellular stores which is essential for contraction - this is ***mediated via (Latent) L-type VGCa²⁺ channels - occurs more slowly*** Ca2+ current activates rapidly within a few milliseconds but upstroke is more dependent on Na+ current (I_Na)

Question 45

Describe the role of K⁺ currents in cardiac AP

Answer 45

Gradual activation of K⁺ currents (moving outwards) that balances but then overcome inward flow of Ca²⁺ Large K⁺ currents that is inactive during the plateau starts to flow once the cells have been partially repolarised I_K1 is responsible for fully repolarising the cell I_K1 is large and flows during diastoles, it stabilises the resting membrane potential

Question 46

Describe the phases of SA node Action potential

Answer 46

Only has phase 0,3 and 4 No Early repolarisation or plateau phase

Question 47

How is phase 4 in SA node AP different from cardiac myocytes

Answer 47

In SA node, phase 4 (resting membrane potential) is now becomes ***pre-potential*** this is because AP doesnt flatline and go to resting potential but start to increase slowly. this is due to (Transient***) T-type Ca²⁺ channels*** (faster) and Na+ ***funny current (I_f)***

Question 48

Describe how SNS affect SA node and it's corresponding AP graph

Answer 48

Positive chronotropy by increasing the slope of phase 4 (pre-potential) in SA node this is due to increased **cAMP which activates Na+ funny currents**

Question 49

Describe the mechanism in which SNS activity increases **ionotropy**

Answer 49

It increases Ca²⁺ dynamics in myocytes by: * increasing Ca influx * hence there's more Ca²⁺ uptake into intracellular stores * More Ca²⁺ Release from intracellular stores

Question 50

what are the channels involved in SAN and AVN nodal depolarisation phases? what is the difference between function of SAN and AVN

Answer 50

SAN - pacemaker AVN - gatekeeper potassium funny current channels activated by hyperpolarisation and then changes to sodium funn current in phase 4

Question 51

What are the channels involved in bundle and cardio myocyte action potential phases ? what is the difference between bundle and cardio myocytes function

Answer 51

Bundle - conducting action potential throughout the ventricles Cardio myocyte- contraction N.b:/ TO- transient outward current