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Physiology, neurobiology and cell signalling > Lecture 15: Control of the heart and circulation > Flashcards

Lecture 15: Control of the heart and circulation Flashcards

Monday 17th February 2025

1
Q
  • The heart is under the control of the autonomic nervous system.
  • The heart is innervated by both the sympathetic and parasympathetic nervous systems.
  • Blood vessels are only innervated by the sympathetic nervous system.
A
  • The heart is under the control of the autonomic nervous system.
  • The heart is innervated by both the sympathetic and parasympathetic nervous systems.
  • Blood vessels are only innervated by the sympathetic nervous system.
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2
Q

Is it true that Pacemakers and atrial muscle are innervated by parasympathetic/sympathetic nerves?

A

Yes, innervated by both

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3
Q

How does the sympathetic nervous system influence the heart ?

A
  • Sympathetic drives the heart through noradrenaline
  • Increased rate: a positive chronotropic effect
  • Increased conduction: a positive dromotropic effect
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4
Q

How does the parasympathetic nervous system influence the heart ?

A

Parasympathetic slows the heart through acetylcholine

Decreased rate: a negative chronotropic effect

Decreased conduction: a negative dromotropic effect
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5
Q

How are chronotropic effects exerted?

A

By altering the pacemaker potential.

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6
Q

What are Chronotropic effects?

A

Changes in heart rate

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7
Q

What are dromotropic effects?

A

Dromotropic effects refer to changes in the speed of electrical conduction through the heart — especially through the atrioventricular (AV) node.

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8
Q

Ventricular msucles are innervated by…

A

Ventricular muscles are innervated
by sympathetic nerves only

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9
Q

What nervous sytem affects the contractility of the heart?

A

Only the sympathetic nervous system
alters contractility of the heart

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10
Q

How does the sympathetic nervous system affect the contractility of the heart?

A
  • increases contractility through Noradrenaline enhancing Ca2+ release in myocytes.
  • a positive inotropic effect
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11
Q

Does the parasympathetic nervous system have any effect on contractility?

A

No

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12
Q

What is a positive inotropic effect?

A

💪 Positive inotropic effect = increased strength of heart contraction

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13
Q

Does the sympatheitc nervous sytem affect Starling’s law?

A

Yes

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14
Q

How does the sympathetic nervous system affect Starling’s law?

A
  • the sympathetic nervous system amplifies the effects of Starling’s law by increasing both the contractility of the heart and the heart rate, allowing the heart to pump more blood in response to higher preload or during periods of higher demand.
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15
Q

Do sympathetic nerves have vasoconstrictor action?

A

Yes

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16
Q

Why do sympathetic nerves tonically release noradrenaline onto smooth muscle?

A
  • 1) Control resistance of systemic circulation
  • 2) Regulate flow to organs or tissues
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17
Q

How can sympathetic nerves cause vasocontriction?

A

By increasing noradrenaline release to smooth muscle.

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18
Q

How can sympathetic nerves cause dilation?

A

By increasing flow to the capillaries

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19
Q

How does noradrenaline work on smooth msucle?

A
  • Noradrenaline works through myosin light chain kinase and phosphatase
  • Noradrenalien acts on α1 and α2 receptors to mobilise Ca2+ in smooth muscle
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20
Q

What are the determinants of blood pressure?

A

Blood volume

Venous return

Contractility

Filling pressure

Stroke volume

Heart rate

Diameter of arterioles

Total peripheral resistance

Cardiac output

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21
Q

What is mean arterial blood pressure determined by?

A

Mean arterial blood pressure is determine by cardiac out put and peripheral resistance

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22
Q

Is it true that we need constant blood pressure in spite of changing requirements?

A

Yes

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23
Q

What alters cardiac output and peripheral resistance to control the blood pressure?

A

The baroreceptor reflex

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24
Q

Peripheral nerves from carotid body sense blood pressure and alter autonomic drive

A

Peripheral nerves from carotid body sense blood pressure and alter autonomic drive

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25
Is it true that the baroreceptor reflex alters cardiac output and peripheral resistance?
Yes
26
How does the baroreceptor reflex alter cardiac output and peripheral resistance?
- The baroreceptors signal to the vasomotor centres. - This goes down to the parasympathetic portions of the heart and the sympathetic, which affects both the heart and the blood vessels. - If we sense a decrease in blood pressure, we'll decrease carotid sinus nerve frequency. - This will tell the vasomotor centre that the blood pressure has dropped and this will inhibit parasympathetic nervous system to allow the heart to beat faster. - The sympathetic nervous system will then be stimulated so that the heart can beat faster(+ bllod volume). - All of this will increase the blood prssure. -
27
The effects of the sympathetic nervous system are very widespread. Affects most things that govern our blood pressure.
The effects of the sympathetic nervous system are very widespread. Affects most things that govern our blood pressure. Parasympathetic only really affects heart rate.
28
Is increasing blood volume the long term solution for regulating blood pressure?
Yes
29
What does the kidney secrete to regulate blood volume?
Secretion of renin by the kidney is an important factor in regulating blood volume
30
How does renin secretion regulate blood volume?
- Renin secretion: The kidneys release renin when blood pressure or volume is low. - Renin converts angiotensinogen: Renin turns angiotensinogen (from the liver) into angiotensin I. - Angiotensin I becomes Angiotensin II: ACE (mainly in the lungs) converts angiotensin I to angiotensin II. - Angiotensin II effects: - Causes blood vessels to constrict (raises blood pressure). - Stimulates aldosterone release, which makes kidneys retain sodium and water (increases blood volume). - Triggers ADH release, promoting water retention. - Increased blood volume and pressure: Blood volume and pressure rise, helping restore normal levels.
31
what rapid thing does Angiotensin II do to affect the circulation?
Powerful vasoconstrictor – increase peripheral resistance – increase venous tone
32
Atrial stretch receptors...
- Sense filling pressure - Point of highest pressure - Release hormone ANP, which increases excretion by decreasing the amount of ADH, causing vasodilation, inhibittng aldosterone and renin.
33
In summary, ANP helps balance fluid and blood pressure by promoting the elimination of excess sodium and water, acting as a counter-regulatory hormone to the renin-angiotensin-aldosterone system (RAAS).
In summary, ANP helps balance fluid and blood pressure by promoting the elimination of excess sodium and water, acting as a counter-regulatory hormone to the renin-angiotensin-aldosterone system (RAAS).
34
Do Atrial stretch receptors help regulate extracellular fluid volume?
Yes
35
What is the endocrine function of the atrial stretch receptors?
To secrete atrial natriuretic peptide/factor (ANP).
36
How can blood flow to a particular tissue be modified?
By adjusting vasomotor tone
37
Resistance to flow varies inversely with r 4 (from Poiseuille’s Law)
Resistance to flow varies inversely with r 4 (from Poiseuille’s Law)
38
How can blood flow to a particular tissue be modifed?
By paracrine signals
39
Sympathetic innervation..
This is part of the autonomic nervous system that usually causes vasoconstriction (narrowing of blood vessels) through neurotransmitters like noradrenaline (NA).
40
Vasomotor tone...
The level of constriction in blood vessels, controlled by sympathetic nerves. High tone = more constricted.
41
Paracrine signaling...
Local signaling where cells release substances (like potassium and adenosine) that act on nearby cells/tissues.
42
🧪 Metabolites' Role:
Potassium (K⁺) and Adenosine are byproducts of active tissues (e.g., working muscles or brain cells). These metabolites cause vasodilation (relaxing the blood vessels), countering the sympathetic vasoconstriction. As a result, blood flow increases to the metabolically active area — very important for oxygen and nutrient delivery.
43
Metabolites are washed away by blood flow: Once blood flow increases, these chemicals get diluted/removed, which helps reset the tone — a form of self-limiting control.
Metabolites are washed away by blood flow: Once blood flow increases, these chemicals get diluted/removed, which helps reset the tone — a form of self-limiting control.
44
is adenosine a potent vasodilator?
Yes
45
Do vasodilator metabolites ensure local control exceeds global drives to blood flow ?
Yes
46
WHat other factors control the blood flow of the microcirculation?
- Myogenic contraction of vascular smooth muscle - Factors released from endothelial cells e.g. NO - Circulating factors, e.g., angiotensin II
47
What is global control of blood flow monitored by?
Vasoconstriction
48
Does the total blood flow to the brain remain constant?
Yes
49
When does loss of consciousness occur?
Loss of consciousness (fainting or syncope) occurs if blood pressure drops sufficiently
50
51
Vessels in the pulmonary circulation...
Vessels in the pulmonary circulation are thin walled and highly compliant
52
53
Why does the pulmonary circulation have a high compliance?
No change in resistance respiratory pump large changes in blood pressure Allows lung to be more compliant
54
Why does the pulmonary circulation have low resistance?
Short distance Larger diameter
55
Why is low pulmonary pressure essential?
Low pulmonary pressure is essential for stopping fluid build up in the lung
56
In the pulmonary circulaiton is hydrostatic pressure less than oncotic pressure?
Yes
57
Filtration pressure =
Filtration pressure = hydrostatic pressure – oncotic pressure
58
What is vessel dilation in the pulmonary circulation governed by?
Vessel dilation in the pulmonary circulation is governed by oxygen levels and adenosine
59
low oxygen levels result in vasoconstriction
low oxygen levels result in vasoconstriction
60
What does hypoxia induce?
Hypoxia induces adenosine release + causes vasodilation in the systemic circulation Hypoxia induces adenosine release causes vasoconstriction in the pulmonary circulation
61
Does hypoxia induced vasoconstriction stop blood flow to areas of dead lung?
Yes
62
Are the arteries in the pulmonary circuit under a similar pressure as in veins?
Yes
63
To summarise, this lecture has considered:
The autonomic nervous system (ANS) as a modulator of the heart, regulating rate and contractility ANS as a modulator of the circulation regulating resistance of arteries and capacitance of veins The factors that determine blood pressure The baroreceptor reflex The importance of filling pressure in determining cardiac output The importance of factors controlling ecf and plasma volume in determining filling pressure The control of blood flow to metabolising tissues by metabolites Other factors that control blood flow
64

Physiology, neurobiology and cell signalling (20 decks)

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