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Control of the cardiovascular system

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Reverend Dr. David C.M. Taylor School of Medical Education dcmt_at_liverpool.ac.uk http://pcwww.liv.ac.uk/~dcmt/cvs09.ppt What is the role of the cardiovascular system? – PowerPoint PPT presentation

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Title: Control of the cardiovascular system


1
Control of the cardiovascular system
  • Reverend Dr. David C.M. Taylor
  • School of Medical Education
  • dcmt_at_liverpool.ac.uk
  • http//pcwww.liv.ac.uk/dcmt/cvs09.ppt

2
What is the role of the cardiovascular system?
3
Blood Pressure
  • Depends upon the amount of blood leaving the
    heart
  • cardiac output
  • and the resistance of the vasculature
  • total peripheral resistance

4
Peripheral Resistance
5
Peripheral resistance 2
6
Cardiac Output
  • Heart rate x stroke volume

7
Factors affecting stroke volume
Preload
Afterload
Contractility
8
Preload
  • increased end-diastolic volume stretches the
    heart
  • cardiac muscles stretch and contract more
    forcefully
  • Frank-Starling Law of the heart

9
Starlings Law
2.2 ?m
3.8 ?m
1.8 ?m
100 80 60 40 20
Tension developed
40 60 80 100 120 140 160
Percentage sarcomere length (100 2.2 ?m)
10
Contractility-Inotropic effect
  • positive inotropic agents
  • increase available intracellular Ca2
  • increase number of actinomyosin binding sites
  • increase force of contraction
  • positive inotropic agents
  • sympathetic stimulation
  • catecholamines
  • glucagon
  • thyroid hormones
  • increased extracellular Ca2

11
Afterload
  • decreased arterial blood pressure during diastole
  • decreased afterload
  • semilunar valves open sooner when blood pressure
    in pulmonary artery aorta is lower
  • afterload
  • blood pressure
  • viscosity of blood
  • elasticity of arteries

12
(No Transcript)
13
Heart Rate
  • Nervous system
  • increased sympathetic
  • decreased parasympathetic
  • Chemicals
  • catecholamines
  • thyroid hormones
  • moderate Ca2 increase

14
Heart Rate 2
  • Other factors
  • age
  • gender
  • fitness
  • body temperature

15
Pacemaker activity
  • The rhythm of the pump is provided by the
    pacemaker activity of some specialized muscle
    cells in the wall of the right atrium - the
    sinoatrial node

16
Chronotropic effect
17
Hypertension
  • David Taylor
  • School of Medical Education

18
Hypertension
  • Excellent article
  • ABC of Hypertension The pathophysiology of
    hypertension, Beevers G, Lip GYH and OBrien E
    (2001) BMJ, 322912-916
  • Upto 5 of patients with hypertension have it as
    secondary to some other disease (e.g. renal
    disease)
  • The rest have essential hypertension

19
The story so far...
  • http//pcwww.liv.ac.uk/dcmt/cvs09.ppt
  • intrinsic (Starlings Law)
  • extrinsic (principally autonomic)

Stroke volume
Cardiac output
Heart rate
20
Postulated mechanism
  • Increased sympathetic activity
  • Leads to increased cardiac output
  • And peripheral vasoconstriction (to protect the
    capillary beds)
  • Drop in blood flow
  • Triggers renin-angiotensin system

21
Evidence
  • Cross transplantation studies show that essential
    hypertension has its origins in the kidneys.
  • Human and animal studies
  • Little evidence that stress is involved
  • But, of course, drugs that decrease sympathetic
    activity lower blood pressure.

22
Control
Autonomic N.S.
Volume
ADH
Pressure
Chemicals
Angiotensin
Local Blood Flow
23
Pressure
  • Sensed by baroreceptors
  • in carotid arteries and aortic arch
  • an increase in pressure causes a decrease in
    sympathetic activity
  • a decrease in pressure causes an increase in
    sympathetic activity

24
Volume
  • Sensed by atrial volume receptors
  • A decrease in volume
  • causes an increase in ADH secretion
  • and a decrease in ANF secretion

25
Chemicals
  • A decrease in O2, or more usually an increase in
    CO2 or H2 causes an increase in chemoreceptor
    activity which
  • increases sympathetic activity

26
Local Blood Flow (kidney)
Vasoconstriction
27
Hormones
  • Angiotensin II is a vasoconstrictor
  • Aldosterone increases vascular sensitivity to
    Angiotensin II
  • ADH (anti-diuretic hormone) increases water
    reabsorption
  • ANF decreases sodium reabsorption

28
Overview
ADH
vol
baro
veins
capillary pressure
chemo
renin/angiotensin
aldosterone
kidney
29
Shock
  • David Taylor
  • School of Medical Education

30
Shock
  • Stage 1 Compensated/Nonprogressive
  • mechanisms work as planned
  • Stage 2 Decompensation/Progressive
  • if blood volume drops more than 15 - 25
  • Stage 3 Irreversible

31
Progressive shock
  • depression of cardiac activity
  • bp lt60 mmHg poor flow through coronary arteries
    leads to ischemia
  • depression of vasoconstriction
  • bp 40 - 50 mmHg
  • increased capillary permeability
  • caused by hypoxia
  • clotting, cell destruction, acidosis
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