1. Neural Regulation of the Circulation

2. Neural control of blood flow
 affects blood flow in large segments
of the systemic circulation,
 shifting blood flow from the non-
muscular vascular bed to the muscles
during exercise
 changing the blood flow in the skin to
control body temperature.

3. Innervation of the Circulatory
System
 Cardiac innervation
 Innervation of blood vessels
 Sympathetic vasoconstrictor fiber
 Sympathetic vasodilator fiber
 Parasympathetic nerve fiber to
peripheral vessels

4. Cardiac innervation
 Sympathetic nerve – noradrenergic fiber;
Parasympathetic nerve- cholinergic fiber
 Noradrenergic sympathetic nerve
 to the heart increase the cardiac rate (chronotropic
effect)
 the force of cardiac contraction (inotropic effect).
 Cholinergic vagal cardiac fibers decrease the
heart rate.

6. Cardiac innervation (contin.)
 moderate amount of tonic discharge in
the cardiac sympathetic nerves at rest
 a good deal of tonic vagal discharge
(vagal tone) in humans
 When the vagi are cut in experiment
animals, the heart rate rises

7. Innervation of blood vessels
 Sympathetic
vasoconstrictor fiber
 Distribution: Almost all
segments of the
circulation.
 The innervation is
powerful in the kidneys,
gut, spleen and skin,
 is less potent in both
skeletal and cardiac muscle
and in the brain.

8. Innervation of blood vessels
Sympathetic vasoconstrictor fiber
(contin.)
Almost all vessels, such as arteries, arterioles,
venules and veins are innervated,
except the capillaries, precapillary sphincters and
most of the metarterioles.
Tone: Usually the sympathetic vasoconstrictor
fibers keep tonic.

12. Innervation of blood vessels
 3) Parasympathetic nerve fiber to peripheral
vessels
 Parasympathetic nerve fibers innervate vessels
of the blood vessels in
 Meninges
 the salivary glands,
 the liver
 the viscera in pelvis
 the external genitals.
 Importance: Regulate the blood flow of these
organs in some special situations.

13. Cardiovascular System
Blood flow and blood pressure are monitored and ultimately controlled by
the brain. Peripheral signals are fed to the brain on a beat to beat basis, so
that alterations in blood flow can occur to meet the changing metabolic
demands of the body’s tissues.
Blood flow in part, depends on maintaining an appropriate BP.
Three main factors influencing BP are:
1. Cardiac Output
2. Peripheral Resistance
3. Blood Volume
Remember Blood Flow = D Pressure
Resistance
By rearranging so Pressure is isolated, this becomes
Blood Pressure = Blood Flow X Resistance OR
= CO X Peripheral Resistance

16. Arterial Blood Pressure
• Systolic pressure – pressure exerted on
arterial walls during ventricular contraction
• Diastolic pressure – lowest level of arterial
pressure during a ventricular cycle
• Pulse pressure – the difference between
systolic and diastolic pressure
• Mean arterial pressure (MAP) – pressure
that propels the blood to the tissues
• MAP = diastolic pressure + 1/3 pulse
pressure

17. Factors affecting ABP:
Sex : M > F due to hormones/ equal at menopause.
Age : Elderly > children due to atherosclerosis.
Emotions : due to secretion of adrenaline & noradrenaline.
Exercise : due to  venous return.
Hormones : (e.g. Adrenaline, noradrenaline, thyroid H).
Gravity :  Lower limbs > upper limbs.
Sleep :  due to  venous return.
Pregnancy : due to  metabolism.

18. Cardiovascular System
Neural Control of Peripheral Resistance aims to:
1. Alter blood distribution in response to specific demands.
2. Maintain appropriate MAP by changing vessel diameter.
Neural Control of the cardiovascular system originates in the Cardiac Centres
found in the Medulla.
Cardio -Acceleratory Centre sends Sympathetic Neurones down the spine to
between T1 and T5, where they exit to the periphery.
Cardio - Inhibitory Centre originates with the Vagus Nucleus in the medulla
and this Parasympathetic Nerve leaves the cranium as the Vagus (X) Nerve.
Vasomotor Centre - is a cluster of sympathetic fibres in the Medulla.
- transmits impulses via sympathetic vasomotor fibres
from T1 to L2 to blood vessels (arterioles)
Vasoconstriction is caused by increased frequency of impulses (Noradrenaline)
Vasodilation is caused by decreased frequency of impulses.

19. Cardiovascular System
Brainstem contains:
Pons
Medulla
In the Medulla are the:
Cardiac Acceleratory Centre
Cardiac Inhibitory Centre
Vasomotor Centre

20. I. Short-Term Regulation of
Blood Pressure:
• Rapidly Acting Pressure Control Mechanisms,
Acting Within Seconds or Minutes.
A. Baroreceptor reflexes
Change peripheral resistance, heart rate, and stroke
volume in response to changes in blood pressure
B. Chemoreceptor reflexes
Sensory receptors sensitive to oxygen, carbon dioxide,
and pH levels of blood
C. Central nervous system ischemic response
Results from high carbon dioxide or low pH levels in
medulla and increases peripheral resistance

21. Local mechanisms affect MAP:

22. Baroreceptor Reflex Control

25. Cardiovascular System
Baroreceptors are found in
• Carotid Sinuses (blood going to brain) and
• Aortic Arch (systemic blood going to body)
As MAP increases this stretches the receptors and they send a fast train
of impulses to the Vasomotor Centre. This results in a decrease in the
frequency of impulses from the Vasomotor Centre and arterioles dilate.
Final result is vasodilation and decreases MAP.
At the same time impulses are also relayed to the Cardiac Centre where
CIC activity increases (stimulating the Vagus nerve) - decreases HR and
SV.
CAC activity decreases (inhibiting Sympathetic nerves) - decreases CO.

27. Chemoreceptor Reflex Control

29. General control of MAP:

30. II. Pressure Control Mechanisms that Act
After Many Minutes : Intermediate
Mechanisms
• Fluid shift
• Renin – – Movement of fluid from
Angiotensin interstitial spaces into capillaries
in response to decrease in blood
system pressure to maintain blood
volume
• Stress-relaxation
– Adjustment of blood vessel
smooth muscle to respond to
change in blood volume

31. Renin-Angiotensin-Aldosterone
Mechanism

32. Sequential events by
which increased salt
intake increases the
arterial pressure, but
feedback decrease
in activity of the
renin angiotensin
system returns the
arterial pressure
almost to the normal
level.

33. Hypertension Caused by a
Renin-Secreting Tumor or
by Infusion of Angiotensin
II.
Effect of placing a
constricting clamp on the
renal artery of one kidney
after the other kidney has
been removed. The
resulting hypertension is
called "one-kidney"
Goldblatt hypertension.

34. III. Long-Term Regulation
of Blood Pressure
• Renal –Body fluid mechanism
• Hormones: Vasopressin (ADH),
Atrial natriuretic factor, erythropoietin,
aldosterone.
Importance:
 It takes a few hours to show significant
response for these mechanisms.
 Return the arterial pressure all the way
back.

36. • Typical renal urinary output curve measured in a
perfused isolated kidney, showing pressure diuresis
when the arterial pressure rises above normal.

37. Atrial natriuretic factor
Hormone released from cardiac muscle cells
when atrial blood pressure increases,
simulating an increase in urinary production,
causing a decrease in blood volume and
blood pressure.

38. Vasopressin (ADH)
Mechanism